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Sample records for 2d fermi surface

  1. Recovering the Fermi surface with 2D-ACAR spectroscopy in samples with defects

    NASA Astrophysics Data System (ADS)

    Dugdale, S. B.; Laverock, J.

    2014-04-01

    When two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) experiments are performed in metals containing defects, conventional analysis in which the measured momentum distribution is folded back into the first Brillouin zone is rendered ineffective due to the contribution from positrons annihilating from the defect. However, by working with the radial anisotropy of the spectrum, it is shown that an image of the Fermi surface can be recovered since the defect contribution is essentially isotropic.

  2. Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS.

    PubMed

    Ali, Mazhar N; Schoop, Leslie M; Garg, Chirag; Lippmann, Judith M; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S P

    2016-12-01

    Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual "butterfly"-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 10(5) percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a "dip" is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states.

  3. Butterfly magnetoresistance, quasi-2D Dirac Fermi surface and topological phase transition in ZrSiS

    PubMed Central

    Ali, Mazhar N.; Schoop, Leslie M.; Garg, Chirag; Lippmann, Judith M.; Lara, Erik; Lotsch, Bettina; Parkin, Stuart S. P.

    2016-01-01

    Magnetoresistance (MR), the change of a material’s electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. We report the observation of an unusual “butterfly”-shaped titanic angular magnetoresistance (AMR) in the nonmagnetic Dirac material, ZrSiS, which we find to be the most conducting sulfide known, with a 2-K resistivity as low as 48(4) nΩ⋅cm. The MR in ZrSiS is large and positive, reaching nearly 1.8 × 105 percent at 9 T and 2 K at a 45° angle between the applied current (I || a) and the applied field (90° is H || c). Approaching 90°, a “dip” is seen in the AMR, which, by analyzing Shubnikov de Haas oscillations at different angles, we find to coincide with a very sharp topological phase transition unlike any seen in other known Dirac/Weyl materials. We find that ZrSiS has a combination of two-dimensional (2D) and 3D Dirac pockets comprising its Fermi surface and that the combination of high-mobility carriers and multiple pockets in ZrSiS allows for large property changes to occur as a function of angle between applied fields. This makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons as well as opens the door to creating devices focused on switching between different parts of the Fermi surface and different topological states. PMID:28028541

  4. Radiofrequency Spectroscopy and Thermodynamics of Fermi Gases in the 2D to Quasi-2D Dimensional Crossover

    NASA Astrophysics Data System (ADS)

    Cheng, Chingyun; Kangara, Jayampathi; Arakelyan, Ilya; Thomas, John

    2016-05-01

    We tune the dimensionality of a strongly interacting degenerate 6 Li Fermi gas from 2D to quasi-2D, by adjusting the radial confinement of pancake-shaped clouds to control the radial chemical potential. In the 2D regime with weak radial confinement, the measured pair binding energies are in agreement with 2D-BCS mean field theory, which predicts dimer pairing energies in the many-body regime. In the qausi-2D regime obtained with increased radial confinement, the measured pairing energy deviates significantly from 2D-BCS theory. In contrast to the pairing energy, the measured radii of the cloud profiles are not fit by 2D-BCS theory in either the 2D or quasi-2D regimes, but are fit in both regimes by a beyond mean field polaron-model of the free energy. Supported by DOE, ARO, NSF, and AFOSR.

  5. Strain-induced Fermi contour anisotropy of GaAs (311)A 2D holes

    NASA Astrophysics Data System (ADS)

    Shabani, Javad; Shayegan, Mansour; Winkler, Roland

    2008-03-01

    There is considerable current interest in electronic properties of two-dimensional (2D) carriers whose energy bands are spin-split at finite values of in-plane wave vector, thanks to the spin-orbit interaction and the lack of inversion symmetry. We report experimental and theoretical results revealing that the spin-subband Fermi contours of the heavy and light heavy-holes (HHh and HHl) can be tuned in high mobility GaAs (311)A 2D hole systems via the application of symmetry-breaking in-plane strain. Our calculations show that the HHl spin-subband Fermi contour is circular but the HHh spin-subband Fermi contour is distorted. Experimentally, we probe the Fermi contour anisotropy by measuring the magneto-resistance commensurability peaks induced by square arrays of antidots. When the spin splitting is sufficiently large, the magneto-resistance trace exhibits two peaks, providing clear evidence for spin-resolved ballistic transport. The experimental results are in good agreement with the calculations, and confirm that the majority spin-subband (HHh) has a severely distorted Fermi contour whose anisotropy can be tuned with strain while Fermi contour of the minority spin-subband (HHl) remains nearly isotropic.

  6. Fermi surface measurements of lutetium

    NASA Astrophysics Data System (ADS)

    Johanson, W. R.; Crabtree, G. W.; Schmidt, F. A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101¯0) and (112¯0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  7. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-03-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  8. Fermi surface measurements of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1982-01-01

    We report de Haas-van Alphen (dHvA) measurements of the Fermi surface of Lutetium at temperatures down to .3K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a non-magnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earths from Gd to Tm. No complete frequency branches were observed, indicating that there are no closed pieces of surface. We observed all but one orbit predicted by relativistic-augmented-plane wave (RAPW) calculations of Keeton and Loucks, and the data support a geometry that is in good qualitative agreement with the existence of nested open electron and hole sheets.

  9. Fermi surface of YBCO by DHVA

    SciTech Connect

    Smith, J.L.; Fowler, C.M.; Freeman, B.L.; Hults, W.L.; King, J.C.; Mueller, F.M.

    1991-01-01

    These proceedings demonstrate how far scientist have come in the last four years of high temperature superconductivity. Knowledge of the energy bands and Fermi surfaces from experiment has come rather late. Photoemission, first showed proof of the validity of the energy band calculations. Positron annihilation, presented by West, after a rough start, is now giving evidence of the Fermi surface. Both of these techniques involve electronic excitations and hence, although they show the Fermi surface, do not put as severe a constraint on various models for superconductivity as does the de Haas-van Alphen (dHvA) effect. This is a true measurement of the electronic ground state in an applied magnetic field where the frequency of oscillatory magnetization yields extremal cross-sectional areas of the Fermi surface. The authors have already reported some of their Fermi surface work at two conferences but present here discussion of several more important aspects of the work. 11 refs., 2 figs.

  10. Experimental studies of spin-imbalanced Fermi gases in 2D geometries

    NASA Astrophysics Data System (ADS)

    Thomas, John

    We study the thermodynamics of a quasi-two-dimensional Fermi gas, which is not quite two-dimensional (2D), but far from three dimensional (3D). This system offers opportunities to test predictions that cross interdisciplinary boundaries, such as enhanced superfluid transition temperatures in spin-imbalanced quasi-2D superconductors, and provides important benchmarks for calculations of the phase diagrams. In the experiments, an ultra-cold Fermi gas is confined in an infrared CO2 laser standing-wave, which produces periodic pancake-shaped potential wells, separated by 5.3 μm. To study the thermodynamics, we load an ultra-cold mixture of N1 = 800 spin 1/2 -up and N2 2D-BCS theory, but can be fit by a 2D-polaron gas model, where each atom is surrounded by a cloud of particle-hole pairs of the opposite spin. However, this model fails to predict a transition to a spin-balanced central region as N2/N1is increased. Supported by the physics divisions of ARO, AFOSR, and NSF and by the Division of Materials Science and Engineering, the Office of Basic Energy Sciences, DOE.

  11. Quantum chaos on a critical Fermi surface.

    PubMed

    Patel, Aavishkar A; Sachdev, Subir

    2017-02-21

    We compute parameters characterizing many-body quantum chaos for a critical Fermi surface without quasiparticle excitations. We examine a theory of [Formula: see text] species of fermions at nonzero density coupled to a [Formula: see text] gauge field in two spatial dimensions and determine the Lyapunov rate and the butterfly velocity in an extended random-phase approximation. The thermal diffusivity is found to be universally related to these chaos parameters; i.e., the relationship is independent of [Formula: see text], the gauge-coupling constant, the Fermi velocity, the Fermi surface curvature, and high-energy details.

  12. FFLO Superfluids in 2D Spin-Orbit Coupled Fermi Gases

    PubMed Central

    Zheng, Zhen; Gong, Ming; Zhang, Yichao; Zou, Xubo; Zhang, Chuanwei; Guo, Guangcan

    2014-01-01

    We show that the combination of spin-orbit coupling and in-plane Zeeman field in a two-dimensional degenerate Fermi gas can lead to a larger parameter region for Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phases than that using spin-imbalanced Fermi gases. The resulting FFLO superfluids are also more stable due to the enhanced energy difference between FFLO and conventional Bardeen-Cooper-Schrieffer (BCS) excited states. We clarify the crucial role of the symmetry of Fermi surface on the formation of finite momentum pairing. The phase diagram for FFLO superfluids is obtained in the BCS-BEC crossover region and possible experimental observations of FFLO phases are discussed. PMID:25288379

  13. Fermi Surface of the Most Dilute Superconductor

    NASA Astrophysics Data System (ADS)

    Lin, Xiao; Zhu, Zengwei; Fauqué, Benoît; Behnia, Kamran

    2013-04-01

    The origin of superconductivity in bulk SrTiO3 is a mystery since the nonmonotonous variation of the critical transition with carrier concentration defies the expectations of the crudest version of the BCS theory. Here, employing the Nernst effect, an extremely sensitive probe of tiny bulk Fermi surfaces, we show that, down to concentrations as low as 5.5×1017cm-3, the system has both a sharp Fermi surface and a superconducting ground state. The most dilute superconductor currently known therefore has a metallic normal state with a Fermi energy as little as 1.1 meV on top of a band gap as large as 3 eV. The occurrence of a superconducting instability in an extremely small, single-component, and barely anisotropic Fermi surface implies strong constraints for the identification of the pairing mechanism.

  14. Topology of Fermi surfaces and anomaly inflows

    NASA Astrophysics Data System (ADS)

    Adem, Alejandro; Camarena, Omar Antolín; Semenoff, Gordon W.; Sheinbaum, Daniel

    2016-11-01

    We derive a rigorous classification of topologically stable Fermi surfaces of non-interacting, discrete translation-invariant systems from electronic band theory, adiabatic evolution and their topological interpretations. For systems on an infinite crystal it is shown that there can only be topologically unstable Fermi surfaces. For systems on a half- space and with a gapped bulk, our derivation naturally yields a K -theory classification. Given the d - 1-dimensional surface Brillouin zone X s of a d-dimensional half-space, our result implies that different classes of globally stable Fermi surfaces belong in K -1 (Xs) for systems with only discrete translation-invariance. This result has a chiral anomaly inflow interpretation, as it reduces to the spectral flow for d = 2. Through equivariant homotopy methods we extend these results for symmetry classes AI, AII, C and D and discuss their corresponding anomaly inflow interpretation.

  15. Fermi surface determination from momentum density projections

    NASA Astrophysics Data System (ADS)

    Leitner, Michael; Weber, Josef Andreas; Ceeh, Hubert

    2016-06-01

    The problem of determining a metal’s Fermi surface from measured projections of the electron or electron/positron momentum densities, such as those obtained by Compton scattering or angular correlation of positron annihilation radiation, respectively, is examined in a Bayesian formulation. A consistent approach with an explicit treatment of the Fermi surface already at the reconstruction stage is presented, and its advantages compared to previous practice are discussed. A validation of the proposed method on simulated data shows its systematic accuracy to be very satisfactory and its statistical precision on modest experimental data to be surprisingly good.

  16. The success of Fermi gas model for overall scaling of 2D metal-to-insulator transition data

    NASA Astrophysics Data System (ADS)

    Cheremisin, M. V.

    2017-03-01

    The melting condition for two-dimensional Wigner solid (Platzman and Fukuyama, 1974) [14] is shown to contain an error of a factor of π. The analysis of experimental data for apparent 2D metal-to-insulator transition shows that the Wigner solidification (Tanatar and Ceperley, 1989) [16] has been never achieved. Within routine Fermi gas model both the metallic and insulating behavior of different 2D system for actual range of carrier densities and temperatures is explained.

  17. Unconventional Fermi surface in an insulating state

    NASA Astrophysics Data System (ADS)

    Tan, B. S.; Hsu, Y.-T.; Zeng, B.; Hatnean, M. Ciomaga; Harrison, N.; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J.-H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-01

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  18. Unconventional Fermi surface in an insulating state

    SciTech Connect

    Harrison, Neil; Tan, B. S.; Hsu, Y. -T.; Zeng, B.; Hatnean, M. Ciomaga; Zhu, Z.; Hartstein, M.; Kiourlappou, M.; Srivastava, A.; Johannes, M. D.; Murphy, T. P.; Park, J. -H.; Balicas, L.; Lonzarich, G. G.; Balakrishnan, G.; Sebastian, Suchitra E.

    2015-07-17

    Insulators occur in more than one guise; a recent finding was a class of topological insulators, which host a conducting surface juxtaposed with an insulating bulk. Here, we report the observation of an unusual insulating state with an electrically insulating bulk that simultaneously yields bulk quantum oscillations with characteristics of an unconventional Fermi liquid. We present quantum oscillation measurements of magnetic torque in high-purity single crystals of the Kondo insulator SmB6, which reveal quantum oscillation frequencies characteristic of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6. As a result, the quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior.

  19. Fermi surface reconstruction in high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Taillefer, Louis

    2009-03-01

    The recent observation of quantum oscillations in underdoped high-Tc superconductors (1), combined with their negative Hall coefficient at low temperature (2), reveals that the Fermi surface of hole-doped cuprates includes a small electron pocket. This strongly suggests that the large hole Fermi surface characteristic of the overdoped regime undergoes a reconstruction caused by the onset of some order which breaks translational symmetry. Here we consider the possibility that this order is ``stripe'' order, a form of combined charge / spin modulation observed most clearly in materials like Eu- doped and Nd-doped LSCO. In these materials, the onset of stripe order coincides with major changes in transport properties (3), providing strong evidence that stripe order is indeed the cause of Fermi-surface reconstruction. We identify the critical doping where this reconstruction occurs and show that the temperature dependence of transport coefficients at that doping is typical of metals at a quantum critical point (4). We discuss an interpretation of the pseudogap as a fluctuating precursor of the stripe-ordered phase.This work was performed in collaboration with L. Balicas, D.A. Bonn, J. Chang, O. Cyr-Choinière, R. Daou, N. Doiron- Leyraud, W.N. Hardy, N.E. Hussey, F. Lalibert'e, D. LeBoeuf, S.Y. Li, R. Liang, C. Proust, H. Takagi, and J.S. Zhou.(1) N. Doiron-Leyraud et al., Nature 447, 565 (2007).(2) D. LeBoeuf et al., Nature 450, 533 (2007).(3) R. Daou et al., Nature Physics, in press (DOI 10.1038/nphys1109); http://arXiv.org/abs/0806.2881.(4) R. Daou et al., to be published; http://arXiv.org/abs/0810.4280.

  20. Entanglement rules for holographic Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Roychowdhury, Dibakar

    2016-08-01

    In this paper, based on the notion of Gauge/Gravity duality, we explore the laws of entanglement thermodynamics for most generic classes of Quantum Field Theories with hyperscaling violation. In our analysis, we note that for Quantum Field Theories with compressible quark like excitation, the first law of entanglement thermodynamics gets modified due to the presence of an additional term that could be identified as the entanglement chemical potential associated with hidden Fermi surfaces of the boundary theory. Most notably, we find that the so called entanglement chemical potential does not depend on the size of the entangling region and is purely determined by the quark d.o.f. encoded within the entangling region.

  1. Fermi surface and electron correlation effects of ferromagnetic iron

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Hoinkis, M.; Rotenberg, Eli; Blaha, P.; Claessen, R.

    2005-10-01

    The electronic band structure of bulk ferromagnetic iron is explored by angle-resolved photoemission for electron correlation effects. Fermi surface cross sections as well as band maps are contrasted with density functional calculations. The Fermi vectors and band parameters obtained from photoemission and their prediction from band theory are analyzed in detail. Generally good agreement is found for the Fermi surface. A bandwidth reduction for shallow bands of ˜30% is observed. Additional strong quasiparticle renormalization effects are found near the Fermi level, leading to a considerable mass enhancement. The role of electronic correlation effects and the electronic coupling to magnetic excitations is discussed in view of the experimental results.

  2. Spin texture on the Fermi surface of tensile-strained HgTe

    NASA Astrophysics Data System (ADS)

    Zaheer, Saad; Young, S. M.; Cellucci, D.; Teo, J. C. Y.; Kane, C. L.; Mele, E. J.; Rappe, Andrew M.

    2013-01-01

    We present ab initio and k·p calculations of the spin texture on the Fermi surface of tensile-strained HgTe, which is obtained by stretching the zinc-blende lattice along the (111) axis. Tensile-strained HgTe is a semimetal with pointlike accidental degeneracies between a mirror symmetry protected twofold degenerate band and two nondegenerate bands near the Fermi level. The Fermi surface consists of two ellipsoids which contact at the point where the Fermi level crosses the twofold degenerate band along the (111) axis. However, the spin texture of occupied states indicates that neither ellipsoid carries a compensating Chern number. Consequently, the spin texture is locked in the plane perpendicular to the (111) axis, exhibits a nonzero winding number in that plane, and changes winding number from one end of the Fermi ellipsoids to the other. The change in the winding of the spin texture suggests the existence of singular points. An ordered alloy of HgTe with ZnTe has the same effect as stretching the zinc-blende lattice in the (111) direction. We present ab initio calculations of ordered HgxZn1-xTe that confirm the existence of a spin texture locked in a 2D plane on the Fermi surface with different winding numbers on either end.

  3. Towards a complete Fermi surface in underdoped high Tc superconductors

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    The discovery of magnetic quantum oscillations in underdoped high Tc superconductors raised many questions, and initiated a quest to understand the origin of the Fermi surface the like of which had not been seen since the very first discovery of quantum oscillations in elemental bismuth. While studies of the Fermi surface of materials are today mostly assisted by computer codes for calculating the electronic band structure, this was not the case in the underdoped high Tc materials. The Fermi surface was shown to reconstructed into small pockets, yet there was no hint of a viable order parameter. Crucial clues to understanding the origin of the Fermi surface were provided by the small value of the observed Fermi surface cross-section, the negative Hall coefficient and the small electronic heat capacity at high magnetic fields. We also know that the magnetic fields were likely to be too weak to destroy the pseudogap and that vortex pinning effects could be seen to persist to high magnetic fields at low temperatures. I will show that the Fermi surface that appears to fit best with the experimental observations is a small electron pocket formed by connecting the nodal `Fermi arcs' seen in photoemission experiments, corresponding to a density-wave state with two different orthogonal ordering vectors. The existence of such order has subsequently been detected by x-ray scattering experiments, thereby strengthening the case for charge ordering being responsible for reconstructing the Fermi surface. I will discuss new efforts to understand the relationship between the charge ordering and the pseudogap state, discussing the fate of the quasiparticles in the antinodal region and the dimensionality of the Fermi surface. The author acknowledges contributions from Suchitra Sebastian, Brad Ramshaw, Mun Chan, Yu-Te Hsu, Mate Hartstein, Gil Lonzarich, Beng Tan, Arkady Shekhter, Fedor Balakirev, Ross McDonald, Jon Betts, Moaz Altarawneh, Zengwei Zhu, Chuck Mielke, James Day, Doug

  4. Fermi-surface reconstruction by stripe order in cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Laliberté, Francis

    2012-02-01

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBCO, application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order [1,2,3]. In another cuprate, Eu-LSCO, the onset of stripe order - a modulation of spin and charge densities - at low temperature is well established [4]. By a comparative study of thermoelectric transport in the cuprates YBCO and Eu-LSCO, we show that the two materials exhibit a very similar process of Fermi-surface reconstruction as a function of temperature and doping [5,6]. This strongly suggests that Fermi-surface reconstruction is caused by stripe order in both cases, compelling evidence that stripe order is a generic tendency of hole-doped cuprates.[4pt] Work done in collaboration with J. Chang, N. Doiron-Leyraud, E. Hassinger, R. Daou, D. LeBoeuf, M. Rondeau, B. J. Ramshaw, R. Liang, D. A. Bonn, W. N. Hardy, S. Pyon, T. Takayama, H. Takagi, I. Sheikin, L. Malone, C. Proust, K. Behnia and L. Taillefer.[4pt] [1] N. Doiron-Leyraud et al., Nature 447, 565 (2007).[0pt] [2] D. LeBoeuf et al., Nature 450, 533 (2007).[0pt] [3] D. LeBoeuf et al., Phys. Rev. B 83, 054506 (2011).[0pt] [4] J. Fink et al., Phys. Rev. B 83, 092503 (2011).[0pt] [5] J. Chang et al., Phys. Rev. Lett. 104, 057005 (2010).[0pt] [6] F. Lalibert'e et al., Nat. Commun. 2, 432 (2011).

  5. Manipulating superconductivity in ruthenates through Fermi surface engineering

    NASA Astrophysics Data System (ADS)

    Hsu, Yi-Ting; Cho, Weejee; Rebola, Alejandro Federico; Burganov, Bulat; Adamo, Carolina; Shen, Kyle M.; Schlom, Darrell G.; Fennie, Craig J.; Kim, Eun-Ah

    2016-07-01

    The key challenge in superconductivity research is to go beyond the historical mode of discovery-driven research. We put forth a new strategy, which is to combine theoretical developments in the weak-coupling renormalization-group approach with the experimental developments in lattice-strain-driven Fermi surface engineering. For concreteness we theoretically investigate how superconducting tendencies will be affected by strain engineering of ruthenates' Fermi surface. We first demonstrate that our approach qualitatively reproduces recent experiments under uniaxial strain. We then note that the order of a few percent strain, readily accessible to epitaxial thin films, can bring the Fermi surface close to van Hove singularity. Using the experimental observation of the change in the Fermi surface under biaxial epitaxial strain and ab initio calculations, we predict Tc for triplet pairing to be maximized by getting close to the van Hove singularities without tuning on to the singularity.

  6. Design Application Translates 2-D Graphics to 3-D Surfaces

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Fabric Images Inc., specializing in the printing and manufacturing of fabric tension architecture for the retail, museum, and exhibit/tradeshow communities, designed software to translate 2-D graphics for 3-D surfaces prior to print production. Fabric Images' fabric-flattening design process models a 3-D surface based on computer-aided design (CAD) specifications. The surface geometry of the model is used to form a 2-D template, similar to a flattening process developed by NASA's Glenn Research Center. This template or pattern is then applied in the development of a 2-D graphic layout. Benefits of this process include 11.5 percent time savings per project, less material wasted, and the ability to improve upon graphic techniques and offer new design services. Partners include Exhibitgroup/Giltspur (end-user client: TAC Air, a division of Truman Arnold Companies Inc.), Jack Morton Worldwide (end-user client: Nickelodeon), as well as 3D Exhibits Inc., and MG Design Associates Corp.

  7. Fracture surfaces of heterogeneous materials: A 2D solvable model

    NASA Astrophysics Data System (ADS)

    Katzav, E.; Adda-Bedia, M.; Derrida, B.

    2007-05-01

    Using an elastostatic description of crack growth based on the Griffith criterion and the principle of local symmetry, we present a stochastic model describing the propagation of a crack tip in a 2D heterogeneous brittle material. The model ensures the stability of straight cracks and allows for the study of the roughening of fracture surfaces. When neglecting the effect of the nonsingular stress, the problem becomes exactly solvable and yields analytic predictions for the power spectrum of the paths. This result suggests an alternative to the conventional power law analysis often used in the analysis of experimental data.

  8. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    NASA Astrophysics Data System (ADS)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  9. Complexity and Fermi surface deformation in compressed lithium

    NASA Astrophysics Data System (ADS)

    Rodriguez-Prieto, A.; Bergara, A.; Silkin, V. M.; Echenique, P. M.

    2006-11-01

    Recently reported structural complexity and enhanced temperature superconducting transitions in lithium under pressure have increased the interest in light alkalies, otherwise considered as simple and well-known systems under normal conditions. Here we present an analysis of the pressure-induced Fermi surface deformation in lithium and its relation to the observed complexity. According to our calculations, the Fermi surface becomes increasingly anisotropic with pressure and at 8GPa contacts the Brillouin zone boundary inducing a Hume-Rothery mechanism explaining the bcc-fcc transition. Around 30GPa increasing cooper-like necks and an extended nesting are observed in the Fermi surface in the fcc phase, enhancing the electronic susceptibility response function and inducing a strong phonon softening. This softening, besides preluding the transition to complex structures and providing a better understanding of the observed superconductivity, is expected to induce other yet unexplored anomalies in compressed lithium.

  10. 3D surface configuration modulates 2D symmetry detection.

    PubMed

    Chen, Chien-Chung; Sio, Lok-Teng

    2015-02-01

    We investigated whether three-dimensional (3D) information in a scene can affect symmetry detection. The stimuli were random dot patterns with 15% dot density. We measured the coherence threshold, or the proportion of dots that were the mirror reflection of the other dots in the other half of the image about a central vertical axis, at 75% accuracy with a 2AFC paradigm under various 3D configurations produced by the disparity between the left and right eye images. The results showed that symmetry detection was difficult when the corresponding dots across the symmetry axis were on different frontoparallel or inclined planes. However, this effect was not due to a difference in distance, as the observers could detect symmetry on a slanted surface, where the depth of the two sides of the symmetric axis was different. The threshold was reduced for a hinge configuration where the join of two slanted surfaces coincided with the axis of symmetry. Our result suggests that the detection of two-dimensional (2D) symmetry patterns is subject to the 3D configuration of the scene; and that coplanarity across the symmetry axis and consistency between the 2D pattern and 3D structure are important factors for symmetry detection.

  11. 2D Gridded Surface Data Value-Added Product

    SciTech Connect

    Tang, Q; Xie, S

    2015-08-30

    This report describes the Atmospheric Radiation Measurement (ARM) Best Estimate (ARMBE) 2-dimensional (2D) gridded surface data (ARMBE2DGRID) value-added product. Spatial variability is critically important to many scientific studies, especially those that involve processes of great spatial variations at high temporal frequency (e.g., precipitation, clouds, radiation, etc.). High-density ARM sites deployed at the Southern Great Plains (SGP) allow us to observe the spatial patterns of variables of scientific interests. The upcoming megasite at SGP with its enhanced spatial density will facilitate the studies at even finer scales. Currently, however, data are reported only at individual site locations at different time resolutions for different datastreams. It is difficult for users to locate all the data they need and requires extra effort to synchronize the data. To address these problems, the ARMBE2DGRID value-added product merges key surface measurements at the ARM SGP sites and interpolates the data to a regular 2D grid to facilitate the data application.

  12. Fermi surface, magnetic, and superconducting properties in actinide compounds

    NASA Astrophysics Data System (ADS)

    Ōnuki, Yoshichika; Settai, Rikio; Haga, Yoshinori; Machida, Yo; Izawa, Koichi; Honda, Fuminori; Aoki, Dai

    2014-08-01

    The de Haas-van Alphen effect, which is a powerful method to explore Fermi surface properties, has been observed in cerium, uranium, and nowadays even in neptunium and plutonium compounds. Here, we present the results of several studies concerning the Fermi surface properties of the heavy fermion superconductors UPt3 and NpPd5Al2, and of the ferromagnetic pressure-induced superconductor UGe2, together with those of some related compounds for which fascinating anisotropic superconductivity, magnetism, and heavy fermion behavior has been observed. xml:lang="fr"

  13. Exotic Paired States with Anisotropic Spin-Dependent Fermi Surfaces

    SciTech Connect

    Feiguin, Adrian E.; Fisher, Matthew P. A.

    2009-07-10

    We propose a model for realizing exotic paired states in cold Fermi gases by using a spin-dependent optical lattice to engineer mismatched Fermi surfaces for each hyperfine species. The BCS phase diagram shows a stable paired superfluid state with coexisting pockets of momentum space with gapless unpaired carriers, similar to the Sarma state in polarized mixtures, but in our case the system is unpolarized. We propose the possible existence of an exotic 'Cooper-pair Bose-metal' phase, which has a gap for single fermion excitations but gapless and uncondensed 'Cooper-pair' excitations residing on a 'Bose surface' in momentum space.

  14. ROLE OF NUCLEONIC FERMI SURFACE DEPLETION IN NEUTRON STAR COOLING

    SciTech Connect

    Dong, J. M.; Zuo, W.; Lombardo, U.; Zhang, H. F.

    2016-01-20

    The Fermi surface depletion of beta-stable nuclear matter is calculated to study its effects on several physical properties that determine the neutron star (NS) thermal evolution. The neutron and proton Z factors measuring the corresponding Fermi surface depletions are calculated within the Brueckner–Hartree–Fock approach, employing the AV18 two-body force supplemented by a microscopic three-body force. Neutrino emissivity, heat capacity, and in particular neutron {sup 3}PF{sub 2} superfluidity, turn out to be reduced, especially at high baryonic density, to such an extent that the cooling rates of young NSs are significantly slowed.

  15. Giant magnetoresistance, three-dimensional Fermi surface and origin of resistivity plateau in YSb semimetal.

    PubMed

    Pavlosiuk, Orest; Swatek, Przemysław; Wiśniewski, Piotr

    2016-12-09

    Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by magnetic field, when time-reversal symmetry (protecting surface states in topological insulators) is broken. Similar features were observed in a simple rock-salt-structure LaSb, leading to a suggestion of the possible non-trivial topology of 2D states in this compound. We show that its sister compound YSb is also characterized by giant magnetoresistance exceeding one thousand percent and low-temperature plateau of resistivity. We thus performed in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance, and Shubnikov-de Haas effect measurements, which reveals only three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance data accounts very well for its low-temperature upturn behavior. The field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding effective mass anisotropy perfectly agreeing with electronic structure and quantum oscillations analysis, thus providing further support for 3D-Fermi surface scenario of magnetotransport, without necessity of invoking topologically non-trivial 2D states. We discuss data implying that analogous field-induced properties of LaSb can also be well understood in the framework of 3D multiband model.

  16. Giant magnetoresistance, three-dimensional Fermi surface and origin of resistivity plateau in YSb semimetal

    PubMed Central

    Pavlosiuk, Orest; Swatek, Przemysław; Wiśniewski, Piotr

    2016-01-01

    Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by magnetic field, when time-reversal symmetry (protecting surface states in topological insulators) is broken. Similar features were observed in a simple rock-salt-structure LaSb, leading to a suggestion of the possible non-trivial topology of 2D states in this compound. We show that its sister compound YSb is also characterized by giant magnetoresistance exceeding one thousand percent and low-temperature plateau of resistivity. We thus performed in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance, and Shubnikov–de Haas effect measurements, which reveals only three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance data accounts very well for its low-temperature upturn behavior. The field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding effective mass anisotropy perfectly agreeing with electronic structure and quantum oscillations analysis, thus providing further support for 3D-Fermi surface scenario of magnetotransport, without necessity of invoking topologically non-trivial 2D states. We discuss data implying that analogous field-induced properties of LaSb can also be well understood in the framework of 3D multiband model. PMID:27934949

  17. Giant magnetoresistance, three-dimensional Fermi surface and origin of resistivity plateau in YSb semimetal

    NASA Astrophysics Data System (ADS)

    Pavlosiuk, Orest; Swatek, Przemysław; Wiśniewski, Piotr

    2016-12-01

    Very strong magnetoresistance and a resistivity plateau impeding low temperature divergence due to insulating bulk are hallmarks of topological insulators and are also present in topological semimetals where the plateau is induced by magnetic field, when time-reversal symmetry (protecting surface states in topological insulators) is broken. Similar features were observed in a simple rock-salt-structure LaSb, leading to a suggestion of the possible non-trivial topology of 2D states in this compound. We show that its sister compound YSb is also characterized by giant magnetoresistance exceeding one thousand percent and low-temperature plateau of resistivity. We thus performed in-depth analysis of YSb Fermi surface by band calculations, magnetoresistance, and Shubnikov–de Haas effect measurements, which reveals only three-dimensional Fermi sheets. Kohler scaling applied to magnetoresistance data accounts very well for its low-temperature upturn behavior. The field-angle-dependent magnetoresistance demonstrates a 3D-scaling yielding effective mass anisotropy perfectly agreeing with electronic structure and quantum oscillations analysis, thus providing further support for 3D-Fermi surface scenario of magnetotransport, without necessity of invoking topologically non-trivial 2D states. We discuss data implying that analogous field-induced properties of LaSb can also be well understood in the framework of 3D multiband model.

  18. Massively Parallel Computation of Soil Surface Roughness Parameters on A Fermi GPU

    NASA Astrophysics Data System (ADS)

    Li, Xiaojie; Song, Changhe

    2016-06-01

    Surface roughness is description of the surface micro topography of randomness or irregular. The standard deviation of surface height and the surface correlation length describe the statistical variation for the random component of a surface height relative to a reference surface. When the number of data points is large, calculation of surface roughness parameters is time-consuming. With the advent of Graphics Processing Unit (GPU) architectures, inherently parallel problem can be effectively solved using GPUs. In this paper we propose a GPU-based massively parallel computing method for 2D bare soil surface roughness estimation. This method was applied to the data collected by the surface roughness tester based on the laser triangulation principle during the field experiment in April 2012. The total number of data points was 52,040. It took 47 seconds on a Fermi GTX 590 GPU whereas its serial CPU version took 5422 seconds, leading to a significant 115x speedup.

  19. Magnetic breakdown in an array of overlapping Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Kadigrobov, A. M.; Radić, D.; Bjeliš, A.

    2015-03-01

    We develop a theoretical framework for a magnetic breakdown in an array of circular two-dimensional bands with a finite overlap of neighboring Fermi surfaces due to the presence of a presumably weak periodic potential, and apply the obtained results to the electron bands in carbon honeycomb structures of doped graphene and intercalated graphite compounds. In contrast to the standard treatment, inaugurated more than fifty years ago by Slutskin and Kadigrobov, with electron semiclassical trajectories encircling significantly overlapping Fermi surfaces, we examine a configuration in which bands are related in a way that the Fermi surfaces only slightly overlap, forming internal band pockets with areas of the size comparable to the area of the quantum magnetic flux for a given external magnetic field. Such band configuration has to be treated quantum mechanically. The calculation leads to the results for magnetic breakdown coefficients comprising an additional large factor with respect to the standard results, proportional to the ratio of the Fermi energy and the cyclotron energy. Also, these coefficients show oscillating dependence on energy, as well as on the wave number of periodic potential. Both mentioned elements enable the adjustment of the preferred wave vector of possible magnetic breakdown induced density wave instability at the highest possible critical temperature.

  20. Fermi surface behavior in the ABJM M2-brane theory

    NASA Astrophysics Data System (ADS)

    DeWolfe, Oliver; Henriksson, Oscar; Rosen, Christopher

    2015-06-01

    We calculate fermionic Green's functions for states of the three-dimensional Aharony-Bergman-Jafferis-Maldacena M2-brane theory at large N using the gauge-gravity correspondence. We embed extremal black brane solutions in four-dimensional maximally supersymmetric gauged supergravity, obtain the linearized Dirac equations for each spin-1 /2 mode that cannot mix with a gravitino, and solve these equations with infalling boundary conditions to calculate retarded Green's functions. For generic values of the chemical potentials, we find Fermi surfaces with universally non-Fermi liquid behavior, matching the situation for four-dimensional N =4 super-Yang-Mills. Fermi surface singularities appear and disappear discontinuously at the point where all chemical potentials are equal, reminiscent of a quantum critical point. One limit of parameter space has zero entropy at zero temperature, and fermionic fluctuations are perfectly stable inside an energy region around the Fermi surface. An ambiguity in the quantization of the fermions is resolved by supersymmetry.

  1. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    PubMed

    Kargarian, Mehdi; Randeria, Mohit; Lu, Yuan-Ming

    2016-08-02

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at [Formula: see text] where gapless states on the side surfaces are protected only near [Formula: see text] We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2 Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

  2. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    PubMed Central

    Kargarian, Mehdi; Randeria, Mohit

    2016-01-01

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments. PMID:27436895

  3. Life on the edge: a beginner’s guide to the Fermi surface

    NASA Astrophysics Data System (ADS)

    Dugdale, S. B.

    2016-05-01

    The concept of the Fermi surface is at the very heart of our understanding of the metallic state. Displaying intricate and often complicated shapes, the Fermi surfaces of real metals are both aesthetically beautiful and subtly powerful. A range of examples is presented of the startling array of physical phenomena whose origin can be traced to the shape of the Fermi surface, together with experimental observations of the particular Fermi surface features.

  4. Unconventional fermi surface instabilities in the kagome Hubbard model.

    PubMed

    Kiesel, Maximilian L; Platt, Christian; Thomale, Ronny

    2013-03-22

    We investigate the competing Fermi surface instabilities in the kagome tight-binding model. Specifically, we consider on-site and short-range Hubbard interactions in the vicinity of van Hove filling of the dispersive kagome bands where the fermiology promotes the joint effect of enlarged density of states and nesting. The sublattice interference mechanism devised by Kiesel and Thomale [Phys. Rev. B 86, 121105 (2012)] allows us to explain the intricate interplay between ferromagnetic fluctuations and other ordering tendencies. On the basis of the functional renormalization group used to obtain an adequate low-energy theory description, we discover finite angular momentum spin and charge density wave order, a twofold degenerate d-wave Pomeranchuk instability, and f-wave superconductivity away from van Hove filling. Together, this makes the kagome Hubbard model the prototypical scenario for several unconventional Fermi surface instabilities.

  5. Are the surface Fermi arcs in Dirac semimetals topologically protected?

    NASA Astrophysics Data System (ADS)

    Kargarian, Mehdi; Randeria, Mohit; Lu, Yuan-Ming

    2016-08-01

    Motivated by recent experiments probing anomalous surface states of Dirac semimetals (DSMs) Na3Bi and Cd3As2, we raise the question posed in the title. We find that, in marked contrast to Weyl semimetals, the gapless surface states of DSMs are not topologically protected in general, except on time-reversal-invariant planes of surface Brillouin zone. We first demonstrate this finding in a minimal four-band model with a pair of Dirac nodes at k=(0,0,±Q),k=(0,0,±Q), where gapless states on the side surfaces are protected only near kz=0.kz=0. We then validate our conclusions about the absence of a topological invariant protecting double Fermi arcs in DSMs, using a K-theory analysis for space groups of Na3Bi and Cd3As2. Generically, the arcs deform into a Fermi pocket, similar to the surface states of a topological insulator, and this pocket can merge into the projection of bulk Dirac Fermi surfaces as the chemical potential is varied. We make sharp predictions for the doping dependence of the surface states of a DSM that can be tested by angle-resolved photoemission spectroscopy and quantum oscillation experiments.

  6. Towards Quantum Simulation of the 2D Fermi Hubbard Model - Development of a Local Probe of Density and Spin Ordering

    DTIC Science & Technology

    2013-10-24

    high-resolution imaging using this optical transition should be feasible. With ultracold rubidium -87, we observe a quantum phase transition between a...degenerate gases of both 87Rb and 40K in the apparatus described in §3.1. In March 2012, we observed our first Bose Einstein condensate (BEC) of rubidium in...sympathetically cooled in our apparatus. In the spring of 2012, we used cold rubidium to bring potassium to Fermi degeneracy in the magnetic trap. Sympathetic

  7. Fermi-surface reconstruction by stripe order in cuprate superconductors

    PubMed Central

    Laliberté, F.; Chang, J.; Doiron-Leyraud, N.; Hassinger, E.; Daou, R.; Rondeau, M.; Ramshaw, B.J.; Liang, R.; Bonn, D.A.; Hardy, W.N.; Pyon, S.; Takayama, T.; Takagi, H.; Sheikin, I.; Malone, L.; Proust, C.; Behnia, K.; Taillefer, Louis

    2011-01-01

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa2Cu3Oy (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La1.8−xEu0.2SrxCuO4 (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates. PMID:21847106

  8. Fermi-surface reconstruction by stripe order in cuprate superconductors.

    PubMed

    Laliberté, F; Chang, J; Doiron-Leyraud, N; Hassinger, E; Daou, R; Rondeau, M; Ramshaw, B J; Liang, R; Bonn, D A; Hardy, W N; Pyon, S; Takayama, T; Takagi, H; Sheikin, I; Malone, L; Proust, C; Behnia, K; Taillefer, Louis

    2011-08-16

    The origin of pairing in a superconductor resides in the underlying normal state. In the cuprate high-temperature superconductor YBa(2)Cu(3)O(y) (YBCO), application of a magnetic field to suppress superconductivity reveals a ground state that appears to break the translational symmetry of the lattice, pointing to some density-wave order. Here we use a comparative study of thermoelectric transport in the cuprates YBCO and La(1.8-x)Eu(0.2)Sr(x)CuO(4) (Eu-LSCO) to show that the two materials exhibit the same process of Fermi-surface reconstruction as a function of temperature and doping. The fact that in Eu-LSCO this reconstruction coexists with spin and charge modulations that break translational symmetry shows that stripe order is the generic non-superconducting ground state of hole-doped cuprates.

  9. Ultrasonic probe of the AuZn Fermi surface.

    SciTech Connect

    Svitelskiy, O.; Suslov, A. V.; Singleton, J. M.; Lashley, J. C.

    2005-01-01

    We, for the first time, apply the ultrasonic pulse-echo technique to explore the Fermi surface of the martensite phase of the single crystalline AuZn shape memory alloy. The ultrasonic measurements were performed in the magnetic fields of up to 45 T in the temperature range of 0.07 < T < 300 K. In the martensite phase (T < 64 K), the oscillations of the speed of the longitudinal sound wave propagating in the (110) direction indicated a strong acoustic de Haas - van Alphen effect. In addition to the earlier described oscillations with frequencies of 1140 and 4720 Tesla, we observed a new frequency of 120 Tesla, which was predicted theoretically. Corresponding effective masses were in favorable agreement with those expected from band structure calculations.

  10. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    PubMed Central

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-01-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier–Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence. PMID:27845342

  11. Surface to bulk Fermi arcs via Weyl nodes as topological defects

    NASA Astrophysics Data System (ADS)

    Kim, Kun Woo; Lee, Woo-Ram; Kim, Yong Baek; Park, Kwon

    2016-11-01

    A hallmark of Weyl semimetal is the existence of surface Fermi arcs. An intriguing question is what determines the connectivity of surface Fermi arcs, when multiple pairs of Weyl nodes are present. To answer this question, we show that the locations of surface Fermi arcs are predominantly determined by the condition that the Zak phase integrated along the normal-to-surface direction is . The Zak phase can reveal the peculiar topological structure of Weyl semimetal directly in the bulk. Here, we show that the winding of the Zak phase around each projected Weyl node manifests itself as a topological defect of the Wannier-Stark ladder, energy eigenstates under an electric field. Remarkably, this leads to bulk Fermi arcs, open-line segments in the bulk spectra. Bulk Fermi arcs should exist in conjunction with surface counterparts to conserve the Weyl fermion number under an electric field, which is supported by explicit numerical evidence.

  12. Electronic structure model of the hidden order and Fermi surface gapping in URu2Si2

    NASA Astrophysics Data System (ADS)

    Oppeneer, Peter; Elgazzar, Saad; Rusz, Jan; Suzuki, Michi-To; Mydosh, John

    2009-03-01

    The hidden order (HO) in the heavy-fermion superconductor URu2Si2 has been studied for more than 20 years, without that the nature of this unusual phase could be uncovered. We present a microscopic explanation for the mechanism of the hidden order, on the basis of state-of-the-art electronic structure calculations. In particular, we show that our calculations explain very well all the known properties of the paramagnetic and large moment antiferromagnetic (LMAF) phases. Exploiting the known experimental equivalence between the Fermi surface properties of the LMAF and HO phases, we identify the Fermi surface ``hot spots'' where a Fermi surface instability is lifted through spontaneous symmetry breaking, causing a surprisingly large Fermi surface gapping. We quantify that symmetry breaking through collective modes of antiferromagnetic moment excitations can induce a substantial Fermi surface gapping that consistently explains the transport properties and entropy loss of the HO phase.

  13. Quantum oscillations from surface Fermi arcs in Weyl and Dirac semimetals.

    PubMed

    Potter, Andrew C; Kimchi, Itamar; Vishwanath, Ashvin

    2014-10-20

    In a magnetic field, electrons in metals repeatedly traverse closed magnetic orbits around the Fermi surface. The resulting oscillations in the density of states enable powerful experimental techniques for measuring a metal's Fermi surface structure. On the other hand, the surface states of Weyl semimetals consist of disjoint, open Fermi arcs raising the question of whether they can be observed by standard quantum oscillatory techniques. Here, we find that the open Fermi arcs participate in unusual closed magnetic orbits by traversing the bulk of the sample to connect opposite surfaces. These orbits have anomalous features that are impossible for conventional surface states, and result in quantum oscillations that contain observable signatures of the topological character of the bulk Weyl semimetal. We also apply our predictions to the compounds Cd3As2 and Na3Bi that were recently proposed to be three-dimensional Dirac (doubled Weyl) semimetals, and propose experimental signatures of their possible Fermi arc states.

  14. Electronic structure and Fermi surface of UNZ ( Z=Se and Te) by ab initio calculations

    NASA Astrophysics Data System (ADS)

    Samsel-Czekała, M.

    2010-05-01

    The electronic structures of ferromagnetic (FM) UNTe and its nonmagnetically ordered (NMO) isostructural (tetragonal P4/nmm ) and isoelectronic counterpart, UNSe, have been calculated from first principles in the framework of the fully relativistic and full-potential local-orbital band-structure code within local-spin density approximation (LSDA) including also an orbital polarization correction by Eriksson, Brooks, and Johansson (OPB). The results predict that both ternaries have a covalently metallic character and solely uranium atoms, located in (001) planes, form a metallic bond due to the U5f-6d electrons. The U5f electrons contribute also to a covalent bond with the ligand N and Te or Se atoms and they reveal a dual character, i.e., partly localized and itinerant. Contrary to UNSe, UNTe is a collinear FM with the magnetic moment alignment along the c axis, as observed experimentally in the past and now is well reproduced by the LSDA+OPB calculations. In NMO states of both systems, band pseudogaps are opening merely ˜0.25eV below the Fermi level, which cause an instability of the metallic state under small perturbations leading to a semiconducting behavior. The two-band Fermi surfaces (FSs) of both compounds (in NMO state) have similar quasi-two-dimensional (Q2D) properties with nesting vectors along the [100] direction. In turn, UNTe in the FM state possesses three-band FS with also Q2D properties and nesting features along the [100] and [110] directions, being important, e.g., in arising such collective phenomena as superconductivity.

  15. Fermi surface and quantum well states of V(110) films on W(110)

    NASA Astrophysics Data System (ADS)

    Krupin, Oleg; Rotenberg, Eli; Kevan, S. D.

    2007-09-01

    Using angle-resolved photoemission spectroscopy, we have measured the Fermi surface of V(110) films epitaxially grown on a W(110) substrate. We compare our results for thicker films to existing calculations and measurements for bulk vanadium and find generally very good agreement. For thinner films, we observe and analyse a diverse array of quantum well states that split and distort the Fermi surface segments. We have searched unsuccessfully for a thickness-induced topological transition associated with contact between the zone-centre jungle gym and zone-boundary hole ellipsoid Fermi surface segments. We also find no evidence for ferromagnetic splitting of any bands on this surface.

  16. Surface Tension Components Based Selection of Cosolvents for Efficient Liquid Phase Exfoliation of 2D Materials.

    PubMed

    Shen, Jianfeng; Wu, Jingjie; Wang, Man; Dong, Pei; Xu, Jingxuan; Li, Xiaoguang; Zhang, Xiang; Yuan, Junhua; Wang, Xifan; Ye, Mingxin; Vajtai, Robert; Lou, Jun; Ajayan, Pulickel M

    2016-05-01

    A proper design of direct liquid phase exfoliation (LPE) for 2D materials as graphene, MoS2 , WS2 , h-BN, Bi2 Se3 , MoSe2 , SnS2 , and TaS2 with common cosolvents is carried out based on considering the polar and dispersive components of surface tensions of various cosolvents and 2D materials. It has been found that the exfoliation efficiency is enhanced by matching the ratio of surface tension components of cosolvents to that of the targeted 2D materials, based on which common cosolvents composed of IPA/water, THF/water, and acetone/water can be designed for sufficient LPE process. In this context, the library of low-toxic and low-cost solvents with low boiling points for LPE is infinitely enlarged when extending to common cosolvents. Polymer-based composites reinforced with a series of different 2D materials are compared with each other. It is demonstrated that the incorporation of cosolvents-exfoliated 2D materials can substantially improve the mechanical and thermal properties of polymer matrices. Typically, with the addition of 0.5 wt% of such 2D material as MoS2 nanosheets, the tensile strength and Young's modulus increased up to 74.85% and 136.97%, respectively. The different enhancement effect of 2D materials is corresponded to the intrinsic properties and LPE capacity of 2D materials.

  17. Gold-induced nanowires on the Ge(100) surface yield a 2D and not a 1D electronic structure

    NASA Astrophysics Data System (ADS)

    de Jong, N.; Heimbuch, R.; Eliëns, S.; Smit, S.; Frantzeskakis, E.; Caux, J.-S.; Zandvliet, H. J. W.; Golden, M. S.

    2016-06-01

    Atomic nanowires on semiconductor surfaces induced by the adsorption of metallic atoms have attracted a lot of attention as possible hosts of the elusive, one-dimensional Tomonaga-Luttinger liquid. The Au/Ge(100) system in particular is the subject of controversy as to whether the Au-induced nanowires do indeed host exotic, 1D (one-dimensional) metallic states. In light of this debate, we report here a thorough study of the electronic properties of high quality nanowires formed at the Au/Ge(100) surface. The high-resolution ARPES data show the low-lying Au-induced electronic states to possess a dispersion relation that depends on two orthogonal directions in k space. Comparison of the E (kx,ky) surface measured using high-resolution ARPES to tight-binding calculations yields hopping parameters in the two different directions that differ by approximately factor of two. Additionally, by pinpointing the Au-induced surface states in the first, second, and third surface Brillouin zones and analyzing their periodicity in k||, the nanowire propagation direction seen clearly in STM can be imported into the ARPES data. We find that the larger of the two hopping parameters corresponds, in fact, to the direction perpendicular to the nanowires (tperp). This proves that the Au-induced electron pockets possess a two-dimensional, closed Fermi surface, and this firmly places the Au/Ge(100) nanowire system outside potential hosts of a Tomonaga-Luttinger liquid. We combine these ARPES data with scanning tunneling spectroscopic measurements of the spatially resolved electronic structure and find that the spatially straight—wirelike—conduction channels observed up to energies of order one electron volt below the Fermi level do not originate from the Au-induced states seen in the ARPES data. The former are rather more likely to be associated with bulk Ge states that are localized to the subsurface region. Despite our proof of the 2D (two-dimentional) nature of the Au

  18. Phase diagram of electronic systems with quadratic Fermi nodes in 2 <d <4 : 2 +ɛ expansion, 4 -ɛ expansion, and functional renormalization group

    NASA Astrophysics Data System (ADS)

    Janssen, Lukas; Herbut, Igor F.

    2017-02-01

    Several materials in the regime of strong spin-orbit interaction such as HgTe, the pyrochlore iridate Pr2Ir2O7 , and the half-Heusler compound LaPtBi, as well as various systems related to these three prototype materials, are believed to host a quadratic band touching point at the Fermi level. Recently, it has been proposed that such a three-dimensional gapless state is unstable to a Mott-insulating ground state at low temperatures when the number of band touching points N at the Fermi level is smaller than a certain critical number Nc. We further substantiate and quantify this scenario by various approaches. Using ɛ expansion near two spatial dimensions, we show that Nc=64 /(25 ɛ2) +O (1 /ɛ ) and demonstrate that the instability for N 2 <d <4 . Directly in d =3 we therewith find Nc=1.86 , and thus again above the physical N =1 . All these results are consistent with the prediction that the interacting ground state of pure, unstrained HgTe, and possibly also Pr2Ir2O7 , is a strong topological insulator with a dynamically generated gap—a topological Mott insulator.

  19. Point-contact spectroscopy in Co-doped CaFe2As2: nodal superconductivity and topological Fermi surface transition

    NASA Astrophysics Data System (ADS)

    Gonnelli, R. S.; Tortello, M.; Daghero, D.; Kremer, K.; Bukowski, Z.; Zhigadlo, N. D.; Karpinski, J.

    2012-06-01

    We performed point-contact Andreev-reflection spectroscopy measurements in Ca(Fe1-xCox)2As2 single crystals with effective x = 0.060 ± 0.005. The spectra of ab-plane contacts show a zero-bias maximum and broad shoulders at about 5-6 meV. Their fit with the three-dimensional Blonder-Tinkham-Klapwijk (BTK) model (making use of an analytical expression for the Fermi surface that mimics the one calculated from first principles) shows that this compound presents a large isotropic gap on the quasi-2D electronlike Fermi surface sheets and a smaller anisotropic (possibly nodal) gap on the 3D holelike Fermi surface pockets centered at the Z point in the Brillouin zone. These results nicely fit into the theoretical picture for the appearance of nodal superconductivity in 122 compounds.

  20. Fermi surface, charge-density-wave gap, and kinks in 2H- TaSe2

    NASA Astrophysics Data System (ADS)

    Rossnagel, K.; Rotenberg, Eli; Koh, H.; Smith, N. V.; Kipp, L.

    2005-09-01

    The Fermi surface of the layered charge-density-wave compound 2H-TaSe2 is measured by angle-resolved photoemission as a function of temperature. A surprising Fermi-surface topology and a Fermi-surface branch-dependent charge-density-wave gap are found. In the charge-density-wave state band hybridization effects are strong and responsible for kinks in the band dispersions at relatively high binding energy. The implications of the results on the charge-density-wave mechanism are discussed.

  1. Fermi-Surface Reconstruction and Complex Phase Equilibria in CaFe2As2

    NASA Astrophysics Data System (ADS)

    Gofryk, K.; Saparov, B.; Durakiewicz, T.; Chikina, A.; Danzenbächer, S.; Vyalikh, D. V.; Graf, M. J.; Sefat, A. S.

    2014-05-01

    Fermi-surface topology governs the relationship between magnetism and superconductivity in iron-based materials. Using low-temperature transport, angle-resolved photoemission, and x-ray diffraction, we show unambiguous evidence of large Fermi-surface reconstruction in CaFe2As2 at magnetic spin-density-wave and nonmagnetic collapsed-tetragonal (cT) transitions. For the cT transition, the change in the Fermi-surface topology has a different character with no contribution from the hole part of the Fermi surface. In addition, the results suggest that the pressure effect in CaFe2As2 is mainly leading to a rigid-band-like change of the valence electronic structure. We discuss these results and their implications for magnetism and superconductivity in this material.

  2. The Fermi surface and f-valence electron count of UPt{sub 3}.

    SciTech Connect

    McMullan, G. J.; Rourke, P. M. C.; Norman, M. R.; Huxley, A. D.; Doiron-Layraud, N.; Flouquet, J.; Lonzarich, G. G.; McCollam, A.; Julian, S. R.; Materials Science Division; MRC Lab. Molecular Biology; Univ. of Toronto; School of Phys. Edinburgh; Univ. de Sherbrooke; CEA Univ. of Cambridge

    2008-01-01

    Combining old and new de Haas-van Alphen (dHvA) and magnetoresistance data, we arrive at a detailed picture of the Fermi surface of the heavy fermion superconductor UPt{sub 3}. Our work was partially motivated by a new proposal that two 5f valence electrons per formula unit in UPt{sub 3} are localized by correlation effects--agreement with previous dHvA measurements of the Fermi surface was invoked in its support. Comprehensive comparison with our new observations shows that this 'partially localized' model fails to predict the existence of a major sheet of the Fermi surface, and is therefore less compatible with experiment than the originally proposed 'fully itinerant' model of the electronic structure of UPt{sub 3}. In support of this conclusion, we offer a more complete analysis of the fully itinerant band structure calculation, where we find a number of previously unrecognized extremal orbits on the Fermi surface.

  3. Fermi-surface reconstruction and complex phase equilibria in CaFe2As2.

    PubMed

    Gofryk, K; Saparov, B; Durakiewicz, T; Chikina, A; Danzenbächer, S; Vyalikh, D V; Graf, M J; Sefat, A S

    2014-05-09

    Fermi-surface topology governs the relationship between magnetism and superconductivity in iron-based materials. Using low-temperature transport, angle-resolved photoemission, and x-ray diffraction, we show unambiguous evidence of large Fermi-surface reconstruction in CaFe2As2 at magnetic spin-density-wave and nonmagnetic collapsed-tetragonal (cT) transitions. For the cT transition, the change in the Fermi-surface topology has a different character with no contribution from the hole part of the Fermi surface. In addition, the results suggest that the pressure effect in CaFe2As2 is mainly leading to a rigid-band-like change of the valence electronic structure. We discuss these results and their implications for magnetism and superconductivity in this material.

  4. Strong phonon anomalies and Fermi surface nesting of simple cubic Polonium

    NASA Astrophysics Data System (ADS)

    Belabbes, A.; Zaoui, A.; Ferhat, M.

    2010-12-01

    The unknown lattice dynamics of simple cubic Polonium is calculated using first-principles density-functional perturbation theory with pseudopotentials and a plane-wave basis set. We notice several phonon anomalies, in particular along major symmetry directions namely M-R, R-Γ, Γ-M, M-X, and X-Γ. The analysis of the Fermi surface strongly suggests that the observed phonon anomalies are Kohn anomalies arising from strong Fermi surface nesting.

  5. Unusual dimensionality effects and surface charge density in 2D Mg(OH)2.

    PubMed

    Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M; Tongay, Sefaattin

    2016-02-05

    We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics.

  6. Unusual dimensionality effects and surface charge density in 2D Mg(OH)2

    PubMed Central

    Suslu, Aslihan; Wu, Kedi; Sahin, Hasan; Chen, Bin; Yang, Sijie; Cai, Hui; Aoki, Toshihiro; Horzum, Seyda; Kang, Jun; Peeters, Francois M.; Tongay, Sefaattin

    2016-01-01

    We present two-dimensional Mg(OH)2 sheets and their vertical heterojunctions with CVD-MoS2 for the first time as flexible 2D insulators with anomalous lattice vibration and chemical and physical properties. New hydrothermal crystal growth technique enabled isolation of environmentally stable monolayer Mg(OH)2 sheets. Raman spectroscopy and vibrational calculations reveal that the lattice vibrations of Mg(OH)2 have fundamentally different signature peaks and dimensionality effects compared to other 2D material systems known to date. Sub-wavelength electron energy-loss spectroscopy measurements and theoretical calculations show that Mg(OH)2 is a 6 eV direct-gap insulator in 2D, and its optical band gap displays strong band renormalization effects from monolayer to bulk, marking the first experimental confirmation of confinement effects in 2D insulators. Interestingly, 2D-Mg(OH)2 sheets possess rather strong surface polarization (charge) effects which is in contrast to electrically neutral h-BN materials. Using 2D-Mg(OH)2 sheets together with CVD-MoS2 in the vertical stacking shows that a strong change transfer occurs from n-doped CVD-MoS2 sheets to Mg(OH)2, naturally depleting the semiconductor, pushing towards intrinsic doping limit and enhancing overall optical performance of 2D semiconductors. Results not only establish unusual confinement effects in 2D-Mg(OH)2, but also offer novel 2D-insulating material with unique physical, vibrational, and chemical properties for potential applications in flexible optoelectronics. PMID:26846617

  7. Effects of Surface Ligand Density on Lipid-Monolayer-mediated 2D Assembly of Proteins

    SciTech Connect

    Fukuto, M.; Wang, S; Lohr, M; Kewalramani, S; Yang, L

    2010-01-01

    The two-dimensional (2D) assembly of the protein streptavidin on a biotin-bearing lipid monolayer was studied as a function of the surface density of biotin, a protein-binding ligand, by means of in situ X-ray scattering and optical Brewster angle microscopy measurements at the liquid-vapor interface. Although this model system has been studied extensively, the relationship between the surface biotin density and the adsorption, 2D phase behavior, and binding state of streptavidin has yet to be determined quantitatively. The observed equilibrium phase behavior provides direct structural evidence that the 2D crystallization of the lipid-bound streptavidin occurs as a density-driven first-order phase transition. The minimum biotin density required for the 2D crystallization of streptavidin is found to be remarkably close to the density of the ligand-binding sites in the protein crystal. Moreover, both above and below this transition, the observed biotin-density dependence of protein adsorption is well described by the binding of biotin-bearing lipids at both of the two available sites per streptavidin molecule. These results imply that even in the low-density noncrystalline phase, the bound proteins share a common, fixed orientation relative to the surface normal, and that the 2D crystallization occurs when the lateral protein density reaches 50-70% of the 2D crystal density. This study demonstrates that in addition to a well-defined molecular orientation, high lateral packing density is essential to the 2D crystallization of proteins.

  8. Surface Fermi arc connectivity in the type-II Weyl semimetal candidate WTe2

    NASA Astrophysics Data System (ADS)

    Sánchez-Barriga, J.; Vergniory, M. G.; Evtushinsky, D.; Aguilera, I.; Varykhalov, A.; Blügel, S.; Rader, O.

    2016-10-01

    We perform ultrahigh-resolution angle-resolved photoemission experiments at a temperature T =0.8 K on the type-II Weyl semimetal candidate WTe2. We find a surface Fermi arc connecting the bulk electron and hole pockets on the (001) surface. Our results show that the surface Fermi arc connectivity to the bulk bands is strongly mediated by distinct surface resonances dispersing near the border of the surface-projected bulk band gap. By comparing the experimental results to first-principles calculations, we argue that the coupling to these surface resonances, which are topologically trivial, is compatible with the classification of WTe2 as a type-II Weyl semimetal hosting topological Fermi arcs. We further support our conclusion by a systematic characterization of the bulk and surface character of the different bands and discuss the similarity of our findings to the case of topological insulators.

  9. Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics

    NASA Astrophysics Data System (ADS)

    Wang, Z. F.; Liu, Feng

    2015-07-01

    Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1 /3 monolayer halogen coverage. The s p3 dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (˜106 m /s ) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

  10. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions

    PubMed Central

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-01-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes. PMID:27551687

  11. Visualizing weakly bound surface Fermi arcs and their correspondence to bulk Weyl fermions.

    PubMed

    Batabyal, Rajib; Morali, Noam; Avraham, Nurit; Sun, Yan; Schmidt, Marcus; Felser, Claudia; Stern, Ady; Yan, Binghai; Beidenkopf, Haim

    2016-08-01

    Fermi arcs are the surface manifestation of the topological nature of Weyl semimetals, enforced by the bulk-boundary correspondence with the bulk Weyl nodes. The surface of tantalum arsenide, similar to that of other members of the Weyl semimetal class, hosts nontopological bands that obscure the exploration of this correspondence. We use the spatial structure of the Fermi arc wave function, probed by scanning tunneling microscopy, as a spectroscopic tool to distinguish and characterize the surface Fermi arc bands. We find that, as opposed to nontopological states, the Fermi arc wave function is weakly affected by the surface potential: it spreads rather uniformly within the unit cell and penetrates deeper into the bulk. Fermi arcs reside predominantly on tantalum sites, from which the topological bulk bands are derived. Furthermore, we identify a correspondence between the Fermi arc dispersion and the energy and momentum of the bulk Weyl nodes that classify this material as topological. We obtain these results by introducing an analysis based on the role the Bloch wave function has in shaping quantum electronic interference patterns. It thus carries broader applicability to the study of other electronic systems and other physical processes.

  12. 3D surface reconstruction of apples from 2D NIR images

    NASA Astrophysics Data System (ADS)

    Zhu, Bin; Jiang, Lu; Cheng, Xuemei; Tao, Yang

    2005-11-01

    Machine vision methods are widely used in apple defect detection and quality grading applications. Currently, 2D near-infrared (NIR) imaging of apples is often used to detect apple defects because the image intensity of defects is different from normal apple parts. However, a drawback of this method is that the apple calyx also exhibits similar image intensity to the apple defects. Since an apple calyx often appears in the NIR image, the false alarm rate is high with the 2D NIR imaging method. In this paper, a 2D NIR imaging method is extended to a 3D reconstruction so that the apple calyx can be differentiated from apple defects according to their different 3D depth information. The Lambertian model is used to evaluate the reflectance map of the apple surface, and then Pentland's Shape-From-Shading (SFS) method is applied to reconstruct the 3D surface information of the apple based on Fast Fourier Transform (FFT). Pentland's method is directly derived from human perception properties, making it close to the way human eyes recover 3D information from a 2D scene. In addition, the FFT reduces the computation time significantly. The reconstructed 3D apple surface maps are shown in the results, and different depths of apple calyx and defects are obtained correctly.

  13. 11B and 27Al NMR spin-lattice relaxation and Knight shift of Mg1-xAlxB2: Evidence for an anisotropic Fermi surface

    NASA Astrophysics Data System (ADS)

    Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.

    2002-10-01

    We report a detailed study of the 11B and 27Al NMR spin-lattice relaxation rates (1/T1) and the 27Al Knight shift (K) in Mg1-xAlxB2, 0<=x<=1. The evolution of (1/T1T) and K with x is in excellent agreement with the prediction of ab initio calculations of a highly anisotropic Fermi surface, consisting mainly of hole-type two-dimensional (2D) cylindrical sheets from bonding 2px,y boron orbitals. The density of states at the Fermi level also decreases sharply on Al doping and the 2D sheets collapse at x~0.55, where the superconducting phase disappears.

  14. Elastic shape analysis of cylindrical surfaces for 3D/2D registration in endometrial tissue characterization.

    PubMed

    Samir, Chafik; Kurtek, Sebastian; Srivastava, Anuj; Canis, Michel

    2014-05-01

    We study the problem of joint registration and deformation analysis of endometrial tissue using 3D magnetic resonance imaging (MRI) and 2D trans-vaginal ultrasound (TVUS) measurements. In addition to the different imaging techniques involved in the two modalities, this problem is complicated due to: 1) different patient pose during MRI and TVUS observations, 2) the 3D nature of MRI and 2D nature of TVUS measurements, 3) the unknown intersecting plane for TVUS in MRI volume, and 4) the potential deformation of endometrial tissue during TVUS measurement process. Focusing on the shape of the tissue, we use expert manual segmentation of its boundaries in the two modalities and apply, with modification, recent developments in shape analysis of parametric surfaces to this problem. First, we extend the 2D TVUS curves to generalized cylindrical surfaces through replication, and then we compare them with MRI surfaces using elastic shape analysis. This shape analysis provides a simultaneous registration (optimal reparameterization) and deformation (geodesic) between any two parametrized surfaces. Specifically, it provides optimal curves on MRI surfaces that match with the original TVUS curves. This framework results in an accurate quantification and localization of the deformable endometrial cells for radiologists, and growth characterization for gynecologists and obstetricians. We present experimental results using semi-synthetic data and real data from patients to illustrate these ideas.

  15. Surface wave phase velocities from 2-D surface wave tomography studies in the Anatolian plate

    NASA Astrophysics Data System (ADS)

    Arif Kutlu, Yusuf; Erduran, Murat; Çakır, Özcan; Vinnik, Lev; Kosarev, Grigoriy; Oreshin, Sergey

    2014-05-01

    We study the Rayleigh and Love surface wave fundamental mode propagation beneath the Anatolian plate. To examine the inter-station phase velocities a two-station method is used along with the Multiple Filter Technique (MFT) in the Computer Programs in Seismology (Herrmann and Ammon, 2004). The near-station waveform is deconvolved from the far-station waveform removing the propagation effects between the source and the station. This method requires that the near and far stations are aligned with the epicentre on a great circle path. The azimuthal difference of the earthquake to the two-stations and the azimuthal difference between the earthquake and the station are restricted to be smaller than 5o. We selected 3378 teleseismic events (Mw >= 5.7) recorded by 394 broadband local stations with high signal-to-noise ratio within the years 1999-2013. Corrected for the instrument response suitable seismogram pairs are analyzed with the two-station method yielding a collection of phase velocity curves in various period ranges (mainly in the range 25-185 sec). Diffraction from lateral heterogeneities, multipathing, interference of Rayleigh and Love waves can alter the dispersion measurements. In order to obtain quality measurements, we select only smooth portions of the phase velocity curves, remove outliers and average over many measurements. We discard these average phase velocity curves suspected of suffering from phase wrapping errors by comparing them with a reference Earth model (IASP91 by Kennett and Engdahl, 1991). The outlined analysis procedure yields 3035 Rayleigh and 1637 Love individual phase velocity curves. To obtain Rayleigh and Love wave travel times for a given region we performed 2-D tomographic inversion for which the Fast Marching Surface Tomography (FMST) code developed by N. Rawlinson at the Australian National University was utilized. This software package is based on the multistage fast marching method by Rawlinson and Sambridge (2004a, 2004b). The

  16. Self-surface charge exfoliation and electrostatically coordinated 2D hetero-layered hybrids

    PubMed Central

    Yang, Min-Quan; Xu, Yi-Jun; Lu, Wanheng; Zeng, Kaiyang; Zhu, Hai; Xu, Qing-Hua; Ho, Ghim Wei

    2017-01-01

    At present, the technological groundwork of atomically thin two-dimensional (2D) hetero-layered structures realized by successive thin film epitaxial growth is in principle constrained by lattice matching prerequisite as well as low yield and expensive production. Here, we artificially coordinate ultrathin 2D hetero-layered metal chalcogenides via a highly scalable self-surface charge exfoliation and electrostatic coupling approach. Specifically, bulk metal chalcogenides are spontaneously exfoliated into ultrathin layers in a surfactant/intercalator-free medium, followed by unconstrained electrostatic coupling with a dissimilar transition metal dichalcogenide, MoSe2, into scalable hetero-layered hybrids. Accordingly, surface and interfacial-dominated photocatalysis reactivity is used as an ideal testbed to verify the reliability of diverse 2D ultrathin hetero-layered materials that reveal high visible-light photoreactivity, efficient charge transfer and intimate contact interface for stable cycling and storage purposes. Such a synthetic approach renders independent thickness and composition control anticipated to advance the development of ‘design-and-build' 2D layered heterojunctions for large-scale exploration and applications. PMID:28146147

  17. Self-surface charge exfoliation and electrostatically coordinated 2D hetero-layered hybrids

    NASA Astrophysics Data System (ADS)

    Yang, Min-Quan; Xu, Yi-Jun; Lu, Wanheng; Zeng, Kaiyang; Zhu, Hai; Xu, Qing-Hua; Ho, Ghim Wei

    2017-02-01

    At present, the technological groundwork of atomically thin two-dimensional (2D) hetero-layered structures realized by successive thin film epitaxial growth is in principle constrained by lattice matching prerequisite as well as low yield and expensive production. Here, we artificially coordinate ultrathin 2D hetero-layered metal chalcogenides via a highly scalable self-surface charge exfoliation and electrostatic coupling approach. Specifically, bulk metal chalcogenides are spontaneously exfoliated into ultrathin layers in a surfactant/intercalator-free medium, followed by unconstrained electrostatic coupling with a dissimilar transition metal dichalcogenide, MoSe2, into scalable hetero-layered hybrids. Accordingly, surface and interfacial-dominated photocatalysis reactivity is used as an ideal testbed to verify the reliability of diverse 2D ultrathin hetero-layered materials that reveal high visible-light photoreactivity, efficient charge transfer and intimate contact interface for stable cycling and storage purposes. Such a synthetic approach renders independent thickness and composition control anticipated to advance the development of `design-and-build' 2D layered heterojunctions for large-scale exploration and applications.

  18. Surface effects on electronic transport of 2D chalcogenide thin films and nanostructures.

    PubMed

    Jung, Yeonwoong; Shen, Jie; Cha, Judy J

    2014-01-01

    The renewed interest in two-dimensional materials, particularly transition metal dichalcogenides, has been explosive, evident in a number of review and perspective articles on the topic. Our ability to synthesize and study these 2D materials down to a single layer and to stack them to form van der Waals heterostructures opens up a wide range of possibilities from fundamental studies of nanoscale effects to future electronic and optoelectronic applications. Bottom-up and top-down synthesis and basic electronic properties of 2D chalcogenide materials have been covered in great detail elsewhere. Here, we bring attention to more subtle effects: how the environmental, surface, and crystal defects modify the electronic band structure and transport properties of 2D chalcogenide nanomaterials. Surface effects such as surface oxidation and substrate influence may dominate the overall transport properties, particularly in single layer chalcogenide devices. Thus, understanding such effects is critical for successful applications based on these materials. In this review, we discuss two classes of chalcogenides - Bi-based and Mo-based chalcogenides. The first are topological insulators with unique surface electronic properties and the second are promising for flexible optoelectronic applications as well as hydrogen evolution catalytic reactions.

  19. Formation and properties of a terpyridine-based 2D MOF on the surface of water

    NASA Astrophysics Data System (ADS)

    Koitz, Ralph; Hutter, Jürg; Iannuzzi, Marcella

    2016-06-01

    Two-dimensional networks inspired by graphene are of prime importance in nanoscience. We present a computational study of an infinite molecular sheet confined on a water surface to assess its properties and formation mechanism. Terpyridine-based ligand molecules are interlinked by Zn ions to form an extended 2D metal-organic framework. We show that the network is stable on the water surface, and that the substrate affects the dynamic properties of the sheet, exhibiting a confining effect and flattening the sheet by 30%. We use metadynamics to characterize the process of network formation and breaking and determine an intra-network binding energy of 143 kJ mol-1. Based on this mechanistic insight we propose that the 2D network strength can be tuned by varying the rigidity of the ligand through its chemical structure.

  20. Probing Critical Surfaces in Momentum Space Using Real-Space Entanglement Entropy: Bose versus Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Kun; Lai, Hsin-Hua

    A co-dimension one critical surface in the momentum space can be either a familiar Fermi surface, which separates occupied states from empty ones in the non-interacting fermion case, or a novel Bose surface, where gapless bosonic excitations are anchored. Their presence gives rise to logarithmic violation of entanglement entropy area law. When they are convex, we show that the shape of these critical surfaces can be determined by inspecting the leading logarithmic term of real space entanglement entropy. The fundamental difference between a Fermi surface and a Bose surface is revealed by the fact that the logarithmic terms in entanglement entropies differ by a factor of two: SlogBose = 2SlogFermi , even when they have identical geometry. Our method has remarkable similarity with determining Fermi surface shape using quantum oscillation. We also discuss possible probes of concave critical surfaces in momentum space. HHL and KY acknowledge the National Science Foundation through Grants No. DMR-1004545, DMR-1157490, No. DMR-1442366, and State of Florida. HHL is also partially supported by NSF Grant No. DMR-1309531, and the Smalley Postdoctoral Fellowship in Quantum Ma.

  1. Quantum Oscillation Studies of the Fermi Surface of LaFePO

    SciTech Connect

    Carrington, A.

    2010-05-26

    We review recent experimental measurements of the Fermi surface of the iron-pnictide superconductor LaFePO using quantum oscillation techniques. These studies show that the Fermi surface topology is close to that predicted by first principles density functional theory calculations, consisting of quasi-twodimensional electron-like and hole-like sheets. The total volume of the two hole sheets is almost equal to that of the two electron sheets, and the hole and electron Fermi surface sheets are close to a nesting condition. No evidence for the predicted three dimensional pocket arising from the Fe d{sub z}{sup 2} band is found. Measurements of the effective mass suggest a renormalisation of around two, close to the value for the overall band renormalisation found in recent angle resolved photoemission measurements.

  2. Hall Effect in the Vortex Lattice of d-Wave Superconductors with Anisotropic Fermi Surfaces

    NASA Astrophysics Data System (ADS)

    Kohno, Wataru; Ueki, Hikaru; Kita, Takafumi

    2017-02-01

    On the basis of the augmented quasiclassical theory of superconductivity with the Lorentz force, we study the magnetic field dependence of the charge distribution due to the Lorentz force in a d-wave vortex lattice with anisotropic Fermi surfaces. Owing to the competition between the energy-gap and Fermi surface anisotropies, the charge profile in the vortex lattice changes dramatically with increasing magnetic field because of the overlaps of each nearest vortex-core charge. In addition, the accumulated charge in the core region may reverse its sign as a function of magnetic field. This strong field dependence of the vortex-core charge cannot be observed in the model with an isotropic Fermi surface.

  3. The effect of polarity and surface states on the Fermi level at III-nitride surfaces

    SciTech Connect

    Reddy, P; Bryan, I; Bryan, Z; Guo, W; Hussey, L; Collazo, R; Sitar, Z

    2014-09-28

    Surface states and their influence on the Fermi level at the surface of GaN and AlN are studied using x-ray photoelectron spectroscopy (XPS). The effect of polarity on surface electronic properties was studied. Accurate modeling of the valence band edge and comparison with XPS data revealed the presence of donor surface states at 1.4 eV and acceptor states at energies > 2.7 eV from the valence band in GaN. Al polar AlN showed acceptor states at energies > 3.3 eV. Density of acceptor surface states was estimated to be between 10(13) and 10(14) eV(-1) cm(-2) in both GaN and AlN. The shift in charge neutrality levels and barrier heights due to polarity and the density of surface states on AlN and GaN were estimated from XPS measurements. Theoretical modeling and comparison with XPS data implied full compensation of spontaneous polarization charge by charged surface states. Barrier height measurements also reveal a dependence on polarity with phi(metal-polar)>phi(non-polar)>phi(nitrogen-polar) suggesting that the N-polar surface is the most suitable for Ohmic contacts. (C) 2014 AIP Publishing LLC.

  4. Spin-polarized standing waves at an electronically matched interface detected by Fermi-surface photoemission

    NASA Astrophysics Data System (ADS)

    Schäfer, J.; Hoinkis, M.; Rotenberg, Eli; Blaha, P.; Claessen, R.

    2007-03-01

    Highly spin-polarized reflection at an interface of a ferromagnetic thin film is made visible by photoelectron spectroscopy. The technique of k -space mapping of the exchange-split Fermi surface is employed to detect standing waves confined to the ferromagnetic layer. A drastic spin asymmetry of this effect is achieved for a specific matching of the Fermi-surface topologies of film and substrate, respectively. For Fe(110) films on a W substrate, intense standing waves are obtained exclusively for majority states, while minority states are virtually unaffected by the boundary.

  5. Defining an optimal surface chemistry for pluripotent stem cell culture in 2D and 3D

    NASA Astrophysics Data System (ADS)

    Zonca, Michael R., Jr.

    Surface chemistry is critical for growing pluripotent stem cells in an undifferentiated state. There is great potential to engineer the surface chemistry at the nanoscale level to regulate stem cell adhesion. However, the challenge is to identify the optimal surface chemistry of the substrata for ES cell attachment and maintenance. Using a high-throughput polymerization and screening platform, a chemically defined, synthetic polymer grafted coating that supports strong attachment and high expansion capacity of pluripotent stem cells has been discovered using mouse embryonic stem (ES) cells as a model system. This optimal substrate, N-[3-(Dimethylamino)propyl] methacrylamide (DMAPMA) that is grafted on 2D synthetic poly(ether sulfone) (PES) membrane, sustains the self-renewal of ES cells (up to 7 passages). DMAPMA supports cell attachment of ES cells through integrin beta1 in a RGD-independent manner and is similar to another recently reported polymer surface. Next, DMAPMA has been able to be transferred to 3D by grafting to synthetic, polymeric, PES fibrous matrices through both photo-induced and plasma-induced polymerization. These 3D modified fibers exhibited higher cell proliferation and greater expression of pluripotency markers of mouse ES cells than 2D PES membranes. Our results indicated that desirable surfaces in 2D can be scaled to 3D and that both surface chemistry and structural dimension strongly influence the growth and differentiation of pluripotent stem cells. Lastly, the feasibility of incorporating DMAPMA into a widely used natural polymer, alginate, has been tested. Novel adhesive alginate hydrogels have been successfully synthesized by either direct polymerization of DMAPMA and methacrylic acid blended with alginate, or photo-induced DMAPMA polymerization on alginate nanofibrous hydrogels. In particular, DMAPMA-coated alginate hydrogels support strong ES cell attachment, exhibiting a concentration dependency of DMAPMA. This research provides a

  6. Two-dimensional Josephson vortex lattice and anomalously slow decay of the Fraunhofer oscillations in a ballistic SNS junction with a warped Fermi surface

    NASA Astrophysics Data System (ADS)

    Ostroukh, V. P.; Baxevanis, B.; Akhmerov, A. R.; Beenakker, C. W. J.

    2016-09-01

    The critical current of a Josephson junction is an oscillatory function of the enclosed magnetic flux Φ , because of quantum interference modulated with periodicity h /2 e . We calculate these Fraunhofer oscillations in a two-dimensional (2D) ballistic superconductor-normal-metal-superconductor (SNS) junction. For a Fermi circle the amplitude of the oscillations decays as 1 /Φ or faster. If the Fermi circle is strongly warped, as it is on a square lattice near the band center, we find that the amplitude decays slower, ∝1 /√{Φ } , when the magnetic length lm=√{ℏ /e B } drops below the separation L of the NS interfaces. The crossover to the slow decay of the critical current is accompanied by the appearance of a 2D array of current vortices and antivortices in the normal region, which form a bipartite rectangular lattice with lattice constant ≃lm2/L . The 2D lattice vanishes for a circular Fermi surface, when only the usual single row of Josephson vortices remains.

  7. Fermi surface of underdoped cuprate revealed by quantum oscillations and Hall effect

    NASA Astrophysics Data System (ADS)

    Proust, Cyril

    2008-03-01

    Despite twenty years of research, the phase diagram of high temperature superconductors remains enigmatic. A central issue is the origin of the differences in the physical properties of these copper oxides doped to opposite sides of the superconducting region. In the overdoped regime, the material behaves as a reasonably conventional metal, with a large Fermi surface [1]. The underdoped regime, however, is highly anomalous and appears to have no coherent Fermi surface, but only disconnected `Fermi arcs' [2]. We have reported the observation of quantum oscillations in the electrical resistance of the oxygen-ordered copper oxides YBa2Cu3O6.5 [3] and YBa2Cu4O8 [4], establishing the existence of a coherent closed Fermi surface at low temperature in the underdoped side of the phase diagram of cuprates, once superconductivity is suppressed by a large magnetic field. The low oscillation frequency reveals a Fermi surface made of small pockets, in contrast to the large cylinder characteristic of the overdoped regime. Moreover, the negative sign of the Hall effect at low temperature reveals that these pockets are electron-like rather than hole-like. We propose that the Fermi surface of these Y-based cuprates consists of both electron and hole pockets, probably arising from a reconstruction of the FS [5]. Work in collaboration with N Doiron-Leyraud, D. LeBoeuf and L. Taillefer from the University of Sherbrooke, J. Levallois and B. Vignolle from the LNCMP, A. Bangura and N. Hussey from the University of Bristol and R. Liang, D. Bonn, W. Hardy from the University of British Columbia. [1] N Hussey et al, Nature 425, 814 (2003) [2] M. Norman et al, Nature 392, 157 (1998) [3] N. Doiron-Leyraud et al, Nature 447, 565 (2007) [4] A. Bangura et al, submitted to Phys. Rev. Lett (arXiv: 0707.4461) [5] D. LeBoeuf et al, Nature 450, 533 (2007)

  8. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    PubMed Central

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; Bansil, Arun

    2015-01-01

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. We show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping. PMID:26084605

  9. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    DOE PAGES

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; ...

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  10. Momentum-resolved view of mixed 2D and nonbulklike 3D electronic structure of the surface state on SrTiO3 (001)

    NASA Astrophysics Data System (ADS)

    Plumb, N. C.; Salluzzo, M.; Razzoli, E.; Mansson, M.; Krempasky, J.; Matt, C. E.; Schmitt, T.; Shi, M.; Mesot, J.; Patthey, L.; Radovic, M.

    2014-03-01

    The recent discovery of a metallic surface state on SrTiO3 may open a route to simplified low-dimensional oxide-based conductors, as well as give new insights into interfacial phenomena in heterostructures such as LaAlO3/SrTiO3. Our recent angle-resolved photoemission spectroscopy (ARPES) study demonstrates that not only quasi-2D but also non-bulklike 3D Fermi surface components make up the surface state. Like their more 2D counterparts, the size and character of the 3D components are fixed with respect to a broad range of sample preparations. As seen in previous studies, the surface state can be ``prepared'' by photon irradiation under UHV conditions. An extremely high fraction of the surface valence states are affected by this process, especially in relation to the stability of oxygen core level intensity during the same exposure, which points to a key role of electronic/structural changes that spread over the surface as the metal emerges.

  11. Self-Assembled Si(111) Surface States: 2D Dirac Material for THz Plasmonics.

    PubMed

    Wang, Z F; Liu, Feng

    2015-07-10

    Graphene, the first discovered 2D Dirac material, has had a profound impact on science and technology. In the last decade, we have witnessed huge advances in graphene related fundamental and applied research. Here, based on first-principles calculations, we propose a new 2D Dirac band on the Si(111) surface with 1/3 monolayer halogen coverage. The sp(3) dangling bonds form a honeycomb superstructure on the Si(111) surface that results in an anisotropic Dirac band with a group velocity (∼10(6)  m/s) comparable to that in graphene. Most remarkably, the Si-based surface Dirac band can be used to excite a tunable THz plasmon through electron-hole doping. Our results demonstrate a new way to design Dirac states on a traditional semiconductor surface, so as to make them directly compatible with Si technology. We envision this new type of Dirac material to be generalized to other semiconductor surfaces with broad applications.

  12. The 2D surfaces that generate Newtonian and general relativistic orbits with small eccentricities

    NASA Astrophysics Data System (ADS)

    Middleton, Chad A.

    2015-07-01

    Embedding diagrams prove to be quite useful when learning general relativity as they offer a way of visualizing spacetime curvature through warped two dimensional (2D) surfaces. In this manuscript, we present a different 2D construct that also serves as a useful conceptual tool for gaining insight into gravitation: orbital dynamics—namely, the cylindrically symmetric surfaces that generate Newtonian and general relativistic orbits with small eccentricities. Although we first show that no such surface exists that can exactly reproduce the arbitrary bound orbits of Newtonian gravitation or of general relativity (or, more generally, of any spherically symmetric potential), surfaces do exist that closely approximate the resulting orbital motion for small eccentricities (exactly the regime that describes the motion of the solar system planets). These surfaces help to illustrate the similarities and differences between the two theories of gravitation (i.e., stationary elliptical orbits in Newtonian gravitation and precessing elliptical-like orbits in general relativity) and offer, in this age of 3D printing, an opportunity for students and instructors to experimentally explore the predictions made by each.

  13. Mirror effects and optical meta-surfaces in 2d atomic arrays

    NASA Astrophysics Data System (ADS)

    Shahmoon, Ephraim; Wild, Dominik; Lukin, Mikhail; Yelin, Susanne

    2016-05-01

    Strong optical response of natural and artificial (meta-) materials typically relies on the fact that the lattice constant that separates their constituent particles (atoms or electromagnetic resonators, respectively) is much smaller than the optical wavelength. Here we consider a single layer of a 2d atom array with a lattice constant on the order of an optical wavelength, which can be thought of as a highly dilute 2d metamaterial (meta-surface). Our theoretical analysis shows how strong scattering of resonant incoming light off the array can be controlled by choosing its lattice constant, e.g. allowing the array to operate as a perfect mirror or a retro-reflector for most incident angles of the incoming light. We discuss the prospects for quantum metasurfaces, i.e. the ability to shape the output quantum state of light by controlling the atomic states, and the possible generality of our results as a universal wave phenomena.

  14. Spin Texture on the Fermi Surface of Strained HgTe

    NASA Astrophysics Data System (ADS)

    Zaheer, Saad; Young, Steve; Cellucci, Daniel; Teo, Jeffrey; Kane, Charles; Mele, Eugene; Rappe, Andrew

    2012-02-01

    We present ab initio and k.p calculations of the Fermi surface of strained HgTe obtained by stretching the Zinc-Blende lattice along the (111) axis. Near the Fermi level, strained HgTe exhibits point-like accidental degeneracies between a two-fold degenerate and two non-degenerate bands along the (111) axis. The three bands disperse linearly in all directions about the degenerate points and their low energy physics is described by an effective four band k.p Hamiltonian. The Fermi surface consists of two ellipsoids which contact only at the point where the Fermi level crosses the two-fold degenerate band along the (111) axis. The spin expectation value on both ellipsoids is constrained to vanish along the (111) axis due to mirror symmetry about a plane that contains that axis. Furthermore the winding number of spins around the two ellipsoids changes from one end to the other indicating the existence of singular points in the spin texture. Indeed, the ab initio and k.p calculations confirm the existence of such spin singularities on the Fermi ellipsoids. We show that doping HgTe with Zinc atoms chemically strains the HgTe Zinc-Blende lattice and present ab initio calculations on HgZnTe that confirm the above results.

  15. Direct angle resolved photoelectron spectroscopy (DARPES) on high-Tc films: doping, strains, Fermi surface topology and superconductivity

    NASA Astrophysics Data System (ADS)

    Pavuna, D.; Ariosa, D.; Cancellieri, C.; Cloetta, D.; Abrecht, M.

    2008-03-01

    Since 1997 we systematically perform Direct ARPES ( = DARPES) on in-situ grown, non-cleaved, ultra-thin (<25nm) cuprate films. Specifically, we probe low energy electronic structure and properties of high-Tc films under different degree of epitaxial (compressive vs tensile) strain. In overdoped in-plane compressed La2-xSrxCuO4 (LSCO) thin films we double Tc from 20K to 40K, yet the Fermi surface (FS) remains essentially 2-dimensional (2D). In contrast, tensile strained films show 3-dimensional (3D) dispersion, while Tc is drastically reduced. It seems that the in-plane compressive strain tends to push the apical oxygen far away from the CuO2 plane, enhances the 2D character of the dispersion and increases Tc, while the tensile strain seems to act exactly in the opposite direction and the resulting dispersion is 3D. We have the FS topology for both cases. As the actual lattice of cuprates is 'Napoleon-cake' -like i.e. rigid CuO2 planes alternate with softer 'reservoir' (that strains distort differently) our results tend to rule out 2D rigid lattice mean field models. Finally, we briefly discuss recent successful determination of the FS topology from the observed wavevector quantization by DARPES in cuprate films thinner than 18 units cells (<24nm). Such an approach is of broader interest as it can be extended to other similar confined (ultra-thin) functional oxide systems.

  16. Reconstruction de la surface de Fermi dans l'etat normal d'un supraconducteur a haute Tc: Une etude du transport electrique en champ magnetique intense

    NASA Astrophysics Data System (ADS)

    Le Boeuf, David

    Des mesures de resistance longitudinale et de resistance de Hall en champ magnetique intense transverse (perpendiculaire aux plans CuO2) ont ete effectuees au sein de monocristaux de YBa2Cu3Oy (YBCO) demacles, ordonnes et de grande purete, afin d'etudier l'etat fondamental des supraconducteurs a haute Tc dans le regime sous-dope. Cette etude a ete realisee en fonction du dopage et de l'orientation du courant d'excitation J par rapport a l'axe orthorhombique b de la structure cristalline. Les mesures en champ magnetique intense revelent par suppression de la supraconductivite des oscillations magnetiques des resistances longitudinale et de Hall dans YBa2Cu 3O6.51 et YBa2Cu4O8. La conformite du comportement de ces oscillations quantiques au formalisme de Lifshitz-Kosevich, apporte la preuve de l'existence d'une surface de Fermi fermee a caractere quasi-2D, abritant des quasiparticules coherentes respectant la statistique de Fermi-Dirac, dans la phase pseudogap d'YBCO. La faible frequence des oscillations quantiques, combinee avec l'etude de la partie monotone de la resistance de Hall en fonction de la temperature indique que la surface de Fermi d'YBCO sous-dope comprend une petite poche de Fermi occupee par des porteurs de charge negative. Cette particularite de la surface de Fermi dans le regime sous-dope incompatible avec les calculs de structure de bande est en fort contraste avec la structure electronique presente dans le regime surdope. Cette observation implique ainsi l'existence d'un point critique quantique dans le diagramme de phase d'YBCO, au voisinage duquel la surface de Fermi doit subir une reconstruction induite par l'etablissement d'une brisure de la symetrie de translation du reseau cristallin sous-jacent. Enfin, l'etude en fonction du dopage de la resistance de Hall et de la resistance longitudinale en champ magnetique intense suggere qu'un ordre du type onde de densite (DW) est responsable de la reconstruction de la surface de Fermi. L'analogie de

  17. Investigation on the GPS single scattering from a 2-D largescale sea surface

    NASA Astrophysics Data System (ADS)

    Wei, Yiwen; Guo, Lixin

    2014-05-01

    Global positioning system (GPS) signals reflected from the ocean surface can be used for various remote sensing purposes. In this paper, we develop a facet model to simulate the received GPS single from a 2-D largescale sea surface. In this model, the sea surface is envisaged as a two-scale profile on which the long waves are locally approximated by planar facets. The microscopic profile within a facet is assumed to be represented by a set of sinusoidal ripple patches. The complex reflective function of each modified facet is evaluated by a modified formula of the original Bass and Fuks' two-scale model, in which the phase factor of each facet is with the capillary wave modification. The scattering field and the bistatic scattering coefficient of facet model is derived in detail. With received GPS single, we give a detail analysis of the polarization property, the scattering property of GPS scattering signal over the sea surface.

  18. Backscattering from a statistically rough 2-D surface: Diffraction corrections to geometrical optics cross sections

    NASA Astrophysics Data System (ADS)

    Fuks, Iosif M.

    2007-12-01

    Diffraction corrections (up to terms ˜1/k2) to the geometric optics backscattering cross sections from a statistically rough 2-D perfectly conducting surface were derived for TE- and TM-polarized electromagnetic waves based on the high-frequency asymptotic expansions of electric and magnetic fields at the surface obtained by Fuks (2004). It was shown that at steep incident angles, where the specular reflections play the main part in scattering, diffraction results can be interpreted as scattering by a fictitious surface, the roughness of which is gentler that the real surface at HH polarization and steeper at VV polarization. The HH/VV polarization ratio (dB), being positive at steep incident angles, gradually decreases as the incident angle increases, and it becomes negative for moderate incident angles.

  19. Bogoliubov Fermi Surfaces in Superconductors with Broken Time-Reversal Symmetry

    NASA Astrophysics Data System (ADS)

    Agterberg, D. F.; Brydon, P. M. R.; Timm, C.

    2017-03-01

    It is commonly believed that, in the absence of disorder or an external magnetic field, there are three possible types of superconducting excitation gaps: The gap is nodeless, it has point nodes, or it has line nodes. Here, we show that, for an even-parity nodal superconducting state which spontaneously breaks time-reversal symmetry, the low-energy excitation spectrum generally does not belong to any of these categories; instead, it has extended Bogoliubov Fermi surfaces. These Fermi surfaces can be visualized as two-dimensional surfaces generated by "inflating" point or line nodes into spheroids or tori, respectively. These inflated nodes are topologically protected from being gapped by a Z2 invariant, which we give in terms of a Pfaffian. We also show that superconducting states possessing these Fermi surfaces can be energetically stable. A crucial ingredient in our theory is that more than one band is involved in the pairing; since all candidate materials for even-parity superconductivity with broken time-reversal symmetry are multiband systems, we expect these Z2-protected Fermi surfaces to be ubiquitous.

  20. Skyrmions in quasi-2D chiral magnets with broken bulk and surface inversion symmetry (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Randeria, Mohit; Banerjee, Sumilan; Rowland, James

    2015-09-01

    Most theoretical studies of chiral magnetism, and the resulting spin textures, have focused on 3D systems with broken bulk inversion symmetry, where skyrmions are stabilized by easy-axis anisotropy. In this talk I will describe our results on 2D and quasi-2D systems with broken surface inversion, where we find [1] that skyrmion crystals are much more stable than in 3D, especially for the case of easy-plane anisotropy. These results are of particular interest for thin films, surfaces, and oxide interfaces [2], where broken surface-inversion symmetry and Rashba spin-orbit coupling naturally lead to both the chiral Dzyaloshinskii-Moriya (DM) interaction and to easy-plane compass anisotropy. I will then turn to systems that break both bulk and surface inversion, resulting in two distinct DM terms arising from Dresselhaus and Rashba spin-orbit coupling. I will describe [3] the evolution of the skyrmion structure and of the phase diagram as a function of the ratio of Dresselhaus and Rashba terms, which can be tuned by varying film thickness and strain. [1] S. Banerjee, J. Rowland, O. Erten, and M. Randeria, PRX 4, 031045 (2014). [2] S. Banerjee, O. Erten, and M. Randeria, Nature Phys. 9, 626 (2013). [3] J. Rowland, S. Banerjee and M. Randeria, (unpublished).

  1. Acoustic Receptivity of a Blasius Boundary Layer with 2-D and Oblique Surface Waviness

    NASA Technical Reports Server (NTRS)

    King, Rudolph A.; Breuer, Kenneth S.

    2000-01-01

    An experimental investigation was conducted to examine acoustic receptivity and subsequent boundary-layer instability evolution for a Blasius boundary layer formed on a flat plate in the presence of two-dimensional (2-D) and oblique (3-D) surface waviness. The effect of the non-localized surface roughness geometry and acoustic wave amplitude on the receptivity process was explored. The surface roughness had a well defined wavenumber spectrum with fundamental wavenumber k (sub w). A planar downstream traveling acoustic wave was created to temporally excite the flow near the resonance frequency of an unstable eigenmode corresponding to k (sub ts) = k (sub w). The range of acoustic forcing levels, epsilon, and roughness heights, DELTA h, examined resulted in a linear dependence of receptivity coefficients; however, the larger values of the forcing combination epsilon dot DELTA h resulted in subsequent nonlinear development of the Tollmien-Schlichting (T-S) wave. This study provided the first experimental evidence of a marked increase in the receptivity coefficient with increasing obliqueness of the surface waviness in excellent agreement with theory. Detuning of the 2-D and oblique disturbances was investigated by varying the streamwise wall-roughness wavenumber a,, and measuring the T-S response. For the configuration where laminar-to-turbulent breakdown occurred, the breakdown process was found to be dominated by energy at the fundamental and harmonic frequencies, indicative of K-type breakdown.

  2. Nested 1D-2D approach for urban surface flood modeling

    NASA Astrophysics Data System (ADS)

    Murla, Damian; Willems, Patrick

    2015-04-01

    Floods in urban areas as a consequence of sewer capacity exceedance receive increased attention because of trends in urbanization (increased population density and impermeability of the surface) and climate change. Despite the strong recent developments in numerical modeling of water systems, urban surface flood modeling is still a major challenge. Whereas very advanced and accurate flood modeling systems are in place and operation by many river authorities in support of flood management along rivers, this is not yet the case in urban water management. Reasons include the small scale of the urban inundation processes, the need to have very high resolution topographical information available, and the huge computational demands. Urban drainage related inundation modeling requires a 1D full hydrodynamic model of the sewer network to be coupled with a 2D surface flood model. To reduce the computational times, 0D (flood cones), 1D/quasi-2D surface flood modeling approaches have been developed and applied in some case studies. In this research, a nested 1D/2D hydraulic model has been developed for an urban catchment at the city of Gent (Belgium), linking the underground sewer (minor system) with the overland surface (major system). For the overland surface flood modelling, comparison was made of 0D, 1D/quasi-2D and full 2D approaches. The approaches are advanced by considering nested 1D-2D approaches, including infiltration in the green city areas, and allowing the effects of surface storm water storage to be simulated. An optimal nested combination of three different mesh resolutions was identified; based on a compromise between precision and simulation time for further real-time flood forecasting, warning and control applications. Main streets as mesh zones together with buildings as void regions constitute one of these mesh resolution (3.75m2 - 15m2); they have been included since they channel most of the flood water from the manholes and they improve the accuracy of

  3. Fermi surface of superconducting LaFePO determined by quantum oscillations

    SciTech Connect

    Mcdonald, Ross D; Coldea, A I; Fletcher, J D; Carrington, A; Bangura, A F; Hussey, N E; Analytis, J G; Chu, J-h; Erickson, A S; Fisher, I R

    2008-01-01

    The recent discovery of superconductivity in ferrooxypnictides, which have a maximum transition temperature intermediate between the two other known high temperature superconductors MgB{sub 2} and the cuprate family, has generated huge interest and excitement. The most critical issue is the origin of the pairing mechanism. Whereas superconductivity in MgB{sub 2} has been shown to arise from strong electron-phonon coupling, the pairing glue in cuprate superconductors is thought by many to have a magnetic origin. The oxypnictides are highly susceptible to magnetic instabilities, prompting analogies with cuprate superconductivity. Progress on formulating the correct theory of superconductivity in these materials will be greatly aided by a detailed knowledge of the Fermi surface parameters. Here we report for the first time extensive measurements of quantum oscillations in a Fe-based superconductor, LaFePO, that provide a precise calliper of the size and shape of the Fermi surface and the effective masses of the relevant charge carriers. Our results show that the Fermi surface is composed of nearly-nested electron and hole pockets in broad agreement with the band-structure predictions but with significant enhancement of the quasiparticle masses. The correspondence in the electron and hole Fermi surface areas provides firm experimental evidence that LaFePO, whilst unreconstructed, lies extremely close to a spin-density-wave instability, thus favoring models that invoke such a magnetic origin for high-temperature superconductivity in oxypnictides.

  4. Pseudogap signatures measured in the Fermi surface of underdoped YBCO by quantum oscillations

    NASA Astrophysics Data System (ADS)

    Sebastian, Suchitra E.

    2013-03-01

    Solving the riddle of the pseudogap state in underdoped high temperature superconductors is critical to the understanding of the origin of high temperature superconductivity. Quantum oscillations performed on single crystals of the family of underdoped YBCO cuprates reveal small Fermi surface pockets in the normal state accessed at low temperatures and high magnetic fields. It has been widely thought, however, that high magnetic fields cause this state to be significantly different from the mysterious pseudogap state measured at high temperatures and low magnetic fields. In this talk I will present a quantum oscillation study of underdoped YBa2Cu3O6+x up to magnetic fields of 100 T that reveals a dimensional collapse of the Fermi surface due to a drastic reduction in c-axis hopping, identical to the pseudogap signature measured in the low magnetic field regime. We therefore conclude that the fundamental properties of the pseudogap are encoded in the Fermi surface, an understanding of which is critical to uncovering the origin of the pseudogap in high temperature superconductors. Possible mechanisms are discussed to explain the origin of the Fermi surface in underdoped YBa2Cu3O6+x. This work was performed in collaboration with G. Lonzarich (University of Cambridge), N. Harrison, M. Altarawneh, F. Balakirev (Los Alamos National Laboratory), and R. Liang, W. Hardy, D. Bonn (University of British Columbia)

  5. Topological change of the Fermi surface in low-density Rashba gases: application to superconductivity.

    PubMed

    Cappelluti, E; Grimaldi, C; Marsiglio, F

    2007-04-20

    In this Letter we show how, for small values of the Fermi energy compared to the spin-orbit splitting of Rashba type, a topological change of the Fermi surface leads to an effective reduction of the dimensionality in the electronic density of states in the low charge density regime. We investigate its consequences on the onset of the superconducting instability. We show that the superconducting critical temperature is significantly tuned in this regime by the spin-orbit coupling. We suggest that materials with strong spin-orbit coupling are good candidates for enhanced superconductivity.

  6. Unconventional bulk three-dimensional Fermi surface in Kondo insulating SmB6

    NASA Astrophysics Data System (ADS)

    Tan, Beng

    We report the observation of a paradoxical insulator with a bulk state which is electrically insulating and simultaneously yields quantum oscillations typical of good metals. We present high field measurements of conductivity and magnetic torque in high purity single crystals of the Kondo insulator SmB6 which reveal an activated behavior characteristics of an insulator with an energy gap at the Fermi energy in the former and quantum oscillation of frequencies characteristics of a large three-dimensional conduction electron Fermi surface similar to the metallic rare earth hexaborides such as PrB6 and LaB6 in the latter. The quantum oscillations observed in the magnetic torque measurements are characteristic of an unconventional Fermi liquid - the amplitude strongly increases at low temperatures in a stark contrast to the saturating Lifshitz-Kosevich behavior in conventional metallic states.

  7. Quantum Oscillations, Thermoelectric Coefficients, and the Fermi Surface of Semimetallic WTe2

    NASA Astrophysics Data System (ADS)

    Zhu, Zengwei; Lin, Xiao; Liu, Juan; Fauqué, Benoît; Tao, Qian; Yang, Chongli; Shi, Youguo; Behnia, Kamran

    2015-05-01

    We present a study of angle-resolved quantum oscillations of electric and thermoelectric transport coefficients in semimetallic WTe2, which has the particularity of displaying a large B2 magnetoresistance. The Fermi surface consists of two pairs of electronlike and holelike pockets of equal volumes in a "Russian doll" structure. The carrier density, Fermi energy, mobility, and the mean-free path of the system are quantified. An additional frequency is observed above a threshold field and attributed to the magnetic breakdown across two orbits. In contrast to all other dilute metals, the Nernst signal remains linear in the magnetic field even in the high-field (ωcτ ≫1 ) regime. Surprisingly, none of the pockets extend across the c axis of the first Brillouin zone, making the system a three-dimensional metal with moderate anisotropy in Fermi velocity, yet a large anisotropy in the mean-free path.

  8. Electron–hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator

    PubMed Central

    Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M.; Kato, Reizo

    2016-01-01

    It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron–hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping. PMID:27492864

  9. Impact of Surface Roughness on Capillary Trapping Using 2D-Micromodel Visualization Experiments

    NASA Astrophysics Data System (ADS)

    Geistlinger, Helmut; Attaei-Dadavi, Iman; Vogel, Hans-Jörg

    2016-04-01

    According to experimental observations, capillary trapping is strongly dependent on the roughness of the pore-solid interface. We performed imbibition experiments in the range of capillary numbers (Ca) from 10^-6 to 5x10^-5 using 2D-micromodels, which exhibit a rough surface. The microstructure comprises a double-porosity structure with pronounced macropores. The dynamics of precursor thin-film flow and its importance for capillary trapping is studied. For the first time Thin-Film Dynamics and the Complex Interplay of Thin Film- and Corner Flow for Snap-off Trapping is visualized using fluorescence microscopy. The experimental data for thin-film flow advancement show a square-root time dependence. Contrary to smooth surfaces, we prove by strict thermodynamical arguments that complete wetting is possible in a broad range of contact angles (0 - 90°). We develop a pore-scale model, which describes the front dynamics of thin-film flow on rough surfaces. Furthermore, contact angle hysteresis is considered for rough surfaces. We conduct a comprehensive cluster analysis, studying the influence of viscous forces (capillary number) and buoyancy forces (bond number) on cluster size distribution and comparing the results with predictions from percolation theory. We found that our experimental results agree with theoretical results of percolation theory for Ca = 10^-6: (i) a universal power-like cluster size distribution, (ii) the linear surface-volume relationship of trapped clusters, and (iii) the existence of the cut-off correlation length for the maximal cluster height. The good agreement is a strong argument that the experimental cluster size distribution is caused by a percolation-like trapping process (Ordinary Percolation). [1] H. Geistlinger, I. Ataei-Dadavi, S. Mohammadian, and H.-J. Vogel (2015) The Impact of Pore structure and Surface Roughness on Capillary Trapping for 2D- and 3D-porous media: Comparison with Percolation theory. Special issue: Applications of

  10. Evidence for a small hole pocket in the Fermi surface of underdoped YBa2Cu3Oy

    PubMed Central

    Doiron-Leyraud, N.; Badoux, S.; René de Cotret, S.; Lepault, S.; LeBoeuf, D.; Laliberté, F.; Hassinger, E.; Ramshaw, B. J.; Bonn, D. A.; Hardy, W. N.; Liang, R.; Park, J.-H..; Vignolles, D.; Vignolle, B.; Taillefer, L.; Proust, C.

    2015-01-01

    In underdoped cuprate superconductors, the Fermi surface undergoes a reconstruction that produces a small electron pocket, but whether there is another, as yet, undetected portion to the Fermi surface is unknown. Establishing the complete topology of the Fermi surface is key to identifying the mechanism responsible for its reconstruction. Here we report evidence for a second Fermi pocket in underdoped YBa2Cu3Oy, detected as a small quantum oscillation frequency in the thermoelectric response and in the c-axis resistance. The field-angle dependence of the frequency shows that it is a distinct Fermi surface, and the normal-state thermopower requires it to be a hole pocket. A Fermi surface consisting of one electron pocket and two hole pockets with the measured areas and masses is consistent with a Fermi-surface reconstruction by the charge–density–wave order observed in YBa2Cu3Oy, provided other parts of the reconstructed Fermi surface are removed by a separate mechanism, possibly the pseudogap. PMID:25616011

  11. Fermi surface instabilities in CeRh2Si2 at high magnetic field and pressure

    NASA Astrophysics Data System (ADS)

    Palacio Morales, A.; Pourret, A.; Seyfarth, G.; Suzuki, M.-T.; Braithwaite, D.; Knebel, G.; Aoki, D.; Flouquet, J.

    2015-06-01

    We present thermoelectric power (TEP) studies under pressure and high magnetic field in the antiferromagnet CeRh2Si2 at low temperature. Under a magnetic field, large quantum oscillations are observed in the TEP, S (H ) , in the antiferromagnetic phase. They suddenly disappear when entering in the polarized paramagnetic state at Hc, pointing out an important reconstruction of the Fermi surface. Under pressure, S /T increases strongly at low temperature near the critical pressure Pc, where the antiferromagnetic (AF) order is suppressed, implying the interplay of a Fermi surface change and low-energy excitations driven by spin and valence fluctuations. The difference between the TEP signal in the polarized paramagnetic state above Hc at ambient pressure and in the pressure-induced paramagnetic state above Pc can be explained by different Fermi surfaces. Band-structure calculations at P =0 stress that in the AF phase the 4 f contribution at the Fermi level (EF) is weak, while it is the main contribution in the paramagnetic domain. In the polarized paramagnetic phase the 4 f contribution at EF drops. Large quantum oscillations are observed in the antiferromagnetic state while these disappear in the polarized state above Hc. Comparison is made to the CeRu2Si2 series highly studied for its (H ,T ) phase diagram.

  12. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor.

    PubMed

    Charnukha, A; Thirupathaiah, S; Zabolotnyy, V B; Büchner, B; Zhigadlo, N D; Batlogg, B; Yaresko, A N; Borisenko, S V

    2015-05-21

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe(0.92)Co(0.08)AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors.

  13. Interaction-induced singular Fermi surface in a high-temperature oxypnictide superconductor

    PubMed Central

    Charnukha, A.; Thirupathaiah, S.; Zabolotnyy, V. B.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Yaresko, A. N.; Borisenko, S. V.

    2015-01-01

    In the family of iron-based superconductors, LaFeAsO-type materials possess the simplest electronic structure due to their pronounced two-dimensionality. And yet they host superconductivity with the highest transition temperature Tc ≈ 55K. Early theoretical predictions of their electronic structure revealed multiple large circular portions of the Fermi surface with a very good geometrical overlap (nesting), believed to enhance the pairing interaction and thus superconductivity. The prevalence of such large circular features in the Fermi surface has since been associated with many other iron-based compounds and has grown to be generally accepted in the field. In this work we show that a prototypical compound of the 1111-type, SmFe0.92Co0.08AsO , is at odds with this description and possesses a distinctly different Fermi surface, which consists of two singular constructs formed by the edges of several bands, pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. Such singularities dramatically affect the low-energy electronic properties of the material, including superconductivity. We further argue that occurrence of these singularities correlates with the maximum superconducting transition temperature attainable in each material class over the entire family of iron-based superconductors. PMID:25997611

  14. Potential energy surface and quasiclassical trajectory studies of the N(2D)+H2 reaction

    NASA Astrophysics Data System (ADS)

    Pederson, Lisa A.; Schatz, George C.; Ho, Tak-San; Hollebeek, Timothy; Rabitz, Herschel; Harding, Lawrence B.; Lendvay, György

    1999-05-01

    We present a global potential energy surface for the 1A″ state of NH2 based on application of the reproducing kernel Hilbert space interpolation method to high quality ab initio (multireference configuration interaction) results. Extensive quasiclassical trajectory calculations are performed on this surface to study the N(2D)+H2/D2 reaction dynamics. Comparison is made with calculations on the lower level [first order configuration interaction (FOCI)] surface of Kobayashi, Takayanagi, Yokoyama, Sato, and Tsunashima (KTYST). We find a saddle point energy of 2.3 (1.9) kcal/mol for the perpendicular approach for the second order configuration interaction (SOCI) (SOCI with Davidson correction) surfaces, and a collinear stationary point energy of 5.5 (4.6) kcal/mol. The ordering of these stationary points is reversed compared to the corresponding FOCI results, and the only true reaction path on our surface is perpendicular. The primary reaction mechanism is determined to be C2v insertion to produce short lived (100-300 fs) NH2 intermediates. Angular distributions are found to be primarily forward-backward symmetric, with a slight bias towards backward scattering at low energies. Decay of the NH2's occurs before energy is fully randomized, so the product vibrational distributions are a little hotter than statistical—with vibrational population ratios NH(v″=1)/NH(v″=0)=0.8 and ND(v″=1)/ND(v″=0)=0.9 (near threshold). These ratios, and other aspects of the vibrational product distributions are in excellent agreement with recent laser induced fluorescence studies.

  15. Skyrmions in quasi-2D chiral magnets with broken bulk and surface inversion symmetry

    NASA Astrophysics Data System (ADS)

    Rowland, James; Banerjee, Sumilan; Randeria, Mohit

    2015-03-01

    Most theoretical studies of skyrmions have focused on chiral magnets with broken bulk inversion symmetry, stabilized by easy-axis anisotropy. Recently, we considered 2D systems with broken surface inversion and showed that skyrmion crystals are more stable than in 3D, pointing out the importance of easy-plane anisotropy. In the present work we investigate quasi-2D systems which break both bulk and surface inversion symmetry. The Landau-Ginzburg free energy functional thus contains two Dzyloshinskii-Moriya terms of strength DD and DR arising from Dresselhaus and Rashba spin-orbit coupling respectively. We trace the evolution of the phase diagram as DD /DR is varied, and find that skyrmions are increasingly destabilized with respect to the cone phase as DD increases relative to DR. We find an evolution from vortex-like skyrmions in the pure Dresselhaus limit to hedgehog-like skyrmions in the pure Rashba limit. We discuss the relevance of these results to existing experiments and the prospects of tuning the ratio of Dresselhaus and Rashba spin-orbit coupling via film thickness and strain. Supported by NSF DMR-1410364 (J.R. and M.R.) and DOE-BES DE-SC0005035 (S.B.)

  16. Generalized centripetal force law and quantization of motion constrained on 2D surfaces

    NASA Astrophysics Data System (ADS)

    Liu, Q. H.; Zhang, J.; Lian, D. K.; Hu, L. D.; Li, Z.

    2017-03-01

    For a particle of mass μ moves on a 2D surface f(x) = 0 embedded in 3D Euclidean space of coordinates x, there is an open and controversial problem whether the Dirac's canonical quantization scheme for the constrained motion allows for the geometric potential that has been experimentally confirmed. We note that the Dirac's scheme hypothesizes that the symmetries indicated by classical brackets among positions x and momenta p and Hamiltonian Hc remain in quantum mechanics, i.e., the following Dirac brackets [ x ,Hc ] D and [ p ,Hc ] D holds true after quantization, in addition to the fundamental ones [ x , x ] D, [ x , p ] D and [ p , p ] D. This set of hypotheses implies that the Hamiltonian operator is simultaneously determined during the quantization. The quantum mechanical relations corresponding to the classical mechanical ones p / μ =[ x ,Hc ] D directly give the geometric momenta. The time t derivative of the momenta p ˙ =[ p ,Hc ] D in classical mechanics is in fact the generalized centripetal force law for particle on the 2D surface, which in quantum mechanics permits both the geometric momenta and the geometric potential.

  17. 2D aquifer characterization and improved prediction of hydraulic conductivity using surface Nuclear Magnetic Resonance

    NASA Astrophysics Data System (ADS)

    Dlugosch, Raphael; Günther, Thomas; Müller-Petke, Mike; Yaramanci, Ugur

    2014-05-01

    We present recent studies on the characterization of shallow aquifers using Nuclear Magnetic Resonance (NMR). NMR can help to gather detailed information about the water content and pore size related NMR relaxation time, of porous and water saturated material. The field application of surface NMR uses large wire loops placed at the surface of the Earth allows imaging the subsurface down to around hundred meters. First, a sophisticated inversion scheme is presented to simultaneously determine the two-dimensional (2D) distribution of the water content and the NMR relaxation time (T2*) in the subsurface from a surface NMR survey. The outstanding features of the new inversion scheme are its robustness to noisy data and the potential to distinguish aquifers of different lithology due to their specific NMR relaxation time. The successful application of the inversion scheme is demonstrated on two field cases both characterized by channel structures in the glacial sediments of Northern Germany. Second, we revise the prediction of hydraulic conductivity from NMR measurements for coarse-grained and unconsolidated sediments, commonly found in shallow aquifers. The presented Kozeny-Godefroy model replaces the empirical factors in known relations with physical, structural, and intrinsic NMR parameters. It additionally accounts for bulk water relaxation and is not limited to fast diffusion conditions. This improves the prediction of the hydraulic conductivity for clay-free sediments with grain sizes larger than medium sand. The model is validated by laboratory measurements on glass beads and sand samples. Combining the new inversion scheme and petrophysical model allows 2D imaging of the hydraulic conductivity in the subsurface from a surface NMR survey.

  18. 2D surface temperature measurement of plasma facing components with modulated active pyrometry

    SciTech Connect

    Amiel, S.; Loarer, T.; Pocheau, C.; Roche, H.; Gauthier, E.; Aumeunier, M.-H.; Courtois, X.; Jouve, M.; Balorin, C.; Moncada, V.; Le Niliot, C.; Rigollet, F.

    2014-10-01

    In nuclear fusion devices, such as Tore Supra, the plasma facing components (PFC) are in carbon. Such components are exposed to very high heat flux and the surface temperature measurement is mandatory for the safety of the device and also for efficient plasma scenario development. Besides this measurement is essential to evaluate these heat fluxes for a better knowledge of the physics of plasma-wall interaction, it is also required to monitor the fatigue of PFCs. Infrared system (IR) is used to manage to measure surface temperature in real time. For carbon PFCs, the emissivity is high and known (ε ~ 0.8), therefore the contribution of the reflected flux from environment and collected by the IR cameras can be neglected. However, the future tokamaks such as WEST and ITER will be equipped with PFCs in metal (W and Be/W, respectively) with low and variable emissivities (ε ~ 0.1–0.4). Consequently, the reflected flux will contribute significantly in the collected flux by IR camera. The modulated active pyrometry, using a bicolor camera, proposed in this paper allows a 2D surface temperature measurement independently of the reflected fluxes and the emissivity. Experimental results with Tungsten sample are reported and compared with simultaneous measurement performed with classical pyrometry (monochromatic and bichromatic) with and without reflective flux demonstrating the efficiency of this method for surface temperature measurement independently of the reflected flux and the emissivity.

  19. Densely Packed 2-D Matrix-Addressable Vertical-Cavity Surface-Emitting Laser Arrays

    NASA Astrophysics Data System (ADS)

    Gadallah, Abdel-Sattar; Michalzik, Rainer

    2013-03-01

    We report on design, manufacturing, and characterization of densely packed top-emitting 16 × 16 elements wire-bonded matrix-addressable vertical-cavity surface-emitting laser (VCSEL) arrays, which may find future applications such as non-mechanical particle movement with optical multi-tweezers, confocal microscopy or free-space communications with beam steering capability. The factors that control the packing density such as layer structure, mask design, and VCSEL processing are investigated, aiming to minimize the pitch between VCSELs in the array. Both wet-etched and dry-etched arrays are presented and discussed. The single transverse mode VCSELs in the two-dimensional (2-D) matrix-addressable architecture have threshold currents which vary from 0.5 to 1.6 mA and maximum output powers between 2.4 and 4 mW. A simple analysis of the parasitic ohmic resistances is made.

  20. Fermi-level pinning and intrinsic surface states in cleaved GaP

    NASA Astrophysics Data System (ADS)

    Chiaradia, P.; Fanfoni, M.; Nataletti, P.; de Padova, P.; Brillson, L. J.; Slade, M. L.; Viturro, R. E.; Kilday, D.; Margaritondo, G.

    1989-03-01

    We have performed photoelectron spectroscopy of the clean GaP(110) surface, obtained by cleaving n-type specimens. The results show that Fermi-level stabilization occurs in a wide range of positions. In some cases nearly flat bands were obtained. The surface Fermi-level position in n-type GaP(110) is then due to extrinsic surface states, probably cleavage defects, as in the case of p-type samples. The density of these extrinsic states depends upon the quality of the cleave. Previously the Fermi-level pinning in n-type GaP(110) surfaces instead was attributed to (empty) intrinsic surface states located at 1.6+/-0.1 eV above the valence band. GaP(110) was considered an exception among III-V compounds, since in general atomic relaxation removes intrinsic surface states from the fundamental gap. The present results set a lower bound for the energetic position of the empty surface states slightly below the bottom of the conduction band. Therefore GaP(110) exhibits a gap practically free from intrinsic surface states, like the other III-V compounds so far investigated. We have also performed a spectroscopic study of the empty (intrinsic) surface states on the same surface by measuring the absorption edge of the P 2p core level. The result shows that the wave functions of the empty dangling-bond states, mainly cationic in origin, have a sizable localization on the anion site as well.

  1. Topological transitions of the Fermi surface of osmium under pressure: an LDA+DMFT study

    NASA Astrophysics Data System (ADS)

    Feng, Qingguo; Ekholm, Marcus; Tasnádi, Ferenc; Jönsson, H. Johan M.; Abrikosov, Igor A.

    2017-03-01

    The influence of pressure on the electronic structure of Os has attracted substantial attention recently due to reports on isostructural electronic transitions in this metal. Here, we theoretically investigate the Fermi surface of Os from ambient to high pressure, using density functional theory combined with dynamical mean field theory. We provide a detailed discussion of the calculated Fermi surface and its dependence on the level of theory used for the treatment of the electron–electron interactions. Although we confirm that Os can be classified as weakly correlated metal, the inclusion of local quantum fluctuations between 5{{d}} electrons beyond the local density approximation explains the most recent experimental reports regarding the occurrence of electronic topological transitions in Os.

  2. Magnetic breakdown and Landau level spectra of a tunable double-quantum-well Fermi surface

    SciTech Connect

    Simmons, J.A.; Harff, N.E.; Lyo, S.K.; Klem, J.F.; Boebinger, G.S.; Pfeiffer, L.N.; West, K.W.

    1997-12-31

    By measuring longitudinal resistance, the authors map the Landau level spectra of double quantum wells as a function of both parallel (B{sub {parallel}}) and perpendicular (B{sub {perpendicular}}) magnetic fields. In this continuously tunable highly non-parabolic system, the cyclotron masses of the two Fermi surface orbits change in opposite directions with B{sub {parallel}}. This causes the two corresponding ladders of Landau levels formed at finite B{sub {perpendicular}} to exhibit multiple crossings. They also observe a third set of landau levels, independent of B{sub {parallel}}, which arise from magnetic breakdown of the Fermi surface. Both semiclassical and full quantum mechanical calculations show good agreement with the data.

  3. de Haas--van Alphen effect and Fermi surface of lutetium

    SciTech Connect

    Johanson, W.R.; Crabtree, G.W.; Schmidt, F.A.

    1984-03-01

    We report de Haas--van Alphen measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (1010) and (1120) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earth elements from Gd to Tm. The fact that no complete frequency branches were observed indicates that there are no closed pieces of the Fermi surface. We observed all but one orbit predicted by relativistic augmented-plane-wave calculations of Keeton and Loucks and by recent spin-orbit--linearized-augmented-plane-wave calculations of Tibbetts and Harmon. The data support a geometry similar to that of yttrium, and in good qualitative agreement with energy-band theory.

  4. de Haas-van Alphen effect and Fermi surface of lutetium

    NASA Astrophysics Data System (ADS)

    Johanson, W. R.; Crabtree, G. W.; Schmidt, F. A.

    1984-03-01

    We report de Haas-van Alphen measurements of the Fermi surface of lutetium at temperatures down to 0.3 K and in fields up to 150 kG in the (101¯0) and (112¯0) planes. Lutetium, having a filled 4f shell, serves as a nonmagnetic prototype of the structurally similar (hcp), trivalent, heavy rare-earth elements from Gd to Tm. The fact that no complete frequency branches were observed indicates that there are no closed pieces of the Fermi surface. We observed all but one orbit predicted by relativistic augmented-plane-wave calculations of Keeton and Loucks and by recent spin-orbit-linearized-augmented-plane-wave calculations of Tibbetts and Harmon. The data support a geometry similar to that of yttrium, and in good qualitative agreement with energy-band theory.

  5. Unconventional superconductivity and interaction induced Fermi surface reconstruction in the two-dimensional Edwards model

    NASA Astrophysics Data System (ADS)

    Cho, Dai-Ning; Sykora, Steffen

    We study the possibility of unconventional superconducting pairing in the framework of a novel two-dimensional quantum transport model, where the charge carriers are strongly affected by the correlations and fluctuations of a background medium, described by bosonic degrees of freedom. Using the projective renormalization method (PRM) we find in the half-filled band case an interplay between stable superconducting solutions and a charge-density wave order parameter which determines the ground state in the limit of large bosonic energies. The superconducting pairing mainly appears on a new hole-like Fermi surface, which is formed nearby the center of the Brillouin zone due to strong renormalization of the original fermionic band. In the superconducting state, the Fermi surface splits into two disconnected parts, which are characterized by different sign of the superconducting order parameter.

  6. Neutron Scattering as a Probe of Fermi Surface Nesting in Iron-Based Superconductors

    NASA Astrophysics Data System (ADS)

    Osborn, Raymond

    2013-03-01

    Superconductivity in the iron-based compounds is induced by suppressing a magnetically ordered phase by doping, pressure, or disorder, so it is no surprise that neutron scattering has had an important role in the field, elucidating both the origin of magnetic fluctuations and their role in the unconventional superconductivity. Our investigations of BaFe2As2 doped with potassium, sodium, and phosphor, can be interpreted within the framework of weakly correlated itinerant magnetism, in which Fermi surface nesting between hole pockets at the zone center and electron pockets at the zone boundary is responsible for both the magnetic (SDW) order and the superconductivity. Resonant spin excitations that occur when the superconducting energy gap changes sign on different parts of the Fermi surface were initially observed by inelastic neutron scattering in Ba1-xKxFe2As2 representing the first phase-sensitive evidence of s+/--symmetry. We have since shown that the resonance splits into two with hole-doping because of the growing mismatch in the hole and electron Fermi surface volumes, accompanied by a decrease in the binding energy of the resonance and its spectral weight in accordance with RPA theory. A detailed examination of the phase diagram close to the critical phase boundary for SDW order has identified a new phase that is further evidence of the role of Fermi surface nesting in generating magnetic order. Supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357

  7. Full 2D observation of water surface elevation from SWOT under different flow conditions

    NASA Astrophysics Data System (ADS)

    Domeneghetti, Alessio; Schumann, Guy; Rui, Wei; Durand, Michael; Pavelsky, Tamlin

    2016-04-01

    The upcoming Surface Water and Ocean Topography (SWOT) satellite mission is a joint project of NASA, Centre National d'Etudes Spatiales (CNES, France), the Canadian Space Agency, and the Space Agency of the UK that will provide a first global, high-resolution observation of ocean and terrestrial water surface heights. Characterized by an observation swath of 120 km and an orbit repeat interval of about 21 days, SWOT will provide unprecedented bi-dimensional observations of rivers wider than 50-100 m. Despite many research activities that have investigated potential uses of remotely sensed data from SWOT, potentials and limitations of the spatial observations provided by the satellite mission for flood modeling still remain poorly understood and investigated. In this study we present a first analysis of the spatial observation of water surface elevation that is expected from SWOT for a 140 km reach of the middle-lower portion of the Po River, in Northern Italy. The river stretch is characterized by a main channel varying from 200-500 m in width and a floodplain that can be as wide as 5 km and that is delimited by a system of major embankments. The reconstruction of the hydraulic behavior of the Po River is performed by means of a quasi-2d model built with detailed topographic and bathymetric information (LiDAR, 2 m resolution), while the simulation of the spatial observation sensed by SWOT is performed with a SWOT simulator that mimics the satellite sensor characteristics. Referring to water surface elevations associated with different flow conditions (maximum, minimum and average flow reproduced by means of the quasi-2d numerical model) this work provides a first characterization of the spatial observations provided by SWOT and highlights the strengths and limitations of the expected products. By referring to a real river reach the analysis provides a credible example of the type of spatial observations that will be available after launch of SWOT and offers a first

  8. Stratification and Dissipation Effects in Running 2D Surface and Internal Gravity Waves

    NASA Astrophysics Data System (ADS)

    Kistovich, A. V.; Chashechkin, Yu. D.

    2012-04-01

    Problem of 2D gravity wave propagation inside and along a free surface of a deep viscous stratified fluid is analyzed analytically basing on set of fundamental governing equations that are continuity and Navier-Stokes neglecting by compressibility effects. Conventional boundary conditions taking into account solid films on the free surface where used. In a limit of clean fluid surface the set is transformed into partial differential equation of the fourth order for a stream function. The sense of applied approximations is discussed. In infinitesimal limit the equation is split on independent sub-equations with characteristic dispersion relations describing propagating independent surface and internal waves. Waves are supplemented by fine flow components. Relations between amplitude of regular waves and singular perturbed components corresponding of a fine structure are derived and discussed. Expressions for vorticity and rate of baroclinic generation of vorticity are presented. Waves of finite amplitudes are investigated in the limit of non-viscous fluid. Two kinds of the running surface wave forms for different values of the wave steepness were calculated and discussed. New approximate non-linear equations was solved and a set of solutions for stratified and homogeneous fluids describing running waves of small finite and large steepness of the waves are constructed. Received expressions for drift velocity are transferred into well-known Stokes solutions in limit of small steepness. Calculations of running periodic internal waves are compared with data of laboratory experiments performed on USU "HPC IPMech RAS" under support of Ministry of Education and Science of the Russian Federation (Goscontract No. 16.518.11.7059. Extrapolation results of calculations on the environmental conditions are speculated.

  9. Quantum oscillations from generic surface Fermi arcs and bulk chiral modes in Weyl semimetals

    PubMed Central

    Zhang, Yi; Bulmash, Daniel; Hosur, Pavan; Potter, Andrew C.; Vishwanath, Ashvin

    2016-01-01

    We re-examine the question of quantum oscillations from surface Fermi arcs and chiral modes in Weyl semimetals. By introducing two tools - semiclassical phase-space quantization and a numerical implementation of a layered construction of Weyl semimetals - we discover several important generalizations to previous conclusions that were implicitly tailored to the special case of identical Fermi arcs on top and bottom surfaces. We show that the phase-space quantization picture fixes an ambiguity in the previously utilized energy-time quantization approach and correctly reproduces the numerically calculated quantum oscillations for generic Weyl semimetals with distinctly curved Fermi arcs on the two surfaces. Based on these methods, we identify a ‘magic’ magnetic-field angle where quantum oscillations become independent of sample thickness, with striking experimental implications. We also analyze the stability of these quantum oscillations to disorder, and show that the high-field oscillations are expected to persist in samples whose thickness parametrically exceeds the quantum mean free path. PMID:27033563

  10. Orbital-dependent Fermi surface shrinking as a fingerprint of nematicity in FeSe

    NASA Astrophysics Data System (ADS)

    Fanfarillo, Laura; Mansart, Joseph; Toulemonde, Pierre; Cercellier, Hervé; Le Fèvre, Patrick; Bertran, François; Valenzuela, Belen; Benfatto, Lara; Brouet, Véronique

    2016-10-01

    A large anisotropy in the electronic properties across a structural transition in several correlated systems has been identified as the key manifestation of electronic nematic order, breaking rotational symmetry. In this context, FeSe is attracting tremendous interest, since electronic nematicity develops over a wide range of temperatures, allowing accurate experimental investigation. Here we combine angle-resolved photoemission spectroscopy and theoretical calculations based on a realistic multiorbital model to unveil the microscopic mechanism responsible for the evolution of the electronic structure of FeSe across the nematic transition. We show that the self-energy corrections due to the exchange of spin fluctuations between hole and electron pockets are responsible for an orbital-dependent shrinking of the Fermi surface that affects mainly the x z /y z parts of the Fermi surface. This result is consistent with our experimental observation of the Fermi surface in the high-temperature tetragonal phase, which includes the x y electron sheet that was not clearly resolved before. In the low-temperature nematic phase, we experimentally confirm the appearance of a large (˜50 meV) x z /y z splitting. It can be well reproduced in our model by assuming a moderate splitting between spin fluctuations along the x and y crystallographic directions. Our mechanism shows how the full entanglement between orbital and spin degrees of freedom can make a spin-driven nematic transition equivalent to an effective orbital order.

  11. Observation of field-induced Fermi surface reconstruction in CeRhIn5

    NASA Astrophysics Data System (ADS)

    Yuan, Huiqiu; Jiao, Lin; Weng, Zongfa; Chen, Ye; Steglich, Frank; Graf, David; Singleton, John; Jaime, Marcelo; Bauer, Eric; Thompson, Joe

    2015-03-01

    CeRhIn5 provides a prototype compound for studying quantum criticality and its interplay with superconductivity. Application of pressure suppresses the antiferromagnetic (AF) order and gives rise to superconductivity. A sharp change of Fermi surface was observed just at the pressure-tuning AF quantum critical point (QCP), which was argued to support the scenario of local quantum criticality. By measuring the dHvA oscillations and specific heat in a pulsed magnetic field, we have demonstrated the existence of a field-induced AF QCP around Bc0 =50T in this compound. In this presentation, we will report the measurements of dHvA effect and Hall resistivity of CeRhIn5 performed by using the 45T hybrid magnet and the pulsed field magnet at NHMFL. Field-induced changes of the dHvA frequencies and Hall coefficient are observed around B* =31T. Detailed analyses suggest that the Fermi surface reconstruction at B* corresponds to a localized-itinerant transition of Ce 4f-electrons attributed to the Kondo effect. Our results indicate that multiple quantum phase transitions may exist in CeRhIn5 which can be classified by the measurements of Fermi surface topology.

  12. Fermi surface versus Fermi sea contributions to intrinsic anomalous and spin Hall effects of multiorbital metals in the presence of Coulomb interaction and spin-Coulomb drag

    NASA Astrophysics Data System (ADS)

    Arakawa, Naoya

    2016-06-01

    Anomalous Hall effect (AHE) and spin Hall effect (SHE) are fundamental phenomena, and their potential for application is great. However, we understand the interaction effects unsatisfactorily, and should have clarified issues about the roles of the Fermi sea term and Fermi surface term of the conductivity of the intrinsic AHE or SHE of an interacting multiorbital metal and about the effects of spin-Coulomb drag on the intrinsic SHE. Here, we resolve the first issue and provide the first step about the second issue by developing a general formalism in the linear response theory with appropriate approximations and using analytic arguments. The most striking result is that even without impurities, the Fermi surface term, a non-Berry-curvature term, plays dominant roles at high or slightly low temperatures. In particular, this Fermi surface term causes the temperature dependence of the dc anomalous Hall or spin Hall conductivity due to the interaction-induced quasiparticle damping and the correction of the dc spin Hall conductivity due to the spin-Coulomb drag. Those results revise our understanding of the intrinsic AHE and SHE. We also find that the differences between the dc anomalous Hall and longitudinal conductivities arise from the difference in the dominant multiband excitations. This not only explains why the Fermi sea term such as the Berry-curvature term becomes important in clean and low-temperature case only for interband transports, but also provides the useful principles on treating the electron-electron interaction in an interacting multiorbital metal for general formalism of transport coefficients. Several correspondences between our results and experiments are finally discussed.

  13. Integrated Coupling of Surface and Subsurface Flow with HYDRUS-2D

    NASA Astrophysics Data System (ADS)

    Hartmann, Anne; Šimůnek, Jirka; Wöhling, Thomas; Schütze, Niels

    2016-04-01

    Describing interactions between surface and subsurface flow processes is important to adequately define water flow in natural systems. Since overland flow generation is highly influenced by rainfall and infiltration, both highly spatially heterogeneous processes, overland flow is unsteady and varies spatially. The prediction of overland flow needs to include an appropriate description of the interactions between the surface and subsurface flow. Coupling surface and subsurface water flow is a challenging task. Different approaches have been developed during the last few years, each having its own advantages and disadvantages. A new approach by Weill et al. (2009) to couple overland flow and subsurface flow based on a generalized Richards equation was implemented into the well-known subsurface flow model HYDRUS-2D (Šimůnek et al., 2011). This approach utilizes the one-dimensional diffusion wave equation to model overland flow. The diffusion wave model is integrated in HYDRUS-2D by replacing the terms of the Richards equation in a pre-defined runoff layer by terms defining the diffusion wave equation. Using this approach, pressure and flux continuity along the interface between both flow domains is provided. This direct coupling approach provides a strong coupling of both systems based on the definition of a single global system matrix to numerically solve the coupled flow problem. The advantage of the direct coupling approach, compared to the loosely coupled approach, is supposed to be a higher robustness, when many convergence problems can be avoided (Takizawa et al., 2014). The HYDRUS-2D implementation was verified using a) different test cases, including a direct comparison with the results of Weill et al. (2009), b) an analytical solution of the kinematic wave equation, and c) the results of a benchmark test of Maxwell et al. (2014), that included several known coupled surface subsurface flow models. Additionally, a sensitivity analysis evaluating the effects

  14. Theoretical study of surface plasmons coupling in transition metallic alloy 2D binary grating

    NASA Astrophysics Data System (ADS)

    Dhibi, Abdelhak; Khemiri, Mehdi; Oumezzine, Mohamed

    2016-05-01

    The excitation of a surface plasmon polariton (SPP) wave on a metal-air interface by a 2D diffraction grating is numerically investigated. The grating consists of homogeneous alloys of two metals of a formula AxB1-x, or three metals of a formula AxByCz, where A, B and C could be silver (Ag), copper (Cu), gold (Au) or aluminum (Al). It is observed that all the alloys of two metals present a very small change of surface plasmon resonance (SPR) irrespective of composition x. Moreover, the addition of 25% of Al to two metals alloy is insufficient to change the SPR curves. The influence of the different grating parameters is discussed in details using rigorous coupled-wave analysis (RCWA) method. Furthermore, the SPR is highly dependent on grating periods (dx and dy) and the height of the grating h. The results reveal that dx= dy= 700 nm, h=40 nm and duty cycle w=0.5 are the optimal parameters for exciting SPP.

  15. Split Fermi Surface Properties based on the Relativistic Effect in Superconductor PdBiSe with the Cubic Chiral Crystal Structure

    NASA Astrophysics Data System (ADS)

    Kakihana, Masashi; Nakamura, Ai; Teruya, Atsushi; Harima, Hisatomo; Haga, Yoshinori; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika

    2015-03-01

    We grew single crystals of PdBiSe with the ullmannite-type cubic chiral structure and carried out de Haas-van Alphen (dHvA) experiments to clarify the Fermi surface properties. The Fermi surfaces are found to split into two different Fermi surfaces, reflecting the non-centrosymmetric crystal structure. A splitting energy between two nearly spherical Fermi surfaces named α and α' is determined as 1050-1260 K. These Fermi surfaces are identified to be due the band-149 and -150 electron Fermi surfaces centered at the Γ point from the results of full-potential linearized augmented plane wave (FLAPW) energy band calculations under consideration of a mass correction in the spin-orbit interaction for Bi-6p electrons based on the relativistic effect. The theoretical splitting energy between these Fermi surfaces is 1080-1150 K, which is in good agreement with the experimental value.

  16. What rome does the Fermi surface play in tuning the properties of iron arsenic superconductors?

    NASA Astrophysics Data System (ADS)

    Dhaka, R. S.; Liu, Chang; Fernandes, R. M.; Jiang, Rui; Kondo, T.; Thaler, A.; Schmalian, J.; Bud'Ko, S. L.; Canfield, P. C.; Kaminski, Adam

    2012-02-01

    External control parameters such as pressure or chemical substitution are the key to extend the phase space and achieve high temperature (Tc) superconductivity in the FeAs family. These materials show interesting properties where it is important to understand the role of Fermi surfaces (FS's) in the mechanism of yielding higher Tc. Here, we use angle-resolved photoemission to study the electronic structure of the Ba(Fe1-xRux)2As2 as a function of Ru concentration (x). We find that the substitution of Ru for Fe is isoelectronic, i. e., it does not change the value of the chemical potential. More interestingly, there are no measured significant changes in the shape of the FS or in the Fermi velocity over a wide range [1]. We contrast this unusual behavior with the Co substitution, where even small substitutions induce large changes not only in the size of the FS pockets but also in the FS topology [2]. Given that the suppression of the antiferromagnetic and structural phase has been associated with the emergence of the superconducting state, Ru substitution must achieve this via a mechanism that does not involve changes of the Fermi surface. We speculate that this mechanism relies on magnetic dilution that leads to the reduction of the effective Stoner enhancement. [4pt] [1] R. S. Dhaka, et al., PRL, (2011). [0pt] [2] Chang Liu, et al., Nature Physics, 6, 419 (2010).

  17. Fermi surface and band structure of BiPd from ARPES studies

    NASA Astrophysics Data System (ADS)

    Lohani, H.; Mishra, P.; Gupta, Anurag; Awana, V. P. S.; Sekhar, B. R.

    2017-03-01

    We present a detailed electronic structure study of the non-centrosymmetric superconductor BiPd based on our angle resolved photoemission spectroscopy (ARPES) measurements and Density Functional Theory (DFT) based calculations. We observe a high intensity distribution on the Fermi surface (FS) of this compound resulting from various electron and hole like bands which are present in the vicinity of the Fermi energy (Ef). The near Ef states are primarily composed of Bi-6p with a little admixture of Pd-4dx2-y2/zy orbitals. There are various spin-orbit split bands involved in the crossing of Ef making a complex FS. The FS mainly consists of multi sheets of three dimensions which disfavor the nesting between different sheets of the FS. Our comprehensive study elucidates that BiPd could be a s-wave multiband superconductor.

  18. Segmentation of Textures Defined on Flat vs. Layered Surfaces using Neural Networks: Comparison of 2D vs. 3D Representations.

    PubMed

    Oh, Sejong; Choe, Yoonsuck

    2007-08-01

    Texture boundary detection (or segmentation) is an important capability in human vision. Usually, texture segmentation is viewed as a 2D problem, as the definition of the problem itself assumes a 2D substrate. However, an interesting hypothesis emerges when we ask a question regarding the nature of textures: What are textures, and why did the ability to discriminate texture evolve or develop? A possible answer to this question is that textures naturally define physically distinct (i.e., occluded) surfaces. Hence, we can hypothesize that 2D texture segmentation may be an outgrowth of the ability to discriminate surfaces in 3D. In this paper, we conducted computational experiments with artificial neural networks to investigate the relative difficulty of learning to segment textures defined on flat 2D surfaces vs. those in 3D configurations where the boundaries are defined by occluding surfaces and their change over time due to the observer's motion. It turns out that learning is faster and more accurate in 3D, very much in line with our expectation. Furthermore, our results showed that the neural network's learned ability to segment texture in 3D transfers well into 2D texture segmentation, bolstering our initial hypothesis, and providing insights on the possible developmental origin of 2D texture segmentation function in human vision.

  19. Investigations on electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl

    NASA Astrophysics Data System (ADS)

    Wei, Xiao-Ping; Sun, Weiwei; Zhang, Ya-Ling; Sun, Xiao-Wei; Song, Ting; Wang, Ting; Zhang, Jia-Liang; Su, Hao; Deng, Jian-Bo; Zhu, Xing-Feng

    2017-03-01

    Using full-potential local-orbital minimum-basis along with spin-polarized relativistic Korringa-Kohn-Rostoker methods, we study the electronic, Fermi surface, Curie temperature and optical properties of Zr2CoAl alloy. The alloy with Li2AgSb and Cu2MnAl structures are compared in terms of magnetic properties, and the electronic structures in two structures are also discussed. According to the calculated electronic states, it finds that the Zr2CoAl with Li2AgSb structure is half-metallic ferromagnet with an integral magnetic moment of 2.00μB , meanwhile we also notice the d-d and p-d hybridizations are responsible for the formation of minority-spin gap, furthermore, the fat-bands are applied to discuss the mixture between d and p electrons in the vicinity of the Fermi level. The Fermi surfaces related to the valence bands are constructed, and it is found that the spin-up valence bands 26, 27 and 28 across the Fermi energy dominate the nature of electrons. By mapping the system onto a Heisenberg Hamiltonian, we obtain the exchange coupling parameters, and observe that the Zr(A)-Co(C) and Zr(A)-Zr(B) interactions provide a major contribution for exchange interactions. Based on the calculated exchange coupling parameters, the Curie temperature is estimated to be 287.86 K at equilibrium, and also the dependence of Curie temperature on lattice constant related to the tunable Curie temperature in Zr2CoAl alloy is studied. Finally, we report the optical properties of Zr2CoAl alloy, and present the photon energy dependence of the absorption, the optical conductivity and the loss function.

  20. 2D instabilities of surface gravity waves on a linear shear current

    NASA Astrophysics Data System (ADS)

    Francius, Marc; Kharif, Christian

    2016-04-01

    Periodic 2D surface water waves propagating steadily on a rotational current have been studied by many authors (see [1] and references therein). Although the recent important theoretical developments have confirmed that periodic waves can exist over flows with arbitrary vorticity, their stability and their nonlinear evolution have not been much studied extensively so far. In fact, even in the rather simple case of uniform vorticity (linear shear), few papers have been published on the effect of a vertical shear current on the side-band instability of a uniform wave train over finite depth. In most of these studies [2-5], asymptotic expansions and multiple scales method have been used to obtain envelope evolution equations, which allow eventually to formulate a condition of (linear) instability to long modulational perturbations. It is noted here that this instability is often referred in the literature as the Benjamin-Feir or modulational instability. In the present study, we consider the linear stability of finite amplitude two-dimensional, periodic water waves propagating steadily on the free surface of a fluid with constant vorticity and finite depth. First, the steadily propagating surface waves are computed with steepness up to very close to the highest, using a Fourier series expansions and a collocation method, which constitutes a simple extension of Fenton's method [6] to the cases with a linear shear current. Then, the linear stability of these permanent waves to infinitesimal 2D perturbations is developed from the fully nonlinear equations in the framework of normal modes analysis. This linear stability analysis is an extension of [7] to the case of waves in the presence of a linear shear current and permits the determination of the dominant instability as a function of depth and vorticity for a given steepness. The numerical results are used to assess the accuracy of the vor-NLS equation derived in [5] for the characteristics of modulational

  1. Quantum oscillation signatures of Fermi arc surface states in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Potter, Andrew

    Weyl semimetal states and their crystalline symmetry protected Dirac- analogs have recently been discovered in a variety of materials. These new phases of matter offer an interesting example of topology in the absence of a protecting band- or correlation- gap. The bulk topological character of these materials is revealed upon the application of a magnetic field, which produces chiral Landau level modes that propagate along the field and which mediate inter-valley charge pumping associated with chiral anomaly physics. At a surface, the bulk topology manifests itself in unusual surface states whose Fermi surface consists of disjoint arcs. In this talk, I will describe magnetic field induced quantum oscillation signatures of both the surface and bulk topological features of these materials. These oscillations are associated with unusual magnetic orbits that start on the Fermi arc of one surface, propagate through the bulk on the chiral Landau level, and complete the orbit on the opposite surface. I also will describe some recent experimental evidence for these orbits in Dirac semimetal thin films.

  2. Theoretical study of surface plasmon resonance sensors based on 2D bimetallic alloy grating

    NASA Astrophysics Data System (ADS)

    Dhibi, Abdelhak; Khemiri, Mehdi; Oumezzine, Mohamed

    2016-11-01

    A surface plasmon resonance (SPR) sensor based on 2D alloy grating with a high performance is proposed. The grating consists of homogeneous alloys of formula MxAg1-x, where M is gold, copper, platinum and palladium. Compared to the SPR sensors based a pure metal, the sensor based on angular interrogation with silver exhibits a sharper (i.e. larger depth-to-width ratio) reflectivity dip, which provides a big detection accuracy, whereas the sensor based on gold exhibits the broadest dips and the highest sensitivity. The detection accuracy of SPR sensor based a metal alloy is enhanced by the increase of silver composition. In addition, the composition of silver which is around 0.8 improves the sensitivity and the quality of SPR sensor of pure metal. Numerical simulations based on rigorous coupled wave analysis (RCWA) show that the sensor based on a metal alloy not only has a high sensitivity and a high detection accuracy, but also exhibits a good linearity and a good quality.

  3. Detailed temporally resolved 2-D Velocity Measurements in a Novel Heat Exchanger Surface

    NASA Astrophysics Data System (ADS)

    Guezennec, Yann G.; Ko, Jang-Hyok; Choi, Woong-Chul

    1998-11-01

    Using flow visualization as a primary tool, a novel, high-performance heat transfer surface for compact heat exchangers was designed, specifically for low Reynolds number applications. This geometry was specifically created to enhance or generate strong three-dimensional transport even at low Reynolds number. It consists of a staggered array of "pin" mounted normal to the fins. A 15:1 model of this heat exchanger surface core was built out of Plexiglas to provide optical access and this model was placed in a 1'x1' water channel. The flow speed was adjusted to match the Reynolds based on the hydraulic diameter based on the fin pitch. The flow was seeded with small polystyrene particles and illuminated by a laser sheet from an Argon Ion laser. The fluid motion was recorded using a CCD camera and an S-VHS video recorder. In post-processing, the video records were automatically digitized and processed using a cinematographic PIV technique. The temporal evolution of the 2-D flow field (side view) clearly shows the presence of unsteady, shed vortical regions behind the pins, modulated by the spatially-periodic acceleration/deceleration and meandering of the mean flow between the periodic array of staggered pins. In the perpendicular view (top view), the results show the presence of two strong cross-stream transport mechanisms, mainly the horse-shoe vortex near the pin-fin junctions and the very strong spanwise transport in the separated wake region of the pins. This transport is most likely associated with the strong interaction of the longitudinal vortices (emanating form the horseshoe) and the spanwise vortices from the pin wake. This vortex interaction sets up a strong spanwise pressure gradient inducing large cross-stream transport from the fin to the core flow. Animation of the results illustrating these effects will be presented.

  4. Bilayer honeycomb lattice with ultracold atoms: Multiple Fermi surfaces and incommensurate spin density wave instability

    NASA Astrophysics Data System (ADS)

    Dey, Santanu; Sensarma, Rajdeep

    2016-12-01

    We propose an experimental setup using ultracold atoms to implement a bilayer honeycomb lattice with Bernal stacking. In the presence of a potential bias between the layers and at low densities, fermions placed in this lattice form an annular Fermi sea. The presence of two Fermi surfaces leads to interesting patterns in Friedel oscillations and RKKY interactions in the presence of impurities. Furthermore, a repulsive fermion-fermion interaction leads to a Stoner instability towards an incommensurate spin density wave order with a wave vector equal to the thickness of the Fermi sea. The instability occurs at a critical interaction strength which goes down with the density of the fermions. We find that the instability survives interaction renormalization due to vertex corrections and discuss how this can be seen in experiments. We also track the renormalization group flows of the different couplings between the fermionic degrees of freedom, and find that there are no perturbative instabilities, and that Stoner instability is the strongest instability which occurs at a critical threshold value of the interaction. The critical interaction goes to zero as the chemical potential is tuned towards the band bottom.

  5. The 2-D Curvature of Large Angle Interplanetary MHD Discontinuity Surfaces: IMP-8 and WIND Observations

    NASA Astrophysics Data System (ADS)

    Lepping, R. P.; Wu, C.; McClernan, K.

    2002-12-01

    This study examines the degree of 2-D curvature of solar wind directional discontinuity (DD) surfaces at 1 AU using magnetic field, density, and velocity data from the WIND and IMP-8 spacecraft for a large number (N = 134) of carefully selected events having large ``discontinuity angles" of 90° or greater. The discontinuity angle (ω ) is measured in the DDs current sheet, the normal to which is estimated by field variance analysis. The fundamental analysis depends on estimates of these DD surface normals at the two spacecraft, and the DDs center-times and positions. On average, the transit time from one DD sighting to the other was 36 minutes, and the associated distance along the normal direction was 137 RE. The transition-interval lengths across the DDs are translated into thicknesses and examined for the amount of change between the two spacecraft observing points; average thickness is relatively large, 14 RE. All relevant quantities are examined statistically to establish their distributions, average, and degree of change. A weighted average of the radius of curvature is estimated to be 380 RE, but its most probably value is 290 RE. The average ω is 140° with a relatively large spread (σ =28°). The average direction of propagation is: longitude = 194° and latitude = 7° (but < ∣ lat∣ > = 27°). Various parameters are studied with respect to DD type, defined in terms the ratio of speed of propagation to net speed (``ratio") of the DD surface, (the RD ratio is high and the TD ratio is very low or zero). The results by this definition of type are favorably compared to those from the more conventional method, which depends on the absolute strength of the normal component of the magnetic field. There is little difference in any average parameter value according to type. However, the average ω appears to depend slightly on type with the < ω > for the RDs being smaller. A DDs type was shown to change in either direction between the two observation

  6. Combination of 3D skin surface texture features and 2D ABCD features for improved melanoma diagnosis.

    PubMed

    Ding, Yi; John, Nigel W; Smith, Lyndon; Sun, Jiuai; Smith, Melvyn

    2015-10-01

    Two-dimensional asymmetry, border irregularity, colour variegation and diameter (ABCD) features are important indicators currently used for computer-assisted diagnosis of malignant melanoma (MM); however, they often prove to be insufficient to make a convincing diagnosis. Previous work has demonstrated that 3D skin surface normal features in the form of tilt and slant pattern disruptions are promising new features independent from the existing 2D ABCD features. This work investigates that whether improved lesion classification can be achieved by combining the 3D features with the 2D ABCD features. Experiments using a nonlinear support vector machine classifier show that many combinations of the 2D ABCD features and the 3D features can give substantially better classification accuracy than using (1) single features and (2) many combinations of the 2D ABCD features. The best 2D and 3D feature combination includes the overall 3D skin surface disruption, the asymmetry and all the three colour channel features. It gives an overall 87.8 % successful classification, which is better than the best single feature with 78.0 % and the best 2D feature combination with 83.1 %. These demonstrate that (1) the 3D features have additive values to improve the existing lesion classification and (2) combining the 3D feature with all the 2D features does not lead to the best lesion classification. The two ABCD features not selected by the best 2D and 3D combination, namely (1) the border feature and (2) the diameter feature, were also studied in separate experiments. It found that inclusion of either feature in the 2D and 3D combination can successfully classify 3 out of 4 lesion groups. The only one group not accurately classified by either feature can be classified satisfactorily by the other. In both cases, they have shown better classification performances than those without the 3D feature in the combinations. This further demonstrates that (1) the 3D feature can be used to

  7. Protein adsorption resistant surface on polymer composite based on 2D- and 3D-controlled grafting of phospholipid moieties

    NASA Astrophysics Data System (ADS)

    Hoshi, Toru; Matsuno, Ryosuke; Sawaguchi, Takashi; Konno, Tomohiro; Takai, Madoka; Ishihara, Kazuhiko

    2008-11-01

    To prepare the biocompatible surface, a phosphorylcholine (PC) group was introduced on this hydroxyl group generated by surface hydrolysis on the polymer composite composed of polyethylene (PE) and poly (vinyl acetate) (PVAc) prepared by supercritical carbon dioxide. Two different procedures such as two-dimensional (2D) modification and three-dimensional (3D) modification were applied to obtain the steady biocompatible surface. 2D modification was that PC groups were directly anchored on the surface of the polymer composite. 3D modification was that phospholipid polymer was grafted from the surface of the polymer composite by surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-methacryloyloxyethyl phosphorylcholine (MPC). The surfaces were characterized by X-ray photoelectron spectroscopy, dynamic water contact angle measurements, and atomic force microscope. The effects of the poly(MPC) chain length on the protein adsorption resistivity were investigated. The protein adsorption on the polymer composite surface with PC groups modified by 2D or 3D modification was significantly reduced as compared with that on the unmodified PE. Further, the amount of protein adsorbed on the 3D modified surface that is poly(MPC)-grafted surface decreased with an increase in the chain length of the poly(MPC). The surface with an arbitrary structure and the characteristic can be constructed by using 2D and 3D modification. We conclude that the polymer composites of PE/PVAc with PC groups on the surface are useful for fabricating biomedical devices due to their good mechanical and surface properties.

  8. Fermi Surface Manipulation by External Magnetic Field Demonstrated for a Prototypical Ferromagnet

    NASA Astrophysics Data System (ADS)

    Młyńczak, E.; Eschbach, M.; Borek, S.; Minár, J.; Braun, J.; Aguilera, I.; Bihlmayer, G.; Döring, S.; Gehlmann, M.; Gospodarič, P.; Suga, S.; Plucinski, L.; Blügel, S.; Ebert, H.; Schneider, C. M.

    2016-10-01

    We consider the details of the near-surface electronic band structure of a prototypical ferromagnet, Fe(001). Using high-resolution angle-resolved photoemission spectroscopy, we demonstrate openings of the spin-orbit-induced electronic band gaps near the Fermi level. The band gaps, and thus the Fermi surface, can be manipulated by changing the remanent magnetization direction. The effect is of the order of Δ E =100 meV and Δ k =0.1 Å-1 . We show that the observed dispersions are dominated by the bulk band structure. First-principles calculations and one-step photoemission calculations suggest that the effect is related to changes in the electronic ground state and not caused by the photoemission process itself. The symmetry of the effect indicates that the observed electronic bulk states are influenced by the presence of the surface, which might be understood as related to a Rashba-type effect. By pinpointing the regions in the electronic band structure where the switchable band gaps occur, we demonstrate the significance of spin-orbit interaction even for elements as light as 3 d ferromagnets. These results set a new paradigm for the investigations of spin-orbit effects in the spintronic materials. The same methodology could be used in the bottom-up design of the devices based on the switching of spin-orbit gaps such as electric-field control of magnetic anisotropy or tunneling anisotropic magnetoresistance.

  9. 3D reconstruction of light flux distribution on arbitrary surfaces from 2D multi-photographic images.

    PubMed

    Chen, Xueli; Gao, Xinbo; Chen, Duofang; Ma, Xiaopeng; Zhao, Xiaohui; Shen, Man; Li, Xiangsi; Qu, Xiaochao; Liang, Jimin; Ripoll, Jorge; Tian, Jie

    2010-09-13

    Optical tomography can demonstrate accurate three-dimensional (3D) imaging that recovers the 3D spatial distribution and concentration of the luminescent probes in biological tissues, compared with planar imaging. However, the tomographic approach is extremely difficult to implement due to the complexity in the reconstruction of 3D surface flux distribution from multi-view two dimensional (2D) measurements on the subject surface. To handle this problem, a novel and effective method is proposed in this paper to determine the surface flux distribution from multi-view 2D photographic images acquired by a set of non-contact detectors. The method is validated with comparison experiments involving both regular and irregular surfaces. Reconstruction of the inside probes based on the reconstructed surface flux distribution further demonstrates the potential of the proposed method in its application in optical tomography.

  10. Maximal Cherenkov γ-radiation on Fermi-surface of compact stars

    SciTech Connect

    Akbari-Moghanjoughi, M.

    2014-05-15

    The quantum magnetohydrodynamic model is employed in this paper to study the extraordinary (XO) elliptically polarized electromagnetic wave dispersion in quantum plasmas with spin-1/2 magnetization and relativistic degeneracy effects, considering also the electron-exchange and quantum diffraction of electrons. From the lower and upper calculated XO-modes, it is observed that, for electrons on the surface of the Fermi-sphere, the lower XO-mode can excite the Cherenkov radiation by crossing the Fermi-line, with some proper conditions depending on the values of independent plasma parameters, such as the relativistic-degeneracy, the atomic-number of constituent ions, and the magnetic field strength. Particularly, a lower electron number-density and Cherenkov radiation frequency limits are found to exist, for instance, for given values of the plasma ions atomic-number and the magnetic field strength below which the radiation can not be excited by the electrons on the Fermi-surface. This lower density limit increases by decrease in the atomic-number but decreases with decrease in the strength of the ambient magnetic field. It is remarkable that in this research it is discovered that the maximal Cherenkov-radiation per unit-length (the energy radiated by superluminal electrons traveling through the dielectric medium) coincides with the plasma number-densities, which is present in compact stars with the maximal radiation frequency lying in the gamma-ray spectrum. Current study can provide an important plasma diagnostic tool for a wide plasma density range, be it the solid density, the warm dense matter, the inertial confined or the astrophysical compact plasmas and may reveal an important cooling mechanism for white dwarfs. Current findings may also answer the fundamental astrophysical question on the mysterious origin of intense cosmic gamma-ray emissions.

  11. Effect of the Fermi surface reconstruction on the self-energy of the copper-oxide superconductors

    NASA Astrophysics Data System (ADS)

    Bellafi, B.; Azzouz, M.; Charfi-Kaddour, S.

    2014-11-01

    We calculated the self-energy corrections beyond the mean-field solution of the rotating antiferromagnetism theory using the functional integral approach. The frequency dependence of the scattering rate 1 / τ is evaluated for different temperatures and doping levels, and is compared with other approaches. The general trends we found are fairly consistent with the nearly antiferromagnetic Fermi liquid as far as the k -anisotropy and some aspects of the marginal-Fermi liquid behavior are concerned. The present approach provides the justification from the microscopic point of view for the phenomenology of the marginal Fermi liquid ansatz, which was used in the calculation of several physical properties of the high-TC cuprates within the rotating antiferromagnetism theory. In addition, the expression of self-energy we calculated takes into account the two currently hot issues of the high-TC cuprate superconductors, namely the Fermi surface reconstruction and the hidden symmetry, which are closely related to the pseudogap.

  12. Validation Test Report for the NRL Ocean Surface Flux (NFLUX) Quality Control and 2D Variational Analysis System

    DTIC Science & Technology

    2014-06-11

    Test Report for the NRL Ocean Surface Flux (NFLUX) Quality Control and 2D Variational Analysis System Jackie May Neil VaN de Voorde QinetiQ North...OF RESPONSIBLE PERSON 19b. TELEPHONE NUMBER (include area code) b. ABSTRACT c. THIS PAGE 18. NUMBER OF PAGES 17. LIMITATION OF ABSTRACT Validation Test ...1 2.0 VALIDATION TEST DESIGN

  13. Charge Imbalance Effects on Interlayer Hopping and Fermi Surfaces in Multilayered High-Tc Cuprates

    NASA Astrophysics Data System (ADS)

    Mori, M.; Tohyama, T.; Maekawa, S.

    2006-03-01

    We study doping dependence of interlayer hoppings, t\\bot, in multilayered cuprates with four or more CuO2 planes in a unit cell. When the double occupancy is forbidden in the plane, an effective amplitude of t\\bot in the Gutzwiller approximation is shown to be proportional to the square root of the product of doping rates in adjacent two planes, i.e., teff\\bot\\propto t\\bot\\sqrt{δ1δ2}, where δ1 and δ2 represent the doping rates of the two planes. More than three-layered cuprates have two kinds of CuO2 planes, i.e., inner- and outer planes (IP and OP), resulting in two different values of teff\\bot, i.e., teff\\bot1\\propto t\\bot\\sqrt{δIPδIP} between IP’s, and teff\\bot2\\propto t\\bot\\sqrt{δIPδOP} between IP and OP. Fermi surfaces are calculated in the four-layered t-t'-t''-J model by the mean-field theory. The order parameters, the renormalization factor of t\\bot, and the site-potential making the charge imbalance between IP and OP are self-consistently determined for several doping rates. We show the interlayer splitting of the Fermi surfaces, which may be observed in the angle resolved photoemission spectroscopy measurement.

  14. Quantum oscillations and the Fermi surface of high-temperature cuprate superconductors

    NASA Astrophysics Data System (ADS)

    Vignolle, Baptiste; Vignolles, David; LeBoeuf, David; Lepault, Stéphane; Ramshaw, Brad; Liang, Ruixing; Bonn, D. A.; Hardy, W. N.; Doiron-Leyraud, Nicolas; Carrington, A.; Hussey, N. E.; Taillefer, Louis; Proust, Cyril

    2011-06-01

    Over 20 years since the discovery of high temperature superconductivity in cuprates (Bednorz and Müller, 1986 [1]), the first convincing observation of quantum oscillations in underdoped YBa 2Cu 3O 6.5 (Doiron-Leyraud et al., 2007 [2]) has deeply changed the theoretical landscape relevant to these materials. The Fermi surface is a basic concept of solid state physics, which underpins most physical properties (electrical, thermal, optical, etc.) of a metal. Even in the presence of interactions, this fundamental concept remains robust. While there was little doubt about the existence of a Fermi surface on the overdoped side of the phase diagram of the cuprates, the discovery of quantum oscillations in the underdoped regime was a surprise. The small pockets inferred from the measurements in underdoped YBa 2Cu 3O y contrast with the large orbit found in overdoped Tl 2Ba 2CuO 6 + δ. A central issue in understanding the phase diagram of high temperature superconductors is the origin of this difference at opposite sides of the superconducting dome. This review aims to shed light on this issue by bringing together recent results of quantum oscillation and transport measurements under high magnetic fields in hole-doped cuprates.

  15. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate.

    PubMed

    Shen, Yao; Li, Yao-Dong; Wo, Hongliang; Li, Yuesheng; Shen, Shoudong; Pan, Bingying; Wang, Qisi; Walker, H C; Steffens, P; Boehm, M; Hao, Yiqing; Quintero-Castro, D L; Harriger, L W; Frontzek, M D; Hao, Lijie; Meng, Siqin; Zhang, Qingming; Chen, Gang; Zhao, Jun

    2016-12-05

    A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed 'spinons'). Here we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO4 that reveal broad spin excitations covering a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle-hole excitation of a spinon Fermi surface. Our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.

  16. Fermi surface topology and hot spot distribution in the Kondo lattice system CeB6

    DOE PAGES

    Neupane, Madhab; Alidoust, Nasser; Belopolski, Ilya; ...

    2015-09-18

    Rare-earth hexaborides have attracted considerable attention recently in connection to a variety of correlated phenomena including heavy fermions, superconductivity, and low-temperature magnetic phases. Here, we present high-resolution angle-resolved photoemission spectroscopy studies of trivalent CeB6 and divalent BaB6 rare-earth hexaborides. Here we find that the Fermi surface electronic structure of CeB6 consists of large oval-shaped pockets around the X points of the Brillouin zone, whereas the states around the zone center Γ point are strongly renormalized. Our first-principles calculations agree with our experimental results around the X points but not around the Γ point, indicating areas of strong renormalization located nearmore » Γ. The Ce quasiparticle states participate in the formation of hot spots at the Fermi surface, whereas the incoherent f states hybridize and lead to the emergence of dispersive features absent in the non-$f$ counterpart BaB6. Lastly, our results provide an understanding of the electronic structure in rare-earth hexaborides, which will be useful in elucidating the nature of the exotic low-temperature phases in these materials.« less

  17. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

    NASA Astrophysics Data System (ADS)

    Shen, Yao; Li, Yao-Dong; Wo, Hongliang; Li, Yuesheng; Shen, Shoudong; Pan, Bingying; Wang, Qisi; Walker, H. C.; Steffens, P.; Boehm, M.; Hao, Yiqing; Quintero-Castro, D. L.; Harriger, L. W.; Frontzek, M. D.; Hao, Lijie; Meng, Siqin; Zhang, Qingming; Chen, Gang; Zhao, Jun

    2016-12-01

    A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). Here we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO4 that reveal broad spin excitations covering a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle-hole excitation of a spinon Fermi surface. Our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.

  18. Single reconstructed Fermi surface pocket in an underdoped single-layer cuprate superconductor

    PubMed Central

    Chan, M. K.; Harrison, N.; McDonald, R. D.; Ramshaw, B. J.; Modic, K. A.; Barišić, N.; Greven, M.

    2016-01-01

    The observation of a reconstructed Fermi surface via quantum oscillations in hole-doped cuprates opened a path towards identifying broken symmetry states in the pseudogap regime. However, such an identification has remained inconclusive due to the multi-frequency quantum oscillation spectra and complications accounting for bilayer effects in most studies. We overcome these impediments with high-resolution measurements on the structurally simpler cuprate HgBa2CuO4+δ (Hg1201), which features one CuO2 plane per primitive unit cell. We find only a single oscillatory component with no signatures of magnetic breakdown tunnelling to additional orbits. Therefore, the Fermi surface comprises a single quasi-two-dimensional pocket. Quantitative modelling of these results indicates that a biaxial charge density wave within each CuO2 plane is responsible for the reconstruction and rules out criss-crossed charge stripes between layers as a viable alternative in Hg1201. Lastly, we determine that the characteristic gap between reconstructed pockets is a significant fraction of the pseudogap energy. PMID:27448102

  19. Remarkable doping effects beyond altering Fermi surface on the superconductivity of iron-based superconductors

    NASA Astrophysics Data System (ADS)

    Ye, Z. R.; Zhang, Y.; Chen, F.; Xu, M.; Jiang, J.; Niu, X. H.; Wen, C. H. P.; Xie, B. P.; Feng, D. L.; Xing, L. Y.; Wang, X. C.; Jin, C. Q.

    2014-03-01

    The superconductivity in Fe-based superconductors could be achieved by doping the parent compounds. Previous researches were focusing on the charge carrier density or Fermi surface alteration by doping only. However, the dominating factors based on Fermiology have many inconsistencies, which indicates that some other effects induced by doping are neglected. Using ARPES, we have established the microscopic and more comprehensive picture of doping on the electronic structure beyond altering Fermi surface. We have figured out other two critical effects of doping, scattering and changing correlation. With doping, the dxy-related band around the zone center is found to be much more sensitive than the dxz/dyz-related bands and the strength of the impurity scattering strongly depends on the position of dopants, which resembles the case in cuprates. On the other hand, we observed that the electron correlation decreases with doping, which is universal in various systems of Fe-based superconductors. Moderate electron correlation is critical for the high Tc. The two effects we observed here both are very important for the superconductivity, and explain a lot of previous mysteries and unresolved issues.

  20. Fermi Surface of the Pnictide Superconductor LaRu2 P 2 studied by quantum oscillations

    NASA Astrophysics Data System (ADS)

    Moll, Philip; Balakirev, Fedor; McDonald, Ross; Karpinski, Janusz; Bukowski, Zbigniew; Blaha, Peter; Schwarz, Karlheinz; Batlogg, Bertram

    2011-03-01

    LaRu 2 P2 is a stochiometric pnictide superconductor (Tc ~ 4.1 K) and crystallizes in the ThCr 2 Si 2 structure (the ``122'' pnictide family). We have mapped out its Fermi surface via the deHaas-vanAlphen effect in pulsed magnetic fields up to 60T (LANL/NHMFL). Pronounced oscillations were observed in the magnetic torque measured with a microcantilever setup. Two features are particularly noteworthy: The oscillations can be followed to surprisingly high temperatures beyond 20K, and the main frequency component at θ = 20circ; (θ = 0circ; at HIIc) is at 349T (α -peak), significantly lower than in the related compounds LaFe 2 P2 . A second frequency originating from a larger Fermi surface cross-section at 1921 T (β -peak) is identified. The temperature dependence of the amplitudes is well described by the Lifshitz- Kosevich formalism and gives low effective masses m*/m = 0.80 (α sheet) and 1.09 (β sheet). Therefore, most ``122'' metals appear to have similarly low effective masses.

  1. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

    SciTech Connect

    Shen, Yao; Li, Yao-Dong; Wo, Hongliang; Li, Yuesheng; Shen, Shoudong; Pan, Bingying; Wang, Qisi; Walker, H. C.; Steffens, P.; Boehm, M.; Hao, Yiqing; Quintero-Castro, D. L.; Harriger, L. W.; Frontzek, M. D.; Hao, Lijie; Meng, Siqin; Zhang, Qingming; Chen, Gang; Zhao, Jun

    2016-12-05

    A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). In this paper, we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO4 that reveal broad spin excitations covering a wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Finally, our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.

  2. Evidence for a spinon Fermi surface in a triangular-lattice quantum-spin-liquid candidate

    DOE PAGES

    Shen, Yao; Li, Yao-Dong; Wo, Hongliang; ...

    2016-12-05

    A quantum spin liquid is an exotic quantum state of matter in which spins are highly entangled and remain disordered down to zero temperature. Such a state of matter is potentially relevant to high-temperature superconductivity and quantum-information applications, and experimental identification of a quantum spin liquid state is of fundamental importance for our understanding of quantum matter. Theoretical studies have proposed various quantum-spin-liquid ground states, most of which are characterized by exotic spin excitations with fractional quantum numbers (termed ‘spinons’). In this paper, we report neutron scattering measurements of the triangular-lattice antiferromagnet YbMgGaO4 that reveal broad spin excitations covering amore » wide region of the Brillouin zone. The observed diffusive spin excitation persists at the lowest measured energy and shows a clear upper excitation edge, consistent with the particle–hole excitation of a spinon Fermi surface. Finally, our results therefore point to the existence of a quantum spin liquid state with a spinon Fermi surface in YbMgGaO4, which has a perfect spin-1/2 triangular lattice as in the original proposal of quantum spin liquids.« less

  3. 2D ACAR momentum density study of the nature of the positron surface state on Al(100)

    SciTech Connect

    Berko, S.; Canter, K.F.; Lynn, K.G.; Mills, A.P.; Roellig, L.O.; West, R.N.

    1985-01-01

    The two-dimensional angular correlation of the 2..gamma.. annihilation radiation (2D ACAR) has been measured from an Al(100) surface bombarded by 200-eV positrons. After removing the contribution of fast para-positronium annihilation, the spectrum from positrons annihilating at the surface exhibits a nearly isotropic conical shape with a (7.1 +- 0.5) mrad FWHM. 5 refs., 6 figs.

  4. Destruction of the Fermi surface due to pseudogap fluctuations in correlated systems

    NASA Astrophysics Data System (ADS)

    Sadovskii, M. V.; Kuchinskii, E. Z.; Nekrasov, I. A.

    2007-09-01

    Pseudogap phenomena in strongly correlated systems have essential spatial length scale dependence [M.V. Sadovskii, Physics - Uspekhi 44 (2001) 515]. To merge pseudogap physics and strong electron correlations we generalize the dynamical-mean field theory (DMFT) [A. Georges, G. Kotliar, W. Krauth, M.J. Rozenberg, Rev. Mod. Phys. 68 (1996) 13]. Dependence on correlation length of pseudogap fluctuations via additional (momentum dependent) self-energy Σk is included into conventional DMFT equations. The self-energy Σk describes non-local dynamical correlations induced either by short-ranged collective SDW-like antiferromagnetic spin or CDW-like charge fluctuations [J. Schmalian, D. Pines, B. Stojkovic, Phys. Rev. B 60 (1999) 667; E.Z. Kuchinskii, M.V. Sadovskii, JETP 88 (1999) 347]. Weakly doped one-band Hubbard model with repulsive Coulomb interaction on a square lattice with nearest and next nearest neighbour hopping is numerically investigated within this generalized DMFT + Σk approach [E.Z. Kuchinskii, I.A. Nekrasov, M.V. Sadovskii, JETP Lett. 82 (2005) 198; M.V. Sadovskii, I.A. Nekrasov, E.Z. Kuchinskii, Th. Prushke, V.I. Anisimov, Phys. Rev. B 72 (2005) 155105]. Both types of strongly correlated metals, namely (i) doped Mott insulator and (ii) the case of bandwidth W < U ( U - value of local Coulomb interaction) were considered. Energy dispersions, quasiparticle damping, spectral functions and ARPES spectra calculated within DMFT + Σk, all show a pseudogap effects close to the Fermi level of quasiparticle band. Finally we demonstrate the qualitative picture of quasiparticle band dispersion, Fermi surface “destruction” and “Fermi arcs” formation due to pseudogap fluctuations, which agrees well with observations by ARPES.

  5. Investigation on wide-band scattering of a 2-D target above 1-D randomly rough surface by FDTD method.

    PubMed

    Li, Juan; Guo, Li-Xin; Jiao, Yong-Chang; Li, Ke

    2011-01-17

    Finite-difference time-domain (FDTD) algorithm with a pulse wave excitation is used to investigate the wide-band composite scattering from a two-dimensional(2-D) infinitely long target with arbitrary cross section located above a one-dimensional(1-D) randomly rough surface. The FDTD calculation is performed with a pulse wave incidence, and the 2-D representative time-domain scattered field in the far zone is obtained directly by extrapolating the currently calculated data on the output boundary. Then the 2-D wide-band scattering result is acquired by transforming the representative time-domain field to the frequency domain with a Fourier transform. Taking the composite scattering of an infinitely long cylinder above rough surface as an example, the wide-band response in the far zone by FDTD with the pulsed excitation is computed and it shows a good agreement with the numerical result by FDTD with the sinusoidal illumination. Finally, the normalized radar cross section (NRCS) from a 2-D target above 1-D rough surface versus the incident frequency, and the representative scattered fields in the far zone versus the time are analyzed in detail.

  6. Orbital dependent Rashba splitting and electron-phonon coupling of 2D Bi phase on Cu(100) surface

    SciTech Connect

    Gargiani, Pierluigi; Lisi, Simone; Betti, Maria Grazia; Ibrahimi, Amina Taleb; Bertran, François; Le Fèvre, Patrick; Chiodo, Letizia

    2013-11-14

    A monolayer of bismuth deposited on the Cu(100) surface forms a highly ordered c(2×2) reconstructed phase. The low energy single particle excitations of the c(2×2) Bi/Cu(100) present Bi-induced states with a parabolic dispersion in the energy region close to the Fermi level, as observed by angle-resolved photoemission spectroscopy. The electronic state dispersion, the charge density localization, and the spin-orbit coupling have been investigated combining photoemission spectroscopy and density functional theory, unraveling a two-dimensional Bi phase with charge density well localized at the interface. The Bi-induced states present a Rashba splitting, when the charge density is strongly localized in the Bi plane. Furthermore, the temperature dependence of the spectral density close to the Fermi level has been evaluated. Dispersive electronic states offer a large number of decay channels for transitions coupled to phonons and the strength of the electron-phonon coupling for the Bi/Cu(100) system is shown to be stronger than for Bi surfaces and to depend on the electronic state symmetry and localization.

  7. Fermi level pinning and the charge transfer contribution to the energy of adsorption at semiconducting surfaces

    SciTech Connect

    Krukowski, Stanisław; Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad

    2014-01-28

    It is shown that charge transfer, the process analogous to formation of semiconductor p-n junction, contributes significantly to adsorption energy at semiconductor surfaces. For the processes without the charge transfer, such as molecular adsorption of closed shell systems, the adsorption energy is determined by the bonding only. In the case involving charge transfer, such as open shell systems like metal atoms or the dissociating molecules, the energy attains different value for the Fermi level differently pinned. The Density Functional Theory (DFT) simulation of species adsorption at different surfaces, such as SiC(0001) or GaN(0001) confirms these predictions: the molecular adsorption is independent on the coverage, while the dissociative process adsorption energy varies by several electronvolts.

  8. Recent high-magnetic-field experiments on the 'high Tc' cuprates: Fermi-surface instabilities as a driver for superconductivity

    SciTech Connect

    Singleton, John; Mc Donald, Ross D; Cox, Susan

    2008-01-01

    The authors give a brief review of high-magnetic-field quantum-oscillation measurements on cuprate superconductors. In the case of the underdoped cuprates, a number of small Fermi-surface pockets are observed, probably due to the incommensurate nesting of the predicted (large) hole Fermi surface. The Fermi-surface instabilities that drive this nesting are also likely to result in the incommensurate spin fluctuations observed in inelastic neutron-scattering measurements. They suggest that the unusually high superconducting transitions in the cuprates are driven by an exact mapping of these incommensurate spin fluctuations onto the d{sub x{sup 2}-y{sup 2}} Cooper-pair wavefunction. The maximum energy of the fluctuations {approx} 100s of Kelvin gives an appropriate energy scale for the superconducting transition temperature.

  9. Near doping-independent pocket area from an antinodal Fermi surface instability in underdoped high temperature superconductors.

    PubMed

    Harrison, N

    2011-10-28

    Fermi surface models applied to the underdoped cuprates predict the small pocket area to be strongly dependent on doping whereas quantum oscillations in YBa(2)Cu(3)O(6+x) find precisely the opposite to be true--seemingly at odds with the Luttinger volume. We show that such behavior can be explained by an incommensurate antinodal Fermi surface nesting-type instability--further explaining the doping-dependent superstructures seen in cuprates using scanning tunneling microscopy. We develop a Fermi surface reconstruction scheme involving orthogonal density waves in two dimensions and show that their incommensurate behavior requires momentum-dependent coupling. A cooperative modulation of the charge and bond strength is therefore suggested.

  10. A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class

    PubMed Central

    Huang, Shin-Ming; Xu, Su-Yang; Belopolski, Ilya; Lee, Chi-Cheng; Chang, Guoqing; Wang, BaoKai; Alidoust, Nasser; Bian, Guang; Neupane, Madhab; Zhang, Chenglong; Jia, Shuang; Bansil, Arun; Lin, Hsin; Hasan, M. Zahid

    2015-01-01

    Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials. PMID:26067579

  11. A Weyl Fermion semimetal with surface Fermi arcs in the transition metal monopnictide TaAs class.

    PubMed

    Huang, Shin-Ming; Xu, Su-Yang; Belopolski, Ilya; Lee, Chi-Cheng; Chang, Guoqing; Wang, BaoKai; Alidoust, Nasser; Bian, Guang; Neupane, Madhab; Zhang, Chenglong; Jia, Shuang; Bansil, Arun; Lin, Hsin; Hasan, M Zahid

    2015-06-12

    Weyl fermions are massless chiral fermions that play an important role in quantum field theory but have never been observed as fundamental particles. A Weyl semimetal is an unusual crystal that hosts Weyl fermions as quasiparticle excitations and features Fermi arcs on its surface. Such a semimetal not only provides a condensed matter realization of the anomalies in quantum field theories but also demonstrates the topological classification beyond the gapped topological insulators. Here, we identify a topological Weyl semimetal state in the transition metal monopnictide materials class. Our first-principles calculations on TaAs reveal its bulk Weyl fermion cones and surface Fermi arcs. Our results show that in the TaAs-type materials the Weyl semimetal state does not depend on fine-tuning of chemical composition or magnetic order, which opens the door for the experimental realization of Weyl semimetals and Fermi arc surface states in real materials.

  12. Multifractal and Singularity Maps of soil surface moisture distribution derived from 2D image analysis.

    NASA Astrophysics Data System (ADS)

    Cumbrera, Ramiro; Millán, Humberto; Martín-Sotoca, Juan Jose; Pérez Soto, Luis; Sanchez, Maria Elena; Tarquis, Ana Maria

    2016-04-01

    methods for mapping geochemical anomalies caused by buried sources and for predicting undiscovered mineral deposits in covered areas. Journal of Geochemical Exploration, 122, 55-70. Cumbrera, R., Ana M. Tarquis, Gabriel Gascó, Humberto Millán (2012) Fractal scaling of apparent soil moisture estimated from vertical planes of Vertisol pit images. Journal of Hydrology (452-453), 205-212. Martin Sotoca; J.J. Antonio Saa-Requejo, Juan Grau and Ana M. Tarquis (2016). Segmentation of singularity maps in the context of soil porosity. Geophysical Research Abstracts, 18, EGU2016-11402. Millán, H., Cumbrera, R. and Ana M. Tarquis (2016) Multifractal and Levy-stable statistics of soil surface moisture distribution derived from 2D image analysis. Applied Mathematical Modelling, 40(3), 2384-2395.

  13. Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe.

    PubMed

    Gourgout, A; Pourret, A; Knebel, G; Aoki, D; Seyfarth, G; Flouquet, J

    2016-07-22

    We present thermoelectric power and resistivity measurements in the ferromagnetic superconductor URhGe for a magnetic field applied along the hard magnetization b axis of the orthorhombic crystal. Reentrant superconductivity is observed near the spin reorientation transition at H_{R}=12.75  T, where a first order transition from the ferromagnetic to the polarized paramagnetic state occurs. Special focus is given to the longitudinal configuration, where both the electric and heat current are parallel to the applied field. The validity of the Fermi-liquid T^{2} dependence of the resistivity through H_{R} demonstrates clearly that no quantum critical point occurs at H_{R}. Thus, the ferromagnetic transition line at H_{R} becomes first order implying the existence of a tricritical point at finite temperature. The enhancement of magnetic fluctuations in the vicinity of the tricritical point stimulates the reentrance of superconductivity. The abrupt sign change observed in the thermoelectric power with the thermal gradient applied along the b axis together with the strong anomalies in the other directions is definitive macroscopic evidence that in addition a significant change of the Fermi surface appears through H_{R}.

  14. Fermi surface studies of Co-based Heusler alloys: Ab-initio study

    NASA Astrophysics Data System (ADS)

    Ram, Swetarekha; Kanchana, V.

    2013-02-01

    The electronic, Fermi surface (FS) and magnetic properties of ferromagnetic Heusler alloys Co2XY (X = Cr, Mn, Fe; Y=Al, Ga) have been investigated by means of first principles calculation. Out of these compounds, Co2CrAl is found to be perfectly half-metallic (HM) at ambient. Under pressure HM to nearly HM (NHM) transition is observed around 75 GPa for Co2CrAl and NHM to HM transition is observed around 40 GPa and 18 GPa for Co2CrGa and Co2MnAl, respectively, while no transition is observed for other compounds under study and is also analyzed from the FS studies. The states at the Fermi level in the majority spin are strongly hybridized Co-d and X-d like states. The majority band FS topology change is observed under pressure for the compounds where we observe a transition, while the minority band FS remain unaltered under pressure for all compounds except in Co2FeGa, where we observed an electron sheet at X point instead of hole pocket at Γ point.

  15. Collapse of Ferromagnetism and Fermi Surface Instability near Reentrant Superconductivity of URhGe

    NASA Astrophysics Data System (ADS)

    Gourgout, A.; Pourret, A.; Knebel, G.; Aoki, D.; Seyfarth, G.; Flouquet, J.

    2016-07-01

    We present thermoelectric power and resistivity measurements in the ferromagnetic superconductor URhGe for a magnetic field applied along the hard magnetization b axis of the orthorhombic crystal. Reentrant superconductivity is observed near the spin reorientation transition at HR=12.75 T , where a first order transition from the ferromagnetic to the polarized paramagnetic state occurs. Special focus is given to the longitudinal configuration, where both the electric and heat current are parallel to the applied field. The validity of the Fermi-liquid T2 dependence of the resistivity through HR demonstrates clearly that no quantum critical point occurs at HR. Thus, the ferromagnetic transition line at HR becomes first order implying the existence of a tricritical point at finite temperature. The enhancement of magnetic fluctuations in the vicinity of the tricritical point stimulates the reentrance of superconductivity. The abrupt sign change observed in the thermoelectric power with the thermal gradient applied along the b axis together with the strong anomalies in the other directions is definitive macroscopic evidence that in addition a significant change of the Fermi surface appears through HR.

  16. Effect of Fermi surface nesting on resonant spin excitations in Ba(1-x)K(x)Fe2As2.

    PubMed

    Castellan, J-P; Rosenkranz, S; Goremychkin, E A; Chung, D Y; Todorov, I S; Kanatzidis, M G; Eremin, I; Knolle, J; Chubukov, A V; Maiti, S; Norman, M R; Weber, F; Claus, H; Guidi, T; Bewley, R I; Osborn, R

    2011-10-21

    We report inelastic neutron scattering measurements of the resonant spin excitations in Ba(1-x)K(x)Fe(2)As(2) over a broad range of electron band filling. The fall in the superconducting transition temperature with hole doping coincides with the magnetic excitations splitting into two incommensurate peaks because of the growing mismatch in the hole and electron Fermi surface volumes, as confirmed by a tight-binding model with s(±)-symmetry pairing. The reduction in Fermi surface nesting is accompanied by a collapse of the resonance binding energy and its spectral weight, caused by the weakening of electron-electron correlations.

  17. Angle-resolved photoemission spectroscopy of the insulating NaxWO3: Anderson localization, polaron formation, and remnant Fermi surface.

    PubMed

    Raj, S; Hashimoto, D; Matsui, H; Souma, S; Sato, T; Takahashi, T; Sarma, D D; Mahadevan, Priya; Oishi, S

    2006-04-14

    The electronic structure of the insulating sodium tungsten bronze, Na(0.025)WO(3), is investigated by high-resolution angle-resolved photoemission spectroscopy. We find that near-E(F) states are localized due to the strong disorder arising from random distribution of Na+ ions in the WO(3) lattice, which makes the system insulating. The temperature dependence of photoemission spectra provides direct evidence for polaron formation. The remnant Fermi surface of the insulator is found to be the replica of the real Fermi surface in the metallic system.

  18. Fermi-surface-free superconductivity in underdoped (Bi,Pb)(Sr,La)2CuO6+δ (Bi2201)

    SciTech Connect

    Mistark, Peter; Hafiz, Hasnain; Markiewicz, Robert S.; Bansil, Arun

    2015-06-18

    Fermi-surface-free superconductivity arises when the superconducting order pulls down spectral weight from a band that is completely above the Fermi energy in the normal state. Here, we show that this can arise in hole-doped cuprates when a competing order causes a reconstruction of the Fermi surface. The change in Fermi surface topology is accompanied by a characteristic rise in the spectral weight. Finally, our results support the presence of a trisected superconducting dome, and suggest that superconductivity is responsible for stabilizing the (π,π) magnetic order at higher doping.

  19. 2D dynamic studies combined with the surface curvature analysis to predict Arias Intensity amplification

    NASA Astrophysics Data System (ADS)

    Torgoev, Almaz; Havenith, Hans-Balder

    2016-07-01

    A 2D elasto-dynamic modelling of the pure topographic seismic response is performed for six models with a total length of around 23.0 km. These models are reconstructed from the real topographic settings of the landslide-prone slopes situated in the Mailuu-Suu River Valley, Southern Kyrgyzstan. The main studied parameter is the Arias Intensity (Ia, m/sec), which is applied in the GIS-based Newmark method to regionally map the seismically-induced landslide susceptibility. This method maps the Ia values via empirical attenuation laws and our studies investigate a potential to include topographic input into them. Numerical studies analyse several signals with varying shape and changing central frequency values. All tests demonstrate that the spectral amplification patterns directly affect the amplification of the Ia values. These results let to link the 2D distribution of the topographically amplified Ia values with the parameter called as smoothed curvature. The amplification values for the low-frequency signals are better correlated with the curvature smoothed over larger spatial extent, while those values for the high-frequency signals are more linked to the curvature with smaller smoothing extent. The best predictions are provided by the curvature smoothed over the extent calculated according to Geli's law. The sample equations predicting the Ia amplification based on the smoothed curvature are presented for the sinusoid-shape input signals. These laws cannot be directly implemented in the regional Newmark method, as 3D amplification of the Ia values addresses more problem complexities which are not studied here. Nevertheless, our 2D results prepare the theoretical framework which can potentially be applied to the 3D domain and, therefore, represent a robust basis for these future research targets.

  20. Quasi-one-dimensional Fermi surface of (TMTSF)2NO3

    NASA Astrophysics Data System (ADS)

    Kang, W.; Chung, Ok-Hee

    2009-01-01

    Stereoscopic angular dependence of the interlayer magnetoresistance of the Bechgaard salt (TMTSF)2NO3 is investigated under pressure. This compound is believed to be a semimetal having the quasi-two-dimensional Fermi surface (FS) at low temperature. Previously, a field-induced spin-density-wave (FISDW) transition was reported at 8.5 kbar above ˜20T , which is atypical with a closed FS. We present strong evidence that the FS of this compound remains quasi-one-dimensional under moderate pressure even in the presence of anion ordering. The occurrence of the FISDW is therefore unsurprising. In addition, the possibility of an anion ordering along the b axis will be discussed.

  1. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-Tc Superconductor

    SciTech Connect

    Chen, Y.

    2010-05-03

    We report the discovery of a self-doped multi-layer high T{sub c} superconductor Ba{sub 2}Ca{sub 3}Cu{sub 4}O{sub 8}F{sub 2} (F0234) which contains distinctly different superconducting gap magnitudes along its two Fermi surface(FS) sheets. While formal valence counting would imply this material to be an undoped insulator, it is a self-doped superconductor with a T{sub c} of 60K, possessing simultaneously both electron- and hole-doped FS sheets. Intriguingly, the FS sheet characterized by the much larger gap is the electron-doped one, which has a shape disfavoring two electronic features considered to be important for the pairing mechanism: the van Hove singularity and the antiferromagnetic ({pi}/a, {pi}/a) scattering.

  2. Fermi surface distortion induced by interaction between Rashba and Zeeman effects

    SciTech Connect

    Choi, Won Young; Koo, Hyun Cheol; Chang, Joonyeon; Kim, Hyung-jun; Lee, Kyung-Jin

    2015-05-07

    To evaluate Fermi surface distortion induced by interaction between Rashba and Zeeman effects, the channel resistance in an InAs quantum well layer is investigated with an in-plane magnetic field transverse to the current direction. In the magnetoresistance curve, the critical point occurs at ∼3.5 T, which is approximately half of the independently measured Rashba field. To get an insight into the correlation between the critical point in magnetoresistance curve and the Rashba strength, the channel conductivity is calculated using a two-dimensional free-electron model with relaxation time approximation. The critical point obtained from the model calculation is in agreement with the experiment, suggesting that the observation of critical point can be an alternative method to experimentally determine the Rashba parameter.

  3. Band structure and Fermi surface of electron-doped C60 monolayers.

    PubMed

    Yang, W L; Brouet, V; Zhou, X J; Choi, Hyoung J; Louie, Steven G; Cohen, Marvin L; Kellar, S A; Bogdanov, P V; Lanzara, A; Goldoni, A; Parmigiani, F; Hussain, Z; Shen, Z-X

    2003-04-11

    C60 fullerides are challenging systems because both the electron-phonon and electron-electron interactions are large on the energy scale of the expected narrow band width. We report angle-resolved photoemission data on the band dispersion for an alkali-doped C60 monolayer and a detailed comparison with theory. Compared to the maximum bare theoretical band width of 170 meV, the observed 100-meV dispersion is within the range of renormalization by electron-phonon coupling. This dispersion is only a fraction of the integrated peak width, revealing the importance of many-body effects. Additionally, measurements on the Fermi surface indicate the robustness of the Luttinger theorem even for materials with strong interactions.

  4. Effects of NKG2D haplotypes on the cell-surface expression of NKG2D protein on natural killer and CD8 T cells of peripheral blood among atomic-bomb survivors.

    PubMed

    Imai, Kazue; Hayashi, Tomonori; Yamaoka, Mika; Kajimura, Junko; Yoshida, Kengo; Kusunoki, Yoichiro; Nakachi, Kei

    2012-06-01

    NKG2D is a primary activating receptor that triggers cell-mediated cytotoxicity in NK cells against tumor and virus-infected cells. We previously identified the NKG2D haplotypes in the natural killer gene complex region on chromosome 12p. Two major haplotype alleles, LNK1 and HNK1, were closely related to low and high natural cytotoxic activity phenotypes, respectively. Furthermore, the haplotype of HNK1/HNK1 has revealed a decreased risk of cancer compared with LNK1/LNK1. In the present study, using flow cytometry, we evaluated the functional effects of NKG2D haplotypes and five htSNPs in terms of the cell-surface expression of NKG2D protein on NK and CD8 T cells of peripheral blood among 732 atomic-bomb survivors. NKG2D expression on NK cells showed significant increases, in the order of LNK1/LNK1, LNK1/HNK1 and HNK1/HNK1 haplotypes (p for trend=0.003), or with major homozygous, heterozygous, and minor homozygous genotypes for individual htSNPs (p for trend=0.02-0.003). The same trend was observed for NKG2D expression on CD8 T cells. Our findings indicate that the NKG2D haplotypes are associated with the expression levels of NKG2D protein on NK and CD8 T cells, resulting in inter-individual variations in human cytotoxic response.

  5. Fermi surface splittings in multilayered high-Tc cuprates with charge imbalance

    NASA Astrophysics Data System (ADS)

    Mori, M.; Tohyama, T.; Maekawa, S.

    2006-03-01

    Cuprate superconductors have layered structure of CuO2 planes, which makes conducting blocks separated by an charge- reservoir block. Multilayered high-Tc cuprates, e.g., Ba2Ca3Cu4O8(O1-yFy)2 and HgBa2Ca4Cu5Oy, have two kinds of CuO2 planes in a unit cell; the outer-pyramidal-coordinated-planes (OP's) and the inner- square-coordinated-planes (IP's). The carrier density in the OP is generally different from that in the IP. We call such an inhomogeneous charge-distribution charge imbalance'. We study doping dependence of interlayer hoppings, t, in such a charge-imbalance system in the Gutzwiller approximation. When the double occupancy is forbidden in the CuO2 plane, an effective amplitude of t is shown to be proportional to the square root of the product of doping rates in adjacent two planes. Therefore, the charge imbalance in more than three-layered cuprates results in two different values of t^eff, i.e., t^eff1t√δIP δIP between IP's, and t^eff2t√δIP δOP between IP and OP, where δIP (δOP) is the doping rates in IP (OP). Fermi surfaces are calculated in the four-layered t-t'- t''-J model by the mean-field theory. The order parameters, the renormalization factor of t, and the site- potential making the charge imbalance between IP and OP are self-consistently determined for several doping rates. We show the interlayer splitting of the Fermi surfaces, which may be observed in the angle resolved photoemission spectroscopy measurement. *cond-mat/0511249.

  6. Concentration-dependent supramolecular engineering of hydrogen-bonded nanostructures at surfaces: predicting self-assembly in 2D.

    PubMed

    Ciesielski, Artur; Szabelski, Paweł J; Rżysko, Wojciech; Cadeddu, Andrea; Cook, Timothy R; Stang, Peter J; Samorì, Paolo

    2013-05-08

    We report a joint computational and experimental study on the concentration-dependent self-assembly of a flat C3-symmetric molecule at surfaces. As a model system we have chosen a rigid molecular module, 1,3,5-tris(pyridine-4-ylethynyl)benzene, which can undergo self-association via hydrogen bonding (H-bonding) to form ordered 2D nanostructures. In particular, the lattice Monte Carlo method, combined with density functional calculations, was employed to explore the spontaneous supramolecular organization of this tripod-shaped molecule under surface confinement. We analyzed the stability of different weak H-bonded patterns and the influence of the concentration of the starting molecule on the 2D supramolecular packing. We found that ordered, densely packed monolayers and 2D porous networks are obtained at high and low concentrations, respectively. A concentration-dependent scanning tunneling microscopy investigation of the molecular self-assembly at a graphite-solution interface revealed supramolecular motifs, which are in perfect agreement with those obtained by simulations. Therefore, our computational approach represents a step forward toward the deterministic prediction of molecular self-assembly at surfaces and interfaces.

  7. Plasmonic Excitations of 1D Metal-Dielectric Interfaces in 2D Systems: 1D Surface Plasmon Polaritons

    NASA Astrophysics Data System (ADS)

    Mason, Daniel R.; Menabde, Sergey G.; Yu, Sunkyu; Park, Namkyoo

    2014-04-01

    Surface plasmon-polariton (SPP) excitations of metal-dielectric interfaces are a fundamental light-matter interaction which has attracted interest as a route to spatial confinement of light far beyond that offered by conventional dielectric optical devices. Conventionally, SPPs have been studied in noble-metal structures, where the SPPs are intrinsically bound to a 2D metal-dielectric interface. Meanwhile, recent advances in the growth of hybrid 2D crystals, which comprise laterally connected domains of distinct atomically thin materials, provide the first realistic platform on which a 2D metal-dielectric system with a truly 1D metal-dielectric interface can be achieved. Here we show for the first time that 1D metal-dielectric interfaces support a fundamental 1D plasmonic mode (1DSPP) which exhibits cutoff behavior that provides dramatically improved light confinement in 2D systems. The 1DSPP constitutes a new basic category of plasmon as the missing 1D member of the plasmon family: 3D bulk plasmon, 2DSPP, 1DSPP, and 0D localized SP.

  8. Reduction of Fermi level pinning and recombination at polycrystalline CdTe surfaces by laser irradiation

    SciTech Connect

    Simonds, Brian J.; Kheraj, Vipul; Palekis, Vasilios; Ferekides, Christos; Scarpulla, Michael A.

    2015-06-14

    Laser processing of polycrystalline CdTe is a promising approach that could potentially increase module manufacturing throughput while reducing capital expenditure costs. For these benefits to be realized, the basic effects of laser irradiation on CdTe must be ascertained. In this study, we utilize surface photovoltage spectroscopy (SPS) to investigate the changes to the electronic properties of the surface of polycrystalline CdTe solar cell stacks induced by continuous-wave laser annealing. The experimental data explained within a model consisting of two space charge regions, one at the CdTe/air interface and one at the CdTe/CdS junction, are used to interpret our SPS results. The frequency dependence and phase spectra of the SPS signal are also discussed. To support the SPS findings, low-temperature spectrally-resolved photoluminescence and time-resolved photoluminescence were also measured. The data show that a modest laser treatment of 250 W/cm{sup 2} with a dwell time of 20 s is sufficient to reduce the effects of Fermi level pinning at the surface due to surface defects.

  9. Two-dimensional Fermi surfaces in Kondo insulating SmB6

    NASA Astrophysics Data System (ADS)

    Li, Gang

    There has been renewed interest in Samarium Hexaboride, which is a strongly correlated heavy Fermion material. Hybridization between itinerant electrons and localized orbitals lead to an opening of charge gap at low temperature. However, the resistivity of SmB6 does not diverge at low temperature. Former studies suggested that this residual conductance is contributed by various origins. Recent theoretical developments suggest that the particular symmetry of energy bands of SmB6 may host a topologically non-trivial surface state, i.e., a topological Kondo insulator. To probe the Fermiology of the possible metallic surface state, we use sensitive torque magnetometry to detect the de Haas van Alphen (dHvA) effect due to Landau level quantization on flux-grown crystals, down to He-3 temperature and up to 45 Tesla. Our angular and temperature dependent data suggest two-dimensional Fermi Surfaces lie in both crystalline (001) and (101) surface planes of SmB6.

  10. 2D-ordered dielectric sub-micron bowls on a metal surface: a useful hybrid plasmonic-photonic structure

    NASA Astrophysics Data System (ADS)

    Lan, Yue; Wang, Shiqiang; Yin, Xianpeng; Liang, Yun; Dong, Hao; Gao, Ning; Li, Jian; Wang, Hui; Li, Guangtao

    2016-07-01

    Recently, it has been demonstrated that the combination of periodic dielectric structures with metallic structures provides an efficient means to yield a synergetic optical response or functionality in the resultant hybrid plasmonic-photonic systems. In this work, a new hybrid plasmonic-photonic structure of 2D-ordered dielectric sub-micron bowls on a flat gold surface was proposed, prepared, and theoretically and experimentally characterized. This hybrid structure supports two types of modes: surface plasmon polaritons bound at the metallic surface and waveguided mode of light confined in the cavity of bowls. Optical responses of this hybrid structure as well as the spatial electric field distribution of each mode are found to be strongly dependent on the structural parameters of this system, and thus could be widely modified on demand. Importantly, compared to the widely studied hybrid systems, namely the flat metallic surface coated with a monolayer array of latex spheres, the waveguided mode with strong field enhancement appearing in the cavities of bowls is more facilely accessible and thus suitable for practical use. For demonstration, a 2D-ordered silica sub-micron bowl array deposited on a flat gold surface was fabricated and used as a regenerable platform for fluorescence enhancement by simply accommodating emitters in bowls. All the simulation and experiment results indicate that the 2D-ordered dielectric sub-micron bowls on a metal surface should be a useful hybrid plasmonic-photonic system with great potential for applications such as sensors or tunable emitting devices if appropriate periods and materials are employed.Recently, it has been demonstrated that the combination of periodic dielectric structures with metallic structures provides an efficient means to yield a synergetic optical response or functionality in the resultant hybrid plasmonic-photonic systems. In this work, a new hybrid plasmonic-photonic structure of 2D-ordered dielectric sub

  11. Fermi surfaces, spin-mixing parameter, and colossal anisotropy of spin relaxation in transition metals from ab initio theory

    NASA Astrophysics Data System (ADS)

    Zimmermann, Bernd; Mavropoulos, Phivos; Long, Nguyen H.; Gerhorst, Christian-Roman; Blügel, Stefan; Mokrousov, Yuriy

    2016-04-01

    The Fermi surfaces and Elliott-Yafet spin-mixing parameter (EYP) of several elemental metals are studied by ab initio calculations. We focus first on the anisotropy of the EYP as a function of the direction of the spin-quantization axis [B. Zimmermann et al., Phys. Rev. Lett. 109, 236603 (2012), 10.1103/PhysRevLett.109.236603]. We analyze in detail the origin of the gigantic anisotropy in 5 d hcp metals as compared to 5 d cubic metals by band structure calculations and discuss the stability of our results against an applied magnetic field. We further present calculations of light (4 d and 3 d ) hcp crystals, where we find a huge increase of the EYP anisotropy, reaching colossal values as large as 6000 % in hcp Ti. We attribute these findings to the reduced strength of spin-orbit coupling, which promotes the anisotropic spin-flip hot loops at the Fermi surface. In order to conduct these investigations, we developed an adapted tetrahedron-based method for the precise calculation of Fermi surfaces of complicated shape and accurate Fermi-surface integrals within the full-potential relativistic Korringa-Kohn-Rostoker Green function method.

  12. Direct observation of the multisheet Fermi surface in the strongly correlated transition metal compound ZrZn2.

    PubMed

    Major, Zs; Dugdale, S B; Watts, R J; Santi, G; Alam, M A; Hayden, S M; Duffy, J A; Taylor, J W; Jarlborg, T; Bruno, E; Benea, D; Ebert, H

    2004-03-12

    The existence of flat areas of a Fermi surface (FS), predicted by electronic structure calculations and used in models of both magnetically mediated and phonon-mediated Fulde-Ferrell-Larkin-Ovchinnikov superconducting states, is reported in the paramagnetic phase of the ferromagnetic superconductor ZrZn2 using positron annihilation. The strongly mass-renormalized FS sheet, dominating the Fermi level density of states, is seen for the first time. The delocalization of the magnetization is studied using measured and calculated magnetic Compton profiles.

  13. 3-D Acoustic Scattering from 2-D Rough Surfaces Using A Parabolic Equation Model

    DTIC Science & Technology

    2013-12-01

    acoustic propagation signals, especially at mid- frequencies and higher (e.g., acoustic communications systems). For many years, the effects of rough...of the effect of surface scattering on 3-D propagation , which is critical in evaluating the variability in underwater acoustic propagation . Results...14. SUBJECT TERMS Acoustic Propagation , Acoustic Scattering, Sea Surface Perturbations, Split- Step Fourier Algorithm, Finite Difference Algorithm

  14. Investigation of ellipsometric parameters of 2D microrough surfaces by FDTD.

    PubMed

    Qiu, J; Ran, D F; Liu, Y B; Liu, L H

    2016-07-10

    Ellipsometry is a powerful method for measuring the optical constants of materials and is very sensitive to surface roughness. In previous ellipsometric measurement of optical constants of solid materials with rough surfaces, researchers frequently used effective medium approximation (EMA) with roughness already known to fit the complex refractive index of the material. However, the ignored correlation length, the other important parameter of rough surfaces, will definitely result in fitting errors. Hence it is necessary to consider the influence of surface roughness and correlation length on the ellipsometric parameters Δ (phase difference) and Ψ (azimuth) characterizing practical systems. In this paper, the influence of roughness of two-dimensional randomly microrough surfaces (relative roughness σ/λ ranges from 0.001 to 0.025) of silicon on ellipsometric parameters was simulated by the finite-difference time-domain method which was validated with experimental results. The effects of incident angle, relative roughness, and correlation length were numerically investigated for two-dimensional Gaussian distributed randomly microrough surfaces, respectively. The simulated results showed that compared with the smooth surface, only tiny changes of the ellipsometric parameter Δ could be observed for microrough silicon surface in the vicinity of the Brewster angle, but obviously changes of Ψ occur especially in the vicinity of the Brewster angle. More differences between the ellipsometric parameters of the rough surface and smooth surface can been seen especially in the vicinity of the Brewster angle as the relative roughness σ/λ increases or correlation length τ decreases. The results reveal that when we measure the optical constants of solid materials by ellipsometry, the smaller roughness, larger correlation length and larger incident wavelength will lead to the higher precision of measurements.

  15. Fermi surface topology and the upper critical field in two-band superconductors: application to MgB2.

    PubMed

    Dahm, T; Schopohl, N

    2003-07-04

    Recent measurements of the anisotropy of the upper critical field B(c2) on MgB2 single crystals have shown a puzzling strong temperature dependence. Here, we present a calculation of the upper critical field based on a detailed modeling of band structure calculations that takes into account both the unusual Fermi surface topology and the two gap nature of the superconducting order parameter. Our results show that the strong temperature dependence of the B(c2) anisotropy can be understood as an interplay of the dominating gap on the sigma band, which possesses a small c-axis component of the Fermi velocity, with the induced superconductivity on the pi-band possessing a large c-axis component of the Fermi velocity. We provide analytic formulas for the anisotropy ratio at T=0 and T=T(c) and quantitatively predict the distortion of the vortex lattice based on our calculations.

  16. Fermi surface and extended van Hove singularity in the noncuprate superconductor Sr{sub 2}RuO{sub 4}

    SciTech Connect

    Lu, D.H.; Schmidt, M.; Cummins, T.R.; Schuppler, S.; Lichtenberg, F.; Bednorz, J.G.

    1996-06-01

    We mapped the Fermi surface of the first copper-free layered perovskite superconductor, Sr{sub 2}RuO{sub 4} by high-resolution ({approx_equal}22 meV) angle-resolved photoemission. Three bands cross the Fermi energy, consistent with band structure calculations; one around {Gamma} and two around {bar {ital X}}. The highlight is the observation of an extended van Hove singularity located 17meV below the Fermi level. It extends around {bar {ital M}} for {approx_equal}0.2 A{sup {minus}1} along {Gamma}-{bar {ital M}}-{Gamma} and {bar {ital X}}-{bar {ital M}}-{bar {ital X}} in the projected Brillouin zone. This raises important questions related to the possible role of a van Hove singularity for oxide superconductivity. {copyright} {ital 1996 The American Physical Society.}

  17. The 7 × 1 Fermi Surface Reconstruction in a Two-dimensional f -electron Charge Density Wave System: PrTe3

    PubMed Central

    Lee, Eunsook; Kim, D. H.; Kim, Hyun Woo; Denlinger, J. D.; Kim, Heejung; Kim, Junwon; Kim, Kyoo; Min, B. I.; Min, B. H.; Kwon, Y. S.; Kang, J.-S.

    2016-01-01

    The electronic structure of a charge density wave (CDW) system PrTe3 and its modulated structure in the CDW phase have been investigated by employing ARPES, XAS, Pr 4 f RPES, and first-principles band structure calculation. Pr ions are found to be nearly trivalent, supporting the CDW instability in the metallic Te sheets through partial filling. Finite Pr 4 f spectral weight is observed near the Fermi level, suggesting the non-negligible Pr 4 f contribution to the CDW formation through the Pr 4 f -Te 5p hybridization. The two-fold symmetric features in the measured Fermi surface (FS) of PrTe3 are explained by the calculated FS for the assumed 7 × 1 CDW supercell formation in Te sheets. The shadow bands and the corresponding very weak FSs are observed, which originate from both the band folding due to the 3D interaction of Te sheets with neighboring Pr-Te layers and that due to the CDW-induced FS reconstruction. The straight vertical FSs are observed along kz, demonstrating the nearly 2D character for the near-EF states. The observed linear dichroism reveals the in-plane orbital character of the near-EF Te 5p states. PMID:27453329

  18. Growth of 2D sheets of a MOF on graphene surfaces to yield composites with novel gas adsorption characteristics.

    PubMed

    Kumar, Ram; Jayaramulu, Kolleboyina; Maji, Tapas Kumar; Rao, C N R

    2014-05-28

    Homogeneous graphene-MOF composites based on a 2D pillared-bilayer MOF (Cd-PBM), {[Cd4(azpy)2(pyrdc)4(H2O)2]·9H2O}n (azpy = 4,4'-azopyridine, pyrdc = pyridine-2,3-dicarboxylate), have been synthesized, using both graphene oxide (GO) and benzoic acid functionalized graphene (BFG). The composites GO@Cd-PBM and BFG@Cd-PBM demonstrate growth of the 2D nano-sheets of MOF on the graphene surface. While the pristine MOF, Cd-PBM shows selective CO2 uptake with a single-step type-I adsorption profile, the composites show stepwise CO2 uptake with a large hysteresis. With H2O and MeOH, on the other hand, the composites show a single-step adsorption unlike the parent MOF.

  19. Comparing 2-D screen projections to 1-D goniometric measurements in scattering studies of surface roughness

    NASA Astrophysics Data System (ADS)

    Jones, Laurel R.; Jacques, Steven L.

    2009-02-01

    Video goniometry was used to study the angular dependence of scattering from tissues and test materials. Tissues and standard roughness samples (sandpaper) were placed vertically in front of a 543 nm He-Ne laser with the tissue surface normal at 45° from the incident beam. The scattered light patterns projected onto a screen that was photographed by a digital camera. The scatter pattern showed a specular peak centered at -45° which was described by a Henyey-Greenstein function. The pattern also presented a diffuse Lambertian pattern at 0° (normal to the tissue). The line between the peak specular and the peak Lambertian identified the scattering plane, despite any slight misalignment of the tissue. The analysis utilized a coordinate transform based on mathematics for mapping between a flat Mercator map and a spherical planetary surface. The system was used to study the surface roughness of muscle tissue samples (bovine striated muscle and chicken cardiac muscle).

  20. Statistical Analyses of Brain Surfaces Using Gaussian Random Fields on 2-D Manifolds

    PubMed Central

    Staib, Lawrence H.; Xu, Dongrong; Zhu, Hongtu; Peterson, Bradley S.

    2008-01-01

    Interest in the morphometric analysis of the brain and its subregions has recently intensified because growth or degeneration of the brain in health or illness affects not only the volume but also the shape of cortical and subcortical brain regions, and new image processing techniques permit detection of small and highly localized perturbations in shape or localized volume, with remarkable precision. An appropriate statistical representation of the shape of a brain region is essential, however, for detecting, localizing, and interpreting variability in its surface contour and for identifying differences in volume of the underlying tissue that produce that variability across individuals and groups of individuals. Our statistical representation of the shape of a brain region is defined by a reference region for that region and by a Gaussian random field (GRF) that is defined across the entire surface of the region. We first select a reference region from a set of segmented brain images of healthy individuals. The GRF is then estimated as the signed Euclidean distances between points on the surface of the reference region and the corresponding points on the corresponding region in images of brains that have been coregistered to the reference. Correspondences between points on these surfaces are defined through deformations of each region of a brain into the coordinate space of the reference region using the principles of fluid dynamics. The warped, coregistered region of each subject is then unwarped into its native space, simultaneously bringing into that space the map of corresponding points that was established when the surfaces of the subject and reference regions were tightly coregistered. The proposed statistical description of the shape of surface contours makes no assumptions, other than smoothness, about the shape of the region or its GRF. The description also allows for the detection and localization of statistically significant differences in the shapes of

  1. Chirality transfer from a single chiral molecule to 2D superstructures in alaninol on the Cu(100) surface.

    PubMed

    Contini, G; Gori, P; Ronci, F; Zema, N; Colonna, S; Aschi, M; Palma, A; Turchini, S; Catone, D; Cricenti, A; Prosperi, T

    2011-06-21

    The formation of 2D chiral monolayers obtained by self-assembly of chiral molecules on surfaces has been widely reported in the literature. Control of chirality transfer from a single molecule to surface superstructures is a challenging and important aspect for tailoring the properties of 2D nanostructures. However, despite the wealth of investigations performed in recent years, how chiral transfer takes place on a large scale still remains an open question. In this paper we report a coupling of scanning tunneling microscopy and low energy electron diffraction measurements with an original theoretical approach, combining molecular dynamics and essential dynamics with density functional theory, to investigate self-assembled chiral structures formed when alaninol adsorbs on Cu(100). The peculiarity of this system is related to the formation of tetrameric molecular structures which constitute the building blocks of the self-assembled chiral monolayer. Such characteristics make alaninol/Cu(100) a good candidate to reveal chiral expression changes. We find that the deposition of alaninol enantiomers results in the formation of isolated tetramers that are aligned along the directions of the substrate at low coverage or when geometrical confinement prevents long-range order. Conversely, a rotation of 14° with respect to the Cu(100) unit vectors is observed when small clusters of tetramers are formed. An insight to the process leading to a 2D globally chiral surface has been obtained by monitoring molecular assemblies as they grow from the early stages of adsorption, suggesting that the distinctive orientation of the self-assembled monolayer originates from a balance of cooperating forces which start acting only when tetramers pack together to form small clusters.

  2. Maximally anisotropic point Fermi surface system: VO2 films embedded in TiO2

    NASA Astrophysics Data System (ADS)

    Pardo, Victor

    2010-03-01

    Oxide heterostructures provide an unusually rich canvas for the design of unprecedented electronic states. Here we will discuss multilayer (TiO2)m/(VO2)n nanostructures, namely V^4+:d^1 - Ti^4+:d^0 interfaces, with no polar discontinuity, studied by density functional theory techniques[1]. This system shows a metal-insulator transition with respect to the VO2 layer thickness in our first principles calculations[2]. For n = 1 and 2 VO2 layers, the system is insulating. For 5 and more layers, it is ferromagnetic and half-metallic. For the quantum confined cases of n = 3 and 4 the system is neither insulating nor conducting, instead an unexpected state arises: the Fermi surface is point-like as in graphene, except that extreme anisotropy is present[3]. The electrons (or holes, depending on doping) behave as massless fermions along the zone diagonal in k-space, and as conventional (massive) fermions along the perpendicular direction. Certain characteristics identify this ``semi-Dirac'' phase as resulting from quantum confinement, rather than being an interface phenomenon. This point Fermi surface system differs from graphene not only in its extreme anisotropy, but that it arises in a half-metallic system, so spin degrees of freedom are removed. In this presentation an analysis of the evolution of the electronic structure through this unprecedented insulator-to-metal transition will be provided, and the role of a non-intuitive orbital ordering of the V d^1 ions will be discussed. Also the robustness of the semi-Dirac electronic structure to interfacial disorder and the introduction of spin-orbit coupling in the calculations will be analyzed. [4pt] [1] V. Pardo and W.E. Pickett, Phys. Rev. Lett. 102, 107003 (2009).[0pt] [2] V. Pardo and W.E. Pickett, arXiv:0910.4411.[0pt] [3] S. Banerjee, R.R.P. Singh, V. Pardo and W.E. Pickett, Phys. Rev. Lett. 103, 016402 (2009).

  3. Rayleigh surface wave interaction with the 2D exciton Bose-Einstein condensate

    SciTech Connect

    Boev, M. V.; Kovalev, V. M.

    2015-06-15

    We describe the interaction of a Rayleigh surface acoustic wave (SAW) traveling on the semiconductor substrate with the excitonic gas in a double quantum well located on the substrate surface. We study the SAW attenuation and its velocity renormalization due to the coupling to excitons. Both the deformation potential and piezoelectric mechanisms of the SAW-exciton interaction are considered. We focus on the frequency and excitonic density dependences of the SAW absorption coefficient and velocity renormalization at temperatures both above and well below the critical temperature of Bose-Einstein condensation of the excitonic gas. We demonstrate that the SAW attenuation and velocity renormalization are strongly different below and above the critical temperature.

  4. Surface control of alkyl chain conformations and 2D chiral amplification.

    PubMed

    Hauptmann, Nadine; Scheil, Katharina; Gopakumar, Thiruvancheril G; Otte, Franziska L; Schütt, Christian; Herges, Rainer; Berndt, Richard

    2013-06-19

    Trioctyl-functionalized triazatriangulenium (trioctyl-TATA) deposited on Au(111) and Ag(111) surfaces by electrospray ionization was investigated using low-temperature scanning tunneling microscopy. The molecule surprisingly adsorbs with gauche rather than anti conformations of the octyl groups. We observed chiral amplification in the islands. Only one of the eight possible configurations of the octyl groups was found in homochiral hexagonal networks. Quantum-chemical calculations confirmed and explained the preference for the gauche conformations of adsorbed trioctyl-TATA.

  5. Volterra Series Approach for Nonlinear Aeroelastic Response of 2-D Lifting Surfaces

    NASA Technical Reports Server (NTRS)

    Silva, Walter A.; Marzocca, Piergiovanni; Librescu, Liviu

    2001-01-01

    The problem of the determination of the subcritical aeroelastic response and flutter instability of nonlinear two-dimensional lifting surfaces in an incompressible flow-field via Volterra series approach is addressed. The related aeroelastic governing equations are based upon the inclusion of structural nonlinearities, of the linear unsteady aerodynamics and consideration of an arbitrary time-dependent external pressure pulse. Unsteady aeroelastic nonlinear kernels are determined, and based on these, frequency and time histories of the subcritical aeroelastic response are obtained, and in this context the influence of geometric nonlinearities is emphasized. Conclusions and results displaying the implications of the considered effects are supplied.

  6. 2D quantum gravity on compact Riemann surfaces with non-conformal matter

    NASA Astrophysics Data System (ADS)

    Bilal, Adel; Leduc, Lætitia

    2017-01-01

    We study the gravitational action induced by coupling two-dimensional non-conformal, massive matter to gravity on a compact Riemann surface. We express this gravitational action in terms of finite and well-defined quantities for any value of the mass. A small-mass expansion gives back the Liouville action in the massless limit, the Mabuchi and Aubin-Yau actions to first order, as well as an infinite series of higher-order contributions written in terms of purely geometric quantities.

  7. Fermi surface deformation in a simple iron-based superconductor, FeSe

    NASA Astrophysics Data System (ADS)

    Coldea, Amalia; Watson, Matthew; Kim, Timur; Haghighirad, Amir; McCollam, Alix; Hoesch, Moritz; Schofield, Andrew

    2015-03-01

    One of the outstanding problems in the field superconductivity is the identification of the normal state out of which superconductivity emerges. FeSe is one of the simplest and most intriguing iron-based superconductors, since in its bulk form it undergoes a structural transition before it becomes superconducting, whereas its single-layer form is believed to be a high-temperature superconductor. The nature of the structural transition, occurring in the absence of static magnetism, is rather unusual and how the electronic structure is stabilized by breaking of the rotational symmetry is the key to understand the superconductivity in bulk FeSe. Here we report angle-resolved photoemission spectroscopy measurements on FeSe that gives direct access to the band structure and orbital-dependent effects. We complement our studies on bulk FeSe with low-temperature angular-dependent quantum oscillation measurements using applied magnetic fields that are sufficiently strong to suppress superconductivity and reach the normal state. These studies reveal a strong deformation of Fermi surface through the structural transition driven by electronic correlations and orbital-dependent effects. . This work was supported by EPSRC, UK (EP/I004475/1), Diamond Light Source, UK and HFML, Nijmegen.

  8. Characteristic two-dimensional Fermi surface topology of high-Tc iron-based superconductors.

    PubMed

    Sunagawa, Masanori; Ishiga, Toshihiko; Tsubota, Koji; Jabuchi, Taihei; Sonoyama, Junki; Iba, Keita; Kudo, Kazutaka; Nohara, Minoru; Ono, Kanta; Kumigashira, Hiroshi; Matsushita, Tomohiro; Arita, Masashi; Shimada, Kenya; Namatame, Hirofumi; Taniguchi, Masaki; Wakita, Takanori; Muraoka, Yuji; Yokoya, Takayoshi

    2014-03-14

    Unconventional Cooper pairing originating from spin or orbital fluctuations has been proposed for iron-based superconductors. Such pairing may be enhanced by quasi-nesting of two-dimensional electron and hole-like Fermi surfaces (FS), which is considered an important ingredient for superconductivity at high critical temperatures (high-Tc). However, the dimensionality of the FS varies for hole and electron-doped systems, so the precise importance of this feature for high-Tc materials remains unclear. Here we demonstrate a phase of electron-doped CaFe2As2 (La and P co-doped CaFe2As2) with Tc = 45 K, which is the highest Tc found for the AEFe2As2 bulk superconductors (122-type; AE = Alkaline Earth), possesses only cylindrical hole- and electron-like FSs. This result indicates that FS topology consisting only of two-dimensional sheets is characteristic of both hole- and electron-doped 122-type high-Tc superconductors.

  9. Correlations between neutrons and protons near the Fermi surface and Qα of superheavy nuclei

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Liu, Min; Wu, Xizhen; Meng, Jie

    2016-01-01

    The shell corrections and shell gaps in nuclei are systematically studied with the latest Weizsäcker-Skyrme (WS4) mass model. We find that most of asymmetric nuclei with (sub)shell closures locate along the shell stability line (SSL), N =1.37 Z +13.5 , which might be due to a strong correlation between neutrons and protons near the Fermi surface. The double magicity of nuclei 46Si and 78Ni is predicted according to the corresponding shell gaps, shell corrections, and nuclear deformations. The unmeasured superheavy nuclei, 296118 and 298120, with relatively large shell gaps and shell corrections, also locate along the SSL, whereas the traditional magic nucleus 298Fl evidently deviates from the line. The α -decay energies of superheavy nuclei with Z =113 -126 are simultaneously investigated by using the WS4 model together with the radial basis function corrections. For superheavy nuclei with large shell corrections, the smallest α -decay energy for elements Z =116 , 117, and 118 in their isotope chains locates at N =178 rather than 184.

  10. Evolution of the Fermi surface topology in doped 122 iron pnictides

    NASA Astrophysics Data System (ADS)

    Pan, Lihua; Li, Jian; Tai, Yuan-Yen; Graf, Matthias J.; Zhu, Jian-Xin; Ting, C. S.

    2013-12-01

    Based on the minimum two-orbital model and the phase diagram recently proposed by Tai [Europhys. Lett.EULEEJ0295-507510.1209/0295-5075/103/67001 103, 67001 (2013)] for both electron- and hole-doped 122 iron-based superconducting compounds, we use the Bogoliubov-de-Gennes equations to perform a comprehensive investigation of the evolution of the Fermi surface (FS) topology in the presence of the collinear spin-density-wave (SDW) order as the doping is changed. In the parent compound, the ground state is the SDW order, where the FS is not completely gapped, and two types of Dirac cones, one electron-doped and the other hole-doped emerge in the magnetic Brillouin zone. Our findings are qualitatively consistent with recent angle-resolved photoemission spectroscopy and magnetoresistivity measurements. We also examine the FS evolution of both electron- and hole-doped cases and compare them with measurements, as well as with those obtained by other model Hamiltonians.

  11. Fermi-surface collapse and dynamical scaling near a quantum-critical point

    PubMed Central

    Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

    2010-01-01

    Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh2Si2, a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems. PMID:20668246

  12. Band structure, Fermi surface, superconductivity, and resistivity of actinium under high pressure

    SciTech Connect

    Dakshinamoorthy, M.; Iyakutti, K.

    1984-12-15

    The electronic band structures of fcc actinium (Ac) have been calculated for a wide range of pressures by reducing the unit-cell volume from 1.0V/sub 0/ to 0.5V/sub 0/ with use of the relativistic augmented-plane-wave method. The density of states and Fermi-surface cross sections corresponding to various volumes are obtained. Calculations for the band-structure-related quantities such as electron-phonon mass enhancement factor lambda, superconducting transition temperature T/sub c/, and resistivity rho corresponding to different volumes are performed. It is seen that T/sub c/ increases with pressure, i.e., with decreasing volume. A new empirical relation for the volume dependence of T/sub c/ is proposed and its validity is checked using the T/sub c/ values obtained from the above band-structure results. The resistivity rho first increases with increasing pressure (i.e., with decreasing volume) and then decreases for higher pressures (i.e., for smaller volumes).

  13. Fermi-Compton scattering due to magnetopause surface fluctuations in Jupiter's magnetospheric cavity

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1981-01-01

    The effects of boundary surface fluctuations on a spectrum of electromagnetic radiation trapped in a high Q (quality) cavity are considered. Undulating walls introduce small frequency shifts at reflection to the radiation, and it is argued that the process is entirely analogous to both Fermi (particle) acceleration and inverse Compton scattering. A Fokker-Planck formalism is pursued; it yields a diffusion equation in frequency for which the Green's function and steady-state solutions are found. Applying this analysis to the Jovian continuum radiation discovered by Voyager spacecraft, it is suggested that characteristic diffusion times are greater than 1 year, and that in order to account for the steep frequency spectra observed, an unidentified loss mechanism must operate in the cavity with a decay time constant approximately equal to the characteristic diffusion time divided by 28. A radiator-reactor model of the cavity is investigated to provide an estimate for the intrinsic luminosity of the low frequency (approximately 100 Hz) continuum source whose power is approximately 7 x 10 to the 6th W.

  14. Fermi-surface collapse and dynamical scaling near a quantum-critical point.

    PubMed

    Friedemann, Sven; Oeschler, Niels; Wirth, Steffen; Krellner, Cornelius; Geibel, Christoph; Steglich, Frank; Paschen, Silke; Kirchner, Stefan; Si, Qimiao

    2010-08-17

    Quantum criticality arises when a macroscopic phase of matter undergoes a continuous transformation at zero temperature. While the collective fluctuations at quantum-critical points are being increasingly recognized as playing an important role in a wide range of quantum materials, the nature of the underlying quantum-critical excitations remains poorly understood. Here we report in-depth measurements of the Hall effect in the heavy-fermion metal YbRh(2)Si(2), a prototypical system for quantum criticality. We isolate a rapid crossover of the isothermal Hall coefficient clearly connected to the quantum-critical point from a smooth background contribution; the latter exists away from the quantum-critical point and is detectable through our studies only over a wide range of magnetic field. Importantly, the width of the critical crossover is proportional to temperature, which violates the predictions of conventional theory and is instead consistent with an energy over temperature, E/T, scaling of the quantum-critical single-electron fluctuation spectrum. Our results provide evidence that the quantum-dynamical scaling and a critical Kondo breakdown simultaneously operate in the same material. Correspondingly, we infer that macroscopic scale-invariant fluctuations emerge from the microscopic many-body excitations associated with a collapsing Fermi-surface. This insight is expected to be relevant to the unconventional finite-temperature behavior in a broad range of strongly correlated quantum systems.

  15. Leaf Area Index Estimation in Vineyards from Uav Hyperspectral Data, 2d Image Mosaics and 3d Canopy Surface Models

    NASA Astrophysics Data System (ADS)

    Kalisperakis, I.; Stentoumis, Ch.; Grammatikopoulos, L.; Karantzalos, K.

    2015-08-01

    The indirect estimation of leaf area index (LAI) in large spatial scales is crucial for several environmental and agricultural applications. To this end, in this paper, we compare and evaluate LAI estimation in vineyards from different UAV imaging datasets. In particular, canopy levels were estimated from i.e., (i) hyperspectral data, (ii) 2D RGB orthophotomosaics and (iii) 3D crop surface models. The computed canopy levels have been used to establish relationships with the measured LAI (ground truth) from several vines in Nemea, Greece. The overall evaluation indicated that the estimated canopy levels were correlated (r2 > 73%) with the in-situ, ground truth LAI measurements. As expected the lowest correlations were derived from the calculated greenness levels from the 2D RGB orthomosaics. The highest correlation rates were established with the hyperspectral canopy greenness and the 3D canopy surface models. For the later the accurate detection of canopy, soil and other materials in between the vine rows is required. All approaches tend to overestimate LAI in cases with sparse, weak, unhealthy plants and canopy.

  16. Enhanced field emission properties from surface-modified 2D Cd(OH)2 nanocoins

    NASA Astrophysics Data System (ADS)

    Bagal, Vivekanand S.; Patil, Girish P.; Deore, Amol B.; Baviskar, Prashant K.; Shirale, Dhammanand J.; Chavan, Padmakar G.

    2017-02-01

    Low turn-on field of 2.1 V/µm was found for the emission current density of 10 µA/cm2 and high current density of 403 µA/cm2 was drawn at an applied field of 3.6 V/µm from Au/Cd(OH)2 nanocoins/Cd(OH)2 microsheets (Au/Cd(OH)2NC/Cd(OH)2MS). The observed low turn-on field was found superior to other gold (Au) nanoparticle decorated semiconducting nanostructures reported in the literature. Also the field emission current stability for the preset value of 1 μA over the period of 3 h is found to be good. The Cd(OH)2 nanocoins were grown on Cadmium (Cd) substrate by simple chemical bath deposition technique. Au nanoparticles with average diameter 11 nm were decorated on surface of the Cd(OH)2 nanocoins by sputtering method. Detail characterization such as structural and morphological analysis of Au/Cd(OH)2NC/Cd(OH)2MS has been carried out using X-ray Diffraction, Field Emission Scanning Electron Microscope and Transmission Electron Microscope. To the best of our knowledge, this is the first report on the synthesis and field emission studies of Au/Cd(OH)2NC/Cd(OH)2MS.

  17. Signatures of an annular Fermi sea

    NASA Astrophysics Data System (ADS)

    Jo, Insun; Liu, Yang; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.; Winkler, R.

    2017-01-01

    The concept of a Fermi surface, the constant-energy surface containing all the occupied electron states in momentum, or wave-vector (k ) , space plays a key role in determining electronic properties of conductors. In two-dimensional (2D) carrier systems, the Fermi surface becomes a contour which, in the simplest case, encircles the occupied states. In this case, the area enclosed by the contour, which we refer to as the Fermi sea (FS), is a simple disk. Here we report the observation of an FS with a new topology, namely, an FS in the shape of an annulus. Such an FS is expected in a variety of 2D systems where the energy band dispersion supports a ring of extrema at finite k , but its experimental observation has been elusive. Our study provides (1) theoretical evidence for the presence of an annular FS in 2D hole systems confined to wide GaAs quantum wells and (2) experimental signatures of the onset of its occupation as an abrupt rise in the sample resistance, accompanied by a sudden appearance of Shubnikov-de Haas oscillations at an unexpectedly high frequency whose value does not simply correspond to the (negligible) density of holes contained within the annular FS.

  18. Laser-based linear and nonlinear guided elastic waves at surfaces (2D) and wedges (1D).

    PubMed

    Hess, Peter; Lomonosov, Alexey M; Mayer, Andreas P

    2014-01-01

    The characteristic features and applications of linear and nonlinear guided elastic waves propagating along surfaces (2D) and wedges (1D) are discussed. Laser-based excitation, detection, or contact-free analysis of these guided waves with pump-probe methods are reviewed. Determination of material parameters by broadband surface acoustic waves (SAWs) and other applications in nondestructive evaluation (NDE) are considered. The realization of nonlinear SAWs in the form of solitary waves and as shock waves, used for the determination of the fracture strength, is described. The unique properties of dispersion-free wedge waves (WWs) propagating along homogeneous wedges and of dispersive wedge waves observed in the presence of wedge modifications such as tip truncation or coatings are outlined. Theoretical and experimental results on nonlinear wedge waves in isotropic and anisotropic solids are presented.

  19. Dynamic Linkages Between the Transition Zone & Surface Plate Motions in 2D Models of Subduction

    NASA Astrophysics Data System (ADS)

    Arredondo, K.; Billen, M. I.

    2013-12-01

    feedback to other added processes remain important, which could encourage mineralogical research into multiphase systems. Feedback from the compositionally complex slab to the dynamic trench may improve understanding on the mechanics of slab behavior in the upper and lower mantle and surface behavior of the subducting and overriding plates. Běhounková, M., and H. Cízková, Long-wavelength character of subducted slabs in the lower mantle, Earth and Planetary Science Letters, 275, 43-53, 2008. Fukao, Y., M. Obayashi, T. Nakakuki, and the Deep Slab Project Group, Stagnant slab: A review, Annual Reviews of Earth and Planetary Science, 37, 19-46, 2009. Ricard, Y., E. Mattern, and J. Matas, Synthetic tomographic images of slabs from mineral physics, in Earth's Deep Mantle: Structure, Composition, and Evolution, Geophysical Monograph Series, vol. 160, American Geophysical Union, 2005.

  20. Non-Fermi surface nesting driven commensurate magnetic ordering in Fe-doped S r2Ru O4

    NASA Astrophysics Data System (ADS)

    Zhu, M.; Shanavas, K. V.; Wang, Y.; Zou, T.; Sun, W. F.; Tian, W.; Garlea, V. O.; Podlesnyak, A.; Matsuda, M.; Stone, M. B.; Keavney, D.; Mao, Z. Q.; Singh, D. J.; Ke, X.

    2017-02-01

    S r2Ru O4 , an unconventional superconductor, is known to possess an incommensurate spin-density wave instability driven by Fermi surface nesting. Here we report a static spin-density wave ordering with a commensurate propagation vector qc=(0.25 0.25 0 ) in Fe-doped S r2Ru O4 , despite the magnetic fluctuations persisting at the incommensurate wave vectors qic=(0.3 0.3 L ) as in the parent compound. The latter feature is corroborated by the first-principles calculations, which show that Fe substitution barely changes the nesting vector of the Fermi surface. These results suggest that in addition to the known incommensurate magnetic instability, S r2Ru O4 is also in proximity to a commensurate magnetic tendency that can be stabilized via Fe doping.

  1. Application of Fresnel diffraction from a 2D array of reflective disks in optical profilometry of a flat surface

    NASA Astrophysics Data System (ADS)

    Darudi, Ahmad; Asgari, Pegah; Pourvais, Yousef

    2015-05-01

    Optical methods of three-dimensional profilometry have been of growing interest in both industrial and scientific applications. These techniques provide absolutely non-destructive measurement due to their non-contact nature and maintain their high precision in a large field of view. Most of these techniques however, are based on interferometry which happens to be considerably sensitive to environmental noises such as turbulence and vibration. We have used the phenomena of Fresnel diffraction from phase-steps instead of interferometry to maintain a higher precision and reduce sensitivity to environmental noises. This phenomena has been recently introduced as a method for precise measurement of wavelength, thickness and refractive index. A 2D array of reflective disks are placed above the test surface to provide the required phase-steps. In this paper, theoretical principles of Fresnel diffraction from phase-steps are discussed and the experimental results of testing an optical flat surface are presented. A flat mirror surface has been tested as an optical test surface and is been profiled. The results show that the method is precise and is not sensitive to environmental noises such as vibration and turbulence. Furthermore, the method seems to be a powerful means for testing of curved surfaces, too.

  2. TGF-beta and metalloproteinases differentially suppress NKG2D ligand surface expression on malignant glioma cells.

    PubMed

    Eisele, Günter; Wischhusen, Jörg; Mittelbronn, Michel; Meyermann, Richard; Waldhauer, Inja; Steinle, Alexander; Weller, Michael; Friese, Manuel A

    2006-09-01

    NKG2D ligands (NKG2DL) are expressed by infected and transformed cells. They transmit danger signals to NKG2D-expressing immune cells, leading to lysis of NKG2DL-expressing cells. We here report that the NKG2DL MHC class I-chain-related molecules A and B (MICA/B) and UL16-binding proteins (ULBP) 1-3 are expressed in human brain tumours in vivo, while expression levels are low or undetectable in normal brain. MICA and ULBP2 expression decrease with increasing WHO grade of malignancy, while MICB and ULBP1 are expressed independently of tumour grade. We further delineate two independent mechanisms that can explain these expression patterns: (i) transforming growth factor-beta (TGF-beta) is upregulated during malignant progression and selectively downregulates MICA, ULBP2 and ULBP4 expression, while MICB, ULBP1 and ULBP3 are unaffected. (ii) Cleavage of MICA and ULBP2 is reduced by inhibition of metalloproteinases (MP), whereas no changes in the expression levels of other NKG2DL were detected. Consequently, NKG2DL-dependent NK cell-mediated lysis is enhanced by depletion of TGF-beta or inhibition of MP. Thus, escape from NKG2D-mediated immune surveillance of malignant gliomas in vivo may be promoted by the inhibition of MICA and ULBP2 expression via an autocrine TGF-beta loop and by MP-dependent shedding from the cell surface. Loss of MICA and ULBP2, in contrast to other NKG2DL, may be particularly important in glioma immune escape, and differential regulation of human NKG2DL expression is part of the immunosuppressive properties of human malignant glioma cells.

  3. Layer Dependence and Light Tuning Surface Potential of 2D MoS2 on Various Substrates.

    PubMed

    Li, Feng; Qi, Junjie; Xu, Minxuan; Xiao, Jiankun; Xu, Yuliang; Zhang, Xiankun; Liu, Shuo; Zhang, Yue

    2017-04-01

    Here surface potential of chemical vapor deposition (CVD) grown 2D MoS2 with various layers is reported, and the effect of adherent substrate and light illumination on surface potential of monolayer MoS2 are investigated. The surface potential of MoS2 on Si/SiO2 substrate decreases from 4.93 to 4.84 eV with the increase in the number of layer from 1 to 4 or more. Especially, the surface potentials of monolayer MoS2 are strongly dependent on its adherent substrate, which are determined to be 4.55, 4.88, 4.93, 5.10, and 5.50 eV on Ag, graphene, Si/SiO2 , Au, and Pt substrates, respectively. Light irradiation is introduced to tuning the surface potential of monolayer MoS2 , with the increase in light intensity, the surface potential of MoS2 on Si/SiO2 substrate decreases from 4.93 to 4.74 eV, while increases from 5.50 to 5.56 eV on Pt substrate. The I-V curves on vertical of monolayer MoS2 /Pt heterojunction show the decrease in current with the increase of light intensity, and Schottky barrier height at MoS2 /Pt junctions increases from 0.302 to 0.342 eV. The changed surface potential can be explained by trapped charges on surface, photoinduced carriers, charge transfer, and local electric field.

  4. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    DOE PAGES

    Friedemann, S.; Chang, H.; Gamża, M. B.; ...

    2016-05-12

    One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate ofmore » the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. We find our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.« less

  5. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    PubMed Central

    Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.

    2016-01-01

    One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. Our results point at a large Fermi surface consistent with Luttinger’s theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition. PMID:27174799

  6. Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2

    SciTech Connect

    Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.

    2016-05-12

    One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. We find our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.

  7. Surface-enhanced Raman scattering for 2-D WSe2 hybridized with functionalized gold nanoparticles.

    PubMed

    Kim, Jun Young; Kim, Jeongyong; Joo, Jinsoo

    2016-11-28

    Two-dimensional (2-D) transition metal dichalcogenides, such as MoS2, WSe2, and WS2, are promising materials for application in field effect transistors, optoelectronics, and sensing devices. In this study, 2-D WSe2 samples with various numbers of layers were hybridized with functionalized gold nanoparticles (Au-NPs) to achieve surface-enhanced Raman scattering (SERS). The nanoscale Raman and photoluminescence spectra of the WSe2 layers and WSe2/Au-NP hybrids were measured using a high-resolution laser confocal microscope. The WSe2 exhibited distinct optical characteristics depending on the number of WSe2 layers. The intensities of the Raman characteristic modes of the WSe2 layers were significantly enhanced after hybridization with functionalized Au-NPs, indicating the SERS effect. The SERS effect weakened with increasing the number of WSe2 layers. The SERS effect was more pronounced for mono- and bi-layer WSe2 systems compared with the multi-layer WSe2 systems.

  8. Bimetallic nanostructures as active Raman markers: gold-nanoparticle assembly on 1D and 2D silver nanostructure surfaces.

    PubMed

    Gunawidjaja, Ray; Kharlampieva, Eugenia; Choi, Ikjun; Tsukruk, Vladimir V

    2009-11-01

    It is demonstrated that bimetallic silver-gold anisotropic nanostructures can be easily assembled from various nanoparticle building blocks with well-defined geometries by means of electrostatic interactions. One-dimensional (1D) silver nanowires, two-dimensional (2D) silver nanoplates, and spherical gold nanoparticles are used as representative building blocks for bottom-up assembly. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle-to-particle interaction that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. The Raman activity of the bimetallic nanostructures is compared with that of the individual nanoparticle blocks by using rhodamine 6G solution as the model analyte. The Raman intensity of the best-performing silver-gold nanostructure is comparable with the dense array of silver nanowires and silver nanoplates that were prepared by means of the Langmuir-Blodgett technique. An optimized design of a single-nanostructure substrate for surface-enhanced Raman spectroscopy (SERS), based on a wet-assembly technique proposed here, can serve as a compact and low-cost alternative to fabricated nanoparticle arrays.

  9. Lateral elasticity and X-ray diffraction of protein 2D crystals bound to lipid monolayers at the water surface.

    NASA Astrophysics Data System (ADS)

    Lenne, P. F.; Berge, B.; Renault, A.; Vénien-Bryan, C.; Courty, S.; Konovalov, O.; Legrand, J. F.; Brisson, A.; Balavoine, F.; Lal, J.; Gruebel, G.

    1998-03-01

    We present high resolution X-ray grazing incidence diffraction experiments and macroscopic lateral rigidity measurements performed on two-dimensional crystals of proteins bound to lipid monolayers at the water surface. For four different protein systems, Streptavidin bound to biotinylated lipids, an hystidin-tagged transcription factor HupR bound to Nickel lipids, Annexin-V bound to PS and Cholera toxin subunit-B bound to GM1 lipids, we record a non-zero shear elastic constant. For the three first systems, we observe narrow diffraction peaks and measure the Bragg rods intensities. In the case of Streptavidin we found two different possible structures, one of them exhibiting 19 Bragg rods, diffracting at about 10Åin the plane. After injecting glutaraldehyde (a protein linker) under the already formed 2D-crystals, the shear rigidity increases by a factor of two and additional diffraction peaks appear. This illustrates the correlation between the macroscopic shear elastic constant and the maximum in-plane wave vector transfer of the diffraction pattern, as expected in two dimensions. It also shows the interest of keeping the 2D-crystal in the water for subsequent action of various agents.

  10. The red-shift of surface plasmon absorption of 2D nanogold arrangement from disordered to ordered.

    PubMed

    Tang, Junke; Li, Jinru; Rong, Huiling; Zou, Bingsuo; Jiang, Long

    2008-01-01

    In this article, the changing of surface plasmon resonance (SPR) absorption of 2D arrangement of Au (3 nm) nanoparticles coated with 1-dodecanethiol (C12H25SH), obtained at different desolvation extents, had been investigated. It has been found that an obvious red-shifted happened when these arrays changed from loose, disordered to close-packed and ordered. Both transmission electron microscopy pictures and variation of SPR absorption of these arrays showed that the formation of long range two-dimension (2D) arrangement of nanoparticles coated with C12H25SH might be involved in two stages: At the first stage the particles can move freely and random patterns from loose to close package was driven by the Brownian Movement of solvated particles and as a result the voids were eliminated. The red shift of SPR absorption with the coverage (d lamda/d theta) is relative low. At the second stage, where the particles cannot move freely because of lack of solvent and a long-range two-dimension crystal was formed, the SPR shift to a longer wavelength with a larger d lamda/d theta. It is mainly attributed to the strong increase of the orientation and dipolar moment of the absorbed C12H25SH molecule on nanoparticles.

  11. Homogeneous Atomic Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Yan, Zhenjie; Patel, Parth B.; Hadzibabic, Zoran; Yefsah, Tarik; Struck, Julian; Zwierlein, Martin W.

    2017-03-01

    We report on the creation of homogeneous Fermi gases of ultracold atoms in a uniform potential. In the momentum distribution of a spin-polarized gas, we observe the emergence of the Fermi surface and the saturated occupation of one particle per momentum state: the striking consequence of Pauli blocking in momentum space for a degenerate gas. Cooling a spin-balanced Fermi gas at unitarity, we create homogeneous superfluids and observe spatially uniform pair condensates. For thermodynamic measurements, we introduce a hybrid potential that is harmonic in one dimension and uniform in the other two. The spatially resolved compressibility reveals the superfluid transition in a spin-balanced Fermi gas, saturation in a fully polarized Fermi gas, and strong attraction in the polaronic regime of a partially polarized Fermi gas.

  12. Fermi Surface Evolution and Luttinger Theorem in NaxCoO2: A Systematic Photoemission Study

    SciTech Connect

    Yang, H. B.; Pan, Z. H.; Sekharan, A. K. P.; Sato, T.; Souma, S.; Takahashi, T.; Jin, Rongying; Sales, Brian C; Mandrus, David; Fedorov, A. V.; Wang, Z.; Ding, H.

    2005-01-01

    We report a systematic angle-resolved photoemission study on Na{sub x}CoO{sub 2} for a wide range of Na concentrations (0.3 {le} x {le} 0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around {Gamma} and (ii) its area changes with x according to the Luttinger theorem. We also observed a surface state that exhibits a larger Fermi surface area. The e{prime}{sub g} band and the associated small Fermi surface pockets near the K points predicted by band calculations are found to sink below the Fermi energy in a manner almost independent of the doping and temperature.

  13. Small and nearly isotropic hole-like Fermi surfaces in LiFeAs detected through de Haas-van Alphen effect

    NASA Astrophysics Data System (ADS)

    Zeng, Bin; Watanabe, Daiki; Zhang, Qiu; Li, Gang; Besara, Tiglet; Siegrist, Theo; Xing, Lingyi; Wang, Xiancheng; Jin, Changqing; Goswami, Pallab; Johannes, Michelle; Balicas, Luis

    2014-03-01

    We show a detailed dHvA study unveiling small and nearly isotropic Fermi surface sheets in LiFeAs single crystals, which is not observed by previous dHvA results, as well as the cylindrical electron-like Fermi surfaces. Our results are in partial agreement with the ARPES results, and the small, nearly isotropic Fermi surface should correspond to the hole-like pocket, suggesting a prominent role for the electronic correlations in LiFeAs. The absence of gap nodes, in combination with the coexistence of quasi-two-dimensional and three-dimensional Fermi surfaces, favor an s-wave pairing symmetry for LiFeAs.

  14. Electronic band structure and Fermi surfaces of the quasi-two-dimensional monophosphate tungsten bronze, P4W12O44

    NASA Astrophysics Data System (ADS)

    Paul, S.; Ghosh, A.; Sato, T.; Sarma, D. D.; Takahashi, T.; Wang, E.; Greenblatt, M.; Raj, S.

    2014-02-01

    The electronic structure of quasi-two-dimensional monophosphate tungsten bronze, P4W12O44, has been investigated by high-resolution angle-resolved photoemission spectroscopy and density functional theoretical calculations. Experimental electron-like bands around \\Gamma point and Fermi surfaces have similar shapes as predicted by calculations. Fermi surface mapping at different temperatures shows a depletion of density of states at low temperature in certain flat portions of the Fermi surfaces. These flat portions of the Fermi surfaces satisfy the partial nesting condition with incommensurate nesting vectors q_1 and q_2 , which leads to the formation of charge density waves in this phosphate tungsten bronzes. The setting up of charge density wave in these bronzes can well explain the anomaly observed in its transport properties.

  15. Electronic structure of disordered CuPd alloys by positron-annihilation 2D-ACAR

    SciTech Connect

    Smedskjaer, L.C.; Benedek, R.; Siegel, R.W.; Legnini, D.G.; Stahulak, M.D.; Bansil, A.

    1988-01-01

    We report 2D-ACAR experiments and KKR CPA calculations on alpha-phase single-crystal Cu/sub 1-x/Pd/sub x/ in the range x less than or equal to 0.25. The flattening of the Fermi surface near (110) with increasing x predicted by theory is confirmed by our experimental results. 16 refs., 2 figs.

  16. Fermi Surface and Quasiparticle Excitations of Sr2RhO4

    SciTech Connect

    Baumberger, F.; Ingle, N. J. C.; Meevasana, W.; Lu, D. H.; Perry, R. S.; Mackenzie, A. P.; Hussain, Z; Singh, David J; Shen, Z. X.

    2006-01-01

    The electronic structure of the layered 4d transition metal oxide Sr2RhO4 is investigated by angle resolved photoemission. We find well-defined quasiparticle excitations with a highly anisotropic dispersion, suggesting a quasi-two-dimensional Fermi-liquid-like ground state. Markedly different from the isostructural Sr2RuO4, only two bands with dominant Rh 4dxz;zy character contribute to the Fermi surface. A quantitative analysis of the photoemission quasiparticle band structure is in excellent agreement with bulk data. In contrast, it is found that state-of-the-art density functional calculations in the local density approximation differ significantly from the experimental findings.

  17. Digitized crime scene forensics: automated trace separation of toolmarks on high-resolution 2D/3D CLSM surface data

    NASA Astrophysics Data System (ADS)

    Clausing, Eric; Vielhauer, Claus

    2015-03-01

    Locksmith forensics is an important and very challenging part of classic crime scene forensics. In prior work, we propose a partial transfer to the digital domain, to effectively support forensic experts and present approaches for a full process chain consisting of five steps: Trace positioning, 2D/3D acquisition with a confocal 3D laser scanning microscope, detection by segmentation, trace type determination, and determination of the opening method. In particular the step of trace segmentation on high-resolution 3D surfaces thereby turned out to be the part most difficult to implement. The reason for that is the highly structured and complex surfaces to be analyzed. These surfaces are cluttered with a high number of toolmarks, which overlap and distort each other. In Clausing et al., we present an improved approach for a reliable segmentation of relevant trace regions but without the possibility of separating single traces out of segmented trace regions. However, in our past research, especially features based on shape and dimension turned out to be highly relevant for a fully automated analysis and interpretation. In this paper, we consequently propose an approach for this separation. To achieve this goal, we use our segmentation approach and expand it with a combination of the watershed algorithm with a graph-based analysis. Found sub-regions are compared based on their surface character and are connected or divided depending on their similarity. We evaluate our approach with a test set of about 1,300 single traces on the exemplary locking cylinder component 'key pin' and thereby are able of showing the high suitability of our approach.

  18. Interaction quenches of Fermi gases

    SciTech Connect

    Uhrig, Goetz S.

    2009-12-15

    It is shown that the jump in the momentum distribution of Fermi gases evolves smoothly for small and intermediate times once an interaction between the fermions is suddenly switched on. The jump does not vanish abruptly. The loci in momentum space where the jumps occur are those of the noninteracting Fermi sea. No relaxation of the Fermi surface geometry takes place.

  19. Long-period surface structure stabilized by Fermi surface nesting: Cu (001) - (√(20)×√(20)) R26.6°-In

    NASA Astrophysics Data System (ADS)

    Nakagawa, T.; Yeom, H. W.; Rotenberg, E.; Krenzer, B.; Kevan, S. D.; Okuyama, H.; Nishijima, M.; Aruga, T.

    2006-02-01

    We have studied the atomic and electronic structure of the Cu(001)-(20×20)R26.6°-In surface, which undergoes a reversible transition to a p(2×2) phase at high temperature. Low temperature scanning-tunneling microscopy indicates a p(2×2) structure modulated at the (20×20) periodicity. Angle-resolved photoelectron spectroscopy shows a surface resonance exhibiting gap opening and backfolding along a (20×20) zone boundary. We suggest that the (20×20) structure is stabilized due to the Fermi surface nesting accompanying a surface charge density wave.

  20. Observation of an electron band above the Fermi level in FeTe₀.₅₅Se₀.₄₅ from in-situ surface doping

    SciTech Connect

    Zhang, P.; Richard, P.; Xu, N.; Xu, Y. -M.; Ma, J.; Qian, T.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.; Ding, H.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe₀.₅₅Se₀.₄₅. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe₂₋xSe₂ compound.

  1. Observation of an electron band above the Fermi level in FeTe₀.₅₅Se₀.₄₅ from in-situ surface doping

    DOE PAGES

    Zhang, P.; Richard, P.; Xu, N.; ...

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe₀.₅₅Se₀.₄₅. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe₂₋xSe₂ compound.

  2. Surface Acoustic Waves (SAW)-Based Biosensing for Quantification of Cell Growth in 2D and 3D Cultures

    PubMed Central

    Wang, Tao; Green, Ryan; Nair, Rajesh Ramakrishnan; Howell, Mark; Mohapatra, Subhra; Guldiken, Rasim; Mohapatra, Shyam Sundar

    2015-01-01

    Detection and quantification of cell viability and growth in two-dimensional (2D) and three-dimensional (3D) cell cultures commonly involve harvesting of cells and therefore requires a parallel set-up of several replicates for time-lapse or dose–response studies. Thus, developing a non-invasive and touch-free detection of cell growth in longitudinal studies of 3D tumor spheroid cultures or of stem cell regeneration remains a major unmet need. Since surface acoustic waves (SAWs) permit mass loading-based biosensing and have been touted due to their many advantages including low cost, small size and ease of assembly, we examined the potential of SAW-biosensing to detect and quantify cell growth. Herein, we demonstrate that a shear horizontal-surface acoustic waves (SH-SAW) device comprising two pairs of resonators consisting of interdigital transducers and reflecting fingers can be used to quantify mass loading by the cells in suspension as well as within a 3D cell culture platform. A 3D COMSOL model was built to simulate the mass loading response of increasing concentrations of cells in suspension in the polydimethylsiloxane (PDMS) well in order to predict the characteristics and optimize the design of the SH-SAW biosensor. The simulated relative frequency shift from the two oscillatory circuit systems (one of which functions as control) were found to be concordant to experimental data generated with RAW264.7 macrophage and A549 cancer cells. In addition, results showed that SAW measurements per se did not affect viability of cells. Further, SH-SAW biosensing was applied to A549 cells cultured on a 3D electrospun nanofiber scaffold that generate tumor spheroids (tumoroids) and the results showed the device's ability to detect changes in tumor spheroid growth over the course of eight days. Taken together, these results demonstrate the use of SH-SAW device for detection and quantification of cell growth changes over time in 2D suspension cultures and in 3D cell

  3. Surface Acoustic Waves (SAW)-Based Biosensing for Quantification of Cell Growth in 2D and 3D Cultures.

    PubMed

    Wang, Tao; Green, Ryan; Nair, Rajesh Ramakrishnan; Howell, Mark; Mohapatra, Subhra; Guldiken, Rasim; Mohapatra, Shyam Sundar

    2015-12-19

    Detection and quantification of cell viability and growth in two-dimensional (2D) and three-dimensional (3D) cell cultures commonly involve harvesting of cells and therefore requires a parallel set-up of several replicates for time-lapse or dose-response studies. Thus, developing a non-invasive and touch-free detection of cell growth in longitudinal studies of 3D tumor spheroid cultures or of stem cell regeneration remains a major unmet need. Since surface acoustic waves (SAWs) permit mass loading-based biosensing and have been touted due to their many advantages including low cost, small size and ease of assembly, we examined the potential of SAW-biosensing to detect and quantify cell growth. Herein, we demonstrate that a shear horizontal-surface acoustic waves (SH-SAW) device comprising two pairs of resonators consisting of interdigital transducers and reflecting fingers can be used to quantify mass loading by the cells in suspension as well as within a 3D cell culture platform. A 3D COMSOL model was built to simulate the mass loading response of increasing concentrations of cells in suspension in the polydimethylsiloxane (PDMS) well in order to predict the characteristics and optimize the design of the SH-SAW biosensor. The simulated relative frequency shift from the two oscillatory circuit systems (one of which functions as control) were found to be concordant to experimental data generated with RAW264.7 macrophage and A549 cancer cells. In addition, results showed that SAW measurements per se did not affect viability of cells. Further, SH-SAW biosensing was applied to A549 cells cultured on a 3D electrospun nanofiber scaffold that generate tumor spheroids (tumoroids) and the results showed the device's ability to detect changes in tumor spheroid growth over the course of eight days. Taken together, these results demonstrate the use of SH-SAW device for detection and quantification of cell growth changes over time in 2D suspension cultures and in 3D cell

  4. SOLID-STATE PHYSICS. Scalable T² resistivity in a small single-component Fermi surface.

    PubMed

    Lin, Xiao; Fauqué, Benoît; Behnia, Kamran

    2015-08-28

    Scattering among electrons generates a distinct contribution to electrical resistivity that follows a quadratic temperature (T) dependence. In strongly correlated electron systems, the prefactor A of this T(2) resistivity scales with the magnitude of the electronic specific heat, γ. Here we show that one can change the magnitude of A by four orders of magnitude in metallic strontium titanate (SrTiO3) by tuning the concentration of the carriers and, consequently, the Fermi energy. The T(2) behavior persists in the single-band dilute limit despite the absence of two known mechanisms for T(2) behavior: distinct electron reservoirs and Umklapp processes. The results highlight the absence of a microscopic theory for momentum decay through electron-electron scattering in various Fermi liquids.

  5. Electronic band structure and Fermi surface of ferromagnetic Tb: Experiment and theory

    NASA Astrophysics Data System (ADS)

    Döbrich, K. M.; Bihlmayer, G.; Starke, K.; Prieto, J. E.; Rossnagel, K.; Koh, H.; Rotenberg, E.; Blügel, S.; Kaindl, G.

    2007-07-01

    We have investigated the bulk valence-band structure of Tb metal in the ferromagnetic phase by angle-resolved photoelectron spectroscopy and full-potential-linearized-augmented-plane-wave calculations. The experiments were performed at undulator beamline 7.0.1 of the Advanced Light Source using a three-axis rotatable low-temperature goniometer and a display-type photoelectron spectrometer that give access to a large region of momentum space. The results of our calculations, which make use of recent progress in the theoretical description of the magnetic properties of 4f metals, are in remarkably good agreement with experiment. This can be best seen from a comparison of the electronic structure in high-symmetry directions, at critical points, on Fermi contours, and at band crossings with the Fermi level. To our knowledge, the present work represents the most detailed combined experimental and theoretical study of the electronic structure of a magnetic lanthanide metal to date.

  6. The human NKG2D ligand ULBP2 can be expressed at the cell surface with or without a GPI anchor and both forms can activate NK cells

    PubMed Central

    Fernández-Messina, Lola; Ashiru, Omodele; Agüera-González, Sonia; Reyburn, Hugh T.; Valés-Gómez, Mar

    2011-01-01

    The activating immune receptor NKG2D binds to several stress-induced ligands that are structurally different. MHC-class-I-related chain (MIC) A/B molecules have a transmembrane domain, whereas most UL16 binding proteins (ULBPs) are glycosylphosphatidylinositol (GPI)-linked molecules. The significance of this variability in membrane anchors is unclear. Here, we demonstrate that ULBP2, but not ULBP1 or ULBP3, can reach the cell surface without the GPI modification. Several proteins are expressed at the cell surface as both transmembrane and GPI-linked molecules, either via alternative splicing or by the expression of linked genes. However, to our knowledge, ULBP2 is the first single mammalian cDNA that can be expressed as either a transmembrane or a GPI-anchored protein. The rate of maturation and the levels of cell surface expression of the non-GPI-linked form were lower than those of the GPI-linked ULBP2. Nonetheless, non-GPI ULBP2 was recognised by NKG2D and triggered NK cell cytotoxicity. These data show that differences in membrane attachment by NKG2D ligands are more important for regulation of their surface expression than for cytotoxic recognition by NKG2D and emphasise that detailed characterisation of the cell biology of individual NKG2D ligands will be necessary to allow targeted modulation of this system. PMID:21224393

  7. Fermi Surface and Quasiparticle Dynamics of Na0.7CoO2 Investigated by Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Hasan, M. Z.; Chuang, Y.-D.; Qian, D.; Li, Y. W.; Kong, Y.; Kuprin, A.; Fedorov, A. V.; Kimmerling, R.; Rotenberg, E.; Rossnagel, K.; Hussain, Z.; Koh, H.; Rogado, N. S.; Foo, M. L.; Cava, R. J.

    2004-06-01

    We present the first angle-resolved photoemission study of Na0.7CoO2, the host material of the superconducting NaxCoO2·nH2O series. Our results show a hole-type Fermi surface, a strongly renormalized quasiparticle band, a small Fermi velocity, and a large Hubbard U. The quasiparticle band crosses the Fermi level from M toward Γ suggesting a negative sign of effective single-particle hopping teff (about 10meV) which is on the order of magnetic exchange coupling J in this system. Quasiparticles are well defined only in the T-linear resistivity (non-Fermi-liquid) regime. Unusually small single-particle hopping and unconventional quasiparticle dynamics may have implications for understanding the phase of matter realized in this new class of a strongly interacting quantum system.

  8. Contactless electroreflectance studies of the Fermi level position at the air/GaN interface: Bistable nature of the Ga-polar surface

    NASA Astrophysics Data System (ADS)

    Janicki, Łukasz; Gładysiewicz, Marta; Misiewicz, Jan; Klosek, Kamil; Sobanska, Marta; Kempisty, Paweł; Zytkiewicz, Zbigniew R.; Kudrawiec, Robert

    2017-02-01

    In this paper we show that the surface Fermi level of Ga-polar GaN exhibits a bistable behavior allowing it to be located at two distinct energetic positions at the air/GaN interface which is unusual for other III-V semiconductors such as GaAs or GaSb. To determine the Fermi level position at the air/GaN interface we perform contactless electroreflectance measurements on specially designed UD+ structures [GaN(undoped)/GaN(highly doped)/substrate] doped by Si and Mg. Analyzing the period of Franz-Keldysh oscillation we determine the built-in electric field in the undoped (U) layer. These studies coupled with numerical solutions of the Poisson equation allowed us to determine the position of the Fermi level at the air/GaN interface. We observe a change in the band bending correlated to different Fermi level positions in the doped (D+) layer. We show that depending on the doping type in the D+ layer the Fermi level at the air/GaN interface is located in the upper or lower singularity of surface density of states (SDOS) for Si or Mg doping of D+ layer, respectively. We support our findings with the density functional theory calculations of the SDOS and the dependence of the Fermi level position on the doping concentration in the bulk of a GaN slab.

  9. Direct, experimental evidence of the Fermi surface in YBa sub 2 Cu sub 3 O sub 7-x

    SciTech Connect

    Haghighi, H.; Kaiser, J.H.; Rayner, S.L.; West, R.N. ); Liu, J.Z.; Shelton, R. ); Howell, R.H.; Sterne, P.A.; Solal, F.; Fluss, M.J. )

    1991-04-29

    We report new measurements of the electron-positron momentum spectra of YBa{sub 2}Cu{sub 3}O{sub 7-x} performed with ultra-high statistical precision. These data differ from previous results in two significant respects: They show the D{sub 2} symmetry appropriate for untwinned crystals and, more importantly, they show unmistakable, statistically significant, discontinuities that are evidence of a major Fermi surface section. These results provide a partial answer to a question of special significance to the study of high temperature superconductors i.e. the distribution of the electrons in the material, the electronic structure. Special consideration has been given both experimentally and theoretically to the existence and shape of a Fermi surface in the materials and to the superconducting gap. There are only three experimental techniques that can provide details of the electronic structure at useful resolutions. They are angular correlation of positron annihilation radiation, ACAR, angle resolved photo emission, PE, and de Haas van Alphen measurements. 11 refs., 4 figs.

  10. Tuning the surface Fermi level on p-type gallium nitride nanowires for efficient overall water splitting.

    PubMed

    Kibria, M G; Zhao, S; Chowdhury, F A; Wang, Q; Nguyen, H P T; Trudeau, M L; Guo, H; Mi, Z

    2014-04-30

    Solar water splitting is one of the key steps in artificial photosynthesis for future carbon-neutral, storable and sustainable source of energy. Here we show that one of the major obstacles for achieving efficient and stable overall water splitting over the emerging nanostructured photocatalyst is directly related to the uncontrolled surface charge properties. By tuning the Fermi level on the nonpolar surfaces of gallium nitride nanowire arrays, we demonstrate that the quantum efficiency can be enhanced by more than two orders of magnitude. The internal quantum efficiency and activity on p-type gallium nitride nanowires can reach ~51% and ~4.0 mol hydrogen h(-1) g(-1), respectively. The nanowires remain virtually unchanged after over 50,000 μmol gas (hydrogen and oxygen) is produced, which is more than 10,000 times the amount of photocatalyst itself (~4.6 μmol). The essential role of Fermi-level tuning in balancing redox reactions and in enhancing the efficiency and stability is also elucidated.

  11. Electronic structure, Fermi surface topology and spectroscopic optical properties of LaBaCo2O5.5 compound

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Al-Douri, Y.; Khenata, R.; Khan, Wilayat; Khan, Saleem Ayaz; Azam, Sikander

    2014-08-01

    We have investigated the electronic band structure, Fermi surface topology, chemical bonding and optical properties of LaBaCo2O5.5 compound. The first-principle calculations based on density functional theory (DFT) by means of the full-potential linearized augmented plane-wave method were employed. The atomic positions of LaBaCo2O5.5 compound were optimized by minimizing the forces acting on atoms. We employed the local density approximation (LDA), generalized gradient approximation (GGA) and Engel-Vosko GGA (EVGGA) to treat the exchange correlation potential by solving Kohn-Sham equations. Electronic structure and bonding properties are studied throughout the calculation of densities of states, Fermi surfaces and charge densities. Furthermore, the optical properties are investigated via the calculation of the dielectric tensor component in order to characterize the linear optical properties. Optical spectra are analyzed by means of the electronic structure, which provides theoretical understanding of the conduction mechanism of the investigated compound.

  12. New details of the Fermi surface of 2H-NbSe2 revealed by quantum oscillations in the magnetostriction

    NASA Astrophysics Data System (ADS)

    Sirenko, V.; Gasparini, A.; de Visser, A.; Eremenko, V.; Ibulaev, V.; Bruk, V.

    2009-03-01

    The layered charge-density wave (CDW) superconductor 2H-NbSe2 (TS=7.2 K) is the very first material in which quantum oscillations have been observed in the mixed state by means of magnetization and magnetostriction measurements. The magnetostriction technique offers the advantage that quantum oscillations are particularly pronounced, which is due to pressure sensitivity of the relevant cross-section of the Fermi surface. Moreover, measurements can be performed for a field oriented along the crystallographic axis in contrast to the torque technique that is routinely used. Here we present magnetostriction measurement on a high-quality single-crystalline sample for temperatures 0.25-8.0 K using a sensitive capacitance dilatometer. Two oscillation frequencies are observed at the lowest temperatures for the in-plane orientation of the applied magnetic field. These new data reveal that the Fermi-surface sheet in the first Brillouin zone has two cross-sections, rather than the conventional pan-cake shape.

  13. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure.

    PubMed

    Gruznev, D V; Bondarenko, L V; Tupchaya, A Y; Eremeev, S V; Mihalyuk, A N; Chou, J P; Wei, C M; Zotov, A V; Saranin, A A

    2017-01-25

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), [Formula: see text]-(Tl, Pb) and [Formula: see text]-(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)[Formula: see text] system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] compound contains six Tl atoms and seven Pb atoms per [Formula: see text] unit cell (i.e.  ∼0.67 ML Tl and  ∼0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)[Formula: see text] and (Tl, Pb)/Ge(1 1 1)[Formula: see text] compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)[Formula: see text], these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  14. 2D Tl-Pb compounds on Ge(1 1 1) surface: atomic arrangement and electronic band structure

    NASA Astrophysics Data System (ADS)

    Gruznev, D. V.; Bondarenko, L. V.; Tupchaya, A. Y.; Eremeev, S. V.; Mihalyuk, A. N.; Chou, J. P.; Wei, C. M.; Zotov, A. V.; Saranin, A. A.

    2017-01-01

    Structural transformations and evolution of the electron band structure in the (Tl, Pb)/Ge(1 1 1) system have been studied using low-energy electron diffraction, scanning tunneling microscopy, angle-resolved photoelectron spectroscopy and density functional theory calculations. The two 2D Tl-Pb compounds on Ge(1 1 1), \\sqrt{3}× \\sqrt{3} -(Tl, Pb) and 3× 3 -(Tl, Pb), have been found and their composition, atomic arrangement and electron properties has been characterized. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} compound is almost identical to the alike (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} system from the viewpoint of its atomic structure and electronic properties. They contain 1.0 ML of Tl atoms arranged into a honeycomb network of chained trimers and 1/3 ML of Pb atoms occupying the centers of the honeycomb units. The (Tl, Pb)/Ge(1 1 1)3× 3 compound contains six Tl atoms and seven Pb atoms per 3× 3 unit cell (i.e.  ˜0.67 ML Tl and  ˜0.78 ML Pb). Its atomic structure can be visualized as consisting of Pb hexagons surrounded by Tl trimers. The (Tl, Pb)/Ge(1 1 1)\\sqrt{3}× \\sqrt{3} and (Tl, Pb)/Ge(1 1 1)3× 3 compounds are metallic and their band structures contain spin-split surface-state bands. By analogy with the (Tl, Pb)/Si(1 1 1)\\sqrt{3}× \\sqrt{3} , these (Tl, Pb)/Ge(1 1 1) compounds are believed to be promising objects for prospective studies of superconductivity in one-atom-layer systems.

  15. Fermi surface investigation in the scanning tunneling microscopy of Bi 2Sr 2CaCu 2O 8

    NASA Astrophysics Data System (ADS)

    Voo, K. K.; Wu, W. C.; Chen, H. Y.; Mou, C. Y.

    2004-12-01

    Within the ideal Fermi liquid picture, the impurity-induced spatial modulation of local density of states (LDOS) in the d-wave superconductor Bi 2Sr 2CaCu 2O 8 is investigated at different superconducting (SC) gap sizes. These LDOS spectra are related to the finite-temperature d I/d V spectra in scanning tunneling microscopy (STM), when the Fermi distribution factor is deconvoluted away from d I/d V. We find stripe-like structures even in the zero gap case due to a local-nesting mechanism. This mechanism is different from the octet-scattering mechanism in the d-wave SC (dSC) state proposed by McElroy et al. [K. McElroy, R.W. Simmonds, J.E. Hoffman, D.H. Lee, J. Orenstein, H. Eisaki, S. Uchida, J.C. Davis, Nature 422 (2003) 592]. The zero gap LDOS is related to the normal state d I/d V. The zero gap spectra when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias voltage, in contrast to the point-wise tracing out proposed by McElroy et al. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the octet-scattering mechanism in the dSC state and pointed out that, due to the Umklapp symmetry, there are additional peaks in the reciprocal space that experimentally yet to be found.

  16. Tuning Fermi-surface properties through quantum confinement in metallic metalattices: New metals from old atoms

    NASA Astrophysics Data System (ADS)

    Crespi, Vincent H.; Han, J. E.

    2001-03-01

    We describe a new class of nanoscale structured metals wherein the effects of quantum confinement are combined with dispersive metallic electronic states to induce modifications to the fundamental low-energy microscopic properties of a three-dimensional metal: the density of states, the distribution of Fermi velocities, and the collective electronic response (J. E. Han and Vincent H. Crespi, to appear in Phys. Rev. Lett.). The metalattice, metal-infiltrated colloidal lattice, possesses two very different length scales, lattice constants of metal atoms and of colloidal spheres. We compute the electronic properties of the metalattice using an empirical tight-binding method. As a result of the hierarchy in the two length scales, electronic states bifurcate into two classes with weak and strong dispersion. The dispersive states reflect the symmetry of the colloidal lattice and have major contribution to the transport properties such as inversion of Fermi velocity and optical response. We also discuss the magnetic structure of the metalattice with magnetic infiltrants such as Pd and Rh.

  17. Symmetry-broken electronic structure and uniaxial Fermi surface nesting of untwinned CaFe2As2

    NASA Astrophysics Data System (ADS)

    Wang, Q.; Sun, Z.; Rotenberg, E.; Ronning, F.; Bauer, E. D.; Lin, H.; Markiewicz, R. S.; Lindroos, M.; Barbiellini, B.; Bansil, A.; Dessau, D. S.

    2013-12-01

    We used angle-resolved photoemission spectroscopy to make direct measurements of the electronic structure of the untwinned uniaxial state of CaFe2As2, the parent compound of an iron-based superconductor. The very small photon beam size, combined with the relatively large single-domain area on the crystal surfaces, allowed us to obtain the intrinsic symmetry-broken dispersions and Fermi surface (FS) geometries along the orthogonal Fe-Fe bond directions without any mechanical or magnetic detwinning processes. Comparing the optimized local density approximation calculations, an orbital-dependent band shifting is introduced to obtain better agreement, which is consistent with the development of orbital ordering. More interestingly, unidirectional straight and flat FS segments are observed near the zone center, which indicates the existence of a unidirectional charge density wave order. Our results indicate strong electronic anisotropy in CaFe2As2 and put strong constraints on theories for the iron-pnictide system.

  18. Tuning the metal-insulator transition in NdNiO3 heterostructures via Fermi surface instability and spin fluctuations

    NASA Astrophysics Data System (ADS)

    Dhaka, R. S.; Das, Tanmoy; Plumb, N. C.; Ristic, Z.; Kong, W.; Matt, C. E.; Xu, N.; Dolui, Kapildeb; Razzoli, E.; Medarde, M.; Patthey, L.; Shi, M.; Radović, M.; Mesot, Joël

    2015-07-01

    We employed in situ pulsed laser deposition (PLD) and angle-resolved photoemission spectroscopy (ARPES) to investigate the mechanism of the metal-insulator transition (MIT) in NdNiO3 (NNO) thin films, grown on NdGaO3(110) and LaAlO3(100) substrates. In the metallic phase, we observe three-dimensional hole and electron Fermi surface (FS) pockets formed from strongly renormalized bands with well-defined quasiparticles. Upon cooling across the MIT in NNO/NGO sample, the quasiparticles lose coherence via a spectral weight transfer from near the Fermi level to localized states forming at higher binding energies. In the case of NNO/LAO, the bands are apparently shifted upward with an additional holelike pocket forming at the corner of the Brillouin zone. We find that the renormalization effects are strongly anisotropic and are stronger in NNO/NGO than NNO/LAO. Our study reveals that substrate-induced strain tunes the crystal field splitting, which changes the FS properties, nesting conditions, and spin-fluctuation strength, and thereby controls the MIT via the formation of an electronic order parameter with QAF˜(1 /4 ,1 /4 ,1 /4 ±δ ) .

  19. Density-functional theory calculation of Fermi surface in stripe ordered YBa2Cu3O6.5

    NASA Astrophysics Data System (ADS)

    Blackburn, Simon; Cote, Michel

    2012-02-01

    High temperature superconductors (HTSC) attract a lot of interests since their discovery in 1986. More recently, observations of quantum oscillations in underdoped YBa2Cu3O6.5 (YBCO6.5) at a low frequency suggested a small pocket constitute the Fermi surface (Doiron-Leyraud et al. Nature 447, 565 (2007)). In this work, we present results of density-functional theory (DFT) calculations of YBCO electronic structure. In order to better represent the electron-electron interaction, we add an on-site repulsion term (Hubbard term) on the copper d-orbitals (DFT+U). This method is known to improve DFT calculations for Mott insulators like La2CuO4 and YBCO6.0 since the Hubbard term favors an anti-ferromagnetic ground state. Using this method, we compare various magnetic states calculated with different values of the Hubbard term U. Our results suggest that an atom-centered stripe, similar to the one found in La1.875Sr0.125CuO4 (Tranquada et al. Nature 375 561 (1995)), is consistent with the presence of a Fermi pocket of the size reported in the experiments. We further show that the size of the pocket and the nature of the carriers (electrons or holes) can be varied with pressure suggesting a way to test this hypothesis.

  20. Fermi surface pockets in the underdoped cuprate YBa2Cu4O8, - are they present in low magnetic fields?

    NASA Astrophysics Data System (ADS)

    Cooper, J. R.; Matusiak, M.; Loram, J. W.; Yelland, E. A.; Dabrowski, B.

    2008-03-01

    The observations of quantum oscillations in the underdoped cuprate superconductors, ortho-II YBa2Cu3O6.5 [1] and YBa2Cu4O8 (Y124) [2] at very high magnetic fields and low temperatures could lead to improved understanding of cuprate superconductivity. This will be especially true if the small Fermi surface (FS) pockets are still present at higher temperatures and lower magnetic fields. As pointed out in ref. [2] the pockets appear to have low Fermi energies ˜ 300 K, and could therefore give rise to T-dependent magnetic anisotropy in the normal state associated with Landau-Peierls diamagnetism. We report susceptibility anisotropy data for Y124 crystals up to 300 K, and discuss whether these data and zero field heat capacity data, are consistent with the properties of the FS pockets obtained from high field measurements. [1] N. Doiron-Leyraud, et al., Nature 447,565 (2007) [2] E.A. Yelland et al. arXiv:cond-mat/07070057.

  1. Chiral non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2014-07-01

    A non-Fermi liquid state without time-reversal and parity symmetries arises when a chiral Fermi surface is coupled with a soft collective mode in two space dimensions. The full Fermi surface is described by a direct sum of chiral patch theories, which are decoupled from each other in the low-energy limit. Each patch includes low-energy excitations near a set of points on the Fermi surface with a common tangent vector. General patch theories are classified by the local shape of the Fermi surface, the dispersion of the critical boson, and the symmetry group, which form the data for distinct universality classes. We prove that a large class of chiral non-Fermi liquid states exists as stable critical states of matter. For this, we use a renormalization group scheme where low-energy excitations of the Fermi surface are interpreted as a collection of (1+1)-dimensional chiral fermions with a continuous flavor labeling the momentum along the Fermi surface. Due to chirality, the Wilsonian effective action is strictly UV finite. This allows one to extract the exact scaling exponents although the theories flow to strongly interacting field theories at low energies. In general, the low-energy effective theory of the full Fermi surface includes patch theories of more than one universality classes. As a result, physical responses include multiple universal components at low temperatures. We also point out that, in quantum field theories with extended Fermi surface, a noncommutative structure naturally emerges between a coordinate and a momentum which are orthogonal to each other. We show that the invalidity of patch description for Fermi liquid states is tied with the presence of UV/IR mixing associated with the emergent noncommutativity. On the other hand, UV/IR mixing is suppressed in non-Fermi liquid states due to UV insensitivity, and the patch description is valid.

  2. Using Hydrus 2-D to assess the emitters optimal position for Eggplants under surface and subsurface drip irrigation

    NASA Astrophysics Data System (ADS)

    Ghazouani, Hiba; Autovino, Dario; Douh, Boutheina; Boujelben, Abdel Hamid; Provenznao, Giuseppe; Rallo, Giovanni

    2014-05-01

    The main objective of the work is to assess the emitters optimal position for Eggplant crop (Solanum melongena L.) in a sandy loam soil irrigated with surface or subsurface drip irrigation systems, by means of field measurements and simulations carried out with Hydrus-2D model. Initially, the performance of the model is evaluated on the basis of the comparison between simulated soil water contents (SWC) and the corresponding measured in two plots, in which laterals with coextruded emitters are laid on the soil surface (T0) and at 20 cm depth (T20), respectively. In order to choose the best position of the lateral, the results of different simulation runs, carried out by changing the installation depth of the lateral (5 cm, 15 cm and 45 cm) were compared in terms of ratio between actual transpiration and total amount of water provided during the entire growing season (WUE). Experiments were carried out, from April to June 2007, at Institut Supérieur Agronomique de Chott Mériem (Sousse, Tunisia). In the two plots, plants were spaced 0.40 m along the row and 1.2 m between the rows. Each plot was irrigated by means of laterals with coextruded emitters spaced 0.40 m and discharging a flow rate equal to 4.0 l h-1 at a nominal pressure of 100 kPa. In each plot, spatial and temporal variability of SWCs were acquired with a Time Domain Reflectometry probe (Trime-FM3), on a total of four 70 cm long access tubes, installed along the direction perpendicular to the plant row, at distances of 0, 20, 40 and 60 cm from the emitter. Irrigation water was supplied, accounting for the rainfall, every 7-10 days at the beginning of the crop cycle (March-April) and approximately once a week during the following stages till the harvesting (May-June), for a total of 15 one-hour watering. To run the model, soil evaporation, Ep, and crop transpiration, Tp were determined according to the modified FAO Penman-Monteith equation and the dual crop coefficient approach, whereas soil hydraulics

  3. Inhomogeneous Weyl and Dirac Semimetals: Transport in Axial Magnetic Fields and Fermi Arc Surface States from Pseudo-Landau Levels

    NASA Astrophysics Data System (ADS)

    Grushin, Adolfo G.; Venderbos, Jörn W. F.; Vishwanath, Ashvin; Ilan, Roni

    2016-10-01

    Topological Dirac and Weyl semimetals have an energy spectrum that hosts Weyl nodes appearing in pairs of opposite chirality. Topological stability is ensured when the nodes are separated in momentum space and unique spectral and transport properties follow. In this work, we study the effect of a space-dependent Weyl node separation, which we interpret as an emergent background axial-vector potential, on the electromagnetic response and the energy spectrum of Weyl and Dirac semimetals. This situation can arise in the solid state either from inhomogeneous strain or nonuniform magnetization and can also be engineered in cold atomic systems. Using a semiclassical approach, we show that the resulting axial magnetic field B5 is observable through an enhancement of the conductivity as σ ˜B52 due to an underlying chiral pseudomagnetic effect. We then use two lattice models to analyze the effect of B5 on the spectral properties of topological semimetals. We describe the emergent pseudo-Landau-level structure for different spatial profiles of B5, revealing that (i) the celebrated surface states of Weyl semimetals, the Fermi arcs, can be reinterpreted as n =0 pseudo-Landau levels resulting from a B5 confined to the surface, (ii) as a consequence of position-momentum locking, a bulk B5 creates pseudo-Landau levels interpolating in real space between Fermi arcs at opposite surfaces, and (iii) there are equilibrium bound currents proportional to B5 that average to zero over the sample, which are the analogs of bound currents in magnetic materials. We conclude by discussing how our findings can be probed experimentally.

  4. On the 2D-transition, hysteresis and thermodynamic equilibrium of Kr adsorption on a graphite surface.

    PubMed

    Diao, Rui; Fan, Chunyan; Do, D D; Nicholson, D

    2015-12-15

    The adsorption and desorption of Kr on graphite at temperatures in the range 60-88K, was systematically investigated using a combination of several simulation techniques including: Grand Canonical Monte Carlo (GCMC), Canonical kinetic-Monte Carlo (C-kMC) and the Mid-Density Scheme (MDS). Particular emphasis was placed on the gas-solid, gas-liquid and liquid-solid 2D phase transitions. For temperatures below the bulk triple point, the transition from a 2D-liquid-like monolayer to a 2D-solid-like state is manifested as a sub-step in the isotherm. A further increase in the chemical potential leads to another rearrangement of the 2D-solid-like state from a disordered structure to an ordered structure that is signalled by (1) another sub-step in the monolayer region and (2) a spike in the plot of the isosteric heat versus density at loadings close to the dense monolayer coverage concentration. Whenever a 2D transition occurs in a grand canonical isotherm it is always associated with a hysteresis, a feature that is not widely recognised in the literature. We studied in details this hysteresis with the analysis of the canonical isotherm, obtained with C-kMC, which exhibits a van der Waals (vdW) type loop with a vertical segment in the middle. We complemented the hysteresis loop and the vdW curve with the analysis of the equilibrium transition obtained with the MDS, and found that the equilibrium transition coincides exactly with the vertical segment of the C-kMC isotherm, indicating the co-existence of two phases at equilibrium. We also analysed adsorption at higher layers and found that the 2D-coexistence is also observed, provided that the temperature is well below the triple point. Finally the 2D-critical temperatures were obtained for the first three layers and they are in good agreement with the experimental data in the literature.

  5. Phonon dispersions and Fermi surfaces nesting explaining the variety of charge ordering in titanium-oxypnictides superconductors

    PubMed Central

    Nakano, Kousuke; Hongo, Kenta; Maezono, Ryo

    2016-01-01

    There has been a puzzle between experiments and theoretical predictions on the charge ordering of layered titanium-oxypnictides superconductors. Unconventional mechanisms to explain this discrepancy have been argued so far, even affecting the understanding of superconductivity on the compound. We provide a new theoretical prediction, by which the discrepancy itself is resolved without any complicated unconventional explanation. Phonon dispersions and changes of nesting vectors in Fermi surfaces are clarified to lead to the variety of superlattice structures even for the common crystal structures when without CDW, including orthorhombic 2 × 2 × 1 one for BaTi2As2O, which has not yet been explained successfully so far, being different from tetragonal for BaTi2Sb2O and BaTi2Bi2O. The electronic structure analysis can naturally explain experimental observations about CDW including most latest ones without any cramped unconventional mechanisms. PMID:27430418

  6. Fermi surface and superconductivity in low-density high-mobility δ-doped SrTiO3.

    PubMed

    Kim, M; Bell, C; Kozuka, Y; Kurita, M; Hikita, Y; Hwang, H Y

    2011-09-02

    The electronic structure of low-density n-type SrTiO3 δ-doped heterostructures is investigated by angular dependent Shubnikov-de Haas oscillations. In addition to a controllable crossover from a three- to two-dimensional Fermi surface, clear beating patterns for decreasing dopant layer thicknesses are found. These indicate the lifting of the degeneracy of the conduction band due to subband quantization in the two-dimensional limit. Analysis of the temperature-dependent oscillations shows that similar effective masses are found for all components, associated with the splitting of the light electron pocket. The dimensionality crossover in the superconducting state is found to be distinct from the normal state, resulting in a rich phase diagram as a function of dopant layer thickness.

  7. Fermi Surface and Superconductivity in Low-Density High-Mobility Delta-Doped SrTiO3

    SciTech Connect

    Kim, M.

    2011-08-19

    The electronic structure of low-density n-type SrTiO{sub 3} {delta}-doped heterostructures is investigated by angular dependent Shubnikov-de Haas oscillations. In addition to a controllable crossover from a three- to two-dimensional Fermi surface, clear beating patterns for decreasing dopant layer thicknesses are found. These indicate the lifting of the degeneracy of the conduction band due to subband quantization in the two-dimensional limit. Analysis of the temperature-dependent oscillations shows that similar effective masses are found for all components, associated with the splitting of the light electron pocket. The dimensionality crossover in the superconducting state is found to be distinct from the normal state, resulting in a rich phase diagram as a function of dopant layer thickness.

  8. Doping Evolution of the Underlying Fermi Surface in La_2−xSr_xCuO_4

    SciTech Connect

    Yoshida, T.

    2010-05-03

    We have performed a systematic doping dependent study of La{sub 2-x}Sr{sub x}CuO{sub 4} (LSCO) (0.03 {le} x {le} 0.3) by angle-resolved photoemission spectroscopy. In the entire doping range, the underlying 'Fermi surface' determined from the low energy spectral weight approximately satisfies Luttinger's theorem, even down to the lightly-doped region. This is in strong contrast to the result on Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2} (Na-CCOC), which shows a strong deviation from Luttinger's theorem. The differences between LSCO and Na-CCOC are correlated with the different behaviors of the chemical potential shift and spectral weight transfer induced by hole doping.

  9. Effets Seebeck et Nernst dans les cuprates: Etude de la reconstruction de la surface de Fermi sous champ magnetique intense

    NASA Astrophysics Data System (ADS)

    Laliberte, Francis

    2010-06-01

    Ce memoire presente des mesures de transport thermoelectrique, les effets Seebeck et Nernst, dans une serie d'echantillons de supraconducteurs a haute temperature critique. Des resultats obtenus recemment au Laboratoire National des Champs Magnetiques Intenses a Grenoble sur La1.7Eu0.2Sr0.1 CuO4, La1.675Eu0.2Sr0.125CuO 4, La1.64Eu0.2Sr0.16CuO4, La1.74Eu0.1Sr0.16CuO4 et La 1.4Nd0.4Sr0.2CuO4 sont analyses. Une attention particuliere est accordee aux equations de la theorie semi-classique du transport et leur validite est verifiee. La procedure experimentale et les materiaux utilises pour concevoir les montages de mesures sont expliques en detail. Enfin, un chapitre est dedie a l'explication et l'interpretation des resultats de transport thermoelectrique sur YBa2Cu3O6+delta publies au cours de l'hiver 2010 dans les revues Nature et Physical Review Letters. Les donnees d'effet Seebeck dans les echantillons de La 1.8-x,Eu0.2SrxCuO 4, ou un changement de signe est observe, permettent de conclure a la presence d'une poche d'electrons dans la surface de Fermi qui domine le transport a basse temperature dans la region sous-dopee du diagramme de phase. Cette conclusion est similaire a celle obtenue par des mesures d'effet Hall dans YBa 2Cu3O6+delta et elle cadre bien dans un scenario de reconstruction de la surface de Fermi. Les donnees d'effet Nernst recueillies indiquent que la contribution des fluctuations supraconductrices est limitee a un modeste intervalle de temperature au-dessus de la temperature critique.

  10. The Thomas-Fermi model in the theory of systems of charged particles above the surface of liquid dielectrics

    NASA Astrophysics Data System (ADS)

    Lytvtnenko, D. M.; Slyusarenko, Yu. V.; Kirdin, A. I.

    2012-10-01

    A consistent theory of equilibrium states of same sign charges above the surface of liquid dielectric film located on solid substrate in the presence of external attracting constant electric field is proposed. The approach to the development of the theory is based on the Thomas-Fermi model generalized to the systems under consideration and on the variational principle. The using of self-consistent field model allows formulating a theory containing no adjustable constants. In the framework of the variational principle we obtain the self-consistency equations for the parameters describing the system: the distribution function of charges above the liquid dielectric surface, the electrostatic field potentials in all regions of the system and the surface profile of the liquid dielectric. The self-consistency equations are used to describe the phase transition associated with the formation of spatially periodic structures in the system of charges on liquid dielectric surface. Assuming the non-degeneracy of the gas of charges above the surface of liquid dielectric film the solutions of the self-consistency equations near the critical point are obtained. In the case of the symmetric phase we obtain the expressions for the potentials and electric fields in all regions of the studied system. The distribution of the charges above the surface of liquid dielectric film for the symmetric phase is derived. The system parameters of the phase transition to nonsymmetric phase - the states with a spatially periodic ordering are obtained. We derive the expression determining the period of two-dimensional lattice as a function of physical parameters of the problem - the temperature, the external attractive electric field, the number of electrons per unit of the flat surface area of the liquid dielectric, the density of the dielectric, its surface tension and permittivity, and the permittivity of the solid substrate. The possibility of generalizing the developed theory in the case of

  11. Two-dimensional (2D) infrared correlation study of the structural characterization of a surface immobilized polypeptide film stimulated by pH

    NASA Astrophysics Data System (ADS)

    Chae, Boknam; Son, Seok Ho; Kwak, Young Jun; Jung, Young Mee; Lee, Seung Woo

    2016-11-01

    The pH-induced structural changes to surface immobilized poly (L-glutamic acid) (PLGA) films were examined by Fourier transform infrared (FTIR) spectroscopy and two-dimensional (2D) correlation analysis. Significant spectral changes were observed in the FTIR spectra of the surface immobilized PLGA film between pH 6 and 7. The 2D correlation spectra constructed from the pH-dependent FTIR spectra of the surface immobilized PLGA films revealed the spectral changes induced by the alternations of the protonation state of the carboxylic acid group in the PLGA side chain. When the pH was increased from 6 to 8, weak spectral changes in the secondary structure of the PLGA main chain were induced by deprotonation of the carboxylic acid side group.

  12. All-epitaxial, lithographically defined, current- and mode-confined vertical-cavity surface-emitting laser based on selective interfacial fermi-level pinning

    SciTech Connect

    Ahn, J.; Lu, D.; Deppe, D.G.

    2005-01-10

    An approach is presented to fabricate a current- and mode-confined vertical-cavity surface-emitting laser that is all-epitaxial and lithographically defined. The device uses selective Fermi level pinning to self-align the electrical injection to a mode-confining intracavity phase-shifting mesa.

  13. Remembering Fermi

    SciTech Connect

    Cronin, James

    2005-03-30

    A combination of the discovery of nuclear fission and the circumstances of the 2nd World War brought Enrico Fermi to Chicago, where he led the team that produced the first controlled, self-sustained nuclear chain reaction. Following the war in 1945 Chancellor Hutchins, William Zachariasen, and Walter Bartky convinced Fermi to accept a professorship at the University of Chicago, where the Institute for Nuclear Studies was established. Fermi served as the leading figure in surely the greatest collection of scientists the world has ever seen. Fermi's tenure at Chicago was cut short by his death in 1954. My talk will concentrate on the years 1945-54. Examples of his research notebooks, his speeches, his teaching, and his correspondence will be discussed.

  14. Zeeman-driven Lifshitz transition: a model for the experimentally observed Fermi-surface reconstruction in YbRh2Si2.

    PubMed

    Hackl, Andreas; Vojta, Matthias

    2011-04-01

    The heavy-fermion metal YbRh(2)Si(2) displays a field-driven quantum phase transition where signatures of a Fermi-surface reconstruction have been identified, often interpreted as a breakdown of the Kondo effect. We argue that instead many properties of the material can be consistently described by assuming a Zeeman-driven Lifshitz transition of narrow heavy-fermion bands. Using a suitable quasiparticle model, we find a smeared jump in the Hall constant and lines of maxima in susceptibility and specific heat, very similar to experimental data. An intermediate non-Fermi-liquid regime emerges due to the small effective Fermi energy near the transition. Further experiments to discriminate the different scenarios are proposed.

  15. Effect of hole doping on the electronic structure and the Fermi surface in the Hubbard model within norm-conserving cluster pertubation theory

    SciTech Connect

    Nikolaev, S. V. Ovchinnikov, S. G.

    2012-01-15

    The concentration dependences of the band structure, spectral weight, density of states, and Fermi surface in the paramagnetic state are studied in the Hubbard model within cluster pertubation theory with 2 Multiplication-Sign 2 clusters. Representation of the Hubbard X operators makes it possible to control conservation of the spectral weight in constructing cluster perturbation theory. The calculated value of the ground-state energy is in good agreement with the results obtained using nonperturbative methods such as the quantum Monte Carlo method, exact diagonalization of a 4 Multiplication-Sign 4 cluster, and the variational Monte Carlo method. It is shown that in the case of hole doping, the states in the band gap (in-gap states) lie near the top of the lower Hubbard band for large values of U and near the bottom of the upper band for small U. The concentration dependence of the Fermi surface strongly depends on hopping to second (t Prime ) and third (t Double-Prime ) neighbors. For parameter values typical of HTSC cuprates, the existence of three concentration regions with different Fermi surfaces is demonstrated. It is shown that broadening of the spectral electron density with an energy resolution typical of contemporary ARPES leads to a pattern of arcs with a length depending on the concentration. Only an order-of-magnitude decrease in the linewidth makes it possible to obtain the true Fermi surface from the spectral density. The kinks associated with strong electron correlations are detected in the dispersion relation below the Fermi level.

  16. Surface origin of quasi-2D Shubnikov–de Haas oscillations in Bi{sub 2}Te{sub 2}Se

    SciTech Connect

    Kapustin, A. A. Stolyarov, V. S.; Bozhko, S. I.; Borisenko, D. N.; Kolesnikov, N. N.

    2015-08-15

    Transport measurements at liquid helium temperatures were done on a number of Bi{sub 2}Te{sub 2}Se samples with thicknesses ranging from 30 to 200 μm in order to detect surface states. In each sample we observed Shubnikov–de Haas (SdH) oscillations and sublinear dependence of off-diagonal component of magnetoresistance tensor on magnetic field. The periods of SdH oscillations in inverse magnetic field were found to be the same within 15%. The positions of SdH oscillations are determined by the normal to surface component of magnetic field. We found that the measured conductivity can be well described by a model with two groups of electrons, 2D and 3D. The conductivity of 2D electrons was found to be relatively weakly varying from sample to sample and not depending on thickness in a systematic manner. This behavior can be explained only by their localization on the surface. Comparison of the results of magnetotransport measurements with our scanning tunneling spectroscopy results on atomically smooth Bi{sub 2}Te{sub 2}Se surface in ultrahigh vacuum led us to conclude that the surface electrons are separated from the bulk electrons by a depletion layer approximately 100 nm thick. This effect could provide the dominant contribution of surface electrons to conductivity in samples with thicknesses less than 200 nm.

  17. Fermi surface-Brillouin-zone-induced pseudogap in γ-Mg17Al12 and a possible stabilization mechanism of β-Al3Mg2

    NASA Astrophysics Data System (ADS)

    Mizutani, U.; Kondo, Y.; Nishino, Y.; Inukai, M.; Feuerbacher, M.; Sato, H.

    2010-12-01

    The electronic structure of γ phase in the system Mg17Al12 containing 58 atoms per unit cell with space group I\\bar {4}3m has been calculated by using the WIEN2k-FLAPW program package. A pseudogap is found across the Fermi level. The FLAPW-Fourier spectra at the symmetry points N and Γ of the bcc Brillouin zone revealed that electronic states across the Fermi level at these symmetry points are dominated by |G|2 = 26 and 24 states corresponding to centers of {510} + {431} and {422} zone planes, respectively. The 1253-wave nearly-free-electron (NFE) band calculations identified that a combination of the two Fermi surface-Brillouin-zone (FsBz) interactions associated with |G|2 = 26 and 24 account well for the observed DOS pseudogap in γ-Mg17Al12, most likely leading to the stabilization of this complex metallic compound. The β-Al3Mg2 containing 1178 atoms per cubic unit cell is suggested to be stabilized by satisfying the Hume-Rothery matching condition expressed in terms of e/uc, the number of electrons per unit cell, versus critical |G|2. A critical |G|2 is predicted to be 200 in β-Al3Mg2, which results in 84 Brillouin zone planes interacting almost simultaneously with a more or less spherical Fermi surface.

  18. Electronic liquid-crystal phases, symmetry breaking and Fermi-surface reconstruction in YBa2Cu3O6+x

    NASA Astrophysics Data System (ADS)

    Hinkov, Vladimir

    2009-03-01

    The physics of underdoped cuprates is governed by strong correlations and phase competition, and its understanding remains one of the challenges of condensed-matter research. Here we will discuss our systematic doping- and temperature-dependent neutron-scattering investigation of the spin correlations in underdoped YBa2Cu3O6+x (YBCO) in the context of various proposed symmetry-breaking phases. In YBCO6.45 (Tc=35 K), we observe the spontaneous onset of a one-dimensional, incommensurate (IC) modulation of the low-energy (<10 meV) spin excitations below T˜150 K, Hinkov et al., Science 319, 597 (2008). We interpret our finding as the occurrence of an electronic liquid-crystal phase breaking C4-symmetry, as predicted by Kivelson et al., Nature 393, 550 (1998). Below T˜30 K, we observe the onset of quasi-static spin-correlations with the same IC geometry as the low-energy spin excitations. Their intensity is doubled by the application of a magnetic field of 15 T. First of all, this resolves a long-standing discrepancy with the La2-x(Sr,Ba)xCuO4 family where field-dependent, IC quasi-static spin correlations were reported before (Lake et al., Nature 415, 299 (2002)). More importantly, our results show how the recently reported quantum oscillations in high magnetic fields in YBa2Cu3O6.5 (Doiron-Leyraud et al., Nature 447, 565 (2007)) can be understood in terms of a Fermi-surface reconstruction induced by IC spin modulations. In the lack of experimental evidence for such IC modulations, this mechanism has not been pursued in the past, although it was discussed as a straightforward explanation for Fermi-surface reconstruction. Finally, we will discuss YBCO with a Tc of 10 K. Compared to the previous example, there is an enhancement of the quasi-static spin-correlations. In addition, there is indication for incipient commensurate AF order in reminiscence of the AF parent compound.

  19. Small and nearly isotropic hole-like Fermi surfaces in LiFeAs detected through de Haas-van Alphen effect

    NASA Astrophysics Data System (ADS)

    Zeng, B.; Watanabe, D.; Zhang, Q. R.; Li, G.; Besara, T.; Siegrist, T.; Xing, L. Y.; Wang, X. C.; Jin, C. Q.; Goswami, P.; Johannes, M. D.; Balicas, L.

    2013-10-01

    LiFeAs is unique among the arsenic based Fe-pnictide superconductors because it is the only nearly stoichiometric compound which does not exhibit magnetic order. This is at odds with electronic structure calculations which find a very stable magnetic state and predict cylindrical hole- and electron-like Fermi surface sheets whose geometry suggests spin fluctuations and a possible instability toward long-range ordering at the nesting vector. In fact, a complex magnetic phase diagram is indeed observed in the isostructural NaFeAs compound. Previous angle-resolved photoemission (ARPES) experiments revealed the existence of both hole and electron-like surfaces, but with rather distinct cross-sectional areas and an absence of the nesting that is thought to underpin both magnetic order and superconductivity in the pnictide family of superconductors. These ARPES observations were challenged by subsequent de Haas-van Alphen (dHvA) measurements which detected a few, electron-like Fermi surface sheets in rough agreement with the original band calculations. Here, we show a detailed dHvA study unveiling additional, small and nearly isotropic Fermi surface sheets in LiFeAs single crystals, which ought to correspond to hole-like orbits, as previously observed by ARPES. Therefore, our results reconcile the apparent discrepancy between ARPES and the previous dHvA results. The small size of these Fermi surface pockets suggests a prominent role for the electronic correlations in LiFeAs. The absence of gap nodes, in combination with the coexistence of quasi-two-dimensional and three-dimensional Fermi surfaces, favor an s-wave pairing symmetry for LiFeAs. But similar electron-like Fermi surfaces combined with very different hole pockets between LiFeAs and LiFeP suggest that the nodes in the gap function of LiFeP might be located on the hole pockets. This would be difficult to reconcile with the current understanding of the s± scenario.

  20. Calibration of Modulation Transfer Function of Surface Profilometers with 1D and 2D Binary Pseudo-random Array Standards

    SciTech Connect

    Yashchuk, Valeriy V.; McKinney, Wayne R.; Takacs, Peter Z.

    2008-05-19

    We suggest and describe the use of a binary pseudo-random grating as a standard test surface for calibration of the modulation transfer function of microscopes. Results from calibration of a MicromapTM-570 interferometric microscope are presented.

  1. Sensitivities of Tropical Cyclones to Surface Friction and the Coriolis Parameter in a 2-D Cloud-Resolving Model

    NASA Technical Reports Server (NTRS)

    Chao, Winston C.; Chen, Baode; Tao, Wei-Kuo; Lau, William K. M. (Technical Monitor)

    2002-01-01

    The sensitivities to surface friction and the Coriolis parameter in tropical cyclogenesis are studied using an axisymmetric version of the Goddard cloud ensemble model. Our experiments demonstrate that tropical cyclogenesis can still occur without surface friction. However, the resulting tropical cyclone has very unrealistic structure. Surface friction plays an important role of giving the tropical cyclones their observed smaller size and diminished intensity. Sensitivity of the cyclogenesis process to surface friction. in terms of kinetic energy growth, has different signs in different phases of the tropical cyclone. Contrary to the notion of Ekman pumping efficiency, which implies a preference for the highest Coriolis parameter in the growth rate if all other parameters are unchanged, our experiments show no such preference.

  2. Controlled calculation of the thermal conductivity for a spinon Fermi surface coupled to a U(1) gauge field

    SciTech Connect

    Freire, Hermann

    2014-10-15

    Motivated by recent transport measurements on the candidate spin-liquid phase of the organic triangular lattice insulator EtMe{sub 3}Sb[Pd(dmit){sub 2}]{sub 2}, we perform a controlled calculation of the thermal conductivity at intermediate temperatures in a spin liquid system where a spinon Fermi surface is coupled to a U(1) gauge field. The present computation builds upon the double expansion approach developed by Mross et al. (2010) for small ϵ=z{sub b}−2 (where z{sub b} is the dynamical critical exponent of the gauge field) and large number of fermionic species N. Using the so-called memory matrix formalism that most crucially does not assume the existence of well-defined quasiparticles at low energies in the system, we calculate the temperature dependence of the thermal conductivity κ of this model due to non-critical Umklapp scattering of the spinons for a finite N and small ϵ. Then we discuss the physical implications of such theoretical result in connection with the experimental data available in the literature.

  3. Latent instabilities in metallic LaNiO₃ films by strain control of Fermi-surface topology

    DOE PAGES

    Yoo, Hyang Keun; Hyun, Seung Ill; Moreschini, Luca; ...

    2015-03-04

    Strain control is one of the most promising avenues to search for new emergent phenomena in transition metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO₃ (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized eg-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the kz-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting. A FSmore » superstructure withQ₁ = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q₂ = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins« less

  4. Latent instabilities in metallic LaNiO₃ films by strain control of Fermi-surface topology

    SciTech Connect

    Yoo, Hyang Keun; Hyun, Seung Ill; Moreschini, Luca; Kim, Hyeong -Do; Chang, Young Jun; Sohn, Chang Hee; Jeong, Da Woon; Sinn, Soobin; Kim, Yong Su; Bostwick, Aaron; Rotenberg, Eli; Shim, Ji Hoon; Noh, Tae Won

    2015-03-04

    Strain control is one of the most promising avenues to search for new emergent phenomena in transition metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO₃ (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized eg-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the kz-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting. A FS superstructure withQ₁ = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q₂ = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins

  5. Latent instabilities in metallic LaNiO3 films by strain control of Fermi-surface topology

    NASA Astrophysics Data System (ADS)

    Yoo, Hyang Keun; Hyun, Seung Ill; Moreschini, Luca; Kim, Hyeong-Do; Chang, Young Jun; Sohn, Chang Hee; Jeong, Da Woon; Sinn, Soobin; Kim, Yong Su; Bostwick, Aaron; Rotenberg, Eli; Shim, Ji Hoon; Noh, Tae Won

    2015-03-01

    Strain control is one of the most promising avenues to search for new emergent phenomena in transition-metal-oxide films. Here, we investigate the strain-induced changes of electronic structures in strongly correlated LaNiO3 (LNO) films, using angle-resolved photoemission spectroscopy and the dynamical mean-field theory. The strongly renormalized eg-orbital bands are systematically rearranged by misfit strain to change its fermiology. As tensile strain increases, the hole pocket centered at the A point elongates along the kz-axis and seems to become open, thus changing Fermi-surface (FS) topology from three- to quasi-two-dimensional. Concomitantly, the FS shape becomes flattened to enhance FS nesting. A FS superstructure with Q1 = (1/2,1/2,1/2) appears in all LNO films, while a tensile-strained LNO film has an additional Q2 = (1/4,1/4,1/4) modulation, indicating that some instabilities are present in metallic LNO films. Charge disproportionation and spin-density-wave fluctuations observed in other nickelates might be their most probable origins.

  6. de Haas-van Alphen studies and Fermi surface properties of organic superconductors (ET)[sub 2]X

    SciTech Connect

    Wosnitza, J. . Physikalisches Inst.); Crabtree, G.W.; Williams, J.M.; Wang, H.H.; Carlson, K.D.; Geiser, U. )

    1993-04-01

    de Haas-van Alphen (dHvA) measurements of organic superconductors (ET)[sub 2]X, where ET stands for bis(ethylene)dithiotetrathiafulvalene (or BEDT-TTF) and X = IBr[sub 2], (NH[sub 4])Hg(SCN)[sub 4] and Cu(NCS)[sub 2] are reported. The strong two-dimensionality of the Fermi surface (FS) is clearly seen by the perfect 1/cos([Theta])-behavior of the dHvA frequency. The distinctive kind of beating and the angular dependence of the dHvA signal in [beta]-(ET)[sub 2]IBr[sub 2] gives clear evidence for a lightly corrugated structure of the FS. Due to the nearly cylinder-shape of the FS the bare band structure effective mass, m[sub b], also shows a 1/cos([Theta])-dependence which is responsible for spin splitting zeros at certain angles. At these points, where the fundamental amplitude of the dHvA signal is vanishing, m[sub b] could exactly be determined and by comparison with the independently measured cyclotron effective mass the electron-phonon coupling constant could be estimated. 17 refs, 5 figs.

  7. de Haas-van Alphen studies and Fermi surface properties of organic superconductors (ET){sub 2}X

    SciTech Connect

    Wosnitza, J.; Crabtree, G.W.; Williams, J.M.; Wang, H.H.; Carlson, K.D.; Geiser, U.

    1993-04-01

    de Haas-van Alphen (dHvA) measurements of organic superconductors (ET){sub 2}X, where ET stands for bis(ethylene)dithiotetrathiafulvalene (or BEDT-TTF) and X = IBr{sub 2}, (NH{sub 4})Hg(SCN){sub 4} and Cu(NCS){sub 2} are reported. The strong two-dimensionality of the Fermi surface (FS) is clearly seen by the perfect 1/cos({Theta})-behavior of the dHvA frequency. The distinctive kind of beating and the angular dependence of the dHvA signal in {beta}-(ET){sub 2}IBr{sub 2} gives clear evidence for a lightly corrugated structure of the FS. Due to the nearly cylinder-shape of the FS the bare band structure effective mass, m{sub b}, also shows a 1/cos({Theta})-dependence which is responsible for spin splitting zeros at certain angles. At these points, where the fundamental amplitude of the dHvA signal is vanishing, m{sub b} could exactly be determined and by comparison with the independently measured cyclotron effective mass the electron-phonon coupling constant could be estimated. 17 refs, 5 figs.

  8. Complete Fermi Surface and Surface State in WTe2 Revealed by High-Resolution Laser-Based Angle-Resolved Photoemission Spectroscopy

    NASA Astrophysics Data System (ADS)

    Wang, Chenlu; Zhang, Yan; Liu, Guodong; Mao, Zhiqiang; He, Shaolong; Zhao, Lin; Chen, Chuangtian; Xu, Zuyan; Zhou, Xingjiang

    WTe2, an unique transition metal dichalcogenide, attracts considerable attention recently, which shows an extremely large magnetoresistance (MR) with no saturation under very high field. In this talk, we will present our high resolution laser-ARPES study on WTe2. Our distinctive ARPES system is equipped with the VUV laser and the time-of-flight (TOF) electron energy analyzer, being featured by super-high energy resolution, simultaneous data acquisition for two-dimensional momentum space and much reduced nonlinearity effect. With this advanced apparatus, the very high quality of electronic structure data are obtained for WTe2 which gives a full picture of the Fermi surface. Meanwhile, the obtained systematic temperature dependence of its electronic state leads us to a better understanding on the origin of large magnetoresistance in WTe2.

  9. Surface plasmon hurdles leading to a strongly localized giant field enhancement on two-dimensional (2D) metallic diffraction gratings.

    PubMed

    Brûlé, Yoann; Demésy, Guillaume; Gralak, Boris; Popov, Evgeny

    2015-04-06

    An extensive numerical study of diffraction of a plane monochromatic wave by a single gold cone on a plane gold substrate and by a periodical array of such cones shows formation of curls in the map of the Poynting vector. They result from the interference between the incident wave, the wave reflected by the substrate, and the field scattered by the cone(s). In case of a single cone, when going away from its base along the surface, the main contribution in the scattered field is given by the plasmon surface wave (PSW) excited on the surface. As expected, it has a predominant direction of propagation, determined by the incident wave polarization. Two particular cones with height approximately 1/6 and 1/3 of the wavelength are studied in detail, as they present the strongest absorption and field enhancement when arranged in a periodic array. While the PSW excited by the smaller single cone shows an energy flux globally directed along the substrate surface, we show that curls of the Poynting vector generated with the larger cone touch the diopter surface. At this point, their direction is opposite to the energy flow of the PSW, which is then forced to jump over the vortex regions. Arranging the cones in a two-dimensional subwavelength periodic array (diffraction grating), supporting a specular reflected order only, resonantly strengthens the field intensity at the tip of cones and leads to a field intensity enhancement of the order of 10 000 with respect to the incident wave intensity. The enhanced field is strongly localized on the rounded top of the cones. It is accompanied by a total absorption of the incident light exhibiting large angular tolerances. This strongly localized giant field enhancement can be of much interest in many applications, including fluorescence spectroscopy, label-free biosensing, surface-enhanced Raman scattering (SERS), nonlinear optical effects and photovoltaics.

  10. Vortex cores and vortex motion in superconductors with anisotropic Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Galvis, J. A.; Herrera, E.; Guillamón, I.; Vieira, S.; Suderow, H.

    2017-02-01

    Explaning static and dynamic properties of the vortex lattice in anisotropic superconductors requires a careful characterization of vortex cores. The vortex core contains Andreev bound states whose spatial extension depends on the anisotropy of the electronic band-structure and superconducting gap. This might have an impact on the anisotropy of the superconducting properties and on vortex dynamics. Here we briefly summarize basic concepts to understand anisotropic vortex cores and review vortex core imaging experiments. We further discuss moving vortex lattices and the influence of vortex core shape in vortex motion. We find vortex motion in highly tilted magnetic fields. We associate vortex motion to the vortex entry barrier and the screening currents at the surface. We find preferential vortex motion along the main axis of the vortex lattice. After travelling integers of the intervortex distance, we find that vortices move more slowly due to the washboard potential of the vortex lattice.

  11. Surface Plasmon Resonances in 1D and 2D Arrays of Metal Nanoparticles for the Control of Enhanced Spectroscopies

    DTIC Science & Technology

    2011-01-24

    currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) 2 . REPORT TYPE 3. DATES...SPECTROSCOPIES FA9550-09-1-0579 Noguez, Cecilia Roman-Velazquez, Carlos E. Angulo, Ali M. Instituto de Fisica Universidad Nacional Autonoma de Mexico...representation, nanoshells, nanospheres U U U SAR 2 Cecilia Noguez +52 (55) 5622 5106 Final Technical Report Grant/Contract Title: SURFACE PLASMON

  12. A COUPLED 2 × 2D BABCOCK–LEIGHTON SOLAR DYNAMO MODEL. I. SURFACE MAGNETIC FLUX EVOLUTION

    SciTech Connect

    Lemerle, Alexandre; Charbonneau, Paul; Carignan-Dugas, Arnaud E-mail: paulchar@astro.umontreal.ca

    2015-09-01

    The need for reliable predictions of the solar activity cycle motivates the development of dynamo models incorporating a representation of surface processes sufficiently detailed to allow assimilation of magnetographic data. In this series of papers we present one such dynamo model, and document its behavior and properties. This first paper focuses on one of the model’s key components, namely surface magnetic flux evolution. Using a genetic algorithm, we obtain best-fit parameters of the transport model by least-squares minimization of the differences between the associated synthetic synoptic magnetogram and real magnetographic data for activity cycle 21. Our fitting procedure also returns Monte Carlo-like error estimates. We show that the range of acceptable surface meridional flow profiles is in good agreement with Doppler measurements, even though the latter are not used in the fitting process. Using a synthetic database of bipolar magnetic region (BMR) emergences reproducing the statistical properties of observed emergences, we also ascertain the sensitivity of global cycle properties, such as the strength of the dipole moment and timing of polarity reversal, to distinct realizations of BMR emergence, and on this basis argue that this stochasticity represents a primary source of uncertainty for predicting solar cycle characteristics.

  13. A 2D Gaussian-Beam-Based Method for Modeling the Dichroic Surfaces of Quasi-Optical Systems

    NASA Astrophysics Data System (ADS)

    Elis, Kevin; Chabory, Alexandre; Sokoloff, Jérôme; Bolioli, Sylvain

    2016-08-01

    In this article, we propose an approach in the spectral domain to treat the interaction of a field with a dichroic surface in two dimensions. For a Gaussian beam illumination of the surface, the reflected and transmitted fields are approximated by one reflected and one transmitted Gaussian beams. Their characteristics are determined by means of a matching in the spectral domain, which requires a second-order approximation of the dichroic surface response when excited by plane waves. This approximation is of the same order as the one used in Gaussian beam shooting algorithm to model curved interfaces associated with lenses, reflector, etc. The method uses general analytical formulations for the GBs that depend either on a paraxial or far-field approximation. Numerical experiments are led to test the efficiency of the method in terms of accuracy and computation time. They include a parametric study and a case for which the illumination is provided by a horn antenna. For the latter, the incident field is firstly expressed as a sum of Gaussian beams by means of Gabor frames.

  14. A model of adsorption of albumin on the implant surface titanium and titanium modified carbon coatings (MWCNT-EPD). 2D correlation analysis

    NASA Astrophysics Data System (ADS)

    Wesełucha-Birczyńska, Aleksandra; Stodolak-Zych, Ewa; Piś, Wojciech; Długoń, Elżbieta; Benko, Aleksandra; Błażewicz, Marta

    2016-11-01

    Common materials used as orthopedic implants are titanium and its alloys. To improve its compatibility with the environment of a living organism titanium implant surfaces are covered with bioactive layers of MWCNT. During the insertion into a living organism such material is exposed to direct contact with the patient's blood, which includes proteins - eg. albumin. The adsorption of albumin may constitute one of the early stages of implant surface modification serving cell adhesion. An analysis of this phenomenon in terms of the kinetics of deposition of protein on the surface of the implant confirms its biocompatibility in vivo. The proposed working model of the adsorption of albumin allows for choosing the best of time for the protein to form a stable connection with the surface of the titanium implant. Traditional methods of materials engineering and chemistry allow for the obtaining of information about the presence of a protein on the surface (UV-Vis, the wettability). The application of 2D correlation analysis, in turn, gains insight into the dynamics of the changes associated with the deposition of protein (the formation of a uniform layer, the change in conformation). This analysis has allowed for the selection of an optimal time of protein adsorption to the surface of the implant. Better compatibility with the body of the implant provides its modification by introducing layers that accelerate the material-tissue interactions. Such a composition is a layer of carbon nanotubes (MWCNTs) deposited on titanium by the electrophoretic (EPD) method. Using Raman spectroscopy and analyzing the spectra with the 2D correlation method it is possible to gain insight into the molecular structure of this layer. Our studies indicate that albumin in contact with the surface of titanium has obtained stable conformation after 30 min (confirmed by: UV-Vis, Raman). Shifts of the CH2, CH3 stretching bands position as well as an analysis of the amide I band confirms this

  15. Entanglement in ground and excited states of gapped free-fermion systems and their relationship with Fermi surface and thermodynamic equilibrium properties.

    PubMed

    Storms, Michelle; Singh, Rajiv R P

    2014-01-01

    We study bipartite entanglement entropies in the ground and excited states of free-fermion models, where a staggered potential, μs, induces a gap in the spectrum. Ground-state entanglement entropies satisfy the "area law", and the "area-law" coefficient is found to diverge as a logarithm of the staggered potential, when the system has an extended Fermi surface at μs=0. On the square lattice, we show that the coefficient of the logarithmic divergence depends on the Fermi surface geometry and its orientation with respect to the real-space interface between subsystems and is related to the Widom conjecture as enunciated by Gioev and Klich [ Phys. Rev. Lett. 96 100503 (2006)]. For point Fermi surfaces in two-dimension, the "area-law" coefficient stays finite as μs→0. The von Neumann entanglement entropy associated with the excited states follows a "volume law" and allows us to calculate an entropy density function sV(e), which is substantially different from the thermodynamic entropy density function sT(e), when the lattice is bipartitioned into two equal subsystems but approaches the thermodynamic entropy density as the fraction of sites in the larger subsystem, that is integrated out, approaches unity.

  16. Growth of porous anodized alumina on the sputtered aluminum films with 2D-3D morphology for high specific surface area

    NASA Astrophysics Data System (ADS)

    Liao, M. W.; Chung, C. K.

    2014-08-01

    The porous anodic aluminum oxide (AAO) with high-aspect-ratio pore channels is widely used as a template for fabricating nanowires or other one-dimensional (1D) nanostructures. The high specific surface area of AAO can also be applied to the super capacitor and the supporting substrate for catalysis. The rough surface could be helpful to enhance specific surface area but it generally results in electrical field concentration even to ruin AAO. In this article, the aluminum (Al) films with the varied 2D-3D morphology on Si substrates were prepared using magnetron sputtering at a power of 50 W-185 W for 1 h at a working pressure of 2.5 × 10-1 Pa. Then, AAO was fabricated from the different Al films by means of one-step hybrid pulse anodizing (HPA) between the positive 40 V and the negative -2 V (1 s:1 s) for 3 min in 0.3 M oxalic acid at a room temperature. The microstructure and morphology of Al films were characterized by X-ray diffraction, scanning electron microscope and atomic force microscope, respectively. Some hillocks formed at the high target power could be attributed to the grain texture growth in the normal orientation of Al(1 1 1). The 3D porous AAO structure which is different from the conventional 2D planar one has been successfully demonstrated using HPA on the film with greatly rough hillock-surface formed at the highest power of 185 W. It offers a potential application of the new 3D AAO to high specific surface area devices.

  17. Section 1. Simulation of surface-water integrated flow and transport in two-dimensions: SWIFT2D user's manual

    USGS Publications Warehouse

    Schaffranek, Raymond W.

    2004-01-01

    A numerical model for simulation of surface-water integrated flow and transport in two (horizontal-space) dimensions is documented. The model solves vertically integrated forms of the equations of mass and momentum conservation and solute transport equations for heat, salt, and constituent fluxes. An equation of state for salt balance directly couples solution of the hydrodynamic and transport equations to account for the horizontal density gradient effects of salt concentrations on flow. The model can be used to simulate the hydrodynamics, transport, and water quality of well-mixed bodies of water, such as estuaries, coastal seas, harbors, lakes, rivers, and inland waterways. The finite-difference model can be applied to geographical areas bounded by any combination of closed land or open water boundaries. The simulation program accounts for sources of internal discharges (such as tributary rivers or hydraulic outfalls), tidal flats, islands, dams, and movable flow barriers or sluices. Water-quality computations can treat reactive and (or) conservative constituents simultaneously. Input requirements include bathymetric and topographic data defining land-surface elevations, time-varying water level or flow conditions at open boundaries, and hydraulic coefficients. Optional input includes the geometry of hydraulic barriers and constituent concentrations at open boundaries. Time-dependent water level, flow, and constituent-concentration data are required for model calibration and verification. Model output consists of printed reports and digital files of numerical results in forms suitable for postprocessing by graphical software programs and (or) scientific visualization packages. The model is compatible with most mainframe, workstation, mini- and micro-computer operating systems and FORTRAN compilers. This report defines the mathematical formulation and computational features of the model, explains the solution technique and related model constraints, describes the

  18. Size-selective 2D ordering of gold nanoparticles using surface topography of self-assembled diamide template.

    PubMed

    Sangeetha, Neralagatta M; Blanck, Christian; Nguyen, Thi Thanh Tam; Contal, Christophe; Mésini, Philippe J

    2012-10-23

    Size-selective organization of ~2 nm dodecanethiol stabilized gold nanoparticles (AuNPs) into periodic 1D arrays by using the surface topographical features of a soft template is described. The template consists of micrometer length nanotapes organized into nanosheets with periodic valleys running along their length and is generated by the hierarchical self-assembly of a diamide molecule (BHPB) in cyclohexane. The AuNP ordering achieved simply by mixing the preformed template with the readily available ~2 nm dodecanethiol stabilized AuNPs is comparable to those obtained using programmable DNA and functional block copolymers. The observed periodicity of the AuNP arrays provided valuable structural clues about the organization of nanotapes into nanosheets. Self-assembling BHPB molecules in the presence of AuNPs by heating and cooling the two components led to a comparatively disordered organization because the template structure was changed under these conditions. Moreover, the template could not order larger AuNPs (~5 nm) into a similar 1D array, owing to the steric restriction imposed by the dimension of the valleys on the template. Interestingly, this geometric constraint led to AuNP size sorting when a polydisperse sample (2.5 ± 0.9 nm) was used for organization, with AuNPs attached to the template edges being larger (≥2.2 ± 0.9 nm) than those associated to the inner valleys (1.6 ± 0.8 nm). This is a unique example of size-sorting induced by the surface topographical features of a soft template.

  19. Reduction of Fermi level pinning at Au-MoS2 interfaces by atomic passivation on Au surface

    NASA Astrophysics Data System (ADS)

    Min, Kyung-Ah; Park, Jinwoo; Wallace, Robert M.; Cho, Kyeongjae; Hong, Suklyun

    2017-03-01

    Monolayer molybdenum disulfide (MoS2), which is a semiconducting material with direct band gap of ˜1.8 eV, has drawn much attention for application in field effect transistors (FETs). In this connection, it is very important to understand the Fermi level pinning (FLP) which occurs at metal-semiconductor interfaces. It is known that MoS2 has an n-type contact with Au, which is a high work function metal, representing the strong FLP at Au-MoS2 interfaces. However, such FLP can obstruct the attainment of high performance of field effect devices. In this study, we investigate the reduction of FLP at Au-MoS2 interfaces by atomic passivation on Au(111) using first-principles calculations. To reduce the FLP at Au-MoS2 interfaces, we consider sulfur, oxygen, nitrogen, fluorine, and hydrogen atoms that can passivate the surface of Au(111). Calculations show that passivating atoms prevent the direct contact between Au(111) and MoS2, and thus FLP at Au-MoS2 interfaces is reduced by weak interaction between atom-passivated Au(111) and MoS2. Especially, FLP is greatly reduced at sulfur-passivated Au-MoS2 interfaces with the smallest binding energy. Furthermore, fluorine-passivated Au(111) can form ohmic contact with MoS2, representing almost zero Schottky barrier height (SBH). We suggest that SBH can be controlled depending on the passivating atoms on Au(111).

  20. Blind test of methods for obtaining 2-D near-surface seismic velocity models from first-arrival traveltimes

    USGS Publications Warehouse

    Zelt, Colin A.; Haines, Seth; Powers, Michael H.; Sheehan, Jacob; Rohdewald, Siegfried; Link, Curtis; Hayashi, Koichi; Zhao, Don; Zhou, Hua-wei; Burton, Bethany L.; Petersen, Uni K.; Bonal, Nedra D.; Doll, William E.

    2013-01-01

    Seismic refraction methods are used in environmental and engineering studies to image the shallow subsurface. We present a blind test of inversion and tomographic refraction analysis methods using a synthetic first-arrival-time dataset that was made available to the community in 2010. The data are realistic in terms of the near-surface velocity model, shot-receiver geometry and the data's frequency and added noise. Fourteen estimated models were determined by ten participants using eight different inversion algorithms, with the true model unknown to the participants until it was revealed at a session at the 2011 SAGEEP meeting. The estimated models are generally consistent in terms of their large-scale features, demonstrating the robustness of refraction data inversion in general, and the eight inversion algorithms in particular. When compared to the true model, all of the estimated models contain a smooth expression of its two main features: a large offset in the bedrock and the top of a steeply dipping low-velocity fault zone. The estimated models do not contain a subtle low-velocity zone and other fine-scale features, in accord with conventional wisdom. Together, the results support confidence in the reliability and robustness of modern refraction inversion and tomographic methods.

  1. Topological change of the Fermi surface in ternary iron-pnictides with reduced c/a ratio: A dHvA study of CaFe2P2

    SciTech Connect

    Coldea, Amalia I.; Andrew, C.M.J.; Analytis, J.G.; McDonald, R.D.; Bangura, A.F.; Chu, J.-H.; Fisher, I.R.; Carrington, A.; /Bristol U.

    2010-05-26

    We report a de Haas-van Alphen effect study of the Fermi surface of CaFe{sub 2}P{sub 2} using low temperature torque magnetometry up to 45 T. This system is a close structural analogue of the collapsed tetragonal non-magnetic phase of CaFe{sub 2}As{sub 2}. We find the Fermi surface of CaFe{sub 2}P{sub 2} to differ from other related ternary phosphides in that its topology is highly dispersive in the c-axis, being three-dimensional in character and with identical mass enhancement on both electron and hole pockets ({approx} 1.5). The dramatic change in topology of the Fermi surface suggests that in a state with reduced (c/a) ratio, when bonding between pnictogen layers becomes important, the Fermi surface sheets are unlikely to be nested.

  2. 2D quantum gravity on compact Riemann surfaces and two-loop partition function: A first principles approach

    NASA Astrophysics Data System (ADS)

    Bilal, Adel; Leduc, Laetitia

    2015-07-01

    We study two-dimensional quantum gravity on arbitrary genus Riemann surfaces in the Kähler formalism where the basic quantum field is the (Laplacian of the) Kähler potential. We do a careful first-principles computation of the fixed-area partition function Z [ A ] up to and including all two-loop contributions. This includes genuine two-loop diagrams as determined by the Liouville action, one-loop diagrams resulting from the non-trivial measure on the space of metrics, as well as one-loop diagrams involving various counterterm vertices. Contrary to what is often believed, several such counterterms, in addition to the usual cosmological constant, do and must occur. We consistently determine the relevant counterterms from a one-loop computation of the full two-point Green's function of the Kähler field. Throughout this paper we use the general spectral cutoff regularization developed recently and which is well-suited for multi-loop computations on curved manifolds. At two loops, while all "unwanted" contributions to ln ⁡ (Z [ A ] / Z [A0 ]) correctly cancel, it appears that the finite coefficient of ln ⁡ (A /A0) does depend on the finite part of a certain counterterm coefficient, i.e. on the finite renormalization conditions one has to impose. There exists a choice that reproduces the famous KPZ-scaling, but it seems to be only one consistent choice among others. Maybe, this hints at the possibility that other renormalization conditions could eventually provide a way to circumvent the famous c = 1 barrier.

  3. Multiangular L-band Datasets for Soil Moisture and Sea Surface Salinity Retrieval Measured by Airborne HUT-2D Synthetic Aperture Radiometer

    NASA Astrophysics Data System (ADS)

    Kainulainen, J.; Rautiainen, K.; Seppänen, J.; Hallikainen, M.

    2009-04-01

    SMOS is the European Space Agency's next Earth Explorer satellite due for launch in 2009. It aims for global monitoring of soil moisture and ocean salinity utilizing a new technology concept for remote sensing: two-dimensional aperture synthesis radiometry. The payload of SMOS is Microwave Imaging Radiometer by Aperture Synthesis, or MIRAS. It is a passive instrument that uses 72 individual L-band receivers for measuring the brightness temperature of the Earth. From each acquisition, i.e. integration time or snapshot, MIRAS provides two-dimensional brightness temperature of the scene in the instrument's field of view. Thus, consecutive snapshots provide multiangular measurements of the target once the instrument passes over it. Depending on the position of the target in instrument's swath, the brightness temperature of the target at incidence angles from zero up to 50 degrees can be measured with one overpass. To support the development MIRAS instrument, its calibration, and soil moisture and sea surface salinity retrieval algorithm development, Helsinki University of Technology (TKK) has designed, manufactured and tested a radiometer which operates at L-band and utilizes the same two-dimensional methodology of interferometery and aperture synthesis as MIRAS does. This airborne instrument, called HUT-2D, was designed to be used on board the University's research aircraft. It provides multiangular measurements of the target in its field of view, which spans up to 30 degrees off the boresight of the instrument, which is pointed to the nadir. The number of independent measurements of each target point depends on the flight speed and altitude. In addition to the Spanish Airborne MIRAS demonstrator (AMIRAS), HUT-2D is the only European airborne synthetic aperture radiometer. This paper presents the datasets and measurement campaigns, which have been carried out using the HUT-2D radiometer and are available for the scientific community. In April 2007 HUT-2D participated

  4. Adsorption of gallium on GaN(0001) surface in ammonia-rich conditions: A new effect associated with the Fermi level position

    NASA Astrophysics Data System (ADS)

    Kempisty, Paweł; Strak, Paweł; Sakowski, Konrad; Krukowski, Stanisław

    2014-09-01

    Density functional theory (DFT) calculations were used to study GaN(0001) surface covered with NH3 admolecules and NH2 radicals, corresponding to physical conditions during GaN growth by hydride vapor phase epitaxy (HVPE) and metalorganic vapor phase epitaxy (MOVPE). Using larger representation of the surface i.e. slabs of lateral size 4×4, the effect of the doping was examined. It is shown that for specific surface coverage the electron counting (EC) rule is fulfilled so that the pinning of the Fermi level by surface states and band bending disappears. In this case, according to Krukowski et al. (2013) [14], the doping of the semiconductor (n- or p-type) and the related Fermi level are extremely important for stability of the surface and the adsorption/desorption processes. The difference in adsorption energies of gallium atoms at n- and p-type GaN(0001) surface exceeds the energy gap. This effect is observed in a narrow range of surface coverage, therefore cannot be detected in the calculations using small systems i.e. 2×2 slabs. This new phenomenon may be crucial for the growth of GaN and the incorporation of dopants and impurities into semiconductor crystals.

  5. Momentum density and 2D-ACAR experiments in YBa sub 2 Cu sub 3 O sub 7

    SciTech Connect

    Bansil, A. . Dept. of Physics); Smedskjaer, L.C. )

    1991-12-01

    We compare measured c-projected 2D-ACAR spectrum from an untwinned single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} with the corresponding band theory predictions. Many different one-dimensional sections through the spectrum are considered, together with the characteristic amplitudes and shapes of the spectral anisotropies, with a focus on identifying and delineating Fermi surface signatures in the spectra. The positron data clearly show several distinct features of the ridge Fermi surface predicted by the band theory, and give an indication of the pillbox Fermi sheet. The good agreement between theory and experiment suggests that the band theory framework based on the local density approximation (LDA) is capable of providing a substantially correct description of the momentum density and Fermiology of the normal ground state electronic structure of YBa{sub 2}Cu{sub 3}O{sub 7}.

  6. Xanthomonas citri subsp. citri surface proteome by 2D-DIGE: Ferric enterobactin receptor and other outer membrane proteins potentially involved in citric host interaction.

    PubMed

    Carnielli, Carolina Moretto; Artier, Juliana; de Oliveira, Julio Cezar Franco; Novo-Mansur, Maria Teresa Marques

    2017-01-16

    Xanthomonas citri subsp. citri (XAC) is the causative agent of citrus canker, a disease of great economic impact around the world. Understanding the role of proteins on XAC cellular surface can provide new insights on pathogen-plant interaction. Surface proteome was performed in XAC grown in vivo (infectious) and in vitro (non-infectious) conditions, by labeling intact cells followed by cellular lysis and direct 2D-DIGE analysis. Seventy-nine differential spots were analyzed by mass spectrometry. Highest relative abundance for in vivo condition was observed for spots containing DnaK protein, 60kDa chaperonin, conserved hypothetical proteins, malate dehydrogenase, phosphomannose isomerase, and ferric enterobactin receptors. Elongation factor Tu, OmpA-related proteins, Oar proteins and some Ton-B dependent receptors were found in spots decreased in vivo. Some proteins identified on XAC's surface in infectious condition and predicted to be cytoplasmic, such as DnaK and 60KDa chaperonin, have also been previously found at cellular surface in other microorganisms. This is the first study on XAC surface proteome and results point to mediation of molecular chaperones in XAC-citrus interaction. The approach utilized here can be applied to other pathogen-host interaction systems and help to achieve new insights in bacterial pathogenicity toward promising targets of biotechnological interest.

  7. Landau Theory of Helical Fermi Liquids.

    PubMed

    Lundgren, Rex; Maciejko, Joseph

    2015-08-07

    We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.

  8. Sensitivity of Fermi level position at Ga-polar, N-polar, and nonpolar m-plane GaN surfaces to vacuum and air ambient

    NASA Astrophysics Data System (ADS)

    Janicki, Łukasz; Ramírez-López, Manolo; Misiewicz, Jan; Cywiński, Grzegorz; Boćkowski, Michał; Muzioł, Grzegorz; Chèze, Caroline; Sawicka, Marta; Skierbiszewski, Czesław; Kudrawiec, Robert

    2016-05-01

    Ga-polar, N-polar, and nonpolar m-plane GaN UN+ structures have been examined in air and vacuum ambient by contactless electroreflectance (CER). This technique is very sensitive to the surface electric field that varies with the Fermi level position at the surface. For UN+ GaN structures [i.e., GaN (undoped)/GaN (n-type)/substrate], a homogeneous built-in electric field is expected in the undoped GaN layer that is manifested by Franz-Keldysh oscillation (FKO) in CER spectra. A clear change in FKO has been observed in CER spectra for N-polar and nonpolar m-plane structures when changing from air to vacuum ambient. This means that those surfaces are very sensitive to ambient atmosphere. In contrast to that, only a small change in FKO can be seen in the Ga-polar structure. This clearly shows that the ambient sensitivity of the Fermi level position at the GaN surface varies with the crystallographic orientation and is very high for N-polar and nonpolar m-plane surfaces. This feature of the N-polar and nonpolar m-plane surfaces can be very important for GaN-based devices grown on these crystallographic orientations and can be utilized in some of the devices, e.g., sensors.

  9. Anisotropic non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Sur, Shouvik; Lee, Sung-Sik

    2016-11-01

    We study non-Fermi-liquid states that arise at the quantum critical points associated with the spin density wave (SDW) and charge density wave (CDW) transitions in metals with twofold rotational symmetry. We use the dimensional regularization scheme, where a one-dimensional Fermi surface is embedded in (3 -ɛ ) -dimensional momentum space. In three dimensions, quasilocal marginal Fermi liquids arise both at the SDW and CDW critical points: the speed of the collective mode along the ordering wave vector is logarithmically renormalized to zero compared to that of Fermi velocity. Below three dimensions, however, the SDW and CDW critical points exhibit drastically different behaviors. At the SDW critical point, a stable anisotropic non-Fermi-liquid state is realized for small ɛ , where not only time but also different spatial coordinates develop distinct anomalous dimensions. The non-Fermi liquid exhibits an emergent algebraic nesting as the patches of Fermi surface are deformed into a universal power-law shape near the hot spots. Due to the anisotropic scaling, the energy of incoherent spin fluctuations disperse with different power laws in different momentum directions. At the CDW critical point, on the other hand, the perturbative expansion breaks down immediately below three dimensions as the interaction renormalizes the speed of charge fluctuations to zero within a finite renormalization group scale through a two-loop effect. The difference originates from the fact that the vertex correction antiscreens the coupling at the SDW critical point whereas it screens at the CDW critical point.

  10. 2D equation-of-state model for corona phase molecular recognition on single-walled carbon nanotube and graphene surfaces.

    PubMed

    Ulissi, Zachary W; Zhang, Jingqing; Sresht, Vishnu; Blankschtein, Daniel; Strano, Michael S

    2015-01-13

    Corona phase molecular recognition (CoPhMoRe) has been recently introduced as a means of generating synthetic molecular recognition sites on nanoparticle surfaces. A synthetic heteropolymer is adsorbed and confined to the surface of a nanoparticle, forming a corona phase capable of highly selective molecular recognition due to the conformational imposition of the particle surface on the polymer. In this work, we develop a computationally predictive model for analytes adsorbing onto one type of polymer corona phase composed of hydrophobic anchors on hydrophilic loops around a single-walled carbon nanotube (SWCNT) surface using a 2D equation of state that takes into consideration the analyte-polymer, analyte-nanoparticle, and polymer-nanoparticle interactions using parameters determined independently from molecular simulation. The SWCNT curvature is found to contribute weakly to the overall interaction energy, exhibiting no correlation for three of the corona phases considered, and differences of less than 5% and 20% over a larger curvature range for two other corona phases, respectively. Overall, the resulting model for this anchor-loop CoPhMoRe is able to correctly predict 83% of an experimental 374 analyte-polymer library, generating experimental fluorescence responses within 20% error of the experimental values. The modeling framework presented here represents an important step forward in the design of suitable polymers to target specific analytes.

  11. Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H2/D2 plasmas

    NASA Astrophysics Data System (ADS)

    Cartry, Gilles; Kogut, Dmitry; Achkasov, Kostiantyn; Layet, Jean-Marc; Farley, Thomas; Gicquel, Alix; Achard, Jocelyn; Brinza, Ovidiu; Bieber, Thomas; Khemliche, Hocine; Roncin, Philippe; Simonin, Alain

    2017-02-01

    This paper deals with a study of H‑/D‑ negative ion surface production on diamond in low pressure H2/D2 plasmas. A sample placed in the plasma is negatively biased with respect to plasma potential. Upon positive ion impacts on the sample, some negative ions are formed and detected according to their mass and energy by a mass spectrometer placed in front of the sample. The experimental methods developed to study negative ion surface production and obtain negative ion energy and angle distribution functions are first presented. Different diamond materials ranging from nanocrystalline to single crystal layers, either doped with boron or intrinsic, are then investigated and compared with graphite. The negative ion yields obtained are presented as a function of different experimental parameters such as the exposure time, the sample bias which determines the positive ion impact energy and the sample surface temperature. It is concluded from these experiments that the electronic properties of diamond materials, among them the negative electron affinity, seem to be favourable for negative-ion surface production. However, the negative ion yield decreases with the plasma induced defect density.

  12. Wind-tunnel experiments of turbulent flow over a surface-mounted 2-D block in a thermally-stratified boundary layer

    NASA Astrophysics Data System (ADS)

    Zhang, Wei; Markfort, Corey; Porté-Agel, Fernando

    2014-11-01

    Turbulent flows over complex surface topography have been of great interest in the atmospheric science and wind engineering communities. The geometry of the topography, surface roughness and temperature characteristics as well as the atmospheric thermal stability play important roles in determining momentum and scalar flux distribution. Studies of turbulent flow over simplified topography models, under neutrally stratified boundary-layer conditions, have provided insights into fluid dynamics. However, atmospheric thermal stability has rarely been considered in laboratory experiments, e.g., wind-tunnel experiments. Series of wind-tunnel experiments of thermally-stratified boundary-layer flow over a surface-mounted 2-D block, in a well-controlled boundary-layer wind tunnel, will be presented. Measurements using high-resolution PIV, x-wire/cold-wire anemometry and surface heat flux sensors were conducted to quantify the turbulent flow properties, including the size of the recirculation zone, coherent vortex structures and the subsequent boundary layer recovery. Results will be shown to address thermal stability effects on momentum and scalar flux distribution in the wake, as well as dominant mechanism of turbulent kinetic energy generation and consumption. The authors gratefully acknowledge funding from the Swiss National Foundation (Grant 200021-132122), the National Science Foundation (Grant ATM-0854766) and NASA (Grant NNG06GE256).

  13. Enrico Fermi

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Enrico Fermi was, of all the great physicists of the 20th century, among the most respected and admired. He was respected and admired because of his contributions to both theoretical and experimental physics, because of his leadership in discovering for mankind a powerful new source of energy, and above all, because of his personal character. He was always reliable and trustworthy. He had both of his feet on the ground all the time. He had great strength, but never threw his weight around. He did not play to the gallery. He did not practise one-up-manship. He exemplified, I always believe, the perfect Confucian gentleman...

  14. Quantum Oscillations from Fermi Arcs

    NASA Astrophysics Data System (ADS)

    Pereg-Barnea, Tamar; Refael, Gil; Franz, Marcel; Weber, Heidi; Seradjeh, Babak

    2009-03-01

    Recent experiments[1] in a variety of High Tc superconductors revel 1/B oscillations in the vortex-liquid state. The period of oscillations in underdoped samples is short and can be translated, via the Onsager relation to an area in k-space which makes up a few percents of the Brillouin zone. Quantum oscillations are usually thought of as arising from closed orbits in momentum space along the Fermi surface and are used to measure the Fermi vector. Thus, the observation of quantum oscillations in the cuprates seems to be at odds with the observation of Fermi arcs in ARPES experiments[2] due to their fragmented Fermi surface topology. In this talk we show that quantum oscillations can arise from a partially gapped Fermi surface. We adopt a phenomenological model of arcs which terminate at a regime with a superconducting gap of d-wave symmetry to describe the pseudo gap phase. Without invoking any additional order, quantization of energy is found well below the gap maximum. Semiclassically the quantization condition arises from closed orbits in real-space. When translated to momentum space, the area enclosed by the orbits is much smaller than that of the full Fermi surface. [1]N. Doiron-Leyaraud et al. nature 447, 565 (2007) [2]Kanigel et al. Nature Physics 2 447 (2006)

  15. Aqueous oxidation reaction enabled layer-by-layer corrosion of semiconductor nanoplates into single-crystalline 2D nanocrystals with single layer accuracy and ionic surface capping.

    PubMed

    Ji, Muwei; Xu, Meng; Zhang, Jun; Liu, Jiajia; Zhang, Jiatao

    2016-02-25

    A controllable aqueous oxidation reaction enabled layer-by-layer corrosion has been proposed to prepare high-quality two-dimensional (2D) semiconductor nanocrystals with single layer accuracy and well-retained hexagonal shapes. The appropriate oxidizing agent, such as H2O2, Fe(NO3)3, and HNO3, could not only corrode the layered-crystalline-structured Bi2Te3 nanoplates layer-by-layer to be a single quintuple layer, but also replace the organic barriers to be ionic ligands on the surface synergistically. AFM analysis was used to confirm the layer-by-layer exfoliation from the side to the center. Together with precise XRD, LRTEM and HRTEM characterizations, the controllable oxidation reaction enabled aqueous layer-by-layer corrosion mechanism has been studied.

  16. A quasi-classical trajectory study of the Cl + H2 (D2) reaction on a new BW3 potential energy surface

    NASA Astrophysics Data System (ADS)

    Shu-Bao, Dong; Er-Yin, Feng; Wu-Ying, Huang; Zhi-Feng, Cui

    2005-01-01

    Molecular reaction dynamics of Cl + H2 (D2) has been studied on the latest analytical potential energy surface called BW3 using the Monte Carlo quasi-classical trajectory method. Excitation functions, differential cross sections and angular distributions of HCl and DCl products have been calculated. The excitation functions of the Cl (2P3/2) + n-H2 and Cl(2P3/2) + n-D2 reactions are also studied. The results are compared with those of quasi-classical trajectory [M. Alagia et al.: Phys. Chem. Chem. Phys. 2 (2000); F. J. Aoiz et al.: J. Phys. Chem. 100 (1996)], quantum mechanical (QM) calculations [F. J. Aoiz et al.:J. Chem. Phys. 115 (2001)] and experimental data [S. H. Lee et al.: J. Chem. Phys. 110 (1999); F. Dong et al.: J. Chem. Phys. 115 (2001)]. Discussions are given to some new results.

  17. Thomas-Fermi and Thomas-Fermi-Dirac models in two-dimension - Effect of strong quantizing magnetic field

    NASA Astrophysics Data System (ADS)

    De, Sanchari; Chakrabarty, Somenath

    2017-01-01

    Using Thomas-Fermi (TF) and Thomas-Fermi-Dirac (TFD) models, we have investigated the properties of electron gas inside two-dimensional (2D) Wigner-Seitz (WS) cells in presence of a strong orthogonal quantizing magnetic field. The electron-electron Coulomb exchange interaction in quasi-2D case is obtained. The exact form of exchange term in 2D is derived making the width of the system tending to zero. Further, using the exchange term, the Thomas-Fermi-Dirac equation in 2D is established. It has been observed that only the ionized WS cell can have finite radius in the Thomas-Fermi model, even in presence of a strong quantizing magnetic field. On the other hand, in the Thomas-Fermi-Dirac model a neutral WS cell can have finite radius.

  18. Observation of an electron band above the Fermi level in FeTe{sub 0.55}Se{sub 0.45} from in-situ surface doping

    SciTech Connect

    Zhang, P.; Ma, J.; Qian, T.; Richard, P. Ding, H.; Xu, N.; Xu, Y.-M.; Fedorov, A. V.; Denlinger, J. D.; Gu, G. D.

    2014-10-27

    We used in-situ potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe{sub 0.55}Se{sub 0.45}. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily electron-doped KFe{sub 2−x}Se{sub 2} compound.

  19. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; A. Wylie; W. Quinlan

    2004-10-01

    One of the principal objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, microbial samples were collected from the Trusty Steed prospect area in Grand Traverse County, Michigan. The samples were analyzed using the Microbial Oil Surveying Technique (MOST) technique and revealed only a local (1-point) anomaly. A decision to resample over that point is pending, but drilling has been postponed for the time being. The main news this reporting period is that in the Bear Lake area, northwest Michigan, Federated Oil & Gas Properties' Charlich-Fauble 2-9HD horizontal lateral, has cumulative production of more than 72,000 barrels of oil and is still producing 50 to 75 bopd from a Silurian Niagaran reef reservoir eighteen months after the well was completed. Surface geochemical surveys conducted in the demonstration area were consistent with production results although the ultimate decision to drill was based on interpretation of conventional subsurface and 2D seismic data. The surface geochemical techniques employed were Solid Phase MicroExtraction (SPME) and MOST. The geochemical results have been submitted to World Oil for publication. New geochemical surveys are planned for November in the Springdale quadrangle in Manistee County, Michigan. These surveys will concentrate on sampling over the trace of the proposed horizontal wells rather than a broad grid survey.

  20. 2-D ACAR measurements of Ni/sub 3/A1

    SciTech Connect

    Smedskjaer, L.C.; DasGupta, A.; Legnini, D.G.; Stahulak, M.D.

    1987-07-01

    In connection with a detailed study of the electronic structure and stability of the aluminides (Ni,Fe)/sub 3/Al, 2-D ACAR positron annihilation measurements were made on a Ni/sub 3/Al single crystal to study the Fermi surface. The results for Ni/sub 3/Al have been compared with results for pure Ni. Strong similarities were found for the electronic structures of these materials. Theoretical calculations of the Fermi surface for Ni/sub 3/Al are in good agreement with the experimental results. The GAMMA/sub 16/ sheet, not previously observed in any experiment, has now been observed for the first time in Ni/sub 3/Al. 14 refs., 10 figs.

  1. Thermopower evidence for an abrupt Fermi surface change at the quantum critical point of YbRh2Si2.

    PubMed

    Hartmann, Stefanie; Oeschler, Niels; Krellner, Cornelius; Geibel, Christoph; Paschen, Silke; Steglich, Frank

    2010-03-05

    We present low-temperature thermopower results, S(T), on the heavy-fermion compound YbRh2Si2 in the vicinity of its field-induced quantum critical point (QCP). At B=0, a logarithmic increase of -S(T)/T between 1 and 0.1 K reveals strong non-Fermi-liquid behavior. A pronounced downturn of -S(T)/T below T{max}=0.1 K and a sign change from negative to positive S(T) values at T{0} approximately 30 mK are observed on the low-field side of the Kondo breakdown crossover line T{*}(B). In the field-induced, heavy Landau-Fermi-liquid regime, S(T)/T assumes constant, negative values below T{LFL}. A pronounced crossover in the -S(B)/T isotherms at T{*}(B) sharpens with decreasing T and seems to evolve toward a steplike function for T-->0. This is attributed to an abrupt change of the Fermi volume upon crossing the unconventional QCP of YbRh2Si2.

  2. Fermi surface in the hidden-order state of URu2Si2 under intense pulsed magnetic fields up to 81 T

    NASA Astrophysics Data System (ADS)

    Scheerer, G. W.; Knafo, W.; Aoki, D.; Nardone, M.; Zitouni, A.; Béard, J.; Billette, J.; Barata, J.; Jaudet, C.; Suleiman, M.; Frings, P.; Drigo, L.; Audouard, A.; Matsuda, T. D.; Pourret, A.; Knebel, G.; Flouquet, J.

    2014-04-01

    We present measurements of the resistivity ρx ,x of URu2Si2 high-quality single crystals in pulsed high magnetic fields up to 81 T at a temperature of 1.4 K and up to 60 T at temperatures down to 100 mK. For a field H applied along the magnetic easy axis c, a strong sample dependence of the low-temperature resistivity in the hidden-order phase is attributed to a high carrier mobility. The interplay between the magnetic and orbital properties is emphasized by the angle dependence of the phase diagram, where magnetic transition fields and crossover fields related to the Fermi surface properties follow a 1/cosθ law, θ being the angle between H and c. For H ∥c, a crossover defined at a kink of ρx ,x, as initially reported in [Shishido, Phys. Rev. Lett. 102, 156403 (2009), 10.1103/PhysRevLett.102.156403], is found to be strongly sample dependent: its characteristic field μ0H* varies from ≃20 T in our best sample with a residual resistivity ratio RRR = ρx ,x(300K)/ ρx ,x(2K) of 225 to ≃25 T in a sample with a RRR of 90. A second crossover is defined at the maximum of ρx ,x at the sample-independent low-temperature (LT) characteristic field μ0Hρ,maxLT≃30 T. Fourier analyses of Shubnikov-de Haas oscillations show that Hρ,maxLT coincides with a sudden modification of the Fermi surface, while H* lies in a regime where the Fermi surface is smoothly modified. For H ∥a, (i) no phase transition is observed at low temperature and the system remains in the hidden-order phase up to 81 T, (ii) quantum oscillations surviving up to 7 K are related to a new orbit observed at the frequency Fλ≃1350 T and associated with a low effective mass mλ*=(1±0.5)m0, where m0 is the free electron mass, and (iii) no Fermi surface modification occurs up to 81 T.

  3. Electronic bands, Fermi surface, and elastic properties of new 4.2 K superconductor SrPtAs with a honeycomb structure from first principles calculations

    NASA Astrophysics Data System (ADS)

    Shein, I. R.; Ivanovskii, A. L.

    2011-10-01

    The hexagonal phase SrPtAs (s.g. P6/ mmm; #194) with a honeycomb lattice structure was recently declared as a new low-temperature ( T C ∼ 4.2 K) superconductor. Here, by means of first-principles calculations the optimized structural parameters, electronic bands, Fermi surface, total and partial densities of states, inter-atomic bonding picture, independent elastic constants, bulk and shear moduli for SrPtAs were obtained for the first time and analyzed in comparison with the related layered superconductor SrPt 2As 2.

  4. Observation of the electron ridge Fermi surface in YBa{sub 2}Cu{sub 3}O{sub 7-x} by positron annihilation

    SciTech Connect

    Smedskjaer, L.C.; Fang, Y.; Bailey, K.G.; Welp, U.; Bansil, A.

    1991-04-01

    Positron annihilation (two-dimensional-angular-correlation) experiments on an untwinned single crystal of metallic YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} sample are reported in the c-projection. The measurements were carried out at room temperature and involved 94 Mcounts. An analysis of the spectra reveals clearly for the first time the presence of the electron ridge Fermi surface associated with the one-dimensional chain bands, and orthorhombic anisotropies in momentum density in good agreement with the band theory predictions.

  5. Post-translational modification of the NKG2D ligand RAET1G leads to cell surface expression of a glycosylphosphatidylinositol-linked isoform.

    PubMed

    Ohashi, Maki; Eagle, Robert A; Trowsdale, John

    2010-05-28

    NKG2D is an important activating receptor on lymphocytes. In human, it interacts with two groups of ligands: the major histocompatibility complex class I chain-related A/B (MICA/B) family and the UL-16 binding protein (ULBP) family, also known as retinoic acid early transcript (RAET1). MIC proteins are membrane-anchored, but all of the ULBP/RAET1 proteins, except for RAET1E and RAET1G, are glycosylphosphatidylinositol (GPI)-anchored. To address the reason for these differences we studied the association of RAET1G with the membrane. Using epitope-tagged RAET1G protein in conjunction with antibodies to different parts of the molecule and in pulse-chase experiments, we showed that the C terminus of the protein was cleaved soon after protein synthesis. Endoglycosidase H and peptide N-glycosidase treatment and cell surface immunoprecipitation indicated that most of the protein stayed in the endoplasmic reticulum, but some of the cleaved form was modified in the Golgi and transported to the cell surface. We examined the possibility of GPI anchoring of the protein in three ways: (i) Phosphatidylinositol (PI)-specific phospholipase C released the PI-linked form of the protein. (ii) The surface expression pattern of RAET1G decreased in cells defective in GPI anchoring through mutant GPI-amidase. (iii) Site-directed mutagenesis, to disrupt residues predicted to facilitate GPI-anchoring, resulted in diminished surface expression of RAET1G. Thus, a form of RAET1G is GPI-anchored, in line with most other ULBP/RAET1 family proteins. The cytoplasmic tail and transmembrane domains appear to result from gene duplication and frameshift mutation. Together with our previous results, our data suggest that RAET1G is regulated post-translationally to produce a GPI-anchored isoform.

  6. Post-translational Modification of the NKG2D Ligand RAET1G Leads to Cell Surface Expression of a Glycosylphosphatidylinositol-linked Isoform*

    PubMed Central

    Ohashi, Maki; Eagle, Robert A.; Trowsdale, John

    2010-01-01

    NKG2D is an important activating receptor on lymphocytes. In human, it interacts with two groups of ligands: the major histocompatibility complex class I chain-related A/B (MICA/B) family and the UL-16 binding protein (ULBP) family, also known as retinoic acid early transcript (RAET1). MIC proteins are membrane-anchored, but all of the ULBP/RAET1 proteins, except for RAET1E and RAET1G, are glycosylphosphatidylinositol (GPI)-anchored. To address the reason for these differences we studied the association of RAET1G with the membrane. Using epitope-tagged RAET1G protein in conjunction with antibodies to different parts of the molecule and in pulse-chase experiments, we showed that the C terminus of the protein was cleaved soon after protein synthesis. Endoglycosidase H and peptide N-glycosidase treatment and cell surface immunoprecipitation indicated that most of the protein stayed in the endoplasmic reticulum, but some of the cleaved form was modified in the Golgi and transported to the cell surface. We examined the possibility of GPI anchoring of the protein in three ways: (i) Phosphatidylinositol (PI)-specific phospholipase C released the PI-linked form of the protein. (ii) The surface expression pattern of RAET1G decreased in cells defective in GPI anchoring through mutant GPI-amidase. (iii) Site-directed mutagenesis, to disrupt residues predicted to facilitate GPI-anchoring, resulted in diminished surface expression of RAET1G. Thus, a form of RAET1G is GPI-anchored, in line with most other ULBP/RAET1 family proteins. The cytoplasmic tail and transmembrane domains appear to result from gene duplication and frameshift mutation. Together with our previous results, our data suggest that RAET1G is regulated post-translationally to produce a GPI-anchored isoform. PMID:20304922

  7. Quest for Inexpensive Hydrogen Isotopic Fractionation: Do We Need 2D Quantum Confining in Porous Materials or Are Rough Surfaces Enough? The Case of Ammonia Nanoclusters.

    PubMed

    Mella, Massimo; Curotto, E

    2016-10-05

    We study the adsorption energetics and quantum properties of the molecular hydrogen isotopes H2, D2, and T2 onto the surface of rigid ammonia nanoclusters with quantum simulations and accurate model potential energy surfaces (PES). A highly efficient diffusion Monte Carlo (DMC) algorithm for rigid rotors allowed us to accurately define zero-point adsorption energies for the three isotopes, as well as the degree of translational and rotational delocalization that each affords on the surface. From the data emerges that the quantum adsorption energy (Eads) of T2 can be up to twice the one of H2 at 0 K, suggesting the possibility of exploiting some form of solid ammonia to selectivity separate hydrogen isotopes at low temperatures (≃20 K). This is discussed by focusing on the structural motif that may be more effective for the task. The analysis of the contributions to Eads, however, surprisingly indicates that the average kinetic energy (E(kin)) and rotation energy (Erot(kin)) of T2 can also be, respectively, 2 times and 20 times higher than those of H2; this finding markedly deviates from what is predicted for hydrogen molecules inside carbon nanotubes (CNT) or metallic-organic frameworks (MOF), where E(kin) and Erot(kin) is higher for H2 due to the unavoidable effects of confinement and hindrance to its rotational motion. The rationale for these differences is provided by the geometrical distributions for the rigid rotors, which reveal an increasingly stronger coupling between rotational and translational degrees of freedom upon increasing the isotopic mass. This effect has never been observed before on adsorbing surfaces (e.g., graphite) and is induced by a strongly anisotropic and anharmonic bowl-like potential experienced by the rotors.

  8. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; T.J. Bornhorst; William B. Harrison; W. Quinlan

    2002-04-01

    The fault study continues to find more faults and develop new techniques to visualize them. Data from the Dundee Formation has been used to document 11 major faults in the Michigan Basin which have now been verified using data from other horizons. These faults control the locations of many of the large anticlinal structures in the Michigan Basin and likely controlled fluid movements as well. The surface geochemistry program is also moving along well with emphasis on measuring samples collected last sampling season. The new GC laboratory is now functional and has been fully staffed as of December. The annual project review was held March 7-9 in Tampa, Florida. Contracts are being prepared for drilling the Bower's prospects in Isabella County, Michigan, this spring or summer. A request was made to extend the scope of the project to include the Willison Basin. A demonstration well has been suggested in Burke County, N. Dakota, following a review of 2D seismic and surface geochem. A 3D seismic survey is scheduled for the prospect.

  9. IDO metabolite produced by EBV-transformed B cells inhibits surface expression of NKG2D in NK cells via the c-Jun N-terminal kinase (JNK) pathway.

    PubMed

    Song, Hyunkeun; Park, Hyunjin; Kim, Jiyoung; Park, Gabin; Kim, Yeong-Seok; Kim, Sung Mok; Kim, Daejin; Seo, Su Kil; Lee, Hyun-Kyung; Cho, DaeHo; Hur, Daeyoung

    2011-05-01

    Natural Killer cells are known to play a major role in the innate immune response against viral infections and tumor cells. Several viruses, such as CMV, EBV and HIV-1, have acquired strategies to escape elimination by NK cells. In this study, we observed that EBV infection increased expression of IDO on B cells. To evaluate the function of IDO associated with EBV infection, we investigated whether EBV-induced IDO could modulate expression of NK cell-activation receptor, NKG2D. When NK cells were co-incubated with EBV transformed B cells, surface expression of NKG2D was significantly reduced in NK cells. Incubation with L-kynurenine, an IDO metabolite, down-modulated NKG2D expression in NK cells in a dose- and time-dependent manner. Incubation with the JNK inhibitor SP600125 also inhibited NKG2D expression in NK cells. In addition, we observed that the effect of L-kynurenine was blocked by JNK agonist, anisomycin, suggesting the involvement of the JNK pathway in the signal transduction of L-kynurenine-reduced NKG2D expression. Furthermore, IL-18 significantly reduced L-kynurenine-induced down-regulation of NKG2D expression in NK cells. Taken together, these data indicate that down-regulation of NKG2D by EBV-induced IDO metabolite provides a potential mechanism by which EBV escapes NKG2D-mediated attack by immune cells.

  10. Implementation of a fast analytic ground state potential energy surface for the N({sup 2}D)+H{sub 2} reaction.

    SciTech Connect

    Ho, T.-S.; Rabitz, H.; Aoiz, F. J.; Banares, L.; Vazquez, S. A.; Harding, L. B.; Chemistry; Princeton Univ.; Univ. Complutense

    2003-08-08

    A new implementation is presented for the potential energy surface (PES) of the 1{sup 2}A' state of the N({sup 2}D)+H{sub 2} system based on a set of 2715 ab initio points resulting from the multireference configuration interaction (MRCI) calculations. The implementation is carried out using the reproducing Kernel Hilbert Space interpolation method. Range parameters, via bond-order-like coordinates, are properly chosen to render a sufficiently short-range three-body interaction and a regularization procedure is invoked to yield a globally smooth PES. A fast algorithm, with the help of low-order spline reproducing kernels, is implemented for the computation of the PES and, particularly, its gradients, whose fast evaluation is essential for large scale quasi-classical trajectory calculations. It is found that the new PES can be evaluated more than ten times faster than that of an existing (old) PES based on a smaller number (1141) of data points resulting from the same MRCI calculations and a similar interpolation procedure. Although there is a general good correspondence between the two surfaces, the new PES is in much better agreement with the ab initio calculations, especially in key stationary point regions including the C{sub 2v} minimum, the C{sub 2v} transition state, and the N-H-H linear barrier. Moreover, the new PES is free of spurious small scale features. Analytic gradients are made available in the new PES code to further facilitate quasiclassical trajectory calculations, which have been performed and compared with the results based on the old surface.

  11. Nernst and Seebeck coefficients of the cuprate superconductor YBa2Cu3O6.67: a study of Fermi surface reconstruction.

    PubMed

    Chang, J; Daou, R; Proust, Cyril; Leboeuf, David; Doiron-Leyraud, Nicolas; Laliberté, Francis; Pingault, B; Ramshaw, B J; Liang, Ruixing; Bonn, D A; Hardy, W N; Takagi, H; Antunes, A B; Sheikin, I; Behnia, K; Taillefer, Louis

    2010-02-05

    The Seebeck and Nernst coefficients S and nu of the cuprate superconductor YBa{2}Cu{3}O{y} (YBCO) were measured in a single crystal with doping p=0.12 in magnetic fields up to H=28 T. Down to T=9 K, nu becomes independent of field by H approximately 30 T, showing that superconducting fluctuations have become negligible. In this field-induced normal state, S/T and nu/T are both large and negative in the T-->0 limit, with the magnitude and sign of S/T consistent with the small electronlike Fermi surface pocket detected previously by quantum oscillations and the Hall effect. The change of sign in S(T) at T approximately 50 K is remarkably similar to that observed in La2-xBaxCuO4, La{2-x-y}Nd{y}Sr_{x}CuO{4}, and La{2-x-y}Eu{y}Sr{x}CuO{4}, where it is clearly associated with the onset of stripe order. We propose that a similar density-wave mechanism causes the Fermi surface reconstruction in YBCO.

  12. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    DOE PAGES

    Kim, Hyunsoo; Tanatar, M. A.; Flint, R.; ...

    2015-01-15

    The London penetration depth λ(T) was measured in single crystals of Ce1–xRxCoIn₅, R=La, Nd, and Yb down to Tmin ≈ 50 mK (Tc/Tmin ~50) using a tunnel-diode resonator. In the cleanest samples Δλ(T) is best described by the power law, Δλ(T) ∝ Tn, with n ~ 1, consistent with line nodes. Substitutions of Ce with La, Nd, and Yb lead to similar monotonic suppressions of Tc, however, the effects on Δλ(T) differ. While La and Nd dopings lead to increase of the exponent n and saturation at n ~ 2, as expected for a dirty nodal superconductor, Yb doping leadsmore » to n > 3, suggesting a change from nodal to nodeless superconductivity. As a result, this superconducting gap structure change happens in the same doping range where changes of the Fermi surface topology were reported, implying that the nodal structure and Fermi surface topology are closely linked.« less

  13. Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure

    NASA Astrophysics Data System (ADS)

    Gonnelli, R. S.; Daghero, D.; Tortello, M.; Ummarino, G. A.; Bukowski, Z.; Karpinski, J.; Reuvekamp, P. G.; Kremer, R. K.; Profeta, G.; Suzuki, K.; Kuroki, K.

    2016-05-01

    Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line.

  14. Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure

    PubMed Central

    Gonnelli, R. S.; Daghero, D.; Tortello, M.; Ummarino, G. A.; Bukowski, Z.; Karpinski, J.; Reuvekamp, P. G.; Kremer, R. K.; Profeta, G.; Suzuki, K.; Kuroki, K.

    2016-01-01

    Iron-based compounds (IBS) display a surprising variety of superconducting properties that seems to arise from the strong sensitivity of these systems to tiny details of the lattice structure. In this respect, systems that become superconducting under pressure, like CaFe2As2, are of particular interest. Here we report on the first directional point-contact Andreev-reflection spectroscopy (PCARS) measurements on CaFe2As2 crystals under quasi-hydrostatic pressure, and on the interpretation of the results using a 3D model for Andreev reflection combined with ab-initio calculations of the Fermi surface (within the density functional theory) and of the order parameter symmetry (within a random-phase-approximation approach in a ten-orbital model). The almost perfect agreement between PCARS results at different pressures and theoretical predictions highlights the intimate connection between the changes in the lattice structure, a topological transition in the holelike Fermi surface sheet, and the emergence on the same sheet of an order parameter with a horizontal node line. PMID:27216477

  15. Negative quantum Hall effect in field-induced spin-density-wave states: Dependence on shape of the quasi-one-dimensional Fermi surface

    NASA Astrophysics Data System (ADS)

    Kishigi, Keita; Hasegawa, Yasumasa

    2009-08-01

    The successive transitions of the field-induced spin-density wave, which is labeled by the quantum number N of the Hall conductivity and the nesting vector, are known to depend on the shape of the quasi-one-dimensional Fermi surface. We study the condition for the appearance of the negative N states, where the quantized Hall conductivity changes the sign. We obtain the phase diagram for the negative N states in the parameter space of the higher harmonics in the Fermi surface ( tb' , t3 , and t4 ) to be stabilized with and without the periodic anion potential V in the perpendicular direction to the conducting axis, which are the cases in (TMTSF)2ClO4 and (TMTSF)2PF6 , respectively. The negative N phase is shown to be stabilized for the smaller values of t3 and t4 in the case of the finite V . Comparing with the experiment by Matsunaga [J. Phys. IV 131, 269 (2005)], where the quantum Hall effect is observed in (TMTSF)2ClO4 with various cooling rates, we obtain the parameter regions of t3 and t4 for (TMTSF)2ClO4 ( 0.06≲t3/tb'≲0.23 , 0≲t4/tb'≲0.08 , and V/tb'≲2.0 ).

  16. Fermi-surface topologies and low-temperature phases of the filled skutterudite compounds CeOs4Sb12 and NdOs4Sb12

    NASA Astrophysics Data System (ADS)

    Ho, Pei Chun; Singleton, John; Goddard, Paul A.; Balakirev, Fedor F.; Chikara, Shalinee; Yanagisawa, Tatsuya; Maple, M. Brian; Shrekenhamer, David B.; Lee, Xia; Thomas, Avraham T.

    2016-11-01

    MHz conductivity, torque magnetometer, and magnetization measurements are reported on single crystals of CeOs4Sb12 and NdOs4Sb12 using temperatures down to 0.5 K and magnetic fields of up to 60 tesla. The field-orientation dependence of the de Haas-van Alphen and Shubnikov-de Haas oscillations is deduced by rotating the samples about the [010 ] and [0 1 ¯1 ] directions. The results indicate that NdOs4Sb12 has a similar Fermi surface topology to that of the unusual superconductor PrOs4Sb12 , but with significantly smaller effective masses, supporting the importance of local phonon modes in contributing to the low-temperature heat capacity of NdOs4Sb12 . By contrast, CeOs4Sb12 undergoes a field-induced transition from an unusual semimetal into a high-field, high-temperature state characterized by a single, almost spherical Fermi-surface section. The behavior of the phase boundary and comparisons with models of the band structure lead us to propose that the field-induced phase transition in CeOs4Sb12 is similar in origin to the well-known α -γ transition in Ce and its alloys.

  17. Surface related multiple elimination (SRME) and radon transform forward multiple modeling methods applied to 2D multi-channel seismic profiles from the Chukchi Shelf, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    Ilhan, I.; Coakley, B. J.

    2013-12-01

    The Chukchi Edges project was designed to establish the relationship between the Chukchi Shelf and Borderland and indirectly test theories of opening for the Canada Basin. During this cruise, ~5300 km of 2D multi-channel reflection seismic profiles and other geophysical data (swath bathymetry, gravity, magnetics, sonobuoy refraction seismic) were collected from the RV Marcus G. Langseth across the transition between the Chukchi Shelf and Chukchi Borderland, where the water depths vary from 30 m to over 3 km. Multiples occur when seismic energy is trapped in a layer and reflected from an acoustic interface more than once. Various kinds of multiples occur during seismic data acquisition. These depend on the ray-path the seismic energy follows through the layers. One of the most common multiples is the surface related multiple, which occurs due to strong acoustic impedance contrast between the air and water. The reflected seismic energy from the water surface is trapped within the water column, thus reflects from the seafloor multiple times. Multiples overprint the primary reflections and complicate data interpretation. Both surface related multiple elimination (SRME) and forward parabolic radon transform multiple modeling methods were necessary to attenuate the multiples. SRME is applied to shot gathers starting with the near offset interpolation, multiple estimation using water depths, and subtracting the model multiple from the shot gathers. This method attenuated surface related multiple energy, however, peg-leg multiples remained in the data. The parabolic radon transform method minimized the effect of these multiples. This method is applied to normal moveout (NMO) corrected common mid-point gathers (CMP). The CMP gathers are fitted or modeled with curves estimated from the reference offset, moveout range, moveout increment parameters. Then, the modeled multiples are subtracted from the data. Preliminary outputs of these two methods show that the surface related

  18. From 2-D CuO nanosheets to 3-D hollow nanospheres: interface-assisted synthesis, surface photovoltage properties and photocatalytic activity

    SciTech Connect

    Zhu Jun; Qian Xuefeng

    2010-07-15

    CuO hierarchical hollow nanostructures, assembled by nanosheets, were successfully prepared in n-octanol/aqueous liquid system through a microwave approach. Controlled experiments revealed that both bubble and interface play key roles in determining the self-assembly process of CuO hierarchical hollow nanostructures, and the morphology/size of building blocks and final products could be readily tuned by adjusting reaction parameters. Furthermore, a self-assembly mechanism of aggregation-then-growth process through bubble template was proposed for the formation of the hollow hierarchical architectures. Photocatalytic performance evidenced that the obtained CuO hierarchical hollow nanostructures possessed superior photocatalytic efficiency on RhB than that of non-hollow nanostructures, which could be easily demonstrated by SPS response about the separation and recombination situation of photogenerated charges. - Graphical abstract: From 2-D CuO nanosheets to 3-D hollow nanospheres: interface-assisted synthesis, surface photovoltage properties and photocatalytic activity. Various CuO architectures with different morphologies and sizes, including hierarchical hollow nanostructures were prepared through a synergic bubble-template and interface-assisted approach.

  19. Highly Selective and Repeatable Surface-Enhanced Resonance Raman Scattering Detection for Epinephrine in Serum Based on Interface Self-Assembled 2D Nanoparticles Arrays.

    PubMed

    Zhou, Binbin; Li, Xiaoyun; Tang, Xianghu; Li, Pan; Yang, Liangbao; Liu, Jinhuai

    2017-03-01

    Target analyte detection in complex systems with high selectivity and repeatability is crucial to analytical technology and science. Here we present a two-dimensional (2D) surface-enhanced resonance Raman scattering (SERRS) platform, which takes advantages of the high selectivity of the SERRS sensor as well as the sensitivity and reproducibility of the interfacial SERS platform, for detecting trace epinephrine (EP) in the serum. To realize sensitive and selective detection of EP in a complex system, Au NPs are modified with α,β-nitriloacetic acid and Fe(NO3)3 to form the Au NP-(Fe-NTA) sensor, and as a consequence, EP can be rapidly captured by the sensor on the surface of Au NPs and then delivered at the cyclohexane/water interface. More importantly, we synthesized the extremely stable Au NPs (PVP-stabilized Au NPs), where the presence of PVP prevents aggregation of Au NPs during the self-assembly process and then makes a more uniform distribution of Au NPs with analytes at the cyclohexane/water interface, approximately 2 nm interparticle distance between the Au NPs, which has been proved by synchrotron radiation grazing incidence small-angle X-ray scattering (SR-GISAXS) experiments. The self-assembly method not only effectively avoids the aggregation of Au NPs and decreases the influence of the background signal but also can capture and enrich EP molecules in the cyclohexane/water interface, realizing the sensitive and selective detection of EP in complex serum sample. This strategy overcomes the difficulty of bringing nanostructures together to form efficient interparticle distance with simple fabrication and maximum uniformity and also provides a powerful nanosensor for tracing amounts of analyte molecules in a complex system with the advantages of capturing and enriching of target molecules in the liquid/liquid interface during the self-assembly process. Our SERRS platform opens vast possibilities for repeatability, sensitivity, and selectivity detection of

  20. Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs.

    PubMed

    Xu, Su-Yang; Belopolski, Ilya; Sanchez, Daniel S; Neupane, Madhab; Chang, Guoqing; Yaji, Koichiro; Yuan, Zhujun; Zhang, Chenglong; Kuroda, Kenta; Bian, Guang; Guo, Cheng; Lu, Hong; Chang, Tay-Rong; Alidoust, Nasser; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Hsu, Chuang-Han; Jeng, Horng-Tay; Bansil, Arun; Neupert, Titus; Komori, Fumio; Kondo, Takeshi; Shin, Shik; Lin, Hsin; Jia, Shuang; Hasan, M Zahid

    2016-03-04

    A Weyl semimetal is a new state of matter that hosts Weyl fermions as quasiparticle excitations. The Weyl fermions at zero energy correspond to points of bulk-band degeneracy, called Weyl nodes, which are separated in momentum space and are connected only through the crystal's boundary by an exotic Fermi arc surface state. We experimentally measure the spin polarization of the Fermi arcs in the first experimentally discovered Weyl semimetal TaAs. Our spin data, for the first time, reveal that the Fermi arcs' spin-polarization magnitude is as large as 80% and lies completely in the plane of the surface. Moreover, we demonstrate that the chirality of the Weyl nodes in TaAs cannot be inferred by the spin texture of the Fermi arcs. The observed nondegenerate property of the Fermi arcs is important for establishing its exact topological nature, which reveals that spins on the arc form a novel type of 2D matter. Additionally, the nearly full spin polarization we observed (∼80%) may be useful in spintronic applications.

  1. Nonanalytic corrections to the Fermi-liquid behavior

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Maslov, Dmitrii L.

    2003-10-01

    The issue of nonanalytic corrections to the Fermi-liquid behavior is revisited. Previous studies have indicated that the corrections to the Fermi-liquid forms of the specific heat and the static spin susceptibility (CFL∝T, χFLs=const) are nonanalytic in D⩽3 and scale as δC(T)∝TD, χs(T)∝TD-1, and χs(Q)∝QD-1, with extra logarithms in D=3 and 1. It is shown that these nonanalytic corrections originate from the universal singularities in the dynamical bosonic response functions of a generic Fermi liquid. In contrast to the leading, Fermi-liquid forms which depend on the interaction averaged over the Fermi surface, the nonanalytic corrections are parametrized by only two coupling constants, which are the components of the interaction potential at momentum transfers q=0 and q=2pF. For three-dimensional (3D) systems, a recent result of Belitz, Kirkpatrick, and Vojta for the spin susceptibility is reproduced and the issue why a nonanalytic momentum dependence, χs(Q,T=0)-χFLs∝Q2log Q, is not paralleled by a nonanalyticity in the T dependence [χs(0,T)-χFLs]∝T2 is clarified. For 2D systems, explicit forms of C(T)-CFL∝T2, χ(Q,T=0)-χFL∝|Q|, and χ(0,T)-χFL∝T are obtained. It is shown that earlier calculations of the temperature dependences in two dimensions are incomplete.

  2. Hume-Rothery stabilisation mechanism and d-states-mediated Fermi surface-Brillouin zone interactions in structurally complex metallic alloys

    NASA Astrophysics Data System (ADS)

    Mizutani, U.; Inukai, M.; Sato, H.

    2011-07-01

    The stability of Co2Zn11 and Al8V5 gamma-brasses, both of which are composed of a transition metal element and polyvalent elements Zn or Al, can be discussed in terms of d-states-mediated Fermi surface-Brillouin zone (FsBz) interactions in the context of first-principles full-potential linearised augmented plane wave (FLAPW) band calculations. A FsBz-induced pseudogap is revealed in the FLAPW-Fourier spectrum, though it is hidden behind a much larger d-band in the total density of states. The stability range of three families of complex metallic alloys (CMAs) that include gamma-brasses, RT-, MI- and Tsai-type 1/1-1/1-1/1 approximants and 2/1-2/1-2/1 approximant, each of which is characterised by ? = 18, 50 and 125, respectively, can be well scaled in terms of the number of electrons per unit cell (e/uc) given by the product of the number of atoms per unit cell and the e/a value determined by the Hume-Rothery plot on the basis of the FLAPW-Fourier method. This is taken as the evidence for the justification of the Hume-Rothery stabilisation mechanism for all these CMAs having a pseudogap at the Fermi level.

  3. Nodal-line pairing with 1D-3D coupled Fermi surfaces: A model motivated by Cr-based superconductors

    NASA Astrophysics Data System (ADS)

    Wachtel, Gideon; Kim, Yong Baek

    2016-09-01

    Motivated by the recent discovery of a new family of chromium-based superconductors, we consider a two-band model, where a band of electrons dispersing only in one direction interacts with a band of electrons dispersing in all three directions. Strong 2 kf density fluctuations in the one-dimensional band induces attractive interactions between the three-dimensional electrons, which, in turn, makes the system superconducting. Solving the associated Eliashberg equations, we obtain a gap function which is peaked at the "poles" of the three-dimensional Fermi sphere, and decreases towards the "equator." When strong enough local repulsion is included, the gap actually changes sign around the equator and nodal rings are formed. These nodal rings manifest themselves in several experimentally observable quantities, some of which resemble unconventional observations in the newly discovered superconductors which motivated this work.

  4. Momentum density and 2D-ACAR experiments in YBa{sub 2}Cu{sub 3}O{sub 7}

    SciTech Connect

    Bansil, A.; Smedskjaer, L.C.

    1991-12-01

    We compare measured c-projected 2D-ACAR spectrum from an untwinned single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} with the corresponding band theory predictions. Many different one-dimensional sections through the spectrum are considered, together with the characteristic amplitudes and shapes of the spectral anisotropies, with a focus on identifying and delineating Fermi surface signatures in the spectra. The positron data clearly show several distinct features of the ridge Fermi surface predicted by the band theory, and give an indication of the pillbox Fermi sheet. The good agreement between theory and experiment suggests that the band theory framework based on the local density approximation (LDA) is capable of providing a substantially correct description of the momentum density and Fermiology of the normal ground state electronic structure of YBa{sub 2}Cu{sub 3}O{sub 7}.

  5. Unconventional pairing in doped band insulators on a honeycomb lattice: the role of the disconnected Fermi surface and a possible application to superconducting β-MNCl (M=Hf, Zr).

    PubMed

    Kuroki, Kazuhiko

    2008-12-01

    We investigate the possibility of realizing unconventional superconductivity in doped band insulators on the square and honeycomb lattices. The latter lattice is found to be a good candidate due to the disconnectivity of the Fermi surface. We propose applying the theory to the superconductivity in doped layered nitride β-MNCl (M= Hf, Zr). Finally, we compare two groups of superconductors with disconnected Fermi surface, β-MNCl and the iron pnictides, which have high critical temperature Tc, despite some faults against superconductivity are present.

  6. 2D Dynamic Models of Subduction: Links between Surface Plate Motion and Deformation in the Transition Zone from Observations of Deep Slab Seismicity

    NASA Astrophysics Data System (ADS)

    Arredondo, K.; Billen, M. I.

    2015-12-01

    Observations of seismicity and seismic tomography provide constraints on the geometry of slabs within mantle, while compression/tension axis derived from moment tensor solutions provide constraints on the internal deformation of slabs. However, since these observations provide only a somewhat blurred or incomplete snapshot of the slab in time, it is difficult to directly relate these observations to the evolution of the slab geometry and the forces acting on and within the slab. In contrast, plate tectonic reconstructions provide time-dependent constraints on the surface motion of plates and the trench at subduction zones, which are related to the dynamical evolution of the slab. We use 2D geodynamical simulations of subduction to explore the relationship between dynamical process within the deforming slab and the observations of surface plate motion and the state-of-stress in slabs. Specifically we utilize models that include the extended Boussinesq approximation (shear heating and latent heat terms in the energy equation), a layered lithosphere with pyrolite, harzburgite and basalt/eclogite, compositionally-dependent phase transitions, and a composite rheology with yielding. The models employ a weak crustal layer that decouples the overriding and subducting plates and allows for dynamically determined trench motion. Here we show that, 1) multiple phase transitions increase slab folding, 2) ridge push significantly increases trench retreat, and 3) strength of the weak crustal layer influences slab detachment. Compared to past studies a more realistic treatment of the phase transitions makes trench retreat more difficult to generate: a weaker plate may encourage slab retreat but detaches once the slab tip crosses into the transition zone due to the rapid increase in slab density. As suggested by previous studies, slab folding within the transition zone changes the direction of forces on the slab and causes periodic changes from trench retreat to trench advance. We

  7. Fermi surface reconstruction in (Ba1-xKx)Fe2As2 (0.44 ≤ x ≤ 1) probed by thermoelectric power measurements

    SciTech Connect

    Hodovanets, Halyna; Liu, Yong; Jesche, Anton; Ran, Sheng; Mun, Eun Deok; Lograsso, Thomas A; Bud'ko, Sergey L; Canfield, Paul C

    2014-06-01

    We report in-plane thermoelectric power measurements on single crystals of (Ba1-xKx)Fe2As2(0.44≤x≤1). We observe a minimum in the S|T=const versus x at x~0.55 that can be associated with the change in the topology of the Fermi surface, a Lifshitz transition, related to the electron pockets at the center of M point crossing the Fermi level. This feature is clearly observable below ~75 K. Thermoelectric power also shows a change in the x~0.8–0.9 range, where the maximum in the thermoelectric power collapses into a plateau. This Lifshitz transition is most likely related to the reconstruction of the Fermi surface associated with the transformation of the hole pockets at the M point into four blades as observed by ARPES measurements.

  8. Shubnikov-de Haas quantum oscillations reveal a reconstructed Fermi surface near optimal doping in a thin film of the cuprate superconductor Pr1.86Ce0.14CuO4 ±δ

    NASA Astrophysics Data System (ADS)

    Breznay, Nicholas P.; Hayes, Ian M.; Ramshaw, B. J.; McDonald, Ross D.; Krockenberger, Yoshiharu; Ikeda, Ai; Irie, Hiroshi; Yamamoto, Hideki; Analytis, James G.

    2016-09-01

    We study magnetotransport properties of the electron-doped superconductor Pr2 -xCexCuO4 ±δ with x =0.14 in magnetic fields up to 92 T, and observe Shubnikov-de Haas magnetic quantum oscillations. The oscillations display a single frequency F =255 ±10 T, indicating a small Fermi pocket that is ˜1 % of the two-dimensional Brillouin zone and consistent with a Fermi surface reconstructed from the large holelike cylinder predicted for these layered materials. Despite the low nominal doping, all electronic properties including the effective mass and Hall effect are consistent with overdoped compounds. Our study demonstrates that the exceptional chemical control afforded by high quality thin films will enable Fermi surface studies deep into the overdoped cuprate phase diagram.

  9. Observation of strain-controlled electronic modulations revealed by Fermi surface superstructures in strongly correlated LaNiO3 films

    NASA Astrophysics Data System (ADS)

    Yoo, Hyangkeun; Hyun, Seungill; Moreschini, Luca; Kim, Hyeong-Do; Chang, Youngjun; Sohn, Changhee; Jeong, Dawoon; Sinn, Soobin; Kim, Yongsu; Bostwick, Aaron; Rotenberg, Eli; Shim, Jihoon; Noh, Taewon

    2014-03-01

    Control over the electronic properties of strongly correlated electron systems can be achieved by exploiting the misfit strain that exists in epitaxial films on lattice mismatched substrates. Here, we report a systematic investigation of electronic structures in strongly correlated LaNiO3 films under different strain states, using in situ angle-resolved photoemission spectroscopy and the dynamical mean field theory. LaNiO3 film shows a change of a Fermi surface (FS) topology, driven by interplay between strong electron-electron correlations and misfit strain effects. Additionally, different from compressive strain case, a FS with tensile strain has a large flat region to induce strong FS nesting. As a result, different FS superstructures are observed in the compressive and tensile strain cases, and their origins are attributed to charge disproportionation and spin density waves, respectively. The more details will be discussed in the presentation.

  10. Identical superconducting gap on different Fermi surfaces of Ca(Al0.5Si0.5)2 with the AlB2 structure

    NASA Astrophysics Data System (ADS)

    Tsuda, S.; Yokoya, T.; Shin, S.; Imai, M.; Hase, I.

    2004-03-01

    Angle-resolved photoemission spectroscopy of Ca(Al0.5Si0.5)2 (CaAlSi), which is a superconductor (transition temperature is 7.7 K) with the AlB2 structure, revealed that superconducting gaps on two Fermi surfaces (FSs) with three-dimensional character around Γ(A) and M(L) in the Brillouin zone provide essentially the same superconducting gap value (˜1.2 meV±0.2 meV). This is in contrast to the case of MgB2, in which different FSs exhibit different gap values. The reduced gap value 2Δ(0)/kBTc of ˜4.2±0.2 classifies CaAlSi as a moderately strong-coupling superconductor.

  11. ARPES on Na0.6CoO2: Fermi Surface and Unusual Band Dispersion

    SciTech Connect

    Yang, H. B.; Wang, S. -C.; Sekharan, A. K. P.; Matsui, H.; Souma, S.; Sato, T.; Takahashi, T.; Takeuchi, T.; Campuzano, J. C.; Jin, Rongying; Sales, Brian C; Mandrus, David; Wang, Z.; Ding, H.

    2004-01-01

    The electronic structure of single crystals Na{sub 0.6}CoO{sub 2}, which are closely related to the superconducting Na{sub 0.3}CoO{sub 2} {center_dot} yH{sub 2}O (T{sub c}-5 K), is studied by angle-resolved photoelectron spectroscopy. While the measured Fermi surface (FS) is consistent with the large FS enclosing the {Gamma} point from the band theory, the predicted small FS pockets near the K points are absent. In addition, the band dispersion is found to be highly renormalized, and anisotropic along the two principal axes ({Gamma}-K, {Gamma}-M). Our measurements also indicate that an extended flatband is formed slightly above EF along {Gamma}-K.

  12. Evidence for a spinon Fermi surface in the triangular S =1 quantum spin liquid Ba3NiSb2O9

    NASA Astrophysics Data System (ADS)

    Fâk, B.; Bieri, S.; Canévet, E.; Messio, L.; Payen, C.; Viaud, M.; Guillot-Deudon, C.; Darie, C.; Ollivier, J.; Mendels, P.

    2017-02-01

    Inelastic neutron scattering is used to study the low-energy magnetic excitations in the spin-1 triangular lattice of the 6 H -B phase of Ba3NiSb2O9 . We study two powder samples: Ba3NiSb2O9 synthesized under high pressure and Ba2.5Sr0.5NiSb2O9 in which chemical pressure stabilizes the 6 H -B structure. The measured excitation spectra show broad gapless and nondispersive continua at characteristic wave vectors. Our data rules out most theoretical scenarios that have previously been proposed for this phase, and we find that it is well described by an exotic quantum spin liquid with three flavors of unpaired fermionic spinons, forming a large spinon Fermi surface.

  13. Pressure Evolution of a Field-Induced Fermi Surface Reconstruction and of the Neel Critical Field in CeIn3

    SciTech Connect

    Petrovic, C.; Purcell, K.M.; Graf, D.; Kano, M.; Bourg, J.; Palm, E.C.; Murphy, T.; McDonald, R.; Mielke, C.H.; Altarawneh, M.M.; Hu, R.; Ebihara, T.; Cooley, J.; Schlottmann, P.; Tozer, S.W.

    2009-06-01

    We report high-pressure skin-depth measurements on the heavy fermion material CeIn{sub 3} in magnetic fields up to 64 T using a self-resonant tank circuit based on a tunnel diode oscillator. At ambient pressure, an anomaly in the skin depth is seen at 45 T. The field where this anomaly occurs decreases with applied pressure until approximately 1.0 GPa, where it begins to increase before merging with the antiferromagnetic phase boundary. Possible origins for this transport anomaly are explored in terms of a Fermi surface reconstruction. The critical magnetic field at which the Neel-ordered phase is suppressed, is also mapped as a function of pressure and extrapolates to the previous ambient-pressure measurements at high magnetic fields and high-pressure measurements at zero magnetic field.

  14. Anomalous asymmetry in the Fermi surface of the high-temperature superconductor YBa2Cu4O8 revealed by angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Kondo, Takeshi; Khasanov, R.; Sassa, Y.; Bendounan, A.; Pailhes, S.; Chang, J.; Mesot, J.; Keller, H.; Zhigadlo, N. D.; Shi, M.; Bukowski, Z.; Karpinski, J.; Kaminski, A.

    2009-09-01

    We use microprobe angle-resolved photoemission spectroscopy to study the Fermi surface and band dispersion of the CuO2 planes in the high-temperature superconductor, YBa2Cu4O8 . We find a strong in-plane asymmetry of the electronic structure between directions along a and b axes. The saddle point of the antibonding band lies at a significantly higher energy in the a direction (π,0) than the b direction (0,π) , whereas the bonding band displays the opposite behavior. We demonstrate that the abnormal band shape is due to a strong asymmetry of the bilayer band splitting, likely caused by a nontrivial hybridization between the planes and chains. This asymmetry has an important implication for interpreting key properties of the Y-Ba-Cu-O family, especially the superconducting gap, transport, and results of inelastic neutron scattering.

  15. Fermi Pulsar Analysis

    NASA Video Gallery

    This animation illustrates how analysis of Fermi data reveals new pulsars. Fermi's LAT records the precise arrival time and approximate direction of the gamma rays it detects, but to identify a pul...

  16. Vertical 2D Heterostructures

    NASA Astrophysics Data System (ADS)

    Lotsch, Bettina V.

    2015-07-01

    Graphene's legacy has become an integral part of today's condensed matter science and has equipped a whole generation of scientists with an armory of concepts and techniques that open up new perspectives for the postgraphene area. In particular, the judicious combination of 2D building blocks into vertical heterostructures has recently been identified as a promising route to rationally engineer complex multilayer systems and artificial solids with intriguing properties. The present review highlights recent developments in the rapidly emerging field of 2D nanoarchitectonics from a materials chemistry perspective, with a focus on the types of heterostructures available, their assembly strategies, and their emerging properties. This overview is intended to bridge the gap between two major—yet largely disjunct—developments in 2D heterostructures, which are firmly rooted in solid-state chemistry or physics. Although the underlying types of heterostructures differ with respect to their dimensions, layer alignment, and interfacial quality, there is common ground, and future synergies between the various assembly strategies are to be expected.

  17. Matrix models of 2d gravity

    SciTech Connect

    Ginsparg, P.

    1991-01-01

    These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.

  18. Matrix models of 2d gravity

    SciTech Connect

    Ginsparg, P.

    1991-12-31

    These are introductory lectures for a general audience that give an overview of the subject of matrix models and their application to random surfaces, 2d gravity, and string theory. They are intentionally 1.5 years out of date.

  19. 2D semiconductor optoelectronics

    NASA Astrophysics Data System (ADS)

    Novoselov, Kostya

    The advent of graphene and related 2D materials has recently led to a new technology: heterostructures based on these atomically thin crystals. The paradigm proved itself extremely versatile and led to rapid demonstration of tunnelling diodes with negative differential resistance, tunnelling transistors, photovoltaic devices, etc. By taking the complexity and functionality of such van der Waals heterostructures to the next level we introduce quantum wells engineered with one atomic plane precision. Light emission from such quantum wells, quantum dots and polaritonic effects will be discussed.

  20. Fermi level pinning characterisation on ammonium fluoride-treated surfaces of silicon by energy-filtered doping contrast in the scanning electron microscope

    PubMed Central

    Chee, Augustus K. W.

    2016-01-01

    Two-dimensional dopant profiling using the secondary electron (SE) signal in the scanning electron microscope (SEM) is a technique gaining impulse for its ability to enable rapid and contactless low-cost diagnostics for integrated device manufacturing. The basis is doping contrast from electrical p-n junctions, which can be influenced by wet-chemical processing methods typically adopted in ULSI technology. This paper describes the results of doping contrast studies by energy-filtering in the SEM from silicon p-n junction specimens that were etched in ammonium fluoride solution. Experimental SE micro-spectroscopy and numerical simulations indicate that Fermi level pinning occurred on the surface of the treated-specimen, and that the doping contrast can be explained in terms of the ionisation energy integral for SEs, which is a function of the dopant concentration, and surface band-bending effects that prevail in the mechanism for doping contrast as patch fields from the specimen are suppressed. PMID:27576347

  1. Electronic structure, Dirac points and Fermi arc surface states in three-dimensional Dirac semimetal Na3Bi from angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Aiji, Liang; Chaoyu, Chen; Zhijun, Wang; Youguo, Shi; Ya, Feng; Hemian, Yi; Zhuojin, Xie; Shaolong, He; Junfeng, He; Yingying, Peng; Yan, Liu; Defa, Liu; Cheng, Hu; Lin, Zhao; Guodong, Liu; Xiaoli, Dong; Jun, Zhang; M, Nakatake; H, Iwasawa; K, Shimada; M, Arita; H, Namatame; M, Taniguchi; Zuyan, Xu; Chuangtian, Chen; Hongming, Weng; Xi, Dai; Zhong, Fang; Xing-Jiang, Zhou

    2016-07-01

    The three-dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction band and valence band are connected. They have isolated 3D Dirac nodes in the whole Brillouin zone and can be viewed as a 3D counterpart of graphene. Recent theoretical calculations and experimental results indicate that the 3D Dirac semimetal state can be realized in a simple stoichiometric compound A 3Bi (A = Na, K, Rb). Here we report comprehensive high-resolution angle-resolved photoemission (ARPES) measurements on the two cleaved surfaces, (001) and (100), of Na3Bi. On the (001) surface, by comparison with theoretical calculations, we provide a proper assignment of the observed bands, and in particular, pinpoint the band that is responsible for the formation of the three-dimensional Dirac cones. We observe clear evidence of 3D Dirac cones in the three-dimensional momentum space by directly measuring on the k x -k y plane and by varying the photon energy to get access to different out-of-plane k z s. In addition, we reveal new features around the Brillouin zone corners that may be related with surface reconstruction. On the (100) surface, our ARPES measurements over a large momentum space raise an issue on the selection of the basic Brillouin zone in the (100) plane. We directly observe two isolated 3D Dirac nodes on the (100) surface. We observe the signature of the Fermi-arc surface states connecting the two 3D Dirac nodes that extend to a binding energy of ˜150 meV before merging into the bulk band. Our observations constitute strong evidence on the existence of the Dirac semimetal state in Na3Bi that are consistent with previous theoretical and experimental work. In addition, our results provide new information to clarify on the nature of the band that forms the 3D Dirac cones, on the possible formation of surface reconstruction of the (001) surface, and on the issue of basic Brillouin zone selection for the (100) surface. Project supported by the

  2. 2D Si island nucleation on the Si(111) surface at initial and late growth stages: On the role of step permeability in pyramidlike growth

    NASA Astrophysics Data System (ADS)

    Rogilo, D. I.; Fedina, L. I.; Kosolobov, S. S.; Ranguelov, B. S.; Latyshev, A. V.

    2017-01-01

    Initial and late stages of 2D Si island nucleation and growth (2DNG) on extra-large ( 100 μm) and medium size (1-10 μm) atomically flat Si(111)-(7×7) terraces bordered by step bunches have been studied by in situ REM at T =600-750 °С. At first, the layer-by-layer 2DNG takes place on whole terraces and 2D island concentration dependence on deposition rate R corresponds to critical nucleus size i =1. Continuous 2DNG triggers morphological instabilities: elongated pyramidlike waves and separate pyramids emerge on all terraces at T ≤720 °С and T =750 °С, respectively. Both instabilities arise due to the imbalance of uphill/downhill adatom currents related with large Ehrlich-Schwöbel (ES) barriers and permeability of straight [ 11 bar 2 ] -type step edges. However, the first one is initiated by dominant downhill adatom current to distant sinks: bunches, wave's step edges, and "vacancy" islands emerging on terraces due to 2D island coalescence. As a result, top layer size decreases to the critical terrace width λ where 2DNG takes place. From the analysis of λ ∝ R - χ / 2 scaling at T =650 °C, we have found that i increases from i =2 on a three-layer wave to i =6-8 on a six-layer wave. This authenticates the significance of downhill adatom sink to distant steps related to the step permeability. The second instability type at T >720 °C is related to the raising of uphill adatom current due to slightly larger ES barrier for step-up attachment comparing to the step-down one (EES- 0.9 eV [Phys. Rev. Lett. 111 (2013) 036105]). This leads to "second layer" 2D nucleation on top layers, which triggers the growth of separate pyramids. Because of small difference between ES barriers, net uphill/downhill adatom currents are nearly equivalent, and therefore layer coverage distributions of both instabilities display similar linear slopes.

  3. Active-site structure, binding and redox activity of the heme–thiolate enzyme CYP2D6 immobilized on coated Ag electrodes: a surface-enhanced resonance Raman scattering study

    PubMed Central

    Bonifacio, Alois; Millo, Diego; Keizers, Peter H. J.; Boegschoten, Roald; Commandeur, Jan N. M.; Vermeulen, Nico P. E.; Gooijer, Cees

    2007-01-01

    Surface-enhance resonance Raman scattering spectra of the heme–thiolate enzyme cytochrome P450 2D6 (CYP2D6) adsorbed on Ag electrodes coated with 11-mercaptoundecanoic acid (MUA) were obtained in various experimental conditions. An analysis of these spectra, and a comparison between them and the RR spectra of CYP2D6 in solution, indicated that the enzyme’s active site retained its nature of six-coordinated low-spin heme upon immobilization. Moreover, the spectral changes detected in the presence of dextromethorphan (a CYP2D6 substrate) and imidazole (an exogenous heme axial ligand) indicated that the immobilized enzyme also preserved its ability to reversibly bind a substrate and form a heme–imidazole complex. The reversibility of these processes could be easily verified by flowing alternately solutions of the various compounds and the buffer through a home-built spectroelectrochemical flow cell which contained a sample of immobilized protein, without the need to disassemble the cell between consecutive spectral data acquisitions. Despite immobilized CYP2D6 being effectively reduced by a sodium dithionite solution, electrochemical reduction via the Ag electrode was not able to completely reduce the enzyme, and led to its extensive inactivation. This behavior indicated that although the enzyme’s ability to exchange electrons is not altered by immobilization per se, MUA-coated electrodes are not suited to perform direct electrochemistry of CYP2D6. Electronic supplementary material The online version of this article (doi:10.1007/s00775-007-0303-1) contains supplementary material, which is available to authorized users. PMID:17899220

  4. Quantum oscillations from inside the Fermi sea

    NASA Astrophysics Data System (ADS)

    Pal, Hridis K.

    2017-02-01

    Quantum oscillations are conventionally understood to arise from the Fermi level; hence, they are considered to be a proof of the existence of an underlying Fermi surface. In this article we show that in certain situations quantum oscillations can also arise from inside the Fermi sea. We establish this analytically, supporting it with numerical calculations. Possible scenarios where such unusual behavior can occur are pointed out. In particular, in strongly particle-hole asymmetric insulators, models of which have been recently used in the context of the topological Kondo insulator SmB6, we show that the oscillations arise from inside the filled band, and are not related to the gap.

  5. Fermi-liquid theory for unconventional superconductors

    SciTech Connect

    Sauls, J.A.

    1994-12-31

    Fermi liquid theory is used to generate the Ginzburg-Landau free energy functionals for unconventional superconductors belonging to various representations. The parameters defining the GL functional depend on Fermi surface anisotropy, impurity scattering and the symmetry class of the pairing interaction. As applications the author considers the basic models for the multiple superconducting phases of UPt{sub 3}. An important prediction of the leading order Fermi liquid theory for the two-dimensional representations of the hexagonal symmetry group is that the zero-field equilibrium state exhibits spontaneously broken time-reversal symmetry.

  6. Band structure, Fermi surface, elastic, thermodynamic, and optical properties of AlZr 3 , AlCu 3 , and AlCu 2 Zr: First-principles study

    NASA Astrophysics Data System (ADS)

    Parvin, R.; Parvin, F.; Ali, M. S.; Islam, A. K. M. A.

    2016-08-01

    The electronic properties (Fermi surface, band structure, and density of states (DOS)) of Al-based alloys AlM 3 (M = Zr and Cu) and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation (GGA). The structural parameters and elastic constants are evaluated and compared with other available data. Also, the pressure dependences of mechanical properties of the compounds are studied. The temperature dependence of adiabatic bulk modulus, Debye temperature, specific heat, thermal expansion coefficient, entropy, and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K. The parameters of optical properties (dielectric functions, refractive index, extinction coefficient, absorption spectrum, conductivity, energy-loss spectrum, and reflectivity) of the compounds are calculated and discussed for the first time. The reflectivities of the materials are quite high in the IR-visible-UV region up to ˜ 15 eV, showing that they promise to be good coating materials to avoid solar heating. Some of the properties are also compared with those of the Al-based Ni3Al compound.

  7. Evidence of Fermi surface reconstruction and the formation of small hole pockets in underdoped La2-xSrxCuO4: Far Infrared Hall measurements

    NASA Astrophysics Data System (ADS)

    Schmadel, D. C.; Jenkins, G. S.; Drew, H. D.; Tsukada, I.; Ando, T.

    2008-03-01

    The Hall Effect in La2-xSrxCuO4 films is measured from 3 to 100 meV as a function of temperature from 5K to 300K and carrier doping ranging from severely underdoped (x=0.03) to optimal doped (x=0.15). The behavior of the infrared Hall angle with temperature and frequency is found to be consistent with a simple extended Drude model at all dopings. A significant reduction of the Hall mass is observed when the hole doping level is reduced from optimal doping, which is consistent with a drastic reduction of the Fermi surface volume. These results are similar to earlier mid-IR Hall measurements obtained in underdoped YBCO, [1] and related to the recent observations of quantum oscillations reported in YBCO. [2] [1] L. B. Rigal, et al., Phys. Rev. Lett. 93, 137002 (2004). [2] N. Doiron-Leyraud, et al., Nature, 447 565 (2007); A. F. Bangura, et al., Cond-mat/07074461 and E. A. Yelland, et al., Cond mat/07070057

  8. Fermi surface symmetry and evolution of the electronic structure across the paramagnetic-helimagnetic transition in MnSi/Si(111)

    NASA Astrophysics Data System (ADS)

    Nicolaou, Alessandro; Gatti, Matteo; Magnano, Elena; Le Fèvre, Patrick; Bondino, Federica; Bertran, François; Tejeda, Antonio; Sauvage-Simkin, Michèle; Vlad, Alina; Garreau, Yves; Coati, Alessandro; Guérin, Nicolas; Parmigiani, Fulvio; Taleb-Ibrahimi, Amina

    2015-08-01

    MnSi has been extensively studied for five decades; nonetheless detailed information on the Fermi surface (FS) symmetry is still lacking. This missed information prevents a comprehensive understanding of the nature of the magnetic interaction in this material. Here, by performing angle-resolved photoemission spectroscopy on high-quality MnSi films epitaxially grown on Si(111), we unveil the FS symmetry and the evolution of the electronic structure across the paramagnetic-helimagnetic transition at TC˜40 K , along with the appearance of sharp quasiparticle emission below TC. The shape of the resulting FS is found to fulfill robust nesting effects. These effects can be at the origin of strong magnetic fluctuations not accounted for by the state-of-the-art quasiparticle self-consistent GW approximation. From this perspective, the unforeseen quasiparticle damping detected in the paramagnetic phase and relaxing only below TC, along with the persistence of the d -band splitting well above TC, at odds with a simple Stoner model for itinerant magnetism, opens the search for exotic magnetic interactions favored by FS nesting and affecting the quasiparticle lifetime.

  9. High-performance giant-magnetoresistance junctions based on the all-Heusler architecture with matched energy bands and Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Bai, Zhaoqiang; Cai, Yongqing; Shen, Lei; Han, Guchang; Feng, Yuanping

    2013-04-01

    We present an all-Heusler architecture which could be used as a rational design scheme for achieving high spin-filter efficiency in the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices. A Co2MnSi/Ni2NiSi/Co2MnSi trilayer stack is chosen as the prototype of such an architecture, of which the electronic structure and magnetotransport properties are systematically investigated by first principles approaches. Well matched energy bands and Fermi surfaces between the all-Heusler electrode-spacer pair are found, which, in combination with the electrode half-metallicity, indicate large bulk and interfacial spin-asymmetry, high spin-filter efficiency, and consequently good magnetoresistance performance. Transport calculations further confirm the superiority of the all-Heusler architecture over the conventional Heusler/transition-metal structure by comparing their transmission coefficients and interfacial resistances of parallel conduction electrons, as well as the macroscopic current-voltage characteristics. We suggest future theoretical and experimental efforts in developing high-performance all-Heusler CPP-GMR junctions for the read heads of the next generation high-density hard disk drives.

  10. Structural, electronic transport and optical properties of functionalized quasi-2D TiC2 from first-principles calculations

    NASA Astrophysics Data System (ADS)

    Berdiyorov, G. R.; Madjet, M. E.

    2016-12-01

    Using the first-principles density functional theory, we study the effect of surface functionalization on the structural and optoelectronic properties of recently proposed quasi-two-dimensional material TiC2 [T. Zhao, S. Zhang, Y. Guo, Q. Wang, Nanoscale 8 (2016) 233]. Hydrogenated, fluorinated, oxidized and hydroxylated surfaces are considered. Significant changes in the lattice parameters and partial charge distributions are found due to the surface termination. Direct contribution of the adatoms to the system density of states near the Fermi level is obtained, which has a major impact on the optoelectronic properties of the material. For example, surface termination results in larger absorption in the visible range of the spectrum. The electronic transport is also affected by the surface functionalization: the current in the system can be reduced by an order of magnitude. These findings indicate the importance of the effects of surface passivation on optoelectronic properties of this quasi-2D material.

  11. Long-Wavelength Infrared Surface Plasmons on Ga-Doped ZnO Films Excited via 2D Hole Arrays for Extraordinary Optical Transmission (Preprint)

    DTIC Science & Technology

    2013-10-01

    wavelength infrared regime. EOT is facilitated by the excitation of surface plasmon polaritons (SPPs) and can be tuned utilizing the physical...facilitated by the excitation of surface plasmon polaritons (SPPs) and can be tuned utilizing the physical structure size such as period. Pulse laser deposited...plasmonics, infrared, EOT, doped zinc oxides. 1. INTRODUCTION Surface plasmon polaritons (SPPs) are a means of real-time, label-free biosensing

  12. Anomalies in the Fermi Surface and Band Dispersion of Quasi-One-Dimensional CuO Chains in the High-Temperature Superconductor YBa2Cu4O8

    NASA Astrophysics Data System (ADS)

    Kondo, Takeshi; Khasanov, R.; Karpinski, J.; Kazakov, S. M.; Zhigadlo, N. D.; Bukowski, Z.; Shi, M.; Bendounan, A.; Sassa, Y.; Chang, J.; Pailhés, S.; Mesot, J.; Schmalian, J.; Keller, H.; Kaminski, A.

    2010-12-01

    We have investigated the electronic states in quasi-one-dimensional CuO chains by microprobe angle resolved photoemission spectroscopy. We find that the quasiparticle Fermi surface consists of six disconnected segments, consistent with recent theoretical calculations that predict the formation of narrow, elongated Fermi surface pockets for coupled CuO chains. In addition, we find a strong renormalization effect with a significant kink structure in the band dispersion. The properties of this latter effect [energy scale (˜40meV), temperature dependence, and behavior with Zn-doping] are identical to those of the bosonic mode observed in CuO2 planes of high-temperature superconductors, indicating they have a common origin.

  13. A temperature dependent 2D-ACAR study of untwinned metallic YBa{sub 2}Cu{sub 3}O{sub 7{minus}x}

    SciTech Connect

    Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G.; Bansil, A.

    1992-02-01

    The authors have carried out 2D-ACAR measurements in the c-axis projection on an untwinned single crystal of YBa{sub 2}Cu{sub 3}O{sub 7{minus}x} as a function of temperature, for five temperatures ranging from 30K to 300K. These temperature dependent 2D-ACAR spectra can be approximated by a superposition of two temperature independent spectra with temperature dependent weighting factors. The authors discuss how the temperature dependence of the data can be exploited to obtain a {open_quote}background corrected{close_quote} experimental spectrum, which is found to be in remarkable accord with the corresponding band theory based predictions, including for the first time the overall amplitude of the anisotropy in the 2D-ACAR. The corrected data also show clear signatures of the ridge Fermi surface and an indication of the pillbox surface.

  14. 2D Mesh Manipulation

    DTIC Science & Technology

    2011-11-01

    PLATE A two-dimensional flat plate mesh was created using the Gridgen software package (Ref. 13). This mesh (shown in Fig. 10) closely resembled a...desired tolerance of the projection onto the surface. The geometry file on which the geometry surface is based can be easily generated using Gridgen ...by exporting a curve (or number of curves) under the INPUT/OUTPUT commands in the Gridgen interface (Ref. 13). Initially, the floating boundary

  15. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; W. Quinlan

    2003-10-01

    The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, a new field demonstration, Springdale Prospect in Manistee County, Michigan was begun to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path. The surface geochemistry sampling at the original Bear Lake demonstration site was updated several months after the prospect was confirmed and production begun. As expected, the anomaly appears to be diminishing as the positive (apical) anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir.

  16. The use of surface tension to predict the formation of 2D arrays of latex spheres formed via the Langmuir-Blodgett-like technique.

    PubMed

    Marquez, Maricel; Grady, Brian P

    2004-12-07

    Highly ordered hexagonal arrays of latex spheres on highly ordered pyrolytic graphite (HOPG) have been prepared from a Langmuir-Blodgett-like (LB-like) technique using both polymers and surfactants as spreading agents. The role of spreading agent concentration in forming a well-ordered, stable monolayer at the air-liquid interface was studied by means of atomic force microscopy, scanning electron microscopy, optical microscopy, and surface tension measurements for three different systems: a nonionic surfactant, octylphenoxy poly(ethyleneoxy)ethanol (Igepal CO 630); an anionic surfactant, sodium dodecyl sulfate; and a low-molecular-weight, water-soluble polymer, polyacrylamide. For both the anionic surfactant and the water soluble polymer, a correlation was found between a unique feature in surface tension measurements of the latex-spreading agent mixture and the concentrations at which hexagonal arrays of latex spheres form on the surface of HOPG. For the nonionic surfactant, no ordered structures were found on HOPG for any surfactant concentration, consistent with no appearance of the unique feature in surface tension measurements. These results show that a tensiometer can be used to determine the conditions under which well-ordered latex films have the possibility of forming on a substrate using the LB-like technique; however, other factors, such as pulling speed and surface chemistry, play a role as well.

  17. Justification of the Nonlinear Schrödinger Equation for the Evolution of Gravity Driven 2D Surface Water Waves in a Canal of Finite Depth

    NASA Astrophysics Data System (ADS)

    Düll, Wolf-Patrick; Schneider, Guido; Wayne, C. Eugene

    2016-05-01

    In 1968 V.E. Zakharov derived the Nonlinear Schrödinger equation for the two-dimensional water wave problem in the absence of surface tension, that is, for the evolution of gravity driven surface water waves, in order to describe slow temporal and spatial modulations of a spatially and temporarily oscillating wave packet. In this paper we give a rigorous proof that the wave packets in the two-dimensional water wave problem in a canal of finite depth can be approximated over a physically relevant timespan by solutions of the Nonlinear Schrödinger equation.

  18. A numerical study of steady 2D flow around NACA 0015 and NACA 0012 hydrofoil with free surface using VOF method

    NASA Astrophysics Data System (ADS)

    Adjali, Saadia; Belkadi, Mustapha; Aounallah, Mohammed; Imine, Omar

    2015-05-01

    Accurate simulation of turbulent free surface flows around surface ships has a central role in the optimal design of such naval vessels. The flow problem to be simulated is rich in complexity and poses many modeling challenges because of the existence of breaking waves around the ship hull, and because of the interaction of the two-phase flow with the turbulent boundary layer. In this paper, our goal is to estimate the lift and drag coefficients for NACA 0012 of hydrofoil advancing in calm water under steady conditions with free surface and emerged NACA 0015. The commercial CFD software FLUENT version 14 is used for the computations in the present study. The calculated grid is established using the code computer GAMBIT 2.3.26.The shear stress k-ωSST model is used for turbulence modeling and the volume of fluid technique is employed to simulate the free-surface motion. In this computation, the second order upwind scheme is used for discretizing the convection terms in the momentum transport equations, the Modified HRIC scheme for VOF discretisation. The results obtained compare well with the experimental data.

  19. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR; VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; A. Wylie; W. Quinlan

    2004-01-01

    The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. During this reporting period, a new field demonstration, Springdale Prospect in Manistee County, Michigan was begun to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path. The main news this reporting period is the confirmed discovery of producing hydrocarbons at the State Springdale & O'Driscoll No.16-16 demonstration well in Manistee County. This well was spudded in late November, tested and put on production in December 2003. To date it is flowing nearly 100 barrels of liquid hydrocarbons per day, which is a good well in Michigan. Reserves have not been established yet. The surface geochemistry sampling at the Springdale demonstration site will be repeated this spring after the well has been on production for several months to see if the anomaly pattern changes. We expect that the anomaly will diminish as the original positive (apical) anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir. This is the behavior that we observed at the Bear lake demonstration well reported last quarter.

  20. First principle study of the electronic structure, Fermi surface, electronic charge density and optical properties of ThCu5In and ThCu5Sn single crystals

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2014-02-01

    The electronic structure, Fermi surface, electronic charge density and optical properties of ThCu5In and ThCu5Sn single crystals are studied. The calculations are based on the full potential-linearized augmented plane wave (FPLAPW) method. The exchange and correlation potential is treated by the local density approximation (LDA) and generalized-gradient approximation (GGA), in addition the Engel-Vosko (EV-GGA) formalism was also applied. The DFT calculations show that these compounds have metallic origin. The contribution of different bands was analyzed from total and partial density of states curves. The values of the density of states at Fermi energy (N(EF)) for ThCu5In (ThCu5Sn) is 1.75 (1.63) states/eV unit cell. The bare electronic specific heat coefficient (γ) is found to be equal to 0.30 and 0.28 mJ/mol-K2 for ThCu5In and ThCu5Sn, respectively. The Fermi surface of ThCu5In/ThCu5Sn is composed of three/four bands crossing along the R-Γ direction. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane and it shows the covalent character of Cu-Cu and Sn/In-Cu bonds. The optical properties were also calculated and analyzed.

  1. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; T.J. Bornhorst; S.D. Chittick; William B. Harrison; W. Quinlan

    2001-10-31

    Two major accomplishments resulted from Phase I. One is the success of the surface geochemistry program, which collected over 800 samples from the site of the 1st demonstration well in Vernon Field and has pretty well provided us with the tools to delineate favorable ground from unfavorable. The second is the recent detailed mapping of the Central Michigan Basin that for the first time revealed the presence of at least two major faults that control the location of many of the reservoirs in the Michigan Basin. These faults were located from structure maps obtained by contouring the surface of the Dundee Formation using top picks from 9861 wells in 14 counties. Faults were inferred where the contour lines were most dense (''stacked'').

  2. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; W. Quinlan

    2003-07-01

    The principal objective of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, a field demonstration was undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The surface geochemistry data showed a strong anomaly in the Myrtle Beach area that would justify drilling by itself and even more so in conjunction with the structural interpretation from the 3D seismic data. The Myrtle Beach geochemical survey indicated a good to excellent prospect which was confirmed by drilling. Presented in this quarterly report is the Case History and Well Summary for the Myrtle Beach area in Burke County, North Dakota. This case history presents the important technical details regarding the geochemistry and the two vertical wells that are part of this field demonstration, and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and is being used on all subsequent field demonstrations as they near completion.

  3. Chemical analysis of solid materials by a LIMS instrument designed for space research: 2D elemental imaging, sub-nm depth profiling and molecular surface analysis

    NASA Astrophysics Data System (ADS)

    Moreno-García, Pavel; Grimaudo, Valentine; Riedo, Andreas; Neuland, Maike B.; Tulej, Marek; Broekmann, Peter; Wurz, Peter

    2016-04-01

    Direct quantitative chemical analysis with high lateral and vertical resolution of solid materials is of prime importance for the development of a wide variety of research fields, including e.g., astrobiology, archeology, mineralogy, electronics, among many others. Nowadays, studies carried out by complementary state-of-the-art analytical techniques such as Auger Electron Spectroscopy (AES), X-ray Photoelectron Spectroscopy (XPS), Secondary Ion Mass Spectrometry (SIMS), Glow Discharge Time-of-Flight Mass Spectrometry (GD-TOF-MS) or Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) provide extensive insight into the chemical composition and allow for a deep understanding of processes that might have fashioned the outmost layers of an analyte due to its interaction with the surrounding environment. Nonetheless, these investigations typically employ equipment that is not suitable for implementation on spacecraft, where requirements concerning weight, size and power consumption are very strict. In recent years Laser Ablation/Ionization Mass Spectrometry (LIMS) has re-emerged as a powerful analytical technique suitable not only for laboratory but also for space applications.[1-3] Its improved performance and measurement capabilities result from the use of cutting edge ultra-short femtosecond laser sources, improved vacuum technology and fast electronics. Because of its ultimate compactness, simplicity and robustness it has already proven to be a very suitable analytical tool for elemental and isotope investigations in space research.[4] In this contribution we demonstrate extended capabilities of our LMS instrument by means of three case studies: i) 2D chemical imaging performed on an Allende meteorite sample,[5] ii) depth profiling with unprecedented sub-nm vertical resolution on Cu electrodeposited interconnects[6,7] and iii) preliminary molecular desorption of polymers without assistance of matrix or functionalized substrates.[8] On the whole

  4. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; A. Wylie; W. Quinlan

    2004-04-01

    One of the main objectives of this demonstration project is to test surface geochemical techniques for detecting trace amounts of light hydrocarbons in pore gases as a means of reducing risk in hydrocarbon exploration and production. As part of the project, several field demonstrations were undertaken to assess the validity and usefulness of the microbial surface geochemical technique. The important observations from each of these field demonstrations are briefly reviewed in this annual report. These demonstrations have been successful in identifying the presence or lack of hydrocarbons in the subsurface and can be summarized as follows: (1) The surface geochemistry data showed a fair-to-good microbial anomaly that may indicate the presence of a fault or stratigraphic facies change across the drilling path of the State Springdale & O'Driscoll No.16-16 horizontal demonstration well in Manistee County, Michigan. The well was put on production in December 2003. To date, the well is flowing nearly 100 barrels of liquid hydrocarbons per day plus gas, which is a good well in Michigan. Reserves have not been established yet. Two successful follow-up horizontal wells have also been drilled in the Springdale area. Additional geochemistry data will be collected in the Springdale area in 2004. (2) The surface geochemistry sampling in the Bear Lake demonstration site in Manistee County, Michigan was updated after the prospect was confirmed and production begun; the original subsurface and seismic interpretation used to guide the location of the geochemical survey for the Charlich Fauble re-entry was different than the interpretation used by the operator who ultimately drilled the well. As expected, the anomaly appears to be diminishing as the positive (apical) microbial anomaly is replaced by a negative (edge) anomaly, probably due to the pressure draw-down in the reservoir. (3) The geochemical sampling program over the Vernon Field, Isabella County, Michigan is now

  5. Fermi Galactic Center Zoom

    NASA Video Gallery

    This animation zooms into an image of the Milky Way, shown in visible light, and superimposes a gamma-ray map of the galactic center from NASA's Fermi. Raw data transitions to a view with all known...

  6. Fermi at Six Months

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2009-01-01

    An overview of the Fermi Gamma-ray Space Telescope's first 6 months in operation is provided. The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy rage 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. It contains a Large Area Telescope capable of viewing the entire sky every 3 hours and a Gamma-ray Burst Monitor for viewing the entire unocculted sky. Since its launch on June 11, 2008 Fermi has provided information on pulsars, gamma ray bursts, relativistic jets, the active galactic nucleus, and a globular star cluster. This presentation describes Fermi's development, mission, instruments and recent findings.

  7. Fermi, Szilard and Trinity

    ERIC Educational Resources Information Center

    Anderson, Herbert L.

    1974-01-01

    The final installment of the author's recollections of his work with physicists Enrico Fermi, Leo Szilard and others in developing the first controlled nuclear chain reaction and in preparing the test explosion of the first atomic bomb. (GS)

  8. 2D microwave imaging reflectometer electronics

    SciTech Connect

    Spear, A. G.; Domier, C. W. Hu, X.; Muscatello, C. M.; Ren, X.; Luhmann, N. C.; Tobias, B. J.

    2014-11-15

    A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

  9. 2D microwave imaging reflectometer electronics.

    PubMed

    Spear, A G; Domier, C W; Hu, X; Muscatello, C M; Ren, X; Tobias, B J; Luhmann, N C

    2014-11-01

    A 2D microwave imaging reflectometer system has been developed to visualize electron density fluctuations on the DIII-D tokamak. Simultaneously illuminated at four probe frequencies, large aperture optics image reflections from four density-dependent cutoff surfaces in the plasma over an extended region of the DIII-D plasma. Localized density fluctuations in the vicinity of the plasma cutoff surfaces modulate the plasma reflections, yielding a 2D image of electron density fluctuations. Details are presented of the receiver down conversion electronics that generate the in-phase (I) and quadrature (Q) reflectometer signals from which 2D density fluctuation data are obtained. Also presented are details on the control system and backplane used to manage the electronics as well as an introduction to the computer based control program.

  10. High Dynamics and Precision Optical Measurement Using a Position Sensitive Detector (PSD) in Reflection-Mode: Application to 2D Object Tracking over a Smart Surface

    PubMed Central

    Ivan, Ioan Alexandru; Ardeleanu, Mihai; Laurent, Guillaume J.

    2012-01-01

    When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD. PMID:23223078

  11. High dynamics and precision optical measurement using a position sensitive detector (PSD) in reflection-mode: application to 2D object tracking over a Smart Surface.

    PubMed

    Ivan, Ioan Alexandru; Ardeleanu, Mihai; Laurent, Guillaume J

    2012-12-06

    When related to a single and good contrast object or a laser spot, position sensing, or sensitive, detectors (PSDs) have a series of advantages over the classical camera sensors, including a good positioning accuracy for a fast response time and very simple signal conditioning circuits. To test the performance of this kind of sensor for microrobotics, we have made a comparative analysis between a precise but slow video camera and a custom-made fast PSD system applied to the tracking of a diffuse-reflectivity object transported by a pneumatic microconveyor called Smart-Surface. Until now, the fast system dynamics prevented the full control of the smart surface by visual servoing, unless using a very expensive high frame rate camera. We have built and tested a custom and low cost PSD-based embedded circuit, optically connected with a camera to a single objective by means of a beam splitter. A stroboscopic light source enhanced the resolution. The obtained results showed a good linearity and a fast (over 500 frames per second) response time which will enable future closed-loop control by using PSD.

  12. E-2D Advanced Hawkeye Aircraft (E-2D AHE)

    DTIC Science & Technology

    2015-12-01

    Selected Acquisition Report (SAR) RCS: DD-A&T(Q&A)823-364 E-2D Advanced Hawkeye Aircraft (E-2D AHE) As of FY 2017 President’s Budget Defense...Office Estimate RDT&E - Research, Development, Test, and Evaluation SAR - Selected Acquisition Report SCP - Service Cost Position TBD - To Be Determined

  13. Positron 2D-ACAR experiments and electron-positron momentum density in YBa{sub 2}Cu{sub 3}O{sub 7-x}

    SciTech Connect

    Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G.; Bansil, A.

    1991-12-01

    We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ``background corrected`` experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.

  14. Positron 2D-ACAR experiments and electron-positron momentum density in YBa sub 2 Cu sub 3 O sub 7-x

    SciTech Connect

    Smedskjaer, L.C.; Welp, U.; Fang, Y.; Bailey, K.G. ); Bansil, A. . Dept. of Physics)

    1991-12-01

    We discuss positron annihilation (2D-ACAR) measurements in the C- projection on an untwinned metallic single crystal of YBa{sub 2}Cu{sub 3}O{sub 7-x} as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a background corrected'' experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displays in particular clear signatures of the electron ridge Fermi surface.

  15. V2O5 encapsulated MWCNTs in 2D surface architecture: Complete solid-state bendable highly stabilized energy efficient supercapacitor device

    PubMed Central

    Pandit, Bidhan; Dubal, Deepak P.; Gómez-Romero, Pedro; Kale, Bharat B.; Sankapal, Babasaheb R.

    2017-01-01

    A simple and scalable approach has been reported for V2O5 encapsulation over interconnected multi-walled carbon nanotubes (MWCNTs) network using chemical bath deposition method. Chemically synthesized V2O5/MWCNTs electrode exhibited excellent charge-discharge capability with extraordinary cycling retention of 93% over 4000 cycles in liquid-electrolyte. Electrochemical investigations have been performed to evaluate the origin of capacitive behavior from dual contribution of surface-controlled and diffusion-controlled charge components. Furthermore, a complete flexible solid-state, flexible symmetric supercapacitor (FSS-SSC) device was assembled with V2O5/MWCNTs electrodes which yield remarkable values of specific power and energy densities along with enhanced cyclic stability over liquid configuration. As a practical demonstration, the constructed device was used to lit the ‘VNIT’ acronym assembled using 21 LED’s. PMID:28256550

  16. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI.

    SciTech Connect

    James R. Wood; T.J. Bornhorst; S.D. Chittick; William B. Harrison; W. Quinlan

    2002-01-01

    In this reporting period, we extended the fault study to include more faults and developed new techniques to visualize the faults. We now have used data from the Dundee Formation to document 11 major faults in the Michigan Basin and are in the process of reviewing data from other horizons. These faults appear to control the locations of many of the large anticlinal structures in the Michigan Basin and likely controlled fluid movements as well. The surface geochemistry program is also moving along well with emphasis on measuring samples collected last sampling season. The new laboratory is now functional and has been fully staffed as of December. The annual project review has been set for March 7-9 in Tampa, Florida. Contracts are being prepared for drilling the Bower's prospects in Isabella County, Michigan, this spring or summer.

  17. V2O5 encapsulated MWCNTs in 2D surface architecture: Complete solid-state bendable highly stabilized energy efficient supercapacitor device

    NASA Astrophysics Data System (ADS)

    Pandit, Bidhan; Dubal, Deepak P.; Gómez-Romero, Pedro; Kale, Bharat B.; Sankapal, Babasaheb R.

    2017-03-01

    A simple and scalable approach has been reported for V2O5 encapsulation over interconnected multi-walled carbon nanotubes (MWCNTs) network using chemical bath deposition method. Chemically synthesized V2O5/MWCNTs electrode exhibited excellent charge-discharge capability with extraordinary cycling retention of 93% over 4000 cycles in liquid-electrolyte. Electrochemical investigations have been performed to evaluate the origin of capacitive behavior from dual contribution of surface-controlled and diffusion-controlled charge components. Furthermore, a complete flexible solid-state, flexible symmetric supercapacitor (FSS-SSC) device was assembled with V2O5/MWCNTs electrodes which yield remarkable values of specific power and energy densities along with enhanced cyclic stability over liquid configuration. As a practical demonstration, the constructed device was used to lit the ‘VNIT’ acronym assembled using 21 LED’s.

  18. 2D numerical simulation of impinging jet onto the concave surface by k - w - overline{{v2 }} - f turbulence model

    NASA Astrophysics Data System (ADS)

    Seifi, Zeinab; Nazari, Mohammad Reza; Khalaji, Erfan

    2017-01-01

    In the present article, the characteristics of turbulent jet impinging onto a concave surface is studied using k - w - overline{{v2 }} - f turbulence model. Dependent parameters such as inlet Reynolds number (2960 < Re < 12,000), nozzle-plate distance (4 < H/B < 10), concavity (D/B = 30, 60) of confined and unconfined impinging jet are scrutinized to find out whether this approach would bring any privileges compared to other investigations or not. The obtained results indicate better performance in low nozzle-plate distance in comparison with those mentioned in other literatures. Furthermore, the average Nusselt number of confined impinging jet overtakes unconfined one (similar circumstances) while this trend will decline as relative concavity increases. Moreover, local heat transfer of stagnation area and wall jet goes up and down through nozzle-plate distance enhancement respectively. Finally, the effects of sinusoidal pulsed inlet profile on heat transfer of unconfined impinging jet indicate direct affiliation of amplitude and neutral impact of frequency on Nusselt number distribution.

  19. USING RECENT ADVANCES IN 2D SEISMIC TECHNOLOGY AND SURFACE GEOCHEMISTRY TO ECONOMICALLY REDEVELOP A SHALLOW SHELF CARBONATE RESERVOIR: VERNON FIELD, ISABELLA COUNTY, MI

    SciTech Connect

    James R. Wood; W. Quinlan

    2003-01-01

    Presented in this quarterly report is the Case History and Well Summary for the Vernon Field demonstration project in Isabella County, Michigan. This new case history and well summary format organizes and presents the technical and historical details of the Vernon Field demonstration, as well as the field demonstration results and the applicability of these results to other demonstration projects. This format could be duplicated for other demonstration projects and will be used on all subsequent field demonstrations as they near completion. Planning for the annual project meeting in Tampa, Florida has begun. This meeting will be held March 7-9, 2003 at the same site as the last three meetings. The goals of this project were to: (1) test the use of multi-lateral wells to recover bypassed hydrocarbons and (2) to access the potential of using surface geochemistry to reduce drilling risk. Two new demonstration wells, the State-Smock and the Bowers 4-25, were drilled to test the Dundee Formation at Vernon Field for bypassed oil. Neither well was commercial, although both produced hydrocarbon shows. An extensive geochemical survey in the vicinity of Vernon Field, covering much of Isabella County, has produced a base map for interpretation of anomalies in Michigan. Several potential new anomalies were discovered that could be further investigated.

  20. Regional subsidence modelling in Murcia city (SE Spain) using 1-D vertical finite element analysis and 2-D interpolation of ground surface displacements

    NASA Astrophysics Data System (ADS)

    Tessitore, S.; Fernández-Merodo, J. A.; Herrera, G.; Tomás, R.; Ramondini, M.; Sanabria, M.; Duro, J.; Mulas, J.; Calcaterra, D.

    2015-11-01

    Subsidence is a hazard that may have natural or anthropogenic origin causing important economic losses. The area of Murcia city (SE Spain) has been affected by subsidence due to groundwater overexploitation since the year 1992. The main observed historical piezometric level declines occurred in the periods 1982-1984, 1992-1995 and 2004-2008 and showed a close correlation with the temporal evolution of ground displacements. Since 2008, the pressure recovery in the aquifer has led to an uplift of the ground surface that has been detected by the extensometers. In the present work an elastic hydro-mechanical finite element code has been used to compute the subsidence time series for 24 geotechnical boreholes, prescribing the measured groundwater table evolution. The achieved results have been compared with the displacements estimated through an advanced DInSAR technique and measured by the extensometers. These spatio-temporal comparisons have showed that, in spite of the limited geomechanical data available, the model has turned out to satisfactorily reproduce the subsidence phenomenon affecting Murcia City. The model will allow the prediction of future induced deformations and the consequences of any piezometric level variation in the study area.

  1. Complete active space second order perturbation theory (CASPT2) study of N(2D) + H2O reaction paths on D1 and D0 potential energy surfaces: Direct and roaming pathways

    NASA Astrophysics Data System (ADS)

    Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

    2014-10-01

    We report reaction paths starting from N(2D) + H2O for doublet spin states, D0 and D1. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space. In addition to direct dissociation pathways that would be dominant, three roaming processes, two roaming dissociation, and one roaming isomerization: (1) H2ON → H-O(H)N → H-HON → NO(2Π) + H2, (2) cis-HNOH → HNO-H → H-HNO → NO + H2, (3) H2NO → H-HNO → HNO-H → trans-HNOH, are confirmed on the D0 surface.

  2. Fermi Arc Evolution and Doping Mechanism in High-Temperature Superconductors

    NASA Astrophysics Data System (ADS)

    Sunko, Denis K.; Pelc, Damjan; Požek, Miroslav; Despoja, Vito; Lazic, Predrag

    2015-03-01

    We calculate realistic Fermi surface (FS) evolution of La2-xSrxCuO4 (LSCO) with Sr doping within an extensive ab-initio framework including advanced band-unfolding techniques. We show that ordinary Kohn-Sham DFT+U can reproduce the observed metal-insulator transition and arc growth, when not restricted to the paramagnetic solution space. We elucidate both arc protection and the inadequacy of the rigid-band picture as consequences of a rapid change in orbital symmetry at the Fermi energy: the material undergoes a dimensional crossover along the Fermi surface, between the nodal (2D) and antinodal (3D) regions. In LSCO, this crossover accounts for FS arcs and the antinodal pseudogap, otherwise ubiquitous phenomena in high-Tc cuprates. The same calculation shows that the Sr hole stays localized in the vicinity of the dopand atom, indicating that metallization of the Cu-O plane is due to an orbital transition between Cu and O planar sites, originally proposed by Mazumdar in 1989. We can directly observe effects of the transition in charge transfers among in-plane atoms, which are different than predicted by non-interacting coherent models. This ``ionic doping'' mechanism has close parallels to modern views on the metallization of interfaces.

  3. Imaging high stage river-water intrusion into a contaminated aquifer along a major river corridor using 2D time-lapse surface electrical resistivity tomography

    SciTech Connect

    Wallin, Erin L.; Johnson, Timothy C.; Greenwood, William J.; Zachara, John M.

    2013-03-29

    The Hanford 300 Area is located adjacent to the Columbia River in south-central Washington State, USA, and was a former site for nuclear fuel processing operations. Waste disposal practices resulted in persistent unsaturated zone and groundwater contamination, the primary contaminant of concern being uranium. Uranium behavior at the site is intimately linked with river stage driven groundwater-river water exchange such that understanding the nature of river water intrusion into the 300 Area is critical for predicting uranium desorption and transport. In this paper we use time-lapse electrical resistivity tomography (ERT) to image the inland intrusion of river during high stage conditions. We demonstrate a modified time-lapse inversion approach, whereby the transient water table elevation is explicitly modeled by removing regularization constraints across the water table boundary. This implementation was critical for producing meaningful imaging results. We inverted approximately 1200 data sets (400 per line over 3 lines) using high performance computing resources to produce a time-lapse sequence of changes in bulk conductivity caused by river water intrusion during the 2011 spring runoff cycle over approximately 125 days. The resulting time series for each mesh element was then analyzed using common time series analysis to reveal the timing and location of river water intrusion beneath each line. The results reveal non-uniform flows characterized by preferred flow zones where river water enters and exits quickly with stage increase and decrease, and low permeability zones with broader bulk conductivity ‘break through’ curves and longer river water residence times. The time-lapse ERT inversion approach removes the deleterious effects of changing water table elevation and enables remote and spatial continuous groundwater-river water exchange monitoring using surface based ERT arrays under conditions where groundwater and river water conductivity are in contrast.

  4. Probing the Contact Locally in a Trapped Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Paudel, Rabin; Sagi, Yoav; Drake, Tara; Jin, Deborah

    2013-03-01

    The inherent density inhomogeneity of a trapped gas can complicate interpretation of experiments and can wash out sharp features. This is especially important for a Fermi gas, where interaction effects as well as the local Fermi energy, or Fermi momentum, depend on the density. We report on experiments that use optical pumping with shaped light beams to spatially select the center part of a trapped gas for probing. This technique is compatible with momentum resolved measurements. For a weakly interacting Fermi gas of 40K atoms, we present measurements of the momentum distribution that reveal for the first time a sharp Fermi surface. We then apply this technique to a strongly interacting Fermi gas at the Feshbach resonance, where we measured the temperature dependence of the Tan's contact locally in the trapped gas.

  5. FermiGrid

    SciTech Connect

    Yocum, D.R.; Berman, E.; Canal, P.; Chadwick, K.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Sharma, N.; Timm, S.; /Fermilab

    2007-05-01

    As one of the founding members of the Open Science Grid Consortium (OSG), Fermilab enables coherent access to its production resources through the Grid infrastructure system called FermiGrid. This system successfully provides for centrally managed grid services, opportunistic resource access, development of OSG Interfaces for Fermilab, and an interface to the Fermilab dCache system. FermiGrid supports virtual organizations (VOs) including high energy physics experiments (USCMS, MINOS, D0, CDF, ILC), astrophysics experiments (SDSS, Auger, DES), biology experiments (GADU, Nanohub) and educational activities.

  6. Two Dimensional Effective Electron Mass at the Fermi Level in Quantum Wells of III-V, Ternary and Quaternary Semiconductors.

    PubMed

    Chakrabarti, S; Chatterjee, B; Debbarma, S; Ghatak, K P

    2015-09-01

    In this paper we study the influence of strong electric field on the two dimensional (2D)effective electron mass (EEM) at the Fermi level in quantum wells of III-V, ternary and quaternary semiconductors within the framework of k x p formalism by formulating a new 2D electron energy spectrum. It appears taking quantum wells of InSb, InAs, Hg(1-x)Cd(x)Te and In(1-x)Ga(x)As(1-y)P(y) lattice matched to InP as examples that the EEM increases with decreasing film thickness, increasing electric field and increases with increasing surface electron concentration exhibiting spikey oscillations because of the crossing over of the Fermi level by the quantized level in quantum wells and the quantized oscillation occurs when the Fermi energy touches the sub-band energy. The electric field makes the mass quantum number dependent and the oscillatory mass introduces quantum number dependent mass anisotropy in addition to energy. The EEM increases with decreasing alloy composition where the variations are totally band structure dependent. Under certain limiting conditions all the results for all the cases get simplified into the well-known parabolic energy bands and thus confirming the compatibility test. The content of this paper finds three applications in the fields of nano-science and technology.

  7. First-principles study of the electronic structure, charge density, Fermi surface and optical properties of zintl phases compounds Sr2ZnA2 (A=P, As and Sb)

    NASA Astrophysics Data System (ADS)

    Reshak, A. H.; Azam, Sikander

    2013-11-01

    We present first-principles calculations of the electronic structure, Fermi surface, electronic charge density and optical properties of Sr2ZnA2 (A=P, As and Sb) based on density-functional theory using the local density approximation (LDA), generalized-gradient approximation (GGA) and the Engel-Vosko GGA formalism (EV-GGA). Additionally, modified Becke-Johnson (mBJ) is also used to improve the band splitting results. The calculated band structure and density of states show that Sr2ZnA2 compounds are metallic. The total DOS at Fermi level N(EF) is 72.92, 73.06 and 33.47 states/eV and the bare electronic specific heat coefficient (γ) is 12.64, 5.805 and 12.67 mJ/mol-K2 for Sr2ZnP2, Sr2ZnAs2 and Sr2ZnSb2, respectively. The Fermi surface of Sr2ZnA2 compounds is composed of two bands crossing along the Γ-A direction of Brillouin zone. There exists a strong hybridization between Zn-p/s and Sb-d, Sb-p and Sr-d and also between Sr-s and Sr-p states. The bonding features are analyzed by using the electronic charge density contour in the (101) crystallographic plane. We found that Sr forms an ionic bond with Zn, whereas Zn forms a strong covalent interaction with P/As/Sb atoms. For further insight information about the electronic structure, the optical properties are derived and analyzed.

  8. 2D shear wave velocity mapping of the Hartoušov CO2 degassing area in the Cheb Basin, NW Bohemia (Czech Republic), using Multichannel Analysis of Surface Waves

    NASA Astrophysics Data System (ADS)

    Flores Estrella, H.; Henke, M.

    2015-12-01

    For the characterization of the subsurface of the Hartoušov CO2 degassing area in the Cheb Basin, NW Bohemia, Czech Republic several different approaches have been made. However, no active seismic characterization has been presented, nor published. The Multi­channel Analysis of Surface Waves (MASW) offers an useful tool to estimate vertical and horizontal velocity changes of the shallow subsurface. This can correlate to variations on rock elastic properties and/or fluid content, and represents the subsurface-layering.Surface waves were stimulated using a sledgehammer as source, and were measured with 48 vertical geophones with spacing of 1 m and the roll along method with a setup dis­placement of 2 m. Two source offsets, 10 m and 30 m, were used to increase the data quality and the resolution.The analysis of propagation velocities leads to dispersion curves from which 1D shear wave velocity profiles can be inverted. Those will be interpolated to create a 2D ground stiffness map. The measurements were taken in the NW area of the main degassing zone and are partially in the same spot of former investigations, i.e. CO2 concentration and gas flux measurements, electric and gravimetric surveys and continuous seismic noise mea­surements.Changes in the structure of the 2D velocity maps can be explained potentially with the oc­currence of fluid paths and their diffusion in the subsurface or the existence of the Počatky-Plesná fault zone, which position is not fully understood yet or both features in combination.

  9. Collisions of slow polyatomic ions with surfaces: dissociation and chemical reactions of C2H2+*, C2H3+, C2H4+*, C2H5+, and their deuterated variants C2D2+* and C2D4+* on room-temperature and heated carbon surfaces.

    PubMed

    Jasík, Juraj; Zabka, Jan; Feketeova, Linda; Ipolyi, Imre; Märk, Tilmann D; Herman, Zdenek

    2005-11-17

    Interaction of C2Hn+ (n = 2-5) hydrocarbon ions and some of their isotopic variants with room-temperature and heated (600 degrees C) highly oriented pyrolytic graphite (HOPG) surfaces was investigated over the range of incident energies 11-46 eV and an incident angle of 60 degrees with respect to the surface normal. The work is an extension of our earlier research on surface interactions of CHn+ (n = 3-5) ions. Mass spectra, translational energy distributions, and angular distributions of product ions were measured. Collisions with the HOPG surface heated to 600 degrees C showed only partial or substantial dissociation of the projectile ions; translational energy distributions of the product ions peaked at about 50% of the incident energy. Interactions with the HOPG surface at room temperature showed both surface-induced dissociation of the projectiles and, in the case of radical cation projectiles C2H2+* and C2H4+*, chemical reactions with the hydrocarbons on the surface. These reactions were (i) H-atom transfer to the projectile, formation of protonated projectiles, and their subsequent fragmentation and (ii) formation of a carbon chain build-up product in reactions of the projectile ion with a terminal CH3-group of the surface hydrocarbons and subsequent fragmentation of the product ion to C3H3+. The product ions were formed in inelastic collisions in which the translational energy of the surface-excited projectile peaked at about 32% of the incident energy. Angular distributions of reaction products showed peaking at subspecular angles close to 68 degrees (heated surfaces) and 72 degrees (room-temperature surfaces). The absolute survival probability at the incident angle of 60 degrees was about 0.1% for C2H2+*, close to 1% for C2H4+* and C2H5+, and about 3-6% for C2H3+.

  10. Pairing in a dry Fermi sea

    NASA Astrophysics Data System (ADS)

    Maier, T. A.; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-06-01

    In the traditional Bardeen-Cooper-Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin-fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  11. Fermi TGF detection map

    NASA Video Gallery

    Fermi’s Gamma-ray Burst Monitor detected 130 TGFs from August 2008 to the end of 2010. Thanks to instrument tweaks, the team has been able to improve the detection rate to several TGFs per week. ...

  12. Quasi-two-dimensional Fermi gases at finite temperatures

    NASA Astrophysics Data System (ADS)

    Fischer, Andrea M.; Parish, Meera M.

    2014-12-01

    We consider a Fermi gas with short-range attractive interactions that is confined along one direction by a tight harmonic potential. For this quasi-two-dimensional (quasi-2D) Fermi gas, we compute the pressure equation of state, radiofrequency spectrum, and the superfluid critical temperature Tc using a mean-field theory that accounts for all the energy levels of the harmonic confinement. Our calculation for Tc provides a natural generalization of the Thouless criterion to the quasi-2D geometry, and it correctly reduces to the 3D expression derived from the local density approximation in the limit where the confinement frequency ωz→0 . Furthermore, our results suggest that Tc can be enhanced by relaxing the confinement and perturbing away from the 2D limit.

  13. Fermi surface topology and hot spot distribution in the Kondo lattice system CeB6

    SciTech Connect

    Neupane, Madhab; Alidoust, Nasser; Belopolski, Ilya; Bian, Guang; Xu, Su-Yang; Kim, Dae-Jeong; Shibayev, Pavel P.; Sanchez, Daniel S.; Zheng, Hao; Chang, Tay-Rong; Jeng, Horng-Tay; Riseborough, Peter S.; Lin, Hsin; Bansil, Arun; Durakiewicz, Tomasz; Fisk, Zachary; Hasan, M. Zahid

    2015-09-18

    Rare-earth hexaborides have attracted considerable attention recently in connection to a variety of correlated phenomena including heavy fermions, superconductivity, and low-temperature magnetic phases. Here, we present high-resolution angle-resolved photoemission spectroscopy studies of trivalent CeB6 and divalent BaB6 rare-earth hexaborides. Here we find that the Fermi surface electronic structure of CeB6 consists of large oval-shaped pockets around the X points of the Brillouin zone, whereas the states around the zone center Γ point are strongly renormalized. Our first-principles calculations agree with our experimental results around the X points but not around the Γ point, indicating areas of strong renormalization located near Γ. The Ce quasiparticle states participate in the formation of hot spots at the Fermi surface, whereas the incoherent f states hybridize and lead to the emergence of dispersive features absent in the non-$f$ counterpart BaB6. Lastly, our results provide an understanding of the electronic structure in rare-earth hexaborides, which will be useful in elucidating the nature of the exotic low-temperature phases in these materials.

  14. Optoelectronics with 2D semiconductors

    NASA Astrophysics Data System (ADS)

    Mueller, Thomas

    2015-03-01

    Two-dimensional (2D) atomic crystals, such as graphene and layered transition-metal dichalcogenides, are currently receiving a lot of attention for applications in electronics and optoelectronics. In this talk, I will review our research activities on electrically driven light emission, photovoltaic energy conversion and photodetection in 2D semiconductors. In particular, WSe2 monolayer p-n junctions formed by electrostatic doping using a pair of split gate electrodes, type-II heterojunctions based on MoS2/WSe2 and MoS2/phosphorene van der Waals stacks, 2D multi-junction solar cells, and 3D/2D semiconductor interfaces will be presented. Upon optical illumination, conversion of light into electrical energy occurs in these devices. If an electrical current is driven, efficient electroluminescence is obtained. I will present measurements of the electrical characteristics, the optical properties, and the gate voltage dependence of the device response. In the second part of my talk, I will discuss photoconductivity studies of MoS2 field-effect transistors. We identify photovoltaic and photoconductive effects, which both show strong photoconductive gain. A model will be presented that reproduces our experimental findings, such as the dependence on optical power and gate voltage. We envision that the efficient photon conversion and light emission, combined with the advantages of 2D semiconductors, such as flexibility, high mechanical stability and low costs of production, could lead to new optoelectronic technologies.

  15. Continuous transitions between composite Fermi liquid and Landau Fermi liquid: A route to fractionalized Mott insulators

    NASA Astrophysics Data System (ADS)

    Barkeshli, Maissam; McGreevy, John

    2012-08-01

    One of the most successful theories of a non-Fermi-liquid metallic state is the composite Fermi-liquid (CFL) theory of the half-filled Landau level. In this paper, we study continuous quantum phase transitions out of the CFL state and into a Landau Fermi liquid, in the limit of no disorder and fixed particle number. This transition can be induced by tuning the bandwidth of the Landau level relative to the interaction energy, for instance through an externally applied periodic potential. We find a transition to the Landau Fermi liquid through a gapless Mott insulator with a Fermi surface of neutral fermionic excitations. In the presence of spatial symmetries, we also find a direct continuous transition between the CFL and the Landau Fermi liquid. The transitions have a number of characteristic observable signatures, including the presence of two crossover temperature scales, resistivity jumps, and vanishing compressibility. When the composite fermions are paired instead, our results imply quantum critical points between various non-Abelian topological states, including the ν=1/2 Moore-Read Pfaffian [Ising × U(1) topological order], a version of the Kitaev B phase (Ising topological order), and paired electronic superconductors. To study such transitions, we use a projective construction of the CFL, which goes beyond the conventional framework of flux attachment to include a broader set of quantum fluctuations. These considerations suggest a possible route to fractionalized Mott insulators by starting with fractional quantum Hall states and tuning the Landau-level bandwidth.

  16. 2D Materials for Optical Modulation: Challenges and Opportunities.

    PubMed

    Yu, Shaoliang; Wu, Xiaoqin; Wang, Yipei; Guo, Xin; Tong, Limin

    2017-02-21

    Owing to their atomic layer thickness, strong light-material interaction, high nonlinearity, broadband optical response, fast relaxation, controllable optoelectronic properties, and high compatibility with other photonic structures, 2D materials, including graphene, transition metal dichalcogenides and black phosphorus, have been attracting increasing attention for photonic applications. By tuning the carrier density via electrical or optical means that modifies their physical properties (e.g., Fermi level or nonlinear absorption), optical response of the 2D materials can be instantly changed, making them versatile nanostructures for optical modulation. Here, up-to-date 2D material-based optical modulation in three categories is reviewed: free-space, fiber-based, and on-chip configurations. By analysing cons and pros of different modulation approaches from material and mechanism aspects, the challenges faced by using these materials for device applications are presented. In addition, thermal effects (e.g., laser induced damage) in 2D materials, which are critical to practical applications, are also discussed. Finally, the outlook for future opportunities of these 2D materials for optical modulation is given.

  17. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGES

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; ...

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  18. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    SciTech Connect

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; Markiewicz, R. S.; Bansil, A.; Wilson, S. D.; He, Rui -Hua

    2015-02-23

    We report on an angle resolved photoemission (ARPES) study of bulk electron-doped perovskite iridate, (Sr1-xLax)₃Ir₂O₇. Fermi surface pockets are observed with a total electron count in keeping with that expected from La substitution. Depending on the energy and polarization of the incident photons, these pockets show up in the form of disconnected “Fermi arcs”, reminiscent of those reported recently in surface electron-doped Sr₂IrO₄. Our observed spectral variation is consistent with the coexistence of an electronic supermodulation with structural distortion in the system.

  19. Complete active space second order perturbation theory (CASPT2) study of N({sup 2}D) + H{sub 2}O reaction paths on D{sub 1} and D{sub 0} potential energy surfaces: Direct and roaming pathways

    SciTech Connect

    Isegawa, Miho; Liu, Fengyi; Maeda, Satoshi; Morokuma, Keiji

    2014-10-21

    We report reaction paths starting from N({sup 2}D) + H{sub 2}O for doublet spin states, D{sub 0} and D{sub 1}. The potential energy surfaces are explored in an automated fashion using the global reaction route mapping strategy. The critical points and reaction paths have been fully optimized at the complete active space second order perturbation theory level taking all valence electrons in the active space. In addition to direct dissociation pathways that would be dominant, three roaming processes, two roaming dissociation, and one roaming isomerization: (1) H{sub 2}ON → H–O(H)N → H–HON → NO({sup 2}Π) + H{sub 2}, (2) cis-HNOH → HNO–H → H–HNO → NO + H{sub 2}, (3) H{sub 2}NO → H–HNO → HNO–H → trans-HNOH, are confirmed on the D{sub 0} surface.

  20. Highly crystalline 2D superconductors

    NASA Astrophysics Data System (ADS)

    Saito, Yu; Nojima, Tsutomu; Iwasa, Yoshihiro

    2016-12-01

    Recent advances in materials fabrication have enabled the manufacturing of ordered 2D electron systems, such as heterogeneous interfaces, atomic layers grown by molecular beam epitaxy, exfoliated thin flakes and field-effect devices. These 2D electron systems are highly crystalline, and some of them, despite their single-layer thickness, exhibit a sheet resistance more than an order of magnitude lower than that of conventional amorphous or granular thin films. In this Review, we explore recent developments in the field of highly crystalline 2D superconductors and highlight the unprecedented physical properties of these systems. In particular, we explore the quantum metallic state (or possible metallic ground state), the quantum Griffiths phase observed in out-of-plane magnetic fields and the superconducting state maintained in anomalously large in-plane magnetic fields. These phenomena are examined in the context of weakened disorder and/or broken spatial inversion symmetry. We conclude with a discussion of how these unconventional properties make highly crystalline 2D systems promising platforms for the exploration of new quantum physics and high-temperature superconductors.

  1. Extensions of 2D gravity

    SciTech Connect

    Sevrin, A.

    1993-06-01

    After reviewing some aspects of gravity in two dimensions, I show that non-trivial embeddings of sl(2) in a semi-simple (super) Lie algebra give rise to a very large class of extensions of 2D gravity. The induced action is constructed as a gauged WZW model and an exact expression for the effective action is given.

  2. Extrinsic Cation Selectivity of 2D Membranes

    PubMed Central

    2017-01-01

    From a systematic study of the concentration driven diffusion of positive and negative ions across porous 2D membranes of graphene and hexagonal boron nitride (h-BN), we prove their cation selectivity. Using the current–voltage characteristics of graphene and h-BN monolayers separating reservoirs of different salt concentrations, we calculate the reversal potential as a measure of selectivity. We tune the Debye screening length by exchanging the salt concentrations and demonstrate that negative surface charge gives rise to cation selectivity. Surprisingly, h-BN and graphene membranes show similar characteristics, strongly suggesting a common origin of selectivity in aqueous solvents. For the first time, we demonstrate that the cation flux can be increased by using ozone to create additional pores in graphene while maintaining excellent selectivity. We discuss opportunities to exploit our scalable method to use 2D membranes for applications including osmotic power conversion. PMID:28157333

  3. Static & Dynamic Response of 2D Solids

    SciTech Connect

    Lin, Jerry

    1996-07-15

    NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.

  4. Quasiparticle interference in unconventional 2D systems

    NASA Astrophysics Data System (ADS)

    Chen, Lan; Cheng, Peng; Wu, Kehui

    2017-03-01

    At present, research of 2D systems mainly focuses on two kinds of materials: graphene-like materials and transition-metal dichalcogenides (TMDs). Both of them host unconventional 2D electronic properties: pseudospin and the associated chirality of electrons in graphene-like materials, and spin-valley-coupled electronic structures in the TMDs. These exotic electronic properties have attracted tremendous interest for possible applications in nanodevices in the future. Investigation on the quasiparticle interference (QPI) in 2D systems is an effective way to uncover these properties. In this review, we will begin with a brief introduction to 2D systems, including their atomic structures and electronic bands. Then, we will discuss the formation of Friedel oscillation due to QPI in constant energy contours of electron bands, and show the basic concept of Fourier-transform scanning tunneling microscopy/spectroscopy (FT-STM/STS), which can resolve Friedel oscillation patterns in real space and consequently obtain the QPI patterns in reciprocal space. In the next two parts, we will summarize some pivotal results in the investigation of QPI in graphene and silicene, in which systems the low-energy quasiparticles are described by the massless Dirac equation. The FT-STM experiments show there are two different interference channels (intervalley and intravalley scattering) and backscattering suppression, which associate with the Dirac cones and the chirality of quasiparticles. The monolayer and bilayer graphene on different substrates (SiC and metal surfaces), and the monolayer and multilayer silicene on a Ag(1 1 1) surface will be addressed. The fifth part will introduce the FT-STM research on QPI in TMDs (monolayer and bilayer of WSe2), which allow us to infer the spin texture of both conduction and valence bands, and present spin-valley coupling by tracking allowed and forbidden scattering channels.

  5. The surface-state of the topological insulator Bi2Se3 revealed by cyclotron resonance

    SciTech Connect

    Mcdonald, Ross D; Ayala - Valenzuela, Oscar E; Altarawneh, Moaz M; Analytis, James G

    2011-01-14

    Transport measurements of topological insulators are dominated by the conductivity of the bulk, leading to substantial difficulties in resolving the properties of the surface. To this end, we use high magnetic field, rf- and microwave-spectroscopy to selectively couple to the surface conductivity of Bi2Se3 at high frequency. In the frequency range of a few GHz we observe a crossover from quantum oscillations indicative of a small 3D Fermi surface, to cyclotron resonance indicative of a 2D surface state. By probing the conductivity at reduced skin depths, we have observed a 2D cyclotron resonance from a material whose bulk Fermi-surface is 3D. The frequency-magnetic field scaling of this resonance is inconsistent with the bulk effective mass, but more consistent with the dispersion and band filling of a Dirac-like surface state as observed by ARPES, with substantial manybody renormalization.

  6. Studying Zeolite Catalysts with a 2D Model System

    SciTech Connect

    Boscoboinik, Anibal

    2016-12-07

    Anibal Boscoboinik, a materials scientist at Brookhaven’s Center for Functional Nanomaterials, discusses the surface-science tools and 2D model system he uses to study catalysis in nanoporous zeolites, which catalyze reactions in many industrial processes.

  7. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGES

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; ...

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scatteringmore » creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.« less

  8. Pairing, pseudogap and Fermi arcs in cuprates

    SciTech Connect

    Kaminski, Adam; Kondo, Takeshi; Takeuchi, Tsunehiro; Gu, Genda

    2014-04-29

    We use Angle Resolved Photoemission Spectroscopy (ARPES) to study the relationship between the pseudogap, pairing and Fermi arcs in cuprates. High quality data measured over a wide range of dopings reveals a consistent picture of Fermiology and pairing in these materials. The pseudogap is due to an ordered state that competes with superconductivity rather than preformed pairs. Pairing does occur below Tpair ~ 150K and significantly above Tc, but well below T* and the doping dependence of this temperature scale is distinct from that of the pseudogap. The d-wave gap is present below Tpair, and its interplay with strong scattering creates “artificial” Fermi arcs for Tc ≤ T ≤ Tpair. However, above Tpair, the pseudogap exists only at the antipodal region. This leads to presence of real, gapless Fermi arcs close to the node. The length of these arcs remains constant up to T*, where the full Fermi surface is recovered. As a result, we demonstrate that these findings resolve a number of seemingly contradictory scenarios.

  9. Berry Fermi liquid theory

    NASA Astrophysics Data System (ADS)

    Chen, Jing-Yuan; Son, Dam Thanh

    2017-02-01

    We develop an extension of the Landau Fermi liquid theory to systems of interacting fermions with non-trivial Berry curvature. We propose a kinetic equation and a constitutive relation for the electromagnetic current that together encode the linear response of such systems to external electromagnetic perturbations, to leading and next-to-leading orders in the expansion over the frequency and wave number of the perturbations. We analyze the Feynman diagrams in a large class of interacting quantum field theories and show that, after summing up all orders in perturbation theory, the current-current correlator exactly matches with the result obtained from the kinetic theory.

  10. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe1-xCox)₂As₂

    DOE PAGES

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; ...

    2011-07-25

    We used angle-resolved photoemission spectroscopy and thermoelectric power to study the poorly explored, highly overdoped side of the phase diagram of Ba(Fe1-xCox)₂As₂ high-temperature superconductor. Our data demonstrate that several Lifshitz transitions—topological changes of the Fermi surface—occur for large x. The central hole barrel changes to ellipsoids that are centered at Z at x~0.11 and subsequently disappear around x~0.2; changes in thermoelectric power occur at similar x values. Tc decreases and goes to zero around x~0.15—between the two Lifshitz transitions. Beyond x=0.2 the central pocket becomes electron-like and superconductivity does not exist. Our observations reveal the importance of the underlying Fermiologymore » in electron-doped iron arsenides. We speculate that a likely necessary condition for superconductivity in these materials is the presence of the central hole pockets rather than nesting between central and corner pockets.« less

  11. Conformal Fermi Coordinates

    SciTech Connect

    Dai, Liang; Pajer, Enrico; Schmidt, Fabian E-mail: Enrico.pajer@gmail.com

    2015-11-01

    Fermi Normal Coordinates (FNC) are a useful frame for isolating the locally observable, physical effects of a long-wavelength spacetime perturbation. Their cosmological application, however, is hampered by the fact that they are only valid on scales much smaller than the horizon. We introduce a generalization that we call Conformal Fermi Coordinates (CFC). CFC preserve all the advantages of FNC, but in addition are valid outside the horizon. They allow us to calculate the coupling of long- and short-wavelength modes on all scales larger than the sound horizon of the cosmological fluid, starting from the epoch of inflation until today, by removing the complications of the second order Einstein equations to a large extent, and eliminating all gauge ambiguities. As an application, we present a calculation of the effect of long-wavelength tensor modes on small scale density fluctuations. We recover previous results, but clarify the physical content of the individual contributions in terms of locally measurable effects and ''projection'' terms.

  12. Long-lived magnetoexcitons in 2D-fermion system

    NASA Astrophysics Data System (ADS)

    Kulik, L. V.; Zhuravlev, A. S.; Gorbunov, A. V.; Timofeev, V. B.; Kukushkin, I. V.

    2017-01-01

    The paper addresses the experimental technique that, when applied to a 2D-electron system in the integer quantum Hall regime with filling factor ν = 2 (the Hall insulating state), allows resonant excitation of magnetoexcitons, their detection, control of an ensemble of long-lived triplet excitons and investigation of their radiationless decay related to exciton spin relaxation into the ground state. The technique proposed enables independent control of photoexcited electrons and Fermi-holes using photoinduced resonance reflection spectra as well as estimate with a reasonable degree of accuracy the resulting density of photoinduced electron-hole pairs bound into magnetoexcitons. The mere existence of triplet excitons was directly established by inelastic light scattering spectra which were analyzed to determine the value of singlet-triplet exciton splitting. It was found that the lifetimes of triplet excitons conditioned by electron spin relaxation in highly perfect GaAs/AlGaAs heterostructures with highly mobile 2D electrons are extremely long exceeding 100 μs at T < 1 K. The paper presents a qualitative explanation of the long-spin relaxation lifetimes which are unprecedented for translation-invariant 2D systems. This enabled us to create sufficiently high concentrations of triplet magnetoexcitons, electrically neutral excitations following Bose-Einstein statistics, in a Fermi electron system and investigate their collective properties. At sufficiently high densities of triplet magnetoexcitons and low temperatures, T < 1 K, the degenerate magnetofermionic system exhibits condensation of the triplet magnetoexcitons into a qualitatively new collective state with unusual properties which occurs in the space of generalized moments (magnetic translation vectors). The occurrence of a condensed phase is accompanied with a significant decrease in the viscosity of the photoexcited system, which is responsible for electron spin transport at macroscopic distances, as well

  13. Regulation of ligands for the NKG2D activating receptor

    PubMed Central

    Raulet, David H.; Gasser, Stephan; Gowen, Benjamin G.; Deng, Weiwen; Jung, Heiyoun

    2014-01-01

    NKG2D is an activating receptor expressed by all NK cells and subsets of T cells. It serves as a major recognition receptor for detection and elimination of transformed and infected cells and participates in the genesis of several inflammatory diseases. The ligands for NKG2D are self-proteins that are induced by pathways that are active in certain pathophysiological states. NKG2D ligands are regulated transcriptionally, at the level of mRNA and protein stability, and by cleavage from the cell surface. In some cases, ligand induction can be attributed to pathways that are activated specifically in cancer cells or infected cells. We review the numerous pathways that have been implicated in the regulation of NKG2D ligands, discuss the pathologic states in which those pathways are likely to act, and attempt to synthesize the findings into general schemes of NKG2D ligand regulation in NK cell responses to cancer and infection. PMID:23298206

  14. Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

    DOE PAGES

    Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

    2016-11-22

    Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weakmore » Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.« less

  15. Schottky-barrier-free contacts with two-dimensional semiconductors by surface-engineered MXenes

    SciTech Connect

    Liu, Yuanyue; Xiao, Hai; Goddard, III, William A.

    2016-11-22

    Two-dimensional (2D) metal carbides and nitrides, called MXenes, have attracted great interest for applications such as energy storage. Here we demonstrate their potential as Schottky-barrier-free metal contacts to 2D semiconductors, providing a solution to the contact-resistance problem in 2D electronics. Based on first principles calculations, we find that the surface chemistry strongly affects the Fermi level of MXenes: O termination always increases the work function with respect to that of bare surface, OH always decreases it, while F exhibits either trend depending on the specific material. This phenomenon originates from the effect of surface dipoles, which together with the weak Fermi level pinning, enable Schottky-barrier-free hole (or electron) injection into 2D semiconductors through van der Waals junctions with some of the O-terminated (or all the OH-terminated) MXenes. Furthermore, we suggest synthetic routes to control the surface terminations based on the calculated formation energies. Finally, this study enhances the understanding of the correlation between surface chemistry and electronic/transport properties of 2D materials, and also gives practical predictions for improving 2D electronics.

  16. 2D quasiperiodic plasmonic crystals

    PubMed Central

    Bauer, Christina; Kobiela, Georg; Giessen, Harald

    2012-01-01

    Nanophotonic structures with irregular symmetry, such as quasiperiodic plasmonic crystals, have gained an increasing amount of attention, in particular as potential candidates to enhance the absorption of solar cells in an angular insensitive fashion. To examine the photonic bandstructure of such systems that determines their optical properties, it is necessary to measure and model normal and oblique light interaction with plasmonic crystals. We determine the different propagation vectors and consider the interaction of all possible waveguide modes and particle plasmons in a 2D metallic photonic quasicrystal, in conjunction with the dispersion relations of a slab waveguide. Using a Fano model, we calculate the optical properties for normal and inclined light incidence. Comparing measurements of a quasiperiodic lattice to the modelled spectra for angle of incidence variation in both azimuthal and polar direction of the sample gives excellent agreement and confirms the predictive power of our model. PMID:23209871

  17. Valleytronics in 2D materials

    NASA Astrophysics Data System (ADS)

    Schaibley, John R.; Yu, Hongyi; Clark, Genevieve; Rivera, Pasqual; Ross, Jason S.; Seyler, Kyle L.; Yao, Wang; Xu, Xiaodong

    2016-11-01

    Semiconductor technology is currently based on the manipulation of electronic charge; however, electrons have additional degrees of freedom, such as spin and valley, that can be used to encode and process information. Over the past several decades, there has been significant progress in manipulating electron spin for semiconductor spintronic devices, motivated by potential spin-based information processing and storage applications. However, experimental progress towards manipulating the valley degree of freedom for potential valleytronic devices has been limited until very recently. We review the latest advances in valleytronics, which have largely been enabled by the isolation of 2D materials (such as graphene and semiconducting transition metal dichalcogenides) that host an easily accessible electronic valley degree of freedom, allowing for dynamic control.

  18. Unparticle example in 2D.

    PubMed

    Georgi, Howard; Kats, Yevgeny

    2008-09-26

    We discuss what can be learned about unparticle physics by studying simple quantum field theories in one space and one time dimension. We argue that the exactly soluble 2D theory of a massless fermion coupled to a massive vector boson, the Sommerfield model, is an interesting analog of a Banks-Zaks model, approaching a free theory at high energies and a scale-invariant theory with nontrivial anomalous dimensions at low energies. We construct a toy standard model coupling to the fermions in the Sommerfield model and study how the transition from unparticle behavior at low energies to free particle behavior at high energies manifests itself in interactions with the toy standard model particles.

  19. The Fermi Paradox Is Neither Fermi's Nor a Paradox

    NASA Astrophysics Data System (ADS)

    Gray, Robert H.

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth-and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked 'where is everybody?'- apparently suggesting that we don't see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist, or suggesting its absence is paradoxical. The claim 'they are not here; therefore they do not exist' was first published by Michael Hart, claiming that interstellar travel and colonization of the galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence-cited in the U. S. Congress as a reason for killing NASA's SETI program on one occasion-but evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox. Keywords: Astrobiology, SETI, Fermi paradox, extraterrestrial life

  20. Quantum coherence selective 2D Raman–2D electronic spectroscopy

    PubMed Central

    Spencer, Austin P.; Hutson, William O.; Harel, Elad

    2017-01-01

    Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational–vibrational, electronic–vibrational and electronic–electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment–protein complexes. PMID:28281541

  1. Quantum coherence selective 2D Raman-2D electronic spectroscopy

    NASA Astrophysics Data System (ADS)

    Spencer, Austin P.; Hutson, William O.; Harel, Elad

    2017-03-01

    Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.

  2. Quantum coherence selective 2D Raman-2D electronic spectroscopy.

    PubMed

    Spencer, Austin P; Hutson, William O; Harel, Elad

    2017-03-10

    Electronic and vibrational correlations report on the dynamics and structure of molecular species, yet revealing these correlations experimentally has proved extremely challenging. Here, we demonstrate a method that probes correlations between states within the vibrational and electronic manifold with quantum coherence selectivity. Specifically, we measure a fully coherent four-dimensional spectrum which simultaneously encodes vibrational-vibrational, electronic-vibrational and electronic-electronic interactions. By combining near-impulsive resonant and non-resonant excitation, the desired fifth-order signal of a complex organic molecule in solution is measured free of unwanted lower-order contamination. A critical feature of this method is electronic and vibrational frequency resolution, enabling isolation and assignment of individual quantum coherence pathways. The vibronic structure of the system is then revealed within an otherwise broad and featureless 2D electronic spectrum. This method is suited for studying elusive quantum effects in which electronic transitions strongly couple to phonons and vibrations, such as energy transfer in photosynthetic pigment-protein complexes.

  3. Fermi Level Pinning at Electrical Metal Contacts of Monolayer Molybdenum Dichalcogenides.

    PubMed

    Kim, Changsik; Moon, Inyong; Lee, Daeyeong; Choi, Min Sup; Ahmed, Faisal; Nam, Seunggeol; Cho, Yeonchoo; Shin, Hyeon-Jin; Park, Seongjun; Yoo, Won Jong

    2017-02-28

    Electrical metal contacts to two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) are found to be the key bottleneck to the realization of high device performance due to strong Fermi level pinning and high contact resistances (Rc). Until now, Fermi level pinning of monolayer TMDCs has been reported only theoretically, although that of bulk TMDCs has been reported experimentally. Here, we report the experimental study on Fermi level pinning of monolayer MoS2 and MoTe2 by interpreting the thermionic emission results. We also quantitatively compared our results with the theoretical simulation results of the monolayer structure as well as the experimental results of the bulk structure. We measured the pinning factor S to be 0.11 and -0.07 for monolayer MoS2 and MoTe2, respectively, suggesting a much stronger Fermi level pinning effect, a Schottky barrier height (SBH) lower than that by theoretical prediction, and interestingly similar pinning energy levels between monolayer and bulk MoS2. Our results further imply that metal work functions have very little influence on contact properties of 2D-material-based devices. Moreover, we found that Rc is exponentially proportional to SBH, and these processing parameters can be controlled sensitively upon chemical doping into the 2D materials. These findings provide a practical guideline for depinning Fermi level at the 2D interfaces so that polarity control of TMDC-based semiconductors can be achieved efficiently.

  4. Microwave Assisted 2D Materials Exfoliation

    NASA Astrophysics Data System (ADS)

    Wang, Yanbin

    Two-dimensional materials have emerged as extremely important materials with applications ranging from energy and environmental science to electronics and biology. Here we report our discovery of a universal, ultrafast, green, solvo-thermal technology for producing excellent-quality, few-layered nanosheets in liquid phase from well-known 2D materials such as such hexagonal boron nitride (h-BN), graphite, and MoS2. We start by mixing the uniform bulk-layered material with a common organic solvent that matches its surface energy to reduce the van der Waals attractive interactions between the layers; next, the solutions are heated in a commercial microwave oven to overcome the energy barrier between bulk and few-layers states. We discovered the minutes-long rapid exfoliation process is highly temperature dependent, which requires precise thermal management to obtain high-quality inks. We hypothesize a possible mechanism of this proposed solvo-thermal process; our theory confirms the basis of this novel technique for exfoliation of high-quality, layered 2D materials by using an as yet unknown role of the solvent.

  5. The Statistical Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Maccone, C.

    In this paper is provided the statistical generalization of the Fermi paradox. The statistics of habitable planets may be based on a set of ten (and possibly more) astrobiological requirements first pointed out by Stephen H. Dole in his book Habitable planets for man (1964). The statistical generalization of the original and by now too simplistic Dole equation is provided by replacing a product of ten positive numbers by the product of ten positive random variables. This is denoted the SEH, an acronym standing for “Statistical Equation for Habitables”. The proof in this paper is based on the Central Limit Theorem (CLT) of Statistics, stating that the sum of any number of independent random variables, each of which may be ARBITRARILY distributed, approaches a Gaussian (i.e. normal) random variable (Lyapunov form of the CLT). It is then shown that: 1. The new random variable NHab, yielding the number of habitables (i.e. habitable planets) in the Galaxy, follows the log- normal distribution. By construction, the mean value of this log-normal distribution is the total number of habitable planets as given by the statistical Dole equation. 2. The ten (or more) astrobiological factors are now positive random variables. The probability distribution of each random variable may be arbitrary. The CLT in the so-called Lyapunov or Lindeberg forms (that both do not assume the factors to be identically distributed) allows for that. In other words, the CLT "translates" into the SEH by allowing an arbitrary probability distribution for each factor. This is both astrobiologically realistic and useful for any further investigations. 3. By applying the SEH it is shown that the (average) distance between any two nearby habitable planets in the Galaxy may be shown to be inversely proportional to the cubic root of NHab. This distance is denoted by new random variable D. The relevant probability density function is derived, which was named the "Maccone distribution" by Paul Davies in

  6. NIKE2D96. Static & Dynamic Response of 2D Solids

    SciTech Connect

    Raboin, P.; Engelmann, B.; Halquist, J.O.

    1992-01-24

    NIKE2D is an implicit finite-element code for analyzing the finite deformation, static and dynamic response of two-dimensional, axisymmetric, plane strain, and plane stress solids. The code is fully vectorized and available on several computing platforms. A number of material models are incorporated to simulate a wide range of material behavior including elasto-placicity, anisotropy, creep, thermal effects, and rate dependence. Slideline algorithms model gaps and sliding along material interfaces, including interface friction, penetration and single surface contact. Interactive-graphics and rezoning is included for analyses with large mesh distortions. In addition to quasi-Newton and arc-length procedures, adaptive algorithms can be defined to solve the implicit equations using the solution language ISLAND. Each of these capabilities and more make NIKE2D a robust analysis tool.

  7. The fermi paradox is neither Fermi's nor a paradox.

    PubMed

    Gray, Robert H

    2015-03-01

    The so-called Fermi paradox claims that if technological life existed anywhere else, we would see evidence of its visits to Earth--and since we do not, such life does not exist, or some special explanation is needed. Enrico Fermi, however, never published anything on this topic. On the one occasion he is known to have mentioned it, he asked "Where is everybody?"--apparently suggesting that we do not see extraterrestrials on Earth because interstellar travel may not be feasible, but not suggesting that intelligent extraterrestrial life does not exist or suggesting its absence is paradoxical. The claim "they are not here; therefore they do not exist" was first published by Michael Hart, claiming that interstellar travel and colonization of the Galaxy would be inevitable if intelligent extraterrestrial life existed, and taking its absence here as proof that it does not exist anywhere. The Fermi paradox appears to originate in Hart's argument, not Fermi's question. Clarifying the origin of these ideas is important, because the Fermi paradox is seen by some as an authoritative objection to searching for evidence of extraterrestrial intelligence--cited in the U.S. Congress as a reason for killing NASA's SETI program on one occasion. But evidence indicates that it misrepresents Fermi's views, misappropriates his authority, deprives the actual authors of credit, and is not a valid paradox.

  8. NKG2D receptor and its ligands in host defense

    PubMed Central

    Lanier, Lewis L.

    2015-01-01

    NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8+ T cells, and subsets of CD4+ T cells, iNKT cells, and γδ T cells. In humans NKG2D transmits signals by its association with the DAP10 adapter subunit and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least 8 genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and post-translation. In general healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyper-proliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves a mechanism for the immune system to detect and eliminate cells that have undergone “stress”. Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases. PMID:26041808

  9. NKG2D Receptor and Its Ligands in Host Defense.

    PubMed

    Lanier, Lewis L

    2015-06-01

    NKG2D is an activating receptor expressed on the surface of natural killer (NK) cells, CD8(+) T cells, and subsets of CD4(+) T cells, invariant NKT cells (iNKT), and γδ T cells. In humans, NKG2D transmits signals by its association with the DAP10 adapter subunit, and in mice alternatively spliced isoforms transmit signals either using DAP10 or DAP12 adapter subunits. Although NKG2D is encoded by a highly conserved gene (KLRK1) with limited polymorphism, the receptor recognizes an extensive repertoire of ligands, encoded by at least eight genes in humans (MICA, MICB, RAET1E, RAET1G, RAET1H, RAET1I, RAET1L, and RAET1N), some with extensive allelic polymorphism. Expression of the NKG2D ligands is tightly regulated at the level of transcription, translation, and posttranslation. In general, healthy adult tissues do not express NKG2D glycoproteins on the cell surface, but these ligands can be induced by hyperproliferation and transformation, as well as when cells are infected by pathogens. Thus, the NKG2D pathway serves as a mechanism for the immune system to detect and eliminate cells that have undergone "stress." Viruses and tumor cells have devised numerous strategies to evade detection by the NKG2D surveillance system, and diversification of the NKG2D ligand genes likely has been driven by selective pressures imposed by pathogens. NKG2D provides an attractive target for therapeutics in the treatment of infectious diseases, cancer, and autoimmune diseases.

  10. Fermi's New Pulsar Detection Technique

    NASA Video Gallery

    To locate a pulsar in Fermi LAT data requires knowledge of the object’s sky position, its pulse period, and how the pulse rate slows over time. Computers check many different combinations of posi...

  11. Electronic structure study on 2D hydrogenated Icosagens nitride nanosheets

    NASA Astrophysics Data System (ADS)

    Ramesh, S.; Marutheeswaran, S.; Ramaclus, Jerald V.; Paul, Dolon Chapa

    2014-12-01

    Metal nitride nanosheets has attracted remarkable importance in surface catalysis due to its characteristic ionic nature. In this paper, using density functional theory, we investigate geometric stability and electronic properties of hydrogenated Icosagen nitride nanosheets. Binding energy of the sheets reveals hydrogenation is providing more stability. Band structure of the hydrogenated sheets is found to be n-type semiconductor. Partial density of states shows metals (B, Al, Ga and In) and its hydrogens dominating in the Fermi region. Mulliken charge analysis indications that hydrogenated nanosheets are partially hydridic surface nature except boron nitride.

  12. Pairing in a dry Fermi sea

    SciTech Connect

    Maier, Thomas A.; Staar, Peter; Mishra, V.; Chatterjee, Utpal; Campuzano, J. C.; Scalapino, Douglas J.

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.

  13. Pairing in a dry Fermi sea

    PubMed Central

    Maier, T. A; Staar, P.; Mishra, V.; Chatterjee, U.; Campuzano, J. C.; Scalapino, D. J.

    2016-01-01

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and −k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. Here we report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. In contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability. PMID:27312569

  14. Pairing in a dry Fermi sea

    DOE PAGES

    Maier, Thomas A.; Staar, Peter; Mishra, V.; ...

    2016-06-17

    In the traditional Bardeen–Cooper–Schrieffer theory of superconductivity, the amplitude for the propagation of a pair of electrons with momentum k and -k has a log singularity as the temperature decreases. This so-called Cooper instability arises from the presence of an electron Fermi sea. It means that an attractive interaction, no matter how weak, will eventually lead to a pairing instability. However, in the pseudogap regime of the cuprate superconductors, where parts of the Fermi surface are destroyed, this log singularity is suppressed, raising the question of how pairing occurs in the absence of a Fermi sea. In this paper, wemore » report Hubbard model numerical results and the analysis of angular-resolved photoemission experiments on a cuprate superconductor. Finally, in contrast to the traditional theory, we find that in the pseudogap regime the pairing instability arises from an increase in the strength of the spin–fluctuation pairing interaction as the temperature decreases rather than the Cooper log instability.« less

  15. Evidence of a short-range incommensurate d-wave charge order from a fermionic two-loop renormalization group calculation of a 2D model with hot spots

    SciTech Connect

    Carvalho, Vanuildo S de; Freire, Hermann

    2014-09-15

    The two-loop renormalization group (RG) calculation is considerably extended here for the two-dimensional (2D) fermionic effective field theory model, which includes only the so-called “hot spots” that are connected by the spin-density-wave (SDW) ordering wavevector on a Fermi surface generated by the 2D t−t{sup ′} Hubbard model at low hole doping. We compute the Callan–Symanzik RG equation up to two loops describing the flow of the single-particle Green’s function, the corresponding spectral function, the Fermi velocity, and some of the most important order-parameter susceptibilities in the model at lower energies. As a result, we establish that–in addition to clearly dominant SDW correlations–an approximate (pseudospin) symmetry relating a short-range incommensurated-wave charge order to the d-wave superconducting order indeed emerges at lower energy scales, which is in agreement with recent works available in the literature addressing the 2D spin-fermion model. We derive implications of this possible electronic phase in the ongoing attempt to describe the phenomenology of the pseudogap regime in underdoped cuprates.

  16. Analysis of the antiferromagnetic phase transitions of the 2D Kondo lattice

    NASA Astrophysics Data System (ADS)

    Jones, Barbara

    2010-03-01

    The Kondo lattice continues to present an interesting and relevant challenge, with its interactions between Kondo, RKKY, and coherent order. We present our study[1] of the antiferromagnetic quantum phase transitions of a 2D Kondo-Heisenberg square lattice. Starting from the nonlinear sigma model as a model of antiferromagnetism, we carry out a renormalization group analysis of the competing Kondo-RKKY interaction to one-loop order in an ɛ-expansion. We find a new quantum critical point (QCP) strongly affected by Kondo fluctuations. Near this QCP, there is a breakdown of hydrodynamic behavior, and the spin waves are logarithmically frozen out. The renormalization group results allow us to propose a new phase diagram near the antiferromagnetic fixed point of this 2D Kondo lattice model. The T=0 phase diagram contains four phases separated by a tetracritical point, the new QCP. For small spin fluctuations, we find a stable local magnetic moment antiferromagnet. For stronger coupling, region II is a metallic quantum disordered paramagnet. We find in region III a paramagnetic phase driven by Kondo interactions, with possible ground states of a heavy fermion liquid or a Kondo driven spin-liquid. The fourth phase is a spiral phase, or a large-Fermi-surface antiferromagnetic phase. We will describe these phases in more detail, including possible experimental confirmation of the spiral phase. The existence of the tetracritical point found here would be expected to affect the phase diagram at finite temperatures as well. In addition, It is hoped that these results, and particularly the Kondo interaction paramagnetic phase, will serve to bridge to solutions starting from the opposite limit, of a Kondo effect leading to a heavy fermion ground state. Work in collaboration with T. Tzen Ong. [4pt] [1] T. Ong and B. A. Jones, Phys. Rev. Lett. 103, 066405 (2009).

  17. Secretory pathways generating immunosuppressive NKG2D ligands

    PubMed Central

    Baragaño Raneros, Aroa; Suarez-Álvarez, Beatriz; López-Larrea, Carlos

    2014-01-01

    Natural Killer Group 2 member D (NKG2D) activating receptor, present on the surface of various immune cells, plays an important role in activating the anticancer immune response by their interaction with stress-inducible NKG2D ligands (NKG2DL) on transformed cells. However, cancer cells have developed numerous mechanisms to evade the immune system via the downregulation of NKG2DL from the cell surface, including the release of NKG2DL from the cell surface in a soluble form. Here, we review the mechanisms involved in the production of soluble NKG2DL (sNKG2DL) and the potential therapeutic strategies aiming to block the release of these immunosuppressive ligands. Therapeutically enabling the NKG2D-NKG2DL interaction would promote immunorecognition of malignant cells, thus abrogating disease progression. PMID:25050215

  18. 2D microscopic model of graphene fracture properties

    NASA Astrophysics Data System (ADS)

    Hess, Peter

    2015-05-01

    An analytical two-dimensional (2D) microscopic fracture model based on Morse-type interaction is derived containing no adjustable parameter. From the 2D Young’s moduli and 2D intrinsic strengths of graphene measured by nanoindentation based on biaxial tension and calculated by density functional theory for uniaxial tension the widely unknown breaking force, line or edge energy, surface energy, fracture toughness, and strain energy release rate were determined. The simulated line energy agrees well with ab initio calculations and the fracture toughness of perfect graphene sheets is in good agreement with molecular dynamics simulations and the fracture toughness evaluated for defective graphene using the Griffith relation. Similarly, the estimated critical strain energy release rate agrees well with result of various theoretical approaches based on the J-integral and surface energy. The 2D microscopic model, connecting 2D and three-dimensional mechanical properties in a consistent way, provides a versatile relationship to easily access all relevant fracture properties of pristine 2D solids.

  19. Recovering 3D particle size distributions from 2D sections

    NASA Astrophysics Data System (ADS)

    Cuzzi, Jeffrey N.; Olson, Daniel M.

    2017-03-01

    We discuss different ways to convert observed, apparent particle size distributions from 2D sections (thin sections, SEM maps on planar surfaces, etc.) into true 3D particle size distributions. We give a simple, flexible, and practical method to do this; show which of these techniques gives the most faithful conversions; and provide (online) short computer codes to calculate both 2D-3D recoveries and simulations of 2D observations by random sectioning. The most important systematic bias of 2D sectioning, from the standpoint of most chondrite studies, is an overestimate of the abundance of the larger particles. We show that fairly good recoveries can be achieved from observed size distributions containing 100-300 individual measurements of apparent particle diameter.

  20. Technical Review of the UNET2D Hydraulic Model

    SciTech Connect

    Perkins, William A.; Richmond, Marshall C.

    2009-05-18

    The Kansas City District of the US Army Corps of Engineers is engaged in a broad range of river management projects that require knowledge of spatially-varied hydraulic conditions such as velocities and water surface elevations. This information is needed to design new structures, improve existing operations, and assess aquatic habitat. Two-dimensional (2D) depth-averaged numerical hydraulic models are a common tool that can be used to provide velocity and depth information. Kansas City District is currently using a specific 2D model, UNET2D, that has been developed to meet the needs of their river engineering applications. This report documents a tech- nical review of UNET2D.

  1. NKG2D ligands as therapeutic targets

    PubMed Central

    Spear, Paul; Wu, Ming-Ru; Sentman, Marie-Louise; Sentman, Charles L.

    2013-01-01

    The Natural Killer Group 2D (NKG2D) receptor plays an important role in protecting the host from infections and cancer. By recognizing ligands induced on infected or tumor cells, NKG2D modulates lymphocyte activation and promotes immunity to eliminate ligand-expressing cells. Because these ligands are not widely expressed on healthy adult tissue, NKG2D ligands may present a useful target for immunotherapeutic approaches in cancer. Novel therapies targeting NKG2D ligands for the treatment of cancer have shown preclinical success and are poised to enter into clinical trials. In this review, the NKG2D receptor and its ligands are discussed in the context of cancer, infection, and autoimmunity. In addition, therapies targeting NKG2D ligands in cancer are also reviewed. PMID:23833565

  2. High kappa Dielectrics on InGaAs and GaN: Growth, Interfacial Structural Studies, and Surface Fermi Level Unpinning

    DTIC Science & Technology

    2010-12-24

    MOSFETs and GaN MOSFETs without employing interfacial layers and surface chemical pre-treatments. We have achieved many firsts and made great impacts...hold world record high dc performances of InGaAs MOSFETs , including the drain current, peak transconductance, and peak electron mobility in the self...aligned inversion-channel In0.75Ga0.25As and In0.2Ga0.8As MOSFETs using both in-situ MBE-Al2O3/GGO and ex-situ ALD-Al2O3 gate dielectrics. The high

  3. Pondering the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Webb, Stephen

    The past two decades have witnessed an unprecedented increase in the amount and quality of observational data available to astronomers and cosmologists. Orbiting observatories such as the Hubble Space Telescope and the Wilkinson Microwave Anisotropy Probe (WMAP) have peered at the universe through a variety of windows in the electromagnetic spectrum. Ground-based projects such as the Sloan Digital Sky Survey (Adelman- McCarthy et al., 2008) and the 2dF Galaxy Redshift Survey (Colless et al., 2003) have mapped the distribution of galaxies in exquisite detail. Taken together, data from these and other projects have transformed our understanding of the large-scale structure of the universe, have steadily improved our knowledge of key cosmological parameters, and have provided compelling evidence in favor of a simple cosmological model (Spergel et al., 2009).

  4. Magnetic gating of a 2D topological insulator

    NASA Astrophysics Data System (ADS)

    Dang, Xiaoqian; Burton, J. D.; Tsymbal, Evgeny Y.

    2016-09-01

    Deterministic control of transport properties through manipulation of spin states is one of the paradigms of spintronics. Topological insulators offer a new playground for exploring interesting spin-dependent phenomena. Here, we consider a ferromagnetic ‘gate’ representing a magnetic adatom coupled to the topologically protected edge state of a two-dimensional (2D) topological insulator to modulate the electron transmission of the edge state. Due to the locked spin and wave vector of the transport electrons the transmission across the magnetic gate depends on the mutual orientation of the adatom magnetic moment and the current. If the Fermi energy matches an exchange-split bound state of the adatom, the electron transmission can be blocked due to the full back scattering of the incident wave. This antiresonance behavior is controlled by the adatom magnetic moment orientation so that the transmission of the edge state can be changed from 1 to 0. Expanding this consideration to a ferromagnetic gate representing a 1D chain of atoms shows a possibility to control the spin-dependent current of a strip of a 2D topological insulator by magnetization orientation of the ferromagnetic gate.

  5. Towards functional assembly of 3D and 2D nanomaterials

    NASA Astrophysics Data System (ADS)

    Jacobs, Christopher B.; Wang, Kai; Ievlev, Anton V.; Muckley, Eric S.; Ivanov, Ilia N.

    2016-09-01

    Functional assemblies of materials can be realized by tuning the work function and band gap of nanomaterials by rational material selection and design. Here we demonstrate the structural assembly of 2D and 3D nanomaterials and show that layering a 2D material monolayer on a 3D metal oxide leads to substantial alteration of both the surface potential and optical properties of the 3D material. A 40 nm thick film of polycrystalline NiO was produced by room temperature rf-sputtering, resulting in a 3D nanoparticle assembly. Chemical vapor deposition (CVD) grown 10-30 μm WS2 flakes (2D material) were placed on the NiO surface using a PDMS stamp transfer technique. The 2D/3D WS2/NiO assembly was characterized using confocal micro Raman spectroscopy to evaluate the vibrational properties and using Kelvin probe force microscopy (KPFM) to evaluate the surface potential. Raman maps of the 2D/3D assembly show spatial non-uniformity of the A1g mode ( 418 cm-1) and the disorder-enhanced longitudinal acoustic mode, 2LA(M) ( 350 cm-1), suggesting that the WS2 exists in a strained condition on when transferred onto 3D polycrystalline NiO. KPFM measurements show that single layer WS2 on SiO2 has a surface potential 75 mV lower than that of SiO2, whereas the surface potential of WS2 on NiO is 15 mV higher than NiO, indicating that WS2 could act as electron donor or acceptor depending on the 3D material it is interfaced with. Thus 2D and 3D materials can be organized into functional assemblies with electron flow controlled by the WS2 either as the electron donor or acceptor.

  6. Discovery of a Weyl fermion semimetal and topological Fermi arcs

    NASA Astrophysics Data System (ADS)

    Xu, Su-Yang; Belopolski, Ilya; Alidoust, Nasser; Neupane, Madhab; Bian, Guang; Zhang, Chenglong; Sankar, Raman; Chang, Guoqing; Yuan, Zhujun; Lee, Chi-Cheng; Huang, Shin-Ming; Zheng, Hao; Ma, Jie; Sanchez, Daniel S.; Wang, BaoKai; Bansil, Arun; Chou, Fangcheng; Shibayev, Pavel P.; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid

    2015-08-01

    A Weyl semimetal is a new state of matter that hosts Weyl fermions as emergent quasiparticles and admits a topological classification that protects Fermi arc surface states on the boundary of a bulk sample. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of a Weyl semimetal, tantalum arsenide (TaAs). Using photoemission spectroscopy, we directly observe Fermi arcs on the surface, as well as the Weyl fermion cones and Weyl nodes in the bulk of TaAs single crystals. We find that Fermi arcs terminate on the Weyl fermion nodes, consistent with their topological character. Our work opens the field for the experimental study of Weyl fermions in physics and materials science.

  7. Strongly Correlated States of Ultracold Rotating Dipolar Fermi Gases

    SciTech Connect

    Osterloh, Klaus; Barberan, Nuria; Lewenstein, Maciej

    2007-10-19

    We study strongly correlated ground and excited states of rotating quasi-2D Fermi gases constituted of a small number of dipole-dipole interacting particles with dipole moments polarized perpendicular to the plane of motion. As the number of atoms grows, the system enters an intermediate regime, where ground states are subject to a competition between distinct bulk-edge configurations. This effect obscures their description in terms of composite fermions and leads to the appearance of novel quasihole ground states. In the presence of dipolar interactions, the principal Laughlin state at filling {nu}=1/3 exhibits a substantial energy gap for neutral (total angular momentum conserving) excitations and is well-described as an incompressible Fermi liquid. Instead, at lower fillings, the ground state structure favors crystalline order.

  8. The novel metallic states of the cuprates: Topological Fermi liquids and strange metals

    NASA Astrophysics Data System (ADS)

    Sachdev, Subir; Chowdhury, Debanjan

    2016-12-01

    We review ideas on the nature of the metallic states of the hole-doped cuprate high temperature superconductors, with an emphasis on the connections between the Luttinger theorem for the size of the Fermi surface, topological quantum field theories (TQFTs), and critical theories involving changes in the size of the Fermi surface. We begin with the derivation of the Luttinger theorem for a Fermi liquid, using momentum balance during a process of flux insertion in a lattice electronic model with toroidal boundary conditions. We then review the TQFT of the ℤ spin liquid, and demonstrate its compatibility with the toroidal momentum balance argument. This discussion leads naturally to a simple construction of "topological" Fermi liquid states: the fractionalized Fermi liquid (FL*) and the algebraic charge liquid (ACL). We present arguments for a description of the pseudogap metal of the cuprates using ℤ-FL* or ℤ-ACL states with Ising-nematic order. These pseudogap metal states are also described as Higgs phases of a SU(2) gauge theory. The Higgs field represents local antiferromagnetism, but the Higgs-condensed phase does not have long-range antiferromagnetic order: the magnitude of the Higgs field determines the pseudogap, the reconstruction of the Fermi surface, and the Ising-nematic order. Finally, we discuss the route to the large Fermi surface Fermi liquid via the critical point where the Higgs condensate and Ising nematic order vanish, and the application of Higgs criticality to the strange metal.

  9. Bottom-Up Preparation of Ultrathin 2D Aluminum Oxide Nanosheets by Duplicating Graphene Oxide.

    PubMed

    Huang, Zhifeng; Zhou, Anan; Wu, Jifeng; Chen, Yunqiang; Lan, Xiaoli; Bai, Hua; Li, Lei

    2016-02-24

    2D ultrathin aluminum oxide (2D-Al2O3) nanosheets are prepared by duplicating graphene oxide. An amorphous precursor of the hydroxide of aluminum is first deposited onto graphene oxide sheets, which are then converted into 2D-Al2 O3 nanosheets by calcination, while the graphene oxide is removed. The 2D-Al2O3 nanosheets have a large specific surface area and a superior adsorption capacity to fluoride ions.

  10. Quantitative 2D liquid-state NMR.

    PubMed

    Giraudeau, Patrick

    2014-06-01

    Two-dimensional (2D) liquid-state NMR has a very high potential to simultaneously determine the absolute concentration of small molecules in complex mixtures, thanks to its capacity to separate overlapping resonances. However, it suffers from two main drawbacks that probably explain its relatively late development. First, the 2D NMR signal is strongly molecule-dependent and site-dependent; second, the long duration of 2D NMR experiments prevents its general use for high-throughput quantitative applications and affects its quantitative performance. Fortunately, the last 10 years has witnessed an increasing number of contributions where quantitative approaches based on 2D NMR were developed and applied to solve real analytical issues. This review aims at presenting these recent efforts to reach a high trueness and precision in quantitative measurements by 2D NMR. After highlighting the interest of 2D NMR for quantitative analysis, the different strategies to determine the absolute concentrations from 2D NMR spectra are described and illustrated by recent applications. The last part of the manuscript concerns the recent development of fast quantitative 2D NMR approaches, aiming at reducing the experiment duration while preserving - or even increasing - the analytical performance. We hope that this comprehensive review will help readers to apprehend the current landscape of quantitative 2D NMR, as well as the perspectives that may arise from it.

  11. The Fermiac or Fermi's Trolley

    NASA Astrophysics Data System (ADS)

    Coccetti, F.

    2016-03-01

    The Fermiac, known also as Fermi's trolley or Monte Carlo trolley, is an analog computer used to determine the change in time of the neutron population in a nuclear device, via the Monte Carlo method. It was invented by Enrico Fermi and constructed by Percy King at Los Alamos in 1947, and used for about two years. A replica of the Fermiac was built at INFN mechanical workshops of Bologna in 2015, on behalf of the Museo Storico della Fisica e Centro Studi e Ricerche "Enrico Fermi", thanks to the original drawings made available by Los Alamos National Laboratory (LANL). This reproduction of the Fermiac was put in use, and a simulation was developed.

  12. Review of 2D superconductivity: the ultimate case of epitaxial monolayers

    NASA Astrophysics Data System (ADS)

    Brun, Christophe; Cren, Tristan; Roditchev, Dimitri

    2017-01-01

    order to illustrate their specific properties related to quantum-size effects. In the next section 3 we review the growth methods and structural properties of the presented 2DEG surface-confined superconductors. In section 4, we review the electronic structure and Fermi surface properties as measured by macroscopic ARPES and confront them to ab initio DFT calculations based on the characterized atomic structures of the monolayers. The following section 5 reviews the macroscopic properties inferred from in situ electrical transport measurements methods, including attempts to study the Berezinsky-Kosterlitz-Thouless 2D regime. In the last section 6, we summarize the emerging local spectroscopic properties measured by STS. These latter demonstrate variations of the local superconducting properties at a scale much shorter than the superconducting coherence length due to a combined effect of non-magnetic disorder and two-dimensionality. Further peculiar local spectroscopic effects are presented giving evidence for the presence of a mixed singlet-triplet superconducting order parameter induced by the presence of a strong Rashba spin-orbit coupling term at the surface. These local signatures will be discussed along with ARPES and transport measurements in parallel high magnetic field on closely related systems. Finally, we present in anisotropic Pb and In monolayers the peculiar role played by atomic steps on vortex properties, leading to the observation by STS of mixed Abrikosov-Josephson vortices in agreement with in situ macroscopic transport measurements. From the overview of all recent experimental and theoretical results it appears that these surface 2D superconductors, such as one monolayer of Pb on Si(111), are ideal templates to engineer and realize topological superconductivity.

  13. Studying Zeolite Catalysts with a 2D Model System

    ScienceCinema

    Boscoboinik, Anibal

    2016-12-14

    Anibal Boscoboinik, a materials scientist at Brookhaven’s Center for Functional Nanomaterials, discusses the surface-science tools and 2D model system he uses to study catalysis in nanoporous zeolites, which catalyze reactions in many industrial processes.

  14. Fermi Liquid Instabilities in the Spin Channel

    SciTech Connect

    Wu, Congjun; Sun, Kai; Fradkin, Eduardo; Zhang, Shou-Cheng; /Stanford U., Phys. Dept.

    2010-03-16

    We study the Fermi surface instabilities of the Pomeranchuk type in the spin triplet channel with high orbital partial waves (F{sub l}{sup a} (l > 0)). The ordered phases are classified into two classes, dubbed the {alpha} and {beta}-phases by analogy to the superfluid {sup 3}He-A and B-phases. The Fermi surfaces in the {alpha}-phases exhibit spontaneous anisotropic distortions, while those in the {beta}-phases remain circular or spherical with topologically non-trivial spin configurations in momentum space. In the {alpha}-phase, the Goldstone modes in the density channel exhibit anisotropic overdamping. The Goldstone modes in the spin channel have nearly isotropic underdamped dispersion relation at small propagating wavevectors. Due to the coupling to the Goldstone modes, the spin wave spectrum develops resonance peaks in both the {alpha} and {beta}-phases, which can be detected in inelastic neutron scattering experiments. In the p-wave channel {beta}-phase, a chiral ground state inhomogeneity is spontaneously generated due to a Lifshitz-like instability in the originally nonchiral systems. Possible experiments to detect these phases are discussed.

  15. Annotated Bibliography of EDGE2D Use

    SciTech Connect

    J.D. Strachan and G. Corrigan

    2005-06-24

    This annotated bibliography is intended to help EDGE2D users, and particularly new users, find existing published literature that has used EDGE2D. Our idea is that a person can find existing studies which may relate to his intended use, as well as gain ideas about other possible applications by scanning the attached tables.

  16. Staring 2-D hadamard transform spectral imager

    DOEpatents

    Gentry, Stephen M.; Wehlburg, Christine M.; Wehlburg, Joseph C.; Smith, Mark W.; Smith, Jody L.

    2006-02-07

    A staring imaging system inputs a 2D spatial image containing multi-frequency spectral information. This image is encoded in one dimension of the image with a cyclic Hadamarid S-matrix. The resulting image is detecting with a spatial 2D detector; and a computer applies a Hadamard transform to recover the encoded image.

  17. Fermi Finds Youthful Pulsar Among Ancient Stars

    NASA Video Gallery

    In three years, NASA's Fermi has detected more than 100 gamma-ray pulsars, but something new has appeared. Among a type of pulsar with ages typically numbering a billion years or more, Fermi has fo...

  18. The AGN Jet Model of the Fermi Bubbles

    NASA Astrophysics Data System (ADS)

    Guo, Fulai

    2017-01-01

    The nature and origin of the Fermi bubbles detected in the inner Galaxy remain elusive. In this paper, we briefly discuss some recent theoretical and observational developments, with a focus on the AGN jet model. Analogous to radio lobes observed in massive galaxies, the Fermi bubbles could be naturally produced by a pair of opposing jets emanating nearly along the Galaxy's rotation axis from the Galactic center. Our two-fluid hydrodynamic simulations reproduce quite well the bubble location and shape, and interface instabilities at the bubble surface could be effectively suppressed by shear viscosity. We briefly comment on some potential issues related to our model, which may lead to future progress.

  19. Fermi Liquid Behavior in Quasi 1-D Conductors via Angular Magnetoresistance Oscillations

    NASA Astrophysics Data System (ADS)

    Lee, I. J.; Naughton, M. J.

    1998-03-01

    A body of evidence appears to be developing which suggests that electronic conduction in the q1D TMTSF molecular conductors can not be explained solely by Fermi liquid theory. Recent magnetotransport(G.M. Danner and P.M. Chaikin, Phys. Rev. Lett., 75), 4690 (1995). and photoemission(F. Zwick, et al. al.,) Phys. Rev. Lett., 79, 3982 (1997). experiments even point to a lack of a Fermi surface. We present angular-dependent magnetoresistance data on (TMTSF)_2PF6 under pressure, accompanied by calculations/simulations based on Boltzman transport (which explicitly require the existence of a Fermi surface). Based on rather good agreement between the two results, we maintain that a Fermi liquid description works, at least for the pressures employed. We will attempt to define the parameter space where Fermi liquid theory works, and where other (e.g. Luttinger) theories may be required.

  20. Competing coexisting phases in 2D water

    NASA Astrophysics Data System (ADS)

    Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire

    2016-05-01

    The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules.

  1. Competing coexisting phases in 2D water

    PubMed Central

    Zanotti, Jean-Marc; Judeinstein, Patrick; Dalla-Bernardina, Simona; Creff, Gaëlle; Brubach, Jean-Blaise; Roy, Pascale; Bonetti, Marco; Ollivier, Jacques; Sakellariou, Dimitrios; Bellissent-Funel, Marie-Claire

    2016-01-01

    The properties of bulk water come from a delicate balance of interactions on length scales encompassing several orders of magnitudes: i) the Hydrogen Bond (HBond) at the molecular scale and ii) the extension of this HBond network up to the macroscopic level. Here, we address the physics of water when the three dimensional extension of the HBond network is frustrated, so that the water molecules are forced to organize in only two dimensions. We account for the large scale fluctuating HBond network by an analytical mean-field percolation model. This approach provides a coherent interpretation of the different events experimentally (calorimetry, neutron, NMR, near and far infra-red spectroscopies) detected in interfacial water at 160, 220 and 250 K. Starting from an amorphous state of water at low temperature, these transitions are respectively interpreted as the onset of creation of transient low density patches of 4-HBonded molecules at 160 K, the percolation of these domains at 220 K and finally the total invasion of the surface by them at 250 K. The source of this surprising behaviour in 2D is the frustration of the natural bulk tetrahedral local geometry and the underlying very significant increase in entropy of the interfacial water molecules. PMID:27185018

  2. Emergence of topological bands on the surface of ZrSnTe crystal

    NASA Astrophysics Data System (ADS)

    Lou, R.; Ma, J.-Z.; Xu, Q.-N.; Fu, B.-B.; Kong, L.-Y.; Shi, Y.-G.; Richard, P.; Weng, H.-M.; Fang, Z.; Sun, S.-S.; Wang, Q.; Lei, H.-C.; Qian, T.; Ding, H.; Wang, S.-C.

    2016-06-01

    By using angle-resolved photoemission spectroscopy combined with first-principles calculations, we reveal that the topmost unit cell of ZrSnTe crystal hosts two-dimensional (2D) electronic bands of the topological insulator (TI) state, although such a TI state is defined with a curved Fermi level instead of a global band gap. Furthermore, we find that by modifying the dangling bonds on the surface through hydrogenation, this 2D band structure can be manipulated so that the expected global energy gap is most likely to be realized. This facilitates the practical applications of 2D TI in heterostructural devices and those with surface decoration and coverage. Since ZrSnTe belongs to a large family of compounds having the similar crystal and band structures, our findings shed light on identifying more 2D TI candidates and superconductor-TI heterojunctions supporting topological superconductors.

  3. Experimental validation of equations for 2D DIC uncertainty quantification.

    SciTech Connect

    Reu, Phillip L.; Miller, Timothy J.

    2010-03-01

    Uncertainty quantification (UQ) equations have been derived for predicting matching uncertainty in two-dimensional image correlation a priori. These equations include terms that represent the image noise and image contrast. Researchers at the University of South Carolina have extended previous 1D work to calculate matching errors in 2D. These 2D equations have been coded into a Sandia National Laboratories UQ software package to predict the uncertainty for DIC images. This paper presents those equations and the resulting error surfaces for trial speckle images. Comparison of the UQ results with experimentally subpixel-shifted images is also discussed.

  4. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    DOE PAGES

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes amore » phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.« less

  5. Bosonic models with Fermi-liquid kinematics: realizations and properties

    NASA Astrophysics Data System (ADS)

    Goldbart, Paul; Gopalakrishnan, Sarang; Lamacraft, Austen

    2011-03-01

    We consider models of interacting bosons in which the single-particle kinetic energy achieves its minimum on a surface in momentum space. The kinematics of such models resembles that resulting from Pauli blocking in Fermi liquids; therefore, Shankar's renormalization-group treatment of Fermi liquids can be adapted to investigate phase transitions in these bosonic systems. We explore possible experimental realizations of such models in cold atomic gases: e.g., via spin-orbit coupling, multimode-cavity-mediated interactions, and Cooper pairing of Fermi gases in spin-dependent lattices. We address the phase structure and critical behavior of the resulting models within the framework of Ref., focusing in particular on Bose-Einstein condensation and on quantum versions of the Brazovskii transition from a superfluid to a supersolid.

  6. Fractionalized Fermi liquid in a Kondo-Heisenberg model

    SciTech Connect

    Tsvelik, A. M.

    2016-10-10

    The Kondo-Heisenberg model is used as a controllable tool to demonstrate the existence of a peculiar metallic state with unbroken translational symmetry where the Fermi surface volume is not controlled by the total electron density. Here, I use a nonperturbative approach where the strongest interactions are taken into account by means of exact solution, and corrections are controllable. The resulting metallic state represents a fractionalized Fermi liquid where well defined quasiparticles coexist with gapped fractionalized collective excitations, in agreement with the general requirements formulated by T. Senthil et al. [Phys. Rev. Lett. 90, 216403 (2003)]. Furthermore, the system undergoes a phase transition to an ordered phase (charge density wave or superconducting), at the transition temperature which is parametrically small in comparison to the quasiparticle Fermi energy.

  7. Fermi's β-DECAY Theory

    NASA Astrophysics Data System (ADS)

    Yang, Chen Ning

    2013-05-01

    Throughout his lifetime Enrico Fermi (1901-1954) had considered his 1934 β-decay theory as his most important contribution to theoretical physics. E. Segrè (1905-1989) had vividly written about an episode at the inception of that paper:1...

  8. CCC and the Fermi paradox

    NASA Astrophysics Data System (ADS)

    Gurzadyan, V. G.; Penrose, R.

    2016-01-01

    Within the scheme of conformal cyclic cosmology (CCC), information can be transmitted from aeon to aeon. Accordingly, the "Fermi paradox" and the SETI programme --of communication by remote civilizations-- may be examined from a novel perspective: such information could, in principle, be encoded in the cosmic microwave background. The current empirical status of CCC is also discussed.

  9. Economics and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Hosek, W. R.

    A resolution of the Fermi paradox is proposed using common economic assumptions that should apply to all intelligent, planet-bound civilizations. It is argued that seemingly rational decisions about resource allocation will lead all civilizations to forego the commitment to interstellar exploration and colonization. Consequently humans have not, and will not, be visited by them and humans will not visit other civilizations.

  10. Fermi's Large Area Telescope (LAT)

    NASA Video Gallery

    Fermi’s Large Area Telescope (LAT) is the spacecraft’s main scientificinstrument. This animation shows a gamma ray (purple) entering the LAT,where it is converted into an electron (red) and a...

  11. 2D Hexagonal Boron Nitride (2D-hBN) Explored for the Electrochemical Sensing of Dopamine.

    PubMed

    Khan, Aamar F; Brownson, Dale A C; Randviir, Edward P; Smith, Graham C; Banks, Craig E

    2016-10-04

    Crystalline 2D hexagonal boron nitride (2D-hBN) nanosheets are explored as a potential electrocatalyst toward the electroanalytical sensing of dopamine (DA). The 2D-hBN nanosheets are electrically wired via a drop-casting modification process onto a range of commercially available carbon supporting electrodes, including glassy carbon (GC), boron-doped diamond (BDD), and screen-printed graphitic electrodes (SPEs). 2D-hBN has not previously been explored toward the electrochemical detection/electrochemical sensing of DA. We critically evaluate the potential electrocatalytic performance of 2D-hBN modified electrodes, the effect of supporting carbon electrode platforms, and the effect of "mass coverage" (which is commonly neglected in the 2D material literature) toward the detection of DA. The response of 2D-hBN modified electrodes is found to be largely dependent upon the interaction between 2D-hBN and the underlying supporting electrode material. For example, in the case of SPEs, modification with 2D-hBN (324 ng) improves the electrochemical response, decreasing the electrochemical oxidation potential of DA by ∼90 mV compared to an unmodified SPE. Conversely, modification of a GC electrode with 2D-hBN (324 ng) resulted in an increased oxidation potential of DA by ∼80 mV when compared to the unmodified electrode. We explore the underlying mechanisms of the aforementioned examples and infer that electrode surface interactions and roughness factors are critical considerations. 2D-hBN is utilized toward the sensing of DA in the presence of the common interferents ascorbic acid (AA) and uric acid (UA). 2D-hBN is found to be an effective electrocatalyst in the simultaneous detection of DA and UA at both pH 5.0 and 7.4. The peak separations/resolution between DA and UA increases by ∼70 and 50 mV (at pH 5.0 and 7.4, respectively, when utilizing 108 ng of 2D-hBN) compared to unmodified SPEs, with a particularly favorable response evident in pH 5.0, giving rise to a

  12. STEM education and Fermi problems

    NASA Astrophysics Data System (ADS)

    Holubova, Renata

    2017-01-01

    One of the research areas of Physics education is the study of the educational process. Investigations in this area are aimed for example on the teaching and learning process and its results. The conception of STEM education (Science, Technology, Engineering, and Mathematics) is discussed - it is one possible approach to the preparation of the curriculum and the focus on the educational process at basic and secondary schools. At schools in the Czech Republic STEM is much more realized by the application of interdisciplinary relations between subjects Physics-Nature-Technique. In both conceptions the aim is to support pupils' creativity, critical thinking, cross-curricular links. In this context the possibility of using Fermi problems in teaching Physics was discussed (as an interdisciplinary and constructivist activity). The aim of our research was the analysis of Fermi problems solving strategies, the ability of pupils to solve Fermi problems. The outcome of our analysis was to find out methods and teaching strategies which are important to use in teaching - how to solve qualitative and interdisciplinary tasks in physics. In this paper the theoretical basis of STEM education and Fermi problems will be presented. The outcome of our findings based on the research activities will be discussed so as our experiences from 10 years of Fermi problems competition that takes place at the Science Faculty, Palacky University in Olomouc. Changes in competencies of solving tasks by our students (from the point of view in terms of modern, activating teaching methods recommended by theory of Physics education and other science subjects) will be identified.

  13. Lattice QCD with mismatched fermi surfaces.

    PubMed

    Yamamoto, Arata

    2014-04-25

    We study two flavor fermions with mismatched chemical potentials in quenched lattice QCD. We first consider a large isospin chemical potential, where a charged pion is condensed, and then introduce a small mismatch between the chemical potentials of the up quark and the down antiquark. We find that the homogeneous pion condensate is destroyed by the mismatch of the chemical potentials. We also find that the two-point correlation function shows spatial oscillation, which indicates an inhomogeneous ground state, although it is not massless but massive in the present simulation setup.

  14. 2D-3D transition of gold cluster anions resolved

    NASA Astrophysics Data System (ADS)

    Johansson, Mikael P.; Lechtken, Anne; Schooss, Detlef; Kappes, Manfred M.; Furche, Filipp

    2008-05-01

    Small gold cluster anions Aun- are known for their unusual two-dimensional (2D) structures, giving rise to properties very different from those of bulk gold. Previous experiments and calculations disagree about the number of gold atoms nc where the transition to 3D structures occurs. We combine trapped ion electron diffraction and state of the art electronic structure calculations to resolve this puzzle and establish nc=12 . It is shown that theoretical studies using traditional generalized gradient functionals are heavily biased towards 2D structures. For a correct prediction of the 2D-3D crossover point it is crucial to use density functionals yielding accurate jellium surface energies, such as the Tao-Perdew-Staroverov-Scuseria (TPSS) functional or the Perdew-Burke-Ernzerhof functional modified for solids (PBEsol). Further, spin-orbit effects have to be included, and large, flexible basis sets employed. This combined theoretical-experimental approach is promising for larger gold and other metal clusters.

  15. 2D nanostructures for water purification: graphene and beyond.

    PubMed

    Dervin, Saoirse; Dionysiou, Dionysios D; Pillai, Suresh C

    2016-08-18

    Owing to their atomically thin structure, large surface area and mechanical strength, 2D nanoporous materials are considered to be suitable alternatives for existing desalination and water purification membrane materials. Recent progress in the development of nanoporous graphene based materials has generated enormous potential for water purification technologies. Progress in the development of nanoporous graphene and graphene oxide (GO) membranes, the mechanism of graphene molecular sieve action, structural design, hydrophilic nature, mechanical strength and antifouling properties and the principal challenges associated with nanopore generation are discussed in detail. Subsequently, the recent applications and performance of newly developed 2D materials such as 2D boron nitride (BN) nanosheets, graphyne, molybdenum disulfide (MoS2), tungsten chalcogenides (WS2) and titanium carbide (Ti3C2Tx) are highlighted. In addition, the challenges affecting 2D nanostructures for water purification are highlighted and their applications in the water purification industry are discussed. Though only a few 2D materials have been explored so far for water treatment applications, this emerging field of research is set to attract a great deal of attention in the near future.

  16. Fermi level stabilization energy in cadmium oxide

    SciTech Connect

    Speaks, D. T.; Mayer, M. A.; Yu, K. M.; Mao, S. S.; Haller, E. E.; Walukiewicz, W.

    2010-04-08

    We have studied the effects of high concentrations of native point defects on the electrical and optical properties of CdO. The defects were introduced by irradiation with high energy He+, Ne+, Ar+ and C+ ions. Increasing the irradiation damage with particles heavier than He+ increases the electron concentration until a saturation level of 5x1020 cm-3 is reached. In contrast, due to the ionic character and hence strong dynamic annealing of CdO, irradiation with much lighter He+ stabilizes the electron concentration at a much lower level of 1.7x1020 cm-3. A large shift of the optical absorption edge with increasing electron concentration in irradiated samples is explained by the Burstein-Moss shift corrected for electron-electron and electron-ion interactions. The saturation of the electron concentration and the optical absorption edge energy are consistent with a defect induced stabilization of the Fermi energy at 1 eV above the conduction band edge. The result is in a good agreement with previously determined Fermi level pinning energies on CdO surfaces. The results indicate that CdO shares many similarities with InN, as both materials exhibit extremely large electron affinities and an unprecedented propensity for n-type conductivity.

  17. Brittle damage models in DYNA2D

    SciTech Connect

    Faux, D.R.

    1997-09-01

    DYNA2D is an explicit Lagrangian finite element code used to model dynamic events where stress wave interactions influence the overall response of the system. DYNA2D is often used to model penetration problems involving ductile-to-ductile impacts; however, with the advent of the use of ceramics in the armor-anti-armor community and the need to model damage to laser optics components, good brittle damage models are now needed in DYNA2D. This report will detail the implementation of four brittle damage models in DYNA2D, three scalar damage models and one tensor damage model. These new brittle damage models are then used to predict experimental results from three distinctly different glass damage problems.

  18. 2D/3D switchable displays

    NASA Astrophysics Data System (ADS)

    Dekker, T.; de Zwart, S. T.; Willemsen, O. H.; Hiddink, M. G. H.; IJzerman, W. L.

    2006-02-01

    A prerequisite for a wide market acceptance of 3D displays is the ability to switch between 3D and full resolution 2D. In this paper we present a robust and cost effective concept for an auto-stereoscopic switchable 2D/3D display. The display is based on an LCD panel, equipped with switchable LC-filled lenticular lenses. We will discuss 3D image quality, with the focus on display uniformity. We show that slanting the lenticulars in combination with a good lens design can minimize non-uniformities in our 20" 2D/3D monitors. Furthermore, we introduce fractional viewing systems as a very robust concept to further improve uniformity in the case slanting the lenticulars and optimizing the lens design are not sufficient. We will discuss measurements and numerical simulations of the key optical characteristics of this display. Finally, we discuss 2D image quality, the switching characteristics and the residual lens effect.

  19. 2-d Finite Element Code Postprocessor

    SciTech Connect

    Sanford, L. A.; Hallquist, J. O.

    1996-07-15

    ORION is an interactive program that serves as a postprocessor for the analysis programs NIKE2D, DYNA2D, TOPAZ2D, and CHEMICAL TOPAZ2D. ORION reads binary plot files generated by the two-dimensional finite element codes currently used by the Methods Development Group at LLNL. Contour and color fringe plots of a large number of quantities may be displayed on meshes consisting of triangular and quadrilateral elements. ORION can compute strain measures, interface pressures along slide lines, reaction forces along constrained boundaries, and momentum. ORION has been applied to study the response of two-dimensional solids and structures undergoing finite deformations under a wide variety of large deformation transient dynamic and static problems and heat transfer analyses.

  20. LETTER TO THE EDITOR: Instability of a Landau - Fermi liquid as the Mott insulator is approached

    NASA Astrophysics Data System (ADS)

    Furukawa, N.; Rice, T. M.

    1998-06-01

    We examine a two-dimensional Fermi liquid with a Fermi surface which touches the Umklapp surface first at the four points 0953-8984/10/23/001/img1 as the electron density is increased. Umklapp processes at the four patches near 0953-8984/10/23/001/img1 lead the renormalization group equations to scale to strong coupling, resembling the behaviour of a two-leg ladder at half-filling. The incompressible character of the fixed point causes a breakdown of Landau theory at these patches. A further increase in density spreads the incompressible regions so that the open Fermi surface shrinks to four disconnected segments. This non-Landau state, in which parts of the Fermi surface are truncated to form an insulating spin liquid, has many features in common with phenomenological models recently proposed for the cuprate superconductors.