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Sample records for fermi surface

  1. Stability of Fermi surfaces and K theory.

    PubMed

    Horava, Petr

    2005-07-01

    Nonrelativistic Fermi liquids in d+1 dimensions exhibit generalized Fermi surfaces: (d-p)-dimensional submanifolds in the (k,omega)-space supporting gapless excitations. We show that the universality classes of stable Fermi surfaces are classified by K theory, with the pattern of stability determined by Bott periodicity. The Atiyah-Bott-Shapiro construction implies that the low-energy modes near a Fermi surface exhibit relativistic invariance in the transverse p+1 dimensions. This suggests an intriguing parallel between nonrelativistic Fermi liquids and D-branes of string theory. PMID:16090638

  2. Entanglement Entropy and the Fermi Surface

    NASA Astrophysics Data System (ADS)

    Swingle, Brian

    2010-07-01

    Free fermions with a finite Fermi surface are known to exhibit an anomalously large entanglement entropy. The leading contribution to the entanglement entropy of a region of linear size L in d spatial dimensions is S˜Ld-1log⁡L, a result that should be contrasted with the usual boundary law S˜Ld-1. This term depends only on the geometry of the Fermi surface and on the boundary of the region in question. I give an intuitive account of this anomalous scaling based on a low energy description of the Fermi surface as a collection of one-dimensional gapless modes. Using this picture, I predict a violation of the boundary law in a number of other strongly correlated systems.

  3. Fermi surface anisotropy in the cuprates

    NASA Astrophysics Data System (ADS)

    Ramshaw, Brad

    Broken rotational (C4) symmetry is a distinguishing feature for a number of experiments in the underdoped high-Tc cuprates, including electrical resistivity, neutron scattering, Nernst coefficient, and scanning tunneling microscopy. This broken symmetry has not been observed on the Fermi surface, however, with or without the presence of an applied magnetic field. We measure the angle-dependent magnetoresistance-a quantity known to be extremely sensitive to the geometry and symmetry of the Fermi surface-of YBa2Cu3O6.58, and find that the Fermi surface has a clear two-fold symmetry, breaking the C4 symmetry of the copper-oxide plane. We discuss the implications of this finding, including how it fits with recent X-ray measurements in high magnetic fields.

  4. Switchable Fermi surface sheets in greigite

    NASA Astrophysics Data System (ADS)

    Zhang, B.; de Wijs, G. A.; de Groot, R. A.

    2012-07-01

    Greigite (Fe3S4) and magnetite (Fe3O4) are isostructural and isoelectronic ferrimagnets with quite distinct properties. Electronic structure calculations reveal greigite is a normal metal in contrast to half-metallic magnetite. Greigite shows a complex Fermi surface with a unique influence of relativistic effects: The existence of sheets of the Fermi surface depends on the direction of the magnetization. This enables spinorbitronics, spintronics on the level of a single compound rather than a device. Due to its relativistic origin, spin contamination is irrelevant in spinorbitronics and the entire periodic table is available for optimizations.

  5. 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.

  6. Fermi surfaces of surface states on Si(111)-Ag, Au

    NASA Astrophysics Data System (ADS)

    Crain, J. N.; Altmann, K. N.; Bromberger, C.; Himpsel, F. J.

    2002-11-01

    Metallic surface states on semiconducting substrates provide an opportunity to study low-dimensional electrons decoupled from the bulk. Angle resolved photoemission is used to determine the Fermi surface, group velocity, and effective mass for surface states on Si(111)(3)×(3)-Ag, Si(111)(3)×(3)-Au, and Si(111)(21)×(21)-(Ag+Au). For Si(111)(3)×(3)-Ag the Fermi surface consists of small electron pockets populated by electrons from a few % excess Ag. For Si(111)(21)×(21)-(Ag+Au) the pockets increase their size corresponding to a filling by three electrons per unit cell. The (21)×(21) superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the (21)×(21) superlattice.

  7. 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.

  8. Evolution of electron Fermi surface with doping in cobaltates.

    PubMed

    Ma, Xixiao; Lan, Yu; Qin, Ling; Kuang, Lülin; Feng, Shiping

    2016-08-24

    The notion of the electron Fermi surface is one of the characteristic concepts in the field of condensed matter physics, and it plays a crucial role in the understanding of the physical properties of doped Mott insulators. Based on the t-J model, we study the nature of the electron Fermi surface in the cobaltates, and qualitatively reproduce the essential feature of the evolution of the electron Fermi surface with doping. It is shown that the underlying hexagonal electron Fermi surface obeys Luttinger's theorem. The theory also predicts a Fermi-arc phenomenon at the low-doped regime, where the region of the hexagonal electron Fermi surface along the [Formula: see text]-K direction is suppressed by the electron self-energy, and then six disconnected Fermi arcs located at the region of the hexagonal electron Fermi surface along the [Formula: see text]-M direction emerge. However, this Fermi-arc phenomenon at the low-doped regime weakens with the increase of doping. PMID:27351111

  9. Evolution of electron Fermi surface with doping in cobaltates

    NASA Astrophysics Data System (ADS)

    Ma, Xixiao; Lan, Yu; Qin, Ling; Kuang, Lülin; Feng, Shiping

    2016-08-01

    The notion of the electron Fermi surface is one of the characteristic concepts in the field of condensed matter physics, and it plays a crucial role in the understanding of the physical properties of doped Mott insulators. Based on the t-J model, we study the nature of the electron Fermi surface in the cobaltates, and qualitatively reproduce the essential feature of the evolution of the electron Fermi surface with doping. It is shown that the underlying hexagonal electron Fermi surface obeys Luttinger’s theorem. The theory also predicts a Fermi-arc phenomenon at the low-doped regime, where the region of the hexagonal electron Fermi surface along the Γ -K direction is suppressed by the electron self-energy, and then six disconnected Fermi arcs located at the region of the hexagonal electron Fermi surface along the Γ -M direction emerge. However, this Fermi-arc phenomenon at the low-doped regime weakens with the increase of doping.

  10. Fermi surfaces and energy gaps of high-temperature superconductors

    SciTech Connect

    Shen, Z.X.; Dessau, D.S.

    1994-12-31

    In this short paper, the authors describe their recent experimental results from high-temperature superconductors. In the normal state, the data reveals interesting features of the Fermi surfaces and low energy excitations near the Fermi level. In the superconducting state, the data shows a very strong anisotropy in the superconducting gap.

  11. 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

  12. 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.

  13. Observation of Fermi arc surface states in a topological metal.

    PubMed

    Xu, Su-Yang; Liu, Chang; Kushwaha, Satya K; Sankar, Raman; Krizan, Jason W; Belopolski, Ilya; Neupane, Madhab; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Jeng, Horng-Tay; Huang, Cheng-Yi; Tsai, Wei-Feng; Lin, Hsin; Shibayev, Pavel P; Chou, Fang-Cheng; Cava, Robert J; Hasan, M Zahid

    2015-01-16

    The topology of the electronic structure of a crystal is manifested in its surface states. Recently, a distinct topological state has been proposed in metals or semimetals whose spin-orbit band structure features three-dimensional Dirac quasiparticles. We used angle-resolved photoemission spectroscopy to experimentally observe a pair of spin-polarized Fermi arc surface states on the surface of the Dirac semimetal Na3Bi at its native chemical potential. Our systematic results collectively identify a topological phase in a gapless material. The observed Fermi arc surface states open research frontiers in fundamental physics and possibly in spintronics. PMID:25593189

  14. Fermi Surfaces of Surface States on Si(111)

    NASA Astrophysics Data System (ADS)

    Crain, J. N.; Altmann, K. N.; Himpsel, F. J.; Bromberger, C.

    2002-03-01

    Metallic surface states on semi-conducting surfaces provide a unique opportunity to study low-dimensional bands that are decoupled from the bulk. Two such systems that have received much attention for their metallic surface states are Si(111)surd 3× surd 3 - Ag and Si(111) surd 3× surd 3 - Au. We present angle resolved photoemission data mapping the Fermi-surfaces for surd 3× surd 3 - Ag and surd 3× surd 3 - Au, and study the effects of doping the surface with additional Au atoms.[1] For surd 3× surd 3 - Au, an increase in the Au coverage is linked to an increase in the occupancy of the metallic surface state. In the case of surd 3× surd 3 - Ag, the addition of Au forms a new metallic band and a surd 21× surd 21 superlattice that are observed in photoemission. Reference: [1] J N Crain, K N Altmann, C Bromberger, F J Himpsel, submitted to Physics Review B.

  15. Pressure dependence of the Fermi surface of hcp Yb

    NASA Astrophysics Data System (ADS)

    Schirber, J. E.; Beaudry, B. J.; Jepsen, O.

    1981-06-01

    The pressure dependence of Fermi-surface cross sections for principal symmetry directions has been investigated using solid He pressure generation techniques. Careful searches for de Haas-van Alphen signals were conducted from 2 to 9 kbar in both virgin fcc crystals and samples transformed from hcp to fcc. No sign of the frequency reported by Ribault was detected. Results are discussed in terms of theoretically calculated pressure-induced changes in the band structure and Fermi surface of the hcp phase of Yb.

  16. 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"

  17. 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.

  18. Fermi Surface and Magnetic Structure of TmGa3

    NASA Astrophysics Data System (ADS)

    Biasini, M.; Kontrym-Sznajd, G.; Monge, M. A.; Gemmi, M.; Czopnik, A.; Jura, A.

    2001-05-01

    We carry out measurements of the two-dimensional angular correlation of the positron annihilation radiation (2D-ACAR) to reconstruct the complex multisheet Fermi surface (FS) of the cubic rare-earth (RE) compound TmGa3. We discover a correlation between the antiferromagnetic structures and the nesting of the FS along the [110] directions. Moreover, we propose methods to estimate the density of states at the Fermi energy ( EF) and the electronic contribution to the specific heat [we obtain N\\(EF\\) = 13.6 states/Ryd cell and γ = 2.4 mJ/mole K2].

  19. 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.

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

    PubMed

    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 [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. PMID:27436895

  1. 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.

  2. Spatial Variations in the Fermi Surface of Bi-2212

    NASA Astrophysics Data System (ADS)

    Main, Elizabeth; Pivonka, A. E.; Zeljkovic, I.; Gu, G.; Hudson, E. W.; Hoffman, J. E.

    2011-03-01

    In cuprate superconductors, scanning tunneling microscopy can be used to see variations in the Fermi surface on a nanometer length scale caused by doping inhomogeneity. Prior STM studies show that the local wavelength of the checkerboard, a weak charge modulation ascribed to antinodal Fermi surface nesting, varies with the size of the pseudogap in Bi 2 Sr 2 Cu O6 + δ (Bi-2201). Here we report similar STM measurements in Bi-2212. We therefore confirm the local relationship between pseudogap energy and charge ordering wavevector in a second high-Tc superconductor. We acknowledge support from AFOSR PECASE grant FA9550-06-1-0531, AFOSR DURIP grant FA9550-06-1-0359, NSF Career grant DMR-0847433 and NSF grant DMR-0904400.

  3. Heavy fermions. Unconventional Fermi surface in an insulating state.

    PubMed

    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

    2015-07-17

    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. The quantum oscillation amplitude strongly increases at low temperatures, appearing strikingly at variance with conventional metallic behavior. PMID:26138105

  4. Spin fluctuation and Fermi surface instability in ferromagnetic superconductors

    NASA Astrophysics Data System (ADS)

    Aoki, Dai; Gourgout, Adrien; Pourret, Alexandre; Bastien, Gaël; Knebel, Georg; Flouquet, Jacques

    2014-08-01

    We review the ferromagnetic superconductivity observed in the uranium based compounds, namely UGe2, URhGe and UCoGe, where the spin-triplet state is most likely realized. An unusual upper critical field Hc2, which is enhanced under a magnetic field in a certain field direction, is discussed in terms of spin fluctuations and of Fermi surface instabilities. xml:lang="fr"

  5. Magnetic and Fermi Surface Properties of EuGa4

    NASA Astrophysics Data System (ADS)

    Nakamura, Ai; Hiranaka, Yuichi; Hedo, Masato; Nakama, Takao; Miura, Yasunao; Tsutsumi, Hiroki; Mori, Akinobu; Ishida, Kazuhiro; Mitamura, Katsuya; Hirose, Yusuke; Sugiyama, Kiyohiro; Honda, Fuminori; Settai, Rikio; Takeuchi, Tetsuya; Hagiwara, Masayuki; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Haga, Yoshinori; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Harima, Hisatomo; Ōnuki, Yoshichika

    2013-10-01

    We grew a high-quality single crystal EuGa4 with the tetragonal structure by the Ga self-flux method, and measured the electrical resistivity, magnetic susceptibility, high-field magnetization, specific heat, thermoelectric power and de Haas--van Alphen (dHvA) effect, together with the electrical resistivity and thermoelectric power under pressure. EuGa4 is found to be a Eu-divalent compound without anisotropy of the magnetic susceptibility in the paramagnetic state and to reveal the same magnetization curve between H \\parallel [100] and [001] in the antiferromagnetic state, where the antiferromagnetic easy-axis is oriented along the [100] direction below a Néel temperature TN=16.5 K. The magnetization curve is discussed on the basis of a simple two-sublattice model. The Fermi surface in the paramagnetic state was clarified from the results of a dHvA experiment for EuGa4 and an energy band calculation for a non-4f reference compound SrGa4, which consists of a small ellipsoidal hole--Fermi surface and a compensated cube-like electron--Fermi surface with vacant space in center. We observed an anomaly in the temperature dependence of the electrical resistivity and thermoelectric power at TCDW=150 K under 2 GPa. This might correspond to an emergence of the charge density wave (CDW). The similar phenomenon was also observed in EuAl4 at ambient pressure. We discussed the CDW phenomenon on the basis of the present peculiar Fermi surfaces.

  6. Fermi Surface Instabilities in Ferromagnetic Superconductor URhGe

    NASA Astrophysics Data System (ADS)

    Aoki, Dai; Knebel, Georg; Flouquet, Jacques

    2014-09-01

    The field-reentrant (field-reinforced) superconductivity on ferromagnetic superconductors is one of the most interesting topics in unconventional superconductivity. The enhancement of effective mass and the induced ferromagnetic fluctuations play key roles for reentrant superconductivity. However, the associated change of the Fermi surface, which is often observed at (pseudo-) metamagnetic transition, can also be a key ingredient. In order to study the Fermi surface instability, we performed Hall effect measurements in the ferromagnetic superconductor URhGe. The Hall effect of URhGe is well explained by two contributions, namely by the normal Hall effect and by the large anomalous Hall effect due to skew scattering. The large change in the Hall coefficient is observed at low fields between the paramagnetic and ferromagnetic states for H || c-axis (easy-magnetization axis) in the orthorhombic structure, indicating that the Fermi surface is reconstructed in the ferromagnetic state below the Curie temperature (TCurie = 9.5 K). At low temperatures (T ll Ttext{Curie}), when the field is applied along the b-axis, the reentrant superconductivity was observed in both the Hall resistivity and the magnetoresistance below 0.4 K. Above 0.4 K, a large jump with the first-order nature was detected in the Hall resistivity at a spin-reorientation field HR ˜ 12.5 T, demonstrating that the marked change of the Fermi surface occurs between the ferromagnetic state and the polarized state above HR. The results can be understood by the Lifshitz-type transition, induced by the magnetic field or by the change of the effective magnetic field.

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

    NASA Astrophysics Data System (ADS)

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

    Motivated by recent experiments probing double Fermi arcs on the surface 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 Fermi arcs of DSMs are not topologically protected in general, except at certain time-reversal invariant momenta. For a simple 4-band model with a pair of Dirac nodes at k = (0, 0, +/-Q) gapless surface states are protected only at kz = 0. We identify symmetry allowed bulk perturbations that destroy Fermi arcs, but show that they are necessarily ``small'', i.e., higher order than terms kept in usual k . p theory. We validate our conclusions about the absence of a topological invariant protecting the surface states in DSMs using a K-theory analysis for the space groups of Na3Bi and Cd3As2 The authors acknowledge the support of the CEM, an NSF MRSEC, under Grant DMR-1420451.

  8. Fermi surface reconstruction in FeSe under high pressure

    NASA Astrophysics Data System (ADS)

    Terashima, Taichi; Kikugawa, Naoki; Kiswandhi, Andhika; Graf, David; Choi, Eun-Sang; Brooks, James S.; Kasahara, Shigeru; Watashige, Tatsuya; Matsuda, Yuji; Shibauchi, Takasada; Wolf, Thomas; Böhmer, Anna E.; Hardy, Frédéric; Meingast, Christoph; Löhneysen, Hilbert v.; Uji, Shinya

    2016-03-01

    We report Shubnikov-de Haas (SdH) oscillation measurements on FeSe under high pressure up to P =16.1 kbar. We find a sudden change in SdH oscillations at the onset of the pressure-induced antiferromagnetism at P ˜8 kbar. We argue that this change can be attributed to a reconstruction of the Fermi surface by the antiferromagnetic order. The negative d Tc /d P observed in a range between P ˜8 and 12 kbar may be explained by the reduction in the density of states due to the reconstruction. The ratio of the transition temperature to the effective Fermi energy remains high under high pressure: kBTc/EF˜0.1 even at P =16.1 kbar.

  9. Fermi Surface Topology and the ARPES Spectra of BISCO

    NASA Astrophysics Data System (ADS)

    Bansil, A.; Lindroos, M.

    2001-03-01

    The Fermi surface (FS) of BISCO has generated considerable recent controversy with attention focused on whether or not the FS is electron- or hole-like in the vicinity of the M(π,0) symmetry point. Given strong matrix element effects in BISCO[1], care is needed in ascertaining delicate FS features in terms of the the ARPES spectra. With this motivation, we have carried out extensive first-principles simulations of photointensity in the entire (k_x,k_y) plane for emission from the Fermi energy at a photon energy of 21.2 eV. The presence of electron or hole sheets in the underlying spectrum is simulated by varying the Fermi energy appropriately. The simulated ARPES spectra are analyzed using a variety of methods that have been invoked in the recent literature for the purpose of deducing FS topology in BISCO from the ARPES data. While different methods indeed help ameliorate matrix element effects to varying degrees, our study also reveals their limitations. The "renormalization" of the spectrum over a large energy window ( ~600 meV) tends to artificially introduce hole-like features, while the gradient of the total spectral weight has a tendancy to induce spurious electron-like features. These and related issues are discussed. Work supported in part by the U.S.D.O.E. [1] A. Bansil and M. Lindroos, Phys. Rev. Letters 83,5154(1999).

  10. Signature of Fermi surface jumps in positron spectroscopy data

    NASA Astrophysics Data System (ADS)

    Adam, Gh.; Adam, S.

    1999-08-01

    A subtractionless method for solving Fermi surface sheets (FSS), from measured n-axis-projected momentum distribution histograms by two-dimensional angular correlation of the positron—electron annihilation radiation (2D-ACAR) technique, is discussed. The window least squares statistical noise smoothing filter described by Adam et al. [Nucl.Instr. & Meth. A 337 (1993) 188] is first refined such that the window free radial parameters (WRP) are optimally adapted to the data. In an ideal single crystal, the specific jumps induced in the WRP distribution by the existing Fermi surface jumps yield straightforward information on the resolved FSS. In a real crystal, the smearing of the derived WRP optimal values, which originates from positron annihilations with electrons at crystal imperfections, is ruled out by median smoothing of the obtained distribution, over symmetry defined stars of bins. The analysis of a gigacount 2D-ACAR spectrum, measured on the archetypal high- T c compound YBa 2Cu 3O 7- δ at room temperature, illustrates the method. Both electronic FSS, the ridge along ΓX direction and the pillbox centered at the S point of the first Brillouin zone, are resolved.

  11. Fermi Surface of Donor and Acceptor Graphite Intercalation Compounds.

    NASA Astrophysics Data System (ADS)

    Wang, Guonan

    The Fermi surfaces and the electronic properties of the donor-type stage-1 C_8K and stage-2 C_{24}K, as well as the acceptor-type stage-2 BiCl_3, stage-3 HgCl_2 and stage-3 SbF _5 graphite intercalation compounds were investigated by means of the de Haas-van Alphen effect. The dHvA spectra of the stage-1 C_8 K exhibit two dHvA frequencies, 3126 T and 4250 T. The corresponding effective masses were 0.86 m _0 and 0.92 m_0, respectively. The angular dependence of the dHvA frequencies for a direction within +/-18^circ of the c-axis showed that there are both three-dimensional and two dimensional parts of the Fermi surfaces in C _8K. The three-dimensional Fermi surface has a cross-sectional area corresponding to the dHvA frequency of 3126 T. The charge transfer per potassium atom measured from the dHvA effect is 0.97. This implies that the potassium is ionized completely. These dHvA experimental results support both the Tatar and Rabii model and the revised Ohno, Nakao and Kamimura model for C_8K. Two dominant dHvA frequencies were obtained in stage-2 C_{24}K. They are 286 T and 2570 T, respectively. The predictions of Blinowski's model are in agreement with the experimental data. The charge transfer per potassium is found to be 0.88. This suggests that the potassium s-band is above the Fermi level in C_{24}K. The dHvA measurements for the acceptor compounds show that the stage-2 BiCl_3 GIC had two dHvA frequencies, 327T and 1012T, and each stage -3 compound had three dominant frequencies. They are 121T, 523T and 664T for HgCl_2, and 172T, 656T and 852T for SbF_5. The cyclotron masses corresponding to the dHvA frequencies for these compounds were measured from the temperature dependence of the dHvA amplitudes. The theoretical predictions of the dHvA frequencies and the cyclotron masses from the Blinowski's band models for stage-2 and stage-3 compounds are in agreement with the experimental results. The angular dependence of the dHvA frequencies show that the Fermi

  12. Fermi surface evolution and luttinger theorem in naxcoo2: asystematic photoemission study

    SciTech Connect

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

    2005-01-17

    We report a systematic angle-resolved photoemission study on NaxCoO2 for a wide range of Na concentrations (0.3x0.72). In all the metallic samples at different x, we observed (i) only a single holelike Fermi surface centered around 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 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. Contact Potentials, Fermi Level Equilibration, and Surface Charging.

    PubMed

    Peljo, Pekka; Manzanares, José A; Girault, Hubert H

    2016-06-14

    This article focuses on contact electrification from thermodynamic equilibration of the electrochemical potential of the electrons of two conductors upon contact. The contact potential difference generated in bimetallic macro- and nanosystems, the Fermi level after the contact, and the amount and location of the charge transferred from one metal to the other are discussed. The three geometries considered are spheres in contact, Janus particles, and core-shell particles. In addition, the force between the two spheres in contact with each other is calculated and is found to be attractive. A simple electrostatic model for calculating charge distribution and potential profiles in both vacuum and an aqueous electrolyte solution is described. Immersion of these bimetallic systems into an electrolyte solution leads to the formation of an electric double layer at the metal-electrolyte interface. This Fermi level equilibration and the associated charge transfer can at least partly explain experimentally observed different electrocatalytic, catalytic, and optical properties of multimetallic nanosystems in comparison to systems composed of pure metals. For example, the shifts in the surface plasmon resonance peaks in bimetallic core-shell particles seem to result at least partly from contact charging. PMID:27176729

  14. 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

  15. 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.

  16. 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

    2011-01-01

    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. PMID:21847106

  17. Two-dimensional Fermi surfaces in Kondo insulator SmB₆.

    PubMed

    Li, G; Xiang, Z; Yu, F; Asaba, T; Lawson, B; Cai, P; Tinsman, C; Berkley, A; Wolgast, S; Eo, Y S; Kim, Dae-Jeong; Kurdak, C; Allen, J W; Sun, K; Chen, X H; Wang, Y Y; Fisk, Z; Li, Lu

    2014-12-01

    In the Kondo insulator samarium hexaboride (SmB6), strong correlation and band hybridization lead to an insulating gap and a diverging resistance at low temperature. The resistance divergence ends at about 3 kelvin, a behavior that may arise from surface conductance. We used torque magnetometry to resolve the Fermi surface topology in this material. The observed oscillation patterns reveal two Fermi surfaces on the (100) surface plane and one Fermi surface on the (101) surface plane. The measured Fermi surface cross sections scale as the inverse cosine function of the magnetic field tilt angles, which demonstrates the two-dimensional nature of the conducting electronic states of SmB6. PMID:25477456

  18. Indirect measurements of Fermi surface parameters of some chevrel phase materials

    NASA Technical Reports Server (NTRS)

    Woollam, J. A.; Alterovitz, S. A.

    1979-01-01

    A series of measurements of normal state and superconducting properties were made in zero and in high magnetic fields. When these results are combined with a complete set of theoretical expressions, a number of Fermi surface parameters are found.

  19. Hall effect and Fermi surface reconstruction via electron pockets in the high-Tc cuprates

    NASA Astrophysics Data System (ADS)

    Storey, J. G.

    2016-01-01

    The mechanism by which the Fermi surface of high-T c cuprates undergoes a dramatic change from a large hole-like barrel to small arcs or pockets on entering the pseudogap phase remains a question of fundamental importance. Here we calculate the normal-state Hall coefficient from the resonating-valence-bond spin-liquid model developed by Yang, Rice and Zhang. In this model, reconstruction of the Fermi surface occurs via an intermediate regime where the Fermi surface consists of both hole- and electron-like pockets. We find that the doping (x) dependence of the Hall number transitions from 1+x to (x) over this narrow doping range. At low temperatures, a switch from a downturn to an upturn in the Hall coefficient signals the departure of the electron-like pockets from the Fermi surface.

  20. 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.

  1. 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.

  2. Quantum oscillations and the Fermi surface topology of the Weyl semimetal NbP

    NASA Astrophysics Data System (ADS)

    Klotz, J.; Wu, Shu-Chun; Shekhar, Chandra; Sun, Yan; Schmidt, Marcus; Nicklas, Michael; Baenitz, Michael; Uhlarz, M.; Wosnitza, J.; Felser, Claudia; Yan, Binghai

    2016-03-01

    The Weyl semimetal NbP was found to exhibit topological Fermi arcs and exotic magnetotransport properties. Here, we report on magnetic quantum-oscillation measurements on NbP and construct the three-dimensional Fermi surface with the help of band-structure calculations. We reveal a pair of spin-orbit-split electron pockets at the Fermi energy and a similar pair of hole pockets, all of which are strongly anisotropic. The Weyl points that are located in the kz≈π /c plane are found to exist 5 meV above the Fermi energy. Therefore, we predict that the chiral anomaly effect can be realized in NbP by electron doping to drive the Fermi energy to the Weyl points.

  3. 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

  4. 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. PMID:27551687

  5. Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Uedono, A.

    2004-11-01

    The cover picture of this issue, taken from [1], shows a cross section of the Fermi surface in the basal plane of nickel. The measurements were carried out using 2D angular correlation of annihilation radiation (ACAR) experiments. The intersecting plane is normal to the c-axis, passing through the and X points. The light regions correspond to a high electron momentum density. The Fermi surface is presented as two hole surfaces around the point and two electron surfaces around the X point.

  6. Tomographic investigation of fermi level pinning at focused ion beam milled semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Wolf, D.; Lubk, A.; Lenk, A.; Sturm, S.; Lichte, H.

    2013-12-01

    Electron holography in the transmission electron microscope (TEM) offers the spatial and signal resolution for studying effects like Fermi level pinning or dopant concentration variations important for the design of modern electronic devices. To overcome the loss of information along the projection direction, surface effects, and surface damage due to TEM specimen preparation, we apply electron holographic tomography to analyze the 3D potential distribution of semiconductor samples prepared by focused-ion-beam. We observe mid-band gap pinning of the Fermi level at Si surfaces but valence band pinning at Ge surfaces. The pinning extends over tens of nanometers into the bulk.

  7. 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.

  8. 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.

  9. Spin dependent momentum density and Fermi surface of ferromagnetic Ni obtained by positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Uedono, A.

    2004-11-01

    The spin-dependent momentum density and Fermi surface of ferromagnetic Ni have been obtained through positron annihilation experiments. The measurements were carried out through 2D angular correlation of annihilation radiation (ACAR) using longitudinally polarized positrons. The magnetic field direction was reversed in order to study the effect of the spin-dependent positron-electron momentum space density on the Fermi surface of Ni. The results showed that ferromagnetic Ni had different Fermi surfaces for the majority-spin and minority-spin states. The differences due to the spin-states were studied in the momentum space and in the wave vector space. In general, the experimental results showed good agreement with previous theoretical calculations.

  10. Anomalous Fermi-Surface Dependent Pairing in a Self-Doped High-T(c) Superconductor

    SciTech Connect

    Chen, Yulin; Iyo, Akira; Yang, Wanli; Zhou, Xingjiang; Lu, Donghui; Eisaki, Hiroshi; Devereaux, Thomas P.; Hussain, Zahid; Shen, Z.-X.; /Stanford U., Phys. Dept. /SLAC, SSRL /AIST, Tsukuba /Waterloo U. /LBNL, ALS

    2007-02-12

    We report the discovery of a self-doped multilayer 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 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 60 K, possessing simultaneously both electron- and hole-doped Fermi-surface sheets. Intriguingly, the Fermi-surface 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}/{alpha}, {pi}/{alpha}) scattering.

  11. 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.

  12. Hole Fermi surface in Bi2Se3 probed by quantum oscillations

    NASA Astrophysics Data System (ADS)

    Piot, B. A.; Desrat, W.; Maude, D. K.; Orlita, M.; Potemski, M.; Martinez, G.; Hor, Y. S.

    2016-04-01

    Transport and torque magnetometry measurements are performed at high magnetic fields and low temperatures in a series of p-type (Ca-doped) Bi2Se3 crystals. The angular dependence of the Shubnikov-de Haas and de Haas-van Alphen quantum oscillations enables us to determine the Fermi surface of the bulk valence band states as a function of the carrier density. At low density, the angular dependence exhibits a downturn in the oscillations frequency between 0∘ and 90∘, reflecting a bag-shaped hole Fermi surface. The detection of a single frequency for all tilt angles rules out the existence of a Fermi surface with different extremal cross sections down to 24 meV. There is therefore no signature of a camelback in the valence band of our bulk samples, in accordance with the direct band gap predicted by G W calculations.

  13. Pressure tuning the Fermi surface topology of the Weyl semimetal NbP

    NASA Astrophysics Data System (ADS)

    dos Reis, R. D.; Wu, S. C.; Sun, Y.; Ajeesh, M. O.; Shekhar, C.; Schmidt, M.; Felser, C.; Yan, B.; Nicklas, M.

    2016-05-01

    We report on the pressure evolution of the Fermi surface topology of the Weyl semimetal NbP, probed by Shubnikov-de Haas oscillations in the magnetoresistance combined with ab initio calculations of the band structure. Although we observe a drastic effect on the amplitudes of the quantum oscillations, the frequencies only exhibit a weak pressure dependence up to 2.8 GPa. The pressure-induced variations in the oscillation frequencies are consistent with our band-structure calculations. Furthermore, we can relate the changes in the amplitudes to small modifications in the shape of the Fermi surface. Our findings show evidence of the stability of the electronic band structure of NbP and demonstrate the power of combining quantum-oscillation studies and band-structure calculations to investigate pressure effects on the Fermi surface topology in Weyl semimetals.

  14. Origin of Fermi-level pinning at GaAs surfaces and interfaces

    NASA Astrophysics Data System (ADS)

    Colleoni, Davide; Miceli, Giacomo; Pasquarello, Alfredo

    2014-12-01

    Through first-principles simulation methods, we assign the origin of Fermi-level pinning at GaAs surfaces and interfaces to the bistability between the As-As dimer and two As dangling bonds, which transform into each other upon charge trapping. This defect is shown to be naturally formed both at GaAs surfaces upon oxygen deposition and in the near-interface substoichiometric oxide. Using electron-counting arguments, we infer that the identified defect occurs in opposite charge states. The Fermi-level pinning then results from the amphoteric nature of this defect which drives the Fermi level to its defect level. These results account for the experimental characterization at both GaAs surfaces and interfaces within a unified picture, wherein the role of As antisites is elucidated.

  15. Origin of Fermi-level pinning at GaAs surfaces and interfaces.

    PubMed

    Colleoni, Davide; Miceli, Giacomo; Pasquarello, Alfredo

    2014-12-10

    Through first-principles simulation methods, we assign the origin of Fermi-level pinning at GaAs surfaces and interfaces to the bistability between the As-As dimer and two As dangling bonds, which transform into each other upon charge trapping. This defect is shown to be naturally formed both at GaAs surfaces upon oxygen deposition and in the near-interface substoichiometric oxide. Using electron-counting arguments, we infer that the identified defect occurs in opposite charge states. The Fermi-level pinning then results from the amphoteric nature of this defect which drives the Fermi level to its defect level. These results account for the experimental characterization at both GaAs surfaces and interfaces within a unified picture, wherein the role of As antisites is elucidated. PMID:25372411

  16. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    NASA Astrophysics Data System (ADS)

    Charnukha, Aliaksei

    2015-03-01

    In the family of iron-based superconductors, 1111-type materials exhibit superconductivity with the highest transition temperature Tc=55K. Early theoretical predictions of their electronic structure revealed multiple large circular sheets of the Fermi surface. Here we use ARPES to show that two prototypical compounds of the 1111 type are at odds with this description. Their low-energy band structure is formed by the edges of several bands, which are pulled to the Fermi level from the depths of the theoretically predicted band structure by strong electronic interactions. We further demonstrate that although their low-energy electronic looks remarkably similar, the Tc differs by a factor of 2. Upon closer examination we uncover that one of the bands in the higher-Tc compound sinks to 2.3meV below the Fermi level and thus does not produce a Fermi surface. And yet we find that it hosts a superconducting energy gap 10x larger than the same band in the lower-Tc sister compound. Our results show that the Fermi-surface singularities in the iron-oxypnictides dramatically affect their low-energy electronic properties, including superconductivity, and must therefore be explicitly taken into account in any attempt to understand the pairing mechanism.

  17. Quantum phase transitions, frustration, and the Fermi surface in the Kondo lattice model

    NASA Astrophysics Data System (ADS)

    Eidelstein, Eitan; Moukouri, S.; Schiller, Avraham

    2011-07-01

    The quantum phase transition from a spin-Peierls phase with a small Fermi surface to a paramagnetic Luttinger-liquid phase with a large Fermi surface is studied in the framework of a one-dimensional Kondo-Heisenberg model that consists of an electron gas away from half filling, coupled to a spin-1/2 chain by Kondo interactions. The Kondo spins are further coupled to each other with isotropic nearest-neighbor and next-nearest-neighbor antiferromagnetic Heisenberg interactions which are tuned to the Majumdar-Ghosh point. Focusing on three-eighths filling and using the density-matrix renormalization-group (DMRG) method, we show that the zero-temperature transition between the phases with small and large Fermi momenta appears continuous, and involves a new intermediate phase where the Fermi surface is not well defined. The intermediate phase is spin gapped and has Kondo-spin correlations that show incommensurate modulations. Our results appear incompatible with the local picture for the quantum phase transition in heavy fermion compounds, which predicts an abrupt change in the size of the Fermi momentum.

  18. Fermi Surface of Superconducting LaFePO Determined by Quantum Oscillations

    SciTech Connect

    Coldea, A.I.; Fletcher, J.D.; Carrington, A.; Analytis, J.G.; Bangura, A.F.; Chu, J.-H.; Erickson, A.S.; Fisher, I.R.; Hussey, N.E.; McDonald, R.D.; /Los Alamos

    2010-01-11

    We report extensive measurements of quantum oscillations in the normal state of the Fe-based superconductor LaFePO, (T{sub c} {approx} 6 K) using low temperature torque magnetometry and transport in high static magnetic fields (45 T). We find that the Fermi surface is in broad agreement with the band-structure calculations with the quasiparticle mass enhanced by a factor {approx}2. The quasi-two dimensional Fermi surface consist of nearly-nested electron and hole pockets, suggesting proximity to a spin/charge density wave instability.

  19. 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

  20. Coherent quasiparticles with a small fermi surface in lightly doped Sr(3)Ir(2)O(7).

    PubMed

    de la Torre, A; Hunter, E C; Subedi, A; McKeown Walker, S; Tamai, A; Kim, T K; Hoesch, M; Perry, R S; Georges, A; Baumberger, F

    2014-12-19

    We characterize the electron doping evolution of (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z≈0.5 in lightly doped Sr_{3}Ir_{2}O_{7}. PMID:25554897

  1. Coherent quasiparticles with a small Fermi Surface in lightly doped Sr3Ir2O7

    NASA Astrophysics Data System (ADS)

    de la Torre, Alberto; McKeown Walker, Siobhan; Tamai, Anna; Hunter, Emily; Subedi, Alaska; Kim, Timur; Hoesch, Moritz; Perry, Robin; Georges, Antoine; Baumberger, Felix

    2015-03-01

    We characterize the electron doping evolution of (Sr1-xLax)Ir2O7 by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x ~ 0 . 05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3 x / 2 , where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z ~ 0 . 5 in lightly doped Sr3Ir2O7, in stark contrast with underdoped cuprates.

  2. Coherent Quasiparticles with a Small Fermi Surface in Lightly Doped Sr3Ir2O7

    NASA Astrophysics Data System (ADS)

    de la Torre, A.; Hunter, E. C.; Subedi, A.; McKeown Walker, S.; Tamai, A.; Kim, T. K.; Hoesch, M.; Perry, R. S.; Georges, A.; Baumberger, F.

    2014-12-01

    We characterize the electron doping evolution of (Sr1 -xLax)3Ir2O7 by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x ≈0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3 x /2 , where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z ≈0.5 in lightly doped Sr3Ir2O7 .

  3. Quasiparticle interference of the Fermi arcs and surface-bulk connectivity of a Weyl semimetal.

    PubMed

    Inoue, Hiroyuki; Gyenis, András; Wang, Zhijun; Li, Jian; Oh, Seong Woo; Jiang, Shan; Ni, Ni; Bernevig, B Andrei; Yazdani, Ali

    2016-03-11

    Weyl semimetals host topologically protected surface states, with arced Fermi surface contours that are predicted to propagate through the bulk when their momentum matches that of the surface projections of the bulk's Weyl nodes. We used spectroscopic mapping with a scanning tunneling microscope to visualize quasiparticle scattering and interference at the surface of the Weyl semimetal TaAs. Our measurements reveal 10 different scattering wave vectors, which can be understood and precisely reproduced with a theory that takes into account the shape, spin texture, and momentum-dependent propagation of the Fermi arc surface states into the bulk. Our findings provide evidence that Weyl nodes act as sinks for electron transport on the surface of these materials. PMID:26965625

  4. 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.

  5. The low temperature Fermi surface of IrTe2 probed by quantum oscillations.

    NASA Astrophysics Data System (ADS)

    Blake, Samuel; Coldea, Amalia; Watson, Matthew; Narayanan, Arjun; McCollam, Alix; Kasahara, Shigeru; Yamashita, Takuya; Watanabe, Daiki; Shibauchi, Takasada; Matsuda, Yuju; Schoonmaker, Robert

    2014-03-01

    The transition metal dichalcogenide IrTe2 undergoes a structural transition at 280K; doping on the Ir site suppresses this transition and induces superconductivity with Tc of about 3K. The nature of the structural transition is possibly driven by charge disproportionation and the effect this has on the electronic structure of the superconducting state is not fully understood. We report a low temperature investigation of the Fermi surface of IrTe2 from quantum oscillations, using torque measurements performed in magnetic fields up to 33T and temperatures down to 0.3K. The observed extremal areas of the Fermi surface likely correspond to frequencies of a reconstructed Fermi surface, with light effective masses below 0.8me. The angular dependence of these frequencies across multiple crystals of IrTe2 suggests these materials are prone to domain formation upon cooling. We compare our measured Fermi surface with those predicted by electronic structure calculations, based upon the existing structural models, for both above and below the structural transition. This work was supported by EPSRC (UK) and partly by EuroMagnet (EU contract number 228043).

  6. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    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.

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

    PubMed

    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 B(2) 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. PMID:25978245

  8. 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.

  9. Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator.

    PubMed

    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

  10. Fermi Surface and Van Hove Singularities in the Itinerant Metamagnet Sr(3)Ru(2)O(7)

    SciTech Connect

    Tamai, A.; Allan, M.P.; Mercure, J.F.; Meevasana, W.; Dunkel, R.; Lu, D.H.; Perry, R.S.; Mackenzie, A.P.; Singh, D.J.; Shen, Z.-X.; Baumberger, F.; /Scottish U. Research Reactor Ctr. /St. Andrews U.

    2011-01-04

    The low-energy electronic structure of the itinerant metamagnet Sr{sub 3}Ru{sub 2}O{sub 7} is investigated by angle resolved photoemission and density functional calculations. We find well-defined quasiparticle bands with resolution limited line widths and Fermi velocities up to an order of magnitude lower than in single layer Sr{sub 2}RuO{sub 4}. The complete topography, the cyclotron masses and the orbital character of the Fermi surface are determined, in agreement with bulk sensitive de Haas - van Alphen measurements. An analysis of the dxy band dispersion reveals a complex density of states with van Hove singularities (vHs) near the Fermi level; a situation which is favorable for magnetic instabilities.

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

    PubMed

    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

  12. 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

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

    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.

  15. 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

  16. 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

    2015-01-01

    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, 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. PMID:25997611

  17. Fermi surface reconstruction in hole-doped t-J models without long-range antiferromagnetic order

    NASA Astrophysics Data System (ADS)

    Punk, Matthias; Sachdev, Subir

    2012-05-01

    We calculate the Fermi surface of electrons in hole-doped, extended t-J models on a square lattice in a regime where no long-range antiferromagnetic order is present, and no symmetries are broken. Using the “spinon-dopon” formalism of Ribeiro and Wen, we show that short-range antiferromagnetic correlations lead to a reconstruction of the Fermi surface into hole pockets which are not necessarily centered at the antiferromagnetic Brillouin zone boundary. The Brillouin zone area enclosed by the Fermi surface is proportional to the density of dopants away from half-filling, in contrast to the conventional Luttinger theorem, which counts the total electron density. This state realizes a “fractionalized Fermi liquid” (FL*), which has been proposed as a possible ground state of the underdoped cuprates; we note connections to recent experiments. We also discuss the quantum phase transition from the FL* state to the Fermi liquid state with long-range antiferromagnetic order.

  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 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.

  20. Fermi-surface reconstruction and the origin of high-temperature superconductivity.

    SciTech Connect

    Norman, M. R.; Materials Science Division

    2010-01-01

    In crystalline lattices, the conduction electrons form waves, known as Bloch states, characterized by a momentum vector k. The defining characteristic of metals is the surface in momentum space that separates occupied from unoccupied states. This 'Fermi' surface may seem like an abstract concept, but it can be measured and its shape can have profound consequences for the thermal, electronic, and magnetic properties of a material. In the presence of an external magnetic field B, electrons in a metal spiral around the field direction, and within a semiclassical momentum-space picture, orbit around the Fermi surface. Physical properties, such as the magnetization, involve a sum over these orbits, with extremal orbits on the Fermi surface, i.e., orbits with minimal or maximal area, dominating the sum [Fig. 1(a)]. Upon quantization, the resulting electron energy spectrum consists of Landau levels separated by the cyclotron energy, which is proportional to the magnetic field. As the magnetic field causes subsequent Landau levels to cross through the Fermi energy, physical quantities, such as the magnetization or resistivity, oscillate in response. It turns out that the period of these oscillations, when plotted as a function of 1/B, is proportional to the area of the extremal orbit in a plane perpendicular to the applied field [Fig. 1(b)]. The power of the quantum oscillation technique is obvious: By changing the field direction, one can map out the Fermi surface, much like a blind man feeling an elephant. The nature and topology of the Fermi surface in high-T{sub c} cuprates has been debated for many years. Soon after the materials were discovered by Bednorz and Mueller, it was realized that superconductivity was obtained by doping carriers into a parent insulating state. This insulating state appears to be due to strong electronic correlations, and is known as a Mott insulator. In the case of cuprates, the electronic interactions force the electrons on the copper ion

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

    PubMed Central

    Cho, Dai-Ning; Brink, Jeroen van den; Fehske, Holger; Becker, Klaus W.; Sykora, Steffen

    2016-01-01

    We study the competition between unconventional superconducting pairing and charge density wave (CDW) formation for the two-dimensional Edwards Hamiltonian at half filling, a very general two-dimensional transport model in which fermionic charge carriers couple to a correlated background medium. Using the projective renormalization method we find that a strong renormalization of the original fermionic band causes a new hole-like Fermi surface to emerge near the center of the Brillouin zone, before it eventually gives rise to the formation of a charge density wave. On the new, disconnected parts of the Fermi surface superconductivity is induced with a sign-changing order parameter. We discuss these findings in the light of recent experiments on iron-based oxypnictide superconductors. PMID:26935887

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

    NASA Astrophysics Data System (ADS)

    Cho, Dai-Ning; Brink, Jeroen Van Den; Fehske, Holger; Becker, Klaus W.; Sykora, Steffen

    2016-03-01

    We study the competition between unconventional superconducting pairing and charge density wave (CDW) formation for the two-dimensional Edwards Hamiltonian at half filling, a very general two-dimensional transport model in which fermionic charge carriers couple to a correlated background medium. Using the projective renormalization method we find that a strong renormalization of the original fermionic band causes a new hole-like Fermi surface to emerge near the center of the Brillouin zone, before it eventually gives rise to the formation of a charge density wave. On the new, disconnected parts of the Fermi surface superconductivity is induced with a sign-changing order parameter. We discuss these findings in the light of recent experiments on iron-based oxypnictide superconductors.

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

    PubMed

    Cho, Dai-Ning; Brink, Jeroen van den; Fehske, Holger; Becker, Klaus W; Sykora, Steffen

    2016-01-01

    We study the competition between unconventional superconducting pairing and charge density wave (CDW) formation for the two-dimensional Edwards Hamiltonian at half filling, a very general two-dimensional transport model in which fermionic charge carriers couple to a correlated background medium. Using the projective renormalization method we find that a strong renormalization of the original fermionic band causes a new hole-like Fermi surface to emerge near the center of the Brillouin zone, before it eventually gives rise to the formation of a charge density wave. On the new, disconnected parts of the Fermi surface superconductivity is induced with a sign-changing order parameter. We discuss these findings in the light of recent experiments on iron-based oxypnictide superconductors. PMID:26935887

  4. Surface hole accumulation and Fermi level stabilization energy in SnTe

    NASA Astrophysics Data System (ADS)

    Nishitani, Junichi; Detert, Douglas; Beeman, Jeffrey; Yu, Kin Man; Walukiewicz, Wladek

    2014-09-01

    SnTe films were deposited by RF magnetron sputtering. The thickness dependence of the sheet hole concentration indicated the presence of a high hole density surface accumulation layer. Irradiation of SnTe by Ne+ ions led to the saturation of the hole concentration corresponding to a Fermi energy that is 0.5 eV below the valence band edge. The stabilized Fermi energy on the surface and in the heavily damaged bulk is in agreement with the amphoteric native defect model. These results show that SnTe is a unique semiconductor with an extremely high valence band edge located at 4.4 eV below the vacuum level.

  5. 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.

  6. Nodal Fermi surface pocket approaching an optimal quantum critical point in YBCO

    NASA Astrophysics Data System (ADS)

    Sebastian, Suchitra; Tan, Beng; Lonzarich, Gilbert; Ramshaw, Brad; Harrison, Neil; Balakirev, Fedor; Mielke, Chuck; Sabok, S.; Dabrowski, B.; Liang, Ruixing; Bonn, Doug; Hardy, Walter

    2014-03-01

    I present new quantum oscillation measurements over the entire underdoped regime in YBa2Cu3O6+x and YBa2Cu4O8 using ultra-high magnetic fields to destroy superconductivity and access the normal ground state. A robust small nodal Fermi surface created by charge order is found to extend over the entire underdoped range, exhibiting quantum critical signatures approaching optimal doping.

  7. Electron pockets in the Fermi surface of hole-doped high-Tc superconductors.

    PubMed

    LeBoeuf, David; Doiron-Leyraud, Nicolas; Levallois, Julien; Daou, R; Bonnemaison, J-B; Hussey, N E; Balicas, L; Ramshaw, B J; Liang, Ruixing; Bonn, D A; Hardy, W N; Adachi, S; Proust, Cyril; Taillefer, Louis

    2007-11-22

    High-temperature superconductivity in copper oxides occurs when the materials are chemically tuned to have a carrier concentration intermediate between their metallic state at high doping and their insulating state at zero doping. The underlying evolution of the electron system in the absence of superconductivity is still unclear, and a question of central importance is whether it involves any intermediate phase with broken symmetry. The Fermi surface of the electronic states in the underdoped 'YBCO' materials YBa2Cu3O(y) and YBa2Cu4O8 was recently shown to include small pockets, in contrast with the large cylinder that characterizes the overdoped regime, pointing to a topological change in the Fermi surface. Here we report the observation of a negative Hall resistance in the magnetic-field-induced normal state of YBa2Cu3O(y) and YBa2Cu4O8, which reveals that these pockets are electron-like rather than hole-like. We propose that these electron pockets most probably arise from a reconstruction of the Fermi surface caused by the onset of a density-wave phase, as is thought to occur in the electron-doped copper oxides near the onset of antiferromagnetic order. Comparison with materials of the La2CuO4 family that exhibit spin/charge density-wave order suggests that a Fermi surface reconstruction also occurs in those materials, pointing to a generic property of high-transition-temperature (T(c)) superconductors. PMID:18033293

  8. Quantum oscillations and nodal pockets from Fermi surface reconstruction in the underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Harrison, Neil

    2012-02-01

    Fermiology in the underdoped high Tc cuprates presents us with unique challenges, requiring experimentalists to look deeper into the data than is normally required for clues. Recent measurements of an oscillatory chemical potential affecting the oscillations at high magnetic fields provide a strong indication of a single type of carrier pocket. When considered in conjunction with photoemission and specific heat measurements, a Fermi surface comprised almost entirely of nodal pockets is suggested. The mystery of the Fermi surface is deepened, however, by a near doping-independent Fermi surface cross-sectional area and negative Hall and Seebeck coefficients. We explore ways in which these findings can be reconciled, taking an important hint from the diverging effective mass yielded by quantum oscillations at low dopings. The author wishes to thank Suchitra Sebastian, Moaz Atarawneh, Doug Bonn, Walter Hardy, Ruixing Liang, Charles Mielke and Gilbert Lonzarich who have contributed to this work. The work is supported by the NSF through the NHMFL and by the DOE project ``Science at 100 tesla.''

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

    PubMed

    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. 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

  11. Spin-dependent momentum density distribution and Fermi surface of Ho via 2D-ACAR measurements

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.; Uedono, A.

    2004-03-01

    The first direct measurements of the spin-dependent positron-electron momentum density and Fermi surface of Ho are presented. The measurements were performed using two-dimensional angular correlation of annihilation radiation (ACAR) experiments with reversal magnetic field directions parallel and anti-parallel to the polarization direction of the positron. The analysis confirmed that two hybrid bands influence the Fermi surface of Ho. They are 5d-6s conduction hybrid bands and partial hybridization of 4f-5d bands. In fact, the measured Fermi surface revealed the behavior of the magnetic electrons. Further, the reciprocal lattice points revealed the electronic spin density distribution behavior. The general layout of the Fermi surface of Ho showed a multiply connected surface as an open hole running along the A axis with minority spin distribution and two electron surfaces centered on K and H points, respectively. Furthermore, this Fermi surface showed anti-ferromagnetic character. The measured Fermi surface of Ho showed agreement with the results of a previous band structure calculation method. (

  12. Electronic structure, Fermi surface and dHvA effect in YIn3, LuIn3, and YbIn3

    NASA Astrophysics Data System (ADS)

    Antonov, V. N.

    2014-04-01

    The electronic structure, Fermi surface, angle dependence of the cyclotron masses and extremal cross sections of the Fermi surface of RIn3 (R = Y, Lu, and Yb) compounds were investigated from first principles using the fully relativistic Dirac linear muffin-tin orbital method. The effect of the spin-orbit (SO) interaction and Coulomb repulsion U in a frame of the LDA + SO + U method on the Fermi surface, orbital dependence of the cyclotron masses, and extremal cross sections of the Fermi surface are examined in details. A good agreement with experimental data of cyclotron masses and extremal cross sections of the Fermi surface was achieved.

  13. 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.

  14. Observation of strong electron pairing on bands without Fermi surfaces in LiFe1-xCoxAs

    NASA Astrophysics Data System (ADS)

    Miao, H.; Qian, T.; Shi, X.; Richard, P.; Kim, T. K.; Hoesch, M.; Xing, L. Y.; Wang, X.-C.; Jin, C.-Q.; Hu, J.-P.; Ding, H.

    2015-01-01

    In conventional BCS superconductors, the quantum condensation of superconducting electron pairs is understood as a Fermi surface instability, in which the low-energy electrons are paired by attractive interactions. Whether this explanation is still valid in high-Tc superconductors such as cuprates and iron-based superconductors remains an open question. In particular, a fundamentally different picture of the electron pairs, which are believed to be formed locally by repulsive interactions, may prevail. Here we report a high-resolution angle-resolved photoemission spectroscopy study on LiFe1-xCoxAs. We reveal a large and robust superconducting gap on a band sinking below the Fermi level on Co substitution. The observed Fermi-surface-free superconducting order is also the largest over the momentum space, which rules out a proximity effect origin and indicates that the order parameter is not tied to the Fermi surface as a result of a surface instability.

  15. Gyrotropic Magnetic Effect and the Magnetic Moment on the Fermi Surface.

    PubMed

    Zhong, Shudan; Moore, Joel E; Souza, Ivo

    2016-02-19

    The current density j^{B} induced in a clean metal by a slowly-varying magnetic field B is formulated as the low-frequency limit of natural optical activity, or natural gyrotropy. Working with a multiband Pauli Hamiltonian, we obtain from the Kubo formula a simple expression for α_{ij}^{GME}=j_{i}^{B}/B_{j} in terms of the intrinsic magnetic moment (orbital plus spin) of the Bloch electrons on the Fermi surface. An alternate semiclassical derivation provides an intuitive picture of the effect, and takes into account the influence of scattering processes in dirty metals. This "gyrotropic magnetic effect" is fundamentally different from the chiral magnetic effect driven by the chiral anomaly and governed by the Berry curvature on the Fermi surface, and the two effects are compared for a minimal model of a Weyl semimetal. Like the Berry curvature, the intrinsic magnetic moment should be regarded as a basic ingredient in the Fermi-liquid description of transport in broken-symmetry metals. PMID:26943554

  16. Quantum Oscillations without a Fermi Surface and the Anomalous de Haas-van Alphen Effect

    NASA Astrophysics Data System (ADS)

    Knolle, Johannes; Cooper, Nigel R.

    2015-10-01

    The de Haas-van Alphen effect (dHvAE), describing oscillations of the magnetization as a function of magnetic field, is commonly assumed to be a definite sign for the presence of a Fermi surface (FS). Indeed, the effect forms the basis of a well-established experimental procedure for accurately measuring FS topology and geometry of metallic systems, with parameters commonly extracted by fitting to the Lifshitz-Kosevich (LK) theory based on Fermi liquid theory. Here we show that, in contrast to this canonical situation, there can be quantum oscillations even for band insulators of certain types. We provide simple analytic formulas describing the temperature dependence of the quantum oscillations in this setting, showing strong deviations from LK theory. We draw connections to recent experiments and discuss how our results can be used in future experiments to accurately determine, e.g., hybridization gaps in heavy-fermion systems.

  17. Strong interaction effects at a Fermi surface in a model for voltage-biased bilayer graphene

    NASA Astrophysics Data System (ADS)

    Armour, Wes; Hands, Simon; Strouthos, Costas

    2015-12-01

    Monte Carlo simulation of a 2+1 dimensional model of voltage-biased bilayer graphene, consisting of relativistic fermions with chemical potential μ coupled to charged excitations with opposite sign on each layer, has exposed noncanonical scaling of bulk observables near a quantum critical point found at strong coupling. We present a calculation of the quasiparticle dispersion relation E (k ) as a function of exciton source j in the same system, employing partially twisted boundary conditions to boost the number of available momentum modes. The Fermi momentum kF and superfluid gap Δ are extracted in the j →0 limit for three different values of μ , and support a strongly interacting scenario at the Fermi surface with Δ ˜O (μ ) . We propose an explanation for the observation μ

  18. Correlation-Driven Topological Fermi Surface Transition in FeSe.

    PubMed

    Leonov, I; Skornyakov, S L; Anisimov, V I; Vollhardt, D

    2015-09-01

    The electronic structure and phase stability of paramagnetic FeSe is computed by using a combination of ab initio methods for calculating band structure and dynamical mean-field theory. Our results reveal a topological change (Lifshitz transition) of the Fermi surface upon a moderate expansion of the lattice. The Lifshitz transition is accompanied with a sharp increase of the local moments and results in an entire reconstruction of magnetic correlations from the in-plane magnetic wave vector, (π,π) to (π,0). We attribute this behavior to a correlation-induced shift of the van Hove singularity originating from the d(xy) and d(xz)/d(yz) bands at the M point across the Fermi level. We propose that superconductivity is strongly influenced, or even induced, by a van Hove singularity. PMID:26382687

  19. Fermi-surface induced modulation in an optimally doped YBCO superconductor.

    SciTech Connect

    Liu, X.; Islam, Z.; Sinha, S. K.; Moss, S. C.; McQueeney, R. J.; Lang, J. C.; Welp, U.; Univ. of California at San Diego; Univ. of Houston; Iowa State Univ.

    2008-01-01

    We have observed a Fermi-surface (FS) induced lattice modulation in a YBa{sub 2}Cu{sub 3}O{sub 7-x} superconductor with a wave vector along CuO chains; i.e., q{sub 1} = (0,{delta},0). The value of {delta} {approx} 0.21 is twice the Fermi wave vector (2k{sub F}) along b* connecting nearly nested FS 'ridges'. The q{sub 1} modulation exists only within O-vacancy-ordered islands [characterized by q{sub 0} = (1/4,0,0)] and persists well above and below T{sub c}. Our results are consistent with the presence of a FS-induced charge-density wave.

  20. 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.

  1. Surface corrections to the moment of inertia and shell structure in finite Fermi systems

    NASA Astrophysics Data System (ADS)

    Gorpinchenko, D. V.; Magner, A. G.; Bartel, J.; Blocki, J. P.

    2016-02-01

    The moment of inertia for nuclear collective rotations is derived within a semiclassical approach based on the Inglis cranking and Strutinsky shell-correction methods, improved by surface corrections within the nonperturbative periodic-orbit theory. For adiabatic (statistical-equilibrium) rotations it was approximated by the generalized rigid-body moment of inertia accounting for the shell corrections of the particle density. An improved phase-space trace formula allows to express the shell components of the moment of inertia more accurately in terms of the free-energy shell correction. Evaluating their ratio within the extended Thomas-Fermi effective-surface approximation, one finds good agreement with the quantum calculations.

  2. Study of the Fermi surface of molybdenum and chromium via positron annihilation experiments

    NASA Astrophysics Data System (ADS)

    Biasini, Maurizio

    2000-02-01

    A quantitative mapping of the Fermi surface (FS) of molybdenum and chromium was sought by modelling the three-dimensional k-space occupancy with a small number of parameters which were determined by a least-squares fit to the two-dimensional angular correlation of the electron-positron annihilation radiation (2D-ACAR) data subjected to a Lock-Crisp-West (LCW) transformation. The resulting FS topology of molybdenum, unlike what was assumed in previous 2D-ACAR studies, does not support the nesting of its two main FS sheets. In the case of chromium, although the overall discrepancy with the FS expected from the theory is larger, the difference in shape between the same two FS sheets is of lesser extent. According to this analysis the ratio of the electron Fermi volume to the hole Fermi volume is found to deviate from unity, the value expected for compensated metals, for both materials. We suggest that these discrepancies might be due to positron wave function and/or electron-positron many-body distortions not predicted by the theory.

  3. High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides

    PubMed Central

    Charnukha, A.; Evtushinsky, D. V.; Matt, C. E.; Xu, N.; Shi, M.; Büchner, B.; Zhigadlo, N. D.; Batlogg, B.; Borisenko, S. V.

    2015-01-01

    In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials. PMID:26678565

  4. Nonlinear optical conductivity of U (1 ) spin liquids with large spinon Fermi surfaces

    NASA Astrophysics Data System (ADS)

    Ma, Yuan-Fei; Ng, Tai-Kai

    2016-06-01

    In this paper we study the nonlinear current response of U (1 ) spin liquids with large spinon Fermi surfaces under the perturbation of a time-dependent ac electric field E (t ) within the framework of an effective U (1 ) gauge theory. In particular, the third-order nonlinear current response to ac electric fields is derived. We show that as in the case of linear current response, an in-gap power-law (˜ωη ) response is found for the nonlinear current at low frequency. The nonlinear susceptibility may also induce through process of third harmonic generation propagating EM wave with frequency 3 ω inside the spin liquids.

  5. Fermi Surface of Nanocrystalline Embedded Particles in Materials: bcc Cu in Fe

    NASA Astrophysics Data System (ADS)

    Nagai, Y.; Chiba, T.; Tang, Z.; Akahane, T.; Kanai, T.; Hasegawa, M.; Takenaka, M.; Kuramoto, E.

    2001-10-01

    We report that a positron can act as a probe to directly reveal electronic structures of nanocrystalline embedded particles in materials. The Fermi surface (FS) of ``bcc'' Cu nanoparticles in an Fe matrix is observed as the first example. A two-dimensional angular correlation of the positron annihilation radiation (2D-ACAR) method is used to measure the momentum distribution which reflects the FS topology. The obtained 2D-ACAR spectra show strong and characteristic anisotropy associated with the necks of the FS around the \\{110\\} Brillouin zone boundaries of the bcc Cu, which are well reproduced by full-potential linearized argumented plane-wave calculations.

  6. 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.

  7. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  10. Origin of Fermi-level pinning and its control on the n -type Ge(100) surface

    NASA Astrophysics Data System (ADS)

    Kuzmin, Mikhail; Laukkanen, Pekka; Mäkelä, Jaakko; Tuominen, Marjukka; Yasir, Muhammad; Dahl, Johnny; Punkkinen, Marko P. J.; Kokko, Kalevi

    2016-07-01

    Strong Fermi-level pinning (FLP) near the valence-band maximum on n -type Ge surfaces has been a long-standing challenge in semiconductor physics, and the nature of this phenomenon has been heavily debated for years. Here, we report a systematic synchrotron-based photoemission study of atomically well-defined Ge(100) surfaces and interfaces to elucidate the origin of FLP in such systems. It is experimentally shown that the FLP on n -Ge is not due to the dangling-bond, back-bond, and defect states, but is strongly contributed by the evanescent state of the Ge bulk. The conditions required for alleviating the FLP and even the implementation of a flatband structure on Ge(100) are formulated. Such a structure is realized in the BaO/Ge(100) system where one can obtain control over the Fermi-level position in the Ge gap. These findings are not only important from a fundamental viewpoint, but also open a route to producing Ohmic metal-insulator-semiconductor contacts for n -type Ge-based technology.

  11. Magnetic and Fermi Surface Properties of Ferromagnets EuPd2 and EuPt2

    NASA Astrophysics Data System (ADS)

    Nakamura, Ai; Akamine, Hiromu; Ashitomi, Yousuke; Honda, Fuminori; Aoki, Dai; Takeuchi, Tetsuya; Matsubayashi, Kazuyuki; Uwatoko, Yoshiya; Tatetsu, Yasutomi; Maehira, Takahiro; Hedo, Masato; Nakama, Takao; Ōnuki, Yoshichika

    2016-08-01

    We succeeded in growing single crystals of the ferromagnets EuPd2 and EuPt2 with the Laves-type cubic structure by the Bridgman method, namely, heating constituting materials in a Mo crucible up to a high temperature of about 1500 °C. The ferromagnetic properties of EuPd2 and EuPt2 with Curie temperatures of 74 and 100 K, respectively, were confirmed from the results of electrical resistivity, specific heat, and magnetization measurements. The ordered moment is 7 μB/Eu, revealing the Eu-divalent ferromagnetism. The present Eu-divalent electronic state is found to be robust against high pressures of up to 8 GPa and is not changed into the Eu-trivalent state. We also carried out de Haas-van Alphen (dHvA) experiments for EuPd2. The detected dHvA branches in EuPd2 are well explained by the relativistic linearized augmented plane wave (RLAPW) energy band calculations for SrPd2, revealing a closed hole Fermi surface and compensated four closed electron Fermi surfaces.

  12. Fermi surface reconstruction and multiple quantum phase transitions in the antiferromagnet CeRhIn5

    PubMed Central

    Jiao, Lin; Chen, Ye; Kohama, Yoshimitsu; Graf, David; Bauer, E. D.; Singleton, John; Zhu, Jian-Xin; Weng, Zongfa; Pang, Guiming; Shang, Tian; Zhang, Jinglei; Lee, Han-Oh; Park, Tuson; Jaime, Marcelo; Thompson, J. D.; Steglich, Frank; Si, Qimiao; Yuan, H. Q.

    2015-01-01

    Conventional, thermally driven continuous phase transitions are described by universal critical behavior that is independent of the specific microscopic details of a material. However, many current studies focus on materials that exhibit quantum-driven continuous phase transitions (quantum critical points, or QCPs) at absolute zero temperature. The classification of such QCPs and the question of whether they show universal behavior remain open issues. Here we report measurements of heat capacity and de Haas–van Alphen (dHvA) oscillations at low temperatures across a field-induced antiferromagnetic QCP (Bc0 ≈ 50 T) in the heavy-fermion metal CeRhIn5. A sharp, magnetic-field-induced change in Fermi surface is detected both in the dHvA effect and Hall resistivity at B0* ≈ 30 T, well inside the antiferromagnetic phase. Comparisons with band-structure calculations and properties of isostructural CeCoIn5 suggest that the Fermi-surface change at B0* is associated with a localized-to-itinerant transition of the Ce-4f electrons in CeRhIn5. Taken in conjunction with pressure experiments, our results demonstrate that at least two distinct classes of QCP are observable in CeRhIn5, a significant step toward the derivation of a universal phase diagram for QCPs. PMID:25561536

  13. Silicon quantum wires on Ag(1 1 0): Fermi surface and quantum well states

    NASA Astrophysics Data System (ADS)

    Valbuena, M. A.; Avila, J.; Dávila, M. E.; Leandri, C.; Aufray, B.; Le Lay, G.; Asensio, M. C.

    2007-10-01

    One-dimensional Si quantum wires have been grown on silver single crystals upon deposition of ˜0.25 monolayer of Si on Ag(1 1 0) surfaces. Scanning tunneling microscopy (STM) clearly shows parallel 1D Si chains along the [-1 1 0] Ag crystallographic direction. Low Energy Electron Diffraction (LEED) confirms the massively parallel assembly of these selforganized Nanowires (NWs). We have characterized these nano-objects by measuring the dispersion of the NWs valence band at room temperature using Angle-Resolved PhotoEmission Spectroscopy (ARPES). Also, the Fermi Surface (FS) of the Ag(1 1 0) substrate has been mapped before and after the silicon deposition, trying to put in evidence the metallic or semiconductor character of the NWs silicon's states close to the Fermi level. Our results show the existence of well-defined quantum states associated to the silicon super-structure. Both LEED and ARUPS results confirm that the NWs have typical 1D features, however their metallic or semiconductor character could not be confirmed.

  14. 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.

  15. Electronic structure and Fermi surfaces of transition metal carbides with rocksalt structure

    NASA Astrophysics Data System (ADS)

    Paduani, C.

    2008-06-01

    First-principles calculations were carried out to investigate the structural and electronic properties of the metal carbides FeC, CoC, NiC, and PtC in the rocksalt structure. The full-potential linearized augmented-plane wave (FP-LAPW) method was used in the framework of the density-functional theory with the generalized gradient approximation (GGA) for the exchange-correlation potential. Ground state properties are determined and compared with available experimental data. The energy band structures, densities of states, and Fermi surface structures are obtained, which show that these compounds are metallic like the conventional transition metal carbides. There is an extensive hybridization between the metal-d and C-2p states for all the studied carbides, which can form bonding and antibonding states. From FeC to PtC a band narrowing for the hybridized metal-d and C-2p states near to the Fermi level takes place, which is expected to lead to smaller interactions between adjacent atoms. The largest bulk modulus of FeC is expected to be associated with the behavior of valence electrons near the Fermi level, i.e. a higher degree of hybridization between p-d states that are responsible for the chemical bonding results in strengthened interactions. The decrease in the number of bonding orbitals or decrease in metallic valence with the increase in number of 3d electrons from FeC to PtC provides a mechanism for weaker interactions due to the filling of antibonding bands.

  16. Evolution of the Fermi surface of a doped topological insulator with carrier concentration

    NASA Astrophysics Data System (ADS)

    Lahoud, E.; Maniv, E.; Petrushevsky, M. Shaviv; Naamneh, M.; Ribak, A.; Wiedmann, S.; Petaccia, L.; Salman, Z.; Chashka, K. B.; Dagan, Y.; Kanigel, A.

    2013-11-01

    In an ideal bulk topological insulator (TI) conducting surface states protected by time-reversal symmetry enfold an insulating crystal. However, the archetypical TI, Bi2Se3, is actually never insulating; it is in fact a relatively good metal. Nevertheless, it is the most studied system among all the TIs, mainly due to its simple band structure and large spin-orbit gap. Recently, it was shown that copper intercalated Bi2Se3 becomes superconducting and it was suggested as a realization of a topological superconductor. Here we use a combination of techniques that are sensitive to the shape of the Fermi surface (FS): the Shubnikov-de Haas effect and angle-resolved photoemission spectroscopy to study the evolution of the FS shape with carrier concentration, n. We find that as n increases, the FS becomes two-dimensional-like. These results are of crucial importance for understanding the superconducting properties of CuxBi2Se3.

  17. 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.

  18. 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

    2015-01-01

    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

  19. Itinerant 5 f Electrons and the Fermi Surface Properties in an Enhanced Pauli Paramagnet NpGe3

    NASA Astrophysics Data System (ADS)

    Aoki, Dai; Yamagami, Hiroshi; Homma, Yoshiya; Shiokawa, Yoshinobu; Yamamoto, Etsuji; Nakamura, Akio; Haga, Yoshinori; Settai, Rikio; Ōnuki, Yoshichika

    2005-08-01

    We succeeded in growing a high-quality single crystal of an enhanced Pauli paramagnet, NpGe3, by the Bi-flux method, and observed the de Haas-van Alphen (dHvA) effect. The topology of a Fermi surface is well explained by the relativistic linear augmented-plane-wave (LAPW) band calculations based on the 5 f itinerant band model. The Fermi surface consists of a nearly spherical electron-Fermi surface with necks along the < 100 > direction, forming a hollow ball, centered at the R point, which is derived from the single band. The cyclotron effective mass is in the range from 2.6 to 16 m0, which is enhanced approximately 3.5 times from the corresponding band mass.

  20. 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

  1. Magnetic frustration, short-range correlations and the role of the paramagnetic Fermi surface of PdCrO2

    PubMed Central

    Billington, David; Ernsting, David; Millichamp, Thomas E.; Lester, Christopher; Dugdale, Stephen B.; Kersh, David; Duffy, Jonathan A.; Giblin, Sean R.; Taylor, Jonathan W.; Manuel, Pascal; Khalyavin, Dmitry D.; Takatsu, Hiroshi

    2015-01-01

    Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments. PMID:26206589

  2. Magnetic frustration, short-range correlations and the role of the paramagnetic Fermi surface of PdCrO2.

    PubMed

    Billington, David; Ernsting, David; Millichamp, Thomas E; Lester, Christopher; Dugdale, Stephen B; Kersh, David; Duffy, Jonathan A; Giblin, Sean R; Taylor, Jonathan W; Manuel, Pascal; Khalyavin, Dmitry D; Takatsu, Hiroshi

    2015-01-01

    Frustrated interactions exist throughout nature, with examples ranging from protein folding through to frustrated magnetic interactions. Whilst magnetic frustration is observed in numerous electrically insulating systems, in metals it is a rare phenomenon. The interplay of itinerant conduction electrons mediating interactions between localised magnetic moments with strong spin-orbit coupling is likely fundamental to these systems. Therefore, knowledge of the precise shape and topology of the Fermi surface is important in any explanation of the magnetic behaviour. PdCrO2, a frustrated metallic magnet, offers the opportunity to examine the relationship between magnetic frustration, short-range magnetic order and Fermi surface topology. By mapping the short-range order in reciprocal space and experimentally determining the electronic structure, we have identified the dual role played by the Cr electrons in which the itinerant ones on the nested paramagnetic Fermi surface mediate the frustrated magnetic interactions between local moments. PMID:26206589

  3. 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}. PMID:27494485

  4. 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.

  5. Evolution of the Fermi surface of Weyl semimetals in the transition metal pnictide family

    NASA Astrophysics Data System (ADS)

    Liu, Z. K.; Yang, L. X.; Sun, Y.; Zhang, T.; Peng, H.; Yang, H. F.; Chen, C.; Zhang, Y.; Guo, Y. F.; Prabhakaran, D.; Schmidt, M.; Hussain, Z.; Mo, S.-K.; Felser, C.; Yan, B.; Chen, Y. L.

    2016-01-01

    Topological Weyl semimetals (TWSs) represent a novel state of topological quantum matter which not only possesses Weyl fermions (massless chiral particles that can be viewed as magnetic monopoles in momentum space) in the bulk and unique Fermi arcs generated by topological surface states, but also exhibits appealing physical properties such as extremely large magnetoresistance and ultra-high carrier mobility. Here, by performing angle-resolved photoemission spectroscopy (ARPES) on NbP and TaP, we directly observed their band structures with characteristic Fermi arcs of TWSs. Furthermore, by systematically investigating NbP, TaP and TaAs from the same transition metal monopnictide family, we discovered their Fermiology evolution with spin-orbit coupling (SOC) strength. Our experimental findings not only reveal the mechanism to realize and fine-tune the electronic structures of TWSs, but also provide a rich material base for exploring many exotic physical phenomena (for example, chiral magnetic effects, negative magnetoresistance, and the quantum anomalous Hall effect) and novel future applications.

  6. 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. PMID:16712121

  7. Effect of Fermi surface nesting on resonant spin excitations in Ba{<_1-x}K{<_x}Fe{<_2}As{<_2}.

    SciTech Connect

    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.

    2011-01-01

    We report inelastic neutron scattering measurements of the resonant spin excitations in Ba{sub 1-x}K{sub x}Fe{sub 2}As{sub 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{sub {+-}}-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.

  8. Direct observation of nonequivalent Fermi-arc states of opposite surfaces in the noncentrosymmetric Weyl semimetal NbP

    NASA Astrophysics Data System (ADS)

    Souma, S.; Wang, Zhiwei; Kotaka, H.; Sato, T.; Nakayama, K.; Tanaka, Y.; Kimizuka, H.; Takahashi, T.; Yamauchi, K.; Oguchi, T.; Segawa, Kouji; Ando, Yoichi

    2016-04-01

    We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on noncentrosymmetric Weyl semimetal candidate NbP, and determined the electronic states of both Nb- and P-terminated surfaces. We revealed a drastic difference in the Fermi-surface topology between two types of surfaces, whereas the Fermi arcs on both surfaces are likely terminated at the surface projection of the same bulk Weyl nodes. A comparison of the ARPES data with our first-principles band calculations suggests a notable difference in the electronic structure at the Nb-terminated surface between theory and experiment. The present result opens a platform for realizing exotic quantum phenomena arising from the unusual surface properties of Weyl semimetals.

  9. Elastic constants and Fermi surface topology change in Calaverite AuTe{sub 2}: A density functional study

    SciTech Connect

    Gudelli, Vijay Kumar Kanchana, V.

    2014-04-24

    Structural, elastic, electronic and Fermi surface studies of AuTe{sub 2} have been carried out by means of first principles calculations based on density functional theory. The calculated ground state properties agree well with the experiment. Fermi surface and elastic constants are predicted for the first time and from the calculated elastic constants we find the compound to be mechanically stable satisfying the stability criteria of monoclinic structure. In addition, we also find the c-axis to be more compressible than the other two which is also speculated from the present work. The metallic behaviour of this compound is confirmed from the electronic band structure calculation as we find the bands to cross the Fermi level (E{sub F}). In addition, we also observe a FS topology change under pressure which is also explained in the present work.

  10. Fermi surface study of ScAu{sub 2}(Al, In) and ScPd{sub 2}(Sn, Pb) compounds

    SciTech Connect

    Reddy, P. V. Sreenivasa; Kanchana, V.; Vaitheeswaran, G.

    2015-06-24

    A detailed study on the electronic structure and Fermi surface (FS) of superconducting Heusler compounds ScAu{sub 2}(Al, In) and ScPd{sub 2}(Sn, Pb) has been carried out using first principles electronic structure calculations. The spin orbit coupling is found to play a major role in understanding the band structure and FS. Analysis of the data shows the importance of spin orbit coupling effect in the above compounds. The bands which cross Fermi level (EF) are found to be dominated by the Sc d{sub t2g}-states. The calculated total density of states are in good agreement with the experimentally reported value for ScPd{sub 2}Sn. Under compression we find a change in the Fermi surface topology of ScPd{sub 2}Sn at V/V{sub 0} = 0.95 (pressure of≈15 GPa), which is explained using the band structure calculations.

  11. Scattering theory of the chiral magnetic effect in a Weyl semimetal: interplay of bulk Weyl cones and surface Fermi arcs

    NASA Astrophysics Data System (ADS)

    Baireuther, P.; Hutasoit, J. A.; Tworzydło, J.; Beenakker, C. W. J.

    2016-04-01

    We formulate a linear response theory of the chiral magnetic effect in a finite Weyl semimetal, expressing the electrical current density j induced by a slowly oscillating magnetic field B or chiral chemical potential μ in terms of the scattering matrix of Weyl fermions at the Fermi level. Surface conduction can be neglected in the infinite-system limit for δ j/δ μ , but not for δ j/δ B: the chirally circulating surface Fermi arcs give a comparable contribution to the bulk Weyl cones no matter how large the system is, because their smaller number is compensated by an increased flux sensitivity. The Fermi arc contribution to {μ }-1δ j/δ B has the universal value {(e/h)}2, protected by chirality against impurity scattering—unlike the bulk contribution of opposite sign.

  12. 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.

  13. 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.

  14. Fermi surface in local-density-functional theory and in gradient expansions

    NASA Astrophysics Data System (ADS)

    Mearns, Daniel; Kohn, Walter

    1989-05-01

    It has recently been shown that the Kohn-Sham (KS) equations, even with the exact exchange-correlation potential, vxc(r), in general do not yield the exact physical Fermi surface (FS). The latter may be obtained either from the discontinuities of the momentum distribution in the exact ground state or, equally well, from the locus of singularities in q space of the exact density-density response function, χ(q,q) (Kohn effect). The present paper considers approximations in which the exact exchange-correlation energy functional is replaced by a gradient expansion of arbitrary finite order m [e.g., Exc(2)[n] =Fd3 [exc(n(r))n(r)+gxc (n(r))||∇n(r)||2

  15. Modeling the angle-dependent magnetoresistance oscillations of Fermi surfaces with hexagonal symmetry

    NASA Astrophysics Data System (ADS)

    Prentice, Joseph C. A.; Coldea, Amalia I.

    2016-06-01

    By solving the Boltzmann transport equation we investigate theoretically the general form of oscillations in the resistivity caused by varying the direction of an applied magnetic field for the case of quasi-two-dimensional systems on hexagonal lattices. The presence of the angular magnetoresistance oscillations can be used to map out the topology of the Fermi surface and we study how this effect varies as a function of the degree of interplane warping as well as a function of the degree of isotropic scattering. We find that the angular-dependent effect due to in-plane rotation follows the symmetry imposed by the lattice whereas for interplane rotation the degree of warping dictates the dominant features observed in simulations. Our calculations make predictions for specific angle-dependent magnetotransport signatures in magnetic fields expected for quasi-two-dimensional hexagonal compounds similar to PdCoO2 and PtCoO2.

  16. Fermi Surface Evolution Across Multiple Charge Density Wave Transitions in ErTe3

    SciTech Connect

    Moore, R.G.; Brouet, V.; He, R.; Lu, D.H.; Ru, N.; Chu, J.-H.; Fisher, I.R.; Shen, Z.-X.; /SLAC, SSRL /Stanford U., Geballe Lab.

    2010-02-15

    The Fermi surface (FS) of ErTe{sub 3} is investigated using angle-resolved photoemission spectroscopy (ARPES). Low temperature measurements reveal two incommensurate charge density wave (CDW) gaps created by perpendicular FS nesting vectors. A large {Delta}{sub 1} = 175 meV gap arising from a CDW with c* - q{sub CDW1} {approx} 0.70(0)c* is in good agreement with the expected value. A second, smaller {Delta}{sub 2} = 50 meV gap is due to a second CDW with a* - q{sub CDW2} {approx} 0.68(5)a*. The temperature dependence of the FS, the two gaps and possible interaction between the CDWs are examined.

  17. Band structure and fermi surface of Electron-Doped C{sub 60} Monolayers

    SciTech Connect

    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.

    2003-11-06

    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.

  18. Bulk Fermi surface and electronic properties of Cu0.07Bi2Se3

    NASA Astrophysics Data System (ADS)

    Martin, C.; Craciun, V.; Miller, K. H.; Uzakbaiuly, B.; Buvaev, S.; Berger, H.; Hebard, A. F.; Tanner, D. B.

    2013-05-01

    The electronic properties of Cu0.07Bi2Se3 have been investigated using Shubnikov-de Haas and optical reflectance measurements. Quantum oscillations reveal a bulk, three-dimensional Fermi surface with anisotropy kFc/kFab≈ 2 and a modest increase in free-carrier concentration and in scattering rate with respect to the undoped Bi2Se3, also confirmed by reflectivity data. The effective mass is almost identical to that of Bi2Se3. Optical conductivity reveals a strong enhancement of the bound impurity bands with Cu addition, suggesting that a significant number of Cu atoms enter the interstitial sites between Bi and Se layers or may even substitute for Bi. This conclusion is also supported by x-ray diffraction measurements, where a significant increase of microstrain was found in Cu0.07Bi2Se3, compared to Bi2Se3.

  19. 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. PMID:12690192

  20. Fermi surface topology and negative longitudinal magnetoresistance observed in the semimetal NbAs2

    NASA Astrophysics Data System (ADS)

    Shen, Bing; Deng, Xiaoyu; Kotliar, Gabriel; Ni, Ni

    2016-05-01

    We report transverse and longitudinal magnetotransport properties of NbAs2 single crystals. Attributing to the electron-hole compensation, nonsaturating large transverse magnetoresistance reaches up to 8000 at 9 T at 1.8 K with mobility around 1 to 2 m2V-1S-1 . We present a thorough study of angular-dependent Shubnikov-de Haas (SdH) quantum oscillations of NbAs2. Three distinct oscillation frequencies are identified. First-principles calculations reveal four types of Fermi-surface pockets: electron α pocket, hole β pocket, hole γ pocket, and small electron δ pocket. Although the angular dependence of α ,β , and δ agree well with the SdH data, γ pocket is missing in SdH. Negative longitudinal magnetoresistance is observed which may be linked to novel topological states in this material, although systematic study is necessary to ascertain its origin.

  1. Magnetic-field- and temperature-dependent Fermi surface of CeBiPt

    NASA Astrophysics Data System (ADS)

    Wosnitza, J.; Goll, G.; Bianchi, A. D.; Bergk, B.; Kozlova, N.; Opahle, I.; Elgazzar, S.; Richter, Manuel; Stockert, O.; Löhneysen, H. v.; Yoshino, T.; Takabatake, T.

    2006-09-01

    The half-Heusler compounds CeBiPt and LaBiPt are semimetals with very low charge-carrier concentrations as evidenced by Shubnikov de Haas (SdH) and Hall-effect measurements. Neutron-scattering results reveal a simple antiferromagnetic structure in CeBiPt below TN = 1.15 K. The band structure of CeBiPt sensitively depends on temperature, magnetic field and stoichiometry. Above a certain, sample-dependent, threshold field (B>25 T), the SdH signal disappears and the Hall coefficient reduces significantly. These effects are absent in the non-4f compound LaBiPt. Electronic-band-structure calculations can well explain the observed behaviour by a 4f-polarization-induced Fermi-surface modification.

  2. 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.

  3. 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.

  4. 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.

  5. Fermi surface and magnetic structure of rare-earth-Ga3 compounds

    NASA Astrophysics Data System (ADS)

    Biasini, Maurizio; Kontrym-Sznajd, Grazyna; Ferro, Gianclaudio; Czopnik, Andrzej

    2002-03-01

    The measurement of the 2-dimensional angular correlation of the positron annihilation radiation (2D-ACAR), providing a 2D projection of the two-photon electron-positron momentum density, ρ(p), is a powerful tool to investigate the electronic structure of intermetallic compounds. Utilising tomographic reconstruction techniques (G Kontrym-Sznajd et al Mat. Scie. Forum 255-257) 754 (1997) and references therein., the experiment has the unique ability to sample the Brillouin Zone of truly 3-dimensional systems in a cartesian mesh, thus determining their Fermi surface (FS). Our studies have addressed the commensurate and incommensurate antiferromagnetic structures of TmGa3 and ErGa_3, respectively. For both compounds the FSs resulting from the 2D-ACAR experiments are in fair agreement with de Haas van Alphen measurements and with band structure calculations which constrain the 4f electrons to retain a local atomic character (M Biasini at al Phys. Rev. Lett 86), 4616, (2001).. Nevertheless, we discover different nesting features along the [110] directions which can account for the magnetic structures of the two compounds. Moreover, we propose methods to estimate the density of states at the Fermi energy (E_F) and the electronic contribution to the specific heat, γ. We obtain N(E_F)=17 states/ (Ryd cell), γ=2.8 (mJ/mole K^2) and N(E_F)=16 states/ (Ryd cell), γ=2.7 (mJ/mole K^2) for TmGa3 and ErGa_3, respectively.

  6. Competing order, Fermi surface reconstruction, and quantum oscillations in underdoped high-temperature superconductors

    NASA Astrophysics Data System (ADS)

    Dimov, Ivailo; Goswami, Pallab; Jia, Xun; Chakravarty, Sudip

    2008-10-01

    We consider incommensurate order parameters for electrons on a square lattice which reduce to d -density wave order when the ordering wave vector Q is close to Q0=(π/a,π/a) , a being the lattice spacing and describe the associated charge and current distributions within a single-harmonic approximation that conserves current to lowest order. Such incommensurate orders can arise at the mean-field level in extended Hubbard models, but the main goal here is to explore thoroughly the consequences within a Hartree-Fock approximation. We find that Fermi surface reconstruction in the underdoped regime can correctly capture the phenomenology of the recent quantum oscillation experiments that suggest incommensurate order, in particular the de Haas-van Alphen oscillations of the magnetization in high fields and very low temperatures in presumably the mixed state of these superconductors. For 10% hole doping in YBa2Cu3O6+δ , we find in addition to the main frequency around 530 T arising from the electron pocket and a hole frequency at around 1650 T, a new low frequency from a smaller hole pocket at 250 T for which there are some indications that require further investigations. The oscillation corresponding to the electron pocket will be further split due to bilayer coupling, but the splitting is sufficiently small to require more refined measurements. The truly incommensurate d -density wave breaks both time reversal and inversion, but the product of these two symmetry operations is preserved. The resulting Fermi surface splits into spin-up and spin-down sectors that are inversion conjugates. Each of the spin sectors results in a band structure that violates reflection symmetry, which can be determined in spin and angle-resolved photoemission spectroscopies. For those experiments such as the current photoemission experiments or the quantum oscillation measurements that cannot resolve the spin components, the bands will appear to be symmetric because of the equal mixture of

  7. 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.

  8. 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).

  9. Fermi surface of the ferromagnetic semimetal, EuB{sub 6}

    SciTech Connect

    Aronson, M.C.; Sarrao, J.L.; Fisk, Z.; Whitton, M.; Brandt, B.L.

    1999-02-01

    We report the results of magnetoresistance and magnetization measurements on single crystal EuB{sub 6} for temperatures above and below the ferromagnetic ordering temperatures T{sub C}{sup +}=15.3 K and T{sub C}{sup {minus}}=12.5 K, in magnetic fields as large as 30 T. Shubnikov{endash}de Haas and de Haas{endash}van Alphen oscillations were observed with four fundamental frequencies. By comparison to band-structure calculations, we ascribe the orbits to small pockets of electrons and holes, centered at the {ital X} points. The effective masses and extremal areas of the pockets are in good agreement with the predictions of band-structure calculations. We conclude that EuB{sub 6} is an intrinsic semimetal and not a doped insulator. The intrinsic carrier concentration is 1.2{times}10{sup 20} cm{sup {minus}3}, although our sample is somewhat uncompensated, with a 65{percent} surplus of holes. There is no appreciable modification to the Fermi-surface dimensions or carrier masses with the onset of ferromagnetism. {copyright} {ital 1999} {ital The American Physical Society}

  10. Pressure-enhanced superconductivity in A15-type Nb3 Ge via increased Fermi surface nesting

    NASA Astrophysics Data System (ADS)

    Stillwell, Ryan; Jeffries, Jason; McCall, Scott; Jenei, Zsolt; Weir, Sam; Vohra, Yogesh

    The A15-type superconductors are the most widely used superconductors in industrial applications yet the physics behind maximizing the superconducting transition temperature is still not completely understood. The highest transition temperatures found to date have recently been reported for high-pressure hydride materials and it is believed that they too are BCS-type phonon-mediated superconductors, just like the A15-type superconductors. Understanding the electron-phonon coupling has therefore been brought front stage in the search to understand the mechanisms for optimizing high-temperature superconductors. Using a multi-faceted suite of high-pressure techniques we found that Nb3Ge has an isostructural phase transition at high pressure that correlates directly with a bandstructure change seen in high-pressure magnetotransport measurements. Our results suggest that A15-type superconductivity is not only phonon-mediated but that the degree of Fermi surface nesting is a controlling parameter for maximizing the superconducting transition temperature. Lawrence Livermore National Laboratory is operated by Lawrence Livermore National Security, LLC, for the U.S. Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344.

  11. Direct Measurements of Fermi Level Pinning at the Surface of Intrinsically n-Type InGaAs Nanowires.

    PubMed

    Speckbacher, Maximilian; Treu, Julian; Whittles, Thomas J; Linhart, Wojciech M; Xu, Xiaomo; Saller, Kai; Dhanak, Vinod R; Abstreiter, Gerhard; Finley, Jonathan J; Veal, Tim D; Koblmüller, Gregor

    2016-08-10

    Surface effects strongly dominate the intrinsic properties of semiconductor nanowires (NWs), an observation that is commonly attributed to the presence of surface states and their modification of the electronic band structure. Although the effects of the exposed, bare NW surface have been widely studied with respect to charge carrier transport and optical properties, the underlying electronic band structure, Fermi level pinning, and surface band bending profiles are not well explored. Here, we directly and quantitatively assess the Fermi level pinning at the surfaces of composition-tunable, intrinsically n-type InGaAs NWs, as one of the prominent, technologically most relevant NW systems, by using correlated photoluminescence (PL) and X-ray photoemission spectroscopy (XPS). From the PL spectral response, we reveal two dominant radiative recombination pathways, that is, direct near-band edge transitions and red-shifted, spatially indirect transitions induced by surface band bending. The separation of their relative transition energies changes with alloy composition by up to more than ∼40 meV and represent a direct measure for the amount of surface band bending. We further extract quantitatively the Fermi level to surface valence band maximum separation using XPS, and directly verify a composition-dependent transition from downward to upward band bending (surface electron accumulation to depletion) with increasing Ga-content x(Ga) at a crossover near x(Ga) ∼ 0.2. Core level spectra further demonstrate the nature of extrinsic surface states being caused by In-rich suboxides arising from the native oxide layer at the InGaAs NW surface. PMID:27458736

  12. Fermi surface of SrFe2P2 determined by de Haas-van Alphen effect

    SciTech Connect

    Analytis, J.G.

    2010-05-26

    We report measurements of the Fermi surface (FS) of the ternary iron-phosphide SrFe{sub 2}P{sub 2} using the de Haas-van Alphen effect. The calculated FS of this compound is very similar to SrFe{sub 2}As{sub 2}, the parent compound of the high temperature superconductors. Our data show that the Fermi surface is composed of two electron and two hole sheets in agreement with bandstructure calculations. Several of the sheets show strong c-axis warping emphasizing the importance of three-dimensionality in the non-magnetic state of the ternary pnictides. We find that the electron and hole pockets have a different topology, implying that this material does not satisfy a ({pi},{pi}) nesting condition.

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

    DOE PAGESBeta

    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 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  15. Fermi Surface of Sr_{2}RuO_{4}: Spin-Orbit and Anisotropic Coulomb Interaction Effects.

    PubMed

    Zhang, Guoren; Gorelov, Evgeny; Sarvestani, Esmaeel; Pavarini, Eva

    2016-03-11

    The topology of the Fermi surface of Sr_{2}RuO_{4} is well described by local-density approximation calculations with spin-orbit interaction, but the relative size of its different sheets is not. By accounting for many-body effects via dynamical mean-field theory, we show that the standard isotropic Coulomb interaction alone worsens or does not correct this discrepancy. In order to reproduce experiments, it is essential to account for the Coulomb anisotropy. The latter is small but has strong effects; it competes with the Coulomb-enhanced spin-orbit coupling and the isotropic Coulomb term in determining the Fermi surface shape. Its effects are likely sizable in other correlated multiorbital systems. In addition, we find that the low-energy self-energy matrix-responsible for the reshaping of the Fermi surface-sizably differs from the static Hartree-Fock limit. Finally, we find a strong spin-orbital entanglement; this supports the view that the conventional description of Cooper pairs via factorized spin and orbital part might not apply to Sr_{2}RuO_{4}. PMID:27015496

  16. Entanglement in ground and excited states of gapped fermion systems and their relationship with fermi surface and thermodynamic equilibrium properties

    NASA Astrophysics Data System (ADS)

    Storms, Michelle; Singh, Rajiv

    2014-03-01

    We study bipartite entanglement entropies in the ground and excited states of model fermion systems, 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.

  17. 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

  18. Hidden order in URu2Si2 originates from Fermi surface gapping induced by dynamic symmetry breaking.

    PubMed

    Elgazzar, S; Rusz, J; Amft, M; Oppeneer, P M; Mydosh, J A

    2009-04-01

    Spontaneous, collective ordering of electronic degrees of freedom leads to second-order phase transitions that are characterized by an order parameter driving the transition. The notion of a 'hidden order' has recently been used for a variety of materials where a clear phase transition occurs without a known order parameter. The prototype example is the heavy-fermion compound URu(2)Si(2), where a mysterious hidden-order transition occurs at 17.5 K. For more than twenty years this system has been studied theoretically and experimentally without a firm grasp of the underlying physics. Here, we provide a microscopic explanation of the hidden order using density-functional theory calculations. We identify the Fermi surface 'hot spots' where degeneracy induces a Fermi surface instability and quantify how symmetry breaking lifts the degeneracy, causing a surprisingly large Fermi surface gapping. As the mechanism for the hidden order, we deduce spontaneous symmetry breaking through a dynamic mode of antiferromagnetic moment excitations. PMID:19234447

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

    PubMed

    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

  20. Emergent nesting of the Fermi surface from local-moment description of iron-pnictide high-Tc superconductors

    NASA Astrophysics Data System (ADS)

    Rodriguez, Jose P.; Araujo, Miguel A. N.; Sacramento, Pedro D.

    2014-07-01

    We uncover the low-energy spectrum of a t-J model for electrons on a square lattice of spin-1 iron atoms with 3dxz and 3dyz orbital character by applying Schwinger-boson-slave-fermion mean-field theory and by exact diagonalization of one hole roaming over a 4 × 4 × 2 lattice. Hopping matrix elements are set to produce hole bands centered at zero two-dimensional (2D) momentum in the free-electron limit. Holes can propagate coherently in the t-J model below a threshold Hund coupling when long-range antiferromagnetic order across the d + = 3d(x + iy)z and d - = 3d(x - iy)z orbitals is established by magnetic frustration that is off-diagonal in the orbital indices. This leads to two hole-pocket Fermi surfaces centered at zero 2D momentum. Proximity to a commensurate spin-density wave (cSDW) that exists above the threshold Hund coupling results in emergent Fermi surface pockets about cSDW momenta at a quantum critical point (QCP). This motivates the introduction of a new Gutzwiller wavefunction for a cSDW metal state. Study of the spin-fluctuation spectrum at cSDW momenta indicates that the dispersion of the nested band of one-particle states that emerges is electron-type. Increasing Hund coupling past the QCP can push the hole-pocket Fermi surfaces centered at zero 2D momentum below the Fermi energy level, in agreement with recent determinations of the electronic structure of mono-layer iron-selenide superconductors.

  1. Fermi surface nesting and spin density wave instability in the overdoped superconducting iron pnictides

    NASA Astrophysics Data System (ADS)

    Jiang, Hong-Min; Yao, Zi-Jian; Zhang, Fu-Chun

    2012-11-01

    The nesting of electron Fermi pocket with one of the two hole pockets around the Brillouin zone center has been attributed to the spin density wave (SDW) instability in the parent compound of superconducting iron pnictides. We propose here that the second hole Fermi pocket may be nested with the electron pocket in the doped case, which results in a new SDW instability. Our work is motivated by and may explain the recent scanning tunneling spectroscopy (STM) measurements on NaFe1-xCoxAs, which show an asymmetric gap-like feature near the Fermi level in the overdoped regime (Zhou X. et al., Phys. Rev. Lett., 109 (2012) 037002). We use a multi-band model to examine this feature within random phase approximation to include the coupling between the itinerant electron and the local spins.

  2. 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.

  3. Determination of the Fermi surface in high-T{sub c} superconductors by angle-resolved photoemission spectroscopy

    SciTech Connect

    Mesot, J.; Randeria, M.; Norman, M. R.; Kaminski, A.; Fretwell, H. M.; Campuzano, J. C.; Ding, H.; Takeuchi, T.; Sato, T.; Yokoya, T.

    2001-06-01

    We study the normal-state electronic excitations probed by angle-resolved photoemission spectroscopy (ARPES) in Bi{sub 1.6}Pb{sub 0.4}Sr{sub 2}CuO{sub 6} (Bi2201) and Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} (Bi2212). Our main goal is to establish explicit criteria for determining the Fermi surface from ARPES data on strongly interacting systems where sharply defined quasiparticles do not exist and the dispersion is very weak in parts of the Brillouin zone. Additional complications arise from strong matrix element variations within the zone. We present detailed results as a function of incident photon energy, and show simple experimental tests to distinguish between an intensity drop due to matrix element effects and spectral weight loss due to a Fermi crossing. We reiterate the use of polarization selection rules in disentangling the effect of umklapps due to the BiO superlattice in Bi2212. We conclude that, despite all the complications, the Fermi surface can be determined unambiguously; it is a single large hole barrel centered about ({pi},{pi}) in both materials.

  4. Orbital characters and near two-dimensionality of Fermi surfaces in NaFe1-xCoxAs

    NASA Astrophysics Data System (ADS)

    Liu, Z.-H.; Richard, P.; Li, Y.; Jia, L.-L.; Chen, G.-F.; Xia, T.-L.; Wang, D.-M.; He, J.-B.; Yang, H.-B.; Pan, Z.-H.; Valla, T.; Johnson, P. D.; Xu, N.; Ding, H.; Wang, S.-C.

    2012-11-01

    We report a comprehensive study of orbital characters and tridimensional nature of the electronic bands of 111-family in Fe-pnictides superconductors, NaFe1-xCoxAs (x = 0 and 0.05), with angle-resolved photoemission spectroscopy. We determined the orbital characters and the kz dependence of the low-energy electronic structures by tuning the polarization and the energy of the incident photons. We observed two nearly two-dimensional hole-like Fermi surfaces (FS) near the Brillouin zone (BZ) center and two electron-like FS near BZ corner. The bands near the Fermi level (EF) are mainly derived from the Fe 3dxy, 3dyz, and 3dzx orbitals.

  5. 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.

  6. Doping driven small-to-large Fermi surface transition and d-wave superconductivity in a two-dimensional Kondo lattice

    NASA Astrophysics Data System (ADS)

    Eder, R.; Wróbel, P.

    2011-07-01

    We study the two-dimensional Kondo lattice model with an additional Heisenberg exchange between localized spins. In a first step, we use mean-field theory with two order parameters. The first order parameter is a complex pairing amplitude between conduction electrons and localized spins that describes condensation of Kondo (or Zhang-Rice) singlets. A nonvanishing value implies that the localized spins contribute to the Fermi surface volume. The second-order parameter describes singlet pairing between the localized spins and competes with the Kondo-pairing order parameter. Reduction of the carrier density in the conduction band reduces the energy gain due to the formation of the large Fermi surface and induces a phase transition to a state with strong singlet correlations between the localized spins and a Fermi surface that comprises only the conduction electrons. The model thus shows a doping driven change of its Fermi surface volume. At intermediate doping and low temperature, there is a phase where both order parameters coexist, which has a gapped large Fermi surface and dx2-y2 superconductivity. The theory thus qualitatively reproduces the phase diagram of cuprate superconductors. In the second part of this paper, we show how the two phases with different Fermi surface volume emerge in a strong-coupling theory applicable in the limit of large Kondo exchange. The large Fermi surface phase corresponds to a “vacuum” of localized Kondo singlets with uniform phase, and the quasiparticles are spin-1/2 charge fluctuations around this fully paired state. In the small Fermi surface phase, the quasiparticles correspond to propagating Kondo singlets or triplets whereby the phase of a given Kondo singlet corresponds to its momentum. In this picture, a phase transition occurs for low filling of the conduction band as well.

  7. Quantum oscillations from the cylindrical Fermi-surface sheet of potassium created by the charge-density wave

    NASA Astrophysics Data System (ADS)

    Lacueva, Graciela; Overhauser, A. W.

    1992-07-01

    Oscillations reported by Dunifer et al. in microwave transmission through thin K layers are found to be periodic in 1/H. The oscillations arise from conduction-electron Landau levels passing through a small cylindrical sheet of the Fermi surface. This cylinder had been envisioned theoretically after incorporating both charge-density-wave and crystalline potentials in Schrödinger's equation. The cylinder's cross-sectional area is found to be πk2F/69, in agreement with the area inferred from the perpendicular-field cyclotron resonance, discovered by Grimes in the surface impedance.

  8. Regulating spin and Fermi surface topology of a quantum metal film by the surface (interface) monatomic layer

    NASA Astrophysics Data System (ADS)

    Matsuda, Iwao

    2012-02-01

    the Rashba-type surface alloy reduces the spin-relaxation time in the ultrathin film significantly [5]. These results demonstrate that spin and Fermi surface topology of a quantum metal film can be regulated by the surface (interface) monatomic layer.[0pt] [1] T. Okuda, Y. Takeichi, K. He, A. Harasawa, A. Kakizaki, and I. Matsuda, Phys. Rev. B 80, 113409 (2009).[0pt] [2] K. He, T. Hirahara, T. Okuda, S. Hasegawa, A. Kakizaki, and I. Matsuda, Phys. Rev. Lett. 101, 107604 (2008).[0pt] [3] K. He, Y. Takeichi, M. Ogawa, T. Okuda, P. Moras, D. Topwal, A. Harasawa, T. Hirahara, C. Carbone, A. Kakizaki, and I. Matsuda, Phys. Rev. Lett. 104, 156805 (2010).[0pt] [4] N. Miyata, R. Hobara, H. Narita, T. Hirahara, S. Hasegawa, and I. Matsuda, Japanese Journal of Applied Physics 50, 036602 (2011).[0pt] [5] N. Miyata, H. Narita, M. Ogawa, A. Harasawa, R. Hobara, T. Hirahara, P. Moras, D.Topwal, C.Carbone, S.Hasegawa, and I. Matsuda, Phys. Rev. B, 83, 195305 (2011).

  9. Electronic Structure and Fermi Surface of the Quaternary Intermetallic Borocarbide Superconductor YNi2B2C from 2D-ACAR

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.

    We measured the angular momentum density distribution of YNi2B2C to acquire information about its electronic structure. The measurements were performed using the full-scale utility of the two-dimensional angular correlation of annihilation radiation (2D-ACAR). The measured spectra clarified that Ni (3d) like state, predominantly, affected the Fermi surface of YNi2B2C. Further, s- and p-like-states enhanced its superconducting properties. The Fermi surface of YNi2B2C. was reconstructed using Fourier transformation followed by the LCW (Loucks, Crisp and West) folding procedure. It showed a large and complex surface similar to that of the high temperature superconductors HTS, with anisotropic properties. It also disclosed the effect of d-like state. Nevertheless, the current Fermi surface could deliver the needed topological information to isolate its features. The general layouts of this Fermi surface are; two large electron surfaces running along Γ-Z direction; as well as an additional large electron surface centered on X point; beside one hole surface centered on 100 point. This Fermi surface was interpreted in view of the earlier results.

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

    DOE PAGESBeta

    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.

  11. 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.

  12. Direct Observation of the Fermi Arc Surface State in the Three-Dimensional Dirac Semimetal Na3Bi

    NASA Astrophysics Data System (ADS)

    Liang, Aiji; Wang, Zhijun; Chen, Chaoyu; Shi, Youguo; Yi, Hemian; Feng, Ya; Xie, Zhuojin; He, Shaolong; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Zhang, Jun; Nakatake, M.; Arita, M.; Shimada, K.; Namatame, H.; Taniguchi, M.; Xu, Zuyan; Chen, Chuangtian; Dai, Xi; Fang, Zhong; Zhou, Xingjiang

    2015-03-01

    The three dimensional (3D) Dirac semimetals have linearly dispersive 3D Dirac nodes where the conduction and valence bands connect to each other. Here we report the direct observation of the linearly dispersive 3D bulk Dirac points at the natural (001) cleaving surface of Na3Bi single crystal by high resolution ARPES. In addition, we have directly observed two separated 3D bulk Dirac nodes by elaborately cleaving Na3Bi samples at a non-natural-cleavage (100) crystalline surface. We further unveil the unusual Fermi-arc surface states connecting the two 3D Dirac nodes. At this unique (100) crystalline surface, the identification of the 3D Dirac semimetal state in Na3Bi paves the way for systematically exploring rich exotic topological physics such as topological insulator and Weyl semimetal state.

  13. Fermi Surface Reconstruction inside the Hidden Order Phase of URu2Si2 Probed by Thermoelectric Measurements

    NASA Astrophysics Data System (ADS)

    Pourret, Alexandre; Palacio-Morales, Alexandra; Krämer, Steffen; Malone, Liam; Nardone, Marc; Aoki, Dai; Knebel, Georg; Flouquet, Jacques

    2013-03-01

    We report thermoelectric measurements of the low carrier heavy fermion compound URu2Si2 at high fields up to 34 T and at low temperatures down to 500 mK. The field dependence of the thermoelectric power (TEP) and the Nernst signal shows successive anomalies deep inside the hidden order (HO) phase. The field position of these anomalies correspond to different changes in the Shubnikov--de Haas frequencies and effective masses around 12, 17, 23, and 30 T. These results indicate successive reconstructions of the Fermi surface, which imply electronic phase transitions well within the HO phase.

  14. 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.

  15. Angle resolved photoemission study of Fermi surfaces and single-particle excitations of quasi-low dimensional materials

    NASA Astrophysics Data System (ADS)

    Gweon, Gey-Hong

    Using angle resolved photoemission spectroscopy (ARPES) as the main experimental tool and the single particle Green's function as the main theoretical tool, materials of various degrees of low dimensionality and different ground states are studied. The underlying theme of this thesis is that of one dimensional physics, which includes charge density waves (CDW's) and the Luttinger liquid (LL). The LL is the prime example of a lattice non-Fermi liquid (non-FL) and CDW fluctuations also give non-FL behaviors. Non-FL physics is an emerging paradigm of condensed matter physics. It is thought by some researchers that one dimensional LL behavior is a key element in solving the high temperature superconductivity problem. TiTe2 is a quasi-2 dimensional (quasi-2D) Fermi liquid (FL) material very well suited for ARPES lineshape studies. I report ARPES spectra at 300 K which show an unusual behavior of a peak moving through the Fermi energy (EF). I also report a good fit of the ARPES spectra at 25 K obtained by using a causal Green's function proposed by K. Matho. SmTe3 is a quasi-2D CDW material. The near EF ARPES spectra and intensity map reveal rich details of an anisotropic gap and imperfectly nested Fermi surface (FS) for a high temperature CDW. A simple model of imperfect nesting can be constructed from these data and predicts a CDW wavevector in very good agreement with the value known from electron diffraction. NaMo6O17 and KMo 6O17 are also quasi-2D CDW materials. The "hidden nesting" or "hidden 1 dimensionality" picture for the CDW is confirmed very well by our direct image of the FS. K0.3MoO3, the so-called "blue bronze," is a quasi-1 dimensional (quasi-1D) CDW material. Even in its metallic phase above the CDW transition temperature, its photoemission spectra show an anomalously weak intensity at EF and no clear metallic Fermi edge. I compare predictions of an LL model and a CDW fluctuation model regarding these aspects, and find that the LL scenario explains them

  16. Bulk Fermi Surface of Charge-Neutral Excitations in SmB6 or Not: A Heat-Transport Study

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Cui, S.; Dong, J. K.; Zhao, D.; Wu, T.; Chen, X. H.; Sun, Kai; Yao, Hong; Li, S. Y.

    2016-06-01

    Recently, there have been increasingly hot debates on whether a bulk Fermi surface of charge-neutral excitations exists in the topological Kondo insulator SmB6 . To unambiguously resolve this issue, we perform the low-temperature thermal conductivity measurements of a high-quality SmB6 single crystal down to 0.1 K and up to 14.5 T. Our experiments show that the residual linear term of thermal conductivity at the zero field is zero, within the experimental accuracy. Furthermore, the thermal conductivity is insensitive to the magnetic field up to 14.5 T. These results demonstrate the absence of fermionic charge-neutral excitations in bulk SmB6 , such as scalar Majorana fermions or spinons and, thus, exclude the existence of a bulk Fermi surface suggested by a recent quantum oscillation study of SmB6 . This puts a strong constraint on the explanation of the quantum oscillations observed in SmB6 .

  17. 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.

  18. Two-dimensional effects at the Fermi level of the c(2×2)-MnCu/Cu( 0 0 1 ) surface alloy

    NASA Astrophysics Data System (ADS)

    Gallego, S.; Soria, F.; Muñoz, M. C.

    2003-02-01

    A detailed study of the electronic structure of the c(2×2)-MnCu/Cu(0 0 1) surface alloy at the Fermi level is presented. We show that the complex topology of the two-dimensional momentum distribution of the electrons is due to the sum of two effects: the projection of the bulk Fermi surface onto the (2×2) plane, and the presence of new electronic states induced by the minority spin band of Mn. The crucial role of the surface potential in the intensity and dispersion of the states is discussed.

  19. Lattice distortion associated with Fermi-surface reconstruction in Sr3Rh4Sn13

    NASA Astrophysics Data System (ADS)

    Kuo, C. N.; Tseng, C. W.; Wang, C. M.; Wang, C. Y.; Chen, Y. R.; Wang, L. M.; Lin, C. F.; Wu, K. K.; Kuo, Y. K.; Lue, C. S.

    2015-04-01

    Superconducting Sr3Rh4Sn13 has been of current interest due to indications of a characteristic phase transition associated with structural distortions in its normal state. To further shed light on the nature of the phase transition, we performed a detailed study of single crystalline Sr3Rh4Sn13 by means of the thermal expansion, electrical resistivity, Hall coefficient, Seebeck coefficient, thermal conductivity, as well as 119Sn nuclear magnetic resonance (NMR) measurements, mainly focusing on the signatures around the phase transition temperature T*=137 K. The phase transition has been characterized by marked features near T* in all measured physical quantities. In particular, the NMR characteristics provide microscopic evidence for the reduction in the electronic Fermi-level density of states (DOSs) below T*. Based on the analysis of the 119Sn NMR spin-lattice relaxation rate, we clearly demonstrated that the Sn 5 s partial Fermi-level DOS in Sr3Rh4Sn13 is reduced by 13% across the phase transition. In this respect, it points to the strong association between electronic and structural instability for the peculiar phase transition in Sr3Rh4Sn13 .

  20. Split Fermi Surface Properties in Ullmannite NiSbS and PdBiSe with the Cubic Chiral Crystal Structure

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    We grew single crystals of ullmannite NiSbS and PbBiSe with the cubic chiral structure and carried out electrical resistivity, specific heat, and de Haas-van Alphen (dHvA) experiments to clarify their Fermi surface properties. The Fermi surfaces were found to split into two, reflecting the non-centrosymmetric crystal structure. The splitting energies between the two nearly spherical electron Fermi surfaces named α and α' were determined as 220 K in NiSbS and 1050 K in PdBiSe for H || [100] or [001]. This difference in splitting energies between the two compounds originates mainly from the fact that the spin-orbit interactions of Ni-3d, Sb-5p, and S-3p electrons in NiSbS are smaller in magnitude than those of Pd-4d, Bi-6p, and Se-4p electrons in PdBiSe, respectively.

  1. Direct observation of bulk Fermi surface at higher Brillouin zones in a heavily hole-doped cuprate

    NASA Astrophysics Data System (ADS)

    Al-Sawai, W.; Sakurai, Y.; Itou, M.; Barbiellini, B.; Mijnarends, P. E.; Markiewicz, R. S.; Kaprzyk, S.; Gillet, J.-M.; Wakimoto, S.; Fujita, M.; Basak, S.; Lin, H.; Bansil, A.; Yamada, K.

    2010-03-01

    We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2-xSrxCuO4 by using Compton scattering. A 2-D momentum density reconstruction [1] from measured Compton profiles, yields a clear FS signature in a higher Brillouin zone centered at p=(1.5,1.5) a.u. The quantitative agreement with density functional theory (DFT) calculations [2] and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. We have also measured the 2-D angular correlation of positron annihilation radiation (2D-ACAR) [3] and noticed a similar quantitative agreement with the DFT simulations. However, 2D-ACAR does not give a clear signature of the FS in the extended momentum space in both theory and experiment. Work supported in part by the US DOE.[1] Y. Tanaka et al., Phys. Rev. B 63, 045120 (2001).[2] S. Sahrakorpi et al., Phys. Rev. Lett. 95, 157601 (2005).[3] L. C. Smedskjaer et al., J. Phys. Chem. Solids 52, 1541 (1991).

  2. Study on the electronic structure and Fermi surface of 3d-transition-metal disilisides CoSi2

    NASA Astrophysics Data System (ADS)

    Hamid, A. S.

    2012-09-01

    We have investigated the electronic structure, the momentum density distribution ρ( p), and the Fermi surface FS of single crystals of the Pyrite-type 3d-transition-metal disilisides CoSi2. The band structure calculations, the density of states DOS, and the FS, in vicinity of Fermi level, have been carried out using the full-potential linearized augmented plane wave FP-LAPW method within generalized gradient approximation GGA for exchange and correlation potential. The measurements have been performed via the 2D angular correlation of annihilation radiation ACAR experiments. ρ( p) has been reconstructed by using the Fourier transformation technique. The FS has been reconstructed within the first Brillion zone BZ through the Locks, Crisp, and West LCW folding procedures. The analysis confirmed that Si 3 sp states hybrid with both Co 3 d- t 2 g and Co 3 d- e g states around Γ and X points, respectively. The dimensions of the FS of CoSi2 have been compared to the present calculations as well as to the earlier results.

  3. 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 ) .

  4. Orientational Tuning of the Fermi Sea of Confined Electrons at the SrTiO3 (110) and (111) Surfaces

    NASA Astrophysics Data System (ADS)

    Rödel, T. C.; Bareille, C.; Fortuna, F.; Baumier, C.; Bertran, F.; Le Fèvre, P.; Gabay, M.; Hijano Cubelos, O.; Rozenberg, M. J.; Maroutian, T.; Lecoeur, P.; Santander-Syro, A. F.

    2014-06-01

    We report the existence of confined electronic states at the (110) and (111) surfaces of SrTiO3. Using angle-resolved photoemission spectroscopy, we find that the corresponding Fermi surfaces, subband masses, and orbital ordering are different from the ones at the (001) surface of SrTiO3. This occurs because the crystallographic symmetries of the surface and subsurface planes and the effective electron masses along the confinement direction influence the symmetry of the electronic structure and the orbital ordering of the t2g manifold. Remarkably, our analysis of the data also reveals that the carrier concentration and thickness are similar for all three surface orientations, despite their different polarities. The orientational tuning of the microscopic properties of two-dimensional electron states at the surface of SrTiO3 echoes the tailoring of macroscopic (e.g., transport) properties reported recently in LaAlO3/SrTiO3 (110) and (111) interfaces, and is promising for searching new types of two-dimensional electronic states in correlated-electron oxides.

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

    PubMed

    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. 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.

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

    NASA Astrophysics Data System (ADS)

    Nakano, Kousuke; Hongo, Kenta; Maezono, Ryo

    2016-07-01

    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.

  9. Pressure effect on the Fermi surface of {alpha}-(ET){sub 2}TlHg(SeCN){sub 4}

    SciTech Connect

    Laukhin, V.N.; Lee, I.J.; Kushch, N.D.

    1996-12-31

    Magnetoresistence studies of the quasi-two dimensional organic conductor {alpha} - (ET){sub 2}TIHg(SeCN){sub 4} have been carried out under hydrostatic pressure, P. Only one series of SdH oscillations was observed at 3.5Fermi surface variations. Slow oscillations with frequency {approximately}47T were also observed at P=0, which were not observed for P=3.5 kbar. These may be connected with some imperfect nesting of the open orbits at ambient pressure, which may result in a destruction of superconductivity in Se-containing compound.

  10. 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

  11. Quasi-two-dimensional Fermi surfaces of the heavy-fermion superconductor Ce2PdIn8

    NASA Astrophysics Data System (ADS)

    Götze, K.; Klotz, J.; Gnida, D.; Harima, H.; Aoki, D.; Demuer, A.; Elgazzar, S.; Wosnitza, J.; Kaczorowski, D.; Sheikin, I.

    2015-09-01

    We report low-temperature de Haas-van Alphen (dHvA) effect measurements in magnetic fields up to 35 T of the heavy-fermion superconductor Ce2PdIn8 . The comparison of the experimental results with band-structure calculations implies that the 4 f electrons are itinerant rather than localized. The cyclotron masses estimated at high field are only moderately enhanced, 8 m0 and 14 m0 , but are substantially larger than the corresponding band masses. The observed angular dependence of the dHvA frequencies suggests quasi-two-dimensional Fermi surfaces in agreement with band-structure calculations. However, the deviation from ideal two-dimensionality is larger than in CeCoIn5, to which Ce2PdIn8 bears a lot of similarities. This subtle distinction accounts for the different superconducting critical temperatures of the two compounds.

  12. Role of Quantum and Surface-State Effects in the Bulk Fermi-Level Position of Ultrathin Bi Films.

    PubMed

    Hirahara, T; Shirai, T; Hajiri, T; Matsunami, M; Tanaka, K; Kimura, S; Hasegawa, S; Kobayashi, K

    2015-09-01

    We performed high-resolution photon-energy and polarization-dependent ARPES measurements on ultrathin Bi(111) films [6-180 bilayers (BL), 2.5-70 nm thick] formed on Si(111). In addition to the extensively studied surface states (SSs), the edge of the bulk valence band was clearly measured by using S-polarized light. We found direct evidence that this valence band edge, which forms a hole pocket in the bulk Bi crystal, does not cross the Fermi level for the 180 BL thick film. This is consistent with the predicted semimetal-to-semiconductor transition due to the quantum-size effect [V.B. Sandomirskii, Sov. Phys. JETP 25, 101 (1967)]. However, it became metallic again when the film thickness was decreased (below 30 BL). A plausible explanation for this phenomenon is the modification of the charge neutrality condition due to the size effect of the SSs. PMID:26382694

  13. 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.

  14. 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

  15. 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.

  16. 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. PMID:21517414

  17. 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.

  18. 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.

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

    PubMed Central

    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

    2015-01-01

    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. PMID:25735658

  20. Transfer of Neutrons from Deep Below the Fermi Surface via the (p,t) Reaction in the N = 90 Region

    NASA Astrophysics Data System (ADS)

    Humby, P.; Wilson, E.; Beausang, C. W.; Simon, A.; Gell, K.; Tarlow, T.; Vyas, G.; Ross, T. J.; Hughes, R. O.; Burke, J. T.; Casperson, R. J.; Koglin, J.; Ota, S.; Allmond, J. M.; McCleskey, M.; McCleskey, E.; Saastamoinen, A.; Chyzh, R.; Dag, M.

    2015-10-01

    The 152,154Sm(p,t) reactions were used to investigate excited states populated by the transfer of neutrons from deep below the Fermi surface. States corresponding to the transfer of at least one neutron from below the N = 82 shell closure are of particular interest since they provide a sensitive probe of the evolution of the shell closure with increasing deformation. In the present work, large quasi-discrete structures were observed in the triton energy spectra at excitation energies of 2-3 MeV and are interpreted in terms of the underlying Nilsson orbitals. The experiment utilized a 25 MeV proton beam from the K-150 cyclotron at the Cyclotron Institute of Texas A&M University and the outgoing charged particles and γ rays were detected using the STARLiTeR array. This work is supported by the U.S. Department of Energy No. DE-FG02-05ER41379, DE-FG52-09NA29467 and DE-NA0001801, the National Science Foundation under PHY-130581, and by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

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

    DOE PAGESBeta

    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; et al

    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

  2. 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

  3. Lifshitz transition in high magnetic fields in UPt2Si2: Magnetoresistivity, Hall effect, magnetostriction and Fermi surface

    NASA Astrophysics Data System (ADS)

    Sullow, S.; Schulze Grachtrup, D.; Steinki, N.; Cakir, Z.; Zwicknagl, G.; Sheikin, I.; Jaime, M.; Mydosh, J. A.

    We have measured the magnetoresistivity and Hall effect of single crystalline UPt2Si2 in DC magnetic fields up to 35 T at temperatures down to 50 mK. Moreover, we have carried out magnetostriction measurements in pulsed magnetic fields up to 55 T for temperatures down to 1.5 K. For the magnetic field applied along the c axis we observe strong changes in the Hall effect at the previously established field induced phase boundaries AFM I <--> III and III <--> V (see Ref.). From a detailed analysis of the Hall effect, we find evidence for topological changes of the Fermi surface due to at least one Lifshitz transition. Furthermore, in the magnetoresistivity and magnetostriction data we find a distinct history dependent anomaly within phase III, indicative of a first order phase transition. We relate our findings to band structure calculations carried out under consideration of the concept of a dual nature of the uranium 5 f electrons with different degrees of localization.

  4. Bilayer splitting versus Fermi-surface warping as an origin of slow oscillations of in-plane magnetoresistance in rare-earth tritellurides

    NASA Astrophysics Data System (ADS)

    Grigoriev, Pavel D.; Sinchenko, Alexander A.; Lejay, Pascal; Hadj-Azzem, Abdellali; Balay, Joël; Leynaud, Olivier; Zverev, Vladimir N.; Monceau, Pierre

    2016-06-01

    Slow oscillations (SlO) of the in-plane magnetoresistance with a frequency less than 4 T are observed in the rare-earth tritellurides and proposed as an effective tool to explore the electronic structure in various strongly anisotropic quasi-two-dimensional compounds. Contrary to the usual Shubnikov-de-Haas oscillations, SlO originate not from small Fermi-surface pockets, but from the entanglement of close frequencies due to a finite interlayer transfer integral, either between the two Te planes forming a bilayer or between two adjacent bilayers. From the observed angular dependence of the frequency and the phase of SlO we argue that they originate from the bilayer splitting rather than from the Fermi-surface warping. The SlO frequency gives the value of the interlayer transfer integral ≈1 meV for TbTe3 and GdTe3.

  5. Correlation between Fermi surface transformations and superconductivity in the electron-doped high-Tc superconductor Nd2 -xCexCuO4

    NASA Astrophysics Data System (ADS)

    Helm, T.; Kartsovnik, M. V.; Proust, C.; Vignolle, B.; Putzke, C.; Kampert, E.; Sheikin, I.; Choi, E.-S.; Brooks, J. S.; Bittner, N.; Biberacher, W.; Erb, A.; Wosnitza, J.; Gross, R.

    2015-09-01

    Two critical points have been revealed in the normal-state phase diagram of the electron-doped cuprate superconductor Nd2 -xCexCuO4 by exploring the Fermi surface properties of high-quality single crystals by high-field magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas effect shows that the weak superlattice potential responsible for the Fermi surface reconstruction in the overdoped regime extrapolates to zero at the doping level xc=0.175 corresponding to the onset of superconductivity. Second, the high-field Hall coefficient exhibits a sharp drop right below optimal doping xopt=0.145 where the superconducting transition temperature is maximum. This drop is most likely caused by the onset of long-range antiferromagnetic ordering. Thus the superconducting dome appears to be pinned by two critical points to the normal state phase diagram.

  6. 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. PMID:24580190

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

    NASA Astrophysics Data System (ADS)

    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), 10.1103/PhysRevLett.96.100503]. 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.

  8. Orbital origin and matrix element effects in the Ag/Si(1 1 1)-( √{3}×√{3})R30° Fermi surface

    NASA Astrophysics Data System (ADS)

    Pérez-Dieste, V.; Sánchez-Royo, J. F.; Avila, J.; Izquierdo, M.; Roca, L.; Tejeda, A.; Asensio, M. C.

    2007-02-01

    The Fermi surface (FS) of the Ag/Si(1 1 1)- √{3}×√{3} reconstruction with an excess of Ag has been mapped by angle resolved photoemission spectroscopy with polarized light in a wide region of the reciprocal space and with different detection geometries. In contrast to previous results, a strong polarization dependence is observed. Applying the dipole selection rules, it is found that the surface state at the Fermi level, S 1 state, has odd symmetry with respect to the mirror plane of the honeycomb-chained triangle structure, indicating that it is mainly derived from Ag 5p x and 5p y orbitals. This conclusion is revised in the new frame of a inequivalent-triangle structure for the Ag/Si(1 1 1)- √{3}×√{3} at room temperature. Besides, strong modulations of the intensity distribution are found that deviate the Fermi surface pattern from its expected two-dimensional periodical behavior.

  9. 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.

  10. Bulk Fermi surface and momentum density in heavily doped La2-xSrxCuO4 using high-resolution Compton scattering and positron annihilation spectroscopies

    NASA Astrophysics Data System (ADS)

    Al-Sawai, W.; Barbiellini, B.; Sakurai, Y.; Itou, M.; Mijnarends, P. E.; Markiewicz, R. S.; Kaprzyk, S.; Wakimoto, S.; Fujita, M.; Basak, S.; Lin, H.; Wang, Yung Jui; Eijt, S. W. H.; Schut, H.; Yamada, K.; Bansil, A.

    2012-03-01

    We have observed the bulk Fermi surface (FS) in an overdoped (x=0.3) single crystal of La2-xSrxCuO4 by using Compton scattering. A two-dimensional (2D) momentum density reconstruction from measured Compton profiles yields a clear FS signature in the third Brillouin zone along [100]. The quantitative agreement between density functional theory (DFT) calculations and momentum density experiment suggests that Fermi-liquid physics is restored in the overdoped regime. In particular the predicted FS topology is found to be in good accord with the corresponding experimental data. We find similar quantitative agreement between the measured 2D angular correlation of positron annihilation radiation (2D-ACAR) spectra and the DFT-based computations. However, 2D-ACAR does not give such a clear signature of the FS in the extended momentum space in either the theory or the experiment.

  11. 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.

  12. Fermi questions

    NASA Astrophysics Data System (ADS)

    Bouffard, Karen

    1999-05-01

    This column contains problems and solutions for the general category of questions known as "Fermi" questions. Forcing the students to use their ability to estimate, giving answers in terms of order-of-magnitude, is not only a challenge for a competition, but a teaching strategy to use in the classroom to develop self-confidence and the ability to analyze answers as to whether or not they make sense, as opposed to relying on the "precision" of a calculator value.

  13. 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.

  14. 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...

  15. 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.

  16. 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.

  17. Fermi surface of MoO2 studied by angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations

    NASA Astrophysics Data System (ADS)

    Moosburger-Will, Judith; Kündel, Jörg; Klemm, Matthias; Horn, Siegfried; Hofmann, Philip; Schwingenschlögl, Udo; Eyert, Volker

    2009-03-01

    A comprehensive study of the electronic properties of monoclinic MoO2 from both an experimental and a theoretical point of view is presented. We focus on the investigation of the Fermi body and the band structure using angle-resolved photoemission spectroscopy, de Haas-van Alphen measurements, and electronic structure calculations. For the latter, the full-potential augmented spherical wave method has been applied. Very good agreement between the experimental and theoretical results is found. In particular, all Fermi surface sheets are correctly identified by all three approaches. Previous controversies concerning additional holelike surfaces centered around the Z and B points could be resolved; these surfaces were artifacts of the atomic-sphere approximation used in the old calculations. Our results underline the importance of electronic structure calculations for the understanding of MoO2 and the neighboring rutile-type early transition-metal dioxides. This includes the low-temperature insulating phases of VO2 and NbO2 , which have crystal structures very similar to that of molybdenum dioxide and display the well-known prominent metal-insulator transitions.

  18. Fermi-level stabilization in the topological insulators Bi2Se3 and Bi2Te3: Origin of the surface electron gas

    NASA Astrophysics Data System (ADS)

    Suh, Joonki; Fu, Deyi; Liu, Xinyu; Furdyna, Jacek K.; Yu, Kin Man; Walukiewicz, Wladyslaw; Wu, Junqiao

    2014-03-01

    Two-dimensional electron gas (2DEG) coexists with topological states on the surface of topological insulators (TIs), while the origin of the 2DEG remains elusive. In this work, electron density in TI thin films (Bi2Se3,Bi2Te3, and their alloys) were manipulated by controlling the density of electronically active native defects with particle irradiation. The measured electron concentration increases with irradiation dose but saturates at different levels for Bi2Se3 and Bi2Te3. The results are in quantitative agreement with the amphoteric defect model, which predicts that electronically active native defects shift the Fermi energy (EF) toward a Fermi stabilization level (EFS) located universally at ˜4.9 eV below the vacuum level. Combined with thickness-dependent data, it is demonstrated that regardless of the bulk doping, the surface EF is always pinned at EFS, producing a band bending and 2DEG on TI film surfaces. Our work elucidates native defect physics of TIs with a model universally applicable to other semiconductors and has critical implications for potential device applications of TIs.

  19. Lifshits quantum phase transitions and rearrangement of the Fermi surface upon a change in the hole concentration in high-temperature superconductors

    SciTech Connect

    Ovchinnikov, S. G. Korshunov, M. M.; Shneyder, E. I.

    2009-11-15

    Changes in the electronic structure in the normal phase of high-T{sub c} superconductors (HTSCs), viz., layered cuprates, are considered. The results of LDA + GTB calculations of the electron structure and the Fermi surface of La{sub 2-x}Sr{sub x}CuO{sub 4} one-layer cuprates with allowance for strong correlations are compared with ARPES and quantum oscillations data. Two critical points x{sub c1} and x{sub c2} are discovered at which the rear-rangement of the Fermi surface takes place. In the vicinity of these points, changes in the thermodynamic properties at low temperatures are determined using the Lifshits ideology concerning 2.5-order quantum phase transitions. A singularity {delta}(C/T) {proportional_to} (x - x{sub e}){sup 1/2} in the electron heat capacity agrees well with the available experimental data in the vicinity of x{sub c1} {approx} 0.15. Sign reversal of the Hall constant upon doping is also considered qualitatively.

  20. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    DOE PAGESBeta

    Kim, Hyunsoo; Tanatar, M. A.; Flint, R.; Petrovic, C.; Hu, Rongwei; White, B. D.; Lum, I. K.; Maple, M. B.; Prozorov, 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

  1. 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

  2. Fermi surface reconstruction and quantum oscillations in underdoped YBa2Cu3O7 -x modeled in a single bilayer with mirror symmetry broken by charge density waves

    NASA Astrophysics Data System (ADS)

    Briffa, A. K. R.; Blackburn, E.; Hayden, S. M.; Yelland, E. A.; Long, M. W.; Forgan, E. M.

    2016-03-01

    Hole-doped high-temperature cuprate superconductors below optimum doping have electronlike Fermi surfaces occupying a small fraction of the Brillouin zone. There is strong evidence that this is linked to charge density wave (CDW) order, which reconstructs the large holelike Fermi surfaces predicted by band structure calculations. Recent experiments have revealed the structure of the two CDW components in the benchmark bilayer material YBa2Cu3O7 -x in high field where quantum oscillation (QO) measurements are performed. We have combined these results with a tight-binding description of the bands in a single bilayer to give a minimal model revealing the essential physics of the situation. Here we show that this approach, combined with the effects of spin-orbit interactions and the pseudogap, gives a good qualitative description of the multiple frequencies seen in the QO observations in this material. Magnetic breakdown through weak CDW splitting of the bands will lead to a field dependence of the QO spectrum and to the observed fourfold symmetry of the results in tilted fields.

  3. Fermi-Surface Topological Phase Transition and Horizontal Order-Parameter Nodes in CaFe2As2 Under Pressure.

    PubMed

    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

  4. 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

    2010-02-01

    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. PMID:20366789

  5. 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.

  6. 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

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

    NASA Astrophysics Data System (ADS)

    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.

    2016-07-01

    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.

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

    PubMed

    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

  9. 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.

  10. Propeller-Like Low Temperature Fermi Surface of Ba1-xKxFe2As2 from Magnetotransport and Photoemission Measurements

    NASA Astrophysics Data System (ADS)

    Evtushinsky, Daniil V.; Kordyuk, Alexander A.; Zabolotnyy, Volodymyr B.; Inosov, Dmytro S.; Kim, Timur K.; Büchner, Bernd; Luo, Huiqian; Wang, Zhaosheng; Wen, Hai-Hu; Sun, Guoli; Lin, Chengtian; Borisenko, Sergey V.

    2011-02-01

    The Hall coefficient of the hole-doped iron arsenide Ba1-xKxFe2As2 (BKFA) is calculated purely on the basis of the electronic structure, revealed in the angle-resolved photoemission spectroscopy (ARPES) experiments, and compared to the one measured directly. The observed agreement allows us to state that upon cooling the Fermi surface (FS) in the optimally doped BKFA gradually evolves to the propeller-like topology, on which the superconductivity develops. Persistence of the notable temperature dependence in both photoemission and magnetotransport experiments well above the spin-density-wave (SDW) transition suggests that the FS reconstruction in BKFA is partially decoupled from the emergence of static magnetism.

  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. Bosonization of the low energy excitations of Fermi liquids

    SciTech Connect

    Castro Neto, A.H.; Fradkin, E. )

    1994-03-07

    We bosonize the low energy excitations of Fermi liquids in any number of dimensions in the limit of long wavelengths. The bosons are a coherent superposition of electron-hole pairs and are related with the displacements of the Fermi surface in some arbitrary direction. A coherent-state path integral for the bosonized theory is derived and it is shown to represent histories of the shape of the Fermi surface. The Landau theory of Fermi liquids can be obtained from the formalism in the absence of nesting of the Fermi surface and singular interactions. We show that the Landau equation for sound waves is exact in the semiclassical approximation for the bosons.

  13. 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...

  14. Fermi level pinning characterisation on ammonium fluoride-treated surfaces of silicon by energy-filtered doping contrast in the scanning electron microscope.

    PubMed

    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

  15. 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

  16. 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

  17. Unveiling Unidentified Fermi Sources

    NASA Astrophysics Data System (ADS)

    Zhang, Lizhong; South Pole Telescope

    2016-01-01

    The Fermi γ-ray Space Telescope (Fermi) has surveyed the entire sky at the highest-energy band of the electromagnetic spectrum. The majority of Fermi sources have counterpart identifications from multi-wavelength large-area surveys, particularly in the radio and x-ray bands. However, around 35% of Fermi sources remain unidentified, a problem exasperated by the low resolution of the telescope. Understanding the nature of unidentified Fermi sources is one of the most pressing problems in γ-ray astronomy. The South Pole Telescope (SPT) has completed a survey covering a 2500 square degrees of the southern extragalactic sky with arcminute resolution at millimeter wavelengths. The mm wavelength is the most efficient means to identify blazars and unidentified Fermi sources. Our analysis shows that the SPT point source catalog provides candidate associations for 40% of the unidentified Fermi sources, showing them to be flat-spectrum radio quasars which are extraordinarily bright at millimeter (mm) wavelengths.

  18. 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.

  19. As-As dimerization, Fermi surfaces and the anomalous electrical transport properties of UAsSe and ThAsSe

    SciTech Connect

    Withers, Ray L. . E-mail: withers@rsc.anu.edu.au; Midden, Herman J.P. van; Prodan, Albert; Midgley, P.A.; Schoenes, J.; Vincent, R.

    2006-07-15

    A temperature dependent electron diffraction study has been carried out on UAsSe to search for evidence of As-As dimerization at low temperature. A highly structured characteristic diffuse intensity distribution, closely related to that recently reported for ThAsSe, has been observed at low temperature and interpreted in terms of a gradual charge density wave type phase transition upon lowering of temperature involving disordered As-As dimerization within (001) planes. Plausible models of the proposed As-As dimerization have been obtained using a group theoretical approach. Electronic band structure calculations of ThAsSe and UAsSe have been used to search for potential Fermi surface nesting wave-vectors. The results are in good agreement with the experimentally observed diffuse intensity distributions in both cases. - Graphical abstract: A typical <001> zone axis EDP of UAsSe taken at {approx}80-90 K. In addition to the strong Bragg reflections of the underlying P4/nmm average structure, note the presence of a highly structured characteristic diffuse intensity distribution arising from disordered As-As dimerization.

  20. Soft X-ray ARPES investigation of the nickelate Fermi surface in exchange biased LaNiO3-LaMnO3 superlattices

    NASA Astrophysics Data System (ADS)

    Bruno, Flavio; McKeown Walker, S.; de la Torre, A.; Tamai, A.; Gibert, M.; Catalano, S.; Triscone, J.-M.; Wang, Z.; Bisti, F.; Strocov, V.; Baumberger, F.

    2015-03-01

    We investigate (111)-oriented superlattices consisting of paramagnetic LaNiO3 (LNO) and ferromagnetic LaMnO3 (LMO). The field dependence of the magnetization in these heterostructures was measured at 5 K after cooling the sample in the presence of a 0.4 T field. Surprisingly, a shift of 15 mT in the magnetization loop towards negative fields along the magnetic field axis was observed. If the same measurement is repeated in a (111) LMO thin film, no exchange bias is observed which implies that LNO is the driving force for the biasing effect exhibited by the heterostructures. Since LNO is a well-known paramagnetic material, the existence of exchange bias in the superlattices implies the existence of an interface-induced magnetic order. Here we use soft x-ray angle resolved photoemission spectroscopy -SX ARPES- to study the electronic band structure of LNO layers in these heterostructures. Due to the increase in photoelectron escape depth in the 500 - 1000 eV energy range, we are able to map the LNO Fermi surface below 7 u.c. of LMO. In this talk we will discuss the similarities and differences in the electronic structure between thin films of (111)-LNO and buried LNO-LMO interfaces.

  1. Electronic structure, Fermi surfaces, and electron-phonon coupling in La-doped Sr2TiO4 and SrTiO3

    NASA Astrophysics Data System (ADS)

    Nie, Yuefeng; Chatterjee, Shouvik; Burganov, Bulat; Monkman, Eric; Harter, John; Shai, Daniel; Lee, Che-Hui; Schlom, Darrell; Shen, Kyle

    2012-02-01

    Sr2TiO4 is a quasi-two-dimensional Ruddlesden-Popper structure analogue to SrTiO3, and is isostructural with the cuprate parent compound La2CuO4. Although the electronic structure of SrTiO3 has been well-explored due to its importance in oxide electronics, little is known about the electronic properties of Sr2TiO4. To investigate this, we synthesized epitaxial La doped Sr2TiO4 and SrTiO3 films on (100) LSAT substrates by molecular beam epitaxy (MBE) and investigated the electronic structure using angle-resolved photoemission spectroscopy (ARPES). The electronic structure of 5% La doped Sr2TiO4 shows a single electron like band with mostly Ti-3dxy character dispersing across the Fermi surface which corresponds well with LDA calculations. This is in contrast to doped SrTiO3 where all three t2g bands are degenerate. We also observed signatures of strong electron-phonon coupling in the quasi-two-dimensional Sr2TiO4 materials which appear to be absent in three-dimensional SrTiO3.

  2. 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.

  3. 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...

  4. 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)

  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. Fermi-surface reconstruction from two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) data using maximum-likelihood fitting of wavelet-like functions

    NASA Astrophysics Data System (ADS)

    G, A., Major; Fretwell, H. M.; Dugdale, S. B.; Alam, M. A.

    1998-11-01

    A novel method for reconstructing the Fermi surface from experimental two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) projections is proposed. In this algorithm, the 3D electron momentum-density distribution is expanded in terms of a basis of wavelet-like functions. The parameters of the model, the wavelet coefficients, are determined by maximizing the likelihood function corresponding to the experimental data and the projections calculated from the model. In contrast to other expansions, in the case of that in terms of wavelets a relatively small number of model parameters are sufficient for representing the relevant parts of the 3D distribution, thus keeping computation times reasonably short. Unlike other reconstruction methods, this algorithm takes full account of the statistical information content of the data and therefore may help to reduce the amount of time needed for data acquisition. An additional advantage of wavelet expansion may be the possibility of retrieving the Fermi surface directly from the wavelet coefficients rather than indirectly using the reconstructed 3D distribution.

  7. Critical Doping for the Onset of Fermi-Surface Reconstruction by Charge-Density-Wave Order in the Cuprate Superconductor La2 -xSrx CuO4

    NASA Astrophysics Data System (ADS)

    Badoux, S.; Afshar, S. A. A.; Michon, B.; Ouellet, A.; Fortier, S.; LeBoeuf, D.; Croft, T. P.; Lester, C.; Hayden, S. M.; Takagi, H.; Yamada, K.; Graf, D.; Doiron-Leyraud, N.; Taillefer, Louis

    2016-04-01

    The Seebeck coefficient S of the cuprate superconductor La2 -xSrxCuO4 (LSCO) was measured in magnetic fields large enough to access the normal state at low temperatures, for a range of Sr concentrations from x =0.07 to x =0.15 . For x =0.11 , 0.12, 0.125, and 0.13, S /T decreases upon cooling to become negative at low temperatures. The same behavior is observed in the Hall coefficient RH (T ) . In analogy with other hole-doped cuprates at similar hole concentrations p , the negative S and RH show that the Fermi surface of LSCO undergoes a reconstruction caused by the onset of charge-density-wave modulations. Such modulations have indeed been detected in LSCO by x-ray diffraction in precisely the same doping range. Our data show that in LSCO this Fermi-surface reconstruction is confined to 0.085

  8. Orthogonal metals: The simplest non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Nandkishore, Rahul; Metlitski, Max A.; Senthil, T.

    2012-07-01

    We present a fractionalized metallic phase which is indistinguishable from the Fermi liquid in conductivity and thermodynamics, but is sharply distinct in one-electron properties, such as the electron spectral function. We dub this phase the “orthogonal metal.” The orthogonal metal and the transition to it from the Fermi liquid are naturally described using a slave-particle representation wherein the electron is expressed as a product of a fermion and a slave Ising spin. We emphasize that when the slave spins are disordered, the result is not a Mott insulator (as erroneously assumed in the prior literature), but rather the orthogonal metal. We construct prototypical ground-state wave functions for the orthogonal metal by modifying the Jastrow factor of Slater-Jastrow wave functions that describe ordinary Fermi liquids. We further demonstrate that the transition from the Fermi liquid to the orthogonal metal can, in some circumstances, provide a simple example of a continuous destruction of a Fermi surface with a critical Fermi surface appearing right at the critical point. We present exactly soluble models that realize an orthogonal metal phase, and the phase transition to the Fermi liquid. These models thus provide valuable solvable examples for phase transitions associated with the death of a Fermi surface.

  9. Pairing in a dry Fermi sea.

    PubMed

    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

  10. Aspects of non-Fermi-liquid metals

    NASA Astrophysics Data System (ADS)

    Pivovarov, Eugene

    We consider several examples of metallic systems that exhibit non-Fermi-liquid behavior. In these examples the system is not a Fermi liquid due to the presence of a "hidden" order. The primary models are density waves with an odd-frequency-dependent order parameter and density waves with d-wave symmetry. In the first model, the same-time correlation functions vanish and there is a conventional Fermi surface. In the second model, the gap vanishes at the nodes. We derive the phase diagrams and study the thermodynamic and kinetic properties. We also consider the effects of competing orders on the phase diagram when the underlying microscopic interaction has a high symmetry.

  11. 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.

  12. 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. ...

  13. More Fermi questions

    NASA Astrophysics Data System (ADS)

    Bouffard, Karen

    1999-09-01

    "Fermi" questions are a popular component of most Physics Olympics meets. Asking students to make a reasonable assumption about a problem and give answers in terms of order of magnitude is not only a great challenge for a competition, but is also a valued teaching strategy in the classroom.

  14. Cooper pairing in non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Metlitski, Max A.; Mross, David F.; Sachdev, Subir; Senthil, T.

    2015-03-01

    States of matter with a sharp Fermi surface but no well-defined Landau quasiparticles arise in a number of physical systems. Examples include (i) quantum critical points associated with the onset of order in metals; (ii) spinon Fermi-surface [U(1) spin-liquid] state of a Mott insulator; (iii) Halperin-Lee-Read composite fermion charge liquid state of a half-filled Landau level. In this work, we use renormalization group techniques to investigate possible instabilities of such non-Fermi liquids in two spatial dimensions to Cooper pairing. We consider the Ising-nematic quantum critical point as an example of an ordering phase transition in a metal, and demonstrate that the attractive interaction mediated by the order-parameter fluctuations always leads to a superconducting instability. Moreover, in the regime where our calculation is controlled, superconductivity preempts the destruction of electronic quasiparticles. On the other hand, the spinon Fermi surface and the Halperin-Lee-Read states are stable against Cooper pairing for a sufficiently weak attractive short-range interaction; however, once the strength of attraction exceeds a critical value, pairing sets in. We describe the ensuing quantum phase transition between (i) U(1 ) and Z2 spin-liquid states; (ii) Halperin-Lee-Read and Moore-Read states.

  15. Fermi Arcs vs. Fermi Pockets in Electron-doped Perovskite Iridates

    PubMed Central

    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

    2015-01-01

    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. PMID:25704850

  16. Fermi arcs vs. fermi pockets in electron-doped perovskite iridates

    DOE PAGESBeta

    He, Junfeng; Hafiz, H.; Mion, Thomas R.; Hogan, T.; Dhital, C.; Chen, X.; Lin, Qisen; Hashimoto, M.; Lu, D. H.; Zhang, Y.; et al

    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.

  17. 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.

  18. Stable non-Fermi-liquid phase of itinerant spin-orbit coupled ferromagnets

    NASA Astrophysics Data System (ADS)

    Bahri, Yasaman; Potter, Andrew C.

    2015-07-01

    Direct (nongradient) coupling between a gapless bosonic field and a Fermi surface results in the destruction of Landau quasiparticles and a breakdown of Fermi liquid theory. Such a non-Fermi-liquid phase arises in spin-orbit coupled ferromagnets with spontaneously broken continuous symmetries due to strong coupling between rotational Goldstone modes and itinerant electrons. These systems provide an experimentally accessible context for studying non-Fermi-liquid physics. Possible examples include low-density Rashba coupled electron gases, which have a natural tendency towards spontaneous ferromagnetism, or topological insulator surface states with proximity-induced ferromagnetism. Crucially, unlike the related case of a spontaneous nematic distortion of the Fermi surface, for which controlled field theory calculations predict that the non-Fermi-liquid regime will be masked by a superconducting dome, we show that the non-Fermi-liquid phase in spin-orbit coupled ferromagnets is stable.

  19. Stable non-Fermi liquid phase of itinerant spin-orbit coupled ferromagnets

    NASA Astrophysics Data System (ADS)

    Bahri, Yasaman; Potter, Andrew

    2015-03-01

    Direct coupling between gapless bosons and a Fermi surface results in the destruction of Landau quasiparticles and a breakdown of Fermi liquid theory. Such a non-Fermi liquid phase arises in spin-orbit coupled ferromagnets with spontaneously broken continuous symmetries due to strong coupling between rotational Goldstone modes and itinerant electrons. These systems provide an experimentally accessible context for studying non-Fermi liquid physics. Possible examples include low-density Rashba coupled electron gases, which have a natural tendency towards spontaneous ferromagnetism, or topological insulator surface states with proximity-induced ferromagnetism. Crucially, unlike the related case of a spontaneous nematic distortion of the Fermi surface, for which the non-Fermi liquid regime is expected to be masked by a superconducting dome, we show that the non-Fermi liquid phase in spin-orbit coupled ferromagnets is stable.

  20. Fermi Surface of Three-Dimensional La1 -xSrxMnO3 Explored by Soft-X-Ray ARPES: Rhombohedral Lattice Distortion and its Effect on Magnetoresistance

    NASA Astrophysics Data System (ADS)

    Lev, L. L.; Krempaský, J.; Staub, U.; Rogalev, V. A.; Schmitt, T.; Shi, M.; Blaha, P.; Mishchenko, A. S.; Veligzhanin, A. A.; Zubavichus, Y. V.; Tsetlin, M. B.; Volfová, H.; Braun, J.; Minár, J.; Strocov, V. N.

    2015-06-01

    Electronic structure of the three-dimensional colossal magnetoresistive perovskite La1 -xSrxMnO3 has been established using soft-x-ray angle-resolved photoemission spectroscopy with its intrinsically sharp definition of three-dimensional electron momentum. The experimental results show much weaker polaronic coupling compared to the bilayer manganites and are consistent with the theoretical band structure including the empirical Hubbard parameter U. The experimental Fermi surface unveils the canonical topology of alternating three-dimensional electron spheres and hole cubes, with their shadow contours manifesting the rhombohedral lattice distortion. This picture has been confirmed by one-step photoemission calculations including displacement of the apical oxygen atoms. The rhombohedral distortion is neutral to the Jahn-Teller effect and thus polaronic coupling, but affects the double-exchange electron hopping and thus the colossal magnetoresistance effect.

  1. Pair momentum distribution in Bi sub 2 Sr sub 2 CaCu sub 2 O sub 8+. delta. measured by positron annihilation: Existence and nature of the Fermi surface

    SciTech Connect

    Chan, L.P. ); Harshman, D.R. ); Lynn, K.G. ); Massidda, S. , PHB Ecublens, CH-105 Lausanne ); Mitzi, D.B. )

    1991-09-02

    We report the first measurement of the positron-electron momentum density in superconducting single-crystal Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}} ({ital T}{sub {ital c}}{approx}90 K). The observed anisotropy exhibits a twofold (rather than fourfold) symmetry, which is attributed to the superlattice modulation along the {ital b} axis of the BiO{sub 2} layers. Subtraction of the superlattice contribution also reveals a pair momentum distribution consistent with the CuO{sub 2} and BiO{sub 2} Fermi surfaces, and in reasonable agreement with the theoretical pair momentum density derived from band theory.

  2. Importance of the Fermi-surface topology to the superconducting state of the electron-doped pnictide Ba(Fe1-xCox)₂As₂

    DOE PAGESBeta

    Liu, Chang; Palczewski, A. D.; Dhaka, R. S.; Kondo, Takeshi; Fernandes, R. M.; Mun, E. D.; Hodovanets, H.; Thaler, A. N.; Schmalian, J.; Bud’ko, S. L.; et al

    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

  3. Photo-Induced Unpinning of Fermi Level in WO3

    PubMed Central

    Malagù, Cesare; Carotta, Maria C.; Comini, Elisabetta; Faglia, Guido; Giberti, Alessio; Guidi, Vincenzo; Maffeis, Thierry G.G.; Martinelli, Giuliano; Sberveglieri, Giorgio; Wilks, Steve P.

    2005-01-01

    Atomic force and high resolution scanning tunneling analyses were carried out on nanostructured WO3 films. It turned out that the band gap measured by scanning tunneling spectroscopy at surface is lower than the band gap reported in the literature. This effect is attributed to the high density of surface states in this material, which allows tunneling into these states. Such a high density of surface states pins the Fermi level resulting in modest surface activity at room temperature. Photo activation of WO3 results in unpinning of the Fermi level and thereby in higher chemical activity at surface.

  4. 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.

  5. Pairing, pseudogap and Fermi arcs in cuprates

    DOE PAGESBeta

    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 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

  6. GRB Studies with Fermi

    NASA Technical Reports Server (NTRS)

    Meegan, Charles A.

    2008-01-01

    This slide presentation reviews the studies of Gamma Ray Bursts (GRB) with the Fermi Gamma Ray Space Telescope. Included are pictures of the observatory, with illustrations of the Large Area Telescope (LAT), and the Gamma-ray Burst Monitor (GBM) including information about both their capabilities. Graphs showing the GBM count rate over time after the GBM trigger for three GRBs, preliminary charts showing the multiple detector light curves the spectroscopy of the main LAT peak and the spectral evolution of GRB 080916C Burst Temporally-extended LAT emission.

  7. Fermi surfaces and p -d hybridization in the diluted magnetic semiconductor Ba1 -xKx(Zn1-yMny) 2As2 studied by soft x-ray angle-resolved photoemission spectroscopy

    NASA Astrophysics Data System (ADS)

    Suzuki, H.; Zhao, G. Q.; Zhao, K.; Chen, B. J.; Horio, M.; Koshiishi, K.; Xu, J.; Kobayashi, M.; Minohara, M.; Sakai, E.; Horiba, K.; Kumigashira, H.; Gu, Bo; Maekawa, S.; Uemura, Y. J.; Jin, C. Q.; Fujimori, A.

    2015-12-01

    The electronic structure of the new diluted magnetic semiconductor Ba1-xKx(Zn1-yMny )2As2 (x =0.30 , y =0.15 ) in single crystal form has been investigated by angle-resolved photoemission spectroscopy (ARPES). Measurements with soft x rays clarify the host valence-band electronic structure primarily composed of the As 4 p states. Two hole pockets around the Γ point, a hole corrugated cylinder surrounding the Γ and Z points, and an electron pocket around the Z point are observed, and explain the metallic transport of Ba1-xKx(Zn1-yMny )2As2 . This is contrasted with Ga1-xMnxAs (GaMnAs), where it is located above the As 4 p valence-band maximum (VBM) and no Fermi surfaces have been clearly identified. Resonance soft x-ray ARPES measurements reveal a nondispersive (Kondo-resonance-like) Mn 3 d impurity band near the Fermi level, as in the case of GaMnAs. However, the impurity band is located well below the VBM, unlike the impurity band in GaMnAs, which is located around and above the VBM. We conclude that, while the strong hybridization between the Mn 3 d and the As 4 p orbitals plays an important role in creating the impurity band and inducing high temperature ferromagnetism in both systems, the metallic transport may predominantly occur in the host valence band in Ba1-xKx(Zn1-yMny )2As2 and in the impurity band in GaMnAs.

  8. Spiraling Fermi arcs in Weyl materials

    NASA Astrophysics Data System (ADS)

    Li, Songci; Andreev, Anton

    In Weyl materials the valence and conduction electron bands touch at an even number of isolated points in the Brillouin zone. In the vicinity of these points the electron dispersion is linear and may be described by the massless Dirac equation. This results in nontrivial topology of Berry connection curvature. One of its consequences is the existence of peculiar surface electron states whose Fermi surfaces form arcs connecting projections of the Weyl points onto the surface plane. Band bending near the boundary of the crystal also produces surface states. We show that in Weyl materials band bending near the crystal surface gives rise to spiral structure of energy surfaces of arc states. The corresponding Fermi surface has the shape of a spiral that winds about the projection of the Weyl point onto the surface plane. The direction of the winding is determined by the helicity of the Weyl point and the sign of the band bending potential. For close valleys arc state morphology may be understood in terms of avoided crossing of oppositely winding spirals. This work is supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences under Award Number DE-FG02-07ER46452.

  9. 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

  10. 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. PMID:25719510

  11. 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

  12. Absence of thermalization in a Fermi liquid

    NASA Astrophysics Data System (ADS)

    Maraga, Anna; Silva, Alessandro; Fabrizio, Michele

    2014-10-01

    We study a weak interaction quench in a three-dimensional Fermi gas. We first show that, under some general assumptions on time-dependent perturbation theory, the perturbative expansion of the long-wavelength structure factor S (q ) is not compatible with the hypothesis that steady-state averages correspond to thermal ones. In particular, S (q ) does develop an analytical component ˜const +O (q2) at q →0 , as implied by thermalization, but, in contrast, it maintains a nonanalytic part ˜|q | characteristic of a Fermi liquid at zero-temperature. In real space, this nonanalyticity corresponds to persisting power-law decaying density-density correlations, whereas thermalization would predict only an exponential decay. We next consider the case of a dilute gas, where one can obtain nonperturbative results in the interaction strength but at lowest order in the density. We find that in the steady state the momentum distribution jump at the Fermi surface remains finite, though smaller than in equilibrium, up to second order in kFf0 , where f0 is the scattering length of two particles in the vacuum. Both results question the emergence of a finite length scale in the quench dynamics as expected by thermalization.

  13. Pairing in a dry Fermi sea

    DOE PAGESBeta

    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, 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

  14. 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...

  15. The Fermi LAT Pulsars

    NASA Astrophysics Data System (ADS)

    Romani, Roger W.

    2011-08-01

    The Large Area Telescope on the Fermi satellite is an impressive pulsar discovery machine, with over 75 pulse detections and counting. The populations of radio-selected, γ-selected and millisecond pulsars are now large enough to display observational patterns in the light curves and luminosities. These patterns are starting to teach us about the physics of the emission zone, which seems dominated by open field lines near the speed of light cylinder. The sample also provides initial inferences about the pulsar population. Apparently a large fraction of neutron stars have a young energetic γ-ray emitting phase, making these objects a good probe of massive star evolution. The long-lived millisecond γ-ray pulsars are even more ubiquitous and may produce a significant fraction of the γ-ray background. In any event, it is clear that the present LAT pulsar sample is dominated by nearby objects, and there is every expectation that the number, and quality, of pulsar detections will increase in years to come.

  16. Quasiparticles and Fermi liquid behaviour in an organic metal

    PubMed Central

    Kiss, T.; Chainani, A.; Yamamoto, H.M.; Miyazaki, T.; Akimoto, T.; Shimojima, T.; Ishizaka, K.; Watanabe, S.; Chen, C.-T.; Fukaya, A.; Kato, R.; Shin, S.

    2012-01-01

    Many organic metals display exotic properties such as superconductivity, spin-charge separation and so on and have been described as quasi-one-dimensional Luttinger liquids. However, a genuine Fermi liquid behaviour with quasiparticles and Fermi surfaces have not been reported to date for any organic metal. Here, we report the experimental Fermi surface and band structure of an organic metal (BEDT-TTF)3Br(pBIB) obtained using angle-resolved photoelectron spectroscopy, and show its consistency with first-principles band structure calculations. Our results reveal a quasiparticle renormalization at low energy scales (effective mass m*=1.9 me) and ω2 dependence of the imaginary part of the self energy, limited by a kink at ~50 meV arising from coupling to molecular vibrations. The study unambiguously proves that (BEDT-TTF)3Br(pBIB) is a quasi-2D organic Fermi liquid with a Fermi surface consistent with Shubnikov-de Haas results. PMID:23011143

  17. Quantum Phase Transitions in a Bose-Fermi Mixture

    NASA Astrophysics Data System (ADS)

    Duchon, Eric; Zhang, Shizhong; Chang, Soon-Yong; Randeria, Mohit; Trivedi, Nandini

    2013-03-01

    Motivated by the recent experimental realization of stable Bose-Fermi mixtures with broad Feshbach resonances, we investigate possible quantum phases and phase transitions in this system using variational Monte Carlo. Within a single-channel model appropriate near broad Feshbach resonances, we show that as the boson-fermion coupling increases, the Bose-Einstein condensate disappears and the atomic Fermi surface is destroyed while the Fermi surface of the composite molecules emerges. We calculate the momentum distribution of atomic and molecular fermions and demonstrate that the atomic fermion's quasi-particle weight Z vanishes at a critical coupling. We would like to acknowledge support from NSF DMR-0907275 (E.D., N.T.) and NSF DMR-1006532 (M.R.).

  18. Strongly Interacting Fermi and Bose-Fermi Gases

    NASA Astrophysics Data System (ADS)

    Lee, Ye-Ryoung; Choi, Jae; Christensen, Caleb; Jo, Gyu-Boong; Wang, Tout; Ketterle, Wolfgang; Pritchard, David

    2010-03-01

    We present our recent progress on the study ultracold gases of ^6Li and ^23Na near homonuclear and heteronuclear Feshbach resonances. We discuss new experimental and theoretical developments on itinerant ferromagnetism in a Fermi gas of ultracold atoms [1]. We also report on ultracold gases of ^6Li and ^23Na, including fermionic LiNa molecules. [4pt] [1] G.-B. Jo, Y.-R. Lee, J.-H. Choi, C.A. Christensen, T.H. Kim, J.H. Thywissen, D.E. Pritchard, and W. Ketterle, Observation of itinerant ferromagnetism in a strongly interacting Fermi gas of ultracold atoms, Science 325, 1521 (2009).

  19. Strongly Interacting Homogeneous Fermi Gases

    NASA Astrophysics Data System (ADS)

    Mukherjee, Biswaroop; Patel, Parth; Yan, Zhenjie; Struck, Julian; Zwierlein, Martin

    2016-05-01

    We present a homogeneous box potential for strongly interacting Fermi gases. The local density approximation (LDA) allows measurements on traditional inhomogeneous traps to observe a continuous distribution of Fermi gases in a single shot, but also suffer from a broadened response due to line-of-sight averaging over varying densities. We trap ultracold Fermionic (6 Li) in an optical homogeneous potential and characterize its flatness through in-situ tomography. A hybrid approach combining a cylindrical optical potential with a harmonic magnetic trap allows us to exploit the LDA and measure local RF spectra without requiring significant image reconstruction. We extract various quantities from the RF spectra such as the Tan's contact, and discuss further measurements of homogeneous Fermi systems under spin imbalance and finite temperature.

  20. 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.

  1. 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...

  2. Spin-Orbit Coupled Fermi Gases across a Feshbach Resonance

    NASA Astrophysics Data System (ADS)

    Yu, Zeng-Qiang; Zhai, Hui

    2011-11-01

    In this Letter we study both ground state properties and the superfluid transition temperature of a spin-1/2 Fermi gas across a Feshbach resonance with a synthetic spin-orbit coupling, using the mean-field theory and the exact solution of two-body problem. We show that a strong spin-orbit coupling can significantly enhance the pairing gap for negative scattering length as, due to increased density of state at Fermi surface. Strong spin-orbit coupling can also significantly enhance the superfluid transition temperature Tc to a sizable fraction of Fermi temperature when as≲0, while it suppresses Tc slightly for positive as. The interaction energy and pair size at resonance are also discussed.

  3. Fermi GBM Early Trigger Characteristics

    SciTech Connect

    Connaughton, Valerie; Briggs, Michael; Paciesas, Bill; Meegan, Charles

    2009-05-25

    Since the launch of the Fermi observatory on June 11 2008, the Gamma-ray Burst Monitor (GBM) has seen approximately 250 triggers of which about 150 were cosmic gamma-ray bursts (GRBs). GBM operates dozens of trigger algorithms covering various energy bands and timescales and is therefore sensitive to a wide variety of phenomena, both astrophysical and not.

  4. 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...

  5. 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.

  6. Fermi, Enrico (1901-54)

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    Italian physicist, created the first controlled chain reaction, founded Argonne National Laboratory. His work on the properties of electrons (spin-half particles like electrons are called fermions after him, and the study of their properties is called Fermi-Dirac statistics) enabled the pressure source in white dwarf stars to be identified, and white dwarf star properties to be calculated by CHAN...

  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. Lectures of Fermi liquid theory

    SciTech Connect

    Bedell, K.S.

    1993-01-01

    The Fermi liquid theory was first introduced by Landau in 1956 to provide a theoretical basis for the properties of strongly correlated Fermi systems. This theory has proven to be crucial for our understanding of a broad range of materials. These include liquid [sup 3]He, [sup 3]He-[sup 4]He mixtures, simple metals, heavy-fermions, and nuclear matter to name a few. In the high temperature superconductors questions have been raised regarding the applicability of Fermi liquid theory to the normal state behavior of these materials. I will not address this issue in these lectures. My focus will be to summarize the foundations of this theory and to explore the consequences. These lectures are in part a summary of the excellent review article by Baym and Pethick and the books by Pines and Nozieres and Baym and Pethick. They include as well a summary of some articles that I have authored and co-authored. In the main body of the lectures I will not make any additional references to the books or articles. In the absence of reading the original materials, my lectures should provide the essentials of a mini-course in Fermi liquid theory.

  9. Lectures of Fermi liquid theory

    SciTech Connect

    Bedell, K.S.

    1993-07-01

    The Fermi liquid theory was first introduced by Landau in 1956 to provide a theoretical basis for the properties of strongly correlated Fermi systems. This theory has proven to be crucial for our understanding of a broad range of materials. These include liquid {sup 3}He, {sup 3}He-{sup 4}He mixtures, simple metals, heavy-fermions, and nuclear matter to name a few. In the high temperature superconductors questions have been raised regarding the applicability of Fermi liquid theory to the normal state behavior of these materials. I will not address this issue in these lectures. My focus will be to summarize the foundations of this theory and to explore the consequences. These lectures are in part a summary of the excellent review article by Baym and Pethick and the books by Pines and Nozieres and Baym and Pethick. They include as well a summary of some articles that I have authored and co-authored. In the main body of the lectures I will not make any additional references to the books or articles. In the absence of reading the original materials, my lectures should provide the essentials of a mini-course in Fermi liquid theory.

  10. Fermi level influence on the adsorption at semiconductor surfaces—ab initio simulations

    NASA Astrophysics Data System (ADS)

    Krukowski, Stanisław; Kempisty, Paweł; Strąk, Paweł

    2013-08-01

    Chemical adsorption of the species at semiconductor surfaces is analyzed showing the existence of the two contributions to adsorption energy: bond creation and charge transfer. It is shown that the energy of quantum surface states is affected by the electric field at the surface, nevertheless, the potential contribution of electron and nuclei cancels out. The charge transfer contribution is Fermi level independent for pinned surfaces. Thus for Fermi level pinned at the surface, the adsorption energy is independent on the Fermi energy, i.e., the doping in the bulk. The DFT simulations of adsorption of hydrogen at clean GaN(0001) and silicon at SiC(0001) surfaces confirmed independence of adsorption energy on the doping in the bulk. For the Fermi level nonpinned surfaces, the charge contribution depends on the position of Fermi level in the bulk. Thus adsorption energy is sensitive to change of the Fermi energy in the bulk, i.e., the doping. The DFT simulations of adsorption of atomic hydrogen at 0.75 ML hydrogen covered GaN(0001) surface confirmed that the adsorption energy may be changed by about 2 eV by the doping change from n- to p-type.

  11. Nonanalytic Magnetic Response of Fermi- and non-Fermi Liquids

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey; Maslov, Dmitrii; Saha, Ronojoy

    2007-03-01

    We revisit the issue of the non-analytic dependence of the static spin susceptibility of a 2D Fermi liquid on temperature and a magnetic field, χs(T, H) = χ0+ A T fχ(μB|H|/T). We show that in a generic Fermi liquid the prefactor A is expressed via complex combinations of the Landau parameters, and does not reduce to the backscattering amplitude, contrary to the case of the specific heat C(T, H). We show that this distinction with the specific heat is mostly relevant near a ferromagnetic QCP -- the non-analytic terms in χs(T,H) are less singular near QCP than those in C(T, H).

  12. 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.

  13. Equal variations of the Fermi level and work function in graphene at the nanoscale.

    PubMed

    Samaddar, Sayanti; Coraux, Johann; Martin, Sylvain C; Grévin, Benjamin; Courtois, Hervé; Winkelmann, Clemens B

    2016-08-18

    If surface effects are neglected, any change of the Fermi level in a semiconductor is expected to result in an equal and opposite change of the work function. However, this is in general not observed in three-dimensional semiconductors, because of Fermi level pinning at the surface. By combining Kelvin probe force microscopy and scanning tunneling spectroscopy on single layer graphene, we measure both the local work function and the charge carrier density. The one-to-one equivalence of changes in the Fermi level and the work function is demonstrated to accurately hold in single layer graphene down to the nanometer scale. PMID:27503569

  14. Adaptation of the Landau-Migdal quasiparticle pattern to strongly correlated Fermi systems

    SciTech Connect

    Khodel, V. A.; Clark, J. W.; Zverev, M. V.

    2011-09-15

    A quasiparticle pattern advanced in Landau's first article on Fermi-liquid theory is adapted to elucidate the properties of a class of strongly correlated Fermi systems characterized by a Lifshitz phase diagram featuring a quantum critical point (QCP) where the density of states diverges. The necessary condition for stability of the Landau Fermi-Liquid state is shown to break down in such systems, triggering a cascade of topological phase transitions that lead, without symmetry violation, to states with multi-connected Fermi surfaces. The end point of this evolution is found to be an exceptional state whose spectrum of single-particle excitations exhibits a completely flat portion at zero temperature. Analysis of the evolution of the temperature dependence of the single-particle spectrum yields results that provide a natural explanation of classical behavior of this class of Fermi systems in the QCP region.

  15. Fermi level stabilization energy in group III-nitrides

    SciTech Connect

    Li, S.X.; Yu, K.M.; Wu, J.; Jones, R.E.; Walukiewicz, W.; AgerIII, J.W.; Shan, W.; Haller, E.E.; Lu, Hai; Schaff, William J.

    2005-01-07

    Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi Stabilization Energy (E{sub FS}), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E{sub FS} is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.

  16. Fermi-level stabilization energy in group III nitrides

    SciTech Connect

    Li, S.X.; Jones, R.E.; Haller, E.E.; Yu, K.M.; Wu, J.; Walukiewicz, W.; Ager, J.W. III; Shan, W.; Lu Hai; Schaff, William J.

    2005-04-15

    Energetic particle irradiation is used to systematically introduce point defects into In{sub 1-x}Ga{sub x}N alloys over the entire composition range. Three types of energetic particles (electrons, protons, and {sup 4}He{sup +}) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi stabilization energy (E{sub FS}), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E{sub FS} is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.

  17. Fermi resonance in optical microcavities

    NASA Astrophysics Data System (ADS)

    Yi, Chang-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min

    2015-04-01

    Fermi resonance is a phenomenon of quantum mechanical superposition, which most often occurs between normal and overtone modes in molecular systems that are nearly coincident in energy. We find that scarred resonances in deformed dielectric microcavities are the very phenomenon of Fermi resonance, that is, a pair of quasinormal modes interact with each other due to coupling and a pair of resonances are generated through an avoided resonance crossing. Then the quantum number difference of a pair of quasinormal modes, which is a consequence of quantum mechanical superposition, equals periodic orbits, whereby the resonances are localized on the periodic orbits. We derive the relation between the quantum number difference and the periodic orbits and confirm it in an elliptic, a rectangular, and a stadium-shaped dielectric microcavity.

  18. Enrico Fermi and the Dolomites

    NASA Astrophysics Data System (ADS)

    Battimelli, Giovanni; de Angelis, Alessandro

    2014-11-01

    Summer vacations in the Dolomites were a tradition among the professors of the Faculty of Mathematical and Physical Sciences at the University of Roma since the end of the XIX century. Beyond the academic walls, people like Tullio Levi-Civita, Federigo Enriques and Ugo Amaldi sr., together with their families, were meeting friends and colleagues in Cortina, San Vito, Dobbiaco, Vigo di Fassa and Selva, enjoying trekking together with scientific discussions. The tradition was transmitted to the next generations, in particular in the first half of the XX century, and the group of via Panisperna was directly connected: Edoardo Amaldi, the son of the mathematician Ugo sr., rented at least during two summers, in 1925 and in 1949, and in the winter of 1960, a house in San Vito di Cadore, and almost every year in the Dolomites; Enrico Fermi was a frequent guest. Many important steps in modern physics, in particular the development of the Fermi-Dirac statistics and the Fermi theory of beta decay, are related to scientific discussions held in the region of the Dolomites.

  19. Fermi Timing and Synchronization System

    SciTech Connect

    Wilcox, R.; Staples, J.; Doolittle, L.; Byrd, J.; Ratti, A.; Kaertner, F.X.; Kim, J.; Chen, J.; Ilday, F.O.; Ludwig, F.; Winter, A.; Ferianis, M.; Danailov, M.; D'Auria, G.

    2006-07-19

    The Fermi FEL will depend critically on precise timing of its RF, laser and diagnostic subsystems. The timing subsystem to coordinate these functions will need to reliably maintain sub-100fs synchronicity between distant points up to 300m apart in the Fermi facility. The technology to do this is not commercially available, and has not been experimentally demonstrated in a working facility. Therefore, new technology must be developed to meet these needs. Two approaches have been researched by different groups working with the Fermi staff. At MIT, a pulse transmission scheme has been developed for synchronization of RF and laser devices. And at LBL, a CW transmission scheme has been developed for RF and laser synchronization. These respective schemes have advantages and disadvantages that will become better understood in coming years. This document presents the work done by both teams, and suggests a possible system design which integrates them both. The integrated system design provides an example of how choices can be made between the different approaches without significantly changing the basic infrastructure of the system. Overall system issues common to any synchronization scheme are also discussed.

  20. Roles of zeros of the Green function in Fermi arc and non-Fermi liquid in the two-dimensional Hubbard model

    NASA Astrophysics Data System (ADS)

    Sakai, Shiro; Motome, Yukitoshi; Imada, Masatoshi

    2009-10-01

    We clarify effects of zeros of the Green function on a Fermi arc and on a non-Fermi liquid behavior in the two-dimensional Hubbard model by means of the cellular dynamical mean-field theory (CDMFT). We study in detail the state with a hole-pocket Fermi surface and zeros of the Green function, which was found for a slightly doped Mott insulator in an earlier CDMFT calculation [T.D. Stanescu, G. Kotliar, Phys. Rev. B 74 (2006) 125110; T.D. Stanescu, M. Civelli, K. Haule, G. Kotliar, Ann. Phys. (N.Y.) 321 (2006) 1682]. As thermal or other extrinsic scatterings of electrons broaden the zeros, regions around the zero surface gain an imaginary part of the self-energy, which strongly suppresses the spectral intensity, especially on the closer side of the hole pocket to the zero surface. Then the rest emerges as a Fermi arc. Quasiparticle weight becomes ill defined on the closer side of the Fermi pocket while it is well defined on the opposite side, which means that a differentiation of electrons occurs in the momentum space, indicating an emergence of a non-Fermi liquid phase.

  1. Nodal to nodeless superconducting energy-gap structure change concomitant with Fermi-surface reconstruction in the heavy-fermion compound CeCoIn5

    SciTech Connect

    Kim, Hyunsoo; Tanatar, M. A.; Flint, R.; Petrovic, C.; Hu, Rongwei; White, B. D.; Lum, I. K.; Maple, M. B.; Prozorov, 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 leads 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.

  2. Bioterrorism and the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Cooper, Joshua

    2013-04-01

    We proffer a contemporary solution to the so-called Fermi Paradox, which is concerned with conflict between Copernicanism and the apparent paucity of evidence for intelligent alien civilizations. In particular, we argue that every community of organisms that reaches its space-faring age will (1) almost immediately use its rocket-building computers to reverse-engineer its genetic chemistry and (2) self-destruct when some individual uses said technology to design an omnicidal pathogen. We discuss some of the possible approaches to prevention with regard to Homo sapiens' vulnerability to bioterrorism, particularly on a short-term basis.

  3. Generalized second-order Thomas-Fermi method for superfluid Fermi systems

    NASA Astrophysics Data System (ADS)

    Pei, J. C.; Fei, Na; Zhang, Y. N.; Schuck, P.

    2015-12-01

    Using the ℏ expansion of the Green's function of the Hartree-Fock-Bogoliubov equation, we extend the second-order Thomas-Fermi approximation to generalized superfluid Fermi systems by including the density-dependent effective mass and the spin-orbit potential. We first implement and examine the full correction terms over different energy intervals of the quasiparticle spectra in calculations of finite nuclei. Final applications of this generalized Thomas-Fermi method are intended for various inhomogeneous superfluid Fermi systems.

  4. Fermi level pinning at the Ge(001) surface—A case for non-standard explanation

    SciTech Connect

    Wojtaszek, Mateusz; Zuzak, Rafal; Godlewski, Szymon; Kolmer, Marek; Lis, Jakub Such, Bartosz; Szymonski, Marek

    2015-11-14

    To explore the origin of the Fermi level pinning in germanium, we investigate the Ge(001) and Ge(001):H surfaces. The absence of relevant surface states in the case of Ge(001):H should unpin the surface Fermi level. This is not observed. For samples with donors as majority dopants, the surface Fermi level appears close to the top of the valence band regardless of the surface structure. Surprisingly, for the passivated surface, it is located below the top of the valence band allowing scanning tunneling microscopy imaging within the band gap. We argue that the well known electronic mechanism behind band bending does not apply and a more complicated scenario involving ionic degrees of freedom is therefore necessary. Experimental techniques involve four point probe electric current measurements, scanning tunneling microscopy, and spectroscopy.

  5. Holographic Fermi liquids in a spontaneously generated lattice

    NASA Astrophysics Data System (ADS)

    Alsup, James; Papantonopoulos, Eleftherios; Siopsis, George; Yeter, Kubra

    2016-05-01

    We discuss fermions in a spontaneously generated holographic lattice background. The lattice structure at the boundary is generated by introducing a higher-derivative interaction term between a U (1 ) gauge field and a scalar field. We solve the equations of motion below the critical temperature at which the lattice forms and analyze the change in the Fermi surface due to the lattice. The fermion band structure is found to exhibit a gap due to lattice effects.

  6. Fermi liquids near Pomeranchuk instabilities

    NASA Astrophysics Data System (ADS)

    Reidy, Kelly Elizabeth

    We explore features of a Fermi liquid near generalized Pomeranchuk instabilities (PIs) starting from both ordered and disordered phases. These PIs can be viewed as quantum critical points in parameter space, and thus provide an alternate viewpoint on quantum criticality. We employ the tractable crossing symmetric equation method, which is a non-perturbative diagrammatic many-particle method used to calculate the Fermi liquid interaction functions and scattering amplitudes. We consider both repulsive and attractive underlying interactions of arbitrary strength. Starting from a ferromagnetically ordered ground state, we find that upon approach to an s-wave instability in one critical channel, the system simultaneously approaches instabilities in non-critical channels. We study origins and implications of this "quantum multicriticality". We also find that a nematic (non-s-wave) instability precedes and is driven by Pomeranchuk instabilities in both the s-wave spin and density channels. Finally, we discuss potential applications of our results to physical systems, such as ferromagnetic superconductors.

  7. Observation of Weyl nodes and Fermi arcs in tantalum phosphide

    PubMed Central

    Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.

    2016-01-01

    A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910

  8. Charge distribution and Fermi level in bimetallic nanoparticles.

    PubMed

    Holmberg, Nico; Laasonen, Kari; Peljo, Pekka

    2016-01-28

    Upon metal-metal contact, a transfer of electrons will occur between the metals until the Fermi levels in both phases are equal, resulting in a net charge difference across the metal-metal interface. Here, we have examined this contact electrification in bimetallic model systems composed of mixed Au-Ag nanoparticles containing ca. 600 atoms using density functional theory calculations. We present a new model to explain this charge transfer by considering the bimetallic system as a nanocapacitor with a potential difference equal to the work function difference, and with most of the transferred charge located directly at the contact interface. Identical results were obtained by considering surface contacts as well as by employing a continuum model, confirming that this model is general and can be applied to any multimetallic structure regardless of geometry or size (going from nano- to macroscale). Furthermore, the equilibrium Fermi level was found to be strongly dependent on the surface coverage of different metals, enabling the construction of scaling relations. We believe that the charge transfer due to Fermi level equilibration has a profound effect on the catalytic, electrocatalytic and other properties of bimetallic particles. Additionally, bimetallic nanoparticles are expected to have very interesting self-assembly for large superstructures due to the surface charge anisotropy between the two metals. PMID:26788999

  9. Criteria for Directly Detecting Topological Fermi Arcs in Weyl Semimetals.

    PubMed

    Belopolski, Ilya; Xu, Su-Yang; Sanchez, Daniel S; Chang, Guoqing; Guo, Cheng; Neupane, Madhab; Zheng, Hao; Lee, Chi-Cheng; Huang, Shin-Ming; Bian, Guang; Alidoust, Nasser; Chang, Tay-Rong; Wang, BaoKai; Zhang, Xiao; Bansil, Arun; Jeng, Horng-Tay; Lin, Hsin; Jia, Shuang; Hasan, M Zahid

    2016-02-12

    The recent discovery of the first Weyl semimetal in TaAs provides the first observation of a Weyl fermion in nature and demonstrates a novel type of anomalous surface state, the Fermi arc. Like topological insulators, the bulk topological invariants of a Weyl semimetal are uniquely fixed by the surface states of a bulk sample. Here we present a set of distinct conditions, accessible by angle-resolved photoemission spectroscopy (ARPES), each of which demonstrates topological Fermi arcs in a surface state band structure, with minimal reliance on calculation. We apply these results to TaAs and NbP. For the first time, we rigorously demonstrate a nonzero Chern number in TaAs by counting chiral edge modes on a closed loop. We further show that it is unreasonable to directly observe Fermi arcs in NbP by ARPES within available experimental resolution and spectral linewidth. Our results are general and apply to any new material to demonstrate a Weyl semimetal. PMID:26919005

  10. Observation of Weyl nodes and Fermi arcs in tantalum phosphide

    NASA Astrophysics Data System (ADS)

    Xu, N.; Weng, H. M.; Lv, B. Q.; Matt, C. E.; Park, J.; Bisti, F.; Strocov, V. N.; Gawryluk, D.; Pomjakushina, E.; Conder, K.; Plumb, N. C.; Radovic, M.; Autès, G.; Yazyev, O. V.; Fang, Z.; Dai, X.; Qian, T.; Mesot, J.; Ding, H.; Shi, M.

    2016-03-01

    A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs.

  11. Observation of Weyl nodes and Fermi arcs in tantalum phosphide.

    PubMed

    Xu, N; Weng, H M; Lv, B Q; Matt, C E; Park, J; Bisti, F; Strocov, V N; Gawryluk, D; Pomjakushina, E; Conder, K; Plumb, N C; Radovic, M; Autès, G; Yazyev, O V; Fang, Z; Dai, X; Qian, T; Mesot, J; Ding, H; Shi, M

    2016-01-01

    A Weyl semimetal possesses spin-polarized band-crossings, called Weyl nodes, connected by topological surface arcs. The low-energy excitations near the crossing points behave the same as massless Weyl fermions, leading to exotic properties like chiral anomaly. To have the transport properties dominated by Weyl fermions, Weyl nodes need to locate nearly at the chemical potential and enclosed by pairs of individual Fermi surfaces with non-zero Fermi Chern numbers. Combining angle-resolved photoemission spectroscopy and first-principles calculation, here we show that TaP is a Weyl semimetal with only a single type of Weyl fermions, topologically distinguished from TaAs where two types of Weyl fermions contribute to the low-energy physical properties. The simple Weyl fermions in TaP are not only of fundamental interests but also of great potential for future applications. Fermi arcs on the Ta-terminated surface are observed, which appear in a different pattern from that on the As-termination in TaAs and NbAs. PMID:26983910

  12. Quantum statistical foundation to the Fermi liquid model and Ginzburg-Landau wave function

    SciTech Connect

    Fujita, Shigeji; Godoy, S. )

    1993-12-01

    An energy eigenvalue equation for a quasi-particle is derived, starting with the Heisenberg equation of motion for an annihilation operator. An elementary derivation of the Fermi liquid model having a sharply defined Fermi surface in the k-space is given, starting with a realistic model of a metal including the Coulomb interaction among and between electrons and lattice-ions. The Ginzburg-Landau wave function [Psi][sub [sigma

  13. Entanglement Entropy of Fermi Liquids via Multidimensional Bosonization

    NASA Astrophysics Data System (ADS)

    Ding, Wenxin; Seidel, Alexander; Yang, Kun

    2012-01-01

    The logarithmic violations of the area law, i.e., an “area law” with logarithmic correction of the form S˜Ld-1log⁡L, for entanglement entropy are found in both 1D gapless fermionic systems with Fermi points and high-dimensional free fermions. This paper shows that both violations are of the same origin, and that, in the presence of Fermi-liquid interactions, such behavior persists for 2D fermion systems. In this paper, we first consider the entanglement entropy of a toy model, namely, a set of decoupled 1D chains of free spinless fermions, to relate both violations in an intuitive way. We then use multidimensional bosonization to rederive the formula by Gioev and Klich [D. Gioev and I. Klich, Entanglement Entropy of Fermions in Any Dimension and the Widom Conjecture, Phys. Rev. Lett.PRLTAO0031-9007 96, 100503 (2006).10.1103/PhysRevLett.96.100503] for free fermions through a low-energy effective Hamiltonian and explicitly show that, in both cases, the logarithmic corrections to the area law share the same origin: the discontinuity at the Fermi surface (points). In the presence of Fermi-liquid (forward-scattering) interactions, the bosonized theory remains quadratic in terms of the original local degrees of freedom, and, after regularizing the theory with a mass term, we are able to calculate the entanglement entropy perturbatively up to second order in powers of the coupling parameter for a special geometry via the replica trick. We show that these interactions do not change the leading scaling behavior for the entanglement entropy of a Fermi liquid. At higher orders, we argue that this should remain true through a scaling analysis.

  14. 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.

  15. Nonanalytic corrections to the specific heat and susceptibility of a two-dimensional Fermi liquid without Galilean invariance

    NASA Astrophysics Data System (ADS)

    Chubukov, Andrey V.; Millis, Andrew J.

    2006-09-01

    We consider the leading nonanalytic temperature dependence of the specific heat and temperature and momentum dependence of the spin susceptibility for two-dimensional fermionic systems with noncircular Fermi surfaces. We demonstrate the crucial role played by Fermi surface curvature. For a Fermi surface with inflection points, we demonstrate that thermal corrections to the uniform susceptibility in D=2 change from χs∝T to χs∝T2/3 for generic inflection points and to χs∝T1/2 for special inflection points along symmetry directions. Errors in previous work are corrected. An application of the results to Sr2RuO4 is given.

  16. Nonanalytic magnetic response of Fermi and non-Fermi liquids

    NASA Astrophysics Data System (ADS)

    Maslov, Dmitrii L.; Chubukov, Andrey V.; Saha, Ronojoy

    2006-12-01

    We study the nonanalytic behavior of the static spin susceptibility of two-dimensional fermions as a function of temperature and magnetic field. For a generic Fermi liquid, χs(T,H)=const+c1max{T,μB∣H∣} , where c1 is shown to be expressed via complicated combinations of the Landau parameters, rather than via the backscattering amplitude, contrary to the case of the specific heat. Near a ferromagnetic quantum critical point, the field dependence acquires a universal form χs-1(H)=const-c2∣H∣3/2 , with c2>0 . This behavior implies a first-order transition into a ferromagnetic state. We establish a criterion for such a transition to win over the transition into an incommensurate phase.

  17. The Nuclear Thomas-Fermi Model

    DOE R&D Accomplishments Database

    Myers, W. D.; Swiatecki, W. J.

    1994-08-01

    The statistical Thomas-Fermi model is applied to a comprehensive survey of macroscopic nuclear properties. The model uses a Seyler-Blanchard effective nucleon-nucleon interaction, generalized by the addition of one momentum-dependent and one density-dependent term. The adjustable parameters of the interaction were fitted to shell-corrected masses of 1654 nuclei, to the diffuseness of the nuclear surface and to the measured depths of the optical model potential. With these parameters nuclear sizes are well reproduced, and only relatively minor deviations between measured and calculated fission barriers of 36 nuclei are found. The model determines the principal bulk and surface properties of nuclear matter and provides estimates for the more subtle, Droplet Model, properties. The predicted energy vs density relation for neutron matter is in striking correspondence with the 1981 theoretical estimate of Friedman and Pandharipande. Other extreme situations to which the model is applied are a study of Sn isotopes from {sup 82}Sn to {sup 170}Sn, and the rupture into a bubble configuration of a nucleus (constrained to spherical symmetry) which takes place when Z{sup 2}/A exceeds about 100.

  18. Optical klystron SASE at FERMI

    NASA Astrophysics Data System (ADS)

    Penco, G.; Allaria, E. M.; De Ninno, G.; Ferrari, E.; Giannessi, L.

    2015-05-01

    The optical klystron enhancement to a self-amplified spontaneous emission (SASE) free electron laser (FEL) has been deeply studied in theory and in simulations. In this FEL scheme, a relativistic electron beam passes through two undulators, separated by a dispersive section. The latter converts the electron-beam energy modulation produced in the first undulator in density modulation, thus enhancing the free-electron laser gain. We report the first experiment that has been carried out at the FERMI facility in Trieste, of enhancement to a SASE FEL by using the optical klystron scheme. XUV photons have been produced with an intensity several orders of magnitude larger than in pure SASE mode. The impact of the uncorrelated energy spread of the electron beam on the optical klystron SASE performance has been also investigated.

  19. Origin of dissipative Fermi arc transport in Weyl semimetals

    NASA Astrophysics Data System (ADS)

    Gorbar, E. V.; Miransky, V. A.; Shovkovy, I. A.; Sukhachov, P. O.

    2016-06-01

    By making use of a low-energy effective model of Weyl semimetals, we show that the Fermi arc transport is dissipative. The origin of the dissipation is the scattering of the surface Fermi arc states into the bulk of the semimetal. It is noticeable that the corresponding scattering rate is nonzero and can be estimated even in a perturbative theory, although in general the reliable calculations of transport properties necessitate a nonperturbative approach. Nondecoupling of the surface and bulk sectors in the low-energy theory of Weyl semimetals invalidates the usual argument of a nondissipative transport due to one-dimensional arc states. This property of Weyl semimetals is in drastic contrast to that of topological insulators, where the decoupling is protected by a gap in the bulk. Within the framework of the linear response theory, we obtain an approximate result for the conductivity due to the Fermi arc states and analyze its dependence on chemical potential, temperature, and other parameters of the model.

  20. Fermi gamma-ray "bubbles" from stochastic acceleration of electrons.

    PubMed

    Mertsch, Philipp; Sarkar, Subir

    2011-08-26

    Gamma-ray data from Fermi Large Area Telescope reveal a bilobular structure extending up to ∼50° above and below the Galactic Center. It has been argued that the gamma rays arise from hadronic interactions of high-energy cosmic rays which are advected out by a strong wind, or from inverse-Compton scattering of relativistic electrons accelerated at plasma shocks present in the bubbles. We explore the alternative possibility that the relativistic electrons are undergoing stochastic 2nd-order Fermi acceleration by plasma wave turbulence through the entire volume of the bubbles. The observed gamma-ray spectral shape is then explained naturally by the resulting hard electron spectrum modulated by inverse-Compton energy losses. Rather than a constant volume emissivity as in other models, we predict a nearly constant surface brightness, and reproduce the observed sharp edges of the bubbles. PMID:21929220

  1. Holographic non-Fermi liquid in a background magnetic field

    NASA Astrophysics Data System (ADS)

    Basu, Pallab; He, Jianyang; Mukherjee, Anindya; Shieh, Hsien-Hang

    2010-08-01

    We study the effects of a nonzero magnetic field on a class of 2+1 dimensional non-Fermi liquids, recently found in [Hong Liu, John McGreevy, and David Vegh, arXiv:0903.2477.] by considering properties of a Fermionic probe in an extremal AdS4 black hole background. Introducing a similar fermionic probe in a dyonic AdS4 black hole geometry, we find that the effect of a magnetic field could be incorporated in a rescaling of the probe fermion’s charge. From this simple fact, we observe interesting effects like gradual disappearance of the Fermi surface and quasiparticle peaks at large magnetic fields and changes in other properties of the system. We also find Landau level like structures and oscillatory phenomena similar to the de-Haas-van Alphen effect.

  2. Self-capacitance of a Thomas--Fermi nanosphere

    SciTech Connect

    Krcmar, Maja; Saslow, Wayne M.; Zangwill, Andrew

    2000-12-04

    We calculate the self-capacitance and charging energy of a spherical nanoparticle in the Thomas--Fermi approximation. The result is C{sub TF}=C{sub 0}[1-p{sup -1}tanhp]/[1-(1-{epsilon}{sup -1})p{sup -1}tanhp], with C{sub TF}{>=}C{sub 0}. Here C{sub 0}=4{pi}{epsilon}{sub 0}R is the classical geometrical value, p=R/l is the ratio of the particle radius R to the Thomas--Fermi screening length l, and {epsilon} is the material dielectric constant. The addition of surface localized states drives C toward C{sub 0}. These results should be relevant to tunneling spectroscopy studies of giant carbon onions and ''large'' semiconductor nanocrystals that do not require a full quantum treatment.

  3. Formation of Gapless Fermi Arcs and Fingerprints of Order in the Pseudogap State of Cuprate Superconductors

    SciTech Connect

    Kondo, Takeshi; Palczewski, Ari D.; Hamaya, Yoichiro; Takeuchi, Tsunehiro; Wen, J. S.; Gu, Genda; Kaminski, Adam

    2013-10-11

    We use angle-resolved photoemission spectroscopy and a new quantitative approach based on the partial density of states to study properties of seemingly disconnected portions of the Fermi surface (FS) that are present in the pseudogap state of cuprates called Fermi arcs. We find that the normal state FS collapses very abruptly into Fermi arcs at the pseudogap temperature (T∗). Surprisingly, the length of the Fermi arcs remains constant over an extended temperature range between T∗ and Tpair, consistent with the presence of an ordered state below T∗. These arcs collapse again at the temperature below which pair formation occurs (Tpair) either to a point or a very short arc, whose length is limited by our experimental resolution. The tips of the arcs span between points defining a set of wave vectors in momentum space, which are the fingerprints of the ordered state that causes the pseudogap.

  4. Formation of Gapless Fermi Arcs and Fingerprints of Order in the Pseudogap State of Cuprate Superconductors

    SciTech Connect

    Kondo, Takeshi; Palczewski, Ari; Hamaya, Yoichiro; Takeuchi, Tsunehiro; Wen, J. S.; Xu, Z. J.; Gu, Genda; Kaminski, Adam

    2013-10-08

    We use angle-resolved photoemission spectroscopy and a new quantitative approach based on the partial density of states to study properties of seemingly disconnected portions of the Fermi surface (FS) that are present in the pseudogap state of cuprates called Fermi arcs. We find that the normal state FS collapses very abruptly into Fermi arcs at the pseudogap temperature (T*). Surprisingly, the length of the Fermi arcs remains constant over an extended temperature range between (T*) and Tpair, consistent with the presence of an ordered state below T*. These arcs collapse again at the temperature below which pair formation occurs (Tpair) either to a point or a very short arc, whose length is limited by our experimental resolution. The tips of the arcs span between points defining a set of wave vectors in momentum space, which are the fingerprints of the ordered state that causes the pseudogap.

  5. Emergence of a Metallic Quantum Solid Phase in a Rydberg-Dressed Fermi Gas

    NASA Astrophysics Data System (ADS)

    Li, Wei-Han; Hsieh, Tzu-Chi; Mou, Chung-Yu; Wang, Daw-Wei

    2016-07-01

    We examine possible low-temperature phases of a repulsively Rydberg-dressed Fermi gas in a three-dimensional free space. It is shown that the collective density excitations develop a roton minimum, which is softened at a wave vector smaller than the Fermi wave vector when the particle density is above a critical value. The mean field calculation shows that, unlike the insulating density wave states often observed in conventional condensed matters, a self-assembled metallic density wave state emerges at low temperatures. In particular, the density wave state supports a Fermi surface and a body-centered-cubic crystal order at the same time with the estimated critical temperature being about one tenth of the noninteracting Fermi energy. Our results suggest the emergence of a fermionic quantum solid that should be observable in the current experimental setup.

  6. Emergence of a Metallic Quantum Solid Phase in a Rydberg-Dressed Fermi Gas.

    PubMed

    Li, Wei-Han; Hsieh, Tzu-Chi; Mou, Chung-Yu; Wang, Daw-Wei

    2016-07-15

    We examine possible low-temperature phases of a repulsively Rydberg-dressed Fermi gas in a three-dimensional free space. It is shown that the collective density excitations develop a roton minimum, which is softened at a wave vector smaller than the Fermi wave vector when the particle density is above a critical value. The mean field calculation shows that, unlike the insulating density wave states often observed in conventional condensed matters, a self-assembled metallic density wave state emerges at low temperatures. In particular, the density wave state supports a Fermi surface and a body-centered-cubic crystal order at the same time with the estimated critical temperature being about one tenth of the noninteracting Fermi energy. Our results suggest the emergence of a fermionic quantum solid that should be observable in the current experimental setup. PMID:27472121

  7. Spin-orbit coupled Fermi liquid theory of ultracold magnetic dipolar fermions

    NASA Astrophysics Data System (ADS)

    Li, Yi; Wu, Congjun

    2012-05-01

    We investigate Fermi liquid states of the ultracold magnetic dipolar Fermi gases in the simplest two-component case including both thermodynamic instabilities and collective excitations. The magnetic dipolar interaction is invariant under the simultaneous spin-orbit rotation but not under either the spin or the orbit one. Therefore, the corresponding Fermi liquid theory is intrinsically spin-orbit coupled. This is a fundamental feature of magnetic dipolar Fermi gases different from electric dipolar ones. The Landau interaction matrix is calculated and is diagonalized in terms of the spin-orbit coupled partial-wave channels of the total angular momentum J. The leading thermodynamic instabilities lie in the channels of ferromagnetism hybridized with the ferronematic order with J=1+ and the spin-current mode with J=1-, where + and - represent even and odd parities, respectively. An exotic propagating collective mode is identified as spin-orbit coupled Fermi surface oscillations in which spin distribution on the Fermi surface exhibits a topologically nontrivial hedgehog configuration.

  8. Crow Instability in Unitary Fermi Gas

    NASA Astrophysics Data System (ADS)

    Gautam, Sandeep

    2013-06-01

    In this paper, we investigate the initiation and subsequent evolution of Crow instability in an inhomogeneous unitary Fermi gas using zero-temperature Galilei-invariant nonlinear Schrödinger equation. Considering a cigar-shaped unitary Fermi gas, we generate the vortex-antivortex pair either by phase-imprinting or by moving a Gaussian obstacle potential. We observe that the Crow instability in a unitary Fermi gas leads to the decay of the vortex-antivortex pair into multiple vortex rings and ultimately into sound waves.

  9. Quantum Mechanical Models Of The Fermi Shuttle

    SciTech Connect

    Sternberg, James

    2011-06-01

    The Fermi shuttle is a mechanism in which high energy electrons are produced in an atomic collision by multiple collisions with a target and a projectile atom. It is normally explained purely classically in terms of the electron's orbits prescribed in the collision. Common calculations to predict the Fermi shuttle use semi-classical methods, but these methods still rely on classical orbits. In reality such collisions belong to the realm of quantum mechanics, however. In this paper we discuss several purely quantum mechanical calculations which can produce the Fermi shuttle. Being quantum mechanical in nature, these calculations produce these features by wave interference, rather than by classical orbits.

  10. Numerical methods for the Poisson-Fermi equation in electrolytes

    NASA Astrophysics Data System (ADS)

    Liu, Jinn-Liang

    2013-08-01

    The Poisson-Fermi equation proposed by Bazant, Storey, and Kornyshev [Phys. Rev. Lett. 106 (2011) 046102] for ionic liquids is applied to and numerically studied for electrolytes and biological ion channels in three-dimensional space. This is a fourth-order nonlinear PDE that deals with both steric and correlation effects of all ions and solvent molecules involved in a model system. The Fermi distribution follows from classical lattice models of configurational entropy of finite size ions and solvent molecules and hence prevents the long and outstanding problem of unphysical divergence predicted by the Gouy-Chapman model at large potentials due to the Boltzmann distribution of point charges. The equation reduces to Poisson-Boltzmann if the correlation length vanishes. A simplified matched interface and boundary method exhibiting optimal convergence is first developed for this equation by using a gramicidin A channel model that illustrates challenging issues associated with the geometric singularities of molecular surfaces of channel proteins in realistic 3D simulations. Various numerical methods then follow to tackle a range of numerical problems concerning the fourth-order term, nonlinearity, stability, efficiency, and effectiveness. The most significant feature of the Poisson-Fermi equation, namely, its inclusion of steric and correlation effects, is demonstrated by showing good agreement with Monte Carlo simulation data for a charged wall model and an L type calcium channel model.

  11. Fermi discovers giant bubbles in Milky Way

    NASA Video Gallery

    Using data from NASA's Fermi Gamma-ray Space Telescope, scientists have recently discovered a gigantic, mysterious structure in our galaxy. This feature looks like a pair of bubbles extending above...

  12. Fermi's Conundrum: Proliferation and Closed Societies

    NASA Astrophysics Data System (ADS)

    Teller, Wendy; Westfall, Catherine

    2007-04-01

    On January 1, 1946 Emily Taft Douglas, a freshman Representative at Large for Illinois, sent a letter to Enrico Fermi. She wanted to know whether, if atomic energy was used for peaceful purposes, it might be possible to clandestinely divert some material for bombs. Douglas first learned about the bomb not quite five months before when Hiroshima was bombed. Even though she was not a scientist she identified a key problem of the nuclear age. Fermi responded with requirements to allow peaceful uses of atomic energy and still outlaw nuclear weapons. First, free interchange of information between people was required, and second, people who reported possible violations had to be protected. Fermi had lived in Mussolini's Italy and worked under the war time secrecy restrictions of the Manhattan Project. He was not optimistic that these conditions could be met. This paper discusses how Douglas came to recognize the proliferation issue and what led Fermi to his solution and his pessimism about its practicality.

  13. RF Spectroscopy on a Homogeneous Fermi Gas

    NASA Astrophysics Data System (ADS)

    Yan, Zhenjie; Mukherjee, Biswaroop; Patel, Parth; Struck, Julian; Zwierlein, Martin

    2016-05-01

    Over the last two decades RF spectroscopy has been established as an indispensable tool to probe a large variety of fundamental properties of strongly interacting Fermi gases. This ranges from measurement of the pairing gap over tan's contact to the quasi-particle weight of Fermi polarons. So far, most RF spectroscopy experiments have been performed in harmonic traps, resulting in an averaged response over different densities. We have realized an optical uniform potential for ultracold Fermi gases of 6 Li atoms, which allows us to avoid the usual problems connected to inhomogeneous systems. Here we present recent results on RF spectroscopy of these homogeneous samples with a high signal to noise ratio. In addition, we report progress on measuring the contact of a unitary Fermi gas across the normal to superfluid transition.

  14. Fermi Sees Antimatter-Hurling Thunderstorms

    NASA Video Gallery

    NASA's Fermi Gamma-ray Space Telescope has detected beams of antimatter launched by thunderstorms. Acting like enormous particle accelerators, the storms can emit gamma-ray flashes, called TGFs, an...

  15. Fermi Proves Supernova Remnants Make Cosmic Rays

    NASA Video Gallery

    The husks of exploded stars produce some of the fastest particles in the cosmos. New findings by NASA's Fermi show that two supernova remnants accelerate protons to near the speed of light. The pro...

  16. ORIGIN OF THE FERMI BUBBLE

    SciTech Connect

    Cheng, K.-S.; Chernyshov, D. O.; Dogiel, V. A.; Ko, C.-M.; Ip, W.-H.

    2011-04-10

    Fermi has discovered two giant gamma-ray-emitting bubbles that extend nearly 10 kpc in diameter north and south of the Galactic center. The existence of the bubbles was first evidenced in X-rays detected by ROSAT and later WMAP detected an excess of radio signals at the location of the gamma-ray bubbles. We propose that periodic star capture processes by the galactic supermassive black hole, Sgr A*, with a capture rate 3 x 10{sup -5} yr{sup -1} and energy release {approx}3 x 10{sup 52} erg per capture can produce very hot plasma {approx}10 keV with a wind velocity {approx}10{sup 8} cm s{sup -1} injected into the halo and heat up the halo gas to {approx}1 keV, which produces thermal X-rays. The periodic injection of hot plasma can produce shocks in the halo and accelerate electrons to {approx}TeV, which produce radio emission via synchrotron radiation and gamma rays via inverse Compton scattering with the relic and the galactic soft photons.

  17. Observation of Fermi Polarons in a Tunable Fermi Liquid of Ultracold Atoms

    SciTech Connect

    Schirotzek, Andre; Wu, C.-H.; Sommer, Ariel; Zwierlein, Martin W.

    2009-06-12

    We have observed Fermi polarons, dressed spin-down impurities in a spin-up Fermi sea of ultracold atoms. The polaron manifests itself as a narrow peak in the impurities' rf spectrum that emerges from a broad incoherent background. We determine the polaron energy and the quasiparticle residue for various interaction strengths around a Feshbach resonance. At a critical interaction, we observe the transition from polaronic to molecular binding. Here, the imbalanced Fermi liquid undergoes a phase transition into a Bose liquid, coexisting with a Fermi sea.

  18. First Light on GRBs with Fermi

    SciTech Connect

    Dermer, Charles D.

    2010-10-15

    Fermi LAT (Large Area Telescope) and GBM (Gamma ray Burst Monitor) observations of GRBs are briefly reviewed, keeping in mind EGRET expectations. Using {gamma}{gamma} constraints on outflow Lorentz factors, leptonic models are pitted against hadronic models, and found to be energetically favored. Interpretation of the Fermi data on GRBs helps establish whether GRBs accelerate cosmic rays, including those reaching {approx_equal}10{sup 20} eV.

  19. BKGE: Fermi-LAT Background Estimator

    NASA Astrophysics Data System (ADS)

    Vasileiou, Vlasios

    2014-11-01

    The Fermi-LAT Background Estimator (BKGE) is a publicly available open-source tool that can estimate the expected background of the Fermi-LAT for any observational conguration and duration. It produces results in the form of text files, ROOT files, gtlike source-model files (for LAT maximum likelihood analyses), and PHA I/II FITS files (for RMFit/XSpec spectral fitting analyses). Its core is written in C++ and its user interface in Python.

  20. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center Team

    2016-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads and a reference manual available on the FSSC website provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide examples of standard analyses, including tips and tricks for improving Fermi science analysis.

  1. TOPOLOGICAL MATTER. Discovery of a Weyl fermion semimetal and topological Fermi arcs.

    PubMed

    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. PMID:26184916

  2. Kaon condensation in baryonic Fermi liquid at high density

    NASA Astrophysics Data System (ADS)

    Paeng, Won-Gi; Rho, Mannque

    2015-01-01

    We formulate kaon condensation in dense baryonic matter with antikaons fluctuating from the Fermi-liquid fixed point. This entails that in the Wilsonian renormalization group (RG) approach, the decimation is effectuated in the baryonic sector to the Fermi surface while in the meson sector to the origin. In writing the kaon-baryon (KN) coupling, we take a generalized hidden local symmetry Lagrangian for the meson sector endowed with a "mended symmetry" that has the unbroken symmetry limit at high density in which the Goldstone π , scalar s , and vectors ρ (and ω ) and a1 become massless. The vector mesons ρ (and ω ) and a1 can be identified as emergent (hidden) local gauge fields and the scalar s as the dilaton field of the spontaneously broken scale invariance at chiral restoration. In matter-free space, when the vector mesons and the scalar meson—whose masses are much greater than that of the pion—are integrated out, then the resulting KN coupling Lagrangian consists of the leading chiral order [O (p1) ] Weinberg-Tomozawa term and the next chiral order [O (p2) ] ΣKN term. In addressing kaon condensation in dense nuclear matter in chiral perturbation theory, one makes an expansion in the "small" Fermi momentum kF. We argue that in the Wilsonian RG formalism with the Fermi-liquid fixed point, the expansion is on the contrary in 1 /kF with the "large" Fermi momentum kF. The kaon-quasinucleon interaction resulting from integrating out the massive mesons consists of a "relevant" term from the scalar exchange (analog to the ΣKN term) and an "irrelevant" term from the vector-meson exchange (analog to the Weinberg-Tomozawa term). It is found that the critical density predicted by the latter approach, controlled by the relevant term with the irrelevant term suppressed, is three times less than that predicted by chiral perturbation theory. This would make kaon condensation take place at a much lower density than previously estimated in chiral perturbation theory.

  3. Upgrading Fermi Without Traveling to Space

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-02-01

    The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope has received an upgrade that increased its sensitivity by a whopping 40% and nobody had to travel to space to make it happen! The difference instead stems from remarkable improvement to the software used to analyze Fermi-LATs data, and it has resulted in a new high-energy map of our sky.Animation (click to watch!) comparing the Pass 7 to the Pass 8 Fermi-LAT analysis, in a region in the constellation Carina. Pass 8 provides more accurate directions for incoming gamma rays, so more of them fall closer to their sources, creating taller spikes and a sharper image. [NASA/DOE/Fermi LAT Collaboration]Pass 8Fermi-LAT has been surveying the whole sky since August 2008. It detects gamma-ray photons by converting them into electron-positron pairs and tracking the paths of these charged particles. But differentiating this signal from the charged cosmic rays that also pass through the detector with a flux that can be 10,000 times larger! is a challenging process. Making this distinction and rebuilding the path of the original gamma ray relies on complex analysis software.Pass 8 is a complete reprocessing of all data collected by Fermi-LAT. The software has gone through many revisions before now, but this is the first revision that has taken into account all of the experience that the Fermi team has gained operating the LAT in its orbital environment.The improvements made in Pass 8 include better background rejection of misclassified charged particles, improvements to the point spread function and effective area of the detector, and an extension of the effective energy range from below 100 MeV to beyond a few hundred GeV. The changes made in Pass 8 have increased the sensitivity of Fermi-LAT by an astonishing 40%.Map of the High-Energy SkySky map of the sources in the 2FHL catalog, classified by their most likely association. Click for a better look! [Ackermann et al. 2016]The first result from the

  4. 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

    2016-03-01

    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. PMID:26991191

  5. Spin Polarization and Texture of the Fermi Arcs in the Weyl Fermion Semimetal TaAs

    NASA Astrophysics Data System (ADS)

    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

    2016-03-01

    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.

  6. FERMI longitudinal diagnostics: results and future challenges

    NASA Astrophysics Data System (ADS)

    Veronese, Marco; Ferrari, E.; Allaria, E.; Cinquegrana, P.; Froelich, L.; Giannessi, L.; Penco, G.; Predonzani, M.; Rossi, F.; Sigalotti, P.; Ferianis, M.

    2015-05-01

    The seeded FEL FERMI has completed the commissioning of both the FEL lines, and it is now providing the user community with a coherent and tunable UV radiation (from 100 nm to 4 nm) in a number of different configurations. These also include original FEL-pump - FEL-probe schemes with twin-seeded FEL pulses. Among the key systems for the operation of FERMI, there is the femtosecond optical timing system and dedicated longitudinal diagnostics, specifically developed for FERMI. In this paper, after a short review of the FERMI optical timing system and of its routinely achieved performances, we focus on the results obtained from the suite of longitudinal diagnostics (Bunch Arrival Monitor, Electro Optical sampling station and RF deflectors) all operating in single shot and with 10s fs resolution which demonstrate the FERMI achieved performances. The longitudinal diagnostics measurements are compared between these device and other device on shot-to-shot basis, looking for correlations between machine parameters. Finally future challenges in terms of improvement of existing diagnostics, planned installations and possible upgrades are discussed.

  7. Extending the Fermi - Swift Joint AGN Sample

    NASA Astrophysics Data System (ADS)

    Shrader, Chris R.; Macomb, D. J.

    2014-01-01

    The Swift BAT and the Fermi LAT each provide excellent sky coverage and have led to impressive compilations of extragalactic source catalogs. For the most part they sample separate AGN subpopulations - Swift the lower-luminosity and relatively nearby Seyfert galaxies while the Fermi sample is dominated by blazars and does not include any radio-quiet objects. The overlap between these samples is among the radio-loud subset of the Swift sample as has been discussed elsewhere in the literature. The observable properties at these two bands - flux and spectral indices - are not expected to be well correlated as they sample different portions of the synchrotron self-Compton (SSC) spectral energy distribution. In this contribution we consider an extension of the high-latitude Swift sample by relaxing the significance cut to less than 5 standard deviations and consider the overlap of that subsample with the Fermi AGN catalog. While such a threshold is generally inadvisable as it introduces the strong possibility of spurious detections, the objects of the overlapping sample which are detected at high significance in Fermi can be considered as reasonably high-confidence Swift detections. For example, there are 190 Swift sub-5-sigma Swift sources that have significance >2-sigma with Fermi counterparts, whereas we predict only ~5 due to statistical fluctuation. We also investigate any coincident INTEGRAL/IBIS observations to further bolster or diminish candidate Swift detections. We present our correlation analyses and offer interpretation in the context of the blazar sequence.

  8. Understanding and Using the Fermi Science Tools

    NASA Astrophysics Data System (ADS)

    Asercion, Joseph; Fermi Science Support Center

    2015-01-01

    The Fermi Science Support Center (FSSC) provides information, documentation, and tools for the analysis of Fermi science data, including both the Large-Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). Source and binary versions of the Fermi Science Tools can be downloaded from the FSSC website, and are supported on multiple platforms. An overview document, the Cicerone, provides details of the Fermi mission, the science instruments and their response functions, the science data preparation and analysis process, and interpretation of the results. Analysis Threads provide the user with step-by-step instructions for many different types of data analysis: point source analysis - generating maps, spectra, and light curves, pulsar timing analysis, source identification, and the use of python for scripting customized analysis chains. The reference manual gives details of the options available for each tool. We present an overview of the structure of the Fermi science tools and documentation, and how to acquire them. We also provide information on recent updates incorporated in the Science Tools as well as upcoming changes that will be included in the upcoming release of the Science Tools in early 2015.

  9. Spectral probes of the holographic Fermi ground state: Dialing between the electron star and AdS Dirac hair

    SciTech Connect

    Cubrovic, Mihailo; Liu Yan; Schalm, Koenraad; Sun Yawen; Zaanen, Jan

    2011-10-15

    We argue that the electron star and the anti-de Sitter (AdS) Dirac hair solution are two limits of the free charged Fermi gas in AdS. Spectral functions of holographic duals to probe fermions in the background of electron stars have a free parameter that quantifies the number of constituent fermions that make up the charge and energy density characterizing the electron star solution. The strict electron star limit takes this number to be infinite. The Dirac hair solution is the limit where this number is unity. This is evident in the behavior of the distribution of holographically dual Fermi surfaces. As we decrease the number of constituents in a fixed electron star background the number of Fermi surfaces also decreases. An improved holographic Fermi ground state should be a configuration that shares the qualitative properties of both limits.

  10. The evolutionary sequence of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Cha, Yongjuan; Zhang, Haojing; Zhang, Xiong; Xiong, Dingrong; Li, Bijun; Dong, Xia; Li, Jin

    2014-02-01

    Using γ-ray data ( α γ , F γ ) detected by Fermi Large Area Telescope (LAT) and black hole mass which has been compiled from literatures for 116 Fermi blazars, we calculated intrinsic γ-ray luminosity, intrinsic bolometric luminosity, intrinsic Eddington ratio and studied the relationships between all above parameters and redshift, between α γ and L γ . Furthermore, we obtained the histograms of key parameters. Our results are the following: (1) The main reason for the evolutionary sequence of three subclasses (HBLs, LBLs, FSRQs) may be Eddington ratio rather than black hole mass; (2) FSRQs occupy in the earlier, high-luminosity, high Eddington ratio, violent phase of the galactic evolution sequence, while BL Lac objects occur in the low luminosity, low Eddington ratio, late phase of the galactic evolution sequence; (3) These results imply that the evolutionary track of Fermi blazars is FSRQs ⟶ LBLs ⟶ HBLs.

  11. The Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    Thompson, Dave; McEnery, Julie

    2011-01-01

    This slide presentation reviews the Gamma Ray Astronomy as enhanced by the Fermi Gamma Ray Space Telescope and Radio Astronomy as a synergistic relationship. Gamma rays often represent a significant part of the energy budget of a source; therefore, gamma-ray studies can be critical to understanding physical processes in such sources. Radio observations offer timing and spatial resolutions vastly superior to anything possible with gamma-ray telescopes; therefore radio is often the key to understanding source structure. Gamma-ray and radio observations can complement each other, making a great team. It reviews the Fermi Guest Investigator (GI) program, and calls for more cooperative work that involves Fermi and the Very Long Baseline Array (VLBA), a system of ten radio telescopes.

  12. Dark lump excitations in superfluid Fermi gases

    NASA Astrophysics Data System (ADS)

    Xu, Yan-Xia; Duan, Wen-Shan

    2012-11-01

    We study the linear and nonlinear properties of two-dimensional matter-wave pulses in disk-shaped superfluid Fermi gases. A Kadomtsev—Petviashvili I (KPI) solitary wave has been realized for superfluid Fermi gases in the limited cases of Bardeen—Cooper—Schrieffer (BCS) regime, Bose—Einstein condensate (BEC) regime, and unitarity regime. One-lump solution as well as one-line soliton solutions for the KPI equation are obtained, and two-line soliton solutions with the same amplitude are also studied in the limited cases. The dependence of the lump propagating velocity and the sound speed of two-dimensional superfluid Fermi gases on the interaction parameter are investigated for the limited cases of BEC and unitarity.

  13. Traveling dark solitons in superfluid Fermi gases

    SciTech Connect

    Liao Renyuan; Brand, Joachim

    2011-04-15

    Families of dark solitons exist in superfluid Fermi gases. The energy-velocity dispersion and number of depleted particles completely determine the dynamics of dark solitons on a slowly varying background density. For the unitary Fermi gas, we determine these relations from general scaling arguments and conservation of local particle number. We find solitons to oscillate sinusoidally at the trap frequency reduced by a factor of 1/{radical}(3). Numerical integration of the time-dependent Bogoliubov-de Gennes equation determines spatial profiles and soliton-dispersion relations across the BEC-BCS crossover, and proves consistent with the scaling relations at unitarity.

  14. Information-driven societies and Fermi's paradox

    NASA Astrophysics Data System (ADS)

    Lampton, Michael

    2013-10-01

    Fermi's paradox is founded on the idea that one or more Galactic extraterrestrial civilizations (ETCs) existed long ago and sustained exploration for millions of years, but in spite of their advanced knowledge, they could not find a way to explore the Galaxy other than with fleets of starships or self replicating probes. Here, I question this second assumption: if advanced technology generally allows long-distance remote sensing, and if ETCs were motivated by gaining information rather than conquest or commerce, then such voyages would be unnecessary, thereby resolving Fermi's paradox.

  15. Observation of Fermi-Arc Spin Texture in TaAs.

    PubMed

    Lv, B Q; Muff, S; Qian, T; Song, Z D; Nie, S M; Xu, N; Richard, P; Matt, C E; Plumb, N C; Zhao, L X; Chen, G F; Fang, Z; Dai, X; Dil, J H; Mesot, J; Shi, M; Weng, H M; Ding, H

    2015-11-20

    We have investigated the spin texture of surface Fermi arcs in the recently discovered Weyl semimetal TaAs using spin- and angle-resolved photoemission spectroscopy. The experimental results demonstrate that the Fermi arcs are spin polarized. The measured spin texture fulfills the requirement of mirror and time-reversal symmetries and is well reproduced by our first-principles calculations, which gives strong evidence for the topologically nontrivial Weyl semimetal state in TaAs. The consistency between the experimental and calculated results further confirms the distribution of chirality of the Weyl nodes determined by first-principles calculations. PMID:26636872

  16. Enrico: Python package to simplify Fermi-LAT analysis

    NASA Astrophysics Data System (ADS)

    Sanchez, David; Deil, Christoph

    2015-01-01

    Enrico analyzes Fermi data. It produces spectra (model fit and flux points), maps and lightcurves for a target by editing a config file and running a python script which executes the Fermi science tool chain.

  17. Fermi level dependent native defect formation: Consequences for metal--semiconductor and semiconductor--semiconductor interfaces

    SciTech Connect

    Walukiewicz, W.

    1988-07-01

    The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration.

  18. Fermi level dependent native defect formation: Consequences for metal-semiconductor and semiconductor-semiconductor interfaces

    SciTech Connect

    Walukiewicz, W.

    1988-02-01

    The amphoteric native defect model of the Schottky barrier formation is used to analyze the Fermi level pinning at metal/semiconductor interfaces for submonolayer metal coverages. It is assumed that the energy required for defect generation is released in the process of surface back-relaxation. Model calculations for metal/GaAs interfaces show a weak dependence of the Fermi level pinning on the thickness of metal deposited at room temperature. This weak dependence indicates a strong dependence of the defect formation energy on the Fermi level, a unique feature of amphoteric native defects. This result is in very good agreement with experimental data. It is shown that a very distinct asymmetry in the Fermi level pinning on p- and n-type GaAs observed at liquid nitrogen temperatures can be understood in terms of much different recombination rates for amphoteric native defects in those two types of materials. Also, it is demonstrated that the Fermi level stabilization energy, a central concept of the amphoteric defect system, plays a fundamental role in other phenomena in semiconductors such as semiconductor/semiconductor heterointerface intermixing and saturation of free carrier concentration. 33 refs., 6 figs.

  19. 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

  20. Fermi Large Area Telescope Second Source Catalog

    NASA Technical Reports Server (NTRS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M; Allafort, A.; Antolini, E; Bonnell, J.; Cannon, A.; Celik O.; Corbet, R.; Davis, D. S.; DeCesar, M. E.; Ferrara, E. C.; Gehrels, N.; Harding, A. K.; Hays, E.; Johnson, T. E.; McConville, W.; McEnery, J. E; Perkins, J. S.; Racusin, J. L; Scargle, J. D.; Stephens, T. E.; Thompson, D. J.; Troja, E.

    2012-01-01

    We present the second catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24-month period. The Second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in 5 energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 11eV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely gamma-ray-producing source classes.

  1. FERMI LARGE AREA TELESCOPE SECOND SOURCE CATALOG

    SciTech Connect

    Nolan, P. L.; Ajello, M.; Allafort, A.; Bechtol, K.; Berenji, B.; Blandford, R. D.; Bloom, E. D.; Abdo, A. A.; Ackermann, M.; Antolini, E.; Bonamente, E.; Atwood, W. B.; Belfiore, A.; Axelsson, M.; Baldini, L.; Bellazzini, R.; Ballet, J.; Bastieri, D.; Bignami, G. F. E-mail: Gino.Tosti@pg.infn.it E-mail: tburnett@u.washington.edu; and others

    2012-04-01

    We present the second catalog of high-energy {gamma}-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely {gamma}-ray-producing source classes.

  2. Radiatively induced Fermi scale and unification

    NASA Astrophysics Data System (ADS)

    Alanne, Tommi; Meroni, Aurora; Sannino, Francesco; Tuominen, Kimmo

    2016-05-01

    We consider extensions of the Standard Model in which the hierarchy between the unification and the Fermi scale emerges radiatively. Within the Pati-Salam framework, we show that it is possible to construct a viable model where the Higgs is an elementary pseudo-Goldstone boson, and the correct hierarchy is generated.

  3. Radio core dominance of Fermi blazars

    NASA Astrophysics Data System (ADS)

    Pei, Zhi-Yuan; Fan, Jun-Hui; Liu, Yi; Yuan, Yi-Hai; Cai, Wei; Xiao, Hu-Bing; Lin, Chao; Yang, Jiang-He

    2016-07-01

    During the first 4 years of mission, Fermi/LAT detected 1444 blazars (3FGL) (Ackermann et al. in Astrophys. J. 810:14, 2015). Fermi/LAT observations of blazars indicate that Fermi blazars are luminous and strongly variable with variability time scales, for some cases, as short as hours. Those observations suggest a strong beaming effect in Fermi/LAT blazars. In the present work, we will investigate the beaming effect in Fermi/LAT blazars using a core-dominance parameter, R = S_{core}/ S_{ext.}, where S_{core} is the core emission, while S_{ext.} is the extended emission. We compiled 1335 blazars with available core-dominance parameter, out of which 169 blazars have γ-ray emission (from 3FGL). We compared the core-dominance parameters, log R, between the 169 Fermi-detected blazars (FDBs) and the rest non-Fermi-detected blazars (non-FDBs), and we found that the averaged values are < log Rrangle = 0.99±0.87 for FDBs and < log Rrangle = -0.62±1.15 for the non-FDBs. A K-S test shows that the probability for the two distributions of FDBs and non-FDBs to come from the same parent distribution is near zero (P =9.12×10^{-52}). Secondly, we also investigated the variability index (V.I.) in the γ-ray band for FDBs, and we found V.I.=(0.12 ±0.07) log R+(2.25±0.10), suggesting that a source with larger log R has larger V.I. value. Thirdly, we compared the mean values of radio spectral index for FDBs and non-FDBs, and we obtained < α_{radio}rangle =0.06±0.35 for FDBs and < α_{radio}rangle =0.57±0.46 for non-FDBs. If γ-rays are composed of two components like radio emission (core and extended components), then we can expect a correlation between log R and the γ-ray spectral index. When we used the radio core-dominance parameter, log R, to investigate the relationship, we found that the spectral index for the core component is α_{γ}|_{core} = 1.11 (a photon spectral index of α_{γ}^{ph}|_{core} = 2.11) and that for the extended component is α_{γ}|_{ext.} = 0

  4. FermiGrid - experience and future plans

    SciTech Connect

    Chadwick, K.; Berman, E.; Canal, P.; Hesselroth, T.; Garzoglio, G.; Levshina, T.; Sergeev, V.; Sfiligoi, I.; Timm, S.; Yocum, D.; /Fermilab

    2007-09-01

    Fermilab supports a scientific program that includes experiments and scientists located across the globe. In order to better serve this community, Fermilab has placed its production computer resources in a Campus Grid infrastructure called 'FermiGrid'. The FermiGrid infrastructure allows the large experiments at Fermilab to have priority access to their own resources, enables sharing of these resources in an opportunistic fashion, and movement of work (jobs, data) between the Campus Grid and National Grids such as Open Science Grid and the WLCG. FermiGrid resources support multiple Virtual Organizations (VOs), including VOs from the Open Science Grid (OSG), EGEE and the Worldwide LHC Computing Grid Collaboration (WLCG). Fermilab also makes leading contributions to the Open Science Grid in the areas of accounting, batch computing, grid security, job management, resource selection, site infrastructure, storage management, and VO services. Through the FermiGrid interfaces, authenticated and authorized VOs and individuals may access our core grid services, the 10,000+ Fermilab resident CPUs, near-petabyte (including CMS) online disk pools and the multi-petabyte Fermilab Mass Storage System. These core grid services include a site wide Globus gatekeeper, VO management services for several VOs, Fermilab site authorization services, grid user mapping services, as well as job accounting and monitoring, resource selection and data movement services. Access to these services is via standard and well-supported grid interfaces. We will report on the user experience of using the FermiGrid campus infrastructure interfaced to a national cyberinfrastructure--the successes and the problems.

  5. Superconductor-Insulator Transition and Fermi-Bose Crossovers

    NASA Astrophysics Data System (ADS)

    Trivedi, Nandini; Loh, Yen Lee; Randeria, Mohit; Chang, Chia-Chen; Scalettar, Richard

    The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally-invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-like SC, with an energy gap for fermions that remains finite across the SIT. The energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insights into important questions about the SIT in solid state systems, our model should be experimentally realizable using ultracold fermions in optical lattices. Ref: arXiv:1507.05641 We gratefully acknowledge support from NSF DMR-1410364 (MR), DOE DE-FG02-07ER46423 (NT), and from the UC Office of the President (CC, RTS).

  6. Superconductor-Insulator Transition and Fermi-Bose Crossovers

    NASA Astrophysics Data System (ADS)

    Loh, Yen Lee; Randeria, Mohit; Trivedi, Nandini; Chang, Chia-Chen; Scalettar, Richard

    2016-04-01

    The direct transition from an insulator to a superconductor (SC) in Fermi systems is a problem of long-standing interest, which necessarily goes beyond the standard BCS paradigm of superconductivity as a Fermi surface instability. We introduce here a simple, translationally invariant lattice fermion model that undergoes a SC-insulator transition (SIT) and elucidate its properties using analytical methods and quantum Monte Carlo simulations. We show that there is a fermionic band insulator to bosonic insulator crossover in the insulating phase and a BCS-to-BEC crossover in the SC. The SIT is always found to be from a bosonic insulator to a BEC-like SC, with an energy gap for fermions that remains finite across the SIT. The energy scales that go critical at the SIT are the gap to pair excitations in the insulator and the superfluid stiffness in the SC. In addition to giving insight into important questions about the SIT in solid-state systems, our model should be experimentally realizable using ultracold fermions in optical lattices.

  7. Entropy excess in strongly correlated Fermi systems near a quantum critical point

    SciTech Connect

    Clark, J.W.; Zverev, M.V.; Khodel, V.A.

    2012-12-15

    A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum {epsilon}(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n{sup 2}(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum {epsilon}(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincare mapping associated with the fundamental Landau equation connecting n(p) and {epsilon}(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario. - Highlights: Black-Right-Pointing-Pointer Extension of Landau

  8. Magnetar Observations with Fermi/GBM

    NASA Technical Reports Server (NTRS)

    Kouveliotou, Chryssa

    2009-01-01

    NASA's Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first year of operations we recorded emission from four magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other three detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP) and a very recently discovered new source, SGR 0418+5729. I report below on the current status of the analyses efforts of the GBM data.

  9. Magnetar Observations in the Fermi Era

    NASA Technical Reports Server (NTRS)

    Kouveliotou, Chryssa

    2009-01-01

    NASA s Fermi Observatory was launched June 11, 2009; the Fermi Gamma Ray Burst Monitor (GBM) began normal operations on July 14, about a month after launch, when the trigger algorithms were enabled. In the first 8 months of operations we recorded emission of three magnetar sources; of these, only one was an old magnetar: SGR 1806+20. The other two detections were: SGR J0501+4516, newly discovered with Swift and extensively monitored with both Swift and GBM, and SGR J1550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP). I report below on the current status of the analyses efforts of all these GBM data sets, combined with data from other satellites (Spitzer, RXTE, Chandra, Swift).

  10. Study of superfluid Bose-Fermi mixture

    NASA Astrophysics Data System (ADS)

    Laurent, Sebastien; Delehaye, Marion; Jin, Shuwei; Pierce, Matthieu; Yefsah, Tarik; Chevy, Frederic; Salomon, Christophe

    2016-05-01

    Using fermionic and bosonic isotopes of lithium we produce and study ultracold Bose-Fermi mixtures. First in a low temperature counterflow experiment, we measure the critical velocity of the system in the BEC-BCS crossover. Around unitarity, we observe a remarkably high superfluid critical velocity which reaches the sound velocity of the strongly interacting Fermi gas. Second, when we increase the temperature of the system slightly above the superfluid transitions we observe an unexpected phase locking of the oscillations of the clouds induced by dissipation. Finally, as suggested in, we explore the nature of the superfluid phase when we impose a spin polarization in the situation where the mean field potential created by the bosons on the fermions tends to cancel out the trapping potential of the latter.

  11. Pulsar timing and the Fermi mission

    NASA Astrophysics Data System (ADS)

    Kerr, Matthew; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Shannon, Ryan; Petroff, Emily; Brook, Paul

    2014-04-01

    We request time to observe 180 pulsars on a regular basis in order to provide the accurate ephemerides necessary for the detection and characterisation of gamma-ray pulsars with the Fermi satellite. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, and to characterise their high energy (phase-resolved) spectra. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability, and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 45 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group and Kyle Watters from Stanford. Currently four students have active projects using the radio datasets.

  12. Young Pulsar Timing and the Fermi Mission

    NASA Astrophysics Data System (ADS)

    Kerr, Matthew; Possenti, Andrea; Manchester, Dick; Johnston, Simon; Hobbs, George; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Shannon, Ryan; Petroff, Emily; Brook, Paul

    2014-10-01

    We request time to observe 230 pulsars on a regular basis in order to provide the accurate ephemerides necessary for the detection and characterisation of gamma-ray pulsars with the Fermi satellite. The main science goals are to increase the number of known gamma-ray pulsars (both radio loud and radio quiet), to determine accurate pulse profiles, and to characterise their high energy (phase-resolved) spectra. In the radio, the observations will also allow us to find glitches, characterise timing noise, investigate dispersion and rotation measure variability, and enhance our knowledge of single pulse phenomenology. To date, we are (co-)authors on 45 papers arising from the collaboration and P574 data. The data have contributed to the PhD theses of Lucas Guillemot and Damien Parent from the Bordeaux Fermi group and Kyle Watters from Stanford. Currently four students have active projects using the radio datasets.

  13. Remarks on Fermi liquid from holography

    SciTech Connect

    Kulaxizi, Manuela; Parnachev, Andrei

    2008-10-15

    We investigate the signatures of Fermi liquid formation in the N=4 super Yang-Mills theory coupled to fundamental hypermultiplet at nonvanishing chemical potential for the global U(1) vector symmetry. At strong 't Hooft coupling the system can be analyzed in terms of the D7-brane dynamics in the AdS{sub 5}xS{sup 5} background. The phases with vanishing and finite charge density are separated at zero temperature by a quantum phase transition. In the case of vanishing hypermultiplet mass, Karch, Son, and Starinets discovered a gapless excitation whose speed equals the speed of sound. We find that this zero sound mode persists to all values of the hypermultiplet mass, and its speed vanishes at the point of phase transition. The value of critical exponent and the ratio of the velocities of zero and first sounds are consistent with the predictions of Landau Fermi liquid theory at strong coupling.

  14. High Energy Neutrinos from the Fermi Bubbles

    SciTech Connect

    Lunardini, Cecilia; Razzaque, Soebur

    2012-06-01

    Recently the Fermi-LAT data have revealed two gamma-ray emitting bubble-shaped structures at the Galactic center. If the observed gamma rays have hadronic origin (collisions of accelerated protons), the bubbles must emit high energy neutrinos as well. This new, Galactic, neutrino flux should trace the gamma-ray emission in spectrum and spatial extent. Its highest energy part, above 20–50 TeV, is observable at a kilometer-scale detector in the northern hemisphere, such as the planned KM3NeT, while interesting constraints on it could be obtained by the IceCube Neutrino Observatory at the South Pole. The detection or exclusion of neutrinos from the Fermi bubbles will discriminate between hadronic and leptonic models, thus bringing unique information on the still mysterious origin of these objects and on the time scale of their formation.

  15. Single impurity in ultracold Fermi superfluids

    SciTech Connect

    Jiang Lei; Baksmaty, Leslie O.; Pu, Han; Hu Hui; Chen Yan

    2011-06-15

    The role of impurities as experimental probes in the detection of quantum material properties is well appreciated. Here we study the effect of a single classical magnetic impurity in trapped ultracold Fermi superfluids. Depending on its shape and strength, a magnetic impurity can induce single or multiple midgap bound states in a superfluid Fermi gas. The multiple midgap states could coincide with the development of a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) phase within the superfluid. As an analog of the scanning tunneling microsope, we propose a modified rf spectroscopic method to measure the local density of states which can be employed to detect these states and other quantum phases of cold atoms. A key result of our self-consistent Bogoliubov-de Gennes calculations is that a magnetic impurity can controllably induce an FFLO state at currently accessible experimental parameters.

  16. Dilute spin-orbit Fermi gases

    NASA Astrophysics Data System (ADS)

    Maldonado-Mundo, Daniel; He, Lianyi; Öhberg, Patrik; Valiente, Manuel

    2014-03-01

    We study repulsive Fermi gases with Rashba spin-orbit coupling in two and three dimensions when they are dilute enough that a single branch of the spectrum is occupied in the non-interacting ground state. We develop an effective renormalizable theory for fermions in the lower branch and obtain the energy of the system in three dimensions to second order in the renormalized coupling constant. We then exploit the non-Galilean-relativistic nature of spin-orbit coupled gases. We find that at finite momentum, the two-dimensional Fermi sea is deformed in a non-trivial way. Using mean-field theory to include interactions, we show that the ground-state of the system acquires a finite momentum, and is consequently deformed, when the interaction is stronger than a critical value. Heriot-Watt University. CM-DTC. SUPA. EPSRC.

  17. Relativistic Beaming Effect in Fermi Blazars

    NASA Astrophysics Data System (ADS)

    Fan, J. H.; Bastieri, D.; Yang, J. H.; Liu, Y.; Wu, D. X.; Li, S. H.

    2014-09-01

    The most identified sources observed by Fermi/LAT are blazars, based on which we can investigate the emission mechanisms and beaming effect in the γ-ray bands for blazars. Here, we used the compiled around 450 Fermi blazars with the available X-ray observations to estimate their Doppler factors and compared them with the integral γ-ray luminosity in the range of 1-100 GeV. It is interesting that the integral γ-ray luminosity is closely correlated with the estimated Doppler factor, for the whole sample. When the dependence of the correlation between them and the X-ray luminosity is removed, the correlation is still strong, which suggests that the γ-ray emissions are strongly beamed.

  18. Ideas by Szilard, physics by Fermi

    SciTech Connect

    Lanouette, W.

    1992-12-01

    An excerpt from William Lanouette's book Genius in the shadows: A biography of Leo Szilard, the man behind the bomb (with Bela Silard). This article covers Szilard's life from early 1933, when he first began contemplating fleeing Germany, to the first self-sustaining nuclear chain reaction on December 2, 1942, and includes a description of his partnership with Enrico Fermi. Part of a series of articles in this magazine commemorating the 50th anniversary of the first controlled chain reaction.

  19. Fractal generalization of Thomas-Fermi model

    NASA Astrophysics Data System (ADS)

    Rekhviashvili, S. Sh.; Sokurov, A. A.

    2016-05-01

    The Thomas-Fermi model is developed for a multielectron neutral atom at an arbitrary metric dimension of the electron cloud. It has been shown that the electron cloud with the reduced dimension should be located in the close vicinity of the nucleus. At a metric dimension of the electron cloud of 2, the differential equation of the model admits an analytical solution. In this case, the screening parameter does not depend on the charge of the nucleus.

  20. Fermi Large Area Telescope Second Source Catalog

    NASA Astrophysics Data System (ADS)

    Nolan, P. L.; Abdo, A. A.; Ackermann, M.; Ajello, M.; Allafort, A.; Antolini, E.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Belfiore, A.; Bellazzini, R.; Berenji, B.; Bignami, G. F.; Blandford, R. D.; Bloom, E. D.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Brandt, T. J.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Campana, R.; Cañadas, B.; Cannon, A.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Ceccanti, M.; Cecchi, C.; Çelik, Ö.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chipaux, R.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Corbet, R.; Cutini, S.; D'Ammando, F.; Davis, D. S.; de Angelis, A.; DeCesar, M. E.; DeKlotz, M.; De Luca, A.; den Hartog, P. R.; de Palma, F.; Dermer, C. D.; Digel, S. W.; Silva, E. do Couto e.; Drell, P. S.; Drlica-Wagner, A.; Dubois, R.; Dumora, D.; Enoto, T.; Escande, L.; Fabiani, D.; Falletti, L.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Focke, W. B.; Fortin, P.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Hill, A. B.; Horan, D.; Hou, X.; Hughes, R. E.; Iafrate, G.; Itoh, R.; Jóhannesson, G.; Johnson, R. P.; Johnson, T. E.; Johnson, A. S.; Johnson, T. J.; Kamae, T.; Katagiri, H.; Kataoka, J.; Katsuta, J.; Kawai, N.; Kerr, M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Lande, J.; Landriu, D.; Latronico, L.; Lemoine-Goumard, M.; Lionetto, A. M.; Llena Garde, M.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Marelli, M.; Massaro, E.; Mazziotta, M. N.; McConville, W.; McEnery, J. E.; Mehault, J.; Michelson, P. F.; Minuti, M.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monte, C.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Naumann-Godo, M.; Norris, J. P.; Nuss, E.; Nymark, T.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paneque, D.; Panetta, J. H.; Parent, D.; Perkins, J. S.; Pesce-Rollins, M.; Pierbattista, M.; Pinchera, M.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Ritz, S.; Rochester, L. S.; Romani, R. W.; Roth, M.; Rousseau, R.; Ryde, F.; Sadrozinski, H. F.-W.; Salvetti, D.; Sanchez, D. A.; Saz Parkinson, P. M.; Sbarra, C.; Scargle, J. D.; Schalk, T. L.; Sgrò, C.; Shaw, M. S.; Shrader, C.; Siskind, E. J.; Smith, D. A.; Spandre, G.; Spinelli, P.; Stephens, T. E.; Strickman, M. S.; Suson, D. J.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Tinebra, F.; Tinivella, M.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vandenbroucke, J.; Van Etten, A.; Van Klaveren, B.; Vasileiou, V.; Vianello, G.; Vitale, V.; Waite, A. P.; Wallace, E.; Wang, P.; Werner, M.; Winer, B. L.; Wood, D. L.; Wood, K. S.; Wood, M.; Yang, Z.; Zimmer, S.

    2012-04-01

    We present the second catalog of high-energy γ-ray sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi), derived from data taken during the first 24 months of the science phase of the mission, which began on 2008 August 4. Source detection is based on the average flux over the 24 month period. The second Fermi-LAT catalog (2FGL) includes source location regions, defined in terms of elliptical fits to the 95% confidence regions and spectral fits in terms of power-law, exponentially cutoff power-law, or log-normal forms. Also included are flux measurements in five energy bands and light curves on monthly intervals for each source. Twelve sources in the catalog are modeled as spatially extended. We provide a detailed comparison of the results from this catalog with those from the first Fermi-LAT catalog (1FGL). Although the diffuse Galactic and isotropic models used in the 2FGL analysis are improved compared to the 1FGL catalog, we attach caution flags to 162 of the sources to indicate possible confusion with residual imperfections in the diffuse model. The 2FGL catalog contains 1873 sources detected and characterized in the 100 MeV to 100 GeV range of which we consider 127 as being firmly identified and 1171 as being reliably associated with counterparts of known or likely γ-ray-producing source classes. We dedicate this paper to the memory of our colleague Patrick Nolan, who died on 2011 November 6. His career spanned much of the history of high-energy astronomy from space and his work on the Large Area Telescope (LAT) began nearly 20 years ago when it was just a concept. Pat was a central member in the operation of the LAT collaboration and he is greatly missed.

  1. "Permanence" - An Adaptationist Solution to Fermi's Paradox?

    NASA Astrophysics Data System (ADS)

    Cirkovic, Milan M.

    A new solution of Fermi's paradox sketched by SF writer Karl Schroeder in his 2002. novel Permanence is investigated. It is argued that this solution is tightly connected with adaptationism - a widely discussed working hypothesis in evolutionary biology. Schroeder's hypothesis has important ramifications for astrobiology, SETI projects, and future studies. Its weaknesses should be explored without succumbing to the emotional reactions often accompanying adaptationist explanations.

  2. Entropy excess in strongly correlated Fermi systems near a quantum critical point

    NASA Astrophysics Data System (ADS)

    Clark, J. W.; Zverev, M. V.; Khodel, V. A.

    2012-12-01

    A system of interacting, identical fermions described by standard Landau Fermi-liquid (FL) theory can experience a rearrangement of its Fermi surface if the correlations grow sufficiently strong, as occurs at a quantum critical point where the effective mass diverges. As yet, this phenomenon defies full understanding, but salient aspects of the non-Fermi-liquid (NFL) behavior observed beyond the quantum critical point are still accessible within the general framework of the Landau quasiparticle picture. Self-consistent solutions of the coupled Landau equations for the quasiparticle momentum distribution n(p) and quasiparticle energy spectrum ɛ(p) are shown to exist in two distinct classes, depending on coupling strength and on whether the quasiparticle interaction is regular or singular at zero momentum transfer. One class of solutions maintains the idempotency condition n2(p)=n(p) of standard FL theory at zero temperature T while adding pockets to the Fermi surface. The other solutions are characterized by a swelling of the Fermi surface and a flattening of the spectrum ɛ(p) over a range of momenta in which the quasiparticle occupancies lie between 0 and 1 even at T=0. The latter, non-idempotent solution is revealed by analysis of a Poincaré mapping associated with the fundamental Landau equation connecting n(p) and ɛ(p) and validated by solution of a variational condition that yields the symmetry-preserving ground state. Significantly, this extraordinary solution carries the burden of a large temperature-dependent excess entropy down to very low temperatures, threatening violation of the Nernst Theorem. It is argued that certain low-temperature phase transitions, notably those involving Cooper-pair formation, offer effective mechanisms for shedding the entropy excess. Available measurements in heavy-fermion compounds provide concrete support for such a scenario.

  3. A Probabilistic Analysis of the Fermi Paradox

    NASA Astrophysics Data System (ADS)

    Solomonides, Evan; Terzian, Yervant

    2016-06-01

    The Fermi paradox uses an appeal to the mediocrity principle to make it seem counterintuitive that humanity has not been contacted by extraterrestrial intelligence. A numerical, statistical analysis was conducted to determine whether this apparent loneliness is, in fact, unexpected. An inequality was derived to relate the frequency of life arising and developing technology on a suitable planet in the galaxy; the average length of time since the first broadcast of such a civilization; and a constant term. An analysis of the sphere reached thus far by human communication was also conducted, considering our local neighborhood and planets of particular interest. These analyses both conclude that the Fermi paradox is not, in fact, unexpected. By the mediocrity principle and numerical modeling, it is actually unlikely that the Earth would have been reached by extraterrestrial communication at this point. We predict that under 1% of the galaxy has been reached at all thus far, and we do not anticipate to be reached until approximately 50% of stars/planets have been reached. We offer a prediction that we should not expect this until at least 1,500 years in the future. Thus the Fermi paradox is not a shocking observation- or lack thereof- and humanity may very well be contacted within our species’ lifespan (we can begin to expect to be contacted 1,500 years in the future).

  4. Fermi/GBM Results of Magnetars

    NASA Technical Reports Server (NTRS)

    Kouveliotou, chryssa

    2011-01-01

    Magnetars are magnetically powered rotating neutron stars with extreme magnetic fields (over 10(exp 14) Gauss). They were discovered in the X- and gamma-rays where they predominantly emit their radiation. Very few sources (roughly 18) have been found since their discovery in 1987. NASA's Fermi Gamma-ray Space Telescope was launched June 11,2009; since then the Fermi Gamma-ray Burst Monitor (GBM) recorded emission from four magnetar sources. Two of these were brand new sources, SGR J0501 +4516, discovered with Swift and extensively monitored with Swift and GBM, SGR J0418+5729, discovered with GBM and the Interplanetary Network (IPN). A third was SGR Jl550-5418, a source originally classified as an Anomalous X-ray Pulsar (AXP IEI547.0-5408), but exhibiting a very prolific outburst with over 400 events recorded in January 2009. In my talk I will give a short history of magnetars and describe how this, once relatively esoteric field, has emerged as a link between several astrophysical areas including Gamma-Ray Bursts. Finally, I will describe the exciting new results of Fermi in this field and the current status of our knowledge of the magnetar population properties and magnetic fields.

  5. Cinema, Fermi problems and general education

    NASA Astrophysics Data System (ADS)

    Efthimiou, C. J.; Llewellyn, R. A.

    2007-05-01

    During the past few years the authors have developed a new approach to the teaching of physical science, a general education course typically found in the curricula of nearly every college and university. This approach, called Physics in Films (Efthimiou and Llewellyn 2006 Phys. Teach. 44 28-33), uses scenes from popular films to illustrate physical principles and has excited student interest and improved student performance. A similar approach at the senior/high-school level, nicknamed Hollywood Physics, has been developed by Chandler (2006 Phys. Teach. 44 290-2 2002 Phys. Teach. 40 420-4). The two approaches may be considered complementary as they target different student groups. The analyses of many of the scenes in Physics in Films are a direct application of Fermi calculations—estimates and approximations designed to make solutions of complex and seemingly intractable problems understandable to the student non-specialist. The intent of this paper is to provide instructors with examples they can use to develop skill in recognizing Fermi problems and making Fermi calculations in their own courses.

  6. Fermi edge singularity in a tunnel junction

    NASA Astrophysics Data System (ADS)

    Zhang, Jin; Sherkunov, Yury; D'Ambrumenil, Nicholas; Muzykantskii, Boris

    2010-03-01

    We present results on the non-equilibrium Fermi edge singularity (FES) problem in tunnel junctions. The FES, which is present in a Fermi gas subject to any sudden change of potential, manifests itself in the final state many body interaction between the electrons in the leads [1]. We establish a connection between the FES problem in a tunnel junction and the Full Counting Statistics (FCS) for the device [2]. We find that the exact profile of the changing potential (or the profile for the barrier opening and closing in the tunnel junction case) strongly affects the overlap between the initial and final state of the Fermi gas. We factorize the contribution to the FES into two approximately independent terms: one is connected with the short time opening process while the other is concerned with the long time asymptotic effect, namely the Anderson orthogonality catastrophe. We consider applications to a localized level coupled through a tunnel barrier to a 1D lead driven out of equilibrium [3]. References: [1] G. Mahan, Phys. Rev. 163, 1612 (1967); P. Nozieres and C. T. De Dominicis, Phys. Rev. 178, 1079 (1969); P. Anderson, Phys. Rev. Lett. 18, 1049 (1967) [2] J. Zhang, Y. Sherkunov, N. d'Ambrumenil, and B. Muzykantskii, ArXiv:0909.3427 [3] D. Abanin and L. Levitov, Phys. Rev. Lett. 94, 186803 (2005)

  7. The TeraFERMI terahertz source at the seeded FERMI free-electron-laser facility

    SciTech Connect

    Perucchi, A.; Di Mitri, S.; Penco, G.; Allaria, E.; Lupi, S.

    2013-02-15

    We describe the project for the construction of a terahertz (THz) beamline to be called TeraFERMI at the seeded FERMI free electron laser (FEL) facility in Trieste, Italy. We discuss topics as the underlying scientific case, the choice of the source, the expected performance, and THz beam propagation. Through electron beam dynamics simulations we show that the installation of the THz source in the beam dump section provides a new approach for compressing the electron bunch length without affecting FEL operation. Thanks to this further compression of the FEL electron bunch, the TeraFERMI facility is expected to provide THz pulses with energies up to the mJ range during normal FEL operation.

  8. The TeraFERMI terahertz source at the seeded FERMI free-electron-laser facility.

    PubMed

    Perucchi, A; Di Mitri, S; Penco, G; Allaria, E; Lupi, S

    2013-02-01

    We describe the project for the construction of a terahertz (THz) beamline to be called TeraFERMI at the seeded FERMI free electron laser (FEL) facility in Trieste, Italy. We discuss topics as the underlying scientific case, the choice of the source, the expected performance, and THz beam propagation. Through electron beam dynamics simulations we show that the installation of the THz source in the beam dump section provides a new approach for compressing the electron bunch length without affecting FEL operation. Thanks to this further compression of the FEL electron bunch, the TeraFERMI facility is expected to provide THz pulses with energies up to the mJ range during normal FEL operation. PMID:23464184

  9. Frustration and time-reversal symmetry breaking for Fermi and Bose-Fermi systems

    NASA Astrophysics Data System (ADS)

    Sacha, Krzysztof; Targońska, Katarzyna; Zakrzewski, Jakub

    2012-05-01

    The modulation of an optical lattice potential that breaks time-reversal symmetry enables the realization of complex tunneling amplitudes in the corresponding tight-binding model. For a superfluid Fermi gas in a triangular lattice potential with complex tunnelings, the pairing function acquires a complex phase, so the frustrated magnetism of fermions can be realized. Bose-Fermi mixtures of bosonic molecules and unbound fermions in the lattice also show interesting behavior. Due to boson-fermion coupling, the fermions become enslaved by the bosons and the corresponding pairing function takes the complex phase determined by the bosons. In the presence of bosons the Fermi system can reveal both gapped and gapless superfluidity.

  10. Virial expansion for a strongly correlated Fermi system and its application to ultracold atomic Fermi gases

    NASA Astrophysics Data System (ADS)

    Liu, Xia-Ji

    2013-03-01

    A strongly correlated Fermi system plays a fundamental role in very different areas of physics, from neutron stars, quark-gluon plasmas, to high temperature superconductors. Despite the broad applicability, it is notoriously difficult to be understood theoretically because of the absence of a small interaction parameter. Recent achievements of ultracold trapped Fermi atoms near a Feshbach resonance have ushered in enormous changes. The unprecedented control of interaction, geometry and purity in these novel systems has led to many exciting experimental results, which are to be urgently understood at both low and finite temperatures. Here we review the latest developments of virial expansion for a strongly correlated Fermi gas and their applications on ultracold trapped Fermi atoms. We show remarkable, quantitative agreements between virial predictions and various recent experimental measurements at about the Fermi degenerate temperature. For equations of state, we discuss a practical way of determining high-order virial coefficients and use it to calculate accurately the long-sought third-order virial coefficient, which is now verified firmly in experiments at ENS and MIT. We discuss also virial expansion of a new many-body parameter-Tan’s contact. We then turn to less widely discussed issues of dynamical properties. For dynamic structure factors, the virial prediction agrees well with the measurement at the Swinburne University of Technology. For single-particle spectral functions, we show that the expansion up to the second order accounts for the main feature of momentum-resolved rf-spectroscopy for a resonantly interacting Fermi gas, as recently reported by JILA. In the near future, more practical applications with virial expansion are possible, owing to the ever-growing power in computation.

  11. Mechanism of Fermi-level stabilization in semiconductors

    SciTech Connect

    Walukiewicz, W.

    1988-03-15

    A striking correlation between the Fermi-level in heavily radiation damaged semiconductors and at metal-semiconductor interfaces is presented. The correlation provides critical evidence supporting the defect model for Schottky-barrier formation. The Fermi-level energy for both situations corresponds to the average energy of the sp/sup 3/ hybrid. In the case of GaAs, a detailed description of the Fermi-level stabilization caused by amphoteric dangling-bond-like defects is given

  12. Fermi Large Area Telescope Third Source Catalog

    NASA Astrophysics Data System (ADS)

    Acero, F.; Ackermann, M.; Ajello, M.; Albert, A.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Belfiore, A.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bogart, J. R.; Bonino, R.; Bottacini, E.; Bregeon, J.; Britto, R. J.; Bruel, P.; Buehler, R.; Burnett, T. H.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Charles, E.; Chaves, R. C. G.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Conrad, J.; Cutini, S.; D'Ammando, F.; de Angelis, A.; DeKlotz, M.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Venere, L.; Drell, P. S.; Dubois, R.; Dumora, D.; Favuzzi, C.; Fegan, S. J.; Ferrara, E. C.; Finke, J.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Hadasch, D.; Harding, A. K.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Iafrate, G.; Jogler, T.; Jóhannesson, G.; Johnson, R. P.; Johnson, A. S.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Kataoka, J.; Katsuta, J.; Kuss, M.; La Mura, G.; Landriu, D.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Massaro, F.; Mayer, M.; Mazziotta, M. N.; McEnery, J. E.; Michelson, P. F.; Mirabal, N.; Mizuno, T.; Moiseev, A. A.; Mongelli, M.; Monzani, M. E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nuss, E.; Ohno, M.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Panetta, J. H.; Perkins, J. S.; Pesce-Rollins, M.; Piron, F.; Pivato, G.; Porter, T. A.; Racusin, J. L.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Reposeur, T.; Rochester, L. S.; Romani, R. W.; Salvetti, D.; Sánchez-Conde, M.; Saz Parkinson, P. M.; Schulz, A.; Siskind, E. J.; Smith, D. A.; Spada, F.; Spandre, G.; Spinelli, P.; Stephens, T. E.; Strong, A. W.; Suson, D. J.; Takahashi, H.; Takahashi, T.; Tanaka, Y.; Thayer, J. G.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Torres, D. F.; Torresi, E.; Tosti, G.; Troja, E.; Van Klaveren, B.; Vianello, G.; Winer, B. L.; Wood, K. S.; Wood, M.; Zimmer, S.; Fermi-LAT Collaboration

    2015-06-01

    We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in the 100 MeV-300 GeV range. Based on the first 4 yr of science data from the Fermi Gamma-ray Space Telescope mission, it is the deepest yet in this energy range. Relative to the Second Fermi LAT catalog, the 3FGL catalog incorporates twice as much data, as well as a number of analysis improvements, including improved calibrations at the event reconstruction level, an updated model for Galactic diffuse γ-ray emission, a refined procedure for source detection, and improved methods for associating LAT sources with potential counterparts at other wavelengths. The 3FGL catalog includes 3033 sources above 4σ significance, with source location regions, spectral properties, and monthly light curves for each. Of these, 78 are flagged as potentially being due to imperfections in the model for Galactic diffuse emission. Twenty-five sources are modeled explicitly as spatially extended, and overall 238 sources are considered as identified based on angular extent or correlated variability (periodic or otherwise) observed at other wavelengths. For 1010 sources we have not found plausible counterparts at other wavelengths. More than 1100 of the identified or associated sources are active galaxies of the blazar class; several other classes of non-blazar active galaxies are also represented in the 3FGL. Pulsars represent the largest Galactic source class. From source counts of Galactic sources we estimate that the contribution of unresolved sources to the Galactic diffuse emission is ˜3% at 1 GeV.

  13. Spectral function and Fermi surface in high- Tc cuprates

    NASA Astrophysics Data System (ADS)

    Ohta, Y.; Tsutsui, K.; Koshibae, W.; Shimozato, T.; Maekawa, S.

    1993-05-01

    An exact-diagonalization technique on small clusters is used to calculate the single-particle spectral function for the one-band and three-band Hubbard models. We show that the strongly momentum-dependent spectral-weight transfer induced by carrier doping leads to the evolution of the dispersion of low-enegy states. The quasiparticle-like band narrowing is examined.

  14. Ong construction for the reconstructed Fermi surface of underdoped cuprates

    NASA Astrophysics Data System (ADS)

    Robinson, P.; Hussey, N. E.

    2015-12-01

    Using the Ong construction for a two-dimensional metal, we show that the sign change in the Hall coefficient RH of underdoped hole-doped cuprates at low temperature is consistent with the emergence of biaxial charge order recently proposed to explain the observation of low-frequency quantum oscillations. The sharp evolution of RH with temperature, however, can only be reconciled by incorporating a highly anisotropic quasiparticle scattering rate. The magnitude and form of the scattering rate extracted from the fitting imply that those quasiparticles at the vertices of the reconstructed pocket(s) approach the boundary of incoherence at the onset of charge order.

  15. Electronic structure, magnetism, and Fermi surfaces of Gd and Tb

    NASA Astrophysics Data System (ADS)

    Ahuja, R.; Auluck, S.; Johansson, B.; Brooks, M. S. S.

    1994-08-01

    We report on local-spin-density calculations for the ferromagnetic rare-earth metals Gd and Tb using the relativistic first-principles linear-muffin-tin-orbital method in the atomic-sphere approximation. We have used a method which treats simultaneously the localized 4f and the conduction-electron spin magnetism. The 4f magnetic moments are obtained from the Russel-Saunders scheme but the radial 4f spin density is a part of the self-consistent density-functional calculations. The calculated conduction-electron moment for Gd is in very good agreement with the measured value. The calculated de Haas-von Alphen frequencies are in agreement with available data.

  16. Decoherence of Impurities in a Fermi Sea of Ultracold Atoms.

    PubMed

    Cetina, Marko; Jag, Michael; Lous, Rianne S; Walraven, Jook T M; Grimm, Rudolf; Christensen, Rasmus S; Bruun, Georg M

    2015-09-25

    We investigate the decoherence of ^{40}K impurities interacting with a three-dimensional Fermi sea of ^{6}Li across an interspecies Feshbach resonance. The decoherence is measured as a function of the interaction strength and temperature using a spin-echo atom interferometry method. For weak to moderate interaction strengths, we interpret our measurements in terms of scattering of K quasiparticles by the Fermi sea and find very good agreement with a Fermi liquid calculation. For strong interactions, we observe significant enhancement of the decoherence rate, which is largely independent of temperature, pointing to behavior that is beyond the scattering of quasiparticles in the Fermi liquid picture. PMID:26451562

  17. Observation strategies with the Fermi Gamma-ray Space Telescope

    NASA Astrophysics Data System (ADS)

    McEnery, Julie E.; Fermi mission Teams

    2015-01-01

    During the first few years of the Fermi mission, the default observation mode has been an all-sky survey, optimized to provide relatively uniform coverage of the entire sky every three hours. Over 95% of the mission has been performed in this observation mode. However, Fermi is capable of flexible survey mode patterns, and inertially pointed observations both of which allow increased coverage of selected parts of the sky. In this presentation, we will describe the types of observations that Fermi can make, the relative advantages and disadvantages of various observations, and provide guidelines to help Fermi users plan and evaluate non-standard observations.

  18. Decoherence of Impurities in a Fermi Sea of Ultracold Atoms

    NASA Astrophysics Data System (ADS)

    Cetina, Marko; Jag, Michael; Lous, Rianne S.; Walraven, Jook T. M.; Grimm, Rudolf; Christensen, Rasmus S.; Bruun, Georg M.

    2015-09-01

    We investigate the decoherence of 40K impurities interacting with a three-dimensional Fermi sea of 6Li across an interspecies Feshbach resonance. The decoherence is measured as a function of the interaction strength and temperature using a spin-echo atom interferometry method. For weak to moderate interaction strengths, we interpret our measurements in terms of scattering of K quasiparticles by the Fermi sea and find very good agreement with a Fermi liquid calculation. For strong interactions, we observe significant enhancement of the decoherence rate, which is largely independent of temperature, pointing to behavior that is beyond the scattering of quasiparticles in the Fermi liquid picture.

  19. Nonlocal Poisson-Fermi model for ionic solvent

    NASA Astrophysics Data System (ADS)

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution.

  20. Nonlocal Poisson-Fermi model for ionic solvent.

    PubMed

    Xie, Dexuan; Liu, Jinn-Liang; Eisenberg, Bob

    2016-07-01

    We propose a nonlocal Poisson-Fermi model for ionic solvent that includes ion size effects and polarization correlations among water molecules in the calculation of electrostatic potential. It includes the previous Poisson-Fermi models as special cases, and its solution is the convolution of a solution of the corresponding nonlocal Poisson dielectric model with a Yukawa-like kernel function. The Fermi distribution is shown to be a set of optimal ionic concentration functions in the sense of minimizing an electrostatic potential free energy. Numerical results are reported to show the difference between a Poisson-Fermi solution and a corresponding Poisson solution. PMID:27575084

  1. Fermi Gamma-Ray Space Telescope

    NASA Technical Reports Server (NTRS)

    McEnery, Julie E.; Michelson, Peter F.; Paclesas, William S.; Ritz, Steven

    2012-01-01

    The Fermi Gamma-ray Space Telescope, launched in June 2008, is an observatory designed to survey the high-energy gamma-ray sky. The primary instrument, the Large Area Telescope (LAT), provides observations from 20 MeV to greater than 300 GeV. A second instrument, the Gamma-ray Burst Monitor (GBM), provides observations of transients from less than 10 keV to 40 MeV. We describe the design and performance of the instruments and their subsystems, the spacecraft and the ground system.

  2. Fermi GBM: Highlights from the First Year

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2009-01-01

    The Fermi Gamma ray Burst Monitor is an all-sky instrument sensitive to photons from about 8 keV to 40 MeV. I will summarize highlights from the first year, including triggered observations of gamma ray bursts, soft gamma ray repeaters, and terrestrial gamma flashes, and observations in the continuous data of X-ray binaries and accreting X-ray pulsars. GBM provides complementary observations to Swift/BAT, observing many of the same sources, but over a wider energy range.

  3. Fermi matrix element with isospin breaking

    NASA Astrophysics Data System (ADS)

    Guichon, P. A. M.; Thomas, A. W.; Saito, K.

    2011-02-01

    Prompted by the level of accuracy now being achieved in tests of the unitarity of the CKM matrix, we consider the possible modification of the Fermi matrix element for the β-decay of a neutron, including possible in-medium and isospin violating corrections. While the nuclear modifications lead to very small corrections once the Behrends-Sirlin-Ademollo-Gatto theorem is respected, the effect of the u-d mass difference on the conclusion concerning Vud is no longer insignificant. Indeed, we suggest that the correction to the value of |+|+| is at the level of 10.

  4. Enhancing Fermi's Capability for Time Domain Astrophysics

    NASA Astrophysics Data System (ADS)

    McEnery, Julie E.; Fermi-LAT Team

    2016-01-01

    All sky monitors, such as the Fermi Gamma-Ray Space Telescope, play a crucial role in detecting transient and variable non-thermal sources for follow up observations by narrow field observatories. In this poster, we describe recent and upcoming improvements in onboard processing, ground analysis pipelines and observatory operations that will to increase the sensitivity to these objects on timescales of seconds to days and reduce the latency for the information to be disseminated to the scientific community. Finally, we will provide examples of some of the expected science returns from these improvements.

  5. Fermi-LAT Observations of Galactic Transients

    NASA Technical Reports Server (NTRS)

    Hays, Elizabeth

    2011-01-01

    This slide presentation reviews the observations of Galactic transients by the Large Area Telescope (LAT) on the Fermi Gamma Ray Space Telescope. The LAT is producing spectacular results for the GeV transient sky, some of which are shown and reviewed. Some of the results in the GeV range that are discussed in this presentation are: (1) New blazars and unidentified transients (2) the jet of the Cygnus X-3 microquasar (3) gamma rays from V407 Cygni nova (4) Fast high-energy gamma-ray flares from the Crab Nebula

  6. Optical Observations Of Fermi LAT Monitored Blazars

    NASA Astrophysics Data System (ADS)

    Cook, Kyle; Carini, M. T.

    2009-01-01

    For the past 8 years the Bell Observatory at Western Kentucky University has been conducting R band monitoring of the variability of approximately 50 Blazars. A subset of these objects are being routinely observed with the LAT instrument on-board the Fermi Space Telescope. Adding the Robotically Controlled Telescope (RCT) at Kitt Peak National Observatory and observations with the AZT-11 telescope at the Crimean Astrophysical Observatory (CRAO), we are intensively monitoring the Blazars on the Lat monitoring list. We present the results of our long term monitoring of the LAT monitored Blazars, as well as the recent contemporaneous optical R band observations we have obtained of the LAT Blazars.

  7. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Connaughton, V.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R. D.; Kippen, R. M.; vonKienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed 79 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds.

  8. Quasicondensation in Two-Dimensional Fermi Gases.

    PubMed

    Wu, Chien-Te; Anderson, Brandon M; Boyack, Rufus; Levin, K

    2015-12-11

    In this paper we follow the analysis and protocols of recent experiments, combined with simple theory, to arrive at a physical understanding of quasi-condensation in two dimensional Fermi gases. A key signature of quasi-condensation, which contains aspects of Berezinskiĭ-Kosterlitz-Thouless behavior, is a strong zero momentum peak in the pair momentum distribution. Importantly, this peak emerges at a reasonably well defined onset temperature. The resulting phase diagram, pair momentum distribution, and algebraic power law decay are compatible with recent experiments throughout the continuum from BEC to BCS. PMID:26705613

  9. Superfluidity of ultracold atomic gases of Fermi-Fermi mixtures on an optical lattice

    NASA Astrophysics Data System (ADS)

    Wang, Jibiao; Chen, Qijin

    Superfluidity of ultracold atomic gases of Fermi-Fermi mixtures has been under active investigation recently. Experimentally, mixtures of 6Li-40K, 171Yb-173Yband6Li-173Yb, for example, have been prepared and cooled down to the quantum degeneracy regime, making the superfluid phase accessible in the near future. In this talk, we will address the superfluidity of ultracold Fermi-Fermi mixtures on 1D through 3D optical lattices, with varying mass and population imbalances and different densities, as they undergo BCS-BEC crossover, within a pairing fluctuation theory which includes self-consistently the important pseudogap effects at finite temperatures. We will present various phase diagrams and show the dramatic combined effects of mass and population imbalances and lattice periodicity. Implications for future experiment will be discussed. References: [1]Q. J. Chen, I. Kosztin, B. Janko, and K. Levin, Phys. Rev. B 59, 7083 (1999). [2] C. -C. Chien, Y. He, Q. J. Chen, and K. Levin, Phys. Rev. A 77, 011601(R) (2008). [3] C. -C. Chien, Q. J. Chen, and K. Levin, Phys. Rev. A 78, 043612 (2008). [4] Q. J. Chen, Phys. Rev. A 86, 023610 (2012). Work supported by NSF of China and the National Basic Research Program of China.

  10. Atomic Fermi-Bose Mixtures in Inhomogeneous and Random Lattices: From Fermi Glass to Quantum Spin Glass and Quantum Percolation

    NASA Astrophysics Data System (ADS)

    Sanpera, A.; Kantian, A.; Sanchez-Palencia, L.; Zakrzewski, J.; Lewenstein, M.

    2004-07-01

    We investigate strongly interacting atomic Fermi-Bose mixtures in inhomogeneous and random optical lattices. We derive an effective Hamiltonian for the system and discuss its low temperature physics. We demonstrate the possibility of controlling the interactions at local level in inhomogeneous but regular lattices. Such a control leads to the achievement of Fermi glass, quantum Fermi spin-glass, and quantum percolation regimes involving bare and/or composite fermions in random lattices.

  11. FERMI Observations of Gamma -Ray Emission From the Moon

    NASA Technical Reports Server (NTRS)

    Abdo, A. A.; Ackermann, M.; Ajello, M.; Atwoo, W. B.; Baldini, I.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R. D.; Bonamente, E.; Borgland, A. W.; Bottacini, E.; Bouvier, A.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Gehrels, N.; Hays, E.; Thompson, D. J.; McEnery, J. E.; Troja, E.

    2012-01-01

    We report on the detection of high-energy ? -ray emission from the Moon during the first 24 months of observations by the Fermi Large Area Telescope (LAT). This emission comes from particle cascades produced by cosmicray (CR) nuclei and electrons interacting with the lunar surface. The differential spectrum of the Moon is soft and can be described as a log-parabolic function with an effective cutoff at 2-3 GeV, while the average integral flux measured with the LAT from the beginning of observations in 2008 August to the end of 2010 August is F(greater than100 MeV) = (1.04 plus or minus 0.01 [statistical error] plus or minus 0.1 [systematic error]) × 10(sup -6) cm(sup -2) s(sup -1). This flux is about a factor 2-3 higher than that observed between 1991 and 1994 by the EGRET experiment on board the Compton Gamma Ray Observatory, F(greater than100 MeV)˜5×10(sup -7) cm(sup -2) s(sup -1), when solar activity was relatively high. The higher gamma -ray flux measured by Fermi is consistent with the deep solar minimum conditions during the first 24 months of the mission, which reduced effects of heliospheric modulation, and thus increased the heliospheric flux of Galactic CRs. A detailed comparison of the light curve with McMurdo Neutron Monitor rates suggests a correlation of the trends. The Moon and the Sun are so far the only known bright emitters of gamma-rays with fast celestial motion. Their paths across the sky are projected onto the Galactic center and high Galactic latitudes as well as onto other areas crowded with high-energy gamma-ray sources. Analysis of the lunar and solar emission may thus be important for studies of weak and transient sources near the ecliptic.

  12. Fermi level shifting of TiO2 nanostructures during dense electronic excitation

    NASA Astrophysics Data System (ADS)

    Kumar, Avesh; Jaiswal, M. K.; Kanjilal, D.; Joshi, Rakesh K.; Mohanty, T.

    2011-07-01

    Scanning Kelvin probe microscopy has been used to understand the modification of work function of TiO2 with swift heavy ion irradiation. The observed increase in contact potential difference (CPD) indicates a shift in Fermi level towards the valence band, which is due to the development of defects during the bombardment of high energy heavy ions. The change in CPD values on ion irradiation is attributed to electronic excitation induced defect concentration and surface roughness.

  13. Fermi level shifting of TiO{sub 2} nanostructures during dense electronic excitation

    SciTech Connect

    Kumar, Avesh; Jaiswal, M. K.; Mohanty, T.; Kanjilal, D.; Joshi, Rakesh K.

    2011-07-04

    Scanning Kelvin probe microscopy has been used to understand the modification of work function of TiO{sub 2} with swift heavy ion irradiation. The observed increase in contact potential difference (CPD) indicates a shift in Fermi level towards the valence band, which is due to the development of defects during the bombardment of high energy heavy ions. The change in CPD values on ion irradiation is attributed to electronic excitation induced defect concentration and surface roughness.

  14. Fermi LAT Observations of LS 5039

    SciTech Connect

    Abdo, A.A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Baughman, B.M.; Bechtol, K.; Bellazzini, R.; Berenji, B.; Blandford, R.D.; Bloom, E.D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brez, A.; Brigida, M.; Bruel, P.; /more authors..

    2012-03-29

    The first results from observations of the high-mass X-ray binary LS 5039 using the Fermi Gamma-ray Space Telescope data between 2008 August and 2009 June are presented. Our results indicate variability that is consistent with the binary period, with the emission being modulated with a period of 3.903 {+-} 0.005 days; the first detection of this modulation at GeV energies. The light curve is characterized by a broad peak around superior conjunction in agreement with inverse Compton scattering models. The spectrum is represented by a power law with an exponential cutoff, yielding an overall flux (100 MeV-300 GeV) of 4.9 {+-} 0.5(stat) {+-} 1.8(syst) x 10{sup -7} photon cm{sup -2} s{sup -1}, with a cutoff at 2.1 {+-} 0.3(stat) {+-} 1.1(syst) GeV and photon index {Gamma} = 1.9 {+-} 0.1(stat) {+-} 0.3(syst). The spectrum is observed to vary with orbital phase, specifically between inferior and superior conjunction. We suggest that the presence of a cutoff in the spectrum may be indicative of magnetospheric emission similar to the emission seen in many pulsars by Fermi.

  15. Fermi (nee GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steve

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  16. Fermi (Formerly GLAST) at Six Months

    NASA Technical Reports Server (NTRS)

    Ritz, Steven M.

    2009-01-01

    The Fermi Gamma-ray Space Telescope, formerly called GLAST, is a mission to measure the cosmic gamma-ray flux in the energy range 20 MeV to more than 300 GeV, with supporting measurements for gamma-ray bursts from 8 keV to 30 MeV. In addition to breakthrough capabilities in energy coverage and localization, the very large field of view enables observations of 20% of the sky at any instant, and the entire sky on a timescale of a few hours. With its recent launch on 11 June 2008, Fermi now opens a new and important window on a wide variety of phenomena, including pulsars, black holes and active galactic nuclei, gamma-ray bursts, the origin of cosmic rays and supernova remnants, and searches for hypothetical new phenomena such as supersymmetric dark matter annihilations. In addition to early results and the science opportunities, this talk includes a description of the instruments and the mission status and plans.

  17. Parity effect in a mesoscopic Fermi gas

    NASA Astrophysics Data System (ADS)

    Hofmann, Johannes; Lobos, Alejandro M.; Galitski, Victor

    2016-06-01

    We develop a quantitative analytic theory that accurately describes the odd-even effect observed experimentally in a one-dimensional, trapped Fermi gas with a small number of particles [G. Zürn et al., Phys. Rev. Lett. 111, 175302 (2013), 10.1103/PhysRevLett.111.175302]. We find that the underlying physics is similar to the parity effect known to exist in ultrasmall mesoscopic superconducting grains and atomic nuclei. However, in contrast to superconducting nanograins, the density (Hartree) correction dominates over the superconducting pairing fluctuations and leads to a much more pronounced odd-even effect in the mesoscopic, trapped Fermi gas. We calculate the corresponding parity parameter and separation energy using both perturbation theory and a path integral framework in the mesoscopic limit, generalized to account for the effects of the trap, pairing fluctuations, and Hartree corrections. Our results are in an excellent quantitative agreement with experimental data and exact diagonalization. Finally, we discuss a few-particle to many-particle crossover between the perturbative mesoscopic regime and nonperturbative many-body physics that the system approaches in the thermodynamic limit.

  18. Lasing in Bose-Fermi mixtures

    PubMed Central

    Kochereshko, Vladimir P.; Durnev, Mikhail V.; Besombes, Lucien; Mariette, Henri; Sapega, Victor F.; Askitopoulos, Alexis; Savenko, Ivan G.; Liew, Timothy C. H.; Shelykh, Ivan A.; Platonov, Alexey V.; Tsintzos, Simeon I.; Hatzopoulos, Z.; Savvidis, Pavlos G.; Kalevich, Vladimir K.; Afanasiev, Mikhail M.; Lukoshkin, Vladimir A.; Schneider, Christian; Amthor, Matthias; Metzger, Christian; Kamp, Martin; Hoefling, Sven; Lagoudakis, Pavlos; Kavokin, Alexey

    2016-01-01

    Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling. PMID:26822483

  19. Ther FERMI FEL project at TRIESTE

    SciTech Connect

    Walker, R.P.; Bulfone, D.; Cargnello, F.

    1995-12-31

    The goal of the FERMI project - Free Electron Radiation and Matching Instrumentation - is to construct a new user facility for FEL radiation beams covering a broad spectral range (2-250 {mu}m) to complement the high brightness VUV/Soft-Xray radiation available from the ELETTRA synchrotron radiation facility at Trieste. A unique feature of the project will be the possibility of carrying out {open_quote}pump-probe{close_quote} experiments using synchronized radiation beams from FERMI and ELETTRA on the same sample. The project was launched at a meeting with Italian FEL experts held in Trieste on the 18th November 1994, chaired by C. Rubbia, as a collaboration between Sincrotrone Trieste, ENEA (Frascati), INFN (Frascati) and the University of Naples (Department of Electronic Engineering). The facility will make use of an existing linac, that forms part of the ELETTRA injection system, and a hall into which the beam can be extracted. In addition, for the first phase of the project equipment will be used from the suspended INFN/ENEA {open_quote}SURF{close_quote} FEL experiment, including the undulator, beam transport magnets and optical cavity. In this first International FEL Conference report on the project, we summarize the main features of the project, concentrating in particular on the most recent activities, including: results of measurements of the linac beam in the FEL mode of operation, further studies of the electron beam transport system including possibilities for bunch length manipulations, and further numerical calculations of the FEL performance.

  20. The first Fermi LAT supernova remnant catalog

    DOE PAGESBeta

    Acero, F.

    2016-05-16

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope. Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude, allows us to determine an upper limit of 22% on the number of GeV candidatesmore » falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, demonstrates the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. As a result, we model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.« less

  1. Orientifolding of the ABJ Fermi gas

    NASA Astrophysics Data System (ADS)

    Okuyama, Kazumi

    2016-03-01

    The grand partition functions of ABJ theory can be factorized into even and odd parts under the reflection of fermion coordinate in the Fermi gas approach. In some cases, the even/odd part of ABJ grand partition function is equal to that of {N}=5O(n)× USp({n}^') theory, hence it is natural to think of the even/odd projection of grand partition function as an orientifolding of ABJ Fermi gas system. By a systematic WKB analysis, we determine the coefficients in the perturbative part of grand potential of such orientifold ABJ theory. We also find the exact form of the first few "half-instanton" corrections coming from the twisted sector of the reflection of fermion coordinate. For the Chern-Simons level k = 2 ,4 ,8 we find closed form expressions of the grand partition functions of orientifold ABJ theory, and for k = 2 , 4 we prove the functional relations among the grand partition functions conjectured in arXiv:1410.7658.

  2. THE SPECTRAL INDEX PROPERTIES OF FERMI BLAZARS

    SciTech Connect

    Fan, J. H.; Yang, J. H.; Yuan, Y. H.; Wang, J.; Gao, Y.

    2012-12-20

    In this paper, a sample of 451 blazars (193 flat spectrum radio quasars (FSRQs), 258 BL Lacertae objects) with corresponding X-ray and Fermi {gamma}-ray data is compiled to investigate the correlation both between the X-ray spectral index and the {gamma}-ray spectral index and between the spectral index and the luminosity, and to compare the spectral indexes {alpha}{sub X}, {alpha}{sub {gamma}}, {alpha}{sub X{gamma}}, and {alpha}{sub {gamma}X{gamma}} for different subclasses. We also investigated the correlation between the X-ray and the {gamma}-ray luminosity. The following results have been obtained. Our analysis indicates that an anti-correlation exists between the X-ray and the {gamma}-ray spectral indexes for the whole sample. However, when we considered the subclasses of blazars (FSRQs, the low-peaked BL Lacertae objects (LBLs) and the high-peaked BL Lacertae objects (HBLs)) separately, there is not a clear relationship for each subclass. Based on the Fermi-detected sources, we can say that the HBLs are different from FSRQs, while the LBLs are similar to FSRQs.

  3. Pulsar candidates towards Fermi unassociated sources

    NASA Astrophysics Data System (ADS)

    Frail, D. A.; Mooley, K. P.; Jagannathan, P.; Intema, H. T.

    2016-09-01

    We report on a search for steep spectrum radio sources within the 95 per cent confidence error ellipses of the Fermi unassociated sources from the Large Area Telescope (LAT). Using existing catalogues and the newly released Giant Metrewave Radio Telescope all-sky survey at 150 MHz, we identify compact radio sources that are bright at MHz frequencies but faint or absent at GHz frequencies. Such steep spectrum radio sources are rare and constitute a sample of pulsar candidates, selected independently of period, dispersion measure, interstellar scattering and orbital parameters. We find point-like, steep spectrum candidates towards 11 Fermi sources. Based on the gamma-ray/radio positional coincidence, the rarity of such radio sources, and the properties of the 3FGL sources themselves, we argue that many of these sources could be pulsars. They may have been missed by previous radio periodicity searches due to interstellar propagation effects or because they lie in an unusually tight binary. If this hypothesis is correct, then renewed gamma-ray and radio periodicity searches at the positions of the steep spectrum radio sources may reveal pulsations.

  4. Lasing in Bose-Fermi mixtures

    NASA Astrophysics Data System (ADS)

    Kochereshko, Vladimir P.; Durnev, Mikhail V.; Besombes, Lucien; Mariette, Henri; Sapega, Victor F.; Askitopoulos, Alexis; Savenko, Ivan G.; Liew, Timothy C. H.; Shelykh, Ivan A.; Platonov, Alexey V.; Tsintzos, Simeon I.; Hatzopoulos, Z.; Savvidis, Pavlos G.; Kalevich, Vladimir K.; Afanasiev, Mikhail M.; Lukoshkin, Vladimir A.; Schneider, Christian; Amthor, Matthias; Metzger, Christian; Kamp, Martin; Hoefling, Sven; Lagoudakis, Pavlos; Kavokin, Alexey

    2016-01-01

    Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling.

  5. THE FERMI GAMMA-RAY BURST MONITOR

    SciTech Connect

    Meegan, Charles; Lichti, Giselher; Bissaldi, Elisabetta; Diehl, Roland; Greiner, Jochen; Von Kienlin, Andreas; Steinle, Helmut; Bhat, P. N.; Briggs, Michael S.; Connaughton, Valerie; Paciesas, W. S.; Preece, Robert; Wilson, Robert B.; Fishman, Gerald; Kouveliotou, Chryssa; Van der Horst, Alexander J.; McBreen, Sheila

    2009-09-01

    The Gamma-Ray Burst Monitor (GBM) will significantly augment the science return from the Fermi Observatory in the study of gamma-ray bursts (GRBs). The primary objective of GBM is to extend the energy range over which bursts are observed downward from the energy range of the Large Area Telescope (LAT) on Fermi into the hard X-ray range where extensive previous data sets exist. A secondary objective is to compute burst locations onboard to allow re-orienting the spacecraft so that the LAT can observe delayed emission from bright bursts. GBM uses an array of 12 sodium iodide scintillators and two bismuth germanate scintillators to detect gamma rays from {approx}8 keV to {approx}40 MeV over the full unocculted sky. The onboard trigger threshold is {approx}0.7 photons cm{sup -2} s{sup -1} (50-300 keV, 1 s peak). GBM generates onboard triggers for {approx}250 GRBs per year.

  6. Fermi's Paradox - The Last Challenge For Copernicanism?

    NASA Astrophysics Data System (ADS)

    Cirkovic, M. M.

    2009-06-01

    We review Fermi's paradox (or the "Great Silence" problem), not only arguably the oldest and crucial problem for the Search for ExtraTerrestrial Intelligence (SETI), but also a conundrum of profound scientific, philosophical and cultural importance. By a simple analysis of observation selection effects, the correct resolution of Fermi's paradox is certain to tell us something about the future of humanity. Already more than three quarters of century old puzzle -- and a quarter of century since the last major review paper in the field by G. David Brin -- has generated many ingenious discussions and hypotheses. We analyze the often tacit methodological assumptions built in various answers to this puzzle and attempt a new classification of the numerous solutions proposed in an already huge literature on the subject. Finally, we consider the ramifications of various classes of hypotheses for the practical SETI projects. Somewhat paradoxically, it seems that the class of (neo)catastrophic hypotheses gives, on the balance, the strongest justification to optimism regarding our current and near-future SETI efforts.

  7. Lasing in Bose-Fermi mixtures.

    PubMed

    Kochereshko, Vladimir P; Durnev, Mikhail V; Besombes, Lucien; Mariette, Henri; Sapega, Victor F; Askitopoulos, Alexis; Savenko, Ivan G; Liew, Timothy C H; Shelykh, Ivan A; Platonov, Alexey V; Tsintzos, Simeon I; Hatzopoulos, Z; Savvidis, Pavlos G; Kalevich, Vladimir K; Afanasiev, Mikhail M; Lukoshkin, Vladimir A; Schneider, Christian; Amthor, Matthias; Metzger, Christian; Kamp, Martin; Hoefling, Sven; Lagoudakis, Pavlos; Kavokin, Alexey

    2016-01-01

    Light amplification by stimulated emission of radiation, well-known for revolutionising photonic science, has been realised primarily in fermionic systems including widely applied diode lasers. The prerequisite for fermionic lasing is the inversion of electronic population, which governs the lasing threshold. More recently, bosonic lasers have also been developed based on Bose-Einstein condensates of exciton-polaritons in semiconductor microcavities. These electrically neutral bosons coexist with charged electrons and holes. In the presence of magnetic fields, the charged particles are bound to their cyclotron orbits, while the neutral exciton-polaritons move freely. We demonstrate how magnetic fields affect dramatically the phase diagram of mixed Bose-Fermi systems, switching between fermionic lasing, incoherent emission and bosonic lasing regimes in planar and pillar microcavities with optical and electrical pumping. We collected and analyzed the data taken on pillar and planar microcavity structures at continuous wave and pulsed optical excitation as well as injecting electrons and holes electronically. Our results evidence the transition from a Bose gas to a Fermi liquid mediated by magnetic fields and light-matter coupling. PMID:26822483

  8. The First Fermi LAT Supernova Remnant Catalog

    NASA Astrophysics Data System (ADS)

    Acero, F.; Ackermann, M.; Ajello, M.; Baldini, L.; Ballet, J.; Barbiellini, G.; Bastieri, D.; Bellazzini, R.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bonino, R.; Bottacini, E.; Brandt, T. J.; Bregeon, J.; Bruel, P.; Buehler, R.; Buson, S.; Caliandro, G. A.; Cameron, R. A.; Caputo, R.; Caragiulo, M.; Caraveo, P. A.; Casandjian, J. M.; Cavazzuti, E.; Cecchi, C.; Chekhtman, A.; Chiang, J.; Chiaro, G.; Ciprini, S.; Claus, R.; Cohen, J. M.; Cohen-Tanugi, J.; Cominsky, L. R.; Condon, B.; Conrad, J.; Cutini, S.; D’Ammando, F.; de Angelis, A.; de Palma, F.; Desiante, R.; Digel, S. W.; Di Venere, L.; Drell, P. S.; Drlica-Wagner, A.; Favuzzi, C.; Ferrara, E. C.; Franckowiak, A.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Giglietto, N.; Giommi, P.; Giordano, F.; Giroletti, M.; Glanzman, T.; Godfrey, G.; Gomez-Vargas, G. A.; Grenier, I. A.; Grondin, M.-H.; Guillemot, L.; Guiriec, S.; Gustafsson, M.; Hadasch, D.; Harding, A. K.; Hayashida, M.; Hays, E.; Hewitt, J. W.; Hill, A. B.; Horan, D.; Hou, X.; Iafrate, G.; Jogler, T.; Jóhannesson, G.; Johnson, A. S.; Kamae, T.; Katagiri, H.; Kataoka, J.; Katsuta, J.; Kerr, M.; Knödlseder, J.; Kocevski, D.; Kuss, M.; Laffon, H.; Lande, J.; Larsson, S.; Latronico, L.; Lemoine-Goumard, M.; Li, J.; Li, L.; Longo, F.; Loparco, F.; Lovellette, M. N.; Lubrano, P.; Magill, J.; Maldera, S.; Marelli, M.; Mayer, M.; Mazziotta, M. N.; Michelson, P. F.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nemmen, R.; Nuss, E.; Ohsugi, T.; Omodei, N.; Orienti, M.; Orlando, E.; Ormes, J. F.; Paneque, D.; Perkins, J. S.; Pesce-Rollins, M.; Petrosian, V.; Piron, F.; Pivato, G.; Porter, T. A.; Rainò, S.; Rando, R.; Razzano, M.; Razzaque, S.; Reimer, A.; Reimer, O.; Renaud, M.; Reposeur, T.; Rousseau, R.; Saz Parkinson, P. M.; Schmid, J.; Schulz, A.; Sgrò, C.; Siskind, E. J.; Spada, F.; Spandre, G.; Spinelli, P.; Strong, A. W.; Suson, D. J.; Tajima, H.; Takahashi, H.; Tanaka, T.; Thayer, J. B.; Thompson, D. J.; Tibaldo, L.; Tibolla, O.; Torres, D. F.; Tosti, G.; Troja, E.; Uchiyama, Y.; Vianello, G.; Wells, B.; Wood, K. S.; Wood, M.; Yassine, M.; den Hartog, P. R.; Zimmer, S.

    2016-05-01

    To uniformly determine the properties of supernova remnants (SNRs) at high energies, we have developed the first systematic survey at energies from 1 to 100 GeV using data from the Fermi Large Area Telescope (LAT). Based on the spatial overlap of sources detected at GeV energies with SNRs known from radio surveys, we classify 30 sources as likely GeV SNRs. We also report 14 marginal associations and 245 flux upper limits. A mock catalog in which the positions of known remnants are scrambled in Galactic longitude allows us to determine an upper limit of 22% on the number of GeV candidates falsely identified as SNRs. We have also developed a method to estimate spectral and spatial systematic errors arising from the diffuse interstellar emission model, a key component of all Galactic Fermi LAT analyses. By studying remnants uniformly in aggregate, we measure the GeV properties common to these objects and provide a crucial context for the detailed modeling of individual SNRs. Combining our GeV results with multiwavelength (MW) data, including radio, X-ray, and TeV, we demonstrate the need for improvements to previously sufficient, simple models describing the GeV and radio emission from these objects. We model the GeV and MW emission from SNRs in aggregate to constrain their maximal contribution to observed Galactic cosmic rays.

  9. Evidence of Fermi bubbles around M31

    NASA Astrophysics Data System (ADS)

    Pshirkov, M. S.; Vasiliev, V. V.; Postnov, K. A.

    2016-06-01

    Gamma-ray haloes can exist around galaxies due to the interaction of escaping galactic cosmic rays with the surrounding gas. We have searched for such a halo around the nearby giant spiral Andromeda galaxy M31 using almost 7 yr of Fermi LAT data at energies above 300 MeV. The presence of a diffuse gamma-ray halo with total photon flux 2.6 ± 0.6 × 10-9 cm-2 s-1, corresponding to a luminosity (0.3-100 GeV) of (3.2 ± 0.6) × 1038 erg s-1 (for a distance of 780 kpc) was found at a 5.3σ confidence level. The halo form does not correspond to the extended baryonic H I disc of M31, as would be expected in hadronic production of gamma photons from cosmic ray interaction, nor it is spherically symmetric, as could be in the case of dark matter annihilation. The best-fitting halo template corresponds to two 6-7.5 kpc bubbles symmetrically located perpendicular to the M31 galactic disc, similar to the `Fermi bubbles' found around the Milky Way centre, which suggests the past activity of the central supermassive black hole or a star formation burst in M31.

  10. Fermi energy tuning with light to control doping profiles during epitaxy

    SciTech Connect

    Sanders, C. E.; Beaton, D. A.; Reedy, R. C.; Alberi, K.

    2015-05-04

    The influence of light stimulation and photogenerated carriers on the process of dopant surface segregation during growth is studied in molecular beam epitaxially grown Si-doped GaAs structures. The magnitude of surface segregation decreases under illumination by above-bandgap photons, wherein splitting of the quasi Fermi levels reduces the band bending at the growth surface and raises the formation energy of compensating defects that can enhance atomic diffusion. We further show that light-stimulated epitaxy can be used as a practical approach to diminish dopant carry-forward in device structures and improve the performance of inverted modulation-doped quantum wells.

  11. "Where is Everybody?" An Account of Fermi's Question

    DOE R&D Accomplishments Database

    Jones, E. M.

    1985-03-01

    Enrico Fermi's famous question, now central to debates about the prevalence of extraterrestrial civilizations, arose during a luncheon conversation with Emil Konopinski, Edward Teller, and Herbert York in the summer of 1950. Fermi's companions on that day have provided accounts of the incident.

  12. Scaling in electron scattering from a relativistic Fermi gas

    SciTech Connect

    W. M. Alberico; A. Molinari; T. William Donnelly; E. L. Kronenberg; Wally Van Orden

    1988-10-01

    Within the context of the relativistic Fermi gas model, the concept of ''y scaling'' for inclusive electron scattering from nuclei is investigated. Specific kinematic shifts of the single-nucleon response in the nuclear medium can be incorporated with this model. Suggested generalizations beyond the strict Fermi gas model, including treatments of separated longitudinal and transverse responses, are also explored.

  13. Collisional Properties of a Polarized Fermi Gas with Resonant Interactions

    SciTech Connect

    Bruun, G. M.; Recati, A.; Stringari, S.; Pethick, C. J.; Smith, H.

    2008-06-20

    Highly polarized mixtures of atomic Fermi gases constitute a novel Fermi liquid. We demonstrate how information on thermodynamic properties may be used to calculate quasiparticle scattering amplitudes even when the interaction is resonant and apply the results to evaluate the damping of the spin dipole mode. We estimate that under current experimental conditions the mode would be intermediate between the hydrodynamic and collisionless limits.

  14. LETTERS AND COMMENTS: Enrico Fermi: a great teacher

    NASA Astrophysics Data System (ADS)

    Lan, Boon Leong

    2002-09-01

    Enrico Fermi was not only a great theoretical and experimental physicist but a great teacher as well. This article highlights Fermi's approaches in both his formal and informal teaching, and as a thesis advisor. The great teacher inspires - William Arthur Ward

  15. Don't Just Stand There--Teach Fermi Problems!

    ERIC Educational Resources Information Center

    Robinson, A. W.

    2008-01-01

    Fermi problems, or order of magnitude estimates, are often used in introductory physics courses. In this paper I will show that first year students studying physics at university do not arrive with the skill set to solve these problems, and they have to be actively taught how to solve them. Once they have been shown how to solve Fermi problems,…

  16. Fermi-Dirac statistics and the number theory

    NASA Astrophysics Data System (ADS)

    Kubasiak, Anna; Korbicz, Jaroslaw K.; Zakrzewski, Jakub; Lewenstein, Maciej

    2005-11-01

    We relate the Fermi-Dirac statistics of an ideal Fermi gas in a harmonic trap to partitions of given integers into distinct parts, studied in number theory. Using methods of quantum statistical physics we derive analytic expressions for cumulants of the probability distribution of the number of different partitions.

  17. ''Where is everybody. '' An account of Fermi's question

    SciTech Connect

    Jones, E.M.

    1985-03-01

    Fermi's famous question, now central to debates about the prevalence of extraterrestrial civilizations, arose during a luncheon conversation with Emil Konopinski, Edward Teller, and Herbert York in the summer of 1950. Fermi's companions on that day have provided accounts of the incident.

  18. Where is everybody? an account of Fermi's question

    NASA Astrophysics Data System (ADS)

    Jones, E. M.

    1985-03-01

    Fermi's famous question, now central to debates about the prevalence of extraterrestrial civilizations, arose during a luncheon conversation with Emil Konopinski, Edward Teller, and Herbert York in the summer of 1950. Fermi's companions on that day have provided accounts of the incident.

  19. Rotonlike Fulde-Ferrell Collective Excitations of an Imbalanced Fermi Gas in a Two-Dimensional Optical Lattice

    SciTech Connect

    Koinov, Zlatko; Mendoza, Rafael; Fortes, Mauricio

    2011-03-11

    We address the question of whether superfluidity can survive in the case of fermion pairing between different species with mismatched Fermi surfaces using as an example a population-imbalanced mixture of {sup 6}Li atomic Fermi gas loaded in a two-dimensional optical lattice at nonzero temperatures. The collective mode is calculated from the Bethe-Salpeter equations in the general random phase approximation assuming a Fulde-Ferrell order parameter. The numerical solution shows that, in addition to low-energy (Goldstone) mode, two rotonlike minima exist, and therefore, the superfluidity can survive in this imbalanced system.

  20. Changing Horses in Midstream: Fermi LAT Computing and SCons

    NASA Astrophysics Data System (ADS)

    Bogart, J. R.; Golpayegani, N.

    2011-07-01

    (For the Fermi LAT Collaboration) Several years into GLAST (now Fermi) offline software development it became evident we would need a replacement for our original build system, the Configuration Management Tool (CMT) developed at CERN, in order to support Mac users and to keep pace with newer compilers and operating system versions on our traditional platforms, Linux and Windows. The open source product SCons emerged as the only viable alternative and development began in earnest several months before Fermi's successful launch in June of 2008. Over two years later the conversion is nearing completion. This paper describes the conversion to and our use of SCons, concentrating on the resulting environment for users and developers and how it was achieved. Topics discussed include SCons and its interaction with Fermi code, GoGui, a cross-platform gui for Fermi developers, and issues specific to Windows developer support.

  1. Detecting Dark Matter annihilation lines with Fermi

    SciTech Connect

    Ylinen, Tomi; Edmonds, Yvonne; Bloom, Elliott D.; Conrad, Jan; /Royal Inst. Tech., Stockholm /Kalmar U. /KIPAC, Menlo Park /SLAC /Stockholm U.

    2009-05-15

    Dark matter constitutes one of the most intriguing but so far unresolved issues in physics today. In many extensions of the Standard Model the existence of a stable Weakly Interacting Massive Particle (WIMP) is predicted. The WIMP is an excellent dark matter particle candidate and one of the most interesting scenarios include an annihilation of two WIMPs into two gamma-rays. If the WIMPs are assumed to be non-relativistic, the resulting photons will both have an energy equal to the mass of the WIMP and manifest themselves as a monochromatic spectral line in the energy spectrum. This type of signal would represent a 'smoking gun' for dark matter, since no other known astrophysical process should be able to produce it. In these proceedings we give an overview of the different approaches to a search for dark matter lines that the Fermi-LAT collaboration is pursuing and the various challenges involved.

  2. Universal Fermi gases in mixed dimensions.

    PubMed

    Nishida, Yusuke; Tan, Shina

    2008-10-24

    We investigate a two-species Fermi gas in which one species is confined in a two-dimensional plane (2D) or one-dimensional line (1D) while the other is free in the three-dimensional space (3D). We discuss the realization of such a system with the interspecies interaction tuned to resonance. When the mass ratio is in the range 0.0351

  3. Universal Fermi Gases in Mixed Dimensions

    SciTech Connect

    Nishida, Yusuke; Tan, Shina

    2008-10-24

    We investigate a two-species Fermi gas in which one species is confined in a two-dimensional plane (2D) or one-dimensional line (1D) while the other is free in the three-dimensional space (3D). We discuss the realization of such a system with the interspecies interaction tuned to resonance. When the mass ratio is in the range 0.0351

  4. Fermi Observation of GRB 080916C

    SciTech Connect

    Piron, F.

    2009-05-25

    We present the observations of the long-duration Gamma-Ray Burst GRB 080916C by the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT). This event was observed from 8 keV to a photon with an energy of 13.2 GeV. It develops over a 1400 s interval during which the highest number of photons with energy above 100 MeV are detected from a burst. The onset of the high-energy (>100 MeV) emission is delayed by {approx}4.5 s with respect to the low-energy (<1 MeV) emission, which is not detected past 200 s. The broad-band spectrum of the burst is consistent with a single spectral form.

  5. Multiwavelength Challenges in the Fermi Era

    NASA Technical Reports Server (NTRS)

    Thompson, D. J.

    2010-01-01

    The gamma-ray surveys of the sky by AGILE and the Fermi Gamma-ray Space Telescope offer both opportunities and challenges for multiwavelength and multi-messenger studies. Gamma-ray bursts, pulsars, binary sources, flaring Active Galactic Nuclei, and Galactic transient sources are all phenomena that can best be studied with a wide variety of instruments simultaneously or contemporaneously. From the gamma-ray side, a principal challenge is the latency from the time of an astrophysical event to the recognition of this event in the data. Obtaining quick and complete multiwavelength coverage of gamma-ray sources of interest can be difficult both in terms of logistics and in terms of generating scientific interest.

  6. The Mirage of the Fermi Scale

    NASA Astrophysics Data System (ADS)

    Antipin, Oleg; Sannino, Francesco; Tuominen, Kimmo

    2013-09-01

    The discovery of a light Higgs boson at Large Hadron Collider may be suggesting that we need to revise our model building paradigms to understand the origin of the weak scale. We explore the possibility that the Fermi scale is not fundamental but rather a derived one, i.e. a low energy mirage. We show that this scenario emerges in a very natural way in models previously used to break the electroweak symmetry dynamically and suggest a simple dynamical framework for this idea. In our model the electroweak scale results from the interplay between two very high energy scales, one typically of the order of ΛUV 1010GeV and the other around MU 1016GeV, although other values are also possible.

  7. The Gamma-ray Universe through Fermi

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2012-01-01

    Gamma rays, the most powerful form of light, reveal extreme conditions in the Universe. The Fermi Gamma-ray Space Telescope and its smaller cousin AGILE have been exploring the gamma-ray sky for several years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge ga.nuna-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

  8. Momentum sharing in imbalanced Fermi systems

    SciTech Connect

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron stars and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.

  9. Momentum sharing in imbalanced Fermi systems

    DOE PAGESBeta

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.

    2014-10-16

    The atomic nucleus is composed of two different kinds of fermions, protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority fermions (usually neutrons) to have a higher average momentum. Our high-energy electron scattering measurements using 12C, 27Al, 56Fe and 208Pb targets show that, even in heavy neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few body systems to neutron starsmore » and may also be observable experimentally in two-spin state, ultra-cold atomic gas systems.« less

  10. The Gamma-ray Sky with Fermi

    NASA Technical Reports Server (NTRS)

    Thompson, David

    2012-01-01

    Gamma rays reveal extreme, nonthermal conditions in the Universe. The Fermi Gamma-ray Space Telescope has been exploring the gamma-ray sky for more than four years, enabling a search for powerful transients like gamma-ray bursts, novae, solar flares, and flaring active galactic nuclei, as well as long-term studies including pulsars, binary systems, supernova remnants, and searches for predicted sources of gamma rays such as dark matter annihilation. Some results include a stringent limit on Lorentz invariance derived from a gamma-ray burst, unexpected gamma-ray variability from the Crab Nebula, a huge gamma-ray structure associated with the center of our galaxy, surprising behavior from some gamma-ray binary systems, and a possible constraint on some WIMP models for dark matter.

  11. Momentum sharing in imbalanced Fermi systems

    NASA Astrophysics Data System (ADS)

    Hen, O.; Sargsian, M.; Weinstein, L. B.; Piasetzky, E.; Hakobyan, H.; Higinbotham, D. W.; Braverman, M.; Brooks, W. K.; Gilad, S.; Adhikari, K. P.; Arrington, J.; Asryan, G.; Avakian, H.; Ball, J.; Baltzell, N. A.; Battaglieri, M.; Beck, A.; Beck, S. May-Tal; Bedlinskiy, I.; Bertozzi, W.; Biselli, A.; Burkert, V. D.; Cao, T.; Carman, D. S.; Celentano, A.; Chandavar, S.; Colaneri, L.; Cole, P. L.; Crede, V.; D'Angelo, A.; De Vita, R.; Deur, A.; Djalali, C.; Doughty, D.; Dugger, M.; Dupre, R.; Egiyan, H.; El Alaoui, A.; El Fassi, L.; Elouadrhiri, L.; Fedotov, G.; Fegan, S.; Forest, T.; Garillon, B.; Garcon, M.; Gevorgyan, N.; Ghandilyan, Y.; Gilfoyle, G. P.; Girod, F. X.; Goetz, J. T.; Gothe, R. W.; Griffioen, K. A.; Guidal, M.; Guo, L.; Hafidi, K.; Hanretty, C.; Hattawy, M.; Hicks, K.; Holtrop, M.; Hyde, C. E.; Ilieva, Y.; Ireland, D. G.; Ishkanov, B. I.; Isupov, E. L.; Jiang, H.; Jo, H. S.; Joo, K.; Keller, D.; Khandaker, M.; Kim, A.; Kim, W.; Klein, F. J.; Koirala, S.; Korover, I.; Kuhn, S. E.; Kubarovsky, V.; Lenisa, P.; Levine, W. I.; Livingston, K.; Lowry, M.; Lu, H. Y.; MacGregor, I. J. D.; Markov, N.; Mayer, M.; McKinnon, B.; Mineeva, T.; Mokeev, V.; Movsisyan, A.; Camacho, C. Munoz; Mustapha, B.; Nadel-Turonski, P.; Niccolai, S.; Niculescu, G.; Niculescu, I.; Osipenko, M.; Pappalardo, L. L.; Paremuzyan, R.; Park, K.; Pasyuk, E.; Phelps, W.; Pisano, S.; Pogorelko, O.; Price, J. W.; Procureur, S.; Prok, Y.; Protopopescu, D.; Puckett, A. J. R.; Rimal, D.; Ripani, M.; Ritchie, B. G.; Rizzo, A.; Rosner, G.; Roy, P.; Rossi, P.; Sabatié, F.; Schott, D.; Schumacher, R. A.; Sharabian, Y. G.; Smith, G. D.; Shneor, R.; Sokhan, D.; Stepanyan, S. S.; Stepanyan, S.; Stoler, P.; Strauch, S.; Sytnik, V.; Taiuti, M.; Tkachenko, S.; Ungaro, M.; Vlassov, A. V.; Voutier, E.; Walford, N. K.; Wei, X.; Wood, M. H.; Wood, S. A.; Zachariou, N.; Zana, L.; Zhao, Z. W.; Zheng, X.; Zonta, I.; aff16

    2014-10-01

    The atomic nucleus is composed of two different kinds of fermions: protons and neutrons. If the protons and neutrons did not interact, the Pauli exclusion principle would force the majority of fermions (usually neutrons) to have a higher average momentum. Our high-energy electron-scattering measurements using 12C, 27Al, 56Fe, and 208Pb targets show that even in heavy, neutron-rich nuclei, short-range interactions between the fermions form correlated high-momentum neutron-proton pairs. Thus, in neutron-rich nuclei, protons have a greater probability than neutrons to have momentum greater than the Fermi momentum. This finding has implications ranging from nuclear few-body systems to neutron stars and may also be observable experimentally in two-spin-state, ultracold atomic gas systems.

  12. Adaptationism Fails to Resolve Fermi's Paradox

    NASA Astrophysics Data System (ADS)

    Cirkovic, M. M.; Dragicevic, I.; Beric-Bjedov, T.

    2005-06-01

    One of the most interesting problems in the nascent discipline of astrobiology is more than half-century old Fermi's paradox: why, considering extraordinary young age of Earth and the Solar System in the Galactic context, don't we perceive much older intelligent communities or signposts of their activity? In spite of a vigorous research activity in recent years, especially bolstered by successes of astrobiology in finding extrasolar planets and extremophiles, this problem (also known as the "Great Silence" or "astrosociological" paradox) remains as open as ever. In a previous paper, we have discussed a particular evolutionary solution suggested by Karl Schroeder based on the currently dominant evolutionary doctrine of adaptationism. Here, we extend that discussion with emphasis on the problems such a solution is bound to face, and conclude that it is ultimately quite unlikely.

  13. Klein factors and Fermi-Bose equivalence

    NASA Astrophysics Data System (ADS)

    Lee, Taejin

    2016-06-01

    Generalizing the kink operator of the Heisenberg spin 1/2 model, we construct a set of Klein factors explicitly such that (1+1)-dimensional fermion theories with an arbitrary number of species are mapped onto the corresponding boson theories with the same number of species and vice versa. The actions for the resultant theories do not possess a nontrivial Klein factor. With this set of Klein factors, we are also able to map the simple boundary states, such as the Neumann and the Dirichlet boundary states, of the fermion (boson) theory onto those of the boson (fermion) theory. Applications of the Fermi-Bose equivalence with the constructed Klein factors to well-known (1+1)-dimensional theories have been discussed.

  14. Fermi GBM Observations of Terrestrial Gamma Flashes

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.; Briggs, M. S.; Fishman, G. J.; Bhat, P. N.; Paciesas, W. S.; Preece, R.; Kippen, R. M.; von Kienlin, A.; Dwyer, J. R.; Smith, D. M.; Holzworth, R.

    2010-01-01

    In its first two years of operation, the Fermi Gamma Ray Burst Monitor (GBM) has observed more than 77 Terrestrial Gamma Flashes (TGFs). The thick Bismuth Germanate (BGO) detectors are excellent for TGF spectroscopy, having a high probability of recording the full energy of an incident photon, spanning a broad energy range from 150 keV to 40 MeV, and recording a large number of photons per TGF. Correlations between GBM TGF triggers and lightning sferics detected with the World-Wide Lightning Location Network indicate that TGFs and lightning are simultaneous to within tens of microseconds. The energy spectra of some TGFs have strong 511 keV positron annihilation lines, indicating that these TGFs contain a large fraction of positrons

  15. Topological superradiance in a degenerate Fermi gas

    NASA Astrophysics Data System (ADS)

    Pan, Jian-Song; Liu, Xiong-Jun; Zhang, Wei; Yi, Wei; Guo, Guang-Can; Yi's Group Team; Liu's Group Team; Zhang's Group Team

    2015-05-01

    We predict the existence of a topological superradiant state in a two-component degenerate Fermi gas in a cavity. The superradiant light generation in the transversely driven cavity mode induces a cavity-assisted spin-orbit coupling in the system and opens a bulk gap at half filling. This mechanism can simultaneously drive a topological phase transition in the system, yielding a topological superradiant state. We map out the steady-state phase diagram of the system in the presence of an effective Zeeman field, and identify a critical tetracritical point beyond which the topological and the conventional superraidiant phase boundaries separate. We propose to detect the topological phase transition based on its signatures in either the momentum distribution of the atoms or in the cavity photon occupation.

  16. The Lorenz-Fermi-Pasta-Ulam experiment

    NASA Astrophysics Data System (ADS)

    Balmforth, N. J.; Pasquero, C.; Provenzale, A.

    2000-04-01

    We consider a chain of Lorenz ’63 systems connected through a local, nearest-neighbour coupling. We refer to the resulting system as the Lorenz-Fermi-Pasta-Ulam lattice because of its similarity to the celebrated experiment conducted by Fermi, Pasta and Ulam. At large coupling strengths, the systems synchronize to a global, chaotic orbit of the Lorenz attractor. For smaller coupling, the synchronized state loses stability. Instead, steady, spatially structured equilibrium states are observed. These steady states are related to the heteroclinic orbits of the system describing stationary solutions to the partial differential equation that emerges on taking the continuum limit of the lattice. Notably, these orbits connect saddle-foci, suggesting the existence of a multitude of such equilibria in relatively wide systems. On lowering the coupling strength yet further, the steady states lose stability in what appear to be always subcritical Hopf bifurcations. This can lead to a variety of time-dependent states with fixed time-averaged spatial structure. Such solutions can be limit cycles, tori or possibly chaotic attractors. “Cluster states” can also occur (though with less regularity), consisting of lattices in which the elements are partitioned into families of synchronized subsystems. Ultimately, for very weak coupling, the lattice loses its time-averaged spatial structure. At this stage, the properties of the lattice are probably chaotic and approximately scale with the lattice size, suggesting that the system is essentially an ensemble of elements that evolve largely independent of one another. The weak interaction, however, is sufficient to induce widespread coherent phases; these are ephemeral states in which the dynamics of one or more subsystems takes a more regular form. We present measures of the complexity of these incoherent lattices, and discuss the concept of a “dynamical horizon” (that is, the distance along the lattice that one subsystem can

  17. From ultracold Fermi Gases to Neutron Stars

    NASA Astrophysics Data System (ADS)

    Salomon, Christophe

    2012-02-01

    Ultracold dilute atomic gases can be considered as model systems to address some pending problem in Many-Body physics that occur in condensed matter systems, nuclear physics, and astrophysics. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold Bose and Fermi gases [1,2,3]. This method allows stringent tests of recent many-body theories. For attractive spin 1/2 fermions with tunable interaction (^6Li), we will show that the gas thermodynamic properties can continuously change from those of weakly interacting Cooper pairs described by Bardeen-Cooper-Schrieffer theory to those of strongly bound molecules undergoing Bose-Einstein condensation. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas. Surprisingly, the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory [3] and we localize the superfluid phase transition. A detailed comparison with theories including recent Monte-Carlo calculations will be presented. Moving away from the unitary gas, the Lee-Huang-Yang and Lee-Yang beyond-mean-field corrections for low density bosonic and fermionic superfluids are quantitatively measured for the first time. Despite orders of magnitude difference in density and temperature, our equation of state can be used to describe low density neutron matter such as the outer shell of neutron stars. [4pt] [1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, Nature 463, 1057 (2010) [0pt] [2] N. Navon, S. Nascimbène, F. Chevy, and C. Salomon, Science 328, 729 (2010) [0pt] [3] S. Nascimbène, N. Navon, S. Pilati, F. Chevy, S. Giorgini, A. Georges, and C. Salomon, Phys. Rev. Lett. 106, 215303 (2011)

  18. Fermi pockets and quantum oscillations of the Hall coefficient in high-temperature superconductors

    PubMed Central

    Chakravarty, Sudip; Kee, Hae-Young

    2008-01-01

    Recent quantum oscillation measurements in high-temperature superconductors in high magnetic fields and low temperatures have ushered in a new era. These experiments explore the normal state from which superconductivity arises and provide evidence of a reconstructed Fermi surface consisting of electron and hole pockets in a regime in which such a possibility was previously considered to be remote. More specifically, the Hall coefficient has been found to oscillate according to the Onsager quantization condition, involving only fundamental constants and the areas of the pockets, but with a sign that is negative. Here, we explain the observations with the theory that the alleged normal state exhibits a hidden order, the d-density wave, which breaks symmetries signifying time reversal, translation by a lattice spacing, and a rotation by an angle π/2, while the product of any two symmetry operations is preserved. The success of our analysis underscores the importance of spontaneous breaking of symmetries, Fermi surface reconstruction, and conventional quasiparticles. We primarily focus on the version of the order that is commensurate with the underlying crystalline lattice, but we also touch on the consequences if the order were to incommensurate. It is shown that whereas commensurate order results in two independent oscillation frequencies as a function of the inverse of the applied magnetic field, incommensurate order leads to three independent frequencies. The oscillation amplitudes, however, are determined by the mobilities of the charge carriers comprising the Fermi pockets. PMID:18577585

  19. Non-Fermi-liquid behavior of large-NB quantum critical metals

    NASA Astrophysics Data System (ADS)

    Fitzpatrick, A. Liam; Kachru, Shamit; Kaplan, Jared; Raghu, S.

    2014-04-01

    The problem of continuous quantum phase transitions in metals involves critical bosons coupled to a Fermi surface. We solve the theory in the limit of a large number, NB, of bosonic flavors, where the bosons transform in the adjoint representation (a matrix representation), while the fermions are in the fundamental representation (a vector representation) of a global SU (NB) flavor symmetry group. The leading large NB solution corresponds to a non-Fermi liquid coupled to Wilson-Fisher bosons. In a certain energy range, the fermion velocity vanishes—resulting in the destruction of the Fermi surface. Subleading 1/NB corrections correspond to a qualitatively different form of Landau damping of the bosonic critical fluctuations. We discuss the model in d =3-ɛ but because of the additional control afforded by large NB, our results are valid down to d =2. In the limit ɛ ≪1, the large NB solution is consistent with the renormalization group analysis of Fitzpatrick et al. [Phys. Rev. B 88, 125116 (2013), 10.1103/PhysRevB.88.125116].

  20. Discovery of the first Weyl fermion semimetal and topological Fermi arcs in TaAs

    NASA Astrophysics Data System (ADS)

    Xu, Suyang; 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; Wang, Baokai; Bansil, Arun; Chou, Fangcheng; Shibayev, Pavel; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid

    Weyl semimetals have opened a new era in condensed matter physics and materials science. They host Weyl fermions as emergent quasiparticles and admit a topological classification that protects Fermi arc surface states on the boundary. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of the first Weyl semimetal, TaAs. 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. The work at Princeton and Princeton-led ARPES measurements were supported by the Gordon and Betty Moore Foundations EPiQS Initiative through Grant GBMF4547 (Hasan) and by U.S. Department of Energy DE-FG-02-05ER46200.

  1. Collapse and revival of the Fermi sea in a Bose-Fermi mixture

    NASA Astrophysics Data System (ADS)

    Iyer, Deepak; Will, Sebastian; Rigol, Marcos

    2014-05-01

    The collapse and revival of quantum fields is one of the most pristine forms of coherent quantum dynamics far from equilibrium. Until now, it has only been observed in the dynamical evolution of bosonic systems. We report on the first observation of the boson mediated collapse and revival of the Fermi sea in a Bose-Fermi mixture. Specifically, we present a simple model which captures the experimental observations shown in the talk titled Observation of Collapse and Revival Dynamics in the Fermionic Component of a Lattice Bose-Fermi Mixture by Sebastian Will. Our theoretical analysis shows why the results are robust to the presence of harmonic traps during the loading or the time evolution phase. It also makes apparent that the fermionic dynamics is independent of whether the bosonic component consists of a coherent state or localized Fock states with random occupation numbers. Because of the robustness of the experimental results, we argue that this kind of collapse and revival experiment can be used to accurately characterize interactions between bosons and fermions in a lattice.

  2. Electron-lattice coupling and partial nesting as the origin of Fermi-Arcs in manganites

    SciTech Connect

    Salafranca Laforga, Juan I; Alvarez, Gonzalo; Dagotto, Elbio R

    2009-01-01

    A tight-binding model for e{sub g} electrons coupled to Jahn-Teller lattice distortions is studied via Monte Carlo simulations. By focusing on the periodicity of the cooperative Jahn-Teller distortions, and the one-particle spectral function, our results clarify the physical origin of the Fermi-arcs phase observed in layered manganites. In a range of parameters where no broken symmetry phase exists, the nearly nested Fermi surface favors certain correlations between Jahn-Teller distortions. The spectral weight near the Brillouin zone edge is suppressed, leading to the pseudogap in the density of states. We discuss the stability of this phase as a function of temperature and coupling strength for different hole dopings.

  3. Hydrogen-bond dynamics and Fermi resonance in high-pressure methane filled ice.

    PubMed

    Klug, D D; Tse, J S; Liu, Zhenxian; Hemley, Russell J

    2006-10-21

    High-pressure, variable temperature infrared spectroscopy and first-principles calculations on the methane filled ice structure (MH-III) at high pressures are used to investigate the vibrational dynamics related to pressure induced modifications in hydrogen bonding. Infrared spectroscopy of isotopically dilute solutions of H(2)O in D(2)O is employed together with first-principles calculations to characterize proton dynamics with the pressure induced shortening of hydrogen bonds. A Fermi resonance is identified and shown to dominate the infrared spectrum in the pressure region between 10 and 30 GPa. Significant differences in the effects of the Fermi resonance observed between 10 and 300 K arise from the double-well potential energy surface of the hydrogen bond and quantum effects associated with the proton dynamics. PMID:17059274

  4. Hydrogen-bond Dynamics and Fermi Resonance in High-pressure Methane Filled Ice

    SciTech Connect

    Klug,D.; Tse, J.; Liu, Z.; Hemley, R.

    2006-01-01

    High-pressure, variable temperature infrared spectroscopy and first-principles calculations on the methane filled ice structure (MH-III) at high pressures are used to investigate the vibrational dynamics related to pressure induced modifications in hydrogen bonding. Infrared spectroscopy of isotopically dilute solutions of H{sub 2}O in D{sub 2}O is employed together with first-principles calculations to characterize proton dynamics with the pressure induced shortening of hydrogen bonds. A Fermi resonance is identified and shown to dominate the infrared spectrum in the pressure region between 10 and 30 GPa. Significant differences in the effects of the Fermi resonance observed between 10 and 300 K arise from the double-well potential energy surface of the hydrogen bond and quantum effects associated with the proton dynamics.

  5. Modified Fermi sphere, pairing gap, and critical temperature for the BCS-BEC crossover

    SciTech Connect

    Floerchinger, S.; Wetterich, C.; Scherer, M. M.

    2010-06-15

    We investigate the phase diagram of two-component fermions in the BCS-BEC (Bose-Einstein condensate) crossover. Using functional renormalization-group equations we calculate the effect of quantum fluctuations on the fermionic self-energy parametrized by a wave-function renormalization, an effective Fermi radius, and the gap. This allows us to follow the modifications of the Fermi surface and the dispersion relation for fermionic excitations throughout the whole crossover region. We also determine the critical temperature of the second-order phase transition to superfluidity. Our results are in agreement with BCS theory including Gorkov's correction for a small negative scattering length a and with an interacting Bose gas for a small positive a. At the unitarity point the result for the gap at zero temperature agrees well with quantum Monte Carlo simulations, while the critical temperature differs.

  6. Electronic structure Fermi liquid theory of high Tc superconductors: Comparison of predictions with experiments

    NASA Technical Reports Server (NTRS)

    Yu, Jaejun; Freeman, A. J.

    1991-01-01

    Predictions of local density functional (LDF) calculations of the electronic structure and transport properties of high T(sub c) superconductors are presented. As evidenced by the excellent agreement with both photoemission and positron annihilation experiments, a Fermi liquid nature of the 'normal' state of the high T(sub c) superconductors become clear for the metallic phase of these oxides. In addition, LDF predictions on the normal state transport properties are qualitatively in agreement with experiments on single crystals. It is emphasized that the signs of the Hall coefficients for the high T(sub c) superconductors are not consistent with the types of dopants (e.g., electron-doped or hole-doped) but are determined by the topology of the Fermi surfaces obtained from the LDF calculations.

  7. Discovery of the first Weyl fermion semimetal and topological Fermi arcs in TaAs

    NASA Astrophysics Data System (ADS)

    Xu, Suyang; 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; Wang, Baokai; Bansil, Arun; Chou, Fangcheng; Shibayev, Pavel; Lin, Hsin; Jia, Shuang; Hasan, M. Zahid

    Weyl semimetals have opened a new era in condensed matter physics and materials science. They host Weyl fermions as emergent quasiparticles and admit a topological classification that protects Fermi arc surface states on the boundary. This unusual electronic structure has deep analogies with particle physics and leads to unique topological properties. We report the experimental discovery of the first Weyl semimetal, TaAs. We directly observe the Weyl fermions and the Fermi arcs in a TaAs single crystal and demonstrate its topological character. Our work opens the field for studying of Weyl fermions in table-top experiments. The work at Princeton and Princeton-led ARPES measurements were supported by the Gordon and Betty Moore Foundations EPiQS Initiative through grant GBMF4547 (Hasan) and by U.S. Department of Energy DE-FG-02-05ER46200.

  8. Non-Fermi liquid behavior and non-universal superconducting gap structure in Fe-pnictides

    NASA Astrophysics Data System (ADS)

    Matsuda, Yuji

    2010-03-01

    The discovery of Fe-pnictide superconductors with Tc exceeding 55 K raises fundamental questions about origin of high-Tc superconductivity. Here we report the systematic studies of the normal-state charge transport, Fermi surface structure and superconducting gap structure in high-quality single crystals of BaFe2(As1-xPx)2 (0 <=x <=0.71), ranging from the SDW state to overdoped Fermi liquid state. Near the SDW boundary, the transport coefficients, including resistivity, Hall coefficient and magnetoresistance, exhibit striking deviations from the Fermi liquid properties [1]. The Fermi surface structure determined by the dHvA effect shows that in the superconducting dome the volume of the electron and hole sheets shrink linearly and the effective masses become strongly enhanced with decreasing x [2]. It is likely that these trends originate from the many-body interaction which gives rise to superconductivity. The penetration depth, thermal conductivity and NMR data for BaFe2(As0.67P0.33)2 (Tc=30 K) provide unambiguous evidence for line nodes in the superconducting gap function [3], in sharp contrast to the other Fe-based compounds with fully gapped structure. This indicates that the gap structure of Fe-based high-Tc superconductors is not universal.[1] S. Kasahara et al., arXiv:0905.4427 [2] H. Shishido et al., arXiv:0910.3634 [3] K. Hashimoto et al., arXiv:0907.4399 [4] K. Hashimoto et al., Phys. Rev. Lett. 102, 017002 (2009), ibid 102, 207001 (2009).

  9. Looking for the Northern Fermi Bubble with HAWC

    NASA Astrophysics Data System (ADS)

    Ayala, Hugo; Zhou, Hao; Huentemeyer, Petra; HAWC Collaboration

    2016-03-01

    The Fermi Bubbles were discovered in the GeV gamma-ray data from the Fermi Telescope in 2010. They extend up to 55° above and below the Galactic Center forming two large and homogeneous regions of spectrally hard gamma-ray emission. Understanding the mechanisms which produce the observed hard spectrum will help understand the origin of the Fermi Bubbles. Both hadronic and leptonic models can describe the spectrum of the bubbles, though the leptonic model can explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff between 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain their spectrum. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With a large field of view and good sensitivity to spatially extended sources, HAWC is the ground-based observatory best suited to detect extended regions like the Fermi Bubbles. We present a search for emission from the Fermi Bubble visible to HAWC.

  10. Transparent Conducting Oxides for Photovoltaics: Manipulation of Fermi Level, Work Function and Energy Band Alignment

    SciTech Connect

    Klein, A.; Körber, C.; Wachau, A.; Säuberlich, F.; Gassenbauer, Y.; Harvey, S.P.; Proffit, Diana E.; Mason, Thomas O.

    2010-11-02

    Doping limits, band gaps, work functions and energy band alignments of undoped and donor-doped transparent conducting oxides ZnO, In{sub 2}O{sub 3}, and SnO{sub 2} as accessed by X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) are summarized and compared. The presented collection provides an extensive data set of technologically relevant electronic properties of photovoltaic transparent electrode materials and illustrates how these relate to the underlying defect chemistry, the dependence of surface dipoles on crystallographic orientation and/or surface termination, and Fermi level pinning.

  11. Attractive and repulsive Fermi polarons in two dimensions.

    PubMed

    Koschorreck, Marco; Pertot, Daniel; Vogt, Enrico; Fröhlich, Bernd; Feld, Michael; Köhl, Michael

    2012-05-31

    The dynamics of a single impurity in an environment is a fundamental problem in many-body physics. In the solid state, a well known case is an impurity coupled to a bosonic bath (such as lattice vibrations); the impurity and its accompanying lattice distortion form a new entity, a polaron. This quasiparticle plays an important role in the spectral function of high-transition-temperature superconductors, as well as in colossal magnetoresistance in manganites. For impurities in a fermionic bath, studies have considered heavy or immobile impurities which exhibit Anderson's orthogonality catastrophe and the Kondo effect. More recently, mobile impurities have moved into the focus of research, and they have been found to form new quasiparticles known as Fermi polarons. The Fermi polaron problem constitutes the extreme, but conceptually simple, limit of two important quantum many-body problems: the crossover between a molecular Bose-Einstein condensate and a superfluid with BCS (Bardeen-Cooper-Schrieffer) pairing with spin-imbalance for attractive interactions, and Stoner's itinerant ferromagnetism for repulsive interactions. It has been proposed that such quantum phases (and other elusive exotic states) might become realizable in Fermi gases confined to two dimensions. Their stability and observability are intimately related to the theoretically debated properties of the Fermi polaron in a two-dimensional Fermi gas. Here we create and investigate Fermi polarons in a two-dimensional, spin-imbalanced Fermi gas, measuring their spectral function using momentum-resolved photoemission spectroscopy. For attractive interactions, we find evidence for a disputed pairing transition between polarons and tightly bound dimers, which provides insight into the elementary pairing mechanism of imbalanced, strongly coupled two-dimensional Fermi gases. Additionally, for repulsive interactions, we study novel quasiparticles--repulsive polarons--the lifetime of which determines the

  12. The Fermi-GBM X-ray burst monitor

    NASA Astrophysics Data System (ADS)

    Linares, M.; Fermi GBM X-ray Burst Collaboration

    2010-12-01

    We discuss the first results of the Fermi-GBM all-sky search for X-ray bursts. The very large field of view and X-ray response of the Fermi-GBM make it a unique instrument to study rare, bright and short-lived X-ray bursts. We are performing a systematic search that exploits such capabilities. We present results on long/intermediate type I X-ray bursts, an unusual kind of thermonuclear bursts from accreting neutron stars, and show how Fermi-GBM is giving for the first time robust measurements of their recurrence time.

  13. Physics of ultracold Fermi gases revealed by spectroscopies

    NASA Astrophysics Data System (ADS)

    Törmä, Päivi

    2016-04-01

    This article provides a brief review of how various spectroscopies have been used to investitage many-body quantum phenomena in the context of ultracold Fermi gases. In particular, work done with RF spectroscopy, Bragg spectroscopy and lattice modulation spectroscopy is considered. The theoretical basis of these spectroscopies, namely linear response theory in the many-body quantum physics context is briefly presented. Experiments related to the BCS-BEC crossover, imbalanced Fermi gases, polarons, possible pseudogap and Fermi liquid behaviour and measuring the contact are discussed. Remaining open problems and goals in the field are sketched from the perspective how spectroscopies could contribute.

  14. Fermi Gamma-Ray Space Telescope Science Overview

    NASA Technical Reports Server (NTRS)

    Thompson, David J.

    2010-01-01

    After more than 2 years of science operations, the Fermi Gamma-ray Space Telescope continues to survey the high-energy sky on a daily basis. In addition to the more than 1400 sources found in the first Fermi Large Area Telescope Catalog (I FGL), new results continue to emerge. Some of these are: (1) Large-scale diffuse emission suggests possible activity from the Galactic Center region in the past; (2) a gamma-ray nova was found, indicating particle acceleration in this binary system; and (3) the Crab Nebula, long thought to be a steady source, has varied in the energy ranges seen by both Fermi instruments.

  15. X.509 Authentication/Authorization in FermiCloud

    SciTech Connect

    Kim, Hyunwoo; Timm, Steven

    2014-11-11

    We present a summary of how X.509 authentication and authorization are used with OpenNebula in FermiCloud. We also describe a history of why the X.509 authentication was needed in FermiCloud, and review X.509 authorization options, both internal and external to OpenNebula. We show how these options can be and have been used to successfully run scientific workflows on federated clouds, which include OpenNebula on FermiCloud and Amazon Web Services as well as other community clouds. We also outline federation options being used by other commercial and open-source clouds and cloud research projects.

  16. Fermi Large Area Telescope Bright Gamma-ray Source List

    SciTech Connect

    Abdo, Aous A.; Ackermann, M.; Ajello, M.; Atwood, W.B.; Axelsson, M.; Baldini, L.; Ballet, J.; Band, D.L.; Barbiellini, Guido; Bastieri, Denis; Bechtol, K.; Bellazzini, R.; Berenji, B.; Bignami, G.F.; Bloom, Elliott D.; Bonamente, E.; Borgland, A.W.; Bregeon, J.; Brigida, M.; Bruel, P.; Burnett, Thompson H.; /more authors..

    2009-05-15

    Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

  17. Thermodynamics of a trapped Bose-Fermi mixture

    SciTech Connect

    Hu, Hui; Liu, Xia-Ji

    2003-08-01

    By using the Hartree-Fock-Bogoliubov equations within the Popov approximation, we investigate the thermodynamic properties of a dilute binary Bose-Fermi mixture confined in an isotropic harmonic trap. For mixtures with an attractive Bose-Fermi interaction, we find a sizable enhancement of the condensate fraction and of the critical temperature of Bose-Einstein condensation with respect to the predictions for a pure interacting Bose gas. Conversely, the influence of the repulsive Bose-Fermi interaction is less pronounced. The possible relevance of our results in current experiments on trapped {sup 87}Rb-{sup 40}K mixtures is discussed.

  18. Fermi-liquid theory of ultracold trapped Fermi gases: Implications for pseudogap physics and other strongly correlated phases

    SciTech Connect

    Chien, Chih-Chun; Levin, K.

    2010-07-15

    We show how Fermi-liquid theory can be applied to ultracold Fermi gases, thereby expanding their ''simulation'' capabilities to a class of problems of interest to multiple physics subdisciplines. We introduce procedures for measuring and calculating position-dependent Landau parameters. This lays the groundwork for addressing important controversial issues: (i) the suggestion that thermodynamically, the normal state of a unitary gas is indistinguishable from a Fermi liquid and (ii) that a fermionic system with strong repulsive contact interactions is associated with either ferromagnetism or localization; this relates as well to {sup 3}He and its p-wave superfluidity.

  19. Millisecond Pulsars at Gamma-Ray Energies: Fermi Detections and Implications

    NASA Technical Reports Server (NTRS)

    Harding, Alice K.

    2011-01-01

    The Fermi Gamma-Ray Space Telescope has revolutionized the study of pulsar physics with the discovery of new populations of radio quiet and millisecond gamma-ray pulsars. The Fermi Large Area Telescope has so far discovered approx.20 new gamma-ray millisecond pulsars (MSPs) by both folding at periods of known radio MSPs or by detecting them as gamma-ray sources that are followed up by radio pulsar searches. The second method has resulted in a phenomenally successful synergy, with -30 new radio MSPs (to date) having been discovered at Fermi unidentified source locations and the gamma-ray pulsations having then been detected in a number of these using the radio timing solutions. Many of the newly discovered MSPs may be suitable for addition to the collection of very stable MSPs used for gravitational wave detection. Detection of such a large number of MSPs was surprising, given that most have relatively low spin-down luminosity and surface field strength. I will discuss their properties and the implications for pulsar particle acceleration and emission, as well as their potential contribution to gamma-ray backgrounds and Galactic cosmic rays.

  20. Redshifts and Optical Identifications of TANAMI/Fermi AGN

    NASA Astrophysics Data System (ADS)

    Pursimo, Tapio; Ojha, Roopesh

    2013-02-01

    We wish to measure redshifts for the opticalidentifications of those gamma-ray loud southern hemisphere extragalactic radio sources being monitored by the TANAMI program that lack them. We also propose imaging of those sources that currently lack optical identifications after which their redshifts will also be measured. The study of blazar physics has been revolutionized by sl Fermi which has ushered in the age of quasi-simultaneous multi-wavelength studies for which knowledge of physical quantities like blazar-jet luminosities and speeds are crucial. TANAMI is the only significant source of milliarcsecond scale radio information for the southern third of the sky. Source redshifts are essential to determine the linear sizes and physical properties of TANAMI/Fermi sources. Please Note: This proposal has been approved for Gemini observing time in Cycle 5 of the Fermi Guest Investigator program (NASA Fermi Cycle 5 - #51378 Pursimo)

  1. Renormalization group and the superconducting susceptibility of a Fermi liquid

    SciTech Connect

    Parameswaran, S. A.; Sondhi, S. L.; Shankar, R.

    2010-11-15

    A free Fermi gas has, famously, a superconducting susceptibility that diverges logarithmically at zero temperature. In this paper we ask whether this is still true for a Fermi liquid and find that the answer is that it does not. From the perspective of the renormalization group for interacting fermions, the question arises because a repulsive interaction in the Cooper channel is a marginally irrelevant operator at the Fermi liquid fixed point and thus is also expected to infect various physical quantities with logarithms. Somewhat surprisingly, at least from the renormalization group viewpoint, the result for the superconducting susceptibility is that two logarithms are not better than one. In the course of this investigation we derive a Callan-Symanzik equation for the repulsive Fermi liquid using the momentum-shell renormalization group, and use it to compute the long-wavelength behavior of the superconducting correlation function in the emergent low-energy theory. We expect this technique to be of broader interest.

  2. Treatment Method for Fermi Barrel Sodium Metal Residues

    SciTech Connect

    Steven R. Sherman; Collin J. Knight

    2005-06-01

    Fermi barrels are 55-gallon drums that once contained bulk sodium metal from the shutdown Fermi 1 breeder reactor facility, and now contain residual sodium metal and other sodium/air reaction products. This report provides a residual sodium treatment method and proposed quality assurance steps that will ensure that all residual sodium is deactivated and removed from the Fermi barrels before disposal. The treatment method is the application of humidified carbon dioxide to the residual sodium followed by a water wash. The experimental application of the treatment method to six Fermi barrels is discussed, and recommendations are provided for further testing and evaluation of the method. Though more testing would allow for a greater refinement of the treatment technique, enough data has been gathered from the tests already performed to prove that 100% compliance with stated waste criteria can be achieved.

  3. Four years of Fermi LAT flare advocate activity

    NASA Astrophysics Data System (ADS)

    Ciprini, Stefano; Fermi-LAT Collaboration

    2012-12-01

    The Fermi Flare Advocate (also known as Gamma-ray Sky Watcher, FA-GSW) service provides for a daily quicklook analysis and review of the high-energy gamma-ray sky seen by the Fermi Large Area Telescope (LAT). The FA-GSW service communicates alerts for potentially new gamma-ray sources, interesting transients and flares. A weekly digest containing the highlights about the GeV gamma-ray sky is published in the web-based Fermi Sky Blog and email for special events are posted through the LAT multifrequency mailing-list. During the first 4 years of Fermi allsky survey, more than 200 Astronomical Telegrams, several alerts to the TeV Cherenkov telescopes, and target of opportunity to Swift and other observatories have been realized. This increased the rate of simultaneous multi-frequency observing campaigns and the level of international scientific cooperation.

  4. Fermi and LIGO Hone in on Gravity Wave Source

    NASA Video Gallery

    Fermi's GBM saw a fading X-ray source at nearly the same moment LIGO detected gravitational waves from a black hole merger in 2015. This movie shows how scientists can narrow down the location of t...

  5. Controlling resonant tunneling in graphene via Fermi velocity engineering

    NASA Astrophysics Data System (ADS)

    Lima, Jonas R. F.; Pereira, Luiz Felipe C.; Bezerra, C. G.

    2016-06-01

    We investigate the resonant tunneling in a single layer graphene superlattice with modulated energy gap and Fermi velocity via an effective Dirac-like Hamiltonian. We calculate the transmission coefficient with the transfer matrix method and analyze the effect of a Fermi velocity modulation on the electronic transmission, in the case of normal and oblique incidence. We find it is possible to manipulate the electronic transmission in graphene by Fermi velocity engineering, and show that it is possible to tune the transmitivity from 0 to 1. We also analyze how a Fermi velocity modulation influences the total conductance and the Fano factor. Our results are relevant for the development of novel graphene-based electronic devices.

  6. GRBs in the Era of Swift and Fermi

    NASA Technical Reports Server (NTRS)

    Racusin, Judy

    2011-01-01

    Utilizing both Swift and Fermi to study GRBs provides us with a unique broad spectral and temporal window into both prompt emission and afterglow studies. Swift has provided key information from GRB follow-up of LAT detected bursts) that has led to ground-based redshift measurements and afterglow broadband light curves and SEDs. We study the X-ray and optical afterglows of Fermi-LAT detected bursts in the context of the hundreds of GRBs discovered by Swift over the last 7 years) in order to better understand the origin of the high-energy gamma-rays. We also briefly describe the efforts to best facilitate joint Swift-Fermi observations. These initial results demonstrate the synergy between Swift and Fermi) and hint at the many interesting discoveries to come.

  7. Chandra and Swift Observations of Unidentified Fermi-LAT Objects

    NASA Astrophysics Data System (ADS)

    Donato, Davide; Cheung, T.; Gehrels, N.

    2010-03-01

    In the last year we targeted some of the unidentified Fermi-LAT objects (UFOs) at high Galactic latitude with Chandra and Swift in order to determine the basic properties (positions, fluxes, hardness ratios) of all X-ray sources within the Fermi-LAT localization circles. These satellites enable us to detect the X-ray conterparts with a flux limit that is at least an order of magnitude lower than achieved in extant RASS data and to further follow-up at other wavelengths, with the ultimate goal to reveal the nature of these enigmatic gamma-ray sources. Here we present the results obtained with 5 Chandra pointings of high Galactic latitude UFOs in the Fermi-LAT 3-months bright source list. The association of detected X-ray sources within the improved 11-months Fermi-LAT localization circles with available optical and radio observations is discussed.

  8. NASA's Fermi Shows How Active Galaxies Can Be

    NASA Video Gallery

    Active galaxies called blazars make up the largest class of objects detected by Fermi's Large Area Telescope (LAT). Massive black holes in the hearts of these galaxies fire particle jets in our dir...

  9. Three years of Transients with Fermi GBM

    NASA Technical Reports Server (NTRS)

    Wilson-Hodge, Colleen A.

    2012-01-01

    The Gamma-ray Burst Monitor (GBM) is an all-sky monitoring instrument, sensitive between 8 keV and 40 MeV, with a primary objective of supporting the Large Area Telescope (LAT) in observations of Gamma-Ray Bursts (GRBs). Both instruments are part of the Fermi Gamma-ray Space Telescope. Together, the GBM and LAT instruments have provided ground-breaking measurements of GRBs that have, after 10 years of focus on GRB afterglows, inspired renewed interest in the prompt emission phase of GRBs and the physical mechanisms that fuel them. In addition to GRB science, GBM has made significant contributions to the astrophysics of galactic transient sources including long-term variations in the Crab nebula, spin state transitions in accretion powered pulsars, state transitions in black hole X-ray binaries, and unprecedented time-resolved spectral studies of soft gamma-ray repeater bursts. Closer to home, GBM also contributes to solar flare and terrestrial gamma flash science.

  10. Quench dynamics of a superfluid Fermi gas

    SciTech Connect

    Warner, G.L.; Leggett, A.J.

    2005-04-01

    With an eye toward the interpretation of so-called 'cosmological' experiments performed on the low-temperature phases of {sup 3}He, in which regions of the superfluid are destroyed by local heating with neutron radiation, we have studied the behavior of a Fermi gas subjected to uniform variations of an attractive BCS interaction parameter {lambda}. In {sup 3}He, the quenches induced by the rapid cooling of the 'hot spots' back through the transition may lead to the formation of vortex loops via the Kibble-Zurek mechanism. A consideration of the free energy available in the quenched region for the production of such vortices reveals that the Kibble-Zurek scaling law gives at best a lower bound on the defect spacing. Further, for quenches that fall far outside the Ginzburg-Landau regime, the dynamics on the pair subspace, as initiated by quantum fluctuations, tends irreversibly to a self-driven steady state with a gap {delta}{sub {infinity}}={epsilon}{sub C}(e{sup 2/N(0){lambda}}-1){sup -1/2}. In weak coupling, this is only half the BCS gap, the extra energy being taken up by the residual collective motion of the pairs.

  11. Fermi-Dirac distributions for quark partons

    NASA Astrophysics Data System (ADS)

    Bourrely, C.; Buccella, F.; Miele, G.; Migliore, G.; Soffer, J.; Tibullo, V.

    1994-09-01

    We propose to use Fermi-Dirac distributions for quark and antiquark partons. It allows a fair description of the x-dependence of the very recent NMC data on the proton and neutron structure functions F {2/ p } (x) and F {2/ n } (x) at Q 2=4 GeV2, as well as the CCFR antiquark distributionxbar q(x). We show that one can also use a corresponding Bose-Einstein expression to describe consistently the gluon distribution. The Pauli exclusion principle, which has been identified to explain the flavor asymmetry of the light-quark sea of the proton, is advocated to guide us for making a simple construction of the polarized parton distributions. We predict the spin dependent structure functions g {1/ p } (x) and g {1/ n } (x) in good agreement with EMC and SLAC data. The quark distributions involve some parameters whose values support well the hypothesis that the violation of the quark parton model sum rules is a consequence of the Pauli principle.

  12. THE FERMI BUBBLES. II. THE POTENTIAL ROLES OF VISCOSITY AND COSMIC-RAY DIFFUSION IN JET MODELS

    SciTech Connect

    Guo Fulai; Mathews, William G.; Oh, S. Peng

    2012-09-10

    The origin of the Fermi bubbles recently detected by the Fermi Gamma-ray Space Telescope in the inner Galaxy is mysterious. In the companion paper Guo and Mathews (Paper I), we use hydrodynamic simulations to show that they could be produced by a recent powerful active galactic nucleus (AGN) jet event. Here, we further explore this scenario to study the potential roles of shear viscosity and cosmic-ray (CR) diffusion on the morphology and CR distribution of the bubbles. We show that even a relatively low level of viscosity ({mu}{sub visc} {approx}> 3 g cm{sup -1} s{sup -1}, or {approx}0.1%-1% of Braginskii viscosity in this context) could effectively suppress the development of Kelvin-Helmholtz instabilities at the bubble surface, resulting in smooth bubble edges as observed. Furthermore, viscosity reduces circulating motions within the bubbles, which would otherwise mix the CR-carrying jet backflow near bubble edges with the bubble interior. Thus viscosity naturally produces an edge-favored CR distribution, an important ingredient to produce the observed flat gamma-ray surface brightness distribution. Generically, such a CR distribution often produces a limb-brightened gamma-ray intensity distribution. However, we show that by incorporating CR diffusion that is strongly suppressed across the bubble surface (as inferred from sharp bubble edges) but is close to canonical values in the bubble interior, we obtain a reasonably flat gamma-ray intensity profile. The similarity of the resulting CR bubble with the observed Fermi bubbles strengthens our previous result in Paper I that the Fermi bubbles were produced by a recent AGN jet event. Studies of the nearby Fermi bubbles may provide a unique opportunity to study the potential roles of plasma viscosity and CR diffusion on the evolution of AGN jets and bubbles.

  13. Fermi resonance in dynamical tunneling in a chaotic billiard

    NASA Astrophysics Data System (ADS)

    Yi, Chang-Hwan; Kim, Ji-Hwan; Yu, Hyeon-Hye; Lee, Ji-Won; Kim, Chil-Min

    2015-08-01

    We elucidate that Fermi resonance ever plays a decisive role in dynamical tunneling in a chaotic billiard. Interacting with each other through an avoided crossing, a pair of eigenfunctions are coupled through tunneling channels for dynamical tunneling. In this case, the tunneling channels are an islands chain and its pair unstable periodic orbit, which equals the quantum number difference of the eigenfunctions. This phenomenon of dynamical tunneling is confirmed in a quadrupole billiard in relation with Fermi resonance.

  14. Double-degenerate Bose-Fermi mixture of strontium

    SciTech Connect

    Tey, Meng Khoon; Schreck, Florian; Stellmer, Simon; Grimm, Rudolf

    2010-07-15

    We report on the attainment of a spin-polarized Fermi sea of {sup 87}Sr in thermal contact with a Bose-Einstein condensate (BEC) of {sup 84}Sr. Interisotope collisions thermalize the fermions with the bosons during evaporative cooling. A degeneracy with T/T{sub F}=0.30(5) is reached for a {sup 87}Sr Fermi sea of 2x10{sup 4} atoms together with an almost pure {sup 84}Sr BEC of 10{sup 5} atoms.

  15. Suppression of Density Fluctuations in a Quantum Degenerate Fermi Gas

    SciTech Connect

    Sanner, Christian; Su, Edward J.; Keshet, Aviv; Gommers, Ralf; Shin, Yong-il; Huang Wujie; Ketterle, Wolfgang

    2010-07-23

    We study density profiles of an ideal Fermi gas and observe Pauli suppression of density fluctuations (atom shot noise) for cold clouds deep in the quantum degenerate regime. Strong suppression is observed for probe volumes containing more than 10 000 atoms. Measuring the level of suppression provides sensitive thermometry at low temperatures. After this method of sensitive noise measurements has been validated with an ideal Fermi gas, it can now be applied to characterize phase transitions in strongly correlated many-body systems.

  16. Spin waves in a persistent spin-current Fermi liquid

    SciTech Connect

    Feldmann, J. D.; Bedell, K. S.

    2010-06-15

    We report two theoretical results for transverse spin waves, which arise in a system with a persistent spin current. Using Fermi liquid theory, we introduce a spin current in the ground state of a polarized or unpolarized Fermi liquid, and we derive the resultant spin waves using the Landau kinetic equation. The resulting spin waves have a q{sup 1} and q{sup 1/2} dispersion to leading order for the polarized and unpolarized systems, respectively.

  17. Unconventional symmetries of Fermi liquid and Cooper pairing properties with electric and magnetic dipolar fermions

    NASA Astrophysics Data System (ADS)

    Li, Yi; Wu, Congjun

    2014-12-01

    The rapid experimental progress of ultra-cold dipolar fermions opens up a whole new opportunity to investigate novel many-body physics of fermions. In this article, we review theoretical studies of the Fermi liquid theory and Cooper pairing instabilities of both electric and magnetic dipolar fermionic systems from the perspective of unconventional symmetries. When the electric dipole moments are aligned by the external electric field, their interactions exhibit the explicit dr^2-3z^2 anisotropy. The Fermi liquid properties, including the single-particle spectra, thermodynamic susceptibilities and collective excitations, are all affected by this anisotropy. The electric dipolar interaction provides a mechanism for the unconventional spin triplet Cooper pairing, which is different from the usual spin-fluctuation mechanism in solids and the superfluid 3He. Furthermore, the competition between pairing instabilities in the singlet and triplet channels gives rise to a novel time-reversal symmetry breaking superfluid state. Unlike electric dipole moments which are induced by electric fields and unquantized, magnetic dipole moments are intrinsic proportional to the hyperfine-spin operators with a Lande factor. Its effects even manifest in unpolarized systems exhibiting an isotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi liquid theory supports a collective sound mode exhibiting a topologically non-trivial spin distribution over the Fermi surface. It also leads to a novel p-wave spin triplet Cooper pairing state whose spin and orbital angular momentum are entangled to the total angular momentum J = 1 dubbed the J-triplet pairing. This J-triplet pairing phase is different from both the spin-orbit coupled 3He-B phase with J = 0 and the spin-orbit decoupled 3He-A phase.

  18. Unconventional symmetries of Fermi liquid and Cooper pairing properties with electric and magnetic dipolar fermions.

    PubMed

    Li, Yi; Wu, Congjun

    2014-12-10

    The rapid experimental progress of ultra-cold dipolar fermions opens up a whole new opportunity to investigate novel many-body physics of fermions. In this article, we review theoretical studies of the Fermi liquid theory and Cooper pairing instabilities of both electric and magnetic dipolar fermionic systems from the perspective of unconventional symmetries. When the electric dipole moments are aligned by the external electric field, their interactions exhibit the explicit d(r(2)-3z(2)) anisotropy. The Fermi liquid properties, including the single-particle spectra, thermodynamic susceptibilities and collective excitations, are all affected by this anisotropy. The electric dipolar interaction provides a mechanism for the unconventional spin triplet Cooper pairing, which is different from the usual spin-fluctuation mechanism in solids and the superfluid (3)He. Furthermore, the competition between pairing instabilities in the singlet and triplet channels gives rise to a novel time-reversal symmetry breaking superfluid state. Unlike electric dipole moments which are induced by electric fields and unquantized, magnetic dipole moments are intrinsic proportional to the hyperfine-spin operators with a Lande factor. Its effects even manifest in unpolarized systems exhibiting an isotropic but spin-orbit coupled nature. The resultant spin-orbit coupled Fermi liquid theory supports a collective sound mode exhibiting a topologically non-trivial spin distribution over the Fermi surface. It also leads to a novel p-wave spin triplet Cooper pairing state whose spin and orbital angular momentum are entangled to the total angular momentum J = 1 dubbed the J-triplet pairing. This J-triplet pairing phase is different from both the spin-orbit coupled (3)He-B phase with J = 0 and the spin-orbit decoupled (3)He-A phase. PMID:25401291

  19. Fermi Large Area Telescope Operations: Progress Over 4 Years

    SciTech Connect

    Cameron, Robert A.; /SLAC

    2012-06-28

    The Fermi Gamma-ray Space Telescope was launched into orbit in June 2008, and is conducting a multi-year gamma-ray all-sky survey, using the main instrument on Fermi, the Large Area Telescope (LAT). Fermi began its science mission in August 2008, and has now been operating for almost 4 years. The SLAC National Accelerator Laboratory hosts the LAT Instrument Science Operations Center (ISOC), which supports the operation of the LAT in conjunction with the Mission Operations Center (MOC) and the Fermi Science Support Center (FSSC), both at NASA's Goddard Space Flight Center. The LAT has a continuous output data rate of about 1.5 Mbits per second, and data from the LAT are stored on Fermi and transmitted to the ground through TDRS and the MOC to the ISOC about 10 times per day. Several hundred computers at SLAC are used to process LAT data to perform event reconstruction, and gamma-ray photon data are subsequently delivered to the FSSC for public release with a few hours of being detected by the LAT. We summarize the current status of the LAT, and the evolution of the data processing and monitoring performed by the ISOC during the first 4 years of the Fermi mission, together with future plans for further changes to detected event data processing and instrument operations and monitoring.

  20. Fermi LAT detection of a new high-energy transient gamma-ray source Fermi J0751-5136

    NASA Astrophysics Data System (ADS)

    Kocevski, D.; Buson, S.

    2016-08-01

    During the week from 18 July through 25 July, 2016, the Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, observed gamma-ray activity from a previously unidentified transient source.