Mott scattering in an elliptically polarized laser field
Attaourti, Y.; Manaut, B.; Taj, S.
2004-08-01
We study Mott scattering in the presence of a strong elliptically polarized field. Using the first Born approximation and the Dirac-Volkov states for the electron, we obtain an analytic formula for the unpolarized differential cross section. This generalizes the results found for the linearly polarized field by Li et al. [ 67, 063409 (2003)] and for the circularly polarized field by Attaourti and Manaut [ 68, 067401 (2003)].
Mott scattering of polarized electrons in a strong laser field
Manaut, B.; Taj, S.; Attaourti, Y.
2005-04-01
We present analytical and numerical results of the relativistic calculation of the transition matrix element S{sub fi} and differential cross sections for Mott scattering of initially polarized Dirac particles (electrons) in the presence of a strong laser field with linear polarization. We use exact Dirac-Volkov wave functions to describe the dressed electrons and the collision process is treated in the first Born approximation. The influence of the laser field on the degree of polarization of the scattered electron is reported.
Concept of a multichannel spin-resolving electron analyzer based on Mott scattering
Strocov, Vladimir N.; Petrov, Vladimir N.; Dil, J. Hugo
2015-01-01
The concept of a multichannel electron spin detector based on optical imaging principles and Mott scattering (iMott) is presented. A multichannel electron image produced by a standard angle-resolving (photo) electron analyzer or microscope is re-imaged by an electrostatic lens at an accelerating voltage of 40 kV onto the Au target. Quasi-elastic electrons bearing spin asymmetry of the Mott scattering are imaged by magnetic lenses onto position-sensitive electron CCDs whose differential signals yield the multichannel spin asymmetry image. Fundamental advantages of this concept include acceptance of inherently divergent electron sources from the electron analyzer or microscope focal plane as well as small aberrations achieved by virtue of high accelerating voltages, as demonstrated by extensive ray-tracing analysis. The efficiency gain compared with the single-channel Mott detector can be a factor of more than 104 which opens new prospects of spin-resolved spectroscopies in application not only to standard bulk and surface systems (Rashba effect, topological insulators, etc.) but also to buried heterostructures. The simultaneous spin detection combined with fast CCD readout enables efficient use of the iMott detectors at X-ray free-electron laser facilities. PMID:25931087
Ueda, S.; Mizuguchi, M.; Kojima, T.; Takanashi, K.; Ishimaru, S.; Tsujikawa, M.; Shirai, M.
2014-03-31
We report ultrahigh-resolution spin-resolved hard X-ray photoemission (HAXPES) for a buried FeNi alloy film. By utilizing the forward Mott scattering in a Au layer on FeNi, our spin-resolved HAXPES method does not require a standard spin detector and allows us to use the multi-channel electron detection system for the high-efficient electron detection as used in conventional photoemission spectroscopy. A combination of the forward Mott scattering and multi-channel detection leads us to measure a clear spin polarization as well as spin-resolved majority and minority states in the Fe 2p core-level spectra without using the standard spin detector. This method enables us to measure spin-resolved core-level spectra for buried ferromagnetic materials.
Enhanced Thermoelectric Power in Graphene: Violation of the Mott Relation by Inelastic Scattering
NASA Astrophysics Data System (ADS)
Ghahari, Fereshte; Xie, Hong-Yi; Taniguchi, Takashi; Watanabe, Kenji; Foster, Matthew S.; Kim, Philip
2016-04-01
We report the enhancement of the thermoelectric power (TEP) in graphene with extremely low disorder. At high temperature we observe that the TEP is substantially larger than the prediction of the Mott relation, approaching to the hydrodynamic limit due to strong inelastic scattering among the charge carriers. However, closer to room temperature the inelastic carrier-optical-phonon scattering becomes more significant and limits the TEP below the hydrodynamic prediction. We support our observation by employing a Boltzmann theory incorporating disorder, electron interactions, and optical phonons.
NASA Astrophysics Data System (ADS)
Hussein, Mahir; Canto, L. Felipe; Donangelo, Raul
2015-04-01
It is found that at a certain critical value of the Sommerfeld parameter the Mott oscillations usually present in the scattering of identical heavy ions, disappear and the cross section becomes quite flat. We call this effect Transverse Isotropy (TI) (L. F. Canto, R. Donangelo and M. S. Hussein, Mod. Phys. Lett. A, 16), 1027 (2001). The critical value of the Sommerfeld parameter at which TI sets in is found to be ηc =√{ 3 s + 2 } , where s is the spin of the nuclei participating in the scattering. No TI is found in the Mott scattering of identical Fermionic nuclei. The critical center of mass energy corresponding to ηc is found to be Ec = 0.40 MeV for α + α (s = 0), and 1.2 MeV for 6 Li + 6 LI (s = 1). We further found that the inclusion of the nuclear interaction induces a significant modification in the TI. This can be verified by calculating the second derivative of the cross section at θ =90° . We suggest measurements at these sub-barrier energies for the purpose of extracting useful information about the nuclear interaction between light heavy ions. Supported by CNPq, FAPESP, FAPERJ, CAPES/ITA.
Lundh, Emil
2011-09-15
The hydrodynamics of a lattice Bose gas in a time-dependent external potential is studied in a mean-field approximation. The conditions under which a Mott insulating region can melt, and the local density can adjust to the new potential, are determined. In the case of a suddenly switched potential, it is found that the Mott insulator stays insulating and the density will not adjust if the switch is too abrupt. This comes about because too rapid currents result in Bloch oscillation-type current reversals. For a stirrer moved through a Mott insulating cloud, it is seen that only if the stirrer starts in a superfluid region and the velocity is comparable to the time scale set by the tunneling will the Mott insulator be affected.
Morimoto, Takahiro; Nagaosa, Naoto
2016-01-01
Relativistic Weyl fermion (WF) often appears in the band structure of three dimensional magnetic materials and acts as a source or sink of the Berry curvature, i.e., the (anti-)monopole. It has been believed that the WFs are stable due to their topological indices except when two Weyl fermions of opposite chiralities annihilate pairwise. Here, we theoretically show for a model including the electron-electron interaction that the Mott gap opens for each WF without violating the topological stability, leading to a topological Mott insulator dubbed Weyl Mott insulator (WMI). This WMI is characterized by several novel features such as (i) energy gaps in the angle-resolved photo-emission spectroscopy (ARPES) and the optical conductivity, (ii) the nonvanishing Hall conductance, and (iii) the Fermi arc on the surface with the penetration depth diverging as approaching to the momentum at which the Weyl point is projected. Experimental detection of the WMI by distinguishing from conventional Mott insulators is discussed with possible relevance to pyrochlore iridates. PMID:26822023
Extrapolation procedures in Mott electron polarimetry
NASA Technical Reports Server (NTRS)
Gay, T. J.; Khakoo, M. A.; Brand, J. A.; Furst, J. E.; Wijayaratna, W. M. K. P.; Meyer, W. V.; Dunning, F. B.
1992-01-01
In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependent of A on either the gold film thickness or the maximum detected electron energy loss in the target. A concentric cylindrical-electrode Mott polarimeter, has been used to study and compare these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy-loss discrimination to yield accurate polarizations when thick foils are used.
A Mott insulator continuously connected to iron pnictide superconductors
NASA Astrophysics Data System (ADS)
Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S.; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng
2016-12-01
Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1-xCuxAs near x~0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ~x=0.05. Our discovery of a Mott-insulating state in NaFe1-xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.
A Mott insulator continuously connected to iron pnictide superconductors.
Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng
2016-12-19
Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1-xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1-xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity.
A Mott insulator continuously connected to iron pnictide superconductors
Song, Yu; Yamani, Zahra; Cao, Chongde; Li, Yu; Zhang, Chenglin; Chen, Justin S.; Huang, Qingzhen; Wu, Hui; Tao, Jing; Zhu, Yimei; Tian, Wei; Chi, Songxue; Cao, Huibo; Huang, Yao-Bo; Dantz, Marcus; Schmitt, Thorsten; Yu, Rong; Nevidomskyy, Andriy H.; Morosan, Emilia; Si, Qimiao; Dai, Pengcheng
2016-01-01
Iron-based superconductivity develops near an antiferromagnetic order and out of a bad-metal normal state, which has been interpreted as originating from a proximate Mott transition. Whether an actual Mott insulator can be realized in the phase diagram of the iron pnictides remains an open question. Here we use transport, transmission electron microscopy, X-ray absorption spectroscopy, resonant inelastic X-ray scattering and neutron scattering to demonstrate that NaFe1−xCuxAs near x≈0.5 exhibits real space Fe and Cu ordering, and are antiferromagnetic insulators with the insulating behaviour persisting above the Néel temperature, indicative of a Mott insulator. On decreasing x from 0.5, the antiferromagnetic-ordered moment continuously decreases, yielding to superconductivity ∼x=0.05. Our discovery of a Mott-insulating state in NaFe1−xCuxAs thus makes it the only known Fe-based material, in which superconductivity can be smoothly connected to the Mott-insulating state, highlighting the important role of electron correlations in the high-Tc superconductivity. PMID:27991514
Thermopower of graphene and the validity of Mott's formula
NASA Astrophysics Data System (ADS)
Ghahari, Fereshte; Taniguchi, Takashi; Watanabe, Kenji; Kim, Philip
2014-03-01
Thermoelectric power (TEP) of graphene is previously measured in the disorder limited transport regime where the semiclassical Mott relation agrees with experimental data. In this presentation, we report the TEP measurement on graphene samples deposited on hexagonal boron nitride substrates where drastic suppression of disorder is achieved. Our results show that at high temperatures the measured thermopower deviates from Mott relation and this deviation is greater for higher mobility samples. We quantify this deviation in both degenerate and non-degenerate regime using Boltzmann transport theory considering different scattering mechanisms in the system.
NASA Astrophysics Data System (ADS)
Lee, Dung-Hai; Kivelson, Steven A.
2003-01-01
There are two classes of Mott insulators in nature, distinguished by their responses to weak doping. With increasing chemical potential, type I Mott insulators undergo a first order phase transition from the undoped to the doped phase. In the presence of long-range Coulomb interactions, this leads to an inhomogeneous state exhibiting “micro-phase separation.” In contrast, in type II Mott insulators charges go in continuously above a critical chemical potential. We show that if the insulating state has a broken symmetry, this increases the likelihood that it will be type I. There exists a close analogy between these two types of Mott insulators and the familiar type I and type II superconductors.
On effective holographic Mott insulators
NASA Astrophysics Data System (ADS)
Baggioli, Matteo; Pujolàs, Oriol
2016-12-01
We present a class of holographic models that behave effectively as prototypes of Mott insulators — materials where electron-electron interactions dominate transport phenomena. The main ingredient in the gravity dual is that the gauge-field dynamics contains self-interactions by way of a particular type of non-linear electrodynamics. The electrical response in these models exhibits typical features of Mott-like states: i) the low-temperature DC conductivity is unboundedly low; ii) metal-insulator transitions appear by varying various parameters; iii) for large enough self-interaction strength, the conductivity can even decrease with increasing doping (density of carriers) — which appears as a sharp manifestation of `traffic-jam'-like behaviour; iv) the insulating state becomes very unstable towards superconductivity at large enough doping. We exhibit some of the properties of the resulting insulator-superconductor transition, which is sensitive to the momentum dissipation rate in a specific way. These models imply a clear and generic correlation between Mott behaviour and significant effects in the nonlinear electrical response. We compute the nonlinear current-voltage curve in our model and find that indeed at large voltage the conductivity is largely reduced.
Emergent heavy fermion behavior at the Wigner-Mott transition.
Merino, Jaime; Ralko, Arnaud; Fratini, Simone
2013-09-20
We study charge ordering driven by Coulomb interactions on triangular lattices relevant to the Wigner-Mott transition in two dimensions. Dynamical mean-field theory reveals the pinball liquid phase, a charge ordered metallic phase containing quasilocalized (pins) coexisting with itinerant (balls) electrons. Based on an effective periodic Anderson model for this phase, we find an antiferromagnetic Kondo coupling between pins and balls and strong quasiparticle renormalization. Non-Fermi liquid behavior can occur in such charge ordered systems due to the spin-flip scattering of itinerant electrons off the pins in analogy with heavy fermion compounds.
Mott transitions in the periodic Anderson model
NASA Astrophysics Data System (ADS)
Logan, David E.; Galpin, Martin R.; Mannouch, Jonathan
2016-11-01
The periodic Anderson model (PAM) is studied within the framework of dynamical mean-field theory, with particular emphasis on the interaction-driven Mott transition it contains, and on resultant Mott insulators of both Mott-Hubbard and charge-transfer type. The form of the PAM phase diagram is first deduced on general grounds using two exact results, over the full range of model parameters and including metallic, Mott, Kondo and band insulator phases. The effective low-energy model which describes the PAM in the vicinity of a Mott transition is then shown to be a one-band Hubbard model, with effective hoppings that are not in general solely nearest neighbour, but decay exponentially with distance. This mapping is shown to have a range of implications for the physics of the problem, from phase boundaries to single-particle dynamics; all of which are confirmed and supplemented by NRG calculations. Finally we consider the locally degenerate, non-Fermi liquid Mott insulator, to describe which requires a two-self-energy description. This is shown to yield a number of exact results for the associated local moment, charge, and interaction-renormalised levels, together with a generalisation of Luttinger’s theorem to the Mott insulator.
Anomalous Metal Phase Emergent on the Verge of an Exciton Mott Transition
NASA Astrophysics Data System (ADS)
Sekiguchi, Fumiya; Mochizuki, Toshimitsu; Kim, Changsu; Akiyama, Hidefumi; Pfeiffer, Loren N.; West, Ken W.; Shimano, Ryo
2017-02-01
We investigate the exciton Mott transition (EMT) by using optical pump-terahertz probe spectroscopy on GaAs, with realizing the condition of Mott's gedanken experiment by the resonant excitation of 1 s excitons. We show that an anomalous metallic phase emerges on the verge of the EMT as manifested by a peculiar enhancement of the quasiparticle mass and scattering rate. From the temperature and density dependence, the observed anomaly is shown to originate from the electron-hole (e -h ) correlation which becomes prominent at low temperatures, possibly suggesting a precursor of e -h Cooper pairing.
Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4
NASA Astrophysics Data System (ADS)
Cao, Yue; Wang, Qiang; Waugh, Justin A.; Reber, Theodore J.; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S.-R.; Plumb, Nicholas C.; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D.; Qi, Tongfei; Hermele, Michael A.; Cao, Gang; Dessau, Daniel S.
2016-04-01
The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates--pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation.
Hallmarks of the Mott-metal crossover in the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4
Cao, Yue; Wang, Qiang; Waugh, Justin A.; Reber, Theodore J.; Li, Haoxiang; Zhou, Xiaoqing; Parham, Stephen; Park, S.-R.; Plumb, Nicholas C.; Rotenberg, Eli; Bostwick, Aaron; Denlinger, Jonathan D.; Qi, Tongfei; Hermele, Michael A.; Cao, Gang; Dessau, Daniel S.
2016-01-01
The physics of doped Mott insulators remains controversial after decades of active research, hindered by the interplay among competing orders and fluctuations. It is thus highly desired to distinguish the intrinsic characters of the Mott-metal crossover from those of other origins. Here we investigate the evolution of electronic structure and dynamics of the hole-doped pseudospin-1/2 Mott insulator Sr2IrO4. The effective hole doping is achieved by replacing Ir with Rh atoms, with the chemical potential immediately jumping to or near the top of the lower Hubbard band. The doped iridates exhibit multiple iconic low-energy features previously observed in doped cuprates—pseudogaps, Fermi arcs and marginal-Fermi-liquid-like electronic scattering rates. We suggest these signatures are most likely an integral part of the material's proximity to the Mott state, rather than from many of the most claimed mechanisms, including preformed electron pairing, quantum criticality or density-wave formation. PMID:27102065
VIEW EASTACROSS SOUTH CLINTON AVENUE AT MOTT STREET CENTERBUILDING 57 ...
VIEW EAST-ACROSS SOUTH CLINTON AVENUE AT MOTT STREET CENTER-BUILDING 57 FLAT SHOP NO 1 (1905) LEFT-BUILDING 51 MOTT STREET GENERATING STATION (1897) - John A. Roebling's Sons Company & American Steel & Wire Company, South Broad, Clark, Elmer, Mott & Hudson Streets, Trenton, Mercer County, NJ
Quantum and classical solutions for statically screened two-dimensional Wannier-Mott excitons
Makowski, Adam J.
2011-08-15
Quantum solutions and classical orbits are discussed for statically screened Wannier-Mott excitons for two closely related potentials: the Stern-Howard potential and a suggested simple focusing one. Bound states and exact ''quantized'' values of screening are obtained as well. For the suggested potential, the scattering matrix, the Regge poles, and the transmission coefficient are calculated exactly. We argue that the simple potential can be utilized in applications instead of the Stern-Howard potential, which is difficult to handle.
A different sort of Mott cell.
Jäck, H M; Beck-Engeser, G; Sloan, B; Wong, M L; Wabl, M
1992-01-01
NYC is a B lymphoma cell line derived from B/W mice. Upon fusion of NYC cells with a plasmacytoma, which itself produces no immunoglobulin, the resulting NYCH hybridoma cells are Mott cells; i.e., they contain large intracellular vesicles filled with immunoglobulin, the so-called Russell bodies. When NYCH.kappa, a variant of NYCH that had lost the ability to produce heavy chain, was transfected with a heavy-chain construct, this concentration of immunoglobulin in the intracellular vesicles occurred only when the transfected immunoglobulin heavy chain had the same variable region as NYC. Moreover, unlike conventional Mott cells, the hybrid cells secrete immunoglobulin at a normal rate. Images PMID:1465384
DYNAMICAL RESPONSE OF QUASI ID MOTT INSULATORS.
ESSLER,F.H.L.TSVELIK,A.M.
2004-01-14
At low energies certain one dimensional Mott insulators can be described in terms of an exactly solvable quantum field theory, the U(1) Thirring model. Using exact results derived from integrability we determine dynamical properties like the frequency dependent optical conductivity and the single-particle Green's function. We discuss the effects of a small temperature and the effects on interchain tunneling in a model of infinitely many weakly coupled chains.
Ferroelectric control of a Mott insulator
Yamada, Hiroyuki; Marinova, Maya; Altuntas, Philippe; Crassous, Arnaud; Bégon-Lours, Laura; Fusil, Stéphane; Jacquet, Eric; Garcia, Vincent; Bouzehouane, Karim; Gloter, Alexandre; Villegas, Javier E.; Barthélémy, Agnès; Bibes, Manuel
2013-01-01
The electric field control of functional properties is an important goal in oxide-based electronics. To endow devices with memory, ferroelectric gating is interesting, but usually weak compared to volatile electrolyte gating. Here, we report a very large ferroelectric field-effect in perovskite heterostructures combining the Mott insulator CaMnO3 and the ferroelectric BiFeO3 in its “supertetragonal” phase. Upon polarization reversal of the BiFeO3 gate, the CaMnO3 channel resistance shows a fourfold variation around room temperature, and a tenfold change at ~200 K. This is accompanied by a carrier density modulation exceeding one order of magnitude. We have analyzed the results for various CaMnO3 thicknesses and explain them by the electrostatic doping of the CaMnO3 layer and the presence of a fixed dipole at the CaMnO3/BiFeO3 interface. Our results suggest the relevance of ferroelectric gates to control orbital- or spin-ordered phases, ubiquitous in Mott systems, and pave the way toward efficient Mott-tronics devices. PMID:24089020
Direct observation of the M2 phase with its Mott transition in a VO2 film
NASA Astrophysics Data System (ADS)
Kim, Hoon; Slusar, Tetiana V.; Wulferding, Dirk; Yang, Ilkyu; Cho, Jin-Cheol; Lee, Minkyung; Choi, Hee Cheul; Jeong, Yoon Hee; Kim, Hyun-Tak; Kim, Jeehoon
2016-12-01
In VO2, the explicit origin of the insulator-to-metal transition is still disputable between Peierls and Mott insulators. Along with the controversy, its second monoclinic (M2) phase has received considerable attention due to the presence of electron correlation in undimerized vanadium ions. However, the origin of the M2 phase is still obscure. Here, we study a granular VO2 film using conductive atomic force microscopy and Raman scattering. Upon the structural transition from monoclinic to rutile, we observe directly an intermediate state showing the coexistence of monoclinic M1 and M2 phases. The conductivity near the grain boundary in this regime is six times larger than that of the grain core, producing a donut-like landscape. Our results reveal an intra-grain percolation process, indicating that VO2 with the M2 phase is a Mott insulator.
Dimensional-crossover-driven Mott transition in the frustrated Hubbard model.
Raczkowski, Marcin; Assaad, Fakher F
2012-09-21
We study the Mott transition in a frustrated Hubbard model with next-nearest neighbor hopping at half-filling. The interplay between interaction, dimensionality, and geometric frustration closes the one-dimensional Mott gap and gives rise to a metallic phase with Fermi surface pockets. We argue that they emerge as a consequence of remnant one-dimensional umklapp scattering at the momenta with vanishing interchain hopping matrix elements. In this pseudogap phase, enhanced d-wave pairing correlations are driven by antiferromagnetic fluctuations. Within the adopted cluster dynamical mean-field theory on the 8 × 2 cluster and down to our lowest temperatures, the transition from one to two dimensions is continuous.
NASA Astrophysics Data System (ADS)
Frandsen, Benjamin A.
Mott insulators are materials in which strong correlations among the electrons induce an unconventional insulating state. Rich interplay between the structural, magnetic, and electronic degrees of freedom resulting from the electron correlation can lead to unusual complexity of Mott materials on the atomic scale, such as microscopically heterogeneous phases or local structural correlations that deviate significantly from the average structure. Such behavior must be studied by suitable experimental techniques, i.e. "local probes", that are sensitive to this local behavior rather than just the bulk, average properties. In this thesis, I will present results from our studies of multiple families of Mott insulators using two such local probes: muon spin relaxation (muSR), a probe of local magnetism; and pair distribution function (PDF) analysis of x-ray and neutron total scattering, a probe of local atomic structure. In addition, I will present the development of magnetic pair distribution function analysis, a novel method for studying local magnetic correlations that is highly complementary to the muSR and atomic PDF techniques. We used muSR to study the phase transition from Mott insulator to metal in two archetypal Mott insulating systems: RENiO3 (RE = rare earth element) and V2O3. In both of these systems, the Mott insulating state can be suppressed by tuning a nonthermal parameter, resulting in a "quantum" phase transition at zero temperature from the Mott insulating state to a metallic state. In RENiO3, this occurs through variation of the rare-earth element in the chemical composition; in V 2O3, through the application of hydrostatic pressure. Our results show that the metallic and Mott insulating states unexpectedly coexist in phase-separated regions across a large portion of parameter space near the Mott quantum phase transition and that the magnitude of the ordered antiferromagnetic moment remains constant across the phase diagram until it is abruptly
Teenage Pregnancy: An Update and Guide to Mott Foundation Resources.
ERIC Educational Resources Information Center
Rugg, Carol D.
This document focuses on the involvement of the Mott Foundation in the problem of teenage pregnancy. After a brief introduction to the topic including statistics on the incidence of teenage pregnancy, methods by which other organizations and foundations have attacked the problem of teenage pregnancy are described. The role of the Mott Foundation…
A low-voltage retarding-field Mott polarimeter for photocathode characterization
McCarter, J. L.; Stutzman, M. L.; Trantham, K. W.; Anderson, T. G.; Cook, A. M.; Gay, T. J.
2010-02-26
Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10^{-4}, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10^{-5}. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.
A low-voltage retarding-field Mott polarimeter for photocathode characterization
NASA Astrophysics Data System (ADS)
McCarter, J. L.; Stutzman, M. L.; Trantham, K. W.; Anderson, T. G.; Cook, A. M.; Gay, T. J.
2010-06-01
Nuclear physics experiments at Thomas Jefferson National Accelerator Facility's CEBAF rely on high polarization electron beams. We describe a recently commissioned system for prequalifying and studying photocathodes for CEBAF with a load-locked, low-voltage polarized electron source coupled to a compact retarding-field Mott polarimeter. The polarimeter uses simplified electrode structures and operates from 5 to 30 kV. The effective Sherman function for this device has been calibrated by comparison with the CEBAF 5 MeV Mott polarimeter. For elastic scattering from a thick gold target at 20 keV, the effective Sherman function is 0.201(5). Its maximum efficiency at 20 keV, defined as the detected count rate divided by the incident particle current, is 5.4(2)×10 -4, yielding a figure-of-merit, or analyzing power squared times efficiency, of 1.0(1)×10 -5. The operating parameters of this new polarimeter design are compared to previously published data for other compact Mott polarimeters of the retarding-field type.
ERIC Educational Resources Information Center
BRIGGS, LARRY; AND OTHERS
ONE-PAGE REPORTS ARE PRESENTED, SUMMARIZING EACH OF THE PROJECTS IN THE MOTT PROGRAM FOR THE FLINT PUBLIC SCHOOLS--WORKSHOPS AND VISITATIONS, ADULT EDUCATION, GRADUATE TRAINING, YOUTH PROGRAMS, THE MOTT CAMP, RECREATION, A BETTER TOMORROW FOR THE URBAN CHILD, THE PERSONALIZED CURRICULUM PROGRAM, MEDICAL-DENTAL HEALTH, INTERUNIVERSITY CLINICAL…
Transient carrier dynamics in a Mott insulator with antiferromagnetic order
NASA Astrophysics Data System (ADS)
Iyoda, Eiki; Ishihara, Sumio
2014-03-01
We study transient dynamics of hole carriers injected into a Mott insulator with antiferromagnetic long-range order. This "dynamical hole doping" contrasts with chemical hole doping. The theoretical framework for the transient carrier dynamics is presented based on the two-dimensional t-J model. The time dependencies of the optical conductivity spectra, as well as the one-particle excitation spectra, are calculated based on the Keldysh Green's function formalism at zero temperature combined with the self-consistent Born approximation. In the early stage after dynamical hole doping, the Drude component appears, and then incoherent components originating from hole-magnon scattering start to grow. Fast oscillatory behavior owing to coherent magnon and slow relaxation dynamics are confirmed in the spectra. The time profiles are interpreted as doped bare holes being dressed by magnon clouds and relaxed into spin polaron quasiparticle states. The characteristic relaxation times for Drude and incoherent peaks strongly depend on the momentum of the dynamically doped hole and the exchange constant. Implications for recent pump-probe experiments are discussed.
Magnetic Behavior of a Mott-Insulator YVO3
NASA Astrophysics Data System (ADS)
Kawano, Hazuki; Yoshizawa, Hideki; Ueda, Yutaka
1994-08-01
As one of the members of the ABO3-type pseudoperovskite oxide family, Y1-xCaxVO3 exhibits an insulator-metal transition upon a change in the dopant calcium ion concentration x. We have reinvestigated the magnetic structure of the parent compound YVO3 with use of the neutron scattering technique. YVO3 orders at T N1=118 K with the so-called C-type antiferromagnetic structure, but changes to the G-type antiferromagnetic structure at T N2˜77 K through a first order transition with lattice distortion. These spin structures differ from those of an early study by Zubkov et al. (Sov. Phys.-JETP 39 (1974) 896). The static moment which contributes to the magnetic long range order is extrapolated to be less than 1.6 µ B at T=0 K. This value of the static moment is more than 20% smaller than 2.0 µ B expected for a localized spin system with S=1, indicating the existence of spin fluctuations in a Mott insulator YVO3.
Quench from Mott Insulator to Superfluid
Zurek, Wojciech H.; Dziarmaga, Jacek; Tylutki, Marek
2012-06-01
We study a linear ramp of the nearest-neighbor tunneling rate in the Bose-Hubbard model driving the system from the Mott insulator state into the superfluid phase. We employ the truncated Wigner approximation to simulate linear quenches of a uniform system in 1...3 dimensions, and in a harmonic trap in 3 dimensions. In all these setups the excitation energy decays like one over third root of the quench time. The -1/3 scaling is explained by an impulse-adiabatic approximation - a variant of the Kibble-Zurek mechanism - describing a crossover from non-adiabatic to adiabatic evolution when the system begins to keep pace with the increasing tunneling rate.
Unusual Mott transition in multiferroic PbCrO 3
Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; ...
2015-11-24
The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. When turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by "bandwidth" control or "band filling." However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. We report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of similar to 3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrentmore » with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at similar to 300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid-gas transition. Moreover, the anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.« less
Unusual Mott transition in multiferroic PbCrO3
Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; Yu, Xiaohui; Zhang, Jianzhong; Wang, Wendan; Bai, Ligang; Qian, Jiang; Yin, Liang; Sullivan, Neil S.; Jin, Changqing; He, Duanwei; Xu, Jian; Zhao, Yusheng
2015-01-01
The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. Turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by “bandwidth” control or “band filling.” However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. Here, we report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of ∼3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at ∼300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid–gas transition. The anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking. PMID:26604314
A scalable neuristor built with Mott memristors
NASA Astrophysics Data System (ADS)
Pickett, Matthew D.; Medeiros-Ribeiro, Gilberto; Williams, R. Stanley
2013-02-01
The Hodgkin-Huxley model for action potential generation in biological axons is central for understanding the computational capability of the nervous system and emulating its functionality. Owing to the historical success of silicon complementary metal-oxide-semiconductors, spike-based computing is primarily confined to software simulations and specialized analogue metal-oxide-semiconductor field-effect transistor circuits. However, there is interest in constructing physical systems that emulate biological functionality more directly, with the goal of improving efficiency and scale. The neuristor was proposed as an electronic device with properties similar to the Hodgkin-Huxley axon, but previous implementations were not scalable. Here we demonstrate a neuristor built using two nanoscale Mott memristors, dynamical devices that exhibit transient memory and negative differential resistance arising from an insulating-to-conducting phase transition driven by Joule heating. This neuristor exhibits the important neural functions of all-or-nothing spiking with signal gain and diverse periodic spiking, using materials and structures that are amenable to extremely high-density integration with or without silicon transistors.
Probing the Mott physics in κ-(BEDT-TTF)₂X salts via thermal expansion.
de Souza, Mariano; Bartosch, Lorenz
2015-02-11
In the field of interacting electron systems the Mott metal-to-insulator (MI) transition represents one of the pivotal issues. The role played by lattice degrees of freedom for the Mott MI transition and the Mott criticality in a variety of materials are current topics under debate. In this context, molecular conductors of the κ-(BEDT-TTF)2X type constitute a class of materials for unraveling several aspects of the Mott physics. In this review, we present a synopsis of literature results with focus on recent expansivity measurements probing the Mott MI transition in this class of materials. Progress in the description of the Mott critical behavior is also addressed.
Electronic Griffiths Phases and Quantum Criticality at Disordered Mott Transitions
NASA Astrophysics Data System (ADS)
Dobrosavljevic, Vladimir
2012-02-01
The effects of disorder are investigated in strongly correlated electronic systems near the Mott metal-insulator transition. Correlation effects are foundootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 102, 206403 (2009). to lead to strong disorder screening, a mechanism restricted to low-lying electronic states, very similar to what is observed in underdoped cuprates. These results suggest, however, that this effect is not specific to disordered d-wave superconductors, but is a generic feature of all disordered Mott systems. In addition, the resulting spatial inhomogeneity rapidly increasesootnotetextE. C. Andrade, E. Miranda, and V. Dobrosavljevic, Phys. Rev. Lett., 104 (23), 236401 (2010). as the Mott insulator is approached at fixed disorder strength. This behavior, which can be described as an Electronic Griffiths Phase, displays all the features expected for disorder-dominated Infinite-Randomness Fixed Point scenario of quantum criticality.
Breakdown of Strong Coupling Expansions for doped Mott Insulators
NASA Astrophysics Data System (ADS)
Phillips, Philip; Galanakis, Dimitrios; Stanescu, Tudor
2005-03-01
We show that doped Mott insulators, such as the copper-oxide superconductors, are asymptotically slaved in that the quasiparticle weight, Z, near half-filling depends critically on the existence of the high energy scale set by the upper Hubbard band. In particular, near half filling, the following dichotomy arises: Z0 when the high energy scale is integrated out but Z=0 in the thermodynamic limit when it is retained. Slavery to the high energy scale arises from quantum interference between electronic excitations across the Mott gap.
A New Class of Jeff = 1 / 2 Mott Insulators
NASA Astrophysics Data System (ADS)
Birol, Turan; Haule, Kristjan
2015-03-01
We predict a novel class of Jeff=1/2 Mott insulators in a family of Ir and Rh fluoride compounds with the K2GeF6 crystal structure that are previously synthesized, but not characterized extensively. First principles calculations in the level of all electron Density Functional Theory + Dynamical Mean Field Theory (DFT+DMFT) indicate that these compounds have large Mott gaps and some of them exhibit unprecedented proximity to the ideal, SU(2) symmetric Jeff=1/2 limit.
Appearance of universal metallic dispersion in a doped Mott insulator
NASA Astrophysics Data System (ADS)
Sahrakorpi, S.; Markiewicz, R. S.; Lin, Hsin; Lindroos, M.; Zhou, X. J.; Yoshida, T.; Yang, W. L.; Kakeshita, T.; Eisaki, H.; Uchida, S.; Komiya, Seiki; Ando, Yoichi; Zhou, F.; Zhao, Z. X.; Sasagawa, T.; Fujimori, A.; Hussain, Z.; Shen, Z.-X.; Bansil, A.
2008-09-01
We have investigated the dispersion renormalization Zdisp in La2-xSrxCuO4 over the wide doping range of x=0.03-0.30 , for binding energies extending to several hundred meV’s. Strong correlation effects conspire in such a way that the system exhibits a local-density-approximation-like dispersion which essentially “undresses” (Zdisp→1) as the Mott insulator is approached. Our finding that the Mott insulator contains “nascent” or “preformed” metallic states with a vanishing spectral weight offers a challenge to existing theoretical scenarios for cuprates.
A new class of polar mott-insulators via heterostructruring
NASA Astrophysics Data System (ADS)
Kim, Chanul; Park, Hyowon; Marianetti, Chris
2014-03-01
We propose simple design rules based on charge transfer and ion size to design a new class of polar Mott insulators in perovskite-based transition metal oxides. Ab Initio DFT+U calculations are then used to selectively scan phase space in double perovskites which have strong potential to be polar and Mott insulating. We begin by exploring pairs of A-type ions (A, A') and pairs of B-type ions (B, B') in AA' BB'O6 which will have nominal charge transfer consistent with valencies that are conducive to a Mott insulator. Additionally, the A-type ions are chosen to have a large size mismatch and are ordered to break symmetry, creating conditions favorable to a polar distortion. We uncover a number of materials which are strong candidates to be polar Mott insulators in experiment, including BaLaVNiO6, BaLaVCoO6, BaLaVCuO6, BaLaCrNiO6, BaBiVCoO6, BaBiVNiO6, and PbLaVNiO6. Furthermore, we show that the magnetic state and the band gap are sensitive to the particular ordering of the transition metals. Finally, we discuss possible applications and the potential to grow these systems in experiment. Functional Accelerated nanoMaterial Engineering, Semiconductor Research Corporation.
Chiral magnetism and spin liquid Mott insulators induced by synthetic gauge fields
NASA Astrophysics Data System (ADS)
Paramekanti, Arun; Hickey, Ciaran; Cincio, Lukasz; Papic, Zlatko; Vellat-Sadashivan, Arun; Sohal, Ramanjit
2016-05-01
Recent experiments using Raman-assisted tunneling or lattice-shaking have realized synthetic gauge fields and optical lattice bands with nontrivial band topology. Here we examine the effect of particle interactions in such bands, focussing on two-component fermions with local Hubbard repulsion. We show that interactions can drive the integer quantum Hall insulator into Mott insulating states which possess noncoplanar chiral magnetic textures and even chiral spin liquids with many-body topological order. We establish our results using a combination of mean field theory, strong coupling expansions, numerical exact diagonalization and DMRG methods. We also discuss possible signatures of such non-coplanar orders in Bragg scattering and noise measurements.
Cole, William S; Zhang, Shizhong; Paramekanti, Arun; Trivedi, Nandini
2012-08-24
Motivated by the experimental realization of synthetic spin-orbit coupling for ultracold atoms, we investigate the phase diagram of the Bose-Hubbard model in a non-Abelian gauge field in two dimensions. Using a strong coupling expansion in the combined presence of spin-orbit coupling and tunable interactions, we find a variety of interesting magnetic Hamiltonians in the Mott insulator (MI), which support magnetic textures such as spin spirals and vortex and Skyrmion crystals. An inhomogeneous mean-field treatment shows that the superfluid (SF) phases inherit these exotic magnetic orders from the MI and display, in addition, unusual modulated current patterns. We present a slave-boson theory which gives insight into such intertwined spin-charge orders in the SF, and discuss signatures of these orders in Bragg scattering, in situ microscopy, and dynamic quench experiments.
Local theory for Mott-Anderson localization
NASA Astrophysics Data System (ADS)
Sen, Sudeshna; Terletska, Hanna; Moreno, Juana; Vidhyadhiraja, N. S.; Jarrell, Mark
2016-12-01
The paramagnetic metallic phase of the Anderson-Hubbard model (AHM) is investigated using a nonperturbative local moment approach within the framework of dynamical mean-field theory with a typical medium. Our focus is on the breakdown of the metallic phase near the metal-insulators transition as seen in the single-particle spectra, scattering rates, and the associated distribution of Kondo scales. We demonstrate the emergence of a universal, underlying low-energy scale, TKpeak. This lies close to the peak of the distribution of Kondo scales obtained within the metallic phase of the paramagnetic AHM. Spectral dynamics for energies ω ≲TKpeak display Fermi liquid universality crossing over to an incoherent universal dynamics for ω ≫TKpeak in the scaling regime. Such universal dynamics indicate that within a local theory the low to moderately low-energy physics is governed by an effective, disorder renormalized Kondo screening.
Theory of high Tc ferrimagnetism in a multiorbital Mott insulator.
Meetei, O Nganba; Erten, Onur; Randeria, Mohit; Trivedi, Nandini; Woodward, Patrick
2013-02-22
We propose a model for the multiorbital material Sr(2)CrOsO(6), an insulator with remarkable magnetic properties and the highest T(c) ~/= 725 K among all perovskites with a net moment. We derive a new criterion for the Mott transition (U(1)U(2))(1/2)>2.5W by using slave-rotor mean field theory, where W is the bandwidth and U(1(2)) are the effective Coulomb interactions on Cr(Os) including Hund's coupling. We show that Sr(2)CrOsO(6) is a Mott insulator, where the large Cr U(1) compensates for the small Os U(2). The spin sector is described by a frustrated antiferromagnetic Heisenberg model that naturally explains the net moment arising from canting and also the observed nonmonotonic magnetization M(T). We predict characteristic magnetic structure factor peaks that can be probed by neutron experiments.
Theoretical prediction of fragile Mott insulators on plaquette Hubbard lattices
NASA Astrophysics Data System (ADS)
Wu, Han-Qing; He, Rong-Qiang; Meng, Zi Yang; Lu, Zhong-Yi
2015-03-01
Employing extensive cellular dynamical mean-field theory calculations with an exact diagonalization impurity solver, we investigate the ground-state phase diagrams and nonmagnetic metal-insulator transitions of the half-filled Hubbard model on two plaquette (the 1/5 depleted and checkerboard) square lattices. We identify three different insulators in the phase diagrams: dimer insulator, antiferromagnetic insulator, and plaquette insulator. We also demonstrate that the plaquette insulator is a novel fragile Mott insulator (FMI) which features a nontrivial one-dimensional irreducible representation of the C4 v crystalline point group and cannot be adiabatically connected to any band insulator with time-reversal symmetry. Furthermore, we study the nonmagnetic quantum phase transitions from the metal to the FMI and find that this Mott metal-insulator transition is characterized by the splitting of the noninteracting bands due to interaction effects.
Magnetic order and Mott transition on the checkerboard lattice
NASA Astrophysics Data System (ADS)
Swain, Nyayabanta; Majumdar, Pinaki
2017-03-01
The checkerboard lattice, with alternating ‘crossed’ plaquettes, serves as the two dimensional analog of the pyrochlore lattice. The corner sharing plaquette structure leads to a hugely degenerate ground state, and no magnetic order, for classical spins with short range antiferromagnetic interaction. For the half-filled Hubbard model on this structure, however, we find that the Mott insulating phase involves virtual electronic processes that generate longer range and multispin couplings. These couplings lift the degeneracy, selecting a ‘flux like’ state in the Mott insulator. Increasing temperature leads, strangely, to a sharp crossover from this state to a ‘120 degree’ correlated state and then a paramagnet. Decrease in the Hubbard repulsion drives the system towards an insulator-metal transition—the moments reduce, and a spin disordered state wins over the flux state. Near the insulator-metal transition the electron system displays a pseudogap extending over a large temperature window.
Optical Properties of a Vibrationally Modulated Solid State Mott Insulator
Kaiser, S.; Clark, S. R.; Nicoletti, D.; Cotugno, G.; Tobey, R. I.; Dean, N.; Lupi, S.; Okamoto, H.; Hasegawa, T.; Jaksch, D.; Cavalleri, A.
2014-01-01
Optical pulses at THz and mid-infrared frequencies tuned to specific vibrational resonances modulate the lattice along chosen normal mode coordinates. In this way, solids can be switched between competing electronic phases and new states are created. Here, we use vibrational modulation to make electronic interactions (Hubbard-U) in Mott-insulator time dependent. Mid-infrared optical pulses excite localized molecular vibrations in ET-F2TCNQ, a prototypical one-dimensional Mott-insulator. A broadband ultrafast probe interrogates the resulting optical spectrum between THz and visible frequencies. A red-shifted charge-transfer resonance is observed, consistent with a time-averaged reduction of the electronic correlation strength U. Secondly, a sideband manifold inside of the Mott-gap appears, resulting from a periodically modulated U. The response is compared to computations based on a quantum-modulated dynamic Hubbard model. Heuristic fitting suggests asymmetric holon-doublon coupling to the molecules and that electron double-occupancies strongly squeeze the vibrational mode. PMID:24448171
Theory of a continuous Mott transition in two dimensions
NASA Astrophysics Data System (ADS)
Senthil, T.
2008-07-01
We study theoretically the zero-temperature phase transition in two dimensions from a Fermi liquid to a paramagnetic Mott insulator with a spinon Fermi surface. We show that the approach to the bandwidth-controlled Mott transition from the metallic side is accompanied by a vanishing quasiparticle residue and a diverging effective mass. The Landau parameters Fs0,Fa0 also diverge. Right at the quantum critical point there is a sharply defined “critical Fermi surface” but no Landau quasiparticle. The critical point has a Tln1/T specific heat and a nonzero T=0 resistivity. We predict an interesting universal resistivity jump in the residual resistivity at the critical point as the transition is approached from the metallic side. The crossovers out of the critical region are also studied. Remarkably the initial crossover out of criticality on the metallic side is to a marginal Fermi liquid metal. At much lower temperatures there is a further crossover into the Landau Fermi liquid. The ratio of the two crossover scales vanishes when approaching the critical point. Similar phenomena are found in the insulating side. The filling-controlled Mott transition is also studied. Implications for experiments on the layered triangular lattice organic material κ-(ET)2Cu2(CN)3 are discussed.
Nonequilibrium electronic transport in a one-dimensional Mott insulator
Heidrich-Meisner, F.; Gonzalez, Ivan; Al-Hassanieh, K. A.; Feiguin, A. E.; Rozenberg, M. J.; Dagotto, Elbio R
2010-01-01
We calculate the nonequilibrium electronic transport properties of a one-dimensional interacting chain at half filling, coupled to noninteracting leads. The interacting chain is initially in a Mott insulator state that is driven out of equilibrium by applying a strong bias voltage between the leads. For bias voltages above a certain threshold we observe the breakdown of the Mott insulator state and the establishment of a steady-state elec- tronic current through the system. Based on extensive time-dependent density-matrix renormalization-group simulations, we show that this steady-state current always has the same functional dependence on voltage, independent of the microscopic details of the model and we relate the value of the threshold to the Lieb-Wu gap. We frame our results in terms of the Landau-Zener dielectric breakdown picture. Finally, we also discuss the real-time evolution of the current, and characterize the current-carrying state resulting from the breakdown of the Mott insulator by computing the double occupancy, the spin structure factor, and the entanglement entropy.
Charge dynamics of the antiferromagnetically ordered Mott insulator
NASA Astrophysics Data System (ADS)
Han, Xing-Jie; Liu, Yu; Liu, Zhi-Yuan; Li, Xin; Chen, Jing; Liao, Hai-Jun; Xie, Zhi-Yuan; Normand, B.; Xiang, Tao
2016-10-01
We introduce a slave-fermion formulation in which to study the charge dynamics of the half-filled Hubbard model on the square lattice. In this description, the charge degrees of freedom are represented by fermionic holons and doublons and the Mott-insulating characteristics of the ground state are the consequence of holon-doublon bound-state formation. The bosonic spin degrees of freedom are described by the antiferromagnetic Heisenberg model, yielding long-ranged (Néel) magnetic order at zero temperature. Within this framework and in the self-consistent Born approximation, we perform systematic calculations of the average double occupancy, the electronic density of states, the spectral function and the optical conductivity. Qualitatively, our method reproduces the lower and upper Hubbard bands, the spectral-weight transfer into a coherent quasiparticle band at their lower edges and the renormalisation of the Mott gap, which is associated with holon-doublon binding, due to the interactions of both quasiparticle species with the magnons. The zeros of the Green function at the chemical potential give the Luttinger volume, the poles of the self-energy reflect the underlying quasiparticle dispersion with a spin-renormalised hopping parameter and the optical gap is directly related to the Mott gap. Quantitatively, the square-lattice Hubbard model is one of the best-characterised problems in correlated condensed matter and many numerical calculations, all with different strengths and weaknesses, exist with which to benchmark our approach. From the semi-quantitative accuracy of our results for all but the weakest interaction strengths, we conclude that a self-consistent treatment of the spin-fluctuation effects on the charge degrees of freedom captures all the essential physics of the antiferromagnetic Mott-Hubbard insulator. We remark in addition that an analytical approximation with these properties serves a vital function in developing a full understanding of the
Spectral evolution with doping of an antiferromagnetic Mott state
NASA Astrophysics Data System (ADS)
Wu, Huan-Kuang; Lee, Ting-Kuo
2017-01-01
Since the discovery of half-filled cuprate to be a Mott insulator, the excitation spectra above the chemical potential for the unoccupied states has attracted much research attention. There were many theoretical works using different numerical techniques to study this problem, but many have reached different conclusions. One of the reasons is the lack of very detailed high-resolution experimental results for the theories to be compared with. Recently, the scanning tunneling spectroscopy [P. Cai et al., Nat. Phys. 12, 1047 (2016), 10.1038/nphys3840; C. Ye et al., Nat. Commun. 4, 1365 (2013), 10.1038/ncomms2369] on lightly doped Mott insulator with an antiferromagnetic order found the presence of in-gap states with energy of order half an eV above the chemical potential. The measured spectral properties with doping are not quite consistent with earlier theoretical works. Although the experiment has disorder and localization effect, but for the energy scale we will study here, a model without disorder is sufficed to illustrate the underlying physics. We perform a diagonalization method on top of the variational Monte Carlo calculation to study the evolution of antiferromagnetic Mott state with doped hole concentration in the Hubbard model. Our results found in-gap states that behave similarly with ones reported by STS. These in-gap states acquire a substantial amount of dynamical spectral weight transferred from the upper Hubbard band. The in-gap states move toward chemical potential with increasing spectral weight as doping increases. Our result also provides information about the energy scale of these in-gap states in relation with the Coulomb coupling strength U .
Bloch oscillations in the Mott-insulator regime
Kolovsky, Andrey R.
2004-07-01
We study the dynamical response of cold interacting atoms in the Mott insulator phase to a static force. As shown in the experiment by [M. Greiner et al., Nature 415, 39 (2002)], this response has resonant character, with the main resonance defined by coincidence of Stark energy and on-site interaction energy. We analyze the dynamics of the atomic momentum distribution, which is the quantity measured in the experiment, for near resonant forcing. The momentum distribution is shown to develop a recurring interference pattern, with a recurrence time which we define in the paper.
ERIC Educational Resources Information Center
Sawyer, Kem Knapp
An illustrated biography for children features Lucretia Mott, one of the pioneers of the movement for womens' rights. Born in 1793, Lucretia Mott was raised a Quaker; her strong spiritual beliefs underlay her outspoken advocacy of equal rights for women and blacks, and against war. Lucretia became a leader among those who wished to abolish…
A comparison of Mott cell morphology of three avian species. II. - Bad behavior by plasmacytes?
Cotter, Paul F; Bakst, Murray R
2017-02-01
Mott cells are atypical plasmacytes recognized microscopically by endoplasmic reticulum (ER) distensions (Russell bodies) a result of retained secretory product (antibody). Originally associated with parasitism, they are observed in a broad spectrum of immunopathology, sometimes involving hypergammaglobulinemia. Few descriptions of Mott cells appear in avian literature. The purpose of the manuscript is to provide examples identified by light microscopy in three poultry species. Transmission electron micrographs (TEM) of plasmacytes from the turkey oviduct mucosa are included for comparison with Mott cell light microscopic images. Wright's stained blood and bone marrow from commercial and specific pathogen free (SPF) chickens, ducks, and turkeys are the sources. Mott cell positive samples commonly occurred with leukocytosis or leukemoid reactions, polymicrobial bacteremia, and fungemia. Atypical granulocytes and leukocytes regularly accompanied Mott cells. It is proposed that circulating Mott cells are "sentinels" indicative of stress, dyscrasia, and pathology. Moreover, Mott cells, like other atypia, complicate the interpretation of simple heterophil/lymphocyte (H/L) ratios. As Mott cells are defective plasmacytes these observations address hematology, immunology, pathology, and welfare issues.
Spectral properties near the Mott transition in the two-dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Kohno, Masanori
2013-03-01
Single-particle excitations near the Mott transition in the two-dimensional (2D) Hubbard model are investigated by using cluster perturbation theory. The Mott transition is characterized by the loss of the spectral weight from the dispersing mode that leads continuously to the spin-wave excitation of the Mott insulator. The origins of the dominant modes of the 2D Hubbard model near the Mott transition can be traced back to those of the one-dimensional Hubbard model. Various anomalous spectral features observed in cuprate high-temperature superconductors, such as the pseudogap, Fermi arc, flat band, doping-induced states, hole pockets, and spinon-like and holon-like branches, as well as giant kink and waterfall in the dispersion relation, are explained in a unified manner as properties near the Mott transition in a 2D system.
The Mott-Hubbard Insulator: localization and topological quantum order
NASA Astrophysics Data System (ADS)
Martin, Richard M.
2010-03-01
An insulating state of condensed matter is characterized by localization of the center of mass of the electrons. This criterion can be addressed in terms of the ground state on a torus with boundary conditions ψK(x1+L,x2, ) = exp( i K L) ψK(x1,x2, ). As shown by Kohn[1], in an insulator the energy is insensitive to K as L ->∞, whereas in an ideal metal it increases as K^2. In addition, Souza, et al. derived expressions for the localization length in terms of the wavefunction as a function of K. The present work generalizes the arguments to provide a fundamental distinction between ``band'' and ``Mott-Hubbard'' insulators. The criteria involve only counting of electrons and experimentally measurable quantities independent of models, and they lead to the requirement that a Mott-Hubbard insulator with no broken local symmetry must have topological quantum order.[4pt] [1] W. Kohn, Phys. Rev. 133, A171 (1964)[0pt] [2] I. Souza, et al., Phys. Rev. B 62, 1666 (2000).
Mott glass phase in a diluted bilayer Heisenberg quantum antiferromagnet
NASA Astrophysics Data System (ADS)
Ma, Nv-Sen; Sandvik, Anders W.; Yao, Dao-Xin
2015-09-01
We use quantum Monte Carlo simulations to study a dimer-diluted S = 1/2 Heisenberg model on a bilayer square lattice with intralayer interaction J1 and interlayer interaction J2. Below the classical percolation threshold pc, the system has three phases reachable by tuning the interaction ratio g = J2/J1: a Néel ordered phase, a gapless quantum glass phase, and a gapped quantum paramagnetic phase. We present the ground-state phase diagram in the plane of dilution p and interaction ratio g. The quantum glass phase is certified to be of the gapless Mott glass type, having a uniform susceptibility vanishing at zero temperature T and following a stretched exponential form at T > 0; χu exp(-b/Tα) with α < 1. At the phase transition point from Neel ordered to Mott glass, we find that the critical exponents are different from those of the clean system described by the standard O(3) universality class in 2+1 dimensions.
Mott-Hubbard Physics in a Patterned GaAs Heterostructure with Honeycomb Topology
NASA Astrophysics Data System (ADS)
Pellegrini, Vittorio
2013-03-01
This talk considers efforts directed towards the design and exploration of novel collective electron states in artificial lattice structures that are realized in semiconductor heterostructures by nanofabrication methods. These studies reveal striking interplays between electron interactions and geometrical constraints (topology). We focus on the honeycomb topology, or ``artificial graphene'' (AG), that supports Dirac fermions. Dirac fermions and the emergence of quantum phases, such as spin liquids and topologically protected states, can be studied by highly demanding inelastic light scattering methods and by electrical transport at low temperatures. In particular, we probed the excitation spectrum of electrons in the honeycomb lattice in a magnetic field identifying collective modes that emerged from the Coulomb interaction, as predicted by the Mott-Hubbard model. These observations allow us to determine the Hubbard gap and suggest the existence of a Coulomb-driven ground state. Studies of electrons confined to artificial lattices should provide key perspectives on strong electron correlation in condensed matter science. Work done in collaboration with A. Singha, M. Gibertini, M. Polini, B. Karmakar, M. Katsnelson, S. Yuan, A. Pinczuk, G. Vignale, L.N. Pfeiffer, K.W. West
Mott-insulator phases of spin-3/2 fermions in the presence of quadratic Zeeman coupling.
Rodríguez, K; Argüelles, A; Colomé-Tatché, M; Vekua, T; Santos, L
2010-07-30
We study the influence of the quadratic Zeeman effect on the Mott-insulator phases of hard-core 1D spin-3/2 fermions. We show that, contrary to spinor bosons, the quadratic Zeeman coupling preserves an SU(2)⊗SU(2) symmetry, leading for large-enough quadratic Zeeman coupling to an isotropic pseudo-spin-1/2 Heisenberg antiferromagnet. Decreasing the quadratic Zeeman coupling, this phase undergoes, depending on the scattering lengths, either a Kosterlitz-Thouless transition into a gapped dimerized phase or a commensurate-incommensurate transition into a gapless spin liquid. This rich phase diagram can be observed experimentally in four-component fermions in optical lattices under similar entropy constraints to those needed for Néel order in spin-1/2 gases.
Mott-insulator phases of spin-3/2 fermions in the presence of quadratic Zeeman coupling
Rodriguez, K.; Argueelles, A.; Colome-Tatche, M.; Vekua, T.; Santos, L.
2010-07-30
We study the influence of the quadratic Zeeman effect on the Mott-insulator phases of hard-core 1D spin-3/2 fermions. We show that, contrary to spinor bosons, the quadratic Zeeman coupling preserves an SU(2) x SU(2) symmetry, leading for large-enough quadratic Zeeman coupling to an isotropic pseudo-spin-1/2 Heisenberg antiferromagnet. Decreasing the quadratic Zeeman coupling, this phase undergoes, depending on the scattering lengths, either a Kosterlitz-Thouless transition into a gapped dimerized phase or a commensurate-incommensurate transition into a gapless spin liquid. This rich phase diagram can be observed experimentally in four-component fermions in optical lattices under similar entropy constraints to those needed for Neel order in spin-1/2 gases.
Cluster Mott insulators and two Curie-Weiss regimes on an anisotropic kagome lattice
NASA Astrophysics Data System (ADS)
Chen, Gang; Kee, Hae-Young; Kim, Yong Baek
2016-06-01
Motivated by recent experiments on the quantum-spin-liquid candidate material LiZn2Mo3O8 , we study a single-band extended Hubbard model on an anisotropic kagome lattice with the 1/6 electron filling. Due to the partial filling of the lattice, the intersite repulsive interaction is necessary to generate Mott insulators, where electrons are localized in clusters rather than at lattice sites. It is shown that these cluster Mott insulators are generally U(1) quantum spin liquids with spinon Fermi surfaces. The nature of charge excitations in cluster Mott insulators can be quite different from conventional Mott insulator and we show that there exists a cluster Mott insulator where charge fluctuations around the hexagonal cluster induce a plaquette charge order (PCO). The spinon excitation spectrum in this spin-liquid cluster Mott insulator is reconstructed due to the PCO so that only 1/3 of the total spinon excitations are magnetically active. Based on these results, we propose that the two Curie-Weiss regimes of the spin susceptibility in LiZn2Mo3O8 may be explained by finite-temperature properties of the cluster Mott insulator with the PCO as well as fractionalized spinon excitations. Existing and possible future experiments on LiZn2Mo3O8 , and other Mo-based cluster magnets are discussed in light of these theoretical predictions.
Ge doping of GaN beyond the Mott transition
NASA Astrophysics Data System (ADS)
Ajay, A.; Schörmann, J.; Jiménez-Rodriguez, M.; Lim, C. B.; Walther, F.; Rohnke, M.; Mouton, I.; Amichi, L.; Bougerol, C.; Den Hertog, M. I.; Eickhoff, M.; Monroy, E.
2016-11-01
We present a study of germanium as n-type dopant in wurtzite GaN films grown by plasma-assisted molecular-beam epitaxy, reaching carrier concentrations of up to 6.7 × 1020 cm-3 at 300 K, well beyond the Mott density. The Ge concentration and free carrier density were found to scale linearly with the Ge flux in the studied range. All the GaN:Ge layers present smooth surface morphology with atomic terraces, without trace of pits or cracks, and the mosaicity of the samples has no noticeable dependence on the Ge concentration. The variation of the GaN:Ge band gap with the carrier concentration is consistent with theoretical calculations of the band gap renormalization due to electron-electron and electron-ion interaction, and Burstein-Moss effect.
Interference in the Mott Insulator State of Distinguishable Particles
NASA Astrophysics Data System (ADS)
Tian, Lin; Fujiwara, Fumitaka; Byrnes, Tim; Yamamoto, Yoshihisa
2008-03-01
Particle statistics plays a crucial role in strongly interacting quantum many-body systems. Here, we study the Hubbard model for distinguishable particles at unit filling. We show that when on-site repulsive interaction dominates over tunneling, the ground state is a Mott insulator state with higher order coherence between the particles. This result can be experimentally confirmed by the recovery of the interference pattern in the density correlation functions and is robust against non- uniformity of the interaction and tunneling parameters. We also show that this state is a maximally entangled state, in contrast to its bosonic counterpart. L. Tian, F. Fujiwara, T. Byrnes, and Y. Yamamoto, preprint, arXiv/0705.2023.
Critical conductance of a one-dimensional doped Mott insulator
NASA Astrophysics Data System (ADS)
Garst, M.; Novikov, D. S.; Stern, Ady; Glazman, L. I.
2008-01-01
We consider the two-terminal conductance of a one-dimensional Mott insulator undergoing the commensurate-incommensurate quantum phase transition to a conducting state. We treat the leads as Luttinger liquids. At a specific value of compressibility of the leads, corresponding to the Luther-Emery point, the conductance can be described in terms of the free propagation of noninteracting fermions with charge e/2 . At that point, the temperature dependence of the conductance across the quantum phase transition is described by a Fermi function. The deviation from the Luther-Emery point in the leads changes the temperature dependence qualitatively. In the metallic state, the low-temperature conductance is determined by the properties of the leads, and is described by the conventional Luttinger-liquid theory. In the insulating state, conductance occurs via activation of e/2 charges, and is independent of the Luttinger-liquid compressibility.
Inhomogeneous field induced magnetoelectric effect in Mott insulators
Boulaevskii, Lev N; Batista, Cristian D
2008-01-01
We consider a Mott insulator like HoMnO{sub 3} whose magnetic lattice is geometrically frustrated and comprises a 3D array of triangular layers with magnetic moments ordered in a 120{sup o} structure. We show that the effect of a uniform magnetic field gradient, {gradient}H, is to redistribute the electronic charge of the magnetically ordered phase leading to a unfirom electric field gradient. The resulting voltage difference between the crystal edges is proportional to the square of the crystal thickness, or inter-edge distance, L. It can reach values of several volts for |{gradient}H| {approx} 0.01 T/cm and L {approx_equal} 1mm, as long as the crystal is free of antiferromagnetic domain walls.
A cylindrically symmetric "micro-Mott" electron polarimeter
NASA Astrophysics Data System (ADS)
Clayburn, N. B.; Brunkow, E.; Burtwistle, S. J.; Rutherford, G. H.; Gay, T. J.
2016-05-01
A small, novel, cylindrically symmetric Mott electron polarimeter is described. The effective Sherman function, Seff, or analyzing power, for 20 kV Au target bias with a 1.3 keV energy loss window is 0.16 ± 0.01, where uncertainty in the measurement is due primarily to uncertainty in the incident electron polarization. For an energy loss window of 0.5 keV, Seff reaches its maximum value of 0.24 ± 0.02. The device's maximum efficiency, I/Io, defined as the detected count rate divided by the incident particle rate, is 3.7 ± 0.2 × 10-4 at 20 keV. The figure-of-merit of the device, η, is defined as Seff2I/Io and equals 9.0 ± 1.6 × 10-6. Potential sources of false asymmetries due to detector electronic asymmetry and beam misalignment have been investigated. The new polarimeter's performance is compared to published results for similar compact retarding-field Mott polarimeters, and it is concluded that this device has a relatively large Seff and low efficiency. SIMION® electron trajectory simulations and Sherman function calculations are presented to explain the differences in performance between this device and previous designs. This design has an Seff that is insensitive to spatial beam fluctuations and, for an energy loss window >0.5 keV, negligible background due to spurious ion and X-ray production at the target.
Single-component molecular material hosting antiferromagnetic and spin-gapped Mott subsystems
NASA Astrophysics Data System (ADS)
Takagi, Rina; Hamai, Takamasa; Gangi, Hiro; Miyagawa, Kazuya; Zhou, Biao; Kobayashi, Akiko; Kanoda, Kazushi
2017-03-01
We investigated a system based solely on a single molecular species, Cu(tmdt) 2, accommodating d and π orbitals within the molecule. 13C nuclear magnetic resonance measurements captured singlet-triplet excitations of π spins indicating the existence of a π -electron-based spin-gapped Mott insulating subsystem, which has been hidden by the large magnetic susceptibility exhibited by the d spins forming antiferromagnetic chains. The present results demonstrate a unique hybrid Mott insulator composed of antiferromagnetic and spin-singlet Mott subsystems with distinctive dimensionalities.
Mott lobes of the S =1 Bose-Hubbard model with three-body interactions
NASA Astrophysics Data System (ADS)
Hincapie-F, A. F.; Franco, R.; Silva-Valencia, J.
2016-09-01
Using the density-matrix renormalization-group method, we studied the ground state of the one-dimensional S =1 Bose-Hubbard model with local three-body interactions, which can be a superfluid or a Mott insulator state. We drew the phase diagram of this model for both ferromagnetic and antiferromagnetic interaction. Regardless of the sign of the spin-dependent coupling, we obtained that the Mott lobes area decreases as the spin-dependent strength increases, which means that the even-odd asymmetry of the two-body antiferromagnetic chain is absent for local three-body interactions. For antiferromagnetic coupling, we found that the density drives first-order superfluid-Mott insulator transitions for even and odd lobes. Ferromagnetic Mott insulator and superfluid states were obtained with a ferromagnetic coupling, and a tendency to a "long-range" order was observed.
Colossal magnetoresistance in a Mott insulator via magnetic field-driven insulator-metal transition
Zhu, M.; Peng, J.; Zou, T.; Prokes, K.; Mahanti, S. D.; Hong, Tao; Mao, Z. Q.; Liu, G. Q.; Ke, X.
2016-05-25
Here, we present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca_{3}Ru_{2}O_{7}. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.
Colossal magnetoresistance in a Mott insulator via magnetic field-driven insulator-metal transition
Zhu, M.; Peng, J.; Zou, T.; ...
2016-05-25
Here, we present a new type of colossal magnetoresistance (CMR) arising from an anomalous collapse of the Mott insulating state via a modest magnetic field in a bilayer ruthenate, Ti-doped Ca3Ru2O7. Such an insulator-metal transition is accompanied by changes in both lattice and magnetic structures. Our findings have important implications because a magnetic field usually stabilizes the insulating ground state in a Mott-Hubbard system, thus calling for a deeper theoretical study to reexamine the magnetic field tuning of Mott systems with magnetic and electronic instabilities and spin-lattice-charge coupling. This study further provides a model approach to search for CMR systemsmore » other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.« less
Universality of pseudogap and emergent order in lightly doped Mott insulators
NASA Astrophysics Data System (ADS)
Battisti, I.; Bastiaans, K. M.; Fedoseev, V.; de la Torre, A.; Iliopoulos, N.; Tamai, A.; Hunter, E. C.; Perry, R. S.; Zaanen, J.; Baumberger, F.; Allan, M. P.
2017-01-01
It is widely believed that high-temperature superconductivity in the cuprates emerges from doped Mott insulators. When extra carriers are inserted into the parent state, the electrons become mobile but the strong correlations from the Mott state are thought to survive--inhomogeneous electronic order, a mysterious pseudogap and, eventually, superconductivity appear. How the insertion of dopant atoms drives this evolution is not known, nor is whether these phenomena are mere distractions specific to hole-doped cuprates or represent genuine physics of doped Mott insulators. Here we visualize the evolution of the electronic states of (Sr1-xLax)2IrO4, which is an effective spin-1/2 Mott insulator like the cuprates, but is chemically radically different. Using spectroscopic-imaging scanning tunnelling microscopy (SI-STM), we find that for a doping concentration of x ~ 5%, an inhomogeneous, phase-separated state emerges, with the nucleation of pseudogap puddles around clusters of dopant atoms. Within these puddles, we observe the same iconic electronic order that is seen in underdoped cuprates. We investigate the genesis of this state and find evidence at low doping for deeply trapped carriers, leading to fully gapped spectra, which abruptly collapse at a threshold of x ~ 4%. Our results clarify the melting of the Mott state, and establish phase separation and electronic order as generic features of doped Mott insulators.
Unusual Mott transition in multiferroic PbCrO _{3}
Wang, Shanmin; Zhu, Jinlong; Zhang, Yi; Yu, Xiaohui; Zhang, Jianzhong; Wang, Wendan; Bai, Ligang; Qian, Jiang; Yin, Liang; Sullivan, Neil S.; Jin, Changqing; He, Duanwei; Xu, Jian; Zhao, Yusheng
2015-11-24
The Mott insulator in correlated electron systems arises from classical Coulomb repulsion between carriers to provide a powerful force for electron localization. When turning such an insulator into a metal, the so-called Mott transition, is commonly achieved by "bandwidth" control or "band filling." However, both mechanisms deviate from the original concept of Mott, which attributes such a transition to the screening of Coulomb potential and associated lattice contraction. We report a pressure-induced isostructural Mott transition in cubic perovskite PbCrO3. At the transition pressure of similar to 3 GPa, PbCrO3 exhibits significant collapse in both lattice volume and Coulomb potential. Concurrent with the collapse, it transforms from a hybrid multiferroic insulator to a metal. For the first time to our knowledge, these findings validate the scenario conceived by Mott. Close to the Mott criticality at similar to 300 K, fluctuations of the lattice and charge give rise to elastic anomalies and Laudau critical behaviors resembling the classic liquid-gas transition. Moreover, the anomalously large lattice volume and Coulomb potential in the low-pressure insulating phase are largely associated with the ferroelectric distortion, which is substantially suppressed at high pressures, leading to the first-order phase transition without symmetry breaking.
On the nature of the Mott transition in multiorbital systems
NASA Astrophysics Data System (ADS)
Facio, Jorge I.; Vildosola, V.; García, D. J.; Cornaglia, Pablo S.
2017-02-01
We analyze the nature of a Mott metal-insulator transition in multiorbital systems using dynamical mean-field theory. The auxiliary multiorbital quantum impurity problem is solved using continuous-time quantum Monte Carlo and the rotationally invariant slave-boson (RISB) mean-field approximation. We focus our analysis on the Kanamori Hamiltonian and find that there are two markedly different regimes determined by the nature of the lowest-energy excitations of the atomic Hamiltonian. The RISB results at T →0 suggest the following rule of thumb for the order of the transition at zero temperature: a second-order transition is to be expected if the lowest-lying excitations of the atomic Hamiltonian are charge excitations, while the transition tends to be first order if the lowest-lying excitations are in the same charge sector as the atomic ground state. At finite temperatures, the transition is first order and its strength, as measured, e.g., by the jump in the quasiparticle weight at the transition, is stronger in the parameter regime where the RISB method predicts a first-order transition at zero temperature. Interestingly, these results seem to apply to a wide variety of models and parameter regimes.
Anderson localization and Mott insulator phase in the time domain
Sacha, Krzysztof
2015-01-01
Particles in space periodic potentials constitute standard models for investigation of crystalline phenomena in solid state physics. Time periodicity of periodically driven systems is a close analogue of space periodicity of solid state crystals. There is an intriguing question if solid state phenomena can be observed in the time domain. Here we show that wave-packets localized on resonant classical trajectories of periodically driven systems are ideal elements to realize Anderson localization or Mott insulator phase in the time domain. Uniform superpositions of the wave-packets form stationary states of a periodically driven particle. However, an additional perturbation that fluctuates in time results in disorder in time and Anderson localization effects emerge. Switching to many-particle systems we observe that depending on how strong particle interactions are, stationary states can be Bose-Einstein condensates or single Fock states where definite numbers of particles occupy the periodically evolving wave-packets. Our study shows that non-trivial crystal-like phenomena can be observed in the time domain. PMID:26074169
Photo-doped carrier dynamics in Mott insulatoring systems
NASA Astrophysics Data System (ADS)
Iyoda, Eiki; Ishihara, Sumio
2013-03-01
Electron/hole doping in Mott insulators, for example two-dimensional cuprates, has been well investigated in relation to high-Tc superconductivity. Especially related to photo-doping, many experiments on photo-induced phase transition in strongly correlated systems have been made. In the usual photo-doping setup, the system is excited with fs-laser pulse and generated electron-hole pairs affect properties of materials. Recently, another type of photo-doped experiment with heterostructure has been made, and hole or electron carriers are dynamically injected through the heterostructure. In this theoretical study, we examine photo-doped carrier dynamics in the t-J model with dynamically doped holes. We formulate dynamics of the carriers by non-equilibrium Green functions. We take an initial state of holes and decompose the non-equilibrium Green's function into a series of equilibrium Green's functions by using Wick's theorem. The effect of the initial distribution appears from the higher terms in the series. We treat magnons with the self-consistent Born approximation. The non-equilibrium Green function derived in this way shows double time dependence. We will present physical quantities in transient process, for example, one-particle excitation spectra for holes.
Infinite bandwidth of a Mott-Hubbard insulator
NASA Astrophysics Data System (ADS)
Freericks, James; Cohn, Jeffrey; van Dongen, Peter; Krishnamurthy, Hulikal
The conventional viewpoint of the strongly correlated electron metal-insulator transition is that a single band splits into two upper and lower Hubbard bands at the metal-insulator transition. Much work has investigated whether this transition is continuous or discontinuous. Here we focus on another aspect and ask the question of whether there are additional upper and lower Hubbard bands, which stretch all the way out to infinity|leading to an infinite bandwidth for the Mott insulator. While we are not yet able to provide a rigorous proof of this result, we use exact diagonalization studies on small clusters to motivate the existence of these additional bands, and we discuss some different methods that might be utilized to provide a rigorous proof of this result. Even though the extra upper and lower Hubbard bands have very low total spectral weight, those states are expected to have extremely long lifetimes, leading to a nontrivial contribution to the transport density of states for dc transport and modifying the high temperature limit for the electrical resistivity. JKF supported by the Department of Energy, Office of Basic Energy Sciences, under Grant No. DE-FG02-08ER46542, and by the McDevitt bequest at Georgetown University. HRK supported by the Indian Science Foundation.
Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators
Dou, Xu; Kotov, Valeri N.; Uchoa, Bruno
2016-01-01
Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity. Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. We discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries. PMID:27553516
Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators
Dou, Xu; Kotov, Valeri N.; Uchoa, Bruno
2016-08-24
Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity.more » Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. Lastly, we discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries.« less
Nature of strong hole pairing in doped Mott antiferromagnets
NASA Astrophysics Data System (ADS)
Zhu, Zheng; Jiang, Hong-Chen; Sheng, D. N.; Weng, Zheng-Yu
2014-06-01
Cooper pairing instability in a Fermi liquid is well understood by the BCS theory, but pairing mechanism for doped Mott insulators still remains elusive. Previously it has been shown by density matrix renormalization group (DMRG) method that a single doped hole is always self-localized due to the quantum destructive interference of the phase string signs hidden in the t-J ladders. Here we report a DMRG investigation of hole binding in the same model, where a novel pairing-glue scheme beyond the BCS realm is discovered. Specifically, we show that, in addition to spin pairing due to superexchange interaction, the strong frustration of the phase string signs on the kinetic energy gets effectively removed by pairing the charges, which results in strong binding of two holes. By contrast, if the phase string signs are ``switched off'' artificially, the pairing strength diminishes significantly even if the superexchange coupling remains the same. In the latter, unpaired holes behave like coherent quasiparticles with pairing drastically weakened, whose sole origin may be attributed to the resonating-valence-bond (RVB) pairing of spins. Such non-BCS pairing mechanism is therefore beyond the RVB picture and may shed important light on the high-Tc cuprate superconductors.
Möbius molecules and fragile Mott insulators
NASA Astrophysics Data System (ADS)
Muechler, Lukas; Maciejko, Joseph; Neupert, Titus; Car, Roberto
2014-12-01
Motivated by the concept of Möbius aromatics in organic chemistry, we extend the recently introduced concept of fragile Mott insulators (FMI) to ring-shaped molecules with repulsive Hubbard interactions threaded by a half-quantum of magnetic flux (h c /2 e ) . In this context, an FMI is the insulating ground state of a finite-size molecule that cannot be adiabatically connected to a single Slater determinant, i.e., to a band insulator, provided that time-reversal and lattice translation symmetries are preserved. Based on exact numerical diagonalization for finite Hubbard interaction strength U and existing Bethe-ansatz studies of the one-dimensional Hubbard model in the large-U limit, we establish a duality between Hubbard molecules with 4 n and 4 n +2 sites, with n integer. A molecule with 4 n sites is an FMI in the absence of flux but becomes a band insulator in the presence of a half-quantum of flux, while a molecule with 4 n +2 sites is a band insulator in the absence of flux but becomes an FMI in the presence of a half-quantum of flux. Including next-nearest-neighbor hoppings gives rise to new FMI states that belong to multidimensional irreducible representations of the molecular point group, giving rise to a rich phase diagram.
Möbius molecules and fragile Mott insulators
NASA Astrophysics Data System (ADS)
Muechler, Lukas; Maciejko, Joseph; Neupert, Titus; Car, Roberto
2015-03-01
Motivated by the concept of Möbius aromatics in organic chemistry, we extend the recently introduced concept of fragile Mott insulators (FMI) to ring-shaped molecules with repulsive Hubbard interactions threaded by a half-quantum of magnetic flux (hc / 2 e). In this context, a FMI is the insulating ground state of a finite-size molecule that cannot be adiabatically connected to a single Slater determinant, i.e., to a band insulator, provided that time-reversal and lattice translation symmetries are preserved. Based on exact numerical diagonalization for finite Hubbard interaction strength U and existing Bethe-ansatz studies of the one-dimensional Hubbard model in the large- U limit, we establish a duality between Hubbard molecules with 4 n and 4 n + 2 sites, with n integer. A molecule with 4 n sites is an FMI in the absence of flux but becomes a band insulator in the presence of a half-quantum of flux, while a molecule with 4 n + 2 sites is a band insulator in the absence of flux but becomes an FMI in the presence of a half-quantum of flux. Including next-nearest-neighbor-hoppings gives rise to new FMI states that belong to multidimensional irreducible representations of the molecular point group, giving rise to a rich phase diagram. Reference: arXiv:1409.6732
Designing Quantum Spin-Orbital Liquids in Artificial Mott Insulators
Dou, Xu; Kotov, Valeri N.; Uchoa, Bruno
2016-08-24
Quantum spin-orbital liquids are elusive strongly correlated states of matter that emerge from quantum frustration between spin and orbital degrees of freedom. A promising route towards the observation of those states is the creation of artificial Mott insulators where antiferromagnetic correlations between spins and orbitals can be designed. We show that Coulomb impurity lattices on the surface of gapped honeycomb substrates, such as graphene on SiC, can be used to simulate SU(4) symmetric spin-orbital lattice models. We exploit the property that massive Dirac fermions form mid-gap bound states with spin and valley degeneracies in the vicinity of a Coulomb impurity. Due to electronic repulsion, the antiferromagnetic correlations of the impurity lattice are driven by a super-exchange interaction with SU(4) symmetry, which emerges from the bound states degeneracy at quarter filling. We propose that quantum spin-orbital liquids can be engineered in artificially designed solid-state systems at vastly higher temperatures than achievable in optical lattices with cold atoms. Lastly, we discuss the experimental setup and possible scenarios for candidate quantum spin-liquids in Coulomb impurity lattices of various geometries.
Characteristics of a Mott field-effect transistor (MottFET) based on La1-xSrxMnO3
NASA Astrophysics Data System (ADS)
Lee, Suyoun; Lee, Keundong; Gwon, Hyojin; Baek, Seung-Hyub; Park, Baeho; Kim, Jin-Sang
2013-03-01
Recently, the metal-insulator transition (MIT) phenomenon shown in transition metal oxides has attracted much interest due to its superior characteristics such as fast switching speed (~ femtoseconds), high on/off ratio, and low power consumption. One example is the MottFET, which utilizes the MIT modulated by electric field through the band-filling in a Mott insulator. In this work, we examined MottFET devices based on La1-xSrxMnO3(LSMO), which is one of the mostly studied Mott insulators and attractive for the potential application in spintronic devices due to its intriguing properties such as colossal magnetoresistance (CMR) and half-metallicity. For the devices with the composition near the boundary of the metal-insulator transition, we confirmed that the conductivity of the channel could be modulated by a gate electric field of moderate strength. In addition, for the future application in spintronic devices, we investigated the dependence of device characteristics on the magnetic field. As the applied magnetic field increased, we found that the current-voltage characteristic showed anomalous behavior, which might be attributed to the electron-electron interaction, spin ordering, and the magnetic impurities in the channel. This work was supported by KIST Grant 2E22731 from Ministry of Educational Science and Technology.
Rademaker, Louk; Vinokur, Valerii M.; Galda, Alexey
2017-01-01
We study numerically the voltage-induced breakdown of a Mott insulating phase in a system of charged classical particles with long-range interactions. At half-filling on a square lattice this system exhibits Mott localization in the form of a checkerboard pattern. We find universal scaling behavior of the current at the dynamic Mott insulator-metal transition and calculate scaling exponents corresponding to the transition. Our results are in agreement, up to a difference in universality class, with recent experimental evidence of a dynamic Mott transition in a system of interacting superconducting vortices. PMID:28300065
Effective field theory and integrability in two-dimensional Mott transition
Bottesi, Federico L.; Zemba, Guillermo R.
2011-08-15
Highlights: > Mott transition in 2d lattice fermion model. > 3D integrability out of 2D. > Effective field theory for Mott transition in 2d. > Double Chern-Simons. > d-Density waves. - Abstract: We study the Mott transition in a two-dimensional lattice spinless fermion model with nearest neighbors density-density interactions. By means of a two-dimensional Jordan-Wigner transformation, the model is mapped onto the lattice XXZ spin model, which is shown to possess a quantum group symmetry as a consequence of a recently found solution of the Zamolodchikov tetrahedron equation. A projection (from three to two space-time dimensions) property of the solution is used to identify the symmetry of the model at the Mott critical point as U{sub q}(sl(2)-circumflex)xU{sub q}(sl(2)-circumflex), with deformation parameter q = -1. Based on this result, the low-energy effective field theory for the model is obtained and shown to be a lattice double Chern-Simons theory with coupling constant k = 1 (with the standard normalization). By further employing the effective filed theory methods, we show that the Mott transition that arises is of topological nature, with vortices in an antiferromagnetic array and matter currents characterized by a d-density wave order parameter. We also analyze the behavior of the system upon weak coupling, and conclude that it undergoes a quantum gas-liquid transition which belongs to the Ising universality class.
A new class of in-plane Ferroelectric Mott insulators via oxide hetorostructuring
NASA Astrophysics Data System (ADS)
Kim, Chanul; Park, Hyowon; Marianetti, Chris
2015-03-01
We propose simple design rules based on charge transfer, cation ordering, and size mismatch to design a new class of in-plane ferroelectric Mott insulators in perovskite-based transition metal oxides. Ab Initio DFT+U calculations are then used to selectively scan phase space based on these rules. We begin by exploring pairs of A-type ions (A, A') and pairs of B-type ions (B, B') in AA' BB'O6 which will have nominal charge transfer consistent with valencies that are conducive to a low Mott gap insulator. Additionally, the A-type ions are chosen to have a large size mismatch and stereochemical effect. The ordering of A/A' and B/B' still retains C4v symmetry which may be spontaneously broken to yield an in-plane ferroelectric. We uncover a number of materials which are strong candidates to be in-plane ferroelectric Mott insulators in experiment, including BaBiVCuO6, BaBiVNiO6, PbLaVCuO6. Finally, we will discuss potential applications of in-plane ferroelectric Mott insulators such as ferroelectric photovoltaics, Mott FET, and optoelectronic devices. Semiconductor Research Corporation (FAME).
NASA Astrophysics Data System (ADS)
Mukherjee, Shantanu; Lee, Wei-Cheng
2015-12-01
The quasiparticle interferences (QPIs) of the featureless Mott insulators are investigated by a T -matrix formalism implemented with the dynamical mean field theory (T -DMFT). In the Mott insulating state, due to the singularity at zero frequency in the real part of the electron self-energy [Re Σ (ω )˜η /ω ] predicted by DMFT, where η can be considered as the "order parameter" for the Mott insulating state, QPIs are completely washed out at small bias voltages. However, a further analysis shows that Re Σ (ω ) serves as an energy-dependent chemical potential shift. As a result, the effective bias voltage seen by the system is e V'=e V -Re Σ (e V ) , which leads to a critical bias voltage e Vc˜√{η } satisfying e V'=0 if and only if η is nonzero. Consequently, the same QPI patterns produced by the noninteracting Fermi surfaces appear at this critical bias voltage e Vc in the Mott insulating state. We propose that this reentry of noninteracting QPI patterns at e Vc could serve as an experimental signature of the Mott insulating state, and the order parameter can be experimentally measured as η ˜(eVc) 2 .
Characterizing Featureless Mott Insulating State by Quasiparticle Interferences - A DMFT Prospect
NASA Astrophysics Data System (ADS)
Mukherjee, Shantanu; Lee, Wei-Cheng
In this talk we discuss the quasiparticle interferences (QPIs) of a Mott insulator using a T-matrix formalism implemented with the dynamical mean-field theory (T-DMFT). In the Mott insulating state, the DMFT predicts a singularity in the real part of electron self energy s (w) at low frequencies, which completely washes out the QPI at small bias voltage. However, the QPI patterns produced by the non-interacting Fermi surfaces can appear at a critical bias voltage in Mott insulating state. The existence of this non-zero critical bias voltage is a direct consequence of the singular behavior of Re[s (w)] /sim n/w with n behaving as the 'order parameter' of Mott insulating state. We propose that this reentry of non-interacting QPI patterns could serve as an experimental signature of Mott insulating state, and the 'order parameter' can be experimentally measured W.C.L acknowledges financial support from start up fund from Binghamton University.
Absence of a direct superfluid to mott insulator transition in disordered bose systems.
Pollet, L; Prokof'ev, N V; Svistunov, B V; Troyer, M
2009-10-02
We prove the absence of a direct quantum phase transition between a superfluid and a Mott insulator in a bosonic system with generic, bounded disorder. We also prove the compressibility of the system on the superfluid-insulator critical line and in its neighborhood. These conclusions follow from a general theorem of inclusions, which states that for any transition in a disordered system, one can always find rare regions of the competing phase on either side of the transition line. Quantum Monte Carlo simulations for the disordered Bose-Hubbard model show an even stronger result, important for the nature of the Mott insulator to Bose glass phase transition: the critical disorder bound Delta(c) corresponding to the onset of disorder-induced superfluidity, satisfies the relation Delta(c)>Eg/2, with Eg/2 the half-width of the Mott gap in the pure system.
Mott transition in the dynamic Hubbard model within slave boson mean-field approach
NASA Astrophysics Data System (ADS)
Le, Duc-Anh
2014-04-01
At zero temperature, the Kotliar-Ruckenstein slave boson mean-field approach is applied to the dynamic Hubbard model. In this paper, the influences of the dynamics of the auxiliary boson field on the Mott transition are investigated. At finite boson frequency, the Mott-type features of the Hubbard model is found to be enhanced by increasing the pseudospin coupling parameter g. For sufficiently large pseudospin coupling g, the Mott transition occurs even for modest values of the bare Hubbard interaction U. The lack of electron-hole symmetry is highlighted through the quasiparticle weight. Our results are in good agreement with the ones obtained by two-site dynamical mean-field theory and determinant quantum Monte Carlo simulation.
Electron–hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator
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
NASA Astrophysics Data System (ADS)
Kim, Beom Hyun; Shirakawa, Tomonori; Yunoki, Seiji
2016-10-01
The t2 g orbitals of an edge-shared transition-metal oxide with a honeycomb lattice structure form dispersionless electronic bands when only hopping mediated by the edge-sharing oxygens is accessible. This is due to the formation of isolated quasimolecular orbitals (QMOs) in each hexagon, introduced recently by Mazin et al. [Phys. Rev. Lett. 109, 197201 (2012)], which stabilizes a band insulating phase for t2g 5 systems. However, with the help of the exact diagonalization method to treat the electron kinetics and correlations on an equal footing, we find that the QMOs are fragile against not only the spin-orbit coupling (SOC) but also the Coulomb repulsion. We show that the electronic phase of t2g 5 systems can vary from a quasimolecular band insulator to a relativistic Jeff=1 /2 Mott insulator with increasing the SOC as well as the Coulomb repulsion. The different electronic phases manifest themselves in electronic excitations observed in optical conductivity and resonant inelastic x-ray scattering. Based on our calculations, we assert that the currently known Ru3 + and Ir4 + based honeycomb systems are far from the quasimolecular band insulator but rather the relativistic Mott insulator.
Kim, Beom Hyun; Shirakawa, Tomonori; Yunoki, Seiji
2016-10-28
The t_{2g} orbitals of an edge-shared transition-metal oxide with a honeycomb lattice structure form dispersionless electronic bands when only hopping mediated by the edge-sharing oxygens is accessible. This is due to the formation of isolated quasimolecular orbitals (QMOs) in each hexagon, introduced recently by Mazin et al. [Phys. Rev. Lett. 109, 197201 (2012)], which stabilizes a band insulating phase for t_{2g}^{5} systems. However, with the help of the exact diagonalization method to treat the electron kinetics and correlations on an equal footing, we find that the QMOs are fragile against not only the spin-orbit coupling (SOC) but also the Coulomb repulsion. We show that the electronic phase of t_{2g}^{5} systems can vary from a quasimolecular band insulator to a relativistic J_{eff}=1/2 Mott insulator with increasing the SOC as well as the Coulomb repulsion. The different electronic phases manifest themselves in electronic excitations observed in optical conductivity and resonant inelastic x-ray scattering. Based on our calculations, we assert that the currently known Ru^{3+} and Ir^{4+} based honeycomb systems are far from the quasimolecular band insulator but rather the relativistic Mott insulator.
Dean, M. P. M.; Cao, Y.; Liu, X.; Wall, S.; Zhu, D.; Mankowsky, R.; Thampy, V.; Chen, X. M.; Vale, J. G.; Casa, D.; Kim, Jungho; Said, A. H.; Juhas, P.; Alonso-Mori, R.; Glownia, J. M.; Robert, A.; Robinson, J.; Sikorski, M.; Song, S.; Kozina, M.; Lemke, H.; Patthey, L.; Owada, S.; Katayama, T.; Yabashi, M.; Tanaka, Yoshikazu; Togashi, T.; Liu, J.; Rayan Serrao, C.; Kim, B. J.; Huber, L.; Chang, C. -L.; McMorrow, D. F.; Forst, M.; Hill, J. P.
2016-05-09
Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity^{1, 2, 3, 4}. Recently, photo-excitation has been used to induce similarly exotic states transiently^{5, 6, 7}. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr_{2}IrO_{4}. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. In conclusion, the marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.
Dean, M. P. M.; Cao, Y.; Liu, X.; ...
2016-05-09
Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity1, 2, 3, 4. Recently, photo-excitation has been used to induce similarly exotic states transiently5, 6, 7. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation,more » exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. In conclusion, the marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.« less
Dean, M P M; Cao, Y; Liu, X; Wall, S; Zhu, D; Mankowsky, R; Thampy, V; Chen, X M; Vale, J G; Casa, D; Kim, Jungho; Said, A H; Juhas, P; Alonso-Mori, R; Glownia, J M; Robert, A; Robinson, J; Sikorski, M; Song, S; Kozina, M; Lemke, H; Patthey, L; Owada, S; Katayama, T; Yabashi, M; Tanaka, Yoshikazu; Togashi, T; Liu, J; Rayan Serrao, C; Kim, B J; Huber, L; Chang, C-L; McMorrow, D F; Först, M; Hill, J P
2016-06-01
Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.
NASA Astrophysics Data System (ADS)
Dean, M. P. M.; Cao, Y.; Liu, X.; Wall, S.; Zhu, D.; Mankowsky, R.; Thampy, V.; Chen, X. M.; Vale, J. G.; Casa, D.; Kim, Jungho; Said, A. H.; Juhas, P.; Alonso-Mori, R.; Glownia, J. M.; Robert, A.; Robinson, J.; Sikorski, M.; Song, S.; Kozina, M.; Lemke, H.; Patthey, L.; Owada, S.; Katayama, T.; Yabashi, M.; Tanaka, Yoshikazu; Togashi, T.; Liu, J.; Rayan Serrao, C.; Kim, B. J.; Huber, L.; Chang, C.-L.; McMorrow, D. F.; Först, M.; Hill, J. P.
2016-06-01
Measuring how the magnetic correlations evolve in doped Mott insulators has greatly improved our understanding of the pseudogap, non-Fermi liquids and high-temperature superconductivity. Recently, photo-excitation has been used to induce similarly exotic states transiently. However, the lack of available probes of magnetic correlations in the time domain hinders our understanding of these photo-induced states and how they could be controlled. Here, we implement magnetic resonant inelastic X-ray scattering at a free-electron laser to directly determine the magnetic dynamics after photo-doping the Mott insulator Sr2IrO4. We find that the non-equilibrium state, 2 ps after the excitation, exhibits strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. These two-dimensional (2D) in-plane Néel correlations recover within a few picoseconds, whereas the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The marked difference in these two timescales implies that the dimensionality of magnetic correlations is vital for our understanding of ultrafast magnetic dynamics.
Pressure-Induced Metallization of the Mott Insulator MnO
Patterson, J R; Aracne, C M; Jackson, D D; Weir, S T; Malba, V; Baker, P A; Vohra, Y K
2004-01-12
High-pressure electrical conductivity experiments have been performed on the Mott insulator MnO to a maximum pressure of 106 GPa. We observe a steady decrease in resistivity to 90 GPa, followed by a large, rapid decrease by a factor of 10{sup 5} between 90 and 106 GPa. Temperature cycling the sample at 87 and 106 GPa shows insulating and metallic behavior at these pressures, respectively. Our observations provide strong evidence for a pressure-induced Mott insulator-to-metal transition with an accompanying magnetic collapse beginning at 90 GPa.
New class of planar ferroelectric Mott insulators via first-principles design
Kim, Chanul; Park, Hyowon; Marianetti, Chris A.
2015-12-11
which is not common in known materials. Here we use first-principles calculations to design layered double perovskite oxides AABBO6 which achieve the aforementioned properties in the context of Mott insulators. In our design rules, the gap is dictated by B/B electronegativity difference in a Mott state, while the polarization is obtained via nominal d0 filling on the B-site, A-type cations bearing lone-pair electrons, and A = A size mismatch. Successful execution is demonstrated in BaBiCuVO6, BaBiNiVO6, BaLaCuVO6, and PbLaCuVO6.
Superfluid to Mott-insulator transition in Bose-Hubbard models.
Capello, Manuela; Becca, Federico; Fabrizio, Michele; Sorella, Sandro
2007-08-03
We study the superfluid-insulator transition in Bose-Hubbard models in one-, two-, and three-dimensional cubic lattices by means of a recently proposed variational wave function. In one dimension, the variational results agree with the expected Berezinskii-Kosterlitz-Thouless scenario of the interaction-driven Mott transition. In two and three dimensions, we find evidence that, across the transition, most of the spectral weight is concentrated at high energies, suggestive of preformed Mott-Hubbard sidebands. This result is compatible with the experimental data by Stoferle et al. [Phys. Rev. Lett. 92, 130403 (2004)].
Mott-insulator transition in a two-dimensional atomic Bose gas.
Spielman, I B; Phillips, W D; Porto, J V
2007-02-23
Cold atoms in periodic potentials are versatile quantum systems for implementing simple models prevalent in condensed matter theory. Here we realize the 2D Bose-Hubbard model by loading a Bose-Einstein condensate into an optical lattice, and study the resulting Mott insulator. The measured momentum distributions agree quantitatively with theory (no adjustable parameters). In these systems, the Mott insulator forms in a spatially discrete shell structure which we probe by focusing on correlations in atom shot noise. These correlations show a marked dependence on the lattice depth, consistent with the changing size of the insulating shell expected from simple arguments.
Spectral properties near the Mott transition in the one-dimensional Hubbard model.
Kohno, Masanori
2010-09-03
The single-particle spectral properties near the Mott transition in the one-dimensional Hubbard model are investigated by using the dynamical density-matrix renormalization group method and the Bethe ansatz. The pseudogap, hole-pocket behavior, spectral-weight transfer, and upper Hubbard band are explained in terms of spinons, holons, antiholons, and doublons. The Mott transition is characterized by the emergence of a gapless mode whose dispersion relation extends up to the order of hopping t (spin exchange J) in the weak (strong) interaction regime caused by infinitesimal doping.
Zhou, Xiaoji; Xu, Xu; Yin, Lan; Liu, W M; Chen, Xuzong
2010-07-19
We propose a new method of detecting quantum coherence of a Bose gas trapped in a one-dimensional optical lattice by measuring the light intensity from Raman scattering in cavity. After pump and displacement process, the intensity or amplitude of scattering light is different for different quantum states of a Bose gas, such as superfluid and Mott-Insulator states. This method can also be useful to detect quantum states of atoms with two components in an optical lattice.
Mott-Hubbard transition and spin-liquid state on the pyrochlore lattice
NASA Astrophysics Data System (ADS)
Swain, Nyayabanta; Tiwari, Rajarshi; Majumdar, Pinaki
2016-10-01
The pyrochlore lattice involves corner-sharing tetrahedra and the resulting geometric frustration is believed to suppress any antiferromagnetic order for Mott insulators on this structure. There are nevertheless short-range correlations which could be vital near the Mott-Hubbard insulator-metal transition. We use a static auxiliary-field-based Monte Carlo to study this problem in real space on reasonably large lattices. The method reduces to unrestricted Hartree-Fock at zero temperature but captures the key magnetic fluctuations at finite temperature. Our results reveal that increasing interaction drives the nonmagnetic (semi) metal to a "spin disordered" metal with small local moments, at some critical coupling, and then, through a small pseudogap window, to a large moment, gapped, Mott insulating phase at a larger coupling. The spin disordered metal has a finite residual resistivity which grows with interaction strength, diverging at the upper coupling. We present the resistivity, optical conductivity, and density of states across the metal-insulator transition and for varying temperature. These results set the stage for the more complex cases of Mott transition in the pyrochlore iridates and molybdates.
Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors
Kasahara, Y.; Takeuchi, Y.; Zadik, R. H.; Takabayashi, Y.; Colman, R. H.; McDonald, R. D.; Rosseinsky, M. J.; Prassides, K.; Iwasa, Y.
2017-01-01
Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (Tc) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field Hc2 of the fulleride superconductors reaches values as high as ∼90 T—the highest among cubic crystals. This is accompanied by a crossover from weak- to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn–Teller effect as the Mott transition is approached. These results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-Tc and high-Hc2. PMID:28211544
THE MOTT FOUNDATION CHILDREN'S HEALTH CENTER--THE WORLD OF STEPHEN SHAKER.
ERIC Educational Resources Information Center
Flint Board of Education, MI.
THE C.S. MOTT FOUNDATION CHILDREN'S HEALTH CENTER WAS BUILT TO SERVE CHILDREN OF THOSE BORDERLINE FAMILIES WHOSE INCOMES PROHIBIT PRIVATE MEDICAL CARE YET MAKE THEM INELIGIBLE FOR DIRECT RELIEF OF ANY KIND. THE NEED FOR SUCH A CENTER WAS PROVED BY THE CHILDREN'S 18,000 VISITS ANNUALLY FOR HEALTH CARE. WHILE PROVIDING CARE FOR CHILDREN WAS THE MAIN…
Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning
Frandsen, Benjamin A.; Liu, Lian; Cheung, Sky C.; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J. S.; Hallas, Alannah M.; Wilson, Murray N.; Cai, Yipeng; Luke, Graeme M.; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U.; Higemoto, Wataru; Billinge, Simon J. L.; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J.
2016-01-01
RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition. PMID:27531192
Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors.
Kasahara, Y; Takeuchi, Y; Zadik, R H; Takabayashi, Y; Colman, R H; McDonald, R D; Rosseinsky, M J; Prassides, K; Iwasa, Y
2017-02-17
Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (Tc) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field Hc2 of the fulleride superconductors reaches values as high as ∼90 T-the highest among cubic crystals. This is accompanied by a crossover from weak- to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn-Teller effect as the Mott transition is approached. These results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-Tc and high-Hc2.
Coulomb Liquid Phases of Bosonic Cluster Mott Insulators on a Pyrochlore Lattice.
Lv, Jian-Ping; Chen, Gang; Deng, Youjin; Meng, Zi Yang
2015-07-17
Employing large-scale quantum Monte Carlo simulations, we reveal the full phase diagram of the extended Hubbard model of hard-core bosons on the pyrochlore lattice with partial fillings. When the intersite repulsion is dominant, the system is in a cluster Mott insulator phase with an integer number of bosons localized inside the tetrahedral units of the pyrochlore lattice. We show that the full phase diagram contains three cluster Mott insulator phases with 1/4, 1/2, and 3/4 boson fillings, respectively. We further demonstrate that all three cluster Mott insulators are Coulomb liquid phases and its low-energy property is described by the emergent compact U(1) quantum electrodynamics. In addition to measuring the specific heat and entropy of the cluster Mott insulators, we investigate the correlation function of the emergent electric field and verify it is consistent with the compact U(1) quantum electrodynamics description. Our result sheds light on the magnetic properties of various pyrochlore systems, as well as the charge physics of the cluster magnets.
ERIC Educational Resources Information Center
Bragg, Debra D.; Barnett, Elisabeth A.
2008-01-01
The Breaking Through (BT) initiative of the Charles Stewart Mott Foundation seeks to prepare low-skilled adults, adult learners who are below college-level in reading, writing and/or mathematics, often lacking a high school diploma, and frequently low-income, to be successful in college and the labor market by strengthening and expanding policies…
Upper critical field reaches 90 tesla near the Mott transition in fulleride superconductors
NASA Astrophysics Data System (ADS)
Kasahara, Y.; Takeuchi, Y.; Zadik, R. H.; Takabayashi, Y.; Colman, R. H.; McDonald, R. D.; Rosseinsky, M. J.; Prassides, K.; Iwasa, Y.
2017-02-01
Controlled access to the border of the Mott insulating state by variation of control parameters offers exotic electronic states such as anomalous and possibly high-transition-temperature (Tc) superconductivity. The alkali-doped fullerides show a transition from a Mott insulator to a superconductor for the first time in three-dimensional materials, but the impact of dimensionality and electron correlation on superconducting properties has remained unclear. Here we show that, near the Mott insulating phase, the upper critical field Hc2 of the fulleride superconductors reaches values as high as ~90 T--the highest among cubic crystals. This is accompanied by a crossover from weak- to strong-coupling superconductivity and appears upon entering the metallic state with the dynamical Jahn-Teller effect as the Mott transition is approached. These results suggest that the cooperative interplay between molecular electronic structure and strong electron correlations plays a key role in realizing robust superconductivity with high-Tc and high-Hc2.
Flat-Band Potential of a Semiconductor: Using the Mott-Schottky Equation
ERIC Educational Resources Information Center
Gelderman, K.; L. Lee; Donne, S. W.
2007-01-01
An experiment is suitable for fourth-year undergraduate and graduate students in which the nature of the semiconductor materials through determination of flat-band potential using the Mott-Schottky equation is explored. The experiment confirms the soundness of the technique.
Competing roles of longitudinal and transverse Hund's terms on Mott transitions
NASA Astrophysics Data System (ADS)
Quan, Ya-Min; Yu, Xiang-Long; Wang, Qing-Wei; Zou, Liang-Jian
2017-02-01
Effects of longitudinal (JZ) and transverse (including spin-flip JX and pair-hopping JP terms) Hund's couplings on Mott transitions of two-orbital Hubbard models are studied by the rotationally invariant slave boson approach. We show that in the half-filled asymmetric systems, the orbital selective Mott phase (OSMP) expands with increasing JX,P /JZ when JX,P /JZ < 1, and has the largest region in the isotropic case (JX,P /JZ = 1); and further increasing spin-flip Hund's coupling to JX,P /JZ > 1 may quickly suppress the OSMP state. In other near-half-filled systems, the transverse Hund's coupling favors or unfavors the OSMP state, depending on the electronic correlation strength of the systems. In the quarter-filled and around systems, a small JX,P /JZ < 1 has less effect on Mott transition, while a large JX,P /JZ > 1 enhances the electron itineracy and considerably increases the critical correlation strength of the Mott transition both in symmetric and asymmetric systems. These results could be addressed by different spin-orbital states favored by JX, JP and JZ components, respectively; and the competing longitudinal and transverse Hund's coupling terms lead to most strong quantum fluctuations in the isotropic system.
Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning
NASA Astrophysics Data System (ADS)
Frandsen, Benjamin A.; Liu, Lian; Cheung, Sky C.; Guguchia, Zurab; Khasanov, Rustem; Morenzoni, Elvezio; Munsie, Timothy J. S.; Hallas, Alannah M.; Wilson, Murray N.; Cai, Yipeng; Luke, Graeme M.; Chen, Bijuan; Li, Wenmin; Jin, Changqing; Ding, Cui; Guo, Shengli; Ning, Fanlong; Ito, Takashi U.; Higemoto, Wataru; Billinge, Simon J. L.; Sakamoto, Shoya; Fujimori, Atsushi; Murakami, Taito; Kageyama, Hiroshi; Alonso, Jose Antonio; Kotliar, Gabriel; Imada, Masatoshi; Uemura, Yasutomo J.
2016-08-01
RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.
Mott transition in a two-leg Bose-Hubbard ladder under an artificial magnetic field
NASA Astrophysics Data System (ADS)
Keleş, Ahmet; Oktel, M. Ö.
2015-01-01
We consider the Bose-Hubbard model on a two-leg ladder under an artificial magnetic field and investigate the superfluid-to-Mott insulator transition in this setting. Recently, this system has been experimentally realized [M. Atala et al., Nature Phys. 10, 588 (2014), 10.1038/nphys2998], albeit in a parameter regime that is far from the Mott transition boundary. Depending on the strength of the magnetic field, the single-particle spectrum has either a single ground state or two degenerate ground states. The transition between these two phases is reflected in the many-particle properties. We first investigate these phases through the Bogoliubov approximation in the superfluid regime and calculate the transition boundary for weak interactions. For stronger interactions the system is expected to form a Mott insulator. We calculate the Mott transition boundary as a function of the magnetic field and interleg coupling with mean-field theory, strong-coupling expansion, and density matrix renormalization group (DMRG). Finally, using the DMRG, we investigate the particle-hole excitation gaps of this system at different filling factors and find peaks at simple fractions, indicating the possibility of correlated phases.
Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning
B. A. Frandsen; Liu, L.; Cheung, S. C.; ...
2016-08-17
RENiO3 (RE=rare-earth element) and V2O3 are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO3) or pressure (V2O3), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO3 and V2O3 is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phasemore » separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.« less
Volume-wise destruction of the antiferromagnetic Mott insulating state through quantum tuning
B. A. Frandsen; Liu, L.; Cheung, S. C.; Guguchia, Z.; Khasanov, R.; Morenzoni, E.; Munsie, T. J.S.; Hallas, A. M.; Wilson, M. N.; Cai, Y.; Luke, G. M.; Chen, B.; Li, W.; Jin, C.; Ding, C; Guo, S.; Ning, F.; Ito, T. U.; Higemoto, W.; Billinge, S. J.L.; Sakamoto, S.; Fujimori, A.; Murakami, T.; Kageyama, H.; Alonso, J. A.; Kotliar, G.; Imada, M.; Uemura, Y. J.
2016-08-17
RENiO_{3} (RE=rare-earth element) and V_{2}O_{3} are archetypal Mott insulator systems. When tuned by chemical substitution (RENiO_{3}) or pressure (V_{2}O_{3}), they exhibit a quantum phase transition (QPT) between an antiferromagnetic Mott insulating state and a paramagnetic metallic state. Because novel physics often appears near a Mott QPT, the details of this transition, such as whether it is first or second order, are important. Here, we demonstrate through muon spin relaxation/rotation (μSR) experiments that the QPT in RENiO_{3} and V_{2}O_{3} is first order: the magnetically ordered volume fraction decreases to zero at the QPT, resulting in a broad region of intrinsic phase separation, while the ordered magnetic moment retains its full value until it is suddenly destroyed at the QPT. These findings bring to light a surprising universality of the pressure-driven Mott transition, revealing the importance of phase separation and calling for further investigation into the nature of quantum fluctuations underlying the transition.
Device Performance of the Mott Insulator LaVO3 as a Photovoltaic Material
NASA Astrophysics Data System (ADS)
Wang, Lingfei; Li, Yongfeng; Bera, Ashok; Ma, Chun; Jin, Feng; Yuan, Kaidi; Yin, Wanjian; David, Adrian; Chen, Wei; Wu, Wenbin; Prellier, Wilfrid; Wei, Suhuai; Wu, Tom
2015-06-01
Searching for solar-absorbing materials containing earth-abundant elements with chemical stability is of critical importance for advancing photovoltaic technologies. Mott insulators have been theoretically proposed as potential photovoltaic materials. In this paper, we evaluate their performance in solar cells by exploring the photovoltaic properties of Mott insulator LaVO3 (LVO). LVO films show an indirect band gap of 1.08 eV as well as strong light absorption over a wide wavelength range in the solar spectrum. First-principles calculations on the band structure of LVO further reveal that the d -d transitions within the upper and lower Mott-Hubbard bands and p -d transitions between the O 2 p and V 3 d band contribute to the absorption in visible and ultraviolet ranges, respectively. Transport measurements indicate strong carrier trapping and the formation of polarons in LVO. To utilize the strong light absorption of LVO and to overcome its poor carrier transport, we incorporate it as a light absorber in solar cells in conjunction with carrier transporters and evaluate its device performance. Our complementary experimental and theoretical results on such prototypical solar cells made of Mott-Hubbard transition-metal oxides pave the road for developing light-absorbing materials and photovoltaic devices based on strongly correlated electrons.
Field-Driven Mott Gap Collapse and Resistive Switch in Correlated Insulators
NASA Astrophysics Data System (ADS)
Mazza, G.; Amaricci, A.; Capone, M.; Fabrizio, M.
2016-10-01
Mott insulators are "unsuccessful metals" in which Coulomb repulsion prevents charge conduction despite a metal-like concentration of conduction electrons. The possibility to unlock the frozen carriers with an electric field offers tantalizing prospects of realizing new Mott-based microelectronic devices. Here we unveil how such unlocking happens in a simple model that shows the coexistence of a stable Mott insulator and a metastable metal. Considering a slab subject to a linear potential drop, we find, by means of the dynamical mean-field theory, that the electric breakdown of the Mott insulator occurs via a first-order insulator-to-metal transition characterized by an abrupt gap collapse in sharp contrast to the standard Zener breakdown. The switch on of conduction is due to the field-driven stabilization of the metastable metallic phase. Outside the region of insulator-metal coexistence, the electric breakdown occurs through a more conventional quantum tunneling across the Hubbard bands tilted by the field. Our findings rationalize recent experimental observations and may offer a guideline for future technological research.
Mechanism and observation of Mott transition in VO2-based two- and three-terminal devices
NASA Astrophysics Data System (ADS)
Kim, Hyun-Tak; Chae, Byung-Gyu; Youn, Doo-Hyeb; Maeng, Sung-Lyul; Kim, Gyungock; Kang, Kwang-Yong; Lim, Yong-Sik
2004-05-01
When holes of about 0.018% are induced into a conduction band (breakdown of critical on-site Coulomb energy), an abrupt first-order Mott metal-insulator transition (MIT) rather than a continuous Hubbard MIT near a critical on-site Coulomb energy U/Uc=1, where U is on-site Coulomb energy between electrons, is observed on an inhomogeneous VO2 film, a strongly correlated Mott insulator. As a result, discontinuous jumps of the density of states on the Fermi surface are observed and inhomogeneity inevitably occurs. The off-current and temperature dependences of the abrupt MIT in a two-terminal device and the gate effect in a three-terminal device are clear evidence that the abrupt Mott MIT was induced by the excitation of holes. Raman spectra measured by a micro-Raman system show an MITs without the structural phase transition. Moreover, the magnitude of the observed jumps DgrJobserved at the abrupt MIT is an average over an inhomogeneous measurement region of the maximum true jump, DgrJtrue, deduced from the Brinkman-Rice picture. A brief discussion of whether VO2 is a Mott insulator or a Peierls insulator is presented.
Spin-orbital fluctuations in the paramagnetic Mott insulator (V1-xCrx)2O3
NASA Astrophysics Data System (ADS)
Leiner, Jonathan; Stone, Matthew; Lumsden, Mark; Bao, Wei; Broholm, Collin
2015-03-01
The phase diagram of rhombohedral V2O3 features several distinct strongly correlated phases as a function of doping, pressure and temperature. When doped with chromium for 180 K
NASA Astrophysics Data System (ADS)
Hattori, Yuma; Iguchi, Satoshi; Sasaki, Takahiko; Iwai, Shinichiro; Taniguchi, Hiromi; Kishida, Hideo
2017-02-01
Raman scattering spectra of the dimer-Mott insulator β'-(BEDT-TTF ) 2IC l2 [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene] under a static electric field are investigated. The application of the electric field induces two additional Raman peaks on both sides of the original peak position of the charge-sensitive Raman mode (ν2) in the spectra. At 10 kV/cm, the original peak almost disappears and only the newly emerging peaks are observed. The emergence of these peaks indicates the field-induced charge disproportionation within the dimer. The temporal change of the Raman signals with the inversion of the electric field suggests a macroscopic domain formation of the charge-disproportionate dimers. This picture is reinforced by the direct measurement of the polarization.
NASA Astrophysics Data System (ADS)
Yamada, Atsushi
2014-12-01
The magnetic properties and Mott transition of the half-filled Hubbard model on the 1/5 -depleted square lattice with frustration are studied at zero temperature by the variational cluster approximation. The (π ,π ) Néel ordering is stable in a wide region of the phase diagram and almost completely veils the nonmagnetic Mott transition for the nonfrustrated case. However, (π ,π ) Néel ordering is severely suppressed by the frustration, and even with moderate frustrations the nonmagnetic Mott transition takes place in the range where the intradimer hoppings are larger than the intraplaquette hoppings.
Superconductivity and bandwidth-controlled Mott metal-insulator transition in 1T-TaS2-xSex
NASA Astrophysics Data System (ADS)
Ang, R.; Miyata, Y.; Ieki, E.; Nakayama, K.; Sato, T.; Liu, Y.; Lu, W. J.; Sun, Y. P.; Takahashi, T.
2013-09-01
We have performed high-resolution angle-resolved photoemission spectroscopy (ARPES) of layered chalcogenide 1T-TaS2-xSex to elucidate the electronic states especially relevant to the occurrence of superconductivity. We found a direct evidence for a Ta-5d-derived electron pocket associated with the superconductivity, which is fragile against a Mott-gap opening observed in the insulating ground state for S-rich samples. In particular, a strong electron-electron interaction-induced Mott gap driven by a Ta 5d orbital also exists in the metallic ground state for Se-rich samples, while finite ARPES intensity near the Fermi level likely originating from a Se 4p orbital survives, indicative of the orbital-selective nature of the Mott transition. Present results suggest that effective electron correlation and p-d hybridization play a crucial role to tune the superconductivity and Mott metal-insulator transition.
ERIC Educational Resources Information Center
Young, Andrew T.
1982-01-01
The correct usage of such terminology as "Rayleigh scattering,""Rayleigh lines,""Raman lines," and "Tyndall scattering" is resolved during an historical excursion through the physics of light-scattering by gas molecules. (Author/JN)
First-order Isostructural Mott transition in highly-compressed MnO
Yoo, C
2004-06-18
We present evidence for an isostructural, first-order Mott transition in MnO at 105 {+-} 5 GPa, based on high-resolution x-ray emission spectroscopy and angle-resolved x-ray diffraction data. The pressure-induced structural/spectral changes provide a coherent picture of MnO phase transitions from paramagnetic B1 to antiferromagnetic distorted B1 at 30 GPa, to paramagnetic B8 at 90 GPa, and to diamagnetic B8 at 105 {+-} 5 GPa. The last is the Mott transition, accompanied by a complete loss of magnetic moment, an {approx}6.6% volume collapse and a visual appearance change to metallic luster consistent with recent resistivity measurements.
Unstable Domain-Wall Solution in the Metal-Mott Insulator Coexisting Regime
NASA Astrophysics Data System (ADS)
Lee, Tsung-Han; Dobrosavljevic, Vladimir; Vucicevic, Jaksa; Tanaskovic, Darko; Miranda, Eduardo
2015-03-01
We employ Dynamical Mean Field Theory (DMFT) with multidimensional optimization (Conjugate Gradient and Broyden method) to investigate the transport properties of the unstable solution in the Mott metal-insulator coexisting regime. Physically, this solution is expected to describe the properties of the domain wall separating the metallic and the Mott-insulating regions in a spatially inhomogeneous case. We show that the multidimensional optimization can efficiently converge not only to the local minima of the free energy, describing the two coexisting phases, but also to the saddle-point describing the unstable solution. This unstable solution represents a new phase of matter: its low temperature transport properties differ qualitatively from both the metal and the insulator, displaying incoherent metallic behavior down to lowest temperatures.
Mott lobes evolution of the spin-1 Bose-Hubbard model
NASA Astrophysics Data System (ADS)
Hincapie-F, A. F.; Franco, R.; Silva-Valencia, J.
2016-02-01
We study spin-1 bosons confined in a one-dimensional optical lattice, taking into consideration both ferromagnetic and antiferromagnetic interaction. Using the density matrix renormalization group, we determine the phase diagram for the two firsts lobes and report the evolution of the first and second Mott lobes with respect to the spin-exchange interaction parameter (U 2). We determine that for the antiferromagnetic case, the first lobe is suppressed while the second grows as |U 2| increases. For the ferromagnetic case, the first and second Mott lobes are suppressed by the spin-exchange interaction parameter. We propose an expresion to describe the evolution of the critical point with the increase in |U 2| for both cases.
Absence of Asymptotic Freedom in Doped Mott Insulators: Breakdown of Strong Coupling Expansions
NASA Astrophysics Data System (ADS)
Phillips, Philip; Galanakis, Dimitrios; Stanescu, Tudor D.
2004-12-01
We show that doped Mott insulators such as the copper-oxide superconductors are asymptotically slaved in that the quasiparticle weight Z near half-filling depends critically on the existence of the high-energy scale set by the upper Hubbard band. In particular, near half-filling, the following dichotomy arises: Z≠0 when the high-energy scale is integrated out but Z=0 in the thermodynamic limit when it is retained. Slavery to the high-energy scale arises from quantum interference between electronic excitations across the Mott gap. Broad spectral features seen in photoemission in the normal state of the cuprates are argued to arise from high-energy slavery.
Extension of the radiative lifetime of Wannier-Mott excitons in semiconductor nanoclusters
Kukushkin, V. A.
2015-01-15
The purpose of the study is to calculate the radiative lifetime of Wannier-Mott excitons in three-dimensional potential wells formed of direct-gap narrow-gap semiconductor nanoclusters in wide-gap semiconductors and assumed to be large compared to the exciton radius. Calculations are carried out for the InAs/GaAs heterosystem. It is shown that, as the nanocluster dimensions are reduced to values on the order of the exciton radius, the exciton radiative lifetime becomes several times longer compared to that in a homogeneous semiconductor. The increase in the radiative lifetime is more pronounced at low temperatures. Thus, it is established that the placement of Wannier-Mott excitons into direct-gap semiconductor nanoclusters, whose dimensions are of the order of the exciton radius, can be used for considerable extension of the exciton radiative lifetime.
Finite mass enhancement across bandwidth controlled Mott transition in NiS2-xSex
NASA Astrophysics Data System (ADS)
Han, Garam; Kyung, W. S.; Kim, Y. K.; Cheng, C. M.; Tsuei, K. D.; Lee, K. D.; Hur, N.; Kim, H.-D.; Kim, C.
One of the most important and still debated issues in the strongly correlated electron systems is on the metal insulator transition (MIT) mechanism. In the bandwidth controlled Mott transition (BCMT) scenario, which Mott originally proposed, MIT occurs through a mass divergence in which the effective mass of the quasi-particle (QP) diverges approaching the MIT. The interpretation is supported by dynamic mean field theory (DMFT) model calculations. However, few direct observations have been made yet due to various experimental restrictions. In this talk, I present systematic angle resolved photoemission studies on the MIT in NiS2-xSex, which is a well-known BCMT material. We observed not only the bandwidth shrinkage but also the coherent quasi-particle peak (QP) which is not of the surface origin. In addition, we experimentally showed the mass of the QP remains finite approaching the MIT. This work was supported by IBS-R009-D1.
NASA Astrophysics Data System (ADS)
Zonno, Irene; Martinez-Otero, Alberto; Hebig, Jan-Christoph; Kirchartz, Thomas
2017-03-01
The Mott-Schottky analysis in the dark is a frequently used method to determine the doping concentration of semiconductors from capacitance-voltage measurements, even for such complex systems as polymer:fullerene blends used for organic solar cells. While the analysis of capacitance-voltage measurements in the dark is relatively well established, the analysis of data taken under illumination is currently not fully understood. Here, we present experiments and simulations to show which physical mechanisms affect the Mott-Schottky analysis under illumination. We show that the mobility of the blend has a major influence on the shape of the capacitance-voltage curve and can be obtained from data taken under reverse bias. In addition, we show that the apparent shift of the built-in voltage observed previously can be explained by a shift of the onset of space-charge-limited collection with illumination intensity.
Ultrafast and reversible control of the exchange interaction in Mott insulators
Mentink, J. H.; Balzer, K.; Eckstein, M.
2015-01-01
The strongest interaction between microscopic spins in magnetic materials is the exchange interaction Jex. Therefore, ultrafast control of Jex holds the promise to control spins on ultimately fast timescales. We demonstrate that time-periodic modulation of the electronic structure by electric fields can be used to reversibly control Jex on ultrafast timescales in extended antiferromagnetic Mott insulators. In the regime of weak driving strength, we find that Jex can be enhanced and reduced for frequencies below and above the Mott gap, respectively. Moreover, for strong driving strength, even the sign of Jex can be reversed and we show that this causes time reversal of the associated quantum spin dynamics. These results suggest wide applications, not only to control magnetism in condensed matter systems, for example, via the excitation of spin resonances, but also to assess fundamental questions concerning the reversibility of the quantum many-body dynamics in cold atom systems. PMID:25819547
Resolving the VO2 controversy: Mott mechanism dominates the insulator-to-metal transition
NASA Astrophysics Data System (ADS)
Nájera, O.; Civelli, M.; Dobrosavljević, V.; Rozenberg, M. J.
2017-01-01
We consider a minimal model to investigate the metal-insulator transition in VO2. We adopt a Hubbard model with two orbitals per unit cell, which captures the competition between Mott and singlet-dimer localization. We solve the model within dynamical mean-field theory, characterizing in detail the metal-insulator transition and finding new features in the electronic states. We compare our results with available experimental data, obtaining good agreement in the relevant model parameter range. Crucially, we can account for puzzling optical conductivity data obtained within the hysteresis region, which we associate with a metallic state characterized by a split heavy quasiparticle band. Our results show that the thermal-driven insulator-to-metal transition in VO2 is compatible with a Mott electronic mechanism, providing fresh insight to a long-standing "chicken-and-egg" debate and calling for further research of "Mottronics" applications of this system.
Site-Selective Mott Transition in a Quasi-One-Dimensional Vanadate V6 O13
NASA Astrophysics Data System (ADS)
Shimizu, Yasuhiro; Aoyama, Satoshi; Jinno, Takaaki; Itoh, Masayuki; Ueda, Yutaka
2015-04-01
The microscopic mechanism of the metal-insulator transition is studied by orbital-resolved 51V NMR spectroscopy in a prototype of the quasi-one-dimensional system V6 O13 . We uncover that the transition involves a site-selective d orbital order lifting twofold orbital degeneracy in one of the two VO6 chains. The other chain leaves paramagnetic moments on the singly occupied dx y orbital across the transition. The two chains respectively stabilize an orbital-assisted spin-Peierls state and an antiferromagnetic long-range order in the ground state. The site-selective Mott transition may be a source of the anomalous metal and the Mott-Peierls duality.
Spin frustration and magnetic ordering in the Mott insulating fcc-Cs3C60
NASA Astrophysics Data System (ADS)
Kasahara, Yuichi; Takeuchi, Yuki; Itou, Tatsuaki; Iwasa, Yoshihiro; Arcon, Denis; Rosseinsky, Matthew; Prassides, Kosmas
2014-03-01
The low-temperature magnetic state at ambient pressure has been investigated by specific heat and nuclear magnetic resonance (NMR) measurements in face-centered-cubic (fcc-) Cs3C60, which is characterized by a Mott insulating state with S = 1 / 2 spins in C603- anions and a geometrical spin frustration inherent in the fcc lattice. Specific heat exhibited no sharp anomaly down to 0.4 K, but both magnetic specific heat and NMR relaxation rate revealed a broad peak around 2.5 K, indicating that the reported antiferromagnetic ordering is accompanied by a gradual freezing of electronic spins with distributed transition temperatures. These results are unexpected in the conventional fcc antiferromagnets. Interplay of geometrical frustration, orientational disorder of C60 molecules, and weak Mottness gives rise to the unique magnetic ground state in fcc-Cs3C60.
New class of planar ferroelectric Mott insulators via first-principles design
NASA Astrophysics Data System (ADS)
Kim, Chanul; Park, Hyowon; Marianetti, Chris A.
2015-12-01
The bulk photovoltaic effect requires a low electronic band gap (i.e., ≈1 -2 eV) and large electronic polarization, which is not common in known materials. Here we use first-principles calculations to design layered double perovskite oxides AA'BB'O6 which achieve the aforementioned properties in the context of Mott insulators. In our design rules, the gap is dictated by B/B' electronegativity difference in a Mott state, while the polarization is obtained via nominal d0 filling on the B-site, A-type cations bearing lone-pair electrons, and A ≠A' size mismatch. Successful execution is demonstrated in BaBiCuVO6, BaBiNiVO6, BaLaCuVO6, and PbLaCuVO6.
First-order melting of a weak spin-orbit mott insulator into a correlated metal
Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Zac; Dean, M. P. M.; Hill, John P.; Islam, Z.; Madhavan, Vidya; Wilson, Stephen D.
2015-06-25
Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr_{1-x}La_{x})_{3}Ir_{2}O_{7} is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.
First-order melting of a weak spin-orbit mott insulator into a correlated metal
Hogan, Tom; Yamani, Z.; Walkup, D.; ...
2015-06-25
Herein, the electronic phase diagram of the weak spin-orbit Mott insulator (Sr1-xLax)3Ir2O7 is determined via an exhaustive experimental study. Upon doping electrons via La substitution, an immediate collapse in resistivity occurs along with a narrow regime of nanoscale phase separation comprised of antiferromagnetic, insulating regions and paramagnetic, metallic puddles persisting until x≈0.04. Continued electron doping results in an abrupt, first-order phase boundary where the Néel state is suppressed and a homogenous, correlated, metallic state appears with an enhanced spin susceptibility and local moments. In conclusion, as the metallic state is stabilized, a weak structural distortion develops and suggests a competingmore » instability with the parent spin-orbit Mott state.« less
Divergent precursors of the Mott-Hubbard transition at the two-particle level.
Schäfer, T; Rohringer, G; Gunnarsson, O; Ciuchi, S; Sangiovanni, G; Toschi, A
2013-06-14
Identifying the fingerprints of the Mott-Hubbard metal-insulator transition may be quite elusive in correlated metallic systems if the analysis is limited to the single particle level. However, our dynamical mean-field calculations demonstrate that the situation changes completely if the frequency dependence of the two-particle vertex functions is considered: The first nonperturbative precursors of the Mott physics are unambiguously identified well inside the metallic regime by the divergence of the local Bethe-Salpeter equation in the charge channel. In the low-temperature limit this occurs for interaction values where incoherent high-energy features emerge in the spectral function, while at high temperatures it is traceable up to the atomic limit.
High pressure metallization of Mott Insulators: Magnetic, structural and electronic properties
Pasternak, M.P.; Hearne, G.; Sterer, E.; Taylor, R.D.; Jeanloz, R.
1993-07-20
High pressure studies of the insulator-metal transition in the (TM)I{sub 2} (TM = V, Fe, Co and Ni) compounds are described. Those divalent transition-metal iodides are structurally isomorphous and classified as Mott Insulators. Resistivity, X-ray diffraction and Moessbauer Spectroscopy were employed to investigate the electronic, structural, and magnetic properties as a function of pressure both on the highly correlated and on the metallic regimes.
NMR study of the superconducting gap variation near the Mott transition in Cs₃C₆₀.
Wzietek, P; Mito, T; Alloul, H; Pontiroli, D; Aramini, M; Riccò, M
2014-02-14
Former extensive studies of superconductivity in the A3C60 compounds, where A is an alkali metal, have led one to consider that Bardeen-Cooper-Schrieffer electron-phonon pairing prevails in those compounds, though the incidence of electronic Coulomb repulsion has been highly debated. The discovery of two isomeric fulleride compounds Cs3C60 which exhibit a transition with pressure from a Mott insulator (MI) to a superconducting (SC) state clearly reopens that question. Using pressure (p) as a single control parameter of the C60 balls lattice spacing, one can now study the progressive evolution of the SC properties when the electronic correlations are increased towards the critical pressure p(c) of the Mott transition. We have used 13C and 133Cs NMR measurements on the cubic phase A15-Cs3C60 just above p(c)=5.0(3) kbar, where the SC transition temperature Tc displays a dome shape with decreasing cell volume. From the T dependence below T(c) of the nuclear spin lattice relaxation rate (T1)(-1) we determine the electronic excitations in the SC state, that is 2Δ, the gap value. The latter is found to be largely enhanced with respect to the Bardeen-Cooper-Schrieffer value established in the case of dense A3C60 compounds. It even increases slightly with decreasing p towards p(c), where T(c) decreases on the SC dome, so that 2Δ/k(B)T(c) increases regularly upon approaching the Mott transition. These results bring clear evidence that the increasing correlations near the Mott transition are not significantly detrimental to superconductivity. They rather suggest that repulsive electron interactions might even reinforce elecron-phonon superconductivity, being then partly responsible for the large T(c) values, as proposed by theoretical models taking the electronic correlations as a key ingredient.
NMR Study of the Superconducting Gap Variation near the Mott Transition in Cs3C60
NASA Astrophysics Data System (ADS)
Wzietek, P.; Mito, T.; Alloul, H.; Pontiroli, D.; Aramini, M.; Riccò, M.
2014-02-01
Former extensive studies of superconductivity in the A3C60 compounds, where A is an alkali metal, have led one to consider that Bardeen-Cooper-Schrieffer electron-phonon pairing prevails in those compounds, though the incidence of electronic Coulomb repulsion has been highly debated. The discovery of two isomeric fulleride compounds Cs3C60 which exhibit a transition with pressure from a Mott insulator (MI) to a superconducting (SC) state clearly reopens that question. Using pressure (p) as a single control parameter of the C60 balls lattice spacing, one can now study the progressive evolution of the SC properties when the electronic correlations are increased towards the critical pressure pc of the Mott transition. We have used C13 and Cs133 NMR measurements on the cubic phase A15-Cs3C60 just above pc=5.0(3) kbar, where the SC transition temperature Tc displays a dome shape with decreasing cell volume. From the T dependence below Tc of the nuclear spin lattice relaxation rate (T1)-1 we determine the electronic excitations in the SC state, that is 2Δ, the gap value. The latter is found to be largely enhanced with respect to the Bardeen-Cooper-Schrieffer value established in the case of dense A3C60 compounds. It even increases slightly with decreasing p towards pc, where Tc decreases on the SC dome, so that 2Δ /kBTc increases regularly upon approaching the Mott transition. These results bring clear evidence that the increasing correlations near the Mott transition are not significantly detrimental to superconductivity. They rather suggest that repulsive electron interactions might even reinforce elecron-phonon superconductivity, being then partly responsible for the large Tc values, as proposed by theoretical models taking the electronic correlations as a key ingredient.
Competing ground states of strongly correlated bosons in the Harper-Hofstadter-Mott model
NASA Astrophysics Data System (ADS)
Natu, Stefan S.; Mueller, Erich J.; Das Sarma, S.
2016-06-01
Using an efficient cluster approach, we study the physics of two-dimensional lattice bosons in a strong magnetic field in the regime where the tunneling is much weaker than the on-site interaction strength. We study both the dilute, hard-core bosons at filling factors much smaller than unity occupation per site and the physics in the vicinity of the superfluid-Mott lobes as the density is tuned away from unity. For hard-core bosons, we carry out extensive numerics for a fixed flux per plaquette ϕ =1 /5 and ϕ =1 /3 . At large flux, the lowest-energy state is a strongly correlated superfluid, analogous to He-4, in which the order parameter is dramatically suppressed, but nonzero. At filling factors ν =1 /2 ,1 , we find competing incompressible states which are metastable. These appear to be commensurate density wave states. For small flux, the situation is reversed and the ground state at ν =1 /2 is an incompressible density wave solid. Here, we find a metastable lattice supersolid phase, where superfluidity and density wave order coexist. We then perform careful numerical studies of the physics near the vicinity of the Mott lobes for ϕ =1 /2 and ϕ =1 /4 . At ϕ =1 /2 , the superfluid ground state has commensurate density wave order. At ϕ =1 /4 , incompressible phases appear outside the Mott lobes at densities n =1.125 and n =1.25 , corresponding to filling fractions ν =1 /2 and 1, respectively. These phases, which are absent in single-site mean-field theory, are metastable and have slightly higher energy than the superfluid, but the energy difference between them shrinks rapidly with increasing cluster size, suggestive of an incompressible ground state. We thus explore the interplay between Mott physics, magnetic Landau levels, and superfluidity, finding a rich phase diagram of competing compressible and incompressible states.
Condensate fraction in a 2D Bose gas measured across the Mott-insulator transition.
Spielman, I B; Phillips, W D; Porto, J V
2008-03-28
We realize a single-band 2D Bose-Hubbard system with Rb atoms in an optical lattice and measure the condensate fraction as a function of lattice depth, crossing from the superfluid to the Mott-insulating phase. We quantitatively identify the location of the superfluid to normal transition by observing when the condensed fraction vanishes. Our measurement agrees with recent quantum Monte Carlo calculations for a finite-sized 2D system to within experimental uncertainty.
Non-local order in Mott insulators, duality and Wilson loops
Rath, Steffen Patrick; Simeth, Wolfgang; Endres, Manuel; Zwerger, Wilhelm
2013-07-15
It is shown that the Mott insulating and superfluid phases of bosons in an optical lattice may be distinguished by a non-local ‘parity order parameter’ which is directly accessible via single site resolution imaging. In one dimension, the lattice Bose model is dual to a classical interface roughening problem. We use known exact results from the latter to prove that the parity order parameter exhibits long range order in the Mott insulating phase, consistent with recent experiments by Endres et al. [M. Endres, M. Cheneau, T. Fukuhara, C. Weitenberg, P. Schauß, C. Gross, L. Mazza, M.C. Bañuls, L. Pollet, I. Bloch, et al., Science 334 (2011) 200]. In two spatial dimensions, the parity order parameter can be expressed in terms of an equal time Wilson loop of a non-trivial U(1) gauge theory in 2+1 dimensions which exhibits a transition between a Coulomb and a confining phase. The negative logarithm of the parity order parameter obeys a perimeter law in the Mott insulator and is enhanced by a logarithmic factor in the superfluid. -- Highlights: •Number statistics of cold atoms in optical lattices show non-local correlations. •These correlations are measurable via single site resolution imaging. •Incompressible phases exhibit an area law in particle number fluctuations. •This leads to long-range parity order of Mott-insulators in one dimension. •Parity order in 2d is connected with a Wilson-loop in a lattice gauge theory.
Transition from a Two-Dimensional Superfluid to a One-Dimensional Mott Insulator
Bergkvist, Sara; Rosengren, Anders; Saers, Robert; Lundh, Emil; Rehn, Magnus; Kastberg, Anders
2007-09-14
A two-dimensional system of atoms in an anisotropic optical lattice is studied theoretically. If the system is finite in one direction, it is shown to exhibit a transition between a two-dimensional superfluid and a one-dimensional Mott insulating chain of superfluid tubes. Monte Carlo simulations are consistent with the expectation that the phase transition is of Kosterlitz-Thouless type. The effect of the transition on experimental time-of-flight images is discussed.
Collective excitations and the nature of Mott transition in undoped gapped graphene.
Jafari, S A
2012-08-01
The particle-hole continuum (PHC) for massive Dirac fermions provides an unprecedented opportunity for the formation of two collective split-off states, one in the singlet and the other in the triplet (spin-1) channel, when the short-range interactions are added to the undoped system. Both states are close in energy and are separated from the continuum of free particle-hole excitations by an energy scale of the order of the gap parameter Δ. They both disperse linearly with two different velocities, reminiscent of spin-charge separation in Luttinger liquids. When the strength of Hubbard interactions is stronger than a critical value, the velocity of singlet excitation, which we interpret as a charge composite boson, becomes zero and renders the system a Mott insulator. Beyond this critical point the low-energy sector is left with a linearly dispersing triplet mode-a characteristic of a Mott insulator. The velocity of the triplet mode at the Mott criticality is twice the velocity of the underlying Dirac fermions. The phase transition line in the space of U and Δ is in qualitative agreement with our previous dynamical mean field theory calculations.
Path to poor coherence in the periodic Anderson model from Mott physics and hybridization
NASA Astrophysics Data System (ADS)
Amaricci, A.; de'Medici, L.; Sordi, G.; Rozenberg, M. J.; Capone, M.
2012-06-01
We investigate the anomalous metal arising from hole-doping the Mott insulating state in the periodic Anderson model. Using dynamical mean-field theory we show that, as opposed to the electron-doped case, in the hole-doped regime the hybridization between localized and delocalized orbitals leads to the formation of composite quasiparticles reminiscent of the Zhang-Rice singlets. We compute the coherence temperature of this state, showing its extremely small value at low doping. As a consequence the weakly doped Mott state deviates from the predictions of Fermi-liquid theory already at small temperatures. The onset of the Zhang-Rice state and of the consequent poor coherence is due to the electronic structure in which both localized and itinerant carriers have to be involved in the formation of the conduction states and to the proximity to the Mott state. By investigating the magnetic properties of this state, we discuss the relation between the anomalous metallic properties and the behavior of the magnetic degrees of freedom.
Continuous Mott transition between a metal and a quantum spin liquid
NASA Astrophysics Data System (ADS)
Mishmash, Ryan V.; González, Iván; Melko, Roger G.; Motrunich, Olexei I.; Fisher, Matthew P. A.
2015-06-01
More than half a century after first being proposed by Sir Nevill Mott, the deceptively simple question of whether the interaction-driven electronic metal-insulator transition may be continuous remains enigmatic. Recent experiments on two-dimensional materials suggest that when the insulator is a quantum spin liquid, lack of magnetic long-range order on the insulating side may cause the transition to be continuous, or only very weakly first order. Motivated by this, we study a half-filled extended Hubbard model on a triangular lattice strip geometry. We argue, through use of large-scale numerical simulations and analytical bosonization, that this model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi surface, i.e., a "spinon metal." These results may provide a rare insight into the development of Mott criticality in strongly interacting two-dimensional materials and represent one of the first numerical demonstrations of a Mott insulating quantum spin liquid phase in a genuinely electronic microscopic model.
High-density two-dimensional small polaron gas in a delta-doped Mott insulator.
Ouellette, Daniel G; Moetakef, Pouya; Cain, Tyler A; Zhang, Jack Y; Stemmer, Susanne; Emin, David; Allen, S James
2013-11-21
Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)(+1) plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 10(14) cm(-2).
High-density Two-Dimensional Small Polaron Gas in a Delta-Doped Mott Insulator
Ouellette, Daniel G.; Moetakef, Pouya; Cain, Tyler A.; Zhang, Jack Y.; Stemmer, Susanne; Emin, David; Allen, S. James
2013-01-01
Heterointerfaces in complex oxide systems open new arenas in which to test models of strongly correlated material, explore the role of dimensionality in metal-insulator-transitions (MITs) and small polaron formation. Close to the quantum critical point Mott MITs depend on band filling controlled by random disordered substitutional doping. Delta-doped Mott insulators are potentially free of random disorder and introduce a new arena in which to explore the effect of electron correlations and dimensionality. Epitaxial films of the prototypical Mott insulator GdTiO3 are delta-doped by substituting a single (GdO)+1 plane with a monolayer of charge neutral SrO to produce a two-dimensional system with high planar doping density. Unlike metallic SrTiO3 quantum wells in GdTiO3 the single SrO delta-doped layer exhibits thermally activated DC and optical conductivity that agree in a quantitative manner with predictions of small polaron transport but with an extremely high two-dimensional density of polarons, ~7 × 1014 cm−2. PMID:24257578
Unquenched eg1 orbital moment in the Mott-insulating antiferromagnet KOsO4
NASA Astrophysics Data System (ADS)
Song, Young-Joon; Ahn, Kyo-Hoon; Lee, Kwan-Woo; Pickett, Warren E.
2014-12-01
Applying the correlated electronic structure method based on density functional theory plus the Hubbard U interaction, we have investigated the tetragonal scheelite structure Mott insulator KOsO4, whose eg1 configuration should be affected only slightly by spin-orbit coupling (SOC). The method reproduces the observed antiferromagnetic Mott-insulating state, populating the Os dz2 majority orbital. The quarter-filled eg manifold is characterized by a symmetry breaking due to the tetragonal structure, and the Os ion shows a crystal field splitting Δcf=1.7 eV from the t2 g complex, which is relatively small considering the high formal oxidation state Os 7 +. The small magnetocrystalline anisotropy before including correlation (i.e., in the metallic state) is increased by more than an order of magnitude in the Mott-insulating state, a result of a strong interplay between large SOC and a strong correlation. In contrast to conventional wisdom that the eg complex will not support orbital magnetism, we find that for the easy axis [100] direction the substantial Os orbital moment ML≈-0.2 μB compensates half of the Os spin moment MS=0.4 μB . The origin of the orbital moment is analyzed and understood in terms of additional spin-orbital lowering of symmetry, and beyond that due to structural distortion, for magnetization along [100]. Further interpretation is assisted by analysis of the spin density and the Wannier function with SOC included.
Ellen N. La Motte: the making of a nurse, writer, and activist.
Williams, Lea M
2015-01-01
This article examines the early career of Ellen N. La Motte (1873-1961) to trace how her training at the Johns Hopkins Training School for Nurses and years spent as a tuberculosis nurse in Baltimore shaped her perception of tuberculosis prevention and women's suffrage. Although studies of tuberculosis have frequently alluded to her work, no sustained biocritical discussion of her development as a nurse and scholar exists. Between 1902, when she graduated from nursing school, and 1914, the start of the Great War, La Motte published a textbook and dozens of articles in journals devoted to nursing and social reform and delivered many speeches at local, regional, and national meetings. In addition, as her reputation as an expert in the field of tuberculosis nursing grew, her advocacy for the vote for women increased, and she used her writing and speaking skills on behalf of the suffrage cause. This article assesses how the skills La Motte acquired during these years helped mold her into a successful and respected nurse, writer, and activist.
Jiang, Cheng-Wei; Ni, I-Chih; Tzeng, Shien-Der; Wu, Cen-Shawn; Kuo, Watson
2014-06-07
How the interparticle tunnelling affects the charge conduction of self-assembled gold nanoparticles is studied by three means: tuning the tunnel barrier width by different molecule modification and by substrate bending, and tuning the barrier height by high-dose electron beam exposure. All approaches indicate that the metal-Mott insulator transition is governed predominantly by the interparticle coupling strength, which can be quantified by the room temperature sheet resistance. The Hubbard gap, following the prediction of quantum fluctuation theory, reduces to zero rapidly as the sheet resistance decreases to the quantum resistance. At very low temperature, the fate of devices near the Mott transition depends on the strength of disorder. The charge conduction is from nearest-neighbour hopping to co-tunnelling between nanoparticles in Mott insulators whereas it is from variable-range hopping through charge puddles in Anderson insulators. When the two-dimensional nanoparticle network is under a unidirectional strain, the interparticle coupling becomes anisotropic so the average sheet resistance is required to describe the charge conduction.
Hidden Mott transition and large-U superconductivity in the two-dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Tocchio, Luca F.; Becca, Federico; Sorella, Sandro
2016-11-01
We consider the one-band Hubbard model on the square lattice by using variational and Green's function Monte Carlo methods, where the variational states contain Jastrow and backflow correlations on top of an uncorrelated wave function that includes BCS pairing and magnetic order. At half-filling, where the ground state is antiferromagnetically ordered for any value of the on-site interaction U , we can identify a hidden critical point UMott, above which a finite BCS pairing is stabilized in the wave function. The existence of this point is reminiscent of the Mott transition in the paramagnetic sector and determines a separation between a Slater insulator (at small values of U ), where magnetism induces a potential energy gain, and a Mott insulator (at large values of U ), where magnetic correlations drive a kinetic energy gain. Most importantly, the existence of UMott has crucial consequences when doping the system: We observe a tendency for phase separation into hole-rich and hole-poor regions only when doping the Slater insulator, while the system is uniform by doping the Mott insulator. Superconducting correlations are clearly observed above UMott, leading to the characteristic dome structure in doping. Furthermore, we show that the energy gain due to the presence of a finite BCS pairing above UMott shifts from the potential to the kinetic sector by increasing the value of the Coulomb repulsion.
Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2
Friedemann, S.; Chang, H.; Gamża, M. B.; ...
2016-05-12
One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate ofmore » the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. We find our results point at a large Fermi surface consistent with Luttinger's theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.« less
Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS2
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
Large Fermi Surface of Heavy Electrons at the Border of Mott Insulating State in NiS_{2}
Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.
2016-05-12
One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS_{2}. 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.
Theoretical description of photo-doping in Mott and charge-transfer insulators
NASA Astrophysics Data System (ADS)
Eckstein, Martin
2012-02-01
Many aspects of photo-excited insulator-to-metal transitions in Mott and charge-transfer systems are theoretically not well understood: How is the photo-doped state related to a chemically doped state? On what timescale do we expect the formation of quasiparticles? To describe the electronic dynamics of Mott insulators, we have used nonequilibrium dynamical mean-field theory (DMFT) in combination with Quantum Monte Carlo and various weak and strong-coupling [1] techniques. In the talk, I will briefly present the current status of this approach and of related cluster approaches for nonequilibrium. I will then discuss results for the photo-doping in the Hubbard model, and in a in a p-d model for charge-transfer insulators. When the onsite Coulomb repulsion U is much larger than the hopping, rapid thermalization of the pump-excited Mott insulator is inhibited by the energetic stabilization of doublon-hole pairs [2], and various types of non-thermal states can arise. Immediately after the excitation process, the system of doublons and holes is too hot to form quasiparticle states, but coupling to a heat-bath of phonons can drive the system into a metallic state with well developed doublon and hole bands. Close to the metal-insulator transition, on the other hand, when U is of the order as the hopping, doublons and holes rapidly thermalize due to the electron-electron interaction, which makes the system a bad metal rather than a Fermi liquid. [4pt] [1] M. Eckstein and Ph. Werner, Phys. Rev. B 82, 115115 (2010).[0pt] [2] M. Eckstein and Ph. Werner, Phys. Rev. B 84, 035122 (2011).
Phase boundary of the boson Mott insulator in a rotating optical lattice
Umucalilar, R. O.; Oktel, M. Oe.
2007-11-15
We consider the Bose-Hubbard model in a two-dimensional rotating optical lattice and investigate the consequences of the effective magnetic field created by rotation. Using a Gutzwiller-type variational wave function, we find an analytical expression for the Mott insulator (MI)-superfluid (SF) transition boundary in terms of the maximum eigenvalue of the Hofstadter butterfly. The dependence of phase boundary on the effective magnetic field is complex, reflecting the self-similar properties of the single particle energy spectrum. Finally, we argue that fractional quantum Hall phases exist close to the MI-SF transition boundaries, including MI states with particle densities greater than one.
Ferromagnetism in the Mott insulator Ba2NaOsO6
Erickson, A.S.; Misra, S.; Miller, G.J.; Harrison, W.A.; Kim, J.M.; Fisher, I.R.; /Stanford U., Appl. Phys. Dept. /Stanford U., Geballe Lab.
2010-01-15
Results are presented of single crystal structural, thermodynamic, and reflectivity measurements of the double-perovskite Ba{sub 2}NaOsO{sub 6}. These characterize the material as a 5d1 ferromagnetic Mott insulator with an ordered moment of {approx} 0.2 {micro}B per formula unit and T{sub C} = 6.8(3) K. The magnetic entropy associated with this phase transition is close to Rln2, indicating that the quartet groundstate anticipated from consideration of the crystal structure is split, consistent with a scenario in which the ferromagnetism is associated with orbital ordering.
Invariance principle for Mott variable range hopping and other walks on point processes
NASA Astrophysics Data System (ADS)
Caputo, P.; Faggionato, A.; Prescott, T.
2013-08-01
We consider a random walk on a homogeneous Poisson point process with energy marks. The jump rates decay exponentially in the A-power of the jump length and depend on the energy marks via a Boltzmann--like factor. The case A=1 corresponds to the phonon-induced Mott variable range hopping in disordered solids in the regime of strong Anderson localization. We prove that for almost every realization of the marked process, the diffusively rescaled random walk, with arbitrary start point, converges to a Brownian motion whose diffusion matrix is positive definite, and independent of the environment. Finally, we extend the above result to other point processes including diluted lattices.
Topological Bose-Mott insulators in a one-dimensional optical superlattice.
Zhu, Shi-Liang; Wang, Z-D; Chan, Y-H; Duan, L-M
2013-02-15
We study topological properties of the Bose-Hubbard model with repulsive interactions in a one-dimensional optical superlattice. We find that the Mott insulator states of the single-component (two-component) Bose-Hubbard model under fractional fillings are topological insulators characterized by a nonzero charge (or spin) Chern number with nontrivial edge states. For ultracold atomic experiments, we show that the topological Chern number can be detected through measuring the density profiles of the bosonic atoms in a harmonic trap.
Antiferromagnetic resonance in the Mott insulator fcc-Cs3C60.
Suzuki, Yuta; Shibasaki, Seiji; Kubozono, Yoshihiro; Kambe, Takashi
2013-09-11
The magnetic ground state of the fcc phase of the Mott insulator Cs3C60 was studied using a low-temperature electron spin resonance technique, and antiferromagnetic resonance (AFMR) below 1.57 K was directly observed at ambient pressure. The AFMR modes for the fcc phase of Cs3C60 were investigated using a conventional two-sublattice model with uniaxial anisotropy, and the spin-flop field was determined to be 4.7 kOe at 1.57 K. The static magnetic exchange interactions and anisotropy field for fcc-Cs3C60 were also estimated.
Okamoto, Satoshi
2013-01-01
The electronic properties of Mott insulators realized in (111) bilayers of perovskite transition-metal oxides are studied. The low-energy effective Hamiltonians for such Mott insulators are derived in the presence of a strong spin-orbit coupling. These models are characterized by the antiferromagnetic Heisenberg interaction and the anisotropic interaction whose form depends on the $d$ orbital occupancy. From exact diagonalization analyses on finite clusters, the ground state phase diagrams are derived, including a Kitaev spin liquid phase in a narrow parameter regime for $t_{2g}$ systems. Slave-boson mean-field analyses indicate the possibility of novel superconducting states induced by carrier doping into the Mott-insulating parent systems, suggesting the present model systems as unique playgrounds for studying correlation-induced novel phenomena. Possible experimental realizations are also discussed.
Electric-field-induced metal maintained by current of the Mott insulator Ca2RuO4
Nakamura, Fumihiko; Sakaki, Mariko; Yamanaka, Yuya; Tamaru, Sho; Suzuki, Takashi; Maeno, Yoshiteru
2013-01-01
Recently, “application of electric field (E-field)” has received considerable attention as a new method to induce novel quantum phenomena since application of E-field can tune the electronic states directly with obvious scientific and industrial advantages over other turning methods. However, E-field-induced Mott transitions are rare and typically require high E-field and low temperature. Here we report that the multiband Mott insulator Ca2RuO4 shows unique insulator-metal switching induced by applying a dry-battery level voltage at room temperature. The threshold field Eth ~40 V/cm is much weaker than the Mott gap energy. Moreover, the switching is accompanied by a bulk structural transition. Perhaps the most peculiar of the present findings is that the induced metal can be maintained to low temperature by a weak current. PMID:23985626
Nomura, Yusuke; Sakai, Shiro; Capone, Massimo; Arita, Ryotaro
2015-08-01
Alkali-doped fullerides A 3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures T c's calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A 3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high T c s-wave superconductivity.
Gate-Tuned Mott Transition in Dilute InAs/GaSb Quantum Wells
NASA Astrophysics Data System (ADS)
Du, Lingjie; Lou, Wenkai; Chang, Kai; Sullivan, Gerard; Du, Rui-Rui
We investigate the origin of the bulk gap in inverted InAs/GaSb quantum wells (QWs) that host spatially-separated electrons and holes using charge-neutral point (CNP) density (n_o~p_o) in gated devices as a tuning parameter. We find two distinct gap regimes: for I), n_o >>5×1010/cm2, a soft gap opens predominately by hybridization, which closes under B// >~10T; for II), approaching the dilute limit n_o~5×1010/cm2, a hard gap opens leading to a true bulk insulator with quantized helical edges, continuously for B// up to 35T. Our results confirm that hard gap is associated with the Quantum Spin Hall (QSH) effect but cannot be explained by single-particle band theory. Instead it originates from many-body correlations. The data are remarkably consistent with a Mott insulator bulk state in the dilute InAs/GaSb bilayers. Specifically, spontaneous exciton binding is a viable mechanism for driving the Mott transition. Our results point to the importance of charge interactions in properties of QSHE in InAs/GaSb, in addition to single-particle band theories. The work in Rice was supported by DOE (measurements) and NSF (materials).
Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations
Eckstein, Martin; Werner, Philipp
2016-01-01
Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid. PMID:26883536
A continuous Mott transition between a metal and a quantum spin liquid
NASA Astrophysics Data System (ADS)
Mishmash, Ryan V.; Gonzalez, Ivan; Melko, Roger G.; Motrunich, Olexei I.; Fisher, Matthew P. A.
2015-03-01
More than half a century after first being proposed by Sir Nevill Mott, the deceptively simple question of whether the interaction-driven electronic metal-insulator transition may be continuous remains enigmatic. Recent experiments on two-dimensional materials suggest that when the insulator is a quantum spin liquid, lack of magnetic long-range order on the insulating side may cause the transition to be continuous, or only very weakly first order. Motivated by this, we study a half-filled extended Hubbard model on a triangular lattice strip geometry. We argue, through use of large-scale numerical simulations and analytical bosonization, that this model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi sea, i.e., a ``spin Bose metal''. These results may provide a rare insight into the development of Mott criticality in strongly interacting two-dimensional materials and elucidate a mechanism by which spin-liquid phases are stabilized in the vicinity of such transitions.
Dimensional crossover and cold-atom realization of topological Mott insulators
Scheurer, Mathias S.; Rachel, Stephan; Orth, Peter P.
2015-01-01
Interacting cold-atomic gases in optical lattices offer an experimental approach to outstanding problems of many body physics. One important example is the interplay of interaction and topology which promises to generate a variety of exotic phases such as the fractionalized Chern insulator or the topological Mott insulator. Both theoretically understanding these states of matter and finding suitable systems that host them have proven to be challenging problems. Here we propose a cold-atom setup where Hubbard on-site interactions give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of an interacting and topological quantum state with fractionalized spinon excitations that inherit the topology of the non-interacting system. Our proposal shall help to pave the way for a controlled experimental investigation of this exotic state of matter in optical lattices. Furthermore, it allows for the investigation of a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers. PMID:25669431
Tuning a strain-induced orbital selective Mott transition in epitaxial VO2
NASA Astrophysics Data System (ADS)
Mukherjee, Shantanu; Quackenbush, N. F.; Paik, H.; Schlueter, C.; Lee, T.-L.; Schlom, D. G.; Piper, L. F. J.; Lee, Wei-Cheng
2016-06-01
We present evidence of strain-induced modulation of electron correlation effects and increased orbital anisotropy in the rutile phase of epitaxial VO2/TiO2 films from hard x-ray photoelectron spectroscopy and soft V L-edge x-ray absorption spectroscopy, respectively. By using the U(1) slave spin formalism, we further argue that the observed anisotropic correlation effects can be understood by a model of orbital selective Mott transition at a filling that is noninteger but close to the half filling. Because the overlaps of wave functions between d orbitals are modified by the strain, orbital-dependent renormalizations of the bandwidths and the onsite energy occur. These renormalizations generally result in different occupation numbers in different orbitals. We find that if the system has a noninteger filling number near the half filling such as for VO2, certain orbitals could reach an occupation number closer to half filling under the strain, resulting in a strong reduction in the quasiparticle weight Zα of that orbital. Our work demonstrates that such an orbital selective Mott transition, defined as the case with Zα=0 in some but not all orbitals, could be accessed by epitaxial-strain engineering of correlated electron systems.
Nomura, Yusuke; Sakai, Shiro; Capone, Massimo; Arita, Ryotaro
2015-01-01
Alkali-doped fullerides A3C60 (A = K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of volume per C60 molecule. We address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably, our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. More remarkably, the critical temperatures Tc’s calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A3C60 is a subtle competition between Hund’s coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund’s coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high Tc s-wave superconductivity. PMID:26601242
NASA Astrophysics Data System (ADS)
Yoshida, Tsuneya; Kawakami, Norio
2016-08-01
We study a bilayer Kane-Mele-Hubbard model with lattice distortion and interlayer spin exchange interaction under cylinder geometry. Our analysis based on real-space dynamical mean field theory with continuous-time quantum Monte Carlo demonstrates the emergence of a topological edge Mott insulating (TEMI) state which hosts gapless edge modes only in collective spin excitations. This is confirmed by the numerical calculations at finite temperatures for the spin-Hall conductivity and the single-particle excitation spectrum; the spin-Hall conductivity is almost quantized, σspinx y˜2 (e /2 π ) , predicting gapless edge modes carrying the spin current, while the helical edge modes in the single-particle spectrum are gapped out with respecting symmetry. It is clarified how the TEMI state evolves from the ordinary spin-Hall insulating state with increasing the Hubbard interaction at a given temperature and then undergoes a phase transition to a trivial Mott insulating state. With a bosonization approach at zero temperature, we further address which collective modes host gapless edge modes in the TEMI state.
Ultra-fast photo-carrier relaxation in Mott insulators with short-range spin correlations
NASA Astrophysics Data System (ADS)
Eckstein, Martin; Werner, Philipp
2016-02-01
Ultra-fast spectroscopy can reveal the interplay of charges with low energy degrees of freedom, which underlies the rich physics of correlated materials. As a potential glue for superconductivity, spin fluctuations in Mott insulators are of particular interest. A theoretical description of the coupled spin and charge degrees of freedom is challenging, because magnetic order is often only short-lived and short-ranged. In this work we theoretically investigate how the spin-charge interactions influence the relaxation of a two-dimensional Mott-Hubbard insulator after photo-excitation. We use a nonequilibrium variant of the dynamical cluster approximation, which, in contrast to single-site dynamical mean-field theory, captures the effect of short-range correlations. The relaxation time is found to scale with the strength of the nearest-neighbor spin correlations, and can be 10–20 fs in the cuprates. Increasing the temperature or excitation density decreases the spin correlations and thus implies longer relaxation times. This may help to distinguish the effect of spin-fluctuations on the charge relaxation from the influence of other bosonic modes in the solid.
NASA Astrophysics Data System (ADS)
Adibi, Elaheh; Jafari, S. Akbar
2016-02-01
Phase transitions in the Hubbard model and ionic Hubbard model at half-filling on the honeycomb lattice are investigated in the strong-coupling perturbation theory which corresponds to an expansion in powers of the hopping t around the atomic limit. Within this formulation we find analytic expressions for the single-particle spectrum, whereby the calculation of the insulating gap is reduced to a simple root finding problem. This enables high-precision determination of the insulating gap that does not require any extrapolation procedure. The critical value of Mott transition on the honeycomb lattice is obtained to be Uc≈2.38 t . Studying the ionic Hubbard model at the lowest order, we find two insulating states, one with Mott character at large U and another with single-particle gap character at large ionic potential Δ . The present approach gives a critical gapless state at U =2 Δ at lowest order. By systematically improving on the perturbation expansion, the density of states around this critical gapless phase reduces.
NASA Astrophysics Data System (ADS)
Barkeshli, Maissam; McGreevy, John
2012-08-01
One of the most successful theories of a non-Fermi-liquid metallic state is the composite Fermi-liquid (CFL) theory of the half-filled Landau level. In this paper, we study continuous quantum phase transitions out of the CFL state and into a Landau Fermi liquid, in the limit of no disorder and fixed particle number. This transition can be induced by tuning the bandwidth of the Landau level relative to the interaction energy, for instance through an externally applied periodic potential. We find a transition to the Landau Fermi liquid through a gapless Mott insulator with a Fermi surface of neutral fermionic excitations. In the presence of spatial symmetries, we also find a direct continuous transition between the CFL and the Landau Fermi liquid. The transitions have a number of characteristic observable signatures, including the presence of two crossover temperature scales, resistivity jumps, and vanishing compressibility. When the composite fermions are paired instead, our results imply quantum critical points between various non-Abelian topological states, including the ν=1/2 Moore-Read Pfaffian [Ising × U(1) topological order], a version of the Kitaev B phase (Ising topological order), and paired electronic superconductors. To study such transitions, we use a projective construction of the CFL, which goes beyond the conventional framework of flux attachment to include a broader set of quantum fluctuations. These considerations suggest a possible route to fractionalized Mott insulators by starting with fractional quantum Hall states and tuning the Landau-level bandwidth.
Dimensional crossover and cold-atom realization of topological Mott insulators.
Scheurer, Mathias S; Rachel, Stephan; Orth, Peter P
2015-02-11
Interacting cold-atomic gases in optical lattices offer an experimental approach to outstanding problems of many body physics. One important example is the interplay of interaction and topology which promises to generate a variety of exotic phases such as the fractionalized Chern insulator or the topological Mott insulator. Both theoretically understanding these states of matter and finding suitable systems that host them have proven to be challenging problems. Here we propose a cold-atom setup where Hubbard on-site interactions give rise to spin liquid-like phases: weak and strong topological Mott insulators. They represent the celebrated paradigm of an interacting and topological quantum state with fractionalized spinon excitations that inherit the topology of the non-interacting system. Our proposal shall help to pave the way for a controlled experimental investigation of this exotic state of matter in optical lattices. Furthermore, it allows for the investigation of a dimensional crossover from a two-dimensional quantum spin Hall insulating phase to a three-dimensional strong topological insulator by tuning the hopping between the layers.
Maximally--localized Wannier Functions in Mott Insulators: the Case of MnO.
NASA Astrophysics Data System (ADS)
Posternak, M.; Baldereschi, A.; Marzari, N.
2000-03-01
Wannier functions can be considered a generalization of ``localized molecular orbitals'' to the case of extended systems. As such, they allow for a clear description of chemical bonds, and provide a convenient basis to study correlation effects. The localization algorithm of Marzari and Vanderbilt(N. Marzari and D. Vanderbilt, Phys. Rev. B 56) 12847 (1997). is combined here with the all--electron FLAPW method, and then applied to the case of antiferromagnetic MnO, a half--filled d shell Mott insulator. Two different one-electron schemes have been explored: local spin density (LSD), and LSD+U. In the latter case, the screened on--site Coulomb interaction U is explicitly included. The observed mixed charge--transfer/Mott--Hubbard character of MnO, as well as the mechanism of superexchange, are discussed in terms of the calculated Wannier functions, which display O 2p/Mn 3d bonding character. The centers of these Wannier functions are either on the Mn sites, or close to the O sites. Finally, their individual contributions to the Born effective charges are also presented.
Breakdown of Hooke’s law of elasticity at the Mott critical endpoint in an organic conductor
Gati, Elena; Garst, Markus; Manna, Rudra S.; Tutsch, Ulrich; Wolf, Bernd; Bartosch, Lorenz; Schubert, Harald; Sasaki, Takahiko; Schlueter, John A.; Lang, Michael
2016-01-01
The Mott metal-insulator transition, a paradigm of strong electron-electron correlations, has been considered as a source of intriguing phenomena. Despite its importance for a wide range of materials, fundamental aspects of the transition, such as its universal properties, are still under debate. We report detailed measurements of relative length changes ΔL/L as a function of continuously controlled helium-gas pressure P for the organic conductor κ-(BEDT-TTF)2Cu[N(CN)2]Cl across the pressure-induced Mott transition. We observe strongly nonlinear variations of ΔL/L with pressure around the Mott critical endpoint, highlighting a breakdown of Hooke’s law of elasticity. We assign these nonlinear strain-stress relations to an intimate, nonperturbative coupling of the critical electronic system to the lattice degrees of freedom. Our results are fully consistent with mean-field criticality, predicted for electrons in a compressible lattice with finite shear moduli. We argue that the Mott transition for all systems that are amenable to pressure tuning shows the universal properties of an isostructural solid-solid transition. PMID:27957540
Nanoscale orbital excitations and the infrared spectrum of a molecular Mott insulator: A15-Cs3C60.
Naghavi, S S; Fabrizio, M; Qin, T; Tosatti, E
2016-10-14
The quantum physics of ions and electrons behind low-energy spectra of strongly correlated molecular conductors, superconductors and Mott insulators is poorly known, yet fascinating especially in orbitally degenerate cases. The fulleride insulator Cs3C60 (A15), one such system, exhibits infrared (IR) spectra with low temperature peak features and splittings suggestive of static Jahn-Teller distortions with a breakdown of orbital symmetry in the molecular site. That is puzzling, since there is no detectable static distortion, and because the features and splittings disappear upon modest heating, which they should not. Taking advantage of the Mott-induced collapse of electronic wavefunctions from lattice-extended to nanoscale localized inside a caged molecular site, we show that the unbroken spin and orbital symmetry of the ion multiplets explains the IR spectrum without adjustable parameters. This demonstrates the importance of a fully quantum treatment of nuclear positions and orbital momenta in the Mott insulator sites, dynamically but not statically distorted. The observed demise of these features with temperature is explained by the thermal population of a multiplet term whose nuclear positions are essentially undistorted, but whose energy is very low-lying. That term is in fact a scaled-down orbital excitation analogous to that of other Mott insulators, with the same spin 1/2 as the ground state, but with a larger orbital momentum of two instead of one.
NASA Astrophysics Data System (ADS)
Yilin, Wang; Li, Huang; Liang, Du; Xi, Dai
2016-03-01
We have studied the doping-driven orbital-selective Mott transition in multi-band Hubbard models with equal band width in the presence of crystal field splitting. Crystal field splitting lifts one of the bands while leaving the others degenerate. We use single-site dynamical mean-field theory combined with continuous time quantum Monte Carlo impurity solver to calculate a phase diagram as a function of total electron filling N and crystal field splitting Δ. We find a large region of orbital-selective Mott phase in the phase diagram when the doping is large enough. Further analysis indicates that the large region of orbital-selective Mott phase is driven and stabilized by doping. Such models may account for the orbital-selective Mott transition in some doped realistic strongly correlated materials. Project supported by the National Natural Science Foundation of China (Grant No. 2011CBA00108) and the National Basic Research Program of China (Grant No. 2013CB921700).
NASA Astrophysics Data System (ADS)
Bodek, K.; Kępka, D.; Rozpędzik, D.; Zejma, J.; Kozela, A.
2017-04-01
A self-calibrating double-Mott polarimeter is proposed for measurement of the spin correlation function of relativistic electron pairs produced in Møller scattering. The polarization of outgoing electrons (appearing when the beam is polarized) is utilized for calibration of effective analyzing powers in the secondary Mott scattering used for spin analysis. The experiment will measure the newly introduced relative spin correlation function. This new observable can be measured with a significantly better accuracy than the regular spin correlation function in a small scale experiment. It is shown that both the spin correlation function and the relative spin correlation function are theoretically equivalent. A specific experimental data analysis scenario is proposed, which effectively eliminates the systematic effects related to the imperfect geometry and detector efficiency.
NASA Astrophysics Data System (ADS)
Wilson, Stephen
2014-03-01
An unusual manifestation of Mott physics dependent on strong spin-orbit interactions has recently been identified in a growing number of classes of 5d transition metal oxides built from Ir4+ ions. Instead of the naively expected increased itinerancy of these iridates due to the larger orbital extent of their 5d valence electrons, the interplay between the amplified relativistic spin-orbit interaction (intrinsic to large Z iridium cations) and their residual on-site Coulomb interaction U, conspires to stabilize a novel class of spin-orbit assisted Mott insulators with a proposed Jeff = 1/2 ground state wavefunction. The identification of this novel spin-orbit Mott state has been the focus of recent interest due to its potential of hosting a variety of new phases driven by correlated electron phenomena (such as high temperature superconductivity or enhanced ferroic behavior) in a strongly spin-orbit coupled setting. Currently, however, there remains very little understanding of how spin-orbit Mott phases respond to carrier doping and, more specifically, how relevant U remains for the charge carriers of a spin-orbit Mott phase once the bandwidth is increased. Here I will present our group's recent experimental work exploring carrier doping and the resulting electronic phase behavior in one such spin-orbit driven Mott material, Sr3Ir2O7, with the ultimate goal of determining the relevance of U and electron correlation effects within the doped system's ground state. Our results reveal the stabilization of an electronically phase separated ground state in B-site doped Sr3Ir2O7, suggestive of an extended regime of localization of in-plane doped carriers within the spin-orbit Mott phase. This results in a percolative metal-to-insulator transition with a novel, global, antiferromagnetic order. The electronic response of B-site doping in Sr3Ir2O7will then be compared with recent results exploring A-site doping if time permits. Supported by NSF CAREER Award DMR-1056625.
NASA Astrophysics Data System (ADS)
Ronning, F.
2002-03-01
One of the most remarkable facts about the high temperature superconductors is their close proximity to an antiferromagnetically ordered Mott insulating phase. This fact suggests that to understand superconductivity in the cuprates we must first understand the insulating regime. Due to material properties the technique of angle resolved photoemission is ideally suited to study the electronic structure in the cuprates. Thus, a natural starting place to unlocking the secrets of high Tc would appears to be with a photoemission investigation of insulating cuprates. This dissertation presents the results of precisely such a study. In particular, we have focused on the compound Ca2-xNaxCuO2Cl2. With increasing Na content this system goes from an antiferromagnetic Mott insulator with a Neel transition of 256K to a superconductor with an optimal transition temperature of 28K. At half filling we have found an asymmetry in the integrated spectral weight, which can be related to the occupation probability, n(k). This has led us to identify a d-wave-like dispersion in the insulator, which in turn implies that the high energy pseudogap as seen by photoemission is a remnant property of the insulator. These results are robust features of the insulator which we found in many different compounds and experimental conditions. By adding Na we were able to study the evolution of the electronic structure across the insulator to metal transition. We found that the chemical potential shifts as holes are doped into the system. This picture is in sharp contrast to the case of La2-xSrxCuO4 where the chemical potential remains fixed and states are created inside the gap. Furthermore, the low energy excitations (ie the Fermi surface) in metallic Ca1.9Na0.1CuO2Cl2 is most well described as a Fermi arc, although the high binding energy features reveal the presence of shadow bands. Thus, the results in this dissertation provide a new avenue for understanding the evolution of the Mott insulator to
NASA Astrophysics Data System (ADS)
Shen, Kyle Michael
The parent compounds of the high-temperature cuprate superconductors are antiferromagnetic Mott insulators. To explain the microscopic mechanism behind high-temperature superconductivity, it is first necessary to understand how the electronic states evolve from the parent Mott insulator into the superconducting compounds. This dissertation presents angle-resolved photoemission spectroscopy (ARPES) studies of one particular family of the cuprate superconductors, Ca 2-xNaxCuO 2Cl2, to investigate how the single-electron excitations develop throughout momentum space as the system is hole doped from the Mott insulator into a superconductor with a transition temperature of 22 K. These measurements indicate that, due to very strong electron-boson interactions, the quasiparticle residue, Z, approaches zero in the parent Mott insulator due to the formation of small lattice polarons. As a result, many fundamental quantities such as the chemical potential, quasiparticle excitations, and the Fermi surface evolve in manners wholly unexpected from conventional weakly-interacting theories. In addition, highly anisotropic interactions have been observed in momentum space where quasiparticle-like excitations persist to low doping levels along the nodal direction of the d-wave super-conducting gap, in contrast to the unusual excitations near the d-wave antinode. This anisotropy may reflect the propensity of the lightly doped cuprates towards forming a competing, charge-ordered state. These results provide a novel and logically consistent explanation of the hole doping evolution of the lineshape, spectral weight, chemical potential, quasiparticle dispersion, and Fermi surface as Ca2- xNaxCuO2Cl2 evolves from the parent Mott insulator into a high-temperature superconductor.
Spin-orbit coupling and electronic charge effects in Mott insulators
Zhu, Shan; Li, You -Quan; Batista, Cristian D.
2014-11-04
We derive the effective charge- and current-density operators for the strong-coupling limit of a single-band Mott insulator in the presence of spin-orbit coupling and show that the spin-orbit contribution to the effective charge density leads to novel mechanisms for multiferroic behavior. In some sense, these mechanisms are the electronic counterpart of the ionic-based mechanisms, which have been proposed for explaining the electric polarization induced by spiral spin orderings. In addition, the new electronic mechanisms are illustrated by considering cycloidal and proper-screw magnetic orderings on sawtooth and kagome lattices. As for the isotropic case, geometric frustration is crucial for achieving thismore » purely electronic coupling between spin and charge degrees of freedom.« less
Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid.
Hickey, Ciarán; Cincio, Lukasz; Papić, Zlatko; Paramekanti, Arun
2016-04-01
Motivated by cold atom experiments on Chern insulators, we study the honeycomb lattice Haldane-Hubbard Mott insulator of spin-1/2 fermions using exact diagonalization and density matrix renormalization group methods. We show that this model exhibits various chiral magnetic orders including a wide regime of triple-Q tetrahedral order. Incorporating third-neighbor hopping frustrates and ultimately melts this tetrahedral spin crystal. From analyzing the low energy spectrum, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid (CSL) with gapped semion excitations. We formulate and study the Chern-Simons-Higgs field theory of the exotic CSL-to-tetrahedral spin crystallization transition.
Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates
Markiewicz, R. S.; Buda, I. G.; Mistark, P.; Lane, C.; Bansil, A.
2017-01-01
We propose a new approach to understand the origin of the pseudogap in the cuprates, in terms of bosonic entropy. The near-simultaneous softening of a large number of different q-bosons yields an extended range of short-range order, wherein the growth of magnetic correlations with decreasing temperature T is anomalously slow. These entropic effects cause the spectral weight associated with the Van Hove singularity (VHS) to shift rapidly and nearly linearly toward half filling at higher T, consistent with a picture of the VHS driving the pseudogap transition at a temperature ~T*. As a byproduct, we develop an order-parameter classification scheme that predicts supertransitions between families of order parameters. As one example, we find that by tuning the hopping parameters, it is possible to drive the cuprates across a transition between Mott and Slater physics, where a spin-frustrated state emerges at the crossover. PMID:28327627
Frenkel-like Wannier-Mott excitons in few-layer Pb I2
NASA Astrophysics Data System (ADS)
Toulouse, Alexis S.; Isaacoff, Benjamin P.; Shi, Guangsha; Matuchová, Marie; Kioupakis, Emmanouil; Merlin, Roberto
2015-04-01
Optical measurements and first-principles calculations of the band structure and exciton states in direct-gap bulk and few-layer Pb I2 indicate that the n =1 exciton is Frenkel-like in nature in that its energy exhibits a weak dependence on thickness down to atomic-length scales. Results reveal large increases in the gap and exciton binding energy with a decreasing number of layers and a transition of the fundamental gap, which becomes indirect for one and two monolayers. Calculated values are in reasonable agreement with a particle-in-a-box model relying on the Wannier-Mott theory of exciton formation. General arguments and existing data suggest that the Frenkel-like character of the lowest exciton is a universal feature of wide-gap layered semiconductors whose effective masses and dielectric constants give bulk Bohr radii that are on the order of the layer spacing.
Spin Andreev-like Reflection in Metal-Mott Insulator Heterostructures
Al-Hassanieh, K. A.; Rincón, Julián; Alvarez, G.; Dagotto, E.
2015-02-09
Here we used the time-dependent density-matrix renormalization group (tDMRG) to study the time evolution of electron wave packets in one-dimensional (1D) metal-superconductor heterostructures. The results show Andreev reflection at the interface, as expected. By combining these results with the well-known single- spin-species electron-hole transformation in the Hubbard model, we predict an analogous spin Andreev reflection in metal-Mott insulator heterostructures. This effect is numerically confirmed using 1D tDMRG, but it is expected to also be present in higher dimensions, as well as in more general Hamiltonians. We present an intuitive picture of the spin reflection, analogous to that of Andreev reflection at metal- superconductor interfaces. This allows us to discuss a novel antiferromagnetic proximity effect. Possible experimental realizations are discussed.
Spin-orbit coupling and electronic charge effects in Mott insulators
Zhu, Shan; Li, You -Quan; Batista, Cristian D.
2014-11-04
We derive the effective charge- and current-density operators for the strong-coupling limit of a single-band Mott insulator in the presence of spin-orbit coupling and show that the spin-orbit contribution to the effective charge density leads to novel mechanisms for multiferroic behavior. In some sense, these mechanisms are the electronic counterpart of the ionic-based mechanisms, which have been proposed for explaining the electric polarization induced by spiral spin orderings. In addition, the new electronic mechanisms are illustrated by considering cycloidal and proper-screw magnetic orderings on sawtooth and kagome lattices. As for the isotropic case, geometric frustration is crucial for achieving this purely electronic coupling between spin and charge degrees of freedom.
Pressure induced metallization of the Mott Insulator VI{sub 2}
Sterer, E.; Pasternak, M.P.; Taylor, R.D.
1993-07-20
Using diamond anvil cells, {sup 129}I Moessbauer spectroscopy (MS) and resistivity measurements were carried out in the layered antiferromagnet VI{sub 2} at 0-45 GPa and 4-300 K. MS to 15 GPa revealed an impressive increase in Neel temperature and a slight increase in transferred hyperfine field. Pressure behavior of R(P,T), in particular near the metal-insulator pressure P{sub c}=44 GPa, is described. Being the lightest transition metal (TM) in the isostructural (TM)I{sub 2} series, the V{sup 2+} (d{sup 3} configuration) represents a typical candidate for a pure Mott-Hubbard gap closure. Results are compared with the heavy TM diiodides such as NiI{sub 2} and CoI{sub 2}, where it is expected that the charge transfer regime prevails. 3 figs, 10 refs.
Surface Effects on the Mott-Hubbard Transition in Archetypal V{2}O{3}.
Lantz, G; Hajlaoui, M; Papalazarou, E; Jacques, V L R; Mazzotti, A; Marsi, M; Lupi, S; Amati, M; Gregoratti, L; Si, L; Zhong, Z; Held, K
2015-12-04
We present an experimental and theoretical study exploring surface effects on the evolution of the metal-insulator transition in the model Mott-Hubbard compound Cr-doped V{2}O{3}. We find a microscopic domain formation that is clearly affected by the surface crystallographic orientation. Using scanning photoelectron microscopy and x-ray diffraction, we find that surface defects act as nucleation centers for the formation of domains at the temperature-induced isostructural transition and favor the formation of microscopic metallic regions. A density-functional theory plus dynamical mean-field theory study of different surface terminations shows that the surface reconstruction with excess vanadyl cations leads to doped, and hence more metallic, surface states, which explains our experimental observations.
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-01-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions. PMID:27185665
NASA Astrophysics Data System (ADS)
Guterding, Daniel; Jeschke, Harald O.; Valentí, Roser
2016-05-01
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
NASA Astrophysics Data System (ADS)
Nataf, Pierre; Lajkó, Miklós; Wietek, Alexander; Penc, Karlo; Mila, Frédéric; Läuchli, Andreas M.
2016-10-01
We show that, in the presence of a π /2 artificial gauge field per plaquette, Mott insulating phases of ultracold fermions with SU (N ) symmetry and one particle per site generically possess an extended chiral phase with intrinsic topological order characterized by an approximate ground space of N low-lying singlets for periodic boundary conditions, and by chiral edge states described by the SU(N ) 1 Wess-Zumino-Novikov-Witten conformal field theory for open boundary conditions. This has been achieved by extensive exact diagonalizations for N between 3 and 9, and by a parton construction based on a set of N Gutzwiller projected fermionic wave functions with flux π /N per triangular plaquette. Experimental implications are briefly discussed.
External pumping of hybrid nanostructures in microcavity with Frenkel and Wannier-Mott excitons
NASA Astrophysics Data System (ADS)
Dubovskiy, O. A.; Agranovich, V. M.
2016-09-01
The exciton-exciton interaction in hybrid nanostructures with resonating Frenkel and Wannier-Mott excitons was investigated in many publications. In microcavity the hybrid nanostructures can be exposed to different types of optical pumping, the most common one being pumping through one of the microcavity side. However, not investigated and thus never been discussed the hybrid excitons generation by pumping of confined quantum wells from the side of empty microcavity without nanostructures in a wave guided configuration. Here, we consider the hybrid excitations in cavity with organic and inorganic quantum wells and with different types of pumping from external source. The frequency dependence for intensity of excitations in hybrid structure is also investigated. The results may be used for search of most effective fluorescence and relaxation processes. The same approach may be used when both quantum wells are organic or inorganic.
Coexistence of Mott and superfluid domains of bosons confined in optical lattice
NASA Astrophysics Data System (ADS)
Khanore, Mukesh; Dey, Bishwajyoti
2015-06-01
We investigate ground state properties of the attractive Bose-gas confined on square optical lattice and superimposed wine-bottle-bottom or Mexican hat trap potential. The system is modeled by two-dimensional Bose-Hubbard model with attractive interactions and inhomogeneous lattice potential. We calculate the energy spectrum, the on-site number fluctuation, local density and local compressibility using numerical exact diagonalization method for incommensurate lattice filling. The trap potential has several degenerate minimum sites distributed along a ring at the wine-bottle-bottom. It is shown that beyond a certain value of the attractive interaction strength there is phase coherent condensate on these degenerate sites with finite value of the on-site number fluctuation and local compressibility giving rise to localized superfluidity or superfluidity on a ring. For the same value of the interaction strength the non-degenerate sites produces Mott region.
Observing quantum trajectories: From Mott's problem to quantum Zeno effect and back
NASA Astrophysics Data System (ADS)
de Gosson, Maurice; Hiley, Basil; Cohen, Eliahu
2016-11-01
The experimental results of Kocsis et al., Mahler et al. and the proposed experiments of Morley et al. show that it is possible to construct "trajectories" in interference regions in a two-slit interferometer. These results call for a theoretical re-appraisal of the notion of a "quantum trajectory" first introduced by Dirac and in the present paper we re-examine this notion from the Bohm perspective based on Hamiltonian flows. In particular, we examine the short-time propagator and the role that the quantum potential plays in determining the form of these trajectories. These trajectories differ from those produced in a typical particle tracker and the key to this difference lies in the active suppression of the quantum potential necessary to produce Mott-type trajectories. We show, using a rigorous mathematical argument, how the active suppression of this potential arises. Finally we discuss in detail how this suppression also accounts for the quantum Zeno effect.
Tuning the Mott transition in a Bose-Einstein condensate by multiple photon absorption.
Creffield, C E; Monteiro, T S
2006-06-02
We study the time-dependent dynamics of a Bose-Einstein condensate trapped in an optical lattice. Modeling the system as a Bose-Hubbard model, we show how applying a periodic driving field can induce coherent destruction of tunneling. In the low-frequency regime, we obtain the novel result that the destruction of tunneling displays extremely sharp peaks when the driving frequency is resonant with the depth of the trapping potential ("multi-photon resonances"), which allows the quantum phase transition between the Mott insulator and the superfluid state to be controlled with high precision. We further show how the waveform of the field can be chosen to maximize this effect.
Sweeping from the superfluid to the Mott phase in the Bose-Hubbard model.
Schützhold, Ralf; Uhlmann, Michael; Xu, Yan; Fischer, Uwe R
2006-11-17
We study the sweep through the quantum phase transition from the superfluid to the Mott state for the Bose-Hubbard model with a time-dependent tunneling rate J(t). In the experimentally relevant case of exponential decay J(t) proportional variant e -gamma t, an adapted mean-field expansion for large fillings n yields a scaling solution for the fluctuations. This enables us to analytically calculate the evolution of the number and phase variations (on-site) and correlations (off-site) for slow (gamma
Electrically tunable transport in the antiferromagnetic Mott insulator Sr2IrO4
NASA Astrophysics Data System (ADS)
Wang, C.; Seinige, H.; Cao, G.; Zhou, J.-S.; Goodenough, J. B.; Tsoi, M.
2015-09-01
Electronic transport properties of the antiferromagnetic Mott insulator S r2Ir O4 have been investigated under extremely high electric biases. Using nanoscale contacts, we apply electric fields up to a few MV/m to a single crystal of S r2Ir O4 and observe a continuous reduction in the material's resistivity with increasing bias, characterized by a reduction in the transport activation energy by as much as 16 % . Temperature-dependent resistivity measurements provide a means to unambiguously retrieve the bias dependence of the activation energy from the Arrhenius plots at different biases. We further demonstrate the feasibility of reversible resistive switching induced by the electric bias, which is of interest for the emerging field of antiferromagnetic spintronics. Our findings demonstrate the potential of electrical means for tuning electronic properties in 5 d transition-metal oxides and suggest a promising path towards development of next-generation functional devices.
Using nonequilibrium dynamics to probe competing orders in a Mott-Peierls system
Wang, Y.; Moritz, B.; Chen, C. -C.; ...
2016-02-24
Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here, we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe antiphase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which provides an approach for characterizing the underlying bosonic modes. The results from this analysis for different electronic momenta show an uneven softeningmore » due to a stronger coupling near kF. As a result, this behavior reflects the strong link between the fermionic momenta, the coupling vertices, and ultimately, the bosonic susceptibilities when multiple phases compete for the ground state of the system.« less
Using nonequilibrium dynamics to probe competing orders in a Mott-Peierls system
Wang, Y.; Moritz, B.; Chen, C. -C.; Jia, C. J.; van Veenendaal, M.; Devereaux, T. P.
2016-02-24
Competition between ordered phases, and their associated phase transitions, are significant in the study of strongly correlated systems. Here, we examine one aspect, the nonequilibrium dynamics of a photoexcited Mott-Peierls system, using an effective Peierls-Hubbard model and exact diagonalization. Near a transition where spin and charge become strongly intertwined, we observe antiphase dynamics and a coupling-strength-dependent suppression or enhancement in the static structure factors. The renormalized bosonic excitations coupled to a particular photoexcited electron can be extracted, which provides an approach for characterizing the underlying bosonic modes. The results from this analysis for different electronic momenta show an uneven softening due to a stronger coupling near k_{F}. As a result, this behavior reflects the strong link between the fermionic momenta, the coupling vertices, and ultimately, the bosonic susceptibilities when multiple phases compete for the ground state of the system.
Mott Electrons in an Artificial Graphenelike Crystal of Rare-Earth Nickelate S.
Middey, Srimanta; Meyers, Derek J.; Doennig, D.; Kareev, M; Liu, Xiaoran; Cao, Yanwei; Yang, Zhenzhong; Shi, Jinan; Gu, Lin; Ryan, Philip J.; Freeland, J. W.; Pentcheva, R.; Chakhalian, J.
2016-02-05
Deterministic control over the periodic geometrical arrangement of the constituent atoms is the backbone of the material properties, which, along with the interactions, define the electronic and magnetic ground state. Following this notion, a bilayer of a prototypical rare-earth nickelate, NdNiO3, combined with a dielectric spacer, LaAlO3, has been layered along the pseudocubic [111] direction. The resulting artificial graphenelike Mott crystal with magnetic 3d electrons has antiferromagnetic correlations. In addition, a combination of resonant X-ray linear dichroism measurements and ab initio calculations reveal the presence of an ordered orbital pattern, which is unattainable in either bulk nickelates or nickelate based heterostructures grown along the [001] direction. These findings highlight another promising venue towards designing new quantum many-body states by virtue of geometrical engineering.
Low energy Mott polarimetry of electrons from negative electron affinity photocathodes
Ciccacci, F.; De Rossi, S.; Campbell, D.M.
1995-08-01
We present data on the spin polarization {ital P} and quantum yield {ital Y} of electrons photoemitted from negative electron affinity semiconductors, including GaAs(100), GaAsP(100) alloy, and strained GaAs layer epitaxially grown on a GaAsP(100) buffer. Near photothreshold the following values for {ital P}({ital Y}) are, respectively, obtained: 26% (2.5{times}10{sup {minus}2}), 40% (1{times}10{sup {minus}3}), and 60% (1.5{times}10{sup {minus}4}). We describe in detail the apparatus used containing a low energy (10--25 keV) Mott polarimeter. The system, completely fitted in a small volume ({similar_to}10{sup 4} cm{sup 3}) ultrahigh vacuum chamber, is intended as a test facility for characterizing candidate photocathode materials for spin polarized electron sources. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Spin Andreev-like Reflection in Metal-Mott Insulator Heterostructures
Al-Hassanieh, K. A.; Rincón, Julián; Alvarez, G.; ...
2015-02-09
Here we used the time-dependent density-matrix renormalization group (tDMRG) to study the time evolution of electron wave packets in one-dimensional (1D) metal-superconductor heterostructures. The results show Andreev reflection at the interface, as expected. By combining these results with the well-known single- spin-species electron-hole transformation in the Hubbard model, we predict an analogous spin Andreev reflection in metal-Mott insulator heterostructures. This effect is numerically confirmed using 1D tDMRG, but it is expected to also be present in higher dimensions, as well as in more general Hamiltonians. We present an intuitive picture of the spin reflection, analogous to that of Andreev reflectionmore » at metal- superconductor interfaces. This allows us to discuss a novel antiferromagnetic proximity effect. Possible experimental realizations are discussed.« less
Chiral spin liquid and emergent anyons in a Kagome lattice Mott insulator.
Bauer, B; Cincio, L; Keller, B P; Dolfi, M; Vidal, G; Trebst, S; Ludwig, A W W
2014-10-10
Topological phases in frustrated quantum spin systems have fascinated researchers for decades. One of the earliest proposals for such a phase was the chiral spin liquid, a bosonic analogue of the fractional quantum Hall effect, put forward by Kalmeyer and Laughlin in 1987. Elusive for many years, recent times have finally seen this phase realized in various models, which, however, remain somewhat artificial. Here we take an important step towards the goal of finding a chiral spin liquid in nature by examining a physically motivated model for a Mott insulator on the Kagome lattice with broken time-reversal symmetry. We discuss the emergent phase from a network model perspective and present an unambiguous numerical identification and characterization of its universal topological properties, including ground-state degeneracy, edge physics and anyonic bulk excitations, by using a variety of powerful numerical probes, including the entanglement spectrum and modular transformations.
Guterding, Daniel; Jeschke, Harald O; Valentí, Roser
2016-05-17
Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.
Mott Electrons in an Artificial Graphenelike Crystal of Rare-Earth Nickelate.
Middey, S; Meyers, D; Doennig, D; Kareev, M; Liu, X; Cao, Y; Yang, Zhenzhong; Shi, Jinan; Gu, Lin; Ryan, P J; Pentcheva, R; Freeland, J W; Chakhalian, J
2016-02-05
Deterministic control over the periodic geometrical arrangement of the constituent atoms is the backbone of the material properties, which, along with the interactions, define the electronic and magnetic ground state. Following this notion, a bilayer of a prototypical rare-earth nickelate, NdNiO_{3}, combined with a dielectric spacer, LaAlO_{3}, has been layered along the pseudocubic [111] direction. The resulting artificial graphenelike Mott crystal with magnetic 3d electrons has antiferromagnetic correlations. In addition, a combination of resonant X-ray linear dichroism measurements and ab initio calculations reveal the presence of an ordered orbital pattern, which is unattainable in either bulk nickelates or nickelate based heterostructures grown along the [001] direction. These findings highlight another promising venue towards designing new quantum many-body states by virtue of geometrical engineering.
Mott metal-insulator transition in a metallic liquid - Gutzwiller molecular dynamics simulations
NASA Astrophysics Data System (ADS)
Barros, Kipton; Chern, Gia-Wei; Batista, Cristian D.; Kress, Joel D.; Kotliar, Gabriel
2015-03-01
Molecular dynamics (MD) simulations are crucial to modern computational physics, chemistry, and materials science, especially when combined with potentials derived from density-functional theory. However, even in state of the art MD codes, the on-site Coulomb repulsion is only treated at the self-consistent Hartree-Fock level. This standard approximation may miss important effects due to electron correlations. The Gutzwiller variational method captures essential correlated-electron physics yet is much faster than, e.g., the dynamical-mean field theory approach. We present our efficient Gutzwiller-MD implementation. With it, we investigate the Mott metal-insulator transition in a metallic fluid and uncover several surprising static and dynamic properties of this system.
Superfluid to Mott insulator transition of hardcore bosons in a superlattice
Hen, Itay; Rigol, Marcos
2009-10-01
We study the superfluid to Mott-insulator transition of hardcore bosons in commensurate superlattices in two and three dimensions. We focus on the special case where the superlattice has period two and the system is at half-filling. We obtain numerical results by using the stochastic series expansion algorithm, and compute various properties of the system, such as the ground-state energy, the density of bosons in the zero-momentum mode, the superfluid density, and the compressibility. We employ finite-size scaling to extrapolate the thermodynamic limit, and find the critical points of the phase transition. We also explore the extent to which several approximate solutions such as mean-field theory, with and without spin-wave corrections, can help one gain analytical insight into the behavior of the system in the vicinity of the phase transition.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics.
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a 'conventional', itinerant QCP can be well understood within Landau's paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an 'unconventional', local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
T-shaped GaAs quantum-wire lasers and the exciton Mott transition.
Yoshita, M; Liu, S M; Okano, M; Hayamizu, Y; Akiyama, H; Pfeiffer, L N; West, K W
2007-07-25
T-shaped GaAs quantum-wire (T-wire) lasers fabricated by the cleaved-edge overgrowth method with molecular beam epitaxy on the interface improved by a growth-interrupt high-temperature anneal are measured to study the laser device physics and fundamental many-body physics in clean one-dimensional (1D) systems. A current-injection T-wire laser that has 20 periods of T-wires in the active region and a 0.5 mm long cavity with high-reflection coatings shows a low threshold current of 0.27 mA at 30 K. The origin of the laser gain above the lasing threshold is studied with the high-quality T-wire lasers by means of optical pumping. The lasing energy is about 5 meV below the photoluminescence (PL) peak of free excitons, and is on the electron-hole (e-h) plasma PL band at a high e-h carrier density. The observed energy shift excludes the laser gain due to free excitons, and it suggests a contribution from the e-h plasma instead. A systematic micro-PL study reveals that the PL evolves with the e-h density from a sharp exciton peak, via a biexciton peak, to an e-h-plasma PL band. The data demonstrate an important role of biexcitons in the exciton Mott transition. Comparison with microscopic theories points out some problems in the picture of the exciton Mott transition.
Foundations of heavy-fermion superconductivity: lattice Kondo effect and Mott physics
NASA Astrophysics Data System (ADS)
Steglich, Frank; Wirth, Steffen
2016-08-01
This article overviews the development of heavy-fermion superconductivity, notably in such rare-earth-based intermetallic compounds which behave as Kondo-lattice systems. Heavy-fermion superconductivity is of unconventional nature in the sense that it is not mediated by electron-phonon coupling. Rather, in most cases the attractive interaction between charge carriers is apparently magnetic in origin. Fluctuations associated with an antiferromagnetic (AF) quantum critical point (QCP) play a major role. The first heavy-fermion superconductor CeCu2Si2 turned out to be the prototype of a larger group of materials for which the underlying, often pressure-induced, AF QCP is likely to be of a three-dimensional (3D) spin-density-wave (SDW) variety. For UBe13, the second heavy-fermion superconductor, a magnetic-field-induced 3D SDW QCP inside the superconducting phase can be conjectured. Such a ‘conventional’, itinerant QCP can be well understood within Landau’s paradigm of order-parameter fluctuations. In contrast, the low-temperature normal-state properties of a few heavy-fermion superconductors are at odds with the Landau framework. They are characterized by an ‘unconventional’, local QCP which may be considered a zero-temperature 4 f-orbital selective Mott transition. Here, as concluded for YbRh2Si2, the breakdown of the Kondo effect concurring with the AF instability gives rise to an abrupt change of the Fermi surface. Very recently, superconductivity was discovered for this compound at ultra-low temperatures. Therefore, YbRh2Si2 along with CeRhIn5 under pressure provide a natural link between the large group of about fifty low-temperature heavy-fermion superconductors and other families of unconventional superconductors with substantially higher T c, e.g. the doped Mott insulators of the perovskite-type cuprates and the organic charge-transfer salts.
NASA Astrophysics Data System (ADS)
Alloul, H.; Ihara, Y.; Mito, T.; Wzietek, P.; Aramini, M.; Pontiroli, D.; Ricco, M.
2013-07-01
The discovery in 1991 of high temperature superconductivity (SC) in A3C60 compounds, where A is an alkali ion, has been initially ascribed to a BCS mechanism, with a weak incidence of electron correlations. However various experimental evidences taken for compounds with distinct alkali content established the interplay of strong correlations and Jahn Teller distortions of the C60 ball. The importance of electronic correlations even in A3C60 has been highlighted by the recent discovery of two expanded fulleride Cs3C60 isomeric phases that are Mott insulators at ambient pressure. Both phases undergo a pressure induced first order Mott transition to SC with a (p, T) phase diagram displaying a dome shaped SC, a common situation encountered nowadays in correlated electron systems. NMR experiments allowed us to establish that the bipartite A15 phase displays Néel order at 47K, while magnetic freezing only occurs at lower temperature in the fcc phase. NMR data do permit us to conclude that well above the critical pressure, the singlet superconductivity found for light alkalis is recovered. However deviations from BCS expectations linked with electronic correlations are found near the Mott transition. So, although SC involves an electron-phonon mechanism, correlations have a significant incidence on the electronic properties, as had been anticipated from DMFT calculations.
A metallic mosaic phase and the origin of Mott-insulating state in 1T-TaS2
Ma, Liguo; Ye, Cun; Yu, Yijun; Lu, Xiu Fang; Niu, Xiaohai; Kim, Sejoong; Feng, Donglai; Tománek, David; Son, Young-Woo; Chen, Xian Hui; Zhang, Yuanbo
2016-01-01
Electron–electron and electron–phonon interactions are two major driving forces that stabilize various charge-ordered phases of matter. In layered compound 1T-TaS2, the intricate interplay between the two generates a Mott-insulating ground state with a peculiar charge-density-wave (CDW) order. The delicate balance also makes it possible to use external perturbations to create and manipulate novel phases in this material. Here, we study a mosaic CDW phase induced by voltage pulses, and find that the new phase exhibits electronic structures entirely different from that of the original Mott ground state. The mosaic phase consists of nanometre-sized domains characterized by well-defined phase shifts of the CDW order parameter in the topmost layer, and by altered stacking relative to the layers underneath. We discover that the nature of the new phase is dictated by the stacking order, and our results shed fresh light on the origin of the Mott phase in 1T-TaS2. PMID:26961788
NASA Astrophysics Data System (ADS)
Xie, Hong-Yi; Foster, Matthew S.
2016-05-01
We study the electric and thermal transport of the Dirac carriers in monolayer graphene using the Boltzmann-equation approach. Motivated by recent thermopower measurements [F. Ghahari, H.-Y. Xie, T. Taniguchi, K. Watanabe, M. S. Foster, and P. Kim, Phys. Rev. Lett. 116, 136802 (2016), 10.1103/PhysRevLett.116.136802], we consider the effects of quenched disorder, Coulomb interactions, and electron-optical-phonon scattering. Via an unbiased numerical solution to the Boltzmann equation we calculate the electrical conductivity, thermopower, and electronic component of the thermal conductivity, and discuss the validity of Mott's formula and of the Wiedemann-Franz law. An analytical solution for the disorder-only case shows that screened Coulomb impurity scattering, although elastic, violates the Wiedemann-Franz law even at low temperature. For the combination of carrier-carrier Coulomb and short-ranged impurity scattering, we observe the crossover from the interaction-limited (hydrodynamic) regime to the disorder-limited (Fermi-liquid) regime. In the former, the thermopower and the thermal conductivity follow the results anticipated by the relativistic hydrodynamic theory. On the other hand, we find that optical phonons become non-negligible at relatively low temperatures and that the induced electron thermopower violates Mott's formula. Combining all of these scattering mechanisms, we obtain the thermopower that quantitatively coincides with the experimental data.
Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material.
Lantz, G; Mansart, B; Grieger, D; Boschetto, D; Nilforoushan, N; Papalazarou, E; Moisan, N; Perfetti, L; Jacques, V L R; Le Bolloc'h, D; Laulhé, C; Ravy, S; Rueff, J-P; Glover, T E; Hertlein, M P; Hussain, Z; Song, S; Chollet, M; Fabrizio, M; Marsi, M
2017-01-09
The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott-Hubbard material V2O3 presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a1g orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A1g coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron-lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems.
Ultrafast evolution and transient phases of a prototype out-of-equilibrium Mott-Hubbard material
NASA Astrophysics Data System (ADS)
Lantz, G.; Mansart, B.; Grieger, D.; Boschetto, D.; Nilforoushan, N.; Papalazarou, E.; Moisan, N.; Perfetti, L.; Jacques, V. L. R.; Le Bolloc'h, D.; Laulhé, C.; Ravy, S.; Rueff, J.-P.; Glover, T. E.; Hertlein, M. P.; Hussain, Z.; Song, S.; Chollet, M.; Fabrizio, M.; Marsi, M.
2017-01-01
The study of photoexcited strongly correlated materials is attracting growing interest since their rich phase diagram often translates into an equally rich out-of-equilibrium behaviour. With femtosecond optical pulses, electronic and lattice degrees of freedom can be transiently decoupled, giving the opportunity of stabilizing new states inaccessible by quasi-adiabatic pathways. Here we show that the prototype Mott-Hubbard material V2O3 presents a transient non-thermal phase developing immediately after ultrafast photoexcitation and lasting few picoseconds. For both the insulating and the metallic phase, the formation of the transient configuration is triggered by the excitation of electrons into the bonding a1g orbital, and is then stabilized by a lattice distortion characterized by a hardening of the A1g coherent phonon, in stark contrast with the softening observed upon heating. Our results show the importance of selective electron-lattice interplay for the ultrafast control of material parameters, and are relevant for the optical manipulation of strongly correlated systems.
On the possibility of many-body localization in a doped Mott insulator
NASA Astrophysics Data System (ADS)
He, Rong-Qiang; Weng, Zheng-Yu
2016-10-01
Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a pure many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel ‘Berry phase’ of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized.
Mott transition in CaFe2O4 at around 50 GPa
NASA Astrophysics Data System (ADS)
Greenberg, Eran; Rozenberg, Gregory Kh.; Xu, Weiming; Pasternak, Moshe P.; McCammon, Catherine; Glazyrin, Konstantin; Dubrovinsky, Leonid S.
2013-12-01
Electrical transport and magnetic properties of CaFe2O4 have been studied at pressures up to 70 GPa using Fe57 Mössbauer spectroscopy (MS), Raman spectroscopy, and electrical resistance measurements. These studies have shown the onset of the Mott transition (MT) at a pressure of around 50 GPa, leading to the collapse of Fe3+ magnetic moments and to the insulator-metal (IM) transition. The observed onset of the MT corroborates with the recently reported isostructural transition accompanied by a 12% decrease in the Fe polyhedral volume. An analysis of the alterations of the electrical transport, magnetic, and structural properties with pressure increase and at the transition range suggests that the coinciding IM transition, magnetic moment, and volume collapse at around 50 GPa are caused by the closure of the Hubbard gap driven by the high-spin to low-spin (HS-LS) transition. At that, since MS did not reveal any evidence of a preceding LS state, it could be inferred that the HS-LS transition immediately leads to an IM transition and complete collapse of magnetism.
Deng, Xiuhao; Jia, Chunjing; Chien, Chih-Chun
2015-02-23
We report that the Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many-body physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photonlike. Standardmore » perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Lastly, experimental realizations and other possible applications of this simulator are also discussed.« less
NASA Astrophysics Data System (ADS)
Li, S.; Kaushal, N.; Wang, Y.; Tang, Y.; Alvarez, G.; Nocera, A.; Maier, T. A.; Dagotto, E.; Johnston, S.
2016-12-01
We study nonlocal correlations in a three-orbital Hubbard model defined on an extended one-dimensional chain using determinant quantum Monte Carlo and density matrix renormalization group methods. We focus on a parameter regime with robust Hund's coupling, which produces an orbital selective Mott phase (OSMP) at intermediate values of the Hubbard U , as well as an orbitally ordered ferromagnetic insulating state at stronger coupling. An examination of the orbital- and spin-correlation functions indicates that the orbital ordering occurs before the onset of magnetic correlations in this parameter regime as a function of temperature. In the OSMP, we find that the self-energy for the itinerant electrons is momentum dependent, indicating a degree of nonlocal correlations while the localized electrons have largely momentum independent self-energies. These nonlocal correlations also produce relative shifts of the holelike and electronlike bands within our model. The overall momentum dependence of these quantities is strongly suppressed in the orbitally ordered insulating phase.
Bosonic analogs of the fractional quantum Hall state in the vicinity of Mott states
NASA Astrophysics Data System (ADS)
Kuno, Yoshihito; Shimizu, Keita; Ichinose, Ikuo
2017-01-01
In this paper, the Bose-Hubbard model (BHM) with the nearest-neighbor (NN) repulsions is studied from the viewpoint of possible bosonic analogs of the fractional quantum Hall (FQH) state in the vicinity of the Mott insulator (MI). First, by means of the Gutzwiller approximation, we obtain the phase diagram of the BHM in a magnetic field. Then, we introduce an effective Hamiltonian describing excess particles on a MI and calculate the vortex density, momentum distribution, and the energy gap. These calculations indicate that the vortex solid forms for small NN repulsions, but a homogeneous featureless "Bose metal" takes the place of it as the NN repulsion increases. We consider particular filling factors at which the bosonic FQH state is expected to form. Chern-Simons (CS) gauge theory to the excess particle is introduced, and a modified Gutzwiller wave function, which describes bosons with attached flux quanta, is introduced. The energy of the excess particles in the bosonic FQH state is calculated using that wave function, and it is compared with the energy of the vortex solid and Bose metal. We found that the energy of the bosonic FQH state is lower than that of the Bose metal and comparable with the vortex solid. Finally, we clarify the condition that the composite fermion appears by using CS theory on the lattice that we previously proposed for studying the electron FQH effect.
Reliability of the one-crossing approximation in describing the Mott transition.
Vildosola, V; Pourovskii, L V; Manuel, L O; Roura-Bas, P
2015-12-09
We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.
Reliability of the one-crossing approximation in describing the Mott transition
NASA Astrophysics Data System (ADS)
Vildosola, V.; Pourovskii, L. V.; Manuel, L. O.; Roura-Bas, P.
2015-12-01
We assess the reliability of the one-crossing approximation (OCA) approach in a quantitative description of the Mott transition in the framework of the dynamical mean field theory (DMFT). The OCA approach has been applied in conjunction with DMFT to a number of heavy-fermion, actinide, transition metal compounds and nanoscale systems. However, several recent studies in the framework of impurity models pointed out serious deficiencies of OCA and raised questions regarding its reliability. Here we consider a single band Hubbard model on the Bethe lattice at finite temperatures and compare the results of OCA to those of a numerically exact quantum Monte Carlo (QMC) method. The temperature-local repulsion U phase diagram for the particle-hole symmetric case obtained by OCA is in good agreement with that of QMC, with the metal-insulator transition captured very well. We find, however, that the insulator to metal transition is shifted to higher values of U and, simultaneously, correlations in the metallic phase are significantly overestimated. This counter-intuitive behaviour is due to simultaneous underestimations of the Kondo scale in the metallic phase and the size of the insulating gap. We trace the underestimation of the insulating gap to that of the second moment of the high-frequency expansion of the impurity spectral density. Calculations of the system away from the particle-hole symmetric case are also presented and discussed.
Infinite single-particle bandwidth of a Mott-Hubbard insulator
NASA Astrophysics Data System (ADS)
Freericks, J. K.; Cohn, J. R.; van Dongen, P. G. J.; Krishnamurthy, H. R.
2016-03-01
The conventional viewpoint of the strongly correlated electron metal-insulator transition is that a single band splits into two upper and lower Hubbard bands at the transition. Much work has investigated whether this transition is continuous or discontinuous. Here we focus on another aspect and ask the question of whether there are additional upper and lower Hubbard bands, which stretch all the way out to infinity — leading to an infinite single-particle bandwidth (or spectral range) for the Mott insulator. While we are not able to provide a rigorous proof of this result, we use exact diagonalization studies on small clusters to motivate the existence of these additional bands, and we discuss some different methods that might be utilized to provide such a proof. Even though the extra upper and lower Hubbard bands have very low total spectral weight, those states are expected to have extremely long lifetimes, leading to a nontrivial contribution to the transport density of states for dc transport and modifying the high temperature limit for the electrical resistivity.
Design of Chern and Mott insulators in buckled 3 d oxide honeycomb lattices
NASA Astrophysics Data System (ADS)
Doennig, David; Baidya, Santu; Pickett, Warren E.; Pentcheva, Rossitza
2016-04-01
Perovskite (La X O3 )2/(LaAlO3)4(111) superlattices with X spanning the entire 3 d transition-metal series combine the strongly correlated, multiorbital nature of electrons in transition-metal oxides with a honeycomb lattice as a key feature. Based on density functional theory calculations including strong interaction effects, we establish trends in the evolution of electronic states as a function of several control parameters: band filling, interaction strength, spin-orbit coupling (SOC), and lattice instabilities. Competition between local pseudocubic and global trigonal symmetry as well as the additional flexibility provided by the magnetic and spin degrees of freedom of 3 d ions lead to a broad array of distinctive broken-symmetry ground states not accessible for the (001)-growth direction, offering a platform to design two-dimensional electronic functionalities. Constraining the symmetry between the two triangular sublattices causes X =Mn , Co, and Ti to emerge as Chern insulators driven by SOC. For X =Mn we illustrate how interaction strength and lattice distortions can tune these systems between a Dirac semimetal, a Chern and a trivial Mott insulator.
On the possibility of many-body localization in a doped Mott insulator
He, Rong-Qiang; Weng, Zheng-Yu
2016-01-01
Many-body localization (MBL) is currently a hot issue of interacting systems, in which quantum mechanics overcomes thermalization of statistical mechanics. Like Anderson localization of non-interacting electrons, disorders are usually crucial in engineering the quantum interference in MBL. For translation invariant systems, however, the breakdown of eigenstate thermalization hypothesis due to a pure many-body quantum effect is still unclear. Here we demonstrate a possible MBL phenomenon without disorder, which emerges in a lightly doped Hubbard model with very strong interaction. By means of density matrix renormalization group numerical calculation on a two-leg ladder, we show that whereas a single hole can induce a very heavy Nagaoka polaron, two or more holes will form bound pair/droplets which are all localized excitations with flat bands at low energy densities. Consequently, MBL eigenstates of finite energy density can be constructed as composed of these localized droplets spatially separated. We further identify the underlying mechanism for this MBL as due to a novel ‘Berry phase’ of the doped Mott insulator, and show that by turning off this Berry phase either by increasing the anisotropy of the model or by hand, an eigenstate transition from the MBL to a conventional quasiparticle phase can be realized. PMID:27752064
NASA Astrophysics Data System (ADS)
Schäfer, T.; Ciuchi, S.; Wallerberger, M.; Thunström, P.; Gunnarsson, O.; Sangiovanni, G.; Rohringer, G.; Toschi, A.
2016-12-01
We analyze the highly nonperturbative regime surrounding the Mott-Hubbard metal-to-insulator transition (MIT) by means of dynamical mean field theory (DMFT) calculations at the two-particle level. By extending the results of Schäfer et al. [Phys. Rev. Lett. 110, 246405 (2013), 10.1103/PhysRevLett.110.246405] we show the existence of infinitely many lines in the phase diagram of the Hubbard model where the local Bethe-Salpeter equations, and the related irreducible vertex functions, become singular in the charge as well as the particle-particle channel. By comparing our numerical data for the Hubbard model with analytical calculations for exactly solvable systems of increasing complexity [disordered binary mixture (BM), Falicov-Kimball (FK), and atomic limit (AL)], we have (i) identified two different kinds of divergence lines; (ii) classified them in terms of the frequency structure of the associated singular eigenvectors; and (iii) investigated their relation to the emergence of multiple branches in the Luttinger-Ward functional. In this way, we could distinguish the situations where the multiple divergences simply reflect the emergence of an underlying, single energy scale ν* below which perturbation theory is no longer applicable, from those where the breakdown of perturbation theory affects, not trivially, different energy regimes. Finally, we discuss the implications of our results on the theoretical understanding of the nonperturbative physics around the MIT and for future developments of many-body algorithms applicable in this regime.
Deng, Xiuhao; Jia, Chunjing; Chien, Chih-Chun
2015-02-23
We report that the Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many-body physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photonlike. Standard perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Lastly, experimental realizations and other possible applications of this simulator are also discussed.
The 'Higgs' amplitude mode at the two-dimensional superfluid/Mott insulator transition.
Endres, Manuel; Fukuhara, Takeshi; Pekker, David; Cheneau, Marc; Schauss, Peter; Gross, Christian; Demler, Eugene; Kuhr, Stefan; Bloch, Immanuel
2012-07-25
Spontaneous symmetry breaking plays a key role in our understanding of nature. In relativistic quantum field theory, a broken continuous symmetry leads to the emergence of two types of fundamental excitation: massless Nambu-Goldstone modes and a massive 'Higgs' amplitude mode. An excitation of Higgs type is of crucial importance in the standard model of elementary particle physics, and also appears as a fundamental collective mode in quantum many-body systems. Whether such a mode exists in low-dimensional systems as a resonance-like feature, or whether it becomes overdamped through coupling to Nambu-Goldstone modes, has been a subject of debate. Here we experimentally find and study a Higgs mode in a two-dimensional neutral superfluid close to a quantum phase transition to a Mott insulating phase. We unambiguously identify the mode by observing the expected reduction in frequency of the onset of spectral response when approaching the transition point. In this regime, our system is described by an effective relativistic field theory with a two-component quantum field, which constitutes a minimal model for spontaneous breaking of a continuous symmetry. Additionally, all microscopic parameters of our system are known from first principles and the resolution of our measurement allows us to detect excited states of the many-body system at the level of individual quasiparticles. This allows for an in-depth study of Higgs excitations that also addresses the consequences of the reduced dimensionality and confinement of the system. Our work constitutes a step towards exploring emergent relativistic models with ultracold atomic gases.
Monte Carlo simulation of 1-10-keV electron scattering in an aluminum target
NASA Astrophysics Data System (ADS)
Kotera, Masatoshi; Murata, Kenji; Nagami, Koichi
1981-12-01
New Monte Carlo simulations of electron scattering based on the single scattering model have been performed in the low-energy region for an aluminum target, where two basic equations are required, namely the elastic scattering cross section and the energy-loss rate. We investigated the screened Rutherford equation and the Mott equation for two different atomic potentials for the former, and the Rao Sahib-Wittry equation (the modified Bethe equation) for the latter. The validity of each model is discussed in a comparison between Monte Carlo results and experimental results such as the electron range, electron backscattering, and electron transmission which have been reported by various authors. Consequently, it was found that a combination of the Mott cross section and the Rao Sahib-Wittry equation showed the best accuracy. However, the accuracy of a previous model with the screened Rutherford equation is not as bad as aniticipated because of the higher accuracy of the Born approximation for light elements such as Al, compared to Au.
NASA Astrophysics Data System (ADS)
Hartmann, Benedikt; Müller, Jens; Sasaki, Takahiko
2014-11-01
We utilize a glasslike structural transition in order to induce a Mott metal-insulator transition in the quasi-two-dimensional organic charge-transfer salt κ -(BEDT-TTF)2Cu [N (CN)2Br ]. In this material, the terminal ethylene groups of the BEDT-TTF molecules can adopt two different structural orientations within the crystal structure, namely eclipsed (E) and staggered (S) with the relative orientation of the outer C-C bonds being parallel and canted, respectively. These two conformations are thermally disordered at room temperature and undergo a glasslike ordering transition at Tg˜75 K. When cooling through Tg, a small fraction that depends on the cooling rate remains frozen in the S configuration, which is of slightly higher energy, corresponding to a controllable degree of structural disorder. We demonstrate that, when thermally coupled to a low-temperature heat bath, a pulsed heating current through the sample causes a very fast relaxation with cooling rates at Tg of the order of several 1000 K /min . The freezing of the structural degrees of freedom causes a decrease of the electronic bandwidth W with increasing cooling rate, and hence a Mott metal-insulator transition as the system crosses the critical ratio (W/U ) c of bandwidth to on-site Coulomb repulsion U . Due to the glassy character of the transition, the effect is persistent below Tg and can be reversibly repeated by melting the frozen configuration upon warming above Tg. Both by exploiting the characteristics of slowly changing relaxation times close to this temperature and by controlling the heating power, the materials can be fine-tuned across the Mott transition. A simple model allows for an estimate of the energy difference between the E and S state as well as the accompanying degree of frozen disorder in the population of the two orientations.
Fitting of m*/m with Divergence Curve for He3 Fluid Monolayer using Hole-driven Mott Transition
NASA Astrophysics Data System (ADS)
Kim, Hyun-Tak
2012-02-01
The electron-electron interaction for strongly correlated systems plays an important role in formation of an energy gap in solid. The breakdown of the energy gap is called the Mott metal-insulator transition (MIT) which is different from the Peierls MIT induced by breakdown of electron-phonon interaction generated by change of a periodic lattice. It has been known that the correlated systems are inhomogeneous. In particular, He3 fluid monolayer [1] and La1-xSrxTiO3 [2] are representative strongly correlated systems. Their doping dependence of the effective mass of carrier in metal, m*/m, indicating the magnitude of correlation (Coulomb interaction) between electrons has a divergence behavior. However, the fitting remains unfitted to be explained by a Mott-transition theory with divergence. In the case of He3 regarded as the Fermi system with one positive charge (2 electrons + 3 protons), the interaction between He3 atoms is regarded as the correlation in strongly correlated system. In this presentation, we introduce a Hole-driven MIT with a divergence near the Mott transition [3] and fit the m*/m curve in He3 [1] and La1-xSrxTiO3 systems with the Hole-driven MIT with m*/m=1/(1-ρ^4) where ρ is band filling. Moreover, it is shown that the physical meaning of the effective mass with the divergence is percolation in which m*/m increases with increasing doping concentration, and that the magnitude of m*/m is constant.[4pt] [1] Phys. Rev. Lett. 90, 115301 (2003).[0pt] [2] Phys. Rev. Lett. 70, 2126 (1993).[0pt] [3] Physica C 341-348, 259 (2000); Physica C 460-462, 1076 (2007).
Collective excitation of an electric dipole on a molecular dimer in an organic dimer-Mott insulator.
Itoh, K; Itoh, H; Naka, M; Saito, S; Hosako, I; Yoneyama, N; Ishihara, S; Sasaki, T; Iwai, S
2013-03-08
The terahertz response in 10-100 cm(-1) was investigated in an organic dimer-Mott (DM) insulator κ-(ET)(2)Cu(2)(CN)(3) that exhibits a relaxorlike dielectric anomaly. An ~30 cm(-1) band in the optical conductivity was attributable to collective excitation of the fluctuating intradimer electric dipoles that are formed by an electron correlation. We succeeded in observing photoinduced enhancement of this ~30 cm(-1) band, reflecting the growth of the electric dipole cluster in the DM phase. Such optical responses in κ-(ET)(2)Cu(2)(CN)(3) reflect an instability near the boundary between the DM-ferroelectric charge ordered phases.
Pressure-induced metallization and structural phase transition of the Mott-Hubbard insulator TiOBr
NASA Astrophysics Data System (ADS)
Kuntscher, C. A.; Frank, S.; Pashkin, A.; Hoffmann, H.; Schönleber, A.; van Smaalen, S.; Hanfland, M.; Glawion, S.; Klemm, M.; Sing, M.; Horn, S.; Claessen, R.
2007-12-01
We investigated the pressure-dependent optical response of the low-dimensional Mott-Hubbard insulator TiOBr by transmittance and reflectance measurements in the infrared and visible frequency range. A suppression of the transmittance above a critical pressure and a concomitant increase of the reflectance are observed, suggesting a pressure-induced metallization of TiOBr. The metallic phase of TiOBr at high pressure is confirmed by the presence of additional excitations extending down to the far-infrared range. The pressure-induced metallization coincides with a structural phase transition, according to the results of x-ray powder diffraction experiments under pressure.
NASA Astrophysics Data System (ADS)
Li, Zhaoguo; Peng, Liping; Zhang, Jicheng; Li, Jia; Zeng, Yong; Luo, Yuechuan; Zhan, Zhiqiang; Meng, Lingbiao; Zhou, Minjie; Wu, Weidong
2017-03-01
We report on the electrical transport properties of polycrystalline germanium thin films which are grown by the DC magnetron sputtering method. The temperature dependent resistance of seven devices are measured from 290 K down to 10 K. The thermal excitation model dominating the transport properties at the high temperature regime (above ∼60 K) is demonstrated and the low temperature electron transport is governed by the variable-range hopping (VRH) mechanism. Moreover, we observed a transition from Efros–Shklovskii to Mott VRH at ∼25 K over the entire VRH conduction regime, which is well described by a universal scaling law.
Study of Low Energy Electron Inelastic Scattering Mechanisms Using Spin Sensitive Techniques
NASA Astrophysics Data System (ADS)
Hsu, Hongbing
1995-01-01
Spin sensitive electron spectroscopies were used to study low energy electron inelastic scattering from metal surfaces and thin films. In these experiments, a beam of spin polarized electrons from a GaAs source is directed on the sample surface, and the spin polarization and intensity are measured as a function of energy loss and scattering angle by a Mott electron polarimeter coupled with a concentric hemispherical energy analyzer. Systematic studies of the angular dependence of inelastically scattered electrons were conducted on a Cu(100) surface, and Mo/Cu(100), non-magnetized Fe/Cu(100), and Co/Cu(100) films. The polarization and intensity of scattered electrons were measured as function of energy loss and scattering angle. Further studies were also conducted on Ag(100) surface and amorphous Cu/Ag(100) films. From the experimental results, the angular distributions of dipole and impact scattered electrons can be determined individually and both are found to peak in the specular scattering direction. Preliminary studies were conducted on magnetized Co/Cu(100) films. The spin dependent scattering intensity asymmetry was measured, with a clearly observable peak at energy loss of ~1 eV, which coincides with the band splitting. The polarizations of secondary electrons produced by an unpolarized primary beam were also measured. The polarizations can be related to the band polarization of magnetized cobalt films.
Polymorphism control of superconductivity and magnetism in Cs(3)C(60) close to the Mott transition.
Ganin, Alexey Y; Takabayashi, Yasuhiro; Jeglic, Peter; Arcon, Denis; Potocnik, Anton; Baker, Peter J; Ohishi, Yasuo; McDonald, Martin T; Tzirakis, Manolis D; McLennan, Alec; Darling, George R; Takata, Masaki; Rosseinsky, Matthew J; Prassides, Kosmas
2010-07-08
The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition
Liu, Guangkun; Kaushal, Nitin; Liu, Shaozhi; ...
2016-06-24
A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)]. In this paper we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. In addition, we study a simplified version of themore » model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. Lastly, we conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations.« less
NASA Astrophysics Data System (ADS)
Zhang, Qi; Gao, Weilu; Watson, John; Manfra, Michael; Kono, Junichiro
2015-03-01
Density-dependent Coulomb interactions can drive electron-hole (e - h) pairs in semiconductors through an excitonic Mott transition from an excitonic gas into an e - h plasma. Theoretical studies suggest that these interactions can be strongly modified by an external magnetic field, including the absence of inter-exciton interactions in the high magnetic field limit in two dimensions, due to an e - h charge symmetry, which results in ultrastable magneto-excitons. Here, we present a systematic experimental study of e - h pairs in photo-excited undoped GaAs quantum wells in magnetic fields with ultrafast terahertz spectroscopy. We simultaneously monitored the dynamics of the intraexcitonic 1 s-2 p transition (which splits into 1 s-2p+ and 1 s-2p- transitions in a magnetic field) and the cyclotron resonance of unbound electrons and holes up to 10 Tesla. We found that the 1 s-2p- absorption feature is robust at high magnetic fields even under high excitation fluences, indicating magnetically enhanced stability of excitons. We will discuss the Mott physics of magneto-excitons as a function of temperature, e - h pair density, optical pump delay time, as well as magnetic field, and also compare two-dimensional excitons in GaAs quantum wells with three-dimensional excitons in bulk GaAs.
NASA Astrophysics Data System (ADS)
Foster, Matthew; Yuzbashyan, Emil
2010-03-01
Rapid progress in cold atom experiments has motivated the study of non-equilibrium many-body dynamics following a sudden deformation of the system Hamiltonian (a ``quantum quench''). Here, we consider the dynamics of localized excitations produced via a quench across a quantum phase boundary separating critical Luttinger liquid and gapped Mott insulating states. Our initial liquid ground state is labeled by a Luttinger interaction parameter K, and subject to a density-inhomogeneity forming external potential. For the Mott insulator, we employ the quantum Sine Gordon model at the Luther-Emery (LE) point. We find that over a wide range of initial K values, the quench induces the production of relativistic, non-dispersive traveling density waves, which we dub ``super-solitons.'' The super-solitons are generated from generic antecedent localized density lumps, and appear to be a robust feature of the post-quench dynamics. An isolated exception occurs for the case of K = KLE; here, the density dynamics are generically dispersive, and depend sensitively upon the shape of the initial inhomogeneity. We show that the super-solitons do not interact, and we demonstrate that an inhomogeneous Luttinger parameter K can be used to produce super-solitons with different characteristics in the same system.
Liu, Guangkun; Kaushal, Nitin; Liu, Shaozhi; Bishop, Christopher B.; Wang, Yan; Johnston, Steve; Alvarez, Gonzalo; Moreo, Adriana; Dagotto, Elbio R.
2016-06-24
A recently introduced one-dimensional three-orbital Hubbard model displays orbital-selective Mott phases with exotic spin arrangements such as spin block states [J. Rincón et al., Phys. Rev. Lett. 112, 106405 (2014)]. In this paper we show that the constrained-path quantum Monte Carlo (CPQMC) technique can accurately reproduce the phase diagram of this multiorbital one-dimensional model, paving the way to future CPQMC studies in systems with more challenging geometries, such as ladders and planes. The success of this approach relies on using the Hartree-Fock technique to prepare the trial states needed in CPQMC. In addition, we study a simplified version of the model where the pair-hopping term is neglected and the Hund coupling is restricted to its Ising component. The corresponding phase diagrams are shown to be only mildly affected by the absence of these technically difficult-to-implement terms. This is confirmed by additional density matrix renormalization group and determinant quantum Monte Carlo calculations carried out for the same simplified model, with the latter displaying only mild fermion sign problems. Lastly, we conclude that these methods are able to capture quantitatively the rich physics of the several orbital-selective Mott phases (OSMP) displayed by this model, thus enabling computational studies of the OSMP regime in higher dimensions, beyond static or dynamic mean-field approximations.
NASA Astrophysics Data System (ADS)
Sajna, A. S.
2016-10-01
We show that a certain class of higher-order excitations in ultracold atoms experiments can be described by straightforward extension of the standard strong coupling approach in the coherent state path integral formalism. It is achieved by theoretical analysis of energy absorption spectroscopy in the three-dimensional system of strongly correlated bosons described by the Bose-Hubbard model. In particular, for unit filling, an explicit form of the single-particle Mott insulator Green function at finite temperatures is derived which goes beyond the standard Hubbard bands description. Moreover, for relevant densities, we calculated the energy absorption rate and performed thermometry on rubidium atomic cloud gas by using previously obtained experimental data. Within the local density approximation, we explain that in such systems the nature of absorption spectrum depends significantly on local chemical potential: (a) the crossover region between lobes is characterized by different types of particle-hole excitations from neighboring Mott lobes and (b) origin of higher-order energy excitations changes from hole type to particle type for higher bosonic densities.
A charge density wave-like instability in a doped spin-orbit-assisted weak Mott insulator
NASA Astrophysics Data System (ADS)
Chu, H.; Zhao, L.; de la Torre, A.; Hogan, T.; Wilson, S. D.; Hsieh, D.
2017-01-01
Layered perovskite iridates realize a rare class of Mott insulators that are predicted to be strongly spin-orbit coupled analogues of the parent state of cuprate high-temperature superconductors. Recent discoveries of pseudogap, magnetic multipolar ordered and possible d-wave superconducting phases in doped Sr2IrO4 have reinforced this analogy among the single layer variants. However, unlike the bilayer cuprates, no electronic instabilities have been reported in the doped bilayer iridate Sr3Ir2O7. Here we show that Sr3Ir2O7 realizes a weak Mott state with no cuprate analogue by using ultrafast time-resolved optical reflectivity to uncover an intimate connection between its insulating gap and antiferromagnetism. However, we detect a subtle charge density wave-like Fermi surface instability in metallic electron doped Sr3Ir2O7 at temperatures (TDW) close to 200 K via the coherent oscillations of its collective modes, which is reminiscent of that observed in cuprates. The absence of any signatures of a new spatial periodicity below TDW from diffraction, scanning tunnelling and photoemission based probes suggests an unconventional and possibly short-ranged nature of this density wave order.
Rayleigh scattering. [molecular scattering terminology redefined
NASA Technical Reports Server (NTRS)
Young, A. T.
1981-01-01
The physical phenomena of molecular scattering are examined with the objective of redefining the confusing terminology currently used. The following definitions are proposed: molecular scattering consists of Rayleigh and vibrational Raman scattering; the Rayleigh scattering consists of rotational Raman lines and the central Cabannes line; the Cabannes line is composed of the Brillouin doublet and the central Gross or Landau-Placzek line. The term 'Rayleigh line' should never be used.
NASA Astrophysics Data System (ADS)
Misumi, Kazuma; Kaneko, Tatsuya; Ohta, Yukinori
2017-02-01
The variational cluster approximation is used to study the isotropic triangular-lattice Hubbard model at half filling, taking into account the nearest-neighbor (t1) and next-nearest-neighbor (t2) hopping parameters for magnetic frustrations. We determine the ground-state phase diagram of the model. In the strong-correlation regime, the 120∘ Néel- and stripe-ordered phases appear, and a nonmagnetic insulating phase emerges in between. In the intermediate correlation regime, the nonmagnetic insulating phase expands to a wider parameter region, which goes into a paramagnetic metallic phase in the weak-correlation regime. The critical phase boundary of the Mott metal-insulator transition is discussed in terms of the van Hove singularity evident in the calculated density of states and single-particle spectral function.
NASA Astrophysics Data System (ADS)
Grant, Paul
We report our preliminary study of electron-phonon mediated Cooper pairing as a component underlying high temperature superconductivity, in the presence of a Hubbard U driven antiferromagnetic ground state, subject to itinerant carrier doping, in the copper oxide perovskites. Our model is based on a proxy CuO fcc cubic-tetragonal structure that contains the basic physics of the electronic structure of copper oxide perovskites readily amenable to numerical analysis. We explore its phase diagram as a function of carrier concentration and coulomb repulsion ranging from the pure Mott-Hubbard AF insulating state to that of a metallic Fermi liquid, focusing on those conditions which might manifest high temperature superconducting behavior. In the Fermi liquid state, we find clear evidence that superconductivity arises from Jahn-Teller instabilities in the CuO bond which guided Bednorz and Mueller on the path to their 1986 discovery.
Tuning bad metal and non-Fermi liquid behavior in a Mott material: Rare-earth nickelate thin films.
Mikheev, Evgeny; Hauser, Adam J; Himmetoglu, Burak; Moreno, Nelson E; Janotti, Anderson; Van de Walle, Chris G; Stemmer, Susanne
2015-11-01
Resistances that exceed the Mott-Ioffe-Regel limit (known as bad metal behavior) and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. We establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to a non-Fermi liquid metal phase and provide a predictive criterion for Anderson localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices.
Tuning bad metal and non-Fermi liquid behavior in a Mott material: Rare-earth nickelate thin films
Mikheev, Evgeny; Hauser, Adam J.; Himmetoglu, Burak; Moreno, Nelson E.; Janotti, Anderson; Van de Walle, Chris G.; Stemmer, Susanne
2015-01-01
Resistances that exceed the Mott-Ioffe-Regel limit (known as bad metal behavior) and non-Fermi liquid behavior are ubiquitous features of the normal state of many strongly correlated materials. We establish the conditions that lead to bad metal and non-Fermi liquid phases in NdNiO3, which exhibits a prototype bandwidth-controlled metal-insulator transition. We show that resistance saturation is determined by the magnitude of Ni eg orbital splitting, which can be tuned by strain in epitaxial films, causing the appearance of bad metal behavior under certain conditions. The results shed light on the nature of a crossover to a non-Fermi liquid metal phase and provide a predictive criterion for Anderson localization. They elucidate a seemingly complex phase behavior as a function of film strain and confinement and provide guidelines for orbital engineering and novel devices. PMID:26601140
Ambipolar transport and magneto-resistance crossover in a Mott insulator, Sr2IrO4
NASA Astrophysics Data System (ADS)
Ravichandran, J.; Serrao, C. R.; Efetov, D. K.; Yi, D.; Oh, Y. S.; Cheong, S.-W.; Ramesh, R.; Kim, P.
2016-12-01
Electric field effect (EFE) controlled magnetoelectric transport in thin films of undoped and La-doped Sr2IrO4 (SIO) is investigated using ionic liquid gating. The temperature dependent resistance measurements exhibit insulating behavior in chemically and EFE doped samples with the band filling up to 10%. The ambipolar transport across the Mott gap is demonstrated by EFE tuning of the channel resistance and chemical doping. We observe a crossover from high temperature negative to low temperature positive magnetoresistance around ˜80-90 K, irrespective of the filling. This temperature and magnetic field dependent crossover is discussed in the light of conduction mechanisms of SIO, especially variable range hopping (VRH), and its relevance to the insulating ground state of SIO.
NASA Astrophysics Data System (ADS)
Cabo Montes de Oca, A.; March, N. H.; Cabo-Bizet, A.
2014-12-01
Former results for a tight-binding (TB) model of CuO planes in La2CuO4 are reinterpreted here to underline their wider implications. It is noted that physical systems being appropriately described by the TB model can exhibit the main strongly correlated electron system (SCES) properties, when they are solved in the HF approximation, by also allowing crystal symmetry breaking effects and noncollinear spin orientations of the HF orbitals. It is argued how a simple 2D square lattice system of Coulomb interacting electrons can exhibit insulator gaps and pseudogap states, and quantum phase transitions as illustrated by the mentioned former works. A discussion is also presented here indicating the possibility of attaining room temperature superconductivity, by means of a surface coating with water molecules of cleaved planes of graphite, being orthogonal to its c-axis. The possibility that 2D arrays of quantum dots can give rise to the same effect is also proposed to consideration. The analysis also furnishes theoretical insight to solve the Mott-Slater debate, at least for the La2CuO4 and TMO band structures. The idea is to apply a properly noncollinear GW scheme to the electronic structure calculation of these materials. The fact is that the GW approach can be viewed as a HF procedure in which the screening polarization is also determined. This directly indicates the possibility of predicting the assumed dielectric constant in the previous works. Thus, the results seem to identify that the main correlation properties in these materials are determined by screening. Finally, the conclusions also seem to be of help for the description of the experimental observations of metal-insulator transitions and Mott properties in atoms trapped in planar photonic lattices.
NASA Astrophysics Data System (ADS)
Paech, Martin; Apel, Walter; Kalinowski, Eva; Jeckelmann, Eric
2014-12-01
We present a large-scale combinatorial-diagrammatic computation of high-order contributions to the strong-coupling Kato-Takahashi perturbation series for the Hubbard model in high dimensions. The ground-state energy of the Mott-insulating phase is determined exactly up to the 15th order in 1 /U . The perturbation expansion is extrapolated to infinite order and the critical behavior is determined using the Domb-Sykes method. We compare the perturbative results with two dynamical mean-field theory (DMFT) calculations using a quantum Monte Carlo method and a density-matrix renormalization group method as impurity solvers. The comparison demonstrates the excellent agreement and accuracy of both extrapolated strong-coupling perturbation theory and quantum Monte Carlo based DMFT, even close to the critical coupling where the Mott insulator becomes unstable.
First-order insulator-to-metal Mott transition in the paramagnetic 3D system GaTa4Se8.
Camjayi, A; Acha, C; Weht, R; Rodríguez, M G; Corraze, B; Janod, E; Cario, L; Rozenberg, M J
2014-08-22
The nature of the Mott transition in the absence of any symmetry breaking remains a matter of debate. We study the correlation-driven insulator-to-metal transition in the prototypical 3D Mott system GaTa(4)Se(8), as a function of temperature and applied pressure. We report novel experiments on single crystals, which demonstrate that the transition is of first order and follows from the coexistence of two states, one insulating and one metallic, that we toggle with a small bias current. We provide support for our findings by contrasting the experimental data with calculations that combine local density approximation with dynamical mean-field theory, which are in very good agreement.
NASA Astrophysics Data System (ADS)
Pinterić, M.; Lazić, P.; Pustogow, A.; Ivek, T.; Kuveždić, M.; Milat, O.; Gumhalter, B.; Basletić, M.; Čulo, M.; Korin-Hamzić, B.; Löhle, A.; Hübner, R.; Sanz Alonso, M.; Hiramatsu, T.; Yoshida, Y.; Saito, G.; Dressel, M.; Tomić, S.
2016-10-01
The Mott insulator κ -(BEDT-TTF ) 2Ag2(CN) 3 forms a highly-frustrated triangular lattice of S =1 /2 dimers with a possible quantum-spin-liquid state. Our experimental and numerical studies reveal the emergence of a slight charge imbalance between crystallographically inequivalent sites, relaxor dielectric response, and hopping dc transport. In a broader perspective we conclude that the universal properties of strongly-correlated charge-transfer salts with spin liquid state are an anion-supported valence band and cyanide-induced quasidegenerate electronic configurations in the relaxed state. The generic low-energy excitations are caused by charged domain walls rather than by fluctuating electric dipoles. They give rise to glassy dynamics characteristic of dimerized Mott insulators, including the sibling compound κ -(BEDT-TTF)2Cu2 (CN )3.
ERIC Educational Resources Information Center
di Francia, Giuliano Toraldo
1973-01-01
The art of deriving information about an object from the radiation it scatters was once limited to visible light. Now due to new techniques, much of the modern physical science research utilizes radiation scattering. (DF)
NASA Astrophysics Data System (ADS)
Hébert, Charles-David; Sémon, Patrick; Tremblay, A.-M. S.
2015-11-01
Layered organic superconductors of the BEDT family are model systems for understanding the interplay of the Mott transition with superconductivity, magnetic order, and frustration, ingredients that are essential to understand superconductivity also in the cuprate high-temperature superconductors. Recent experimental studies on a hole-doped version of the organic compounds reveals an enhancement of superconductivity and a rapid crossover between two different conducting phases above the superconducting dome. One of these phases is a Fermi liquid, the other not. Using plaquette cellular dynamical mean field theory with state-of-the-art continuous-time quantum Monte Carlo calculations, we study this problem with the two-dimensional Hubbard model on the anisotropic triangular lattice. Phase diagrams as a function of temperature T and interaction strength U /t are obtained for anisotropy parameters t'=0.4 t ,t'=0.8 t and for various fillings. As in the case of the cuprates, we find, at finite doping, a first-order transition between two normal-state phases. One of theses phases has a pseudogap while the other does not. At temperatures above the critical point of the first-order transition, there is a Widom line where crossovers occur. The maximum (optimal) superconducting critical temperature Tcm at finite doping is enhanced by about 25% compared with its maximum at half filling and the range of U /t where superconductivity appears is greatly extended. These results are in broad agreement with experiment. Also, increasing frustration (larger t'/t ) significantly reduces magnetic ordering, as expected. This suggests that for compounds with intermediate to high frustration, very light doping should reveal the influence of the first-order transition and associated crossovers. These crossovers could possibly be even visible in the superconducting phase through subtle signatures. We also predict that destroying the superconducting phase by a magnetic field should reveal the
NASA Technical Reports Server (NTRS)
Ricks, Douglas W.
1993-01-01
There are a number of sources of scattering in binary optics: etch depth errors, line edge errors, quantization errors, roughness, and the binary approximation to the ideal surface. These sources of scattering can be systematic (deterministic) or random. In this paper, scattering formulas for both systematic and random errors are derived using Fourier optics. These formulas can be used to explain the results of scattering measurements and computer simulations.
Cluster Dynamical Mean Field Methods and the Momentum-selective Mott transition
NASA Astrophysics Data System (ADS)
Gull, Emanuel
2011-03-01
Innovations in methodology and computational power have enabled cluster dynamical mean field calculations of the Hubbard model with interaction strengths and band structures representative of high temperature copper oxide superconductors, for clusters large enough that the thermodyamic limit behavior may be determined. We present the methods and show how extrapolations to the thermodynamic limit work in practice. We show that the Hubbard model with next-nearest neighbor hopping at intermediate interaction strength captures much of the exotic behavior characteristic of the high temperature superconductors. An important feature of the results is a pseudogap for hole doping but not for electron doping. The pseudogap regime is characterized by a gap for momenta near Brillouin zone face and gapless behavior near the zone diagonal. for dopings outside of the pseudogap regime we find scattering rates which vary around the fermi surface in a way consistent with recent transport measurements. Using the maximum entropy method we calculate spectra, self-energies, and response functions for Raman spectroscopy and optical conductivities, finding results also in good agreement with experiment. Olivier Parcollet, Philipp Werner, Nan Lin, Michel Ferrero, Antoine Georges, Andrew J. Millis; NSF-DMR-0705847.
Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.
Gray, B A; Middey, S; Conti, G; Gray, A X; Kuo, C-T; Kaiser, A M; Ueda, S; Kobayashi, K; Meyers, D; Kareev, M; Tung, I C; Liu, Jian; Fadley, C S; Chakhalian, J; Freeland, J W
2016-09-15
The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.
NASA Astrophysics Data System (ADS)
Reymbaut, A.; Charlebois, M.; Asiani, M. Fellous; Fratino, L.; Sémon, P.; Sordi, G.; Tremblay, A.-M. S.
2016-10-01
The nearest-neighbor superexchange-mediated mechanism for dx2-y2 superconductivity in the one-band Hubbard model faces the challenge that nearest-neighbor Coulomb repulsion can be larger than superexchange. To answer this question, we use cellular dynamical mean-field theory (CDMFT) with a continuous-time quantum Monte Carlo solver to determine the superconducting phase diagram as a function of temperature and doping for on-site repulsion U =9 t and nearest-neighbor repulsion V =0 ,2 t ,4 t . In the underdoped regime, V increases the CDMFT superconducting transition temperature Tcd even though it decreases the superconducting order parameter at low temperature for all dopings. However, in the overdoped regime V decreases Tcd. We gain insight into these paradoxical results through a detailed study of the frequency dependence of the anomalous spectral function, extracted at finite temperature via the MaxEntAux method for analytic continuation. A systematic study of dynamical positive and negative contributions to pairing reveals that even though V has a high-frequency depairing contribution, it also has a low frequency pairing contribution since it can reinforce superexchange through J =4 t2/(U -V ) . Retardation is thus crucial to understanding pairing in doped Mott insulators, as suggested by previous zero-temperature studies. We also comment on the tendency to charge order for large V and on the persistence of d -wave superconductivity over extended-s or s +d wave.
Electric double-layer transistor using layered iron selenide Mott insulator TlFe1.6Se2
Katase, Takayoshi; Hiramatsu, Hidenori; Kamiya, Toshio; Hosono, Hideo
2014-01-01
A1–xFe2–ySe2 (A = K, Cs, Rb, Tl) are recently discovered iron-based superconductors with critical temperatures (Tc) ranging up to 32 K. Their parent phases have unique properties compared with other iron-based superconductors; e.g., their crystal structures include ordered Fe vacancies, their normal states are antiferromagnetic (AFM) insulating phases, and they have extremely high Néel transition temperatures. However, control of carrier doping into the parent AFM insulators has been difficult due to their intrinsic phase separation. Here, we fabricated an Fe-vacancy-ordered TlFe1.6Se2 insulating epitaxial film with an atomically flat surface and examined its electrostatic carrier doping using an electric double-layer transistor (EDLT) structure with an ionic liquid gate. The positive gate voltage gave a conductance modulation of three orders of magnitude at 25 K, and further induced and manipulated a phase transition; i.e., delocalized carrier generation by electrostatic doping is the origin of the phase transition. This is the first demonstration, to the authors' knowledge, of an EDLT using a Mott insulator iron selenide channel and opens a way to explore high Tc superconductivity in iron-based layered materials, where carrier doping by conventional chemical means is difficult. PMID:24591598
Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure
Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J.-W.; Ryan, P. J.; Freeland, J.W.; Chakhalian, J.
2016-01-01
In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states. PMID:26791402
Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures
NASA Astrophysics Data System (ADS)
Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C.-T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.
2016-09-01
The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.
Pai, Ramesh V.; Pandit, Rahul
2005-03-01
We use the finite-size, density-matrix-renormalization-group (FSDMRG) method to obtain the phase diagram of the one-dimensional (d=1) extended Bose-Hubbard model for density {rho}=1 in the U-V plane, where U and V are, respectively, onsite and nearest-neighbor interactions. The phase diagram comprises three phases: superfluid (SF), Mott insulator (MI), and mass-density-wave (MDW). For small values of U and V, we get a reentrant SF-MI-SF phase transition. For intermediate values of interactions the SF phase is sandwiched between MI and MDW phases with continuous SF-MI and SF-MDW transitions. We show, by a detailed, finite-size scaling analysis, that the MI-SF transition is of Kosterlitz-Thouless (KT) type whereas the MDW-SF transition has both KT and two-dimensional Ising characters. For large values of U and V we get a direct, first-order, MI-MDW transition. The MI-SF, MDW-SF, and MI-MDW phase boundaries join at a bicritical point at (U,V)=(8.5{+-}0.05,4.75{+-}0.05)
Chen, Qi-Hui; Li, Peng; Su, Haibin
2016-06-29
By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.
NASA Astrophysics Data System (ADS)
Chen, Qi-Hui; Li, Peng; Su, Haibin
2016-06-01
By generalizing the traditional single-site strong coupling expansion approach to a cluster one, we study the zero-temperature phase diagram of bosonic atoms in a trimerized Kagomé optical lattice. Some new features are present in this system. Due to the strong intra-trimer hopping interaction, there will be a new Mott insulator (MI), which is by definition incompressible but with a fractional filling per trimer. This is different from the traditional MI, which has an integral filling and originates only from the repulsive interaction between particles. We investigate the MI-to-superfluid transition and the nature of the fractional MI by calculating the critical exponents of phase transitions and the low-lying energy excitation spectra of quasiparticles (quasihole). We will show how the low-energy properties of this system can be understood qualitatively as a Bose-Hubbard model in triangular lattice from the point of view of the cluster strong coupling expansion. We also discuss how our results are related to experiment by studying the Bragg spectroscopy.
Engineered Mott ground state in a LaTiO3+δ/LaNiO3 heterostructure
Cao, Yanwei; Liu, Xiaoran; Kareev, M.; ...
2016-01-21
In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO3 have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO3 and a doped Mott insulator LaTiO3+δ, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibitsmore » interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and eg orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.« less
NASA Astrophysics Data System (ADS)
Bhunia, Amit; Bansal, Kanika; Henini, Mohamed; Alshammari, Marzook S.; Datta, Shouvik
2016-10-01
Mostly, optical spectroscopies are used to investigate the physics of excitons, whereas their electrical evidences are hardly explored. Here, we examined a forward bias activated differential capacitance response of GaInP/AlGaInP based multi-quantum well laser diodes to trace the presence of excitons using electrical measurements. Occurrence of "negative activation energy" after light emission is understood as thermodynamical signature of steady state excitonic population under intermediate range of carrier injections. Similar corroborative results are also observed in an InGaAs/GaAs quantum dot laser structure grown by molecular beam epitaxy. With increasing biases, the measured differential capacitance response slowly vanishes. This represents gradual Mott transition of an excitonic phase into an electron-hole plasma in a GaInP/AlGaInP laser diode. This is further substantiated by more and more exponentially looking shapes of high energy tails in electroluminescence spectra with increasing forward bias, which originates from a growing non-degenerate population of free electrons and holes. Such an experimental correlation between electrical and optical properties of excitons can be used to advance the next generation excitonic devices.
Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures
Gray, B. A.; Middey, S.; Conti, G.; ...
2016-09-15
The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In this paper, in pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leadingmore » to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Finally, such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.« less
Parameswaran, S A; Kimchi, Itamar; Turner, Ari M; Stamper-Kurn, D M; Vishwanath, Ashvin
2013-03-22
We study Bose-Hubbard models on tight-binding, non-Bravais lattices, with a filling of one boson per unit cell--and thus fractional site filling. We discuss situations where no classical bosonic insulator, which is a product state of particles on independent sites, is admitted. Nevertheless, we show that it is possible to construct a quantum Mott insulator of bosons if a trivial band insulator of fermions is possible at the same filling. The ground state wave function is simply a permanent of exponentially localized Wannier orbitals. Such a Wannier permanent wave function is featureless in that it respects all lattice symmetries and is the unique ground state of a parent Hamiltonian that we construct. Motivated by the recent experimental demonstration of a kagome optical lattice of bosons, we study this lattice at 1/3 site filling. Previous approaches to this problem have invariably produced either broken-symmetry states or topological order. Surprisingly, we demonstrate that a featureless insulator is a possible alternative and is the exact ground state of a local Hamiltonian. We briefly comment on the experimental relevance of our results to ultracold atoms as well as to 1/3 magnetization plateaus for kagome spin models in an applied field.
Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures
Gray, B. A.; Middey, S.; Conti, G.; Gray, A. X.; Kuo, C.-T.; Kaiser, A. M.; Ueda, S.; Kobayashi, K.; Meyers, D.; Kareev, M.; Tung, I. C.; Liu, Jian; Fadley, C. S.; Chakhalian, J.; Freeland, J. W.
2016-01-01
The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates. PMID:27627855
Multiple scattering technique lidar
NASA Technical Reports Server (NTRS)
Bissonnette, Luc R.
1992-01-01
The Bernouilli-Ricatti equation is based on the single scattering description of the lidar backscatter return. In practice, especially in low visibility conditions, the effects of multiple scattering can be significant. Instead of considering these multiple scattering effects as a nuisance, we propose here to use them to help resolve the problems of having to assume a backscatter-to-extinction relation and specifying a boundary value for a position far remote from the lidar station. To this end, we have built a four-field-of-view lidar receiver to measure the multiple scattering contributions. The system has been described in a number of publications that also discuss preliminary results illustrating the multiple scattering effects for various environmental conditions. Reported here are recent advances made in the development of a method of inverting the multiple scattering data for the determination of the aerosol scattering coefficient.
Partially strong WW scattering
Cheung Kingman; Chiang Chengwei; Yuan Tzuchiang
2008-09-01
What if only a light Higgs boson is discovered at the CERN LHC? Conventional wisdom tells us that the scattering of longitudinal weak gauge bosons would not grow strong at high energies. However, this is generally not true. In some composite models or general two-Higgs-doublet models, the presence of a light Higgs boson does not guarantee complete unitarization of the WW scattering. After partial unitarization by the light Higgs boson, the WW scattering becomes strongly interacting until it hits one or more heavier Higgs bosons or other strong dynamics. We analyze how LHC experiments can reveal this interesting possibility of partially strong WW scattering.
NASA Technical Reports Server (NTRS)
Hong, Byungsik; Maung, Khin Maung; Wilson, John W.; Buck, Warren W.
1989-01-01
The derivations of the Lippmann-Schwinger equation and Watson multiple scattering are given. A simple optical potential is found to be the first term of that series. The number density distribution models of the nucleus, harmonic well, and Woods-Saxon are used without t-matrix taken from the scattering experiments. The parameterized two-body inputs, which are kaon-nucleon total cross sections, elastic slope parameters, and the ratio of the real to the imaginary part of the forward elastic scattering amplitude, are presented. The eikonal approximation was chosen as our solution method to estimate the total and absorptive cross sections for the kaon-nucleus scattering.
NASA Astrophysics Data System (ADS)
Schmitz, R.; Entin-Wohlman, O.; Aharony, A.; Müller-Hartmann, E.
2005-09-01
[Dedicated to Bernhard Mühlschlegel on the occasion ofhis 80th birthday]Using a point-charge calculation of the electrostatic crystal field, we determine the non-degenerate orbital ground state of the ferromagnetic Mott insulator YTiO3, which is found to agree perfectly with experiment. Based on the orbital order, we obtain by perturbation theory an effective spin Hamiltonian that describes the magnetic superexchange between nearest-neighbor Ti ions. The superexchange Hamiltonian includes, in addition to the isotropic Heisenberg coupling, antisymmetric (Dzyaloshinskii-Moriya) and symmetric anisotropy terms, caused by the spin-orbit interaction on the Ti ions. We find ferromagnetic Heisenberg couplings for Ti-Ti bonds in the crystallographic ab planes, but antiferromagnetic ones for Ti-Ti bonds between planes, in contradiction with experiment (which gives ferromagnetic couplings for both). Difficulties in calculating realistic values for the isotropic couplings of YTiO3 have been already reported in the literature. We discuss possible origins for these discrepancies. However, the much smaller values we obtain for the symmetric and antisymmetric anisotropies may be expected to be reliable. We therefore combine the experimentally-deduced isotropic coupling with the calculated anisotropic ones to determine the magnetic order of the Ti ions, which is found to be in satisfactory agreement with experiment. Based on this magnetic order, we derive the spin-wave spectrum. We find an acoustic branch with a very small zone-center gap and three optical spin-wave modes with sizeable zone-center gaps. The acoustic branch reproduces the one reported in experiment, and the optical ones are in a satisfactory agreement with experiment, upon a proper folding of the magnetic Brillouin zone.
NASA Astrophysics Data System (ADS)
Stover, John C.
1991-12-01
Optical scatter is a bothersome source of optical noise, limits resolution and reduces system throughput. However, it is also an extremely sensitive metrology tool. It is employed in a wide variety of applications in the optics industry (where direct scatter measurement is of concern) and is becoming a popular indirect measurement in other industries where its measurement in some form is an indicator of another component property - like roughness, contamination or position. This paper presents a brief review of the current state of this technology as it emerges from university and government laboratories into more general industry use. The bidirectional scatter distribution function (or BSDF) has become the common format for expressing scatter data and is now used almost universally. Measurements made at dozens of laboratories around the country cover the spectrum from the uv to the mid- IR. Data analysis of optical component scatter has progressed to the point where a variety of analysis tools are becoming available for discriminating between the various sources of scatter. Work has progressed on the analysis of rough surface scatter and the application of these techniques to some challenging problems outside the optical industry. Scatter metrology is acquiring standards and formal test procedures. The available scatter data base is rapidly expanding as the number and sophistication of measurement facilities increases. Scatter from contaminants is continuing to be a major area of work as scatterometers appear in vacuum chambers at various laboratories across the country. Another area of research driven by space applications is understanding the non-topographic sources of mid-IR scatter that are associated with Beryllium and other materials. The current flurry of work in this growing area of metrology can be expected to continue for several more years and to further expand to applications in other industries.
Olalde-Velasco, P; Jimenez-Mier, J; Denlinger, JD; Hussain, Z; Yang, WL
2011-07-11
We report the most direct experimental verification of Mott-Hubbard and charge-transfer insulators through x-ray emission spectroscopy in transition-metal (TM) fluorides. The p-d hybridization features in the spectra allow a straightforward energy alignment of the anion-2p and metal-3d valence states, which visually shows the difference between the two types of insulators. Furthermore, in parallel with the theoretical Zaanen-Sawatzky-Allen diagram, a complete experimental systematics of the 3d Coulomb interaction and the 2p-3d charge-transfer energy is reported and could serve as a universal experimental trend for other TM systems including oxides.
NASA Astrophysics Data System (ADS)
Waki, T.; Kajinami, Y.; Tabata, Y.; Nakamura, H.; Yoshida, M.; Takigawa, M.; Watanabe, I.
2010-01-01
Muon spin relaxation (μSR) and nuclear magnetic resonance experiments revealed that the spin-singlet state with an excitation gap of ˜200K is realized from S=1/2Nb4 tetrahedral clusters in a cluster Mott insulator GaNb4S8 . The intercluster cooperative phenomenon to the singlet state at TS=32k is triggered by intracluster Jahn-Teller type structural instability developed from ˜3TS . Referring to the lattice symmetry, the formation of Nb8 octamer ( Nb4-Nb4 bond) is suggested.
Purely bianisotropic scatterers
NASA Astrophysics Data System (ADS)
Albooyeh, M.; Asadchy, V. S.; Alaee, R.; Hashemi, S. M.; Yazdi, M.; Mirmoosa, M. S.; Rockstuhl, C.; Simovski, C. R.; Tretyakov, S. A.
2016-12-01
The polarization response of molecules or meta-atoms to external electric and magnetic fields, which defines the electromagnetic properties of materials, can either be direct (electric field induces electric moment and magnetic field induces magnetic moment) or indirect (magnetoelectric coupling in bianisotropic scatterers). Earlier studies suggest that there is a fundamental bound on the indirect response of all passive scatterers: It is believed to be always weaker than the direct one. In this paper, we prove that there exist scatterers which overcome this bound substantially. Moreover, we show that the amplitudes of electric and magnetic polarizabilities can be negligibly small as compared to the magnetoelectric coupling coefficients. However, we prove that if at least one of the direct-excitation coefficients vanishes, magnetoelectric coupling effects in passive scatterers cannot exist. Our findings open a way to a new class of electromagnetic scatterers and composite materials.
Inelastic Light Scattering Processes
NASA Technical Reports Server (NTRS)
Fouche, Daniel G.; Chang, Richard K.
1973-01-01
Five different inelastic light scattering processes will be denoted by, ordinary Raman scattering (ORS), resonance Raman scattering (RRS), off-resonance fluorescence (ORF), resonance fluorescence (RF), and broad fluorescence (BF). A distinction between fluorescence (including ORF and RF) and Raman scattering (including ORS and RRS) will be made in terms of the number of intermediate molecular states which contribute significantly to the scattered amplitude, and not in terms of excited state lifetimes or virtual versus real processes. The theory of these processes will be reviewed, including the effects of pressure, laser wavelength, and laser spectral distribution on the scattered intensity. The application of these processes to the remote sensing of atmospheric pollutants will be discussed briefly. It will be pointed out that the poor sensitivity of the ORS technique cannot be increased by going toward resonance without also compromising the advantages it has over the RF technique. Experimental results on inelastic light scattering from I(sub 2) vapor will be presented. As a single longitudinal mode 5145 A argon-ion laser line was tuned away from an I(sub 2) absorption line, the scattering was observed to change from RF to ORF. The basis, of the distinction is the different pressure dependence of the scattered intensity. Nearly three orders of magnitude enhancement of the scattered intensity was measured in going from ORF to RF. Forty-seven overtones were observed and their relative intensities measured. The ORF cross section of I(sub 2) compared to the ORS cross section of N2 was found to be 3 x 10(exp 6), with I(sub 2) at its room temperature vapor pressure.
Scattering theory of nonlinear thermoelectricity in quantum coherent conductors.
Meair, Jonathan; Jacquod, Philippe
2013-02-27
We construct a scattering theory of weakly nonlinear thermoelectric transport through sub-micron scale conductors. The theory incorporates the leading nonlinear contributions in temperature and voltage biases to the charge and heat currents. Because of the finite capacitances of sub-micron scale conducting circuits, fundamental conservation laws such as gauge invariance and current conservation require special care to be preserved. We do this by extending the approach of Christen and Büttiker (1996 Europhys. Lett. 35 523) to coupled charge and heat transport. In this way we write relations connecting nonlinear transport coefficients in a manner similar to Mott's relation between the linear thermopower and the linear conductance. We derive sum rules that nonlinear transport coefficients must satisfy to preserve gauge invariance and current conservation. We illustrate our theory by calculating the efficiency of heat engines and the coefficient of performance of thermoelectric refrigerators based on quantum point contacts and resonant tunneling barriers. We identify, in particular, rectification effects that increase device performance.
NASA Technical Reports Server (NTRS)
Hong, Byungsik; Buck, Warren W.; Maung, Khin M.
1989-01-01
Two kinds of number density distributions of the nucleus, harmonic well and Woods-Saxon models, are used with the t-matrix that is taken from the scattering experiments to find a simple optical potential. The parameterized two body inputs, which are kaon-nucleon total cross sections, elastic slope parameters, and the ratio of the real to imaginary part of the forward elastic scattering amplitude, are shown. The eikonal approximation was chosen as the solution method to estimate the total and absorptive cross sections for the kaon-nucleus scattering.
Gangopadhyay, Shruba; Pickett, Warren E.
2015-01-15
The double perovskite Ba2NaOsO6 (BNOO), an exotic example of a very high oxidation state (heptavalent) osmium d1 compound and also uncommon by being a ferromagnetic open d-shell (Mott) insulator without Jahn-Teller (JT) distortion, is modeled using a density functional theory based hybrid functional incorporating exact exchange for correlated electronic orbitals and including the large spin-orbit coupling (SOC). The experimentally observed narrow-gap ferromagnetic insulating ground state is obtained, but only when including spin-orbit coupling, making this a Dirac-Mott insulator. The calculated easy axis along [110] is in accord with experiment, providing additional support that this approach provides a realistic method formore » studying this system. The predicted spin density for [110] spin orientation is nearly cubic (unlike for other directions), providing an explanation for the absence of JT distortion. An orbital moment of –0.4μB strongly compensates the +0.5μB spin moment on Os, leaving a strongly compensated moment more in line with experiment. Remarkably, the net moment lies primarily on the oxygen ions. An insulator-metal transition, by rotating the magnetization direction with an external field under moderate pressure, is predicted as one consequence of strong SOC, and metallization under moderate pressure is predicted. In conclusion, a comparison is made with the isostructural, isovalent insulator Ba2LiOsO6, which, however, orders antiferromagnetically.« less
Environment scattering in GADRAS.
Thoreson, Gregory G.; Mitchell, Dean J; Theisen, Lisa Anne; Harding, Lee T.
2013-09-01
Radiation transport calculations were performed to compute the angular tallies for scattered gamma-rays as a function of distance, height, and environment. Greens Functions were then used to encapsulate the results a reusable transformation function. The calculations represent the transport of photons throughout scattering surfaces that surround sources and detectors, such as the ground and walls. Utilization of these calculations in GADRAS (Gamma Detector Response and Analysis Software) enables accurate computation of environmental scattering for a variety of environments and source configurations. This capability, which agrees well with numerous experimental benchmark measurements, is now deployed with GADRAS Version 18.2 as the basis for the computation of scattered radiation.
Rayleigh Scattering Diagnostics Workshop
NASA Technical Reports Server (NTRS)
Seasholtz, Richard (Compiler)
1996-01-01
The Rayleigh Scattering Diagnostics Workshop was held July 25-26, 1995 at the NASA Lewis Research Center in Cleveland, Ohio. The purpose of the workshop was to foster timely exchange of information and expertise acquired by researchers and users of laser based Rayleigh scattering diagnostics for aerospace flow facilities and other applications. This Conference Publication includes the 12 technical presentations and transcriptions of the two panel discussions. The first panel was made up of 'users' of optical diagnostics, mainly in aerospace test facilities, and its purpose was to assess areas of potential applications of Rayleigh scattering diagnostics. The second panel was made up of active researchers in Rayleigh scattering diagnostics, and its purpose was to discuss the direction of future work.
NASA Technical Reports Server (NTRS)
Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.
1990-01-01
A 5-state close-coupling calculation (5s-5p-4d-6s-6p) was carried out for positron-Rb scattering in the energy range 3.7 to 28.0 eV. In contrast to the results of similar close-coupling calculations for positron-Na and positron-K scattering the (effective) total integrated cross section has an energy dependence which is contrary to recent experimental measurements.
CONTINUOUS ROTATION SCATTERING CHAMBER
Verba, J.W.; Hawrylak, R.A.
1963-08-01
An evacuated scattering chamber for use in observing nuclear reaction products produced therein over a wide range of scattering angles from an incoming horizontal beam that bombards a target in the chamber is described. A helically moving member that couples the chamber to a detector permits a rapid and broad change of observation angles without breaching the vacuum in the chamber. Also, small inlet and outlet openings are provided whose size remains substantially constant. (auth)
Microcavity Enhanced Raman Scattering
NASA Astrophysics Data System (ADS)
Petrak, Benjamin J.
Raman scattering can accurately identify molecules by their intrinsic vibrational frequencies, but its notoriously weak scattering efficiency for gases presents a major obstacle to its practical application in gas sensing and analysis. This work explores the use of high finesse (≈50 000) Fabry-Perot microcavities as a means to enhance Raman scattering from gases. A recently demonstrated laser ablation method, which carves out a micromirror template on fused silica--either on a fiber tip or bulk substrates-- was implemented, characterized, and optimized to fabricate concave micromirror templates ˜10 mum diameter and radius of curvature. The fabricated templates were coated with a high-reflectivity dielectric coating by ion-beam sputtering and were assembled into microcavities ˜10 mum long and with a mode volume ˜100 mum 3. A novel gas sensing technique that we refer to as Purcell enhanced Raman scattering (PERS) was demonstrated using the assembled microcavities. PERS works by enhancing the pump laser's intensity through resonant recirculation at one longitudinal mode, while simultaneously, at a second mode at the Stokes frequency, the Purcell effect increases the rate of spontaneous Raman scattering by a change to the intra-cavity photon density of states. PERS was shown to enhance the rate of spontaneous Raman scattering by a factor of 107 compared to the same volume of sample gas in free space scattered into the same solid angle subtended by the cavity. PERS was also shown capable of resolving several Raman bands from different isotopes of CO2 gas for application to isotopic analysis. Finally, the use of the microcavity to enhance coherent anti-Stokes Raman scattering (CARS) from CO2 gas was demonstrated.
SCRIT electron scattering facility
NASA Astrophysics Data System (ADS)
Tsukada, Kyo
2014-09-01
Electron scattering is the most powerful and reliable tool to investigate the nuclear structure because this reaction has the great advantage that the electron is structureless particle and its interaction is well described by the quantum electrodynamics. As is well known, the charge density distributions of many stable nuclei were determined by elastic electron scattering. Recently, many efforts for studies of unstable nuclei have been made, and the precise information of the structure of unstabe nuclei have been strongly desired. However, due to the difficulty of preparing a short-lived unstable nuclear target, there is no electron scattering on unstable nuclei with a few important exceptions, such as on 3H, 14C and so on. Under these circumstances, we have established a completely new target-forming technique, namely SCRIT (Self-Confining Radioactive isotope Ion Target) which makes electron scattering on unstable nuclei possible. A Dedicated electron scattering facility at RIKEN consists of an electron accelerator with the SCRIT system, an ERIS (Electron-beam-driven RI separator for SCRIT), and a WiSES (Window-frame Spectrometer for Electron Scattering). Feasibility test of the SCRIT and ERIS system have been successfully carried out using the stable nuclei, and more than 1026 [cm-2s-1] luminosity was already achieved. Furthermore, 132Sn, which is one of the important target at the beginning of this project, was also successfully separated in the ERIS. The WiSES with momentum resolution of Δp/p ~ 10-3 consisting of the wide acceptance dipole magnet, two set of drift chambers together with trigger scintillation hodoscope is under construction. Electron scattering on unstable nuclei will start within a year. In this talk, the introduction of our project and the progress of the preparation status will be presented.
Ding, Yang; Yang, Liuxiang; Chen, Cheng-Chien; Kim, Heung-Sik; Han, Myung Joon; Luo, Wei; Feng, Zhenxing; Upton, Mary; Casa, Diego; Kim, Jungho; Gog, Thomas; Zeng, Zhidan; Cao, Gang; Mao, Ho-kwang; van Veenendaal, Michel
2016-05-24
The spin-orbit Mott insulator Sr_{3}Ir_{2}O_{7} provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance and resonant inelastic x-ray scattering measurements on single-crystal Sr_{3}Ir_{2}O_{7} up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the ab plane but an insulating behavior along the c axis. Such an unusual phenomenon resembles the strange metal phase in cuprate superconductors. Since there is no sign of the collapse of spin-orbit or Coulomb interactions in x-ray measurements, this novel insulator-metal transition is potentially driven by a first-order structural change at nearby pressures. Our discovery points to a new approach for synthesizing functional materials.
Monte Carlo eikonal scattering
NASA Astrophysics Data System (ADS)
Gibbs, W. R.; Dedonder, J. P.
2012-08-01
Background: The eikonal approximation is commonly used to calculate heavy-ion elastic scattering. However, the full evaluation has only been done (without the use of Monte Carlo techniques or additional approximations) for α-α scattering.Purpose: Develop, improve, and test the Monte Carlo eikonal method for elastic scattering over a wide range of nuclei, energies, and angles.Method: Monte Carlo evaluation is used to calculate heavy-ion elastic scattering for heavy nuclei including the center-of-mass correction introduced in this paper and the Coulomb interaction in terms of a partial-wave expansion. A technique for the efficient expansion of the Glauber amplitude in partial waves is developed.Results: Angular distributions are presented for a number of nuclear pairs over a wide energy range using nucleon-nucleon scattering parameters taken from phase-shift analyses and densities from independent sources. We present the first calculations of the Glauber amplitude, without further approximation, and with realistic densities for nuclei heavier than helium. These densities respect the center-of-mass constraints. The Coulomb interaction is included in these calculations.Conclusion: The center-of-mass and Coulomb corrections are essential. Angular distributions can be predicted only up to certain critical angles which vary with the nuclear pairs and the energy, but we point out that all critical angles correspond to a momentum transfer near 1 fm-1.
NASA Technical Reports Server (NTRS)
Schaetzel, Klaus
1989-01-01
Since the development of laser light sources and fast digital electronics for signal processing, the classical discipline of light scattering on liquid systems experienced a strong revival plus an enormous expansion, mainly due to new dynamic light scattering techniques. While a large number of liquid systems can be investigated, ranging from pure liquids to multicomponent microemulsions, this review is largely restricted to applications on Brownian particles, typically in the submicron range. Static light scattering, the careful recording of the angular dependence of scattered light, is a valuable tool for the analysis of particle size and shape, or of their spatial ordering due to mutual interactions. Dynamic techniques, most notably photon correlation spectroscopy, give direct access to particle motion. This may be Brownian motion, which allows the determination of particle size, or some collective motion, e.g., electrophoresis, which yields particle mobility data. Suitable optical systems as well as the necessary data processing schemes are presented in some detail. Special attention is devoted to topics of current interest, like correlation over very large lag time ranges or multiple scattering.
NASA Astrophysics Data System (ADS)
Grasselli, Federico; Bertoni, Andrea; Goldoni, Guido
2016-09-01
When composite particles—such as small molecules, nuclei, or photogenerated excitons in semiconductors—are scattered by an external potential, energy may be transferred between the c.m. and the internal degrees of freedom. An accurate dynamical modeling of this effect is pivotal in predicting diverse scattering quantities and reaction cross sections, and allows us to rationalize time-resolved energy and localization spectra. Here, we show that time-dependent scattering of a quantum composite particle with an arbitrary, nonperturbative external potential can be obtained by propagating the c.m. degrees of freedom with a properly designed local self-energy potential. The latter embeds the effect of internal virtual transitions and can be obtained by the knowledge of the stationary internal states. The case is made by simulating Wannier-Mott excitons in one- and two-dimensional semiconductor heterostructures. The self-energy approach shows very good agreement with numerically exact Schrödinger propagation for scattering potentials where a mean-field model cannot be applied, at a dramatically reduced computational cost.
Electromagnetic scattering theory
NASA Technical Reports Server (NTRS)
Bird, J. F.; Farrell, R. A.
1986-01-01
Electromagnetic scattering theory is discussed with emphasis on the general stochastic variational principle (SVP) and its applications. The stochastic version of the Schwinger-type variational principle is presented, and explicit expressions for its integrals are considered. Results are summarized for scalar wave scattering from a classic rough-surface model and for vector wave scattering from a random dielectric-body model. Also considered are the selection of trial functions and the variational improvement of the Kirchhoff short-wave approximation appropriate to large size-parameters. Other applications of vector field theory discussed include a general vision theory and the analysis of hydromagnetism induced by ocean motion across the geomagnetic field. Levitational force-torque in the magnetic suspension of the disturbance compensation system (DISCOS), now deployed in NOVA satellites, is also analyzed using the developed theory.
NASA Astrophysics Data System (ADS)
Gomez, Humberto
2016-06-01
The CHY representation of scattering amplitudes is based on integrals over the moduli space of a punctured sphere. We replace the punctured sphere by a double-cover version. The resulting scattering equations depend on a parameter Λ controlling the opening of a branch cut. The new representation of scattering amplitudes possesses an enhanced redundancy which can be used to fix, modulo branches, the location of four punctures while promoting Λ to a variable. Via residue theorems we show how CHY formulas break up into sums of products of smaller (off-shell) ones times a propagator. This leads to a powerful way of evaluating CHY integrals of generic rational functions, which we call the Λ algorithm.
NASA Astrophysics Data System (ADS)
Bahadur, Birendra
The following sections are included: * INTRODUCTION * CELL DESIGNING * EXPERIMENTAL OBSERVATIONS IN NEMATICS RELATED WITH DYNAMIC SCATTERING * Experimental Observations at D.C. Field and Electrode Effects * Experimental Observation at Low Frequency A.C. Fields * Homogeneously Aligned Nematic Regime * Williams Domains * Dynamic Scattering * Experimental Observation at High Frequency A.C. Field * Other Experimental Observations * THEORETICAL INTERPRETATIONS * Felici Model * Carr-Helfrich Model * D.C. Excitation * Dubois-Violette, de Gennes and Parodi Model * Low Freqency or Conductive Regime * High Frequency or Dielectric Regime * DYNAMIC SCATTERING IN SMECRIC A PHASE * ELECTRO-OPTICAL CHARACTERISTICS AND LIMITATIONS * Contrast Ratio vs. Voltage, Viewing Angle, Cell Gap, Wavelength and Temperature * Display Current vs. Voltage, Cell Gap and Temperature * Switching Time * Effect of Alignment * Effect of Conductivity, Temperature and Frequency * Addressing of DSM LCDs * Limitations of DSM LCDs * ACKNOWLEDGEMENTS * REFERENCES
ZALIZNYAK,I.A.; LEE,S.H.
2004-07-30
Much of our understanding of the atomic-scale magnetic structure and the dynamical properties of solids and liquids was gained from neutron-scattering studies. Elastic and inelastic neutron spectroscopy provided physicists with an unprecedented, detailed access to spin structures, magnetic-excitation spectra, soft-modes and critical dynamics at magnetic-phase transitions, which is unrivaled by other experimental techniques. Because the neutron has no electric charge, it is an ideal weakly interacting and highly penetrating probe of matter's inner structure and dynamics. Unlike techniques using photon electric fields or charged particles (e.g., electrons, muons) that significantly modify the local electronic environment, neutron spectroscopy allows determination of a material's intrinsic, unperturbed physical properties. The method is not sensitive to extraneous charges, electric fields, and the imperfection of surface layers. Because the neutron is a highly penetrating and non-destructive probe, neutron spectroscopy can probe the microscopic properties of bulk materials (not just their surface layers) and study samples embedded in complex environments, such as cryostats, magnets, and pressure cells, which are essential for understanding the physical origins of magnetic phenomena. Neutron scattering is arguably the most powerful and versatile experimental tool for studying the microscopic properties of the magnetic materials. The magnitude of the cross-section of the neutron magnetic scattering is similar to the cross-section of nuclear scattering by short-range nuclear forces, and is large enough to provide measurable scattering by the ordered magnetic structures and electron spin fluctuations. In the half-a-century or so that has passed since neutron beams with sufficient intensity for scattering applications became available with the advent of the nuclear reactors, they have became indispensable tools for studying a variety of important areas of modern science
Quaglioni, S; Navratil, P; Roth, R
2009-12-15
The exact treatment of nuclei starting from the constituent nucleons and the fundamental interactions among them has been a long-standing goal in nuclear physics. Above all nuclear scattering and reactions, which require the solution of the many-body quantum-mechanical problem in the continuum, represent an extraordinary theoretical as well as computational challenge for ab initio approaches.We present a new ab initio many-body approach which derives from the combination of the ab initio no-core shell model with the resonating-group method [4]. By complementing a microscopic cluster technique with the use of realistic interactions, and a microscopic and consistent description of the nucleon clusters, this approach is capable of describing simultaneously both bound and scattering states in light nuclei. We will discuss applications to neutron and proton scattering on sand light p-shell nuclei using realistic nucleon-nucleon potentials, and outline the progress toward the treatment of more complex reactions.
NASA Astrophysics Data System (ADS)
Capone, Massimo; Nomura, Yusuke; Sakai, Shiro; Giovannetti, Gianluca; Arita, Ryotaro
The phase diagram of doped fullerides like Cs3C60 as a function of the spacing between fullerene molecules is characterized by a first-order transition between a Mott insulator and an s-wave superconductor with a dome-shaped behavior of the critical temperature. By means of an ab-initio modeling of the bandstructure, the electron-phonon interaction and the interaction parameter and a Dynamical Mean-Field Theory solution, we reproduce the phase diagram and demonstrate that phonon superconductivity benefits from strong correlations confirming earlier model predictions. The role of correlations is manifest also in infrared measurements carried out by L. Baldassarre. The superconducting phase shares many similarities with ''exotic'' superconductors with electronic pairing, suggesting that the anomalies in the ''normal'' state, rather than the pairing glue, can be the real common element unifying a wide family of strongly correlated superconductors including cuprates and iron superconductors
NASA Astrophysics Data System (ADS)
Bartosch, Lorenz
2012-02-01
We discuss a scaling theory of the lattice response in the vicinity of a finite-temperature critical end point. The thermal expansivity is shown to be more singular than the specific heat such that the Gr"uneisen ratio diverges as the critical point is approached, except for its immediate vicinity. More generally, we express the thermal expansivity in terms of a scaling function which we explicitly evaluate for the two-dimensional Ising universality class. Recent thermal expansivity measurements on the layered organic conductor κ-(BEDT-TTF)2X close to the Mott transition are well described by our theory.[2mm] [1] Lorenz Bartosch, Mariano de Souza, and Michael Lang, Physical Review Letters 104, 245701 (2010).
Buklijas, Tatjana
2017-03-01
London County Council's pathological laboratory in the LCC asylum at Claybury, Essex, was established in 1895 to study the pathology of mental illness. Historians of psychiatry have understood the Claybury laboratory as a predecessor of the Maudsley Hospital in London: not only was this laboratory closed when the Maudsley was opened in 1916, but its director, Frederick Walker Mott, a champion of the 'German' model in psychiatry, was instrumental in the establishment of this institution. Yet, as I argue in this essay, for all the continuities with the Maudsley, the Claybury laboratory should not be seen solely as its predecessor - or as a British answer to continental laboratories such as Theodor Meynert's in Vienna. Rather, as I show using the examples of general paralysis of the insane and 'asylum colitis', the Claybury laboratory is best understood as an attempt to prevent mental illness using a microbiological model.
Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; ...
2016-01-20
In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension ofmore » electron-phonon coupling which persists under highly non-equilibrium conditions.« less
Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.
2016-01-20
In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr_{2}IrO_{4} probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Lastly, due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr_{2}IrO_{4} and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions.
Li, Yuelin; Schaller, Richard D.; Zhu, Mengze; Walko, Donald A.; Kim, Jungho; Ke, Xianglin; Miao, Ludi; Mao, Z. Q.
2016-01-01
In correlated oxides the coupling of quasiparticles to other degrees of freedom such as spin and lattice plays critical roles in the emergence of symmetry-breaking quantum ordered states such as high temperature superconductivity. We report a strong lattice coupling of photon-induced quasiparticles in spin-orbital coupling Mott insulator Sr2IrO4 probed via optical excitation. Combining time-resolved x-ray diffraction and optical spectroscopy techniques, we reconstruct a spatiotemporal map of the diffusion of these quasiparticles. Due to the unique electronic configuration of the quasiparticles, the strong lattice correlation is unexpected but extends the similarity between Sr2IrO4 and cuprates to a new dimension of electron-phonon coupling which persists under highly non-equilibrium conditions. PMID:26787094
Zvonarev, M B; Cheianov, V V; Giamarchi, T
2009-09-11
We investigate the dynamics of the one-dimensional strongly repulsive spin-1/2 Bose-Hubbard model for filling nu
Shen, Kyle Michael
2005-09-02
It is widely believed that many of the exotic physical properties of the high-T{sub c} cuprate superconductors arise from the proximity of these materials to the strongly correlated, antiferromagnetic Mott insulating state. Therefore, one of the fundamental questions in the field of high-temperature superconductivity is to understand the insulator-to-superconductor transition and precisely how the electronic structure of Mott insulator evolves as the first holes are doped into the system. This dissertation presents high-resolution, doping dependent angle-resolved photoemission (ARPES) studies of the cuprate superconductor Ca{sub 2-x}Na{sub x}CuO{sub 2}Cl{sub 2}, spanning from the undoped parent Mott insulator to a high-temperature superconductor with a T{sub c} of 22 K. A phenomenological model is proposed to explain how the spectral lineshape, the quasiparticle band dispersion, and the chemical potential all progress with doping in a logical and self-consistent framework. This model is based on Franck-Condon broadening observed in polaronic systems where strong electron-boson interactions cause the quasiparticle residue, Z, to be vanishingly small. Comparisons of the low-lying states to different electronic states in the valence band strongly suggest that the coupling of the photohole to the lattice (i.e. lattice polaron formation) is the dominant broadening mechanism for the lower Hubbard band states. Combining this polaronic framework with high-resolution ARPES measurements finally provides a resolution to the long-standing controversy over the behavior of the chemical potential in the high-T{sub c} cuprates. This scenario arises from replacing the conventional Fermi liquid quasiparticle interpretation of the features in the Mott insulator by a Franck-Condon model, allowing the reassignment of the position of the quasiparticle pole. As a function of hole doping, the chemical potential shifts smoothly into the valence band while spectral weight is transferred
MacLeod, Bradley A; Horwitz, Noah E; Ratcliff, Erin L; Jenkins, Judith L; Armstrong, Neal R; Giordano, Anthony J; Hotchkiss, Peter J; Marder, Seth R; Campbell, Charles T; Ginger, David S
2012-05-03
We use electroabsorption spectroscopy to measure the change in built-in potential (VBI) across the polymer photoactive layer in diodes where indium tin oxide electrodes are systematically modified using dipolar phosphonic acid self-assembled monolayers (SAMs) with various dipole moments. We find that VBI scales linearly with the work function (Φ) of the SAM-modified electrode over a wide range when using a solution-coated poly(p-phenylenevinylene) derivative as the active layer. However, we measure an interfacial parameter of S = eΔVBI/ΔΦ < 1, suggesting that these ITO/SAM/polymer interfaces deviate from the Schottky-Mott limit, in contrast to what has previously been reported for a number of ambient-processed organic-on-electrode systems. Our results suggest that the energetics at these ITO/SAM/polymer interfaces behave more like metal/organic interfaces previously studied in UHV despite being processed from solution.
NASA Astrophysics Data System (ADS)
Rhee, H. B.; Pickett, W. E.
2014-11-01
We investigate the electronic and magnetic structures and the character and direction of spin and orbital moments of the recently synthesized quadruple perovskite compound CaCo3V4O12 using a selection of methods from density functional theory. Implementing the generalized gradient approximation and the Hubbard U correction (GGA+U ), ferromagnetic spin alignment leads to half-metallicity rather than the observed narrow gap insulating behavior. Including spin-orbit coupling (SOC) leaves a Mott insulating spectrum but with a negligible gap. SOC is crucial for the Mott insulating character of the V d1 ion, breaking the dm =±1 degeneracy and also giving a substantial orbital moment. Evidence is obtained of the large orbital moments on Co that have been inferred from the measured susceptibility. Switching to the orbital polarization (OP) functional, GGA+OP+SOC also displays clear tendencies toward very large orbital moments but in its own distinctive manner. In both approaches, application of SOC, which requires specification of the direction of the spin, introduces large differences in the orbital moments of the three Co ions in the primitive cell. We study a fictitious but simpler cousin compound Ca3CoV4O12 (Ca replacing two of the Co atoms) to probe in a more transparent fashion the interplay of spin and orbital degrees of freedom with the local environment of the planar CoO4 units. The observation is made that the underlying mechanisms seem to be local to a CoO4 plaquette, and that there is very strong coupling of the size of the orbital moment to the spin direction. These facts strongly suggest noncollinear spins, not only on Co but on the V sublattice as well.
Small Angle Neutron Scattering
Urban, Volker S
2012-01-01
Small Angle Neutron Scattering (SANS) probes structural details at the nanometer scale in a non-destructive way. This article gives an introduction to scientists who have no prior small-angle scattering knowledge, but who seek a technique that allows elucidating structural information in challenging situations that thwart approaches by other methods. SANS is applicable to a wide variety of materials including metals and alloys, ceramics, concrete, glasses, polymers, composites and biological materials. Isotope and magnetic interactions provide unique methods for labeling and contrast variation to highlight specific structural features of interest. In situ studies of a material s responses to temperature, pressure, shear, magnetic and electric fields, etc., are feasible as a result of the high penetrating power of neutrons. SANS provides statistical information on significant structural features averaged over the probed sample volume, and one can use SANS to quantify with high precision the structural details that are observed, for example, in electron microscopy. Neutron scattering is non-destructive; there is no need to cut specimens into thin sections, and neutrons penetrate deeply, providing information on the bulk material, free from surface effects. The basic principles of a SANS experiment are fairly simple, but the measurement, analysis and interpretation of small angle scattering data involves theoretical concepts that are unique to the technique and that are not widely known. This article includes a concise description of the basics, as well as practical know-how that is essential for a successful SANS experiment.
Nanowire electron scattering spectroscopy
NASA Technical Reports Server (NTRS)
Hunt, Brian D. (Inventor); Bronikowski, Michael (Inventor); Wong, Eric W. (Inventor); von Allmen, Paul (Inventor); Oyafuso, Fabiano A. (Inventor)
2009-01-01
Methods and devices for spectroscopic identification of molecules using nanoscale wires are disclosed. According to one of the methods, nanoscale wires are provided, electrons are injected into the nanoscale wire; and inelastic electron scattering is measured via excitation of low-lying vibrational energy levels of molecules bound to the nanoscale wire.
Fluorescence and Light Scattering
ERIC Educational Resources Information Center
Clarke, Ronald J.; Oprysa, Anna
2004-01-01
The aim of the mentioned experiment is to aid students in developing tactics for distinguishing between signals originating from fluorescence and light scattering. Also, the experiment provides students with a deeper understanding of the physicochemical bases of each phenomenon and shows that the techniques are actually related.
Small angle neutron scattering
NASA Astrophysics Data System (ADS)
Cousin, Fabrice
2015-10-01
Small Angle Neutron Scattering (SANS) is a technique that enables to probe the 3-D structure of materials on a typical size range lying from ˜ 1 nm up to ˜ a few 100 nm, the obtained information being statistically averaged on a sample whose volume is ˜ 1 cm3. This very rich technique enables to make a full structural characterization of a given object of nanometric dimensions (radius of gyration, shape, volume or mass, fractal dimension, specific area…) through the determination of the form factor as well as the determination of the way objects are organized within in a continuous media, and therefore to describe interactions between them, through the determination of the structure factor. The specific properties of neutrons (possibility of tuning the scattering intensity by using the isotopic substitution, sensitivity to magnetism, negligible absorption, low energy of the incident neutrons) make it particularly interesting in the fields of soft matter, biophysics, magnetic materials and metallurgy. In particular, the contrast variation methods allow to extract some informations that cannot be obtained by any other experimental techniques. This course is divided in two parts. The first one is devoted to the description of the principle of SANS: basics (formalism, coherent scattering/incoherent scattering, notion of elementary scatterer), form factor analysis (I(q→0), Guinier regime, intermediate regime, Porod regime, polydisperse system), structure factor analysis (2nd Virial coefficient, integral equations, characterization of aggregates), and contrast variation methods (how to create contrast in an homogeneous system, matching in ternary systems, extrapolation to zero concentration, Zero Averaged Contrast). It is illustrated by some representative examples. The second one describes the experimental aspects of SANS to guide user in its future experiments: description of SANS spectrometer, resolution of the spectrometer, optimization of spectrometer
A Discrete Scatterer Technique for Evaluating Electromagnetic Scattering from Trees
2016-09-01
ARL-TR-7799 ● SEP 2016 US Army Research Laboratory A Discrete Scatterer Technique for Evaluating Electromagnetic Scattering from...longer needed. Do not return it to the originator. ARL-TR-7799 ● SEP 2016 US Army Research Laboratory A Discrete Scatterer Technique ... Technique for Evaluating Electromagnetic Scattering from Trees 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S
The Classical Scattering of Waves: Some Analogies with Quantum Scattering
1992-01-01
Code . Approved for public release; distribution is unlimited. 13. Abstract (Maximum 200 words). The scattering of waves in classical physics and quantum...both areas. 92-235222’ 14. Subject Terms. IS. Number of Page. Acoustic scattering , shallow water, waveguide propagation . 27 16. Price Code . 17. Security...Numbers. The Classical Scattering of Waves: Some Analogies with Quantum Scattering Contract ,~~ ~ -V ,~Pom Element NO- 0601153N 6. Author(s). t
FDTD scattered field formulation for scatterers in stratified dispersive media.
Olkkonen, Juuso
2010-03-01
We introduce a simple scattered field (SF) technique that enables finite difference time domain (FDTD) modeling of light scattering from dispersive objects residing in stratified dispersive media. The introduced SF technique is verified against the total field scattered field (TFSF) technique. As an application example, we study surface plasmon polariton enhanced light transmission through a 100 nm wide slit in a silver film.
Angle resolved scatter measurement of bulk scattering in transparent ceramics
NASA Astrophysics Data System (ADS)
Sharma, Saurabh; Miller, J. Keith; Shori, Ramesh K.; Goorsky, Mark S.
2015-02-01
Bulk scattering in polycrystalline laser materials (PLM), due to non-uniform refractive index across the bulk, is regarded as the primary loss mechanism leading to degradation of laser performance with higher threshold and lower output power. The need for characterization techniques towards identifying bulk scatter and assessing the quality. Assessment of optical quality and the identification of bulk scatter have been by simple visual inspection of thin samples of PLMs, thus making the measurements highly subjective and inaccurate. Angle Resolved Scatter (ARS) measurement allows for the spatial mapping of scattered light at all possible angles about a sample, mapping the intensity for both forward scatter and back-scatter regions. The cumulative scattered light intensity, in the forward scatter direction, away from the specular beam is used for the comparison of bulk scattering between samples. This technique employ the detection of scattered light at all angles away from the specular beam directions and represented as a 2-D polar map. The high sensitivity of the ARS technique allows us to compare bulk scattering in different PLM samples which otherwise had similar transmitted beam wavefront distortions.
NASA Astrophysics Data System (ADS)
Lee, Mark D.; Jenkins, Stewart D.; Ruostekoski, Janne
2016-06-01
We derive equations for the strongly coupled system of light and dense atomic ensembles. The formalism includes an arbitrary internal-level structure for the atoms and is not restricted to weak excitation of atoms by light. In the low-light-intensity limit for atoms with a single electronic ground state, the full quantum field-theoretical representation of the model can be solved exactly by means of classical stochastic electrodynamics simulations for stationary atoms that represent cold atomic ensembles. Simulations for the optical response of atoms in a quantum degenerate regime require one to synthesize a stochastic ensemble of atomic positions that generates the corresponding quantum statistical position correlations between the atoms. In the case of multiple ground levels or at light intensities where saturation becomes important, the classical simulations require approximations that neglect quantum fluctuations between the levels. We show how the model is extended to incorporate corrections due to quantum fluctuations that result from virtual scattering processes. In the low-light-intensity limit, we illustrate the simulations in a system of atoms in a Mott-insulator state in a two-dimensional optical lattice, where recurrent scattering of light induces strong interatomic correlations. These correlations result in collective many-atom subradiant and superradiant states and a strong dependence of the response on the spatial confinement within the lattice sites.
Scattering of fermions by gravitons
NASA Astrophysics Data System (ADS)
Ulhoa, S. C.; Santos, A. F.; Khanna, Faqir C.
2017-04-01
The interaction between gravitons and fermions is investigated in the teleparallel gravity. The scattering of fermions and gravitons in the weak field approximation is analyzed. The transition amplitudes of M\\varnothing ller, Compton and new gravitational scattering are calculated.
Interface scattering in polycrystalline thermoelectrics
Popescu, Adrian; Haney, Paul M.
2014-03-28
We study the effect of electron and phonon interface scattering on the thermoelectric properties of disordered, polycrystalline materials (with grain sizes larger than electron and phonons' mean free path). Interface scattering of electrons is treated with a Landauer approach, while that of phonons is treated with the diffuse mismatch model. The interface scattering is embedded within a diffusive model of bulk transport, and we show that, for randomly arranged interfaces, the overall system is well described by effective medium theory. Using bulk parameters similar to those of PbTe and a square barrier potential for the interface electron scattering, we identify the interface scattering parameters for which the figure of merit ZT is increased. We find the electronic scattering is generally detrimental due to a reduction in electrical conductivity; however, for sufficiently weak electronic interface scattering, ZT is enhanced due to phonon interface scattering.
NASA Astrophysics Data System (ADS)
Shogh, Shiva; Mohammadpour, Raheleh; Iraji zad, Azam; Taghavinia, Nima
2015-06-01
The structural, electrical, optical, and photovoltaic properties of aggregated submicron nitrogen-doped TiO2 particles (NTiO2) and the influence of utilizing them, in comparison with undoped ones, as the light-scattering layer of dye-sensitized solar cells were investigated. Field emission scanning electron microscope, X-ray diffraction, and diffuse reflectance spectra showed that both type samples have similar morphology, crystal phase, and scattering feature. Moreover, photoluminescence, Mott-Schottkey, and photovoltaic characteristics such as IMPS/IMVS and charge extraction analysis indicated that the NTiO2 layer is an efficient scatterer in two aspects: enhancement of light-harvesting efficiency by having submicron-size centers and modification of the electrical properties such as charge collection efficiency in photoanode. As a result, the overall conversion efficiency reached 7.34 % upon employing NTiO2 as the light-scattering layer, which is 13 % higher than undoped one. This improvement is a consequence of trap density reduction, electrons transfer enhancement in the interface of photoactive/scattering layer, and shunt resistance increment at photoelectrode/electrolyte interface.
Coherent Scatter Imaging Measurements
NASA Astrophysics Data System (ADS)
Ur Rehman, Mahboob
In conventional radiography, anatomical information of the patients can be obtained, distinguishing different tissue types, e.g. bone and soft tissue. However, it is difficult to obtain appreciable contrast between two different types of soft tissues. Instead, coherent x-ray scattering can be utilized to obtain images which can differentiate between normal and cancerous cells of breast. An x-ray system using a conventional source and simple slot apertures was tested. Materials with scatter signatures that mimic breast cancer were buried in layers of fat of increasing thickness and imaged. The result showed that the contrast and signal to noise ratio (SNR) remained high even with added fat layers and short scan times.
Syzygies probing scattering amplitudes
NASA Astrophysics Data System (ADS)
Chen, Gang; Liu, Junyu; Xie, Ruofei; Zhang, Hao; Zhou, Yehao
2016-09-01
We propose a new efficient algorithm to obtain the locally minimal generating set of the syzygies for an ideal, i.e. a generating set whose proper subsets cannot be generating sets. Syzygy is a concept widely used in the current study of scattering amplitudes. This new algorithm can deal with more syzygies effectively because a new generation of syzygies is obtained in each step and the irreducibility of this generation is also verified in the process. This efficient algorithm can also be applied in getting the syzygies for the modules. We also show a typical example to illustrate the potential application of this method in scattering amplitudes, especially the Integral-By-Part(IBP) relations of the characteristic two-loop diagrams in the Yang-Mills theory.
Cable, J.W.
1987-01-01
The diffuse scattering of neutrons from magnetic materials provides unique and important information regarding the spatial correlations of the atoms and the spins. Such measurements have been extensively applied to magnetically ordered systems, such as the ferromagnetic binary alloys, for which the observed correlations describe the magnetic moment fluctuations associated with local environment effects. With the advent of polarization analysis, these techniques are increasingly being applied to study disordered paramagnetic systems such as the spin-glasses and the diluted magnetic semiconductors. The spin-pair correlations obtained are essential in understanding the exchange interactions of such systems. In this paper, we describe recent neutron diffuse scattering results on the atom-pair and spin-pair correlations in some of these disordered magnetic systems. 56 refs.
Vernon, M.F.
1983-07-01
The molecular-beam technique has been used in three different experimental arrangements to study a wide range of inter-atomic and molecular forces. Chapter 1 reports results of a low-energy (0.2 kcal/mole) elastic-scattering study of the He-Ar pair potential. The purpose of the study was to accurately characterize the shape of the potential in the well region, by scattering slow He atoms produced by expanding a mixture of He in N/sub 2/ from a cooled nozzle. Chapter 2 contains measurements of the vibrational predissociation spectra and product translational energy for clusters of water, benzene, and ammonia. The experiments show that most of the product energy remains in the internal molecular motions. Chapter 3 presents measurements of the reaction Na + HCl ..-->.. NaCl + H at collision energies of 5.38 and 19.4 kcal/mole. This is the first study to resolve both scattering angle and velocity for the reaction of a short lived (16 nsec) electronic excited state. Descriptions are given of computer programs written to analyze molecular-beam expansions to extract information characterizing their velocity distributions, and to calculate accurate laboratory elastic-scattering differential cross sections accounting for the finite apparatus resolution. Experimental results which attempted to determine the efficiency of optically pumping the Li(2/sup 2/P/sub 3/2/) and Na(3/sup 2/P/sub 3/2/) excited states are given. A simple three-level model for predicting the steady-state fraction of atoms in the excited state is included.
2010-09-01
we refer to the linear polarization as parallel if the polarization vector is in the scattering plane or perpendicular if the polarization vector is...obvious that the different polarization states can all be represented as linear combinations of any of the independent pairs of polarization states...J.C. (1976) “Improvement of underwater visibility by reduction of backscatter with a circular polarization technique, Applied Optics, 6, 321-330
NASA Astrophysics Data System (ADS)
Bonelli, G.; Bonora, L.; Nesti, F.; Tomasiello, A.; Terna, S.
This is a review of some recent developments in the study of classical solutions of Yang-Mills theories in various dimensions and their significance in the path integral of the corresponding theories. These particular solutions are called instantons because of their kinship with ordinary instantons. Just as ordinary instantons interpolate between different vacua, the new instantons interpolate between different asymptotic states. Therefore they represent scattering phenomena. Here we review the two dimensional and four dimensional Yang-Mills case.
Inverse Scattering and Tomography
1989-11-27
404. [3] J. Duchon, Interpolation des Fonctions de Deux Variables Suivant le Principe de la Flexion des Plaques Minces, RAIRO Analyse Numerique, 10...d’Interpolation des Fonctions de Pusleurs Variables par les D M-splines, RAIRO Analyse Numerigue 12 (1978), 325 - 334. [6] R. Franke, Scattered data...splines, RAIRO Analyse Numerigue 12 (1978), 325-334. [7] I. M. Gelfand and N. Ya. Vilenkin, Generalized Functions, Vol. 4, Academic Press, New York
Neutron scattering in Australia
Knott, R.B.
1994-12-31
Neutron scattering techniques have been part of the Australian scientific research community for the past three decades. The High Flux Australian Reactor (HIFAR) is a multi-use facility of modest performance that provides the only neutron source in the country suitable for neutron scattering. The limitations of HIFAR have been recognized and recently a Government initiated inquiry sought to evaluate the future needs of a neutron source. In essence, the inquiry suggested that a delay of several years would enable a number of key issues to be resolved, and therefore a more appropriate decision made. In the meantime, use of the present source is being optimized, and where necessary research is being undertaken at major overseas neutron facilities either on a formal or informal basis. Australia has, at present, a formal agreement with the Rutherford Appleton Laboratory (UK) for access to the spallation source ISIS. Various aspects of neutron scattering have been implemented on HIFAR, including investigations of the structure of biological relevant molecules. One aspect of these investigations will be presented. Preliminary results from a study of the interaction of the immunosuppressant drug, cyclosporin-A, with reconstituted membranes suggest that the hydrophobic drug interdigitated with lipid chains.
NASA Astrophysics Data System (ADS)
Xie, Ya-Ming; Ji, Xia
Nowadays, with the development of technology, particles with size at nanoscale have been synthesized in experiments. It is noticed that anisotropy is an unavoidable problem in the production of nanospheres. Besides, nonspherical nanoparticles have also been extensively used in experiments. Comparing with spherical model, spheroidal model can give a better description for the characteristics of nonspherical particles. Thus the study of analytical solution for light scattering by spheroidal particles has practical implications. By expanding incident, scattered, and transmitted electromagnetic fields in terms of appropriate vector spheroidal wave functions, an analytic solution is obtained to the problem of light scattering by spheroids. Unknown field expansion coefficients can be determined with the combination of boundary conditions and rotational-translational addition theorems for vector spheroidal wave functions. Based on the theoretical derivation, a Fortran code has been developed to calculate the extinction cross section and field distribution, whose results agree well with those obtain by FDTD simulation. This research is supported by the National Natural Science Foundation of China No. 91230203.
Nanowire Electron Scattering Spectroscopy
NASA Technical Reports Server (NTRS)
Hunt, Brian; Bronikowsky, Michael; Wong, Eric; VonAllmen, Paul; Oyafuso, Fablano
2009-01-01
Nanowire electron scattering spectroscopy (NESS) has been proposed as the basis of a class of ultra-small, ultralow-power sensors that could be used to detect and identify chemical compounds present in extremely small quantities. State-of-the-art nanowire chemical sensors have already been demonstrated to be capable of detecting a variety of compounds in femtomolar quantities. However, to date, chemically specific sensing of molecules using these sensors has required the use of chemically functionalized nanowires with receptors tailored to individual molecules of interest. While potentially effective, this functionalization requires labor-intensive treatment of many nanowires to sense a broad spectrum of molecules. In contrast, NESS would eliminate the need for chemical functionalization of nanowires and would enable the use of the same sensor to detect and identify multiple compounds. NESS is analogous to Raman spectroscopy, the main difference being that in NESS, one would utilize inelastic scattering of electrons instead of photons to determine molecular vibrational energy levels. More specifically, in NESS, one would exploit inelastic scattering of electrons by low-lying vibrational quantum states of molecules attached to a nanowire or nanotube.
Rutherford scattering of electron vortices
NASA Astrophysics Data System (ADS)
Van Boxem, Ruben; Partoens, Bart; Verbeeck, Johan
2014-03-01
By considering a cylindrically symmetric generalization of a plane wave, the first-order Born approximation of screened Coulomb scattering unfolds two new dimensions in the scattering problem: transverse momentum and orbital angular momentum of the incoming beam. In this paper, the elastic Coulomb scattering amplitude is calculated analytically for incoming Bessel beams. This reveals novel features occurring for wide-angle scattering and quantitative insights for small-angle vortex scattering. The result successfully generalizes the well-known Rutherford formula, incorporating transverse and orbital angular momentum into the formalism.
Gravitational scattering of electromagnetic radiation
NASA Technical Reports Server (NTRS)
Brooker, J. T.; Janis, A. I.
1980-01-01
The scattering of electromagnetic radiation by linearized gravitational fields is studied to second order in a perturbation expansion. The incoming electromagnetic radiation can be of arbitrary multipole structure, and the gravitational fields are also taken to be advanced fields of arbitrary multipole structure. All electromagnetic multipole radiation is found to be scattered by gravitational monopole and time-varying dipole fields. No case has been found, however, in which any electromagnetic multipole radiation is scattered by gravitational fields of quadrupole or higher-order multipole structure. This lack of scattering is established for infinite classes of special cases, and is conjectured to hold in general. The results of the scattering analysis are applied to the case of electromagnetic radiation scattered by a moving mass. It is shown how the mass and velocity may be determined by a knowledge of the incident and scattered radiation.
Improved scatter correction using adaptive scatter kernel superposition
NASA Astrophysics Data System (ADS)
Sun, M.; Star-Lack, J. M.
2010-11-01
Accurate scatter correction is required to produce high-quality reconstructions of x-ray cone-beam computed tomography (CBCT) scans. This paper describes new scatter kernel superposition (SKS) algorithms for deconvolving scatter from projection data. The algorithms are designed to improve upon the conventional approach whose accuracy is limited by the use of symmetric kernels that characterize the scatter properties of uniform slabs. To model scatter transport in more realistic objects, nonstationary kernels, whose shapes adapt to local thickness variations in the projection data, are proposed. Two methods are introduced: (1) adaptive scatter kernel superposition (ASKS) requiring spatial domain convolutions and (2) fast adaptive scatter kernel superposition (fASKS) where, through a linearity approximation, convolution is efficiently performed in Fourier space. The conventional SKS algorithm, ASKS, and fASKS, were tested with Monte Carlo simulations and with phantom data acquired on a table-top CBCT system matching the Varian On-Board Imager (OBI). All three models accounted for scatter point-spread broadening due to object thickening, object edge effects, detector scatter properties and an anti-scatter grid. Hounsfield unit (HU) errors in reconstructions of a large pelvis phantom with a measured maximum scatter-to-primary ratio over 200% were reduced from -90 ± 58 HU (mean ± standard deviation) with no scatter correction to 53 ± 82 HU with SKS, to 19 ± 25 HU with fASKS and to 13 ± 21 HU with ASKS. HU accuracies and measured contrast were similarly improved in reconstructions of a body-sized elliptical Catphan phantom. The results show that the adaptive SKS methods offer significant advantages over the conventional scatter deconvolution technique.
Scattering Solar Thermal Concentrators
Giebink, Noel C.
2015-01-31
This program set out to explore a scattering-based approach to concentrate sunlight with the aim of improving collector field reliability and of eliminating wind loading and gross mechanical movement through the use of a stationary collection optic. The approach is based on scattering sunlight from the focal point of a fixed collection optic into the confined modes of a sliding planar waveguide, where it is transported to stationary tubular heat transfer elements located at the edges. Optical design for the first stage of solar concentration, which entails focusing sunlight within a plane over a wide range of incidence angles (>120 degree full field of view) at fixed tilt, led to the development of a new, folded-path collection optic that dramatically out-performs the current state-of-the-art in scattering concentration. Rigorous optical simulation and experimental testing of this collection optic have validated its performance. In the course of this work, we also identified an opportunity for concentrating photovoltaics involving the use of high efficiency microcells made in collaboration with partners at the University of Illinois. This opportunity exploited the same collection optic design as used for the scattering solar thermal concentrator and was therefore pursued in parallel. This system was experimentally demonstrated to achieve >200x optical concentration with >70% optical efficiency over a full day by tracking with <1 cm of lateral movement at fixed latitude tilt. The entire scattering concentrator waveguide optical system has been simulated, tested, and assembled at small scale to verify ray tracing models. These models were subsequently used to predict the full system optical performance at larger, deployment scale ranging up to >1 meter aperture width. Simulations at an aperture widths less than approximately 0.5 m with geometric gains ~100x predict an overall optical efficiency in the range 60-70% for angles up to 50 degrees from normal. However, the
NASA Astrophysics Data System (ADS)
Liu, Peitao; Reticcioli, Michele; Kim, Bongjae; Continenza, Alessandra; Kresse, Georg; Sarma, D. D.; Chen, Xing-Qiu; Franchini, Cesare
2016-11-01
We study the effects of dilute La and Rh substitutional doping on the electronic structure of the relativistic Mott insulator Sr2IrO4 using fully relativistic and magnetically noncollinear density functional theory with the inclusion of an on-site Hubbard U . To model doping effects, we have adopted the supercell approach, that allows for a realistic treatment of structural relaxations and electronic effects beyond a purely rigid band approach. By means of the band unfolding technique we have computed the spectral function and constructed the effective band structure and Fermi surface (FS) in the primitive cell, which are readily comparable with available experimental data. Our calculations clearly indicate that La and Rh doping can be interpreted as effective electron and (fractional) hole doping, respectively. We found that both electron and hole doping induce an insulating-to-metal transition (IMT) but with different characteristics. In Sr2 -xLaxIrO4 the IMT is accompanied by a moderate renormalization of the electronic correlation substantiated by a reduction of the effective on-site Coulomb repulsion U -J from 1.6 eV (x =0 ) to 1.4 eV (metallic regime of x =12.5 % ). The progressive closing of the relativistic Mott gap leads to the emergence of connected elliptical electron pockets at (π /2 ,π /2 ) and less intense features at X on the Fermi surface. The average ordered magnetic moment is slightly reduced upon doping, but the canted antiferromagnetic state is perturbed on the Ir-O planes located near the La atoms. The substitution of Ir with the nominally isovalent Rh is accompanied by a substantial hole transfer from the Rh site to the nearest-neighbor Ir sites. This shifts down the chemical potential, creates almost circular disconnected hole pockets in the FS, and establishes the emergence of a two-dimensional metallic state formed by conducting Rh planes intercalated by insulating Ir planes. Finally, our data indicate that hole doping causes a flipping
Scattering from Superquadric Surfaces
1988-06-01
for any purpose other than in connection with a definitely related Government procurement operation, the United States Government thereby incurs no...Clomparative C’PU times in VPU (VAX 780 Processing Units ) 44 3 I I I I I I I I I I * Chapter 1 | INTRODUCTION I The electromagnetic scattering from a...in the Shadow region (2.4) where ft is the unit normal to the surface. Physical Optics is useful because the form of the assumed currents is 3 simple
Apparent optical density of the scattering medium: influence of scattering
NASA Astrophysics Data System (ADS)
Kiseleva, Irina A.; Sinichkin, Yurii P.
2002-07-01
Comparative analysis of manifestation of finite absorption in scattering media is carried out for different detection geometries. Reflectance spectra were studied for phantom scattering media containing blood and melanin as absorbers. Apparent optical density spectra of phantom media are compared with similar spectra of water solutions of the blood and melanin for same concentrations of absorbers. The influence of scattering properties on optical density spectra is discussed with use of the model of diffuse light propagation in semi-infinite media.
A New Polyethylene Scattering Law Determined Using Inelastic Neutron Scattering
Lavelle, Christopher M; Liu, C; Stone, Matthew B
2013-01-01
Monte Carlo neutron transport codes such as MCNP rely on accurate data for nuclear physics cross-sections to produce accurate results. At low energy, this takes the form of scattering laws based on the dynamic structure factor, S (Q, E). High density polyethylene (HDPE) is frequently employed as a neutron moderator at both high and low temperatures, however the only cross-sections available are for T =300 K, and the evaluation has not been updated in quite some time. In this paper we describe inelastic neutron scattering measurements on HDPE at 5 and 300 K which are used to improve the scattering law for HDPE. We describe the experimental methods, review some of the past HDPE scattering laws, and compare computations using these models to the measured S (Q, E). The total cross-section is compared to available data, and the treatment of the carbon secondary scatterer as a free gas is assessed. We also discuss the use of the measurement itself as a scattering law via the 1 phonon approximation. We show that a scattering law computed using a more detailed model for the Generalized Density of States (GDOS) compares more favorably to this experiment, suggesting that inelastic neutron scattering can play an important role in both the development and validation of new scattering laws for Monte Carlo work.
Protostring scattering amplitudes
NASA Astrophysics Data System (ADS)
Thorn, Charles B.
2016-11-01
We calculate some tree-level scattering amplitudes for a generalization of the protostring, which is a novel string model implied by the simplest string bit models. These bit models produce a light-cone world sheet which supports s integer moded Grassmann fields. In the generalization we supplement this Grassmann world-sheet system with d =24 -s transverse coordinate world-sheet fields. The protostring corresponds to s =24 and the bosonic string to s =0 . The interaction vertex is a simple overlap with no operator insertions at the break/join point. Assuming that s is even we calculate the multistring scattering amplitudes by bosonizing the Grassmann fields, each pair equivalent to one compactified bosonic field, and applying Mandelstam's interacting string formalism to a system of s /2 compactified and d uncompactified bosonic world-sheet fields. We obtain all amplitudes for open strings with no oscillator excitations and for closed strings with no oscillator excitations and zero winding number. We then study in detail some simple special cases. Multistring processes with maximal helicity violation have much simpler amplitudes. We also specialize to general four-string amplitudes and discuss their high energy behavior. Most of these models are not covariant under the full Lorentz group O (d +1 ,1 ). The exceptions are the bosonic string whose Lorentz group is O (25 ,1 ) and the protostring whose Lorentz group is O (1 ,1 ). The models in between only enjoy an O (1 ,1 )×O (d ) spacetime symmetry.
Rayleigh, Raman and particulate scattering
NASA Technical Reports Server (NTRS)
Cochran, W. D.
1982-01-01
Analysis of the visible and near infrared spectra of planetary atmospheres and the multiple scattering of photons within the atmosphere are discussed. Photons detected within the spectral region are solar photons which were scattered by the gas and particles in the planetary atmosphere. An example is given for the incident and emitted fluxes for a hypothetical planet with an effective temperature of 100 K. The absorption spectrum of the planetary atmosphere is discussed in terms of the various scattering processes photons undergo within the atmosphere. Three different physical processes are considered. Rayleigh scattering and Raman scattering by the gas molecules, and scattering by any cloud or dust aerosol particles in the atmosphere. The physics of each of these processes is examined.
Optical investigation of the quasi-two-dimensional Mott system Ca_2-xSr_xRuO4 (0.0<= x<= 2.0)
NASA Astrophysics Data System (ADS)
Lee, J. S.; Noh, T. W.; Lee, Y. S.; Oh, S.-J.; Nakatsuji, S.; Maeno, Y.
2002-03-01
The doping and temperature dependent optical conductivity spectra σ (ω ) in the ab-plane of the quasi-two-dimensional system Ca_2-xSr_xRuO4 (0.0<= x<= 2.0) were investigated. For all over the metallic doping concentration of x>= 0.2, the σ (ω ) show features of the Mott-Hubbard system. However, the insulating spectra of x=0.00 and 0.06 show an unusual two-peak structure around 1.0 and 2.0 eV. From the systematic changes with doping, it was found that both excitations have the correlation-induced Ru 4 d characters. Interestingly, for the x=0.06 sample, softening of the streching phonon mode and strong spectral weight redistribution between these two peaks were observed with decreasing temperature. These could be understood by the orbital occupancy changes with the RuO6 octahedral flattening. Possible connections to the critical behaviors of the specific heat and susceptibility at x=0.5 will be also discussed.
Krakauer, Henry; Zhang, Shiwei
2013-02-21
There are classes of materials that are important to DOE and to the science and technology community, generically referred to as strongly correlated electron systems (SCES), which have proven very difficult to understand and to simulate in a material-specific manner. These range from actinides, which are central to the DOE mission, to transition metal oxides, which include the most promising components of new spin electronics applications as well as the high temperature superconductors, to intermetallic compounds whose heavy fermion characteristics and quantum critical behavior has given rise to some of the most active areas in condensed matter theory. The objective of the CMSN cooperative research team was to focus on the application of these new methodologies to the specific issue of Mott transitions, multi-electron magnetic moments, and dynamical properties correlated materials. Working towards this goal, the W&M team extended its first-principles phaseless auxiliary-field quantum Monte Carlo (AFQMC) method to accurately calculate structural phase transitions and excited states.
Li, Yamei; Ji, Shidong; Gao, Yanfeng; Luo, Hongjie; Jin, Ping
2013-07-24
Vanadium dioxide (VO2) is a key material for thermochromic smart windows that can respond to environmental temperature and modulate near-infrared irradiation by changing from a transparent state at low temperature to a more reflective state at high temperature, while maintaining visible transmittance. Here, we demonstrate for the first time that the Mott phase transition characteristics in VO2 nanoparticles can be remarkably modified by misfit strains occurring at the epitaxial interface between VO2 and the anatase TiO2 of VO2/TiO2 core-shell particles. The heteroepitaxial growth of the as-synthesized particles followed an unprecedented orientation relationship, and an epitaxial growth mechanism is proposed to explain this behavior. A relatively small theoretical coherent misfit (3-11%) and a moderate heating rate (20 °C·min(-1)) in the preparation of the core-shell structure were critically important from the thermodynamic and kinetic perspectives, respectively. The misfit-induced interfacial strain along the uniaxial cR axis increased the transition temperatures, especially on the cooling portion of the heating-cooling cycle, leading to a notably reduced transition hysteresis loop width (from 23.5 to 12.0 °C). Moreover, the optical band gap was also engineered by the interfacial effect. Such a reduced hysteresis showed a benefit for enhancing a rapid response for energy saving thermochromic smart windows.
Two-dimensional superconductivity at a Mott insulator/band insulator interface LaTiO3/SrTiO3.
Biscaras, J; Bergeal, N; Kushwaha, A; Wolf, T; Rastogi, A; Budhani, R C; Lesueur, J
2010-10-05
Transition metal oxides show a great variety of quantum electronic behaviours where correlations often have an important role. The achievement of high-quality epitaxial interfaces involving such materials gives a unique opportunity to engineer artificial structures where new electronic orders take place. One of the most striking result in this area is the recent observation of a two-dimensional electron gas at the interface between a strongly correlated Mott insulator LaTiO(3) and a band insulator SrTiO(3). The mechanism responsible for such a behaviour is still under debate. In particular, the influence of the nature of the insulator has to be clarified. In this article, we show that despite the expected electronic correlations, LaTiO(3)/SrTiO(3) heterostructures undergo a superconducting transition at a critical temperature T(c)(onset)~300 mK. We have found that the superconducting electron gas is confined over a typical thickness of 12 nm and is located mostly on the SrTiO(3) substrate.
NASA Astrophysics Data System (ADS)
Zhou, J.-S.; Cao, L.-P.; Alonso, J. A.; Sanchez-Benitez, J.; Fernandez-Diaz, M. T.; Li, X.; Cheng, J.-G.; Marshall, L. G.; Jin, C.-Q.; Goodenough, J. B.
2016-10-01
Whether CaCr O3 is a Mott insulator or a correlated metal is still controversial. We have performed measurements of magnetization, specific heat, and thermal conductivity on CaCr O3 samples selected from many batches of high-pressure synthesis. The single-crystal CaCr O3 sample exhibits an unprecedentedly sharp transition at a Néel temperature TN≈90 K . The critical behavior of specific heat cannot be rationalized by the renormalization group theory for a second-order magnetic transition. More surprisingly, the thermal conductivity κ exhibits an anomalous drop on cooling through TN, which is opposite to all known influence on κ from either spin or orbital ordering. We have argued, on the basis of anomalies found in all three measurements and structural data, for the coexistence of itinerant π-bonding electrons in a c -axis band and localized x y electrons in x y orbitals responsible for type-C antiferromagnetic order below TN and the occupation of a pure, localized x y orbital undergoing a Bose-Einstein condensate at TN.
Watanabe, Hiroshi; Shirakawa, Tomonori; Yunoki, Seiji
2013-01-11
Based on a microscopic theoretical study, we show that novel superconductivity is induced by carrier doping in layered perovskite Ir oxides where a strong spin-orbit coupling causes an effective total angular momentum J(eff)=1/2 Mott insulator. Using a variational Monte Carlo method, we find an unconventional superconducting state in the ground state phase diagram of a t(2g) three-orbital Hubbard model on the square lattice. This superconducting state is characterized by a d(x(2)-y(2))-wave "pseudospin singlet" formed by the J(eff)=1/2 Kramers doublet, which thus contains interorbital as well as both singlet and triplet components of t(2g) electrons. The superconducting state is found stable only by electron doping, but not by hole doping, for the case of carrier doped Sr2IrO4. We also study an effective single-orbital Hubbard model to discuss the similarities to high-T(c) cuprate superconductors and the multiorbital effects.
NASA Astrophysics Data System (ADS)
Arakawa, Naoya
2016-11-01
I propose the emergence of the spin-orbital-coupled vector chirality in a nonfrustrated Mott insulator with the strong spin-orbit coupling due to a b -plane's inversion-symmetry (IS) breaking. I derive the superexchange interactions for a t2 g-orbital Hubbard model on a square lattice with the strong spin-orbit coupling and the IS-breaking-induced hopping integrals, and explain the microscopic origins of the Dzyaloshinsky-Moriya (DM) -type and the Kitaev-type interactions. Then, by adopting the mean-field approximation to a minimal model including only the Heisenberg-type and the DM-type nearest-neighbor interactions, I show that the IS breaking causes the spin-orbital-coupled chirality as a result of stabilizing the screw state. I also highlight the limit of the hard-pseudospin approximation in discussing the stability of the screw states in the presence of both the DM-type and the Kitaev-type interactions, and discuss its meaning. I finally discuss the effects of tetragonal crystal field and Jeff=3/2 states, and the application to the iridates near the [001 ] surface of Sr2IrO4 and the interface between Sr2IrO4 and Sr3Ir2O7 .
NASA Astrophysics Data System (ADS)
Ogwu, A. A.; Oje, A. M.; Kavanagh, J.
2016-04-01
We report our investigation on chromium oxide thin film coatings that show a negligible ion release during electrochemical corrosion testing in saline solution. The chemical constituents of the films prepared by reactive magnetron sputtering were identified to be predominantly Cr2O3 based on Raman spectroscopy anti-symmetric stretching vibration modes for CrIII-O and other peaks and an FTIR spectroscopy E u vibrational mode at 409 cm-1. X-ray photoelectron spectroscopy, multiplet fitting for 2P 3/2 and 2P 1/2 states also confirmed the predominantly Cr2O3 stoichiometry in the films. The prepared chromium oxide coatings showed superior pitting corrosion resistance compared to the native chromium oxide films on bare uncoated stainless steel when tested under open circuit potential, potentiodynamic polarisation and cyclic voltammetry in saline solution. The chromium ion released into solution during the corrosion testing of stainless steel substrates coated with chromium oxide coatings was found to be negligibly small based on atomic absorption spectroscopy measurements. Our Mott-Schottky analysis investigation showed that the negligibly small ion release from the chromium oxide coated steel substrates is most likely due to a much lower defect density on the surface of the deposited coatings compared to the native oxide layer on the uncoated steel substrates. This opens up the opportunity for using chromium oxide surface coatings in hip, knee and other orthopaedic implants where possible metal ion release in vivo still poses a great challenge.
Engineered Mott ground state in a LaTiO_{3+δ}/LaNiO_{3} heterostructure
Cao, Yanwei; Liu, Xiaoran; Kareev, M.; Choudhury, D.; Middey, S.; Meyers, D.; Kim, J. -W.; Ryan, P. J.; Freeland, J. W.; Chakhalian, J.
2016-01-21
In pursuit of creating cuprate-like electronic and orbital structures, artificial heterostructures based on LaNiO_{3} have inspired a wealth of exciting experimental and theoretical results. However, to date there is a very limited experimental understanding of the electronic and orbital states emerging from interfacial charge transfer and their connections to the modified band structure at the interface. Towards this goal, we have synthesized a prototypical superlattice composed of a correlated metal LaNiO_{3} and a doped Mott insulator LaTiO_{3+δ}, and investigated its electronic structure by resonant X-ray absorption spectroscopy combined with X-ray photoemission spectroscopy, electrical transport and theory calculations. The heterostructure exhibits interfacial charge transfer from Ti to Ni sites, giving rise to an insulating ground state with orbital polarization and e_{g} orbital band splitting. Here, our findings demonstrate how the control over charge at the interface can be effectively used to create exotic electronic, orbital and spin states.
Weak Deeply Virtual Compton Scattering
Ales Psaker; Wolodymyr Melnitchouk; Anatoly Radyushkin
2007-03-01
We extend the analysis of the deeply virtual Compton scattering process to the weak interaction sector in the generalized Bjorken limit. The virtual Compton scattering amplitudes for the weak neutral and charged currents are calculated at the leading twist within the framework of the nonlocal light-cone expansion via coordinate space QCD string operators. Using a simple model, we estimate cross sections for neutrino scattering off the nucleon, relevant for future high intensity neutrino beam facilities.
Advances in total scattering analysis
Proffen, Thomas E; Kim, Hyunjeong
2008-01-01
In recent years the analysis of the total scattering pattern has become an invaluable tool to study disordered crystalline and nanocrystalline materials. Traditional crystallographic structure determination is based on Bragg intensities and yields the long range average atomic structure. By including diffuse scattering into the analysis, the local and medium range atomic structure can be unravelled. Here we give an overview of recent experimental advances, using X-rays as well as neutron scattering as well as current trends in modelling of total scattering data.
Electromagnetic scattering from turbulent plasmas
Resendes, D.G. Instituto Superior Tecnico, Rua Rovisco Pais, Lisboa )
1992-11-15
A self-consistent multiple-scattering theory of vector electromagnetic waves scattered from a turbulent plasma is presented. This approach provides a general and systematic treatment to all orders in turbulence of the scattering of electromagnetic waves in terms of the properties of the turbulent structure of the scattering system and is applicable in the full regime from underdense to overdense plasmas. To illustrate the theory, a plasma consisting of a finite number density of discrete scatterers with a simple geometry and statistical properties is chosen. In this approach the exact solution for a single scatterer is obtained first. From it the configuration-dependent solution for {ital N} scatterers is constructed. Rather than solving explicitly for this solution and then averaging, the averaging operation will be taken first in order to find an approximate equation obeyed by the mean or coherent field. The coherent and incoherent scattering are then determined in terms of the coherent field and the backscatter is evaluated. The coherent and incoherent scattering, our principal results, are expressed in a plane-wave basis in a form suitable for numerical computation. A number of interesting phenomena which may readily be incorporated into the theory are indicated.
Polarization imaging through scattering media
NASA Astrophysics Data System (ADS)
Morgan, Stephen P.; Khong, Manping; Somekh, Michael G.
1995-12-01
The imaging resolution in turbid media is severely degraded by light scattering. Resolution can be improved by extracting the unscattered or weakly scattered light. In this paper the state of polarization of the emerging light is used to discriminate photon pathlength, the more weakly scattered photons maintaining their original polarization state. It is experimentally demonstrated that over a wide range of scatterer concentrations, different particle sizes possess different characteristics. Three distinct regimes are described in detail along with the techniques to improve resolution within these regimes.
Review of light scattering literature
NASA Astrophysics Data System (ADS)
Potts, Marie K.
1994-06-01
This report reviews the recent literature of static and dynamic light scattering of dilute and semidilute polymer solutions and gels, as obtained from the Chemical Abstracts Macromolecular Sections, and an electronic literature search. In general, this review has been confined to the interests of the Polymer Research Branch, specifically experimental light scattering studies of synthetic polymers in solution. In order to further limit the size of this review, light scattering for phase separation studies or particle size analysis have been excluded, as well as light scattering used strictly for size exclusion chromatography detection.
Kegel, Gunter H.R.; Egan, James J
2007-04-18
This project covers four principal areas of research: Elastic and inelastic neutron scattering studies in odd-A terbium, thulium and other highly deformed nuclei near A=160 with special regard to interband transitions and to the investigation of the direct-interaction versus the compound-nucleus excitation process in these nuclei. Examination of new, fast photomultiplier tubes suitable for use in a miniaturized neutron-time-of-flight spectrometer. Measurement of certain inelastic cross sections of 238U. Determination of the multiplicity of prompt fission gamma rays in even-A fissile actinides. Energies and mean lives of fission isomers produced by fast fission of even-Z, even-A actinides. Study of the mean life of 7Be in different host matrices and its possible astro-physical significance.
Fractal radar scattering from soil.
Oleschko, Klaudia; Korvin, Gabor; Figueroa, Benjamin; Vuelvas, Marco Antonio; Balankin, Alexander S; Flores, Lourdes; Carreón, Dora
2003-04-01
A general technique is developed to retrieve the fractal dimension of self-similar soils through microwave (radar) scattering. The technique is based on a mathematical model relating the fractal dimensions of the georadargram to that of the scattering structure. Clear and different fractal signatures have been observed over four geosystems (soils and sediments) compared in this work.
Residue-based scattering factors.
Xu, Hongliang
2016-11-01
A glob is defined as a group of atoms in the crystal which can be chosen in various ways. Globs themselves can be used as scattering elements in the theory of structure determination, just as atoms are used at present. In this paper, amino-acid residues are chosen to form globs and empirical formulas for residue-based scattering factors have been developed.
Scattering matrix theory for stochastic scalar fields.
Korotkova, Olga; Wolf, Emil
2007-05-01
We consider scattering of stochastic scalar fields on deterministic as well as on random media, occupying a finite domain. The scattering is characterized by a generalized scattering matrix which transforms the angular correlation function of the incident field into the angular correlation function of the scattered field. Within the accuracy of the first Born approximation this matrix can be expressed in a simple manner in terms of the scattering potential of the scatterer. Apart from determining the angular distribution of the spectral intensity of the scattered field, the scattering matrix makes it possible also to determine the changes in the state of coherence of the field produced on scattering.
Resonance enhanced dynamic light scattering.
Plum, Markus A; Menges, Bernhard; Fytas, George; Butt, Hans-Jürgen; Steffen, Werner
2011-01-01
We present a novel light scattering setup that enables probing of dynamics near solid surfaces. An evanescent wave generated by a surface plasmon resonance in a metal layer is the incident light field in the dynamic light scattering experiment. The combination of surface plasmon resonance spectroscopy and dynamic light scattering leads to a spatiotemporal resolution extending a few hundred nanometers from the surface and from microseconds to seconds. The comparison with evanescent wave dynamic light scattering identifies the advantages of the presented technique, e.g., surface monitoring, use of metal surfaces, and biorelevant systems. For both evanescent wave geometries, we define the scattering wave vector necessary for the analysis of the experimental relaxation functions.
Huang, H. Y.; Jia, C. J.; Chen, Z. Y.; Wohlfeld, K.; Moritz, B.; Devereaux, T. P.; Wu, W. B.; Okamoto, J.; Lee, W. S.; Hashimoto, M.; He, Y.; Shen, Z. X.; Yoshida, Y.; Eisaki, H.; Mou, C. Y.; Chen, C. T.; Huang, D. J.
2016-01-01
Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O8+δ. Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast, the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors. PMID:26794437
Huang, H. Y.; Jia, C. J.; Chen, Z. Y.; Wohlfeld, K.; Moritz, B.; Devereaux, T. P.; Wu, W. B.; Okamoto, J.; Lee, W. S.; Hashimoto, M.; He, Y.; Shen, Z. X.; Yoshida, Y.; Eisaki, H.; Mou, C. Y.; Chen, C. T.; Huang, D. J.
2016-01-22
Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O8+δ. Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast, the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors.
Huang, H. Y.; Jia, C. J.; Chen, Z. Y.; ...
2016-01-22
Measurements of spin excitations are essential for an understanding of spin-mediated pairing for superconductivity; and resonant inelastic X-ray scattering (RIXS) provides a considerable opportunity to probe high-energy spin excitations. However, whether RIXS correctly measures the collective spin excitations of doped superconducting cuprates remains under debate. Here we demonstrate distinct Raman- and fluorescence-like RIXS excitations of Bi1.5Pb0.6Sr1.54CaCu2O8+δ. Combining photon-energy and momentum dependent RIXS measurements with theoretical calculations using exact diagonalization provides conclusive evidence that the Raman-like RIXS excitations correspond to collective spin excitations, which are magnons in the undoped Mott insulators and evolve into paramagnons in doped superconducting compounds. In contrast,more » the fluorescence-like shifts are due primarily to the continuum of particle-hole excitations in the charge channel. Our results show that under the proper experimental conditions RIXS indeed can be used to probe paramagnons in doped high-Tc cuprate superconductors.« less
Jozwiak, Chris M.; Graff, Jeff; Lebedev, Gennadi; Andresen, Nord; Schmid, Andreas; Fedorov, Alexei; El Gabaly, Farid; Wan, Weishi; Lanzara, Alessandra; Hussain, Zahid
2010-04-13
We describe a spin-resolved electron spectrometer capable of uniquely efficient and high energy resolution measurements. Spin analysis is obtained through polarimetry based on low-energy exchange scattering from a ferromagnetic thin-film target. This approach can achieve a similar analyzing power (Sherman function) as state-of-the-art Mott scattering polarimeters, but with as much as 100 times improved efficiency due to increased reflectivity. Performance is further enhanced by integrating the polarimeter into a time-of-flight (TOF) based energy analysis scheme with a precise and flexible electrostatic lens system. The parallel acquisition of a range of electron kinetic energies afforded by the TOF approach results in an order of magnitude (or more) increase in efficiency compared to hemispherical analyzers. The lens system additionally features a 90 degrees bandpass filter, which by removing unwanted parts of the photoelectron distribution allows the TOF technique to be performed at low electron drift energy and high energy resolution within a wide range of experimental parameters. The spectrometer is ideally suited for high-resolution spin- and angle-resolved photoemission spectroscopy (spin-ARPES), and initial results are shown. The TOF approach makes the spectrometer especially ideal for time-resolved spin-ARPES experiments.
NASA Astrophysics Data System (ADS)
Rodríguez-Núñez, J. J.; Schafroth, S.
1998-06-01
We explore the effect of the self-energy, 0953-8984/10/23/002/img5, having a single pole, 0953-8984/10/23/002/img6, with spectral weight 0953-8984/10/23/002/img7 and quasi-particle lifetime 0953-8984/10/23/002/img8, on the density of states. We obtain the set of parameters 0953-8984/10/23/002/img6, 0953-8984/10/23/002/img7, and 0953-8984/10/23/002/img8 by means of the moment approach (exact sum rules) of Nolting. Due to our choice of self-energy, the system is not a Fermi liquid for any value of the interaction, a result which also holds in the moment approach of Nolting without lifetime effects. Our self-energy satisfies the Kramers - Kronig relationships since it is analytic in one of the complex half-planes. By increasing the value of the local interaction, 0953-8984/10/23/002/img12, at half-filling 0953-8984/10/23/002/img13, there is a transition from a paramagnetic metal to a paramagnetic insulator (a Mott metal - insulator transition) for values of 0953-8984/10/23/002/img12 of the order of 0953-8984/10/23/002/img15 (W is the bandwidth) which is in agreement with numerical results for finite lattices and for an infinite number of dimensions 0953-8984/10/23/002/img16. These results expose the main weakness of the spherical approximation of Nolting: a finite gap for any finite value of the interaction, i.e., an insulator for any finite value of 0953-8984/10/23/002/img12. Lifetime effects are absolutely indispensable to making our scheme work better than that based on improving the narrowing band factor, 0953-8984/10/23/002/img18, beyond that obtained from the spherical approximation of Nolting.
Quantum theory of Thomson scattering
NASA Astrophysics Data System (ADS)
Crowley, B. J. B.; Gregori, G.
2014-12-01
The general theory of the scattering of electromagnetic radiation in atomic plasmas and metals, in the non-relativistic regime, in which account is taken of the Kramers-Heisenberg polarization terms in the Hamiltonian, is described from a quantum mechanical viewpoint. As well as deriving the general formula for the double differential Thomson scattering cross section in an isotropic finite temperature multi-component system, this work also considers closely related phenomena such as absorption, refraction, Raman scattering, resonant (Rayleigh) scattering and Bragg scattering, and derives many essential relationships between these quantities. In particular, the work introduces the concept of scattering strength and the strength-density field which replaces the normal particle density field in the standard treatment of scattering by a collection of similar particles and it is the decomposition of the strength-density correlation function into more familiar-looking components that leads to the final result. Comparisons are made with previous work, in particular that of Chihara [1].
Quantitative Scattering of Melanin Solutions
NASA Astrophysics Data System (ADS)
Riesz, J.; Gilmore, J.; Meredith, P.
2006-06-01
The optical scattering coefficient of a dilute, well solubilised eumelanin solution has been accurately measured as a function of incident wavelength, and found to contribute less than 6% of the total optical attenuation between 210 and 325nm. At longer wavelengths (325nm to 800nm) the scattering was less than the minimum sensitivity of our instrument. This indicates that UV and visible optical density spectra can be interpreted as true absorption with a high degree of confidence. The scattering coefficient vs wavelength was found to be consistent with Rayleigh Theory for a particle radius of 38+-1nm.
Interstellar scattering and resolution limitations
NASA Astrophysics Data System (ADS)
Dennison, Brian
Density irregularities in both the interplanetary medium and the ionized component of the interstellar medium scatter radio waves, resulting in limitations on the achievable resolution. Interplanetary scattering (IPS) is weak for most observational situations, and in principle the resulting phase corruption can be corrected for when observing with sufficiently many array elements. Interstellar scattering (ISS), on the other hand, is usually strong at frequencies below about 8 GHz, in which case intrinsic structure information over a range of angular scales is irretrievably lost. With the earth-space baselines now planned, it will be possible to search directly for interstellar refraction, which is suspected of modulating the fluxes of background sources.
Synthetic Fourier transform light scattering.
Lee, Kyeoreh; Kim, Hyeon-Don; Kim, Kyoohyun; Kim, Youngchan; Hillman, Timothy R; Min, Bumki; Park, Yongkeun
2013-09-23
We present synthetic Fourier transform light scattering, a method for measuring extended angle-resolved light scattering (ARLS) from individual microscopic samples. By measuring the light fields scattered from the sample plane and numerically synthesizing them in Fourier space, the angle range of the ARLS patterns is extended up to twice the numerical aperture of the imaging system with unprecedented sensitivity and precision. Extended ARLS patterns of individual microscopic polystyrene beads, healthy human red blood cells (RBCs), and Plasmodium falciparum-parasitized RBCs are presented.
Timelike Compton Scattering at Jlab
Paremuzyan, Rafayel G.
2014-01-01
It is demonstrated, that with exclusive final state, data from electron scattering experiments that are recorded with loose trigger requirements can be used to analyze photoproduction reactions. A preliminary results on Timelike Compton Scattering using the electroproduction data from the CLAS detector at Jefferson Lab are presented. In particular, using final state (pe{sup -}e{sup +}) photoproduction of vector mesons and timelike photon is studied. Angular asymmetries in Timelike Compton Scattering region is compared with model predictions in the framework of Generalized Parton Distribution.
Superconductivity, antiferromagnetism, and neutron scattering
NASA Astrophysics Data System (ADS)
Tranquada, John M.; Xu, Guangyong; Zaliznyak, Igor A.
2014-01-01
High-temperature superconductivity in both the copper-oxide and the iron-pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues.
Driving trajectories in chaotic scattering.
Macau, Elbert E N; Caldas, Iberê L
2002-02-01
In this work we introduce a general approach for targeting in chaotic scattering that can be used to find a transfer trajectory between any two points located inside the scattering region. We show that this method can be used in association with a control of chaos strategy to drive around and keep a particle inside the scattering region. As an illustration of how powerful this approach is, we use it in a case of practical interest in celestial mechanics in which it is desired to control the evolution of two satellites that evolve around a large central body.
Microwave scattering from laser spark in air
Sawyer, Jordan; Zhang Zhili; Shneider, Mikhail N.
2012-09-15
In this paper, microwave Mie scattering from a laser-induced plasma in atmospheric air is computed. It shows that the scattered microwave transitions from coherent Rayleigh scattering to Mie scattering based on the relative transparency of the laser-induced plasma at the microwave frequency. The microwave penetration in the plasma alters from total transparency to partial shielding due to the sharp increase of the electron number density within the avalanche ionization phase. The transition from Rayleigh scattering to Mie scattering is verified by both the temporal evolution of the scattered microwave and the homogeneity of polar scattering plots.
Integration rules for scattering equations
NASA Astrophysics Data System (ADS)
Baadsgaard, Christian; Bjerrum-Bohr, N. E. J.; Bourjaily, Jacob L.; Damgaard, Poul H.
2015-09-01
As described by Cachazo, He and Yuan, scattering amplitudes in many quantum field theories can be represented as integrals that are fully localized on solutions to the so-called scattering equations. Because the number of solutions to the scattering equations grows quite rapidly, the contour of integration involves contributions from many isolated components. In this paper, we provide a simple, combinatorial rule that immediately provides the result of integration against the scattering equation constraints fo any Möbius-invariant integrand involving only simple poles. These rules have a simple diagrammatic interpretation that makes the evaluation of any such integrand immediate. Finally, we explain how these rules are related to the computation of amplitudes in the field theory limit of string theory.
NEW APPROACHES: Deep inelastic scattering
NASA Astrophysics Data System (ADS)
Allday, J.
1998-01-01
Feynman diagrams can be used to explain deep inelastic scattering, but it must be remembered that the emission and absorption of a photon are not independent events - the underlying field is important.
Scattering theory with path integrals
Rosenfelder, R.
2014-03-15
Starting from well-known expressions for the T-matrix and its derivative in standard nonrelativistic potential scattering, I rederive recent path-integral formulations due to Efimov and Barbashov et al. Some new relations follow immediately.
Double Compton scatter telescope calibration
NASA Technical Reports Server (NTRS)
Dayton, B.; Simone, J.; Green, M.; Long, J.; Zanrosso, E.; Zych, A. D.; White, R. S.
1981-01-01
Calibration techniques for a medium energy gamma ray telescope are described. Gain calibration using Compton edge spectra involves comparisons of pulse height spectra with spectra simulated by a Monte Carlo computer code which includes Compton scattering and pair production, plural scattering and variable energy resolution, and cell size. The telescope considered comprises 56 cells of liquid scintillator in four size groups, with a total liquid volume of 325 l; each cell has its own photomultiplier tube. Energy and angular resolutions and the PMT gain calibration procedure are verified with double scatter data for monoenergetic gamma rays at a known location. Detection probabilities for any cell combination in the two telescope arrays are calculated per steradian as a function of the scattering for a number of different energies with a Van de Graaff accelerator.
Structured light, transmission, and scattering
NASA Astrophysics Data System (ADS)
Andrews, David L.
2011-03-01
Numerous theoretical and experimental studies have established the principle that beams conveying orbital angular momentum offer a rich scope for information transfer. However, it is not clear how far it is practicable to operate such a concept at the single-photon level - especially when such a beam propagates through a system in which scattering can occur. In cases where scattering leads to photon deflection, it produces losses; however in terms of the retention of information content, there should be more concern over forward scattering. Based on a quantum electrodynamical formulation of theory, this paper aims to frame and resolve the key issues. A quantum amplitude is constructed for the representation of single and multiple scattering events in the propagation an individual photon, from a suitably structured beam. The analysis identifies potential limitations of principle, undermining complete fidelity of quantum information transmission.
Optical Waveguide Scattering Reduction. II.
1980-12-01
FAD-AOAR 815 BATTELLEWCOLUMBUS LABS ON F/S 20/6 OPTICAL WAVEGUIDE SCATTER ING REDUC TION. II.(U) 7 DEC 80 0 W VAHEY, N F HARTMAN, R C SHERMAN F3361... OPTICAL WAVEGUIDE SCATTERING REDUCTION II M BATTELLE COLUMBUS LABORATORIES 505 KING AVENUE COLUMBUS, OHIO 43201 DTIC ELECTEf MAY 12 198111 December...reviewed and is approved for publication. DOUGLAS AWIWILLE, Project Engineer KENNETH R. HUTCHINSON, Chief Electro- Optics Techniques and Electro- Optics
Analytical optical scattering in clouds
NASA Technical Reports Server (NTRS)
Phanord, Dieudonne D.
1989-01-01
An analytical optical model for scattering of light due to lightning by clouds of different geometry is being developed. The self-consistent approach and the equivalent medium concept of Twersky was used to treat the case corresponding to outside illumination. Thus, the resulting multiple scattering problem is transformed with the knowledge of the bulk parameters, into scattering by a single obstacle in isolation. Based on the size parameter of a typical water droplet as compared to the incident wave length, the problem for the single scatterer equivalent to the distribution of cloud particles can be solved either by Mie or Rayleigh scattering theory. The super computing code of Wiscombe can be used immediately to produce results that can be compared to the Monte Carlo computer simulation for outside incidence. A fairly reasonable inverse approach using the solution of the outside illumination case was proposed to model analytically the situation for point sources located inside the thick optical cloud. Its mathematical details are still being investigated. When finished, it will provide scientists an enhanced capability to study more realistic clouds. For testing purposes, the direct approach to the inside illumination of clouds by lightning is under consideration. Presently, an analytical solution for the cubic cloud will soon be obtained. For cylindrical or spherical clouds, preliminary results are needed for scattering by bounded obstacles above or below a penetrable surface interface.
An analysis of scatter decomposition
NASA Technical Reports Server (NTRS)
Nicol, David M.; Saltz, Joel H.
1990-01-01
A formal analysis of a powerful mapping technique known as scatter decomposition is presented. Scatter decomposition divides an irregular computational domain into a large number of equal sized pieces, and distributes them modularly among processors. A probabilistic model of workload in one dimension is used to formally explain why, and when scatter decomposition works. The first result is that if correlation in workload is a convex function of distance, then scattering a more finely decomposed domain yields a lower average processor workload variance. The second result shows that if the workload process is stationary Gaussian and the correlation function decreases linearly in distance until becoming zero and then remains zero, scattering a more finely decomposed domain yields a lower expected maximum processor workload. Finally it is shown that if the correlation function decreases linearly across the entire domain, then among all mappings that assign an equal number of domain pieces to each processor, scatter decomposition minimizes the average processor workload variance. The dependence of these results on the assumption of decreasing correlation is illustrated with situations where a coarser granularity actually achieves better load balance.
A Simple Model for Inelastic Scattering.
ERIC Educational Resources Information Center
Loeser, J. G.; And Others
1981-01-01
Describes a model for inelastic scattering obtained by suitably generalizing scattering from a square well. The generalization introduces matrices into the quantum-mechanical scattering equations, which may be solved exactly to give an explicit expression for the scattering matrix. Discusses the results it predicts for a simple example. (Author/SK)
Equilibrium Tail Distribution Due to Touschek Scattering
Nash,B.; Krinsky, S.
2009-05-04
Single large angle Coulomb scattering is referred to as Touschek scattering. In addition to causing particle loss when the scattered particles are outside the momentum aperture, the process also results in a non-Gaussian tail, which is an equilibrium between the Touschek scattering and radiation damping. Here we present an analytical calculation for this equilibrium distribution.
NASA Astrophysics Data System (ADS)
Su, Z. C.; Ning, J. Q.; Deng, Z.; Wang, X. H.; Xu, S. J.; Wang, R. X.; Lu, S. L.; Dong, J. R.; Yang, H.
2016-03-01
Anderson localization is a predominant phenomenon in condensed matter and materials physics. In fact, localized and delocalized states often co-exist in one material. They are separated by a boundary called the mobility edge. Mott transition may take place between these two regimes. However, it is widely recognized that an apparent demonstration of Anderson localization or Mott transition is a challenging task. In this article, we present a direct optical observation of a transition of radiative recombination dominant channels from delocalized (i.e., local extended) states to Anderson localized states in the GaInP base layer of a GaInP/GaAs single junction solar cell by the means of the variable-temperature electroluminescence (EL) technique. It is found that by increasing temperature, we can boost a remarkable transition of radiative recombination dominant channels from the delocalized states to the localized states. The delocalized states are induced by the local atomic ordering domains (InP/GaP monolayer superlattices) while the localized states are caused by random distribution of indium (gallium) content. The efficient transfer and thermal redistribution of carriers between the two kinds of electronic states was revealed to result in both a distinct EL mechanism transition and an electrical resistance evolution with temperature. Our study gives rise to a self-consistent precise picture for carrier localization and transfer in a GaInP alloy, which is an extremely technologically important energy material for fabricating high-efficiency photovoltaic devices.
NASA Astrophysics Data System (ADS)
Hou, Yusheng; Xiang, Hongjun; Gong, Xingao; Key Laboratory of Computational Physical Sciences (Ministry of Education) Collaboration
Based on the density functional theory and our new model Hamiltonian, we have studied the basal-plane antiferromagnetism in the novel Jeff = 1/2 Mott insulator Ba2IrO4. By comparing the magnetic properties of the bulk Ba2IrO4 with those of the single-layer Ba2IrO4, we demonstrate unambiguously that the basal-plane antiferromagnetism is caused by the intralyer magnetic interactions rather than by the previously proposed interlayer ones. In order to reveal the origin of the basal-plane antiferromagnetism, we propose a new model Hamiltonian by adding the single ion anisotropy and pseudo-quadrupole interactions into the general bilinear pseudo-spin Hamiltonian. The obtained magnetic interaction parameters indicate that the single ion anisotropy and pseudo-quadrupole interactions are unexpectedly strong. Systematical Monte Carlo simulations demonstrate that the basal-plane antiferromagnetism is caused by the isotropic Heisenberg, bond-dependent Kitaev and pseudo-quadrupole interactions. Our results show for the first time that the single ion anisotropy and pseudo-quadrupole interaction can play significant roles in establishing the exotic magnetism in the Jeff = 1/2 Mott insulator.
Multiple Scattering Theory of XAFS
NASA Astrophysics Data System (ADS)
Zabinsky, Steven Ira
A multiple scattering theory of XAFS for arbitrary materials with convergence to full multiple scattering calculations and to experiment is presented. It is shown that the multiple scattering expansion converges with a small number of paths. The theory is embodied in an efficient automated computer code that provides accurate theoretical multiple scattering standards for use in experimental analysis. The basis of this work is a new path enumeration and filtering algorithm. Paths are constructed for an arbitrary cluster in order of increasing path length. Filters based on the relative importance of the paths in the plane wave approximation and on the random phase approximation limit the number of paths so that all important paths with effective path length up to the mean free path length (between 10 and 20 A) can be considered. Quantitative expressions for path proliferation and relative path importance are presented. The calculations are compared with full multiple scattering calculations for Cu and Al. In the case of fcc Cu, the path filters reduce the number of paths from 60 billion to only 56 paths in a cluster of radius 12.5 A. These 56 paths are sufficient to converge the calculation to within the uncertainty inherent in the band structure calculation. Based on an analysis of these paths, a new hypothesis is presented for consideration: Single scattering, double scattering, and all orders of scattering that involve only forward or back scattering are sufficient to describe XAFS. Comparison with experiment in Cu, Pt and Ti demonstrate the accuracy of the calculation through the fourth shell. The correlated Debye model is used to determine Debye-Waller factors--the strengths and weaknesses of this approach are discussed. Preliminary results for calculations of the x -ray absorption near edge structure (XANES) have been done. The calculations compare well with Cu, Pt and Ti experiments. The white line in the Pt absorption edge is calculated correctly. There are
Time Dependent Nuclear Scattering Calculations
NASA Astrophysics Data System (ADS)
Weeks, David
2005-04-01
A new time dependent method for calculating scattering matrix elements of two and three body nuclear collisions below 50 Mev is being developed. The procedure closely follows the channel packet method (CPM) used to compute scattering matrix elements for non-adiabatic molecular reactions.ootnotetextT.A.Niday and D.E.Weeks, Chem. Phys. Letters 308 (1999) 106 Currently, one degree of freedom calculations using a simple square well have been completed and a two body scattering calculation using the Yukawa potential is anticipated. To perform nuclear scattering calculations with the CPM that will incorporate the nucleon-nucleon tensor force, we plan to position initial reactant and product channel packets in the asymptotic limit on single coupled potential energy surfaces labeled by the spin, isospin, and total angular momentum of the reactant nucleons. The wave packets will propagated numerically using the split operator method augmented by a coordinate dependant unitary transformation used to diagonalize the potential. Scattering matrix elements will be determined by the Fourier transform of the correlation function between the evolving reactant and product wave packets. A brief outline of the Argonne v18 nucleon-nucleon potentialootnotetextR.B.Wiringa, V.G.J.Stoks, and R.Schiavilla, Physical Review C 51(1995) 38 and the proposed wave packet calculations will be presented.
Scattering apodizer for laser beams
Summers, M.A.; Hagen, W.F.; Boyd, R.D.
1984-01-01
A method is disclosed for apodizing a laser beam to smooth out the production of diffraction peaks due to optical discontinuities in the path of the laser beam, such method comprising introduction of a pattern of scattering elements for reducing the peak intensity in the region of such optical discontinuities, such pattern having smoothly tapering boundaries in which the distribution density of the scattering elements is tapered gradually to produce small gradients in the distribution density, such pattern of scattering elements being effective to reduce and smooth out the diffraction effects which would otherwise be produced. The apodizer pattern may be produced by selectively blasting a surface of a transparent member with fine abrasive particles to produce a multitude of minute pits. In one embodiment, a scattering apodizer pattern is employed to overcome diffraction patterns in a multiple element crystal array for harmonic conversion of a laser beam. The interstices and the supporting grid between the crystal elements are obscured by the gradually tapered apodizer pattern of scattering elements.
Scattering apodizer for laser beams
Summers, Mark A.; Hagen, Wilhelm F.; Boyd, Robert D.
1985-01-01
A method is disclosed for apodizing a laser beam to smooth out the production of diffraction peaks due to optical discontinuities in the path of the laser beam, such method comprising introduction of a pattern of scattering elements for reducing the peak intensity in the region of such optical discontinuities, such pattern having smoothly tapering boundaries in which the distribution density of the scattering elements is tapered gradually to produce small gradients in the distribution density, such pattern of scattering elements being effective to reduce and smooth out the diffraction effects which would otherwise be produced. The apodizer pattern may be produced by selectively blasting a surface of a transparent member with fine abrasive particles to produce a multitude of minute pits. In one embodiment, a scattering apodizer pattern is employed to overcome diffraction patterns in a multiple element crystal array for harmonic conversion of a laser beam. The interstices and the supporting grid between the crystal elements are obscured by the gradually tapered apodizer pattern of scattering elements.
Thomson scattering from laser plasmas
Moody, J D; Alley, W E; De Groot, J S; Estabrook, K G; Glenzer, S H; Hammer, J H; Jadaud, J P; MacGowan, B J; Rozmus, W; Suter, L J; Williams, E A
1999-01-12
Thomson scattering has recently been introduced as a fundamental diagnostic of plasma conditions and basic physical processes in dense, inertial confinement fusion plasmas. Experiments at the Nova laser facility [E. M. Campbell et al., Laser Part. Beams 9, 209 (1991)] have demonstrated accurate temporally and spatially resolved characterization of densities, electron temperatures, and average ionization levels by simultaneously observing Thomson scattered light from ion acoustic and electron plasma (Langmuir) fluctuations. In addition, observations of fast and slow ion acous- tic waves in two-ion species plasmas have also allowed an independent measurement of the ion temperature. These results have motivated the application of Thomson scattering in closed-geometry inertial confinement fusion hohlraums to benchmark integrated radiation-hydrodynamic modeling of fusion plasmas. For this purpose a high energy 4{omega} probe laser was implemented recently allowing ultraviolet Thomson scattering at various locations in high-density gas-filled hohlraum plasmas. In partic- ular, the observation of steep electron temperature gradients indicates that electron thermal transport is inhibited in these gas-filled hohlraums. Hydrodynamic calcula- tions which include an exact treatment of large-scale magnetic fields are in agreement with these findings. Moreover, the Thomson scattering data clearly indicate axial stagnation in these hohlraums by showing a fast rise of the ion temperature. Its timing is in good agreement with calculations indicating that the stagnating plasma will not deteriorate the implosion of the fusion capsules in ignition experiments.
Nonlinear scattering in plasmonic nanostructures
NASA Astrophysics Data System (ADS)
Chu, Shi-Wei
2016-09-01
Nonlinear phenomena provide novel light manipulation capabilities and innovative applications. Recently, we discovered nonlinear saturation on single-particle scattering of gold nanospheres by continuous-wave laser excitation and innovatively applied to improve microscopic resolution down to λ/8. However, the nonlinearity was limited to the green-orange plasmonic band of gold nanosphere, and the underlying mechanism has not yet been fully understood. In this work, we demonstrated that nonlinear scattering exists for various material/geometry combinations, thus expanding the applicable wavelength range. For near-infrared, gold nanorod is used, while for blue-violet, silver nanospheres are adopted. In terms of mechanism, the nonlinearity may originate from interband/intraband absorption, hot electron, or hot lattice, which are spectrally mixed in the case of gold nanosphere. For gold nanorod and silver nanosphere, nonlinear scattering occurs at plasmonic resonances, which are spectrally far from interband/intraband absorptions, so they are excluded. We found that the nonlinear index is much larger than possible contributions from hot electrons in literature. Therefore, we conclude that hot lattice is the major mechanism. In addition, we propose that similar to z-scan, which is the standard method to characterize nonlinearity of a thin sample, laser scanning microscopy should be adopted as the standard method to characterize nonlinearity from a nanostructure. Our work not only provides the physical mechanism of the nonlinear scattering, but also paves the way toward multi-color superresolution imaging based on non-bleaching plasmonic scattering.
Nuclear Scattering from Transition Metals
NASA Astrophysics Data System (ADS)
Hira, Ajit; McKeough, James; Valerio, Mario; Cathey, Tommy
2016-03-01
In view of the continued interest in the scattering of light projectiles by metallic nuclei, we present a computational study of the interactions between different nuclear species of atoms such as H through F (Z <= 9) and the nuclei of Silver, Palladium and other metals. Recent work has shown that neutron scattering can be used to record holographic images of materials. We have developed a FORTRAN computer program to compute stopping cross sections and scattering angles in Ag and other metals for the small nuclear projectiles, using Monte Carlo calculation. This code allows for different angles of incidence. Next, simulations were done in the energy interval from 50 to 210 keV. The computational results thus obtained are compared with relevant experimental data. The data are further analyzed to identify periodic trends in terms of the atomic number of the projectile. Such studies also have potential applications in nuclear physics and in nuclear medicine. Funding from National Science Foundation.
Scattering Polarization in the Chromosphere
NASA Technical Reports Server (NTRS)
Keller, C. U.; Sheeley, N. R., Jr.
1999-01-01
Scattering polarization from the photosphere observed close to the solar limb has recently become of interest to study turbulent magnetic fields, abundances, and radiative transfer effects. We extend these studies by measuring the scattering polarization off the limb, i.e. in the chromosphere. However, instrumental effects are much more pronounced and more complicated than those affecting on-disk measurements. In particular, scattered light from the telescope mirrors leads to a new type of instrumental polarization that we describe in detail. The differences between the linearly polarized spectra on the disk and off the limb are often very substantial. Here we show the profiles of HeI D(sub 3), the OI triplet at 777 nm, and the Nal D lines. The change in the latter is in reasonable agreement with the recent modeling efforts of atomic polarization in the lower level by Landi Degl'Innocenti (1998).
Scattering calculations and confining interactions
NASA Technical Reports Server (NTRS)
Buck, Warren W.; Maung, Khin M.
1993-01-01
Most of the research work performed under this grant were concerned with strong interaction processes ranging from kaon-nucleon interaction to proton-nucleus scattering calculations. Research performed under this grant can be categorized into three groups: (1) parametrization of fundamental interactions, (2) development of formal theory, and (3) calculations based upon the first two. Parametrizations of certain fundamental interactions, such as kaon-nucleon interaction, for example, were necessary because kaon-nucleon scattering amplitude was needed to perform kaon-nucleus scattering calculations. It was possible to calculate kaon-nucleon amplitudes from the first principle, but it was unnecessary for the purpose of the project. Similar work was also done for example for anti-protons and anti-nuclei. Formal developments to some extent were also pursued so that consistent calculations can be done.
Theory of waves incoherently scattered
NASA Technical Reports Server (NTRS)
Bauer, P.
1974-01-01
Electromagnetic waves impinging upon a plasma at frequencies larger than the plasma frequency, suffer weak scattering. The scattering arises from the existence of electron density fluctuations. The received signal corresponds to a particular spatial Fourier component of the fluctuations, the wave vector of which is a function of the wavelength of the radiowave. Wavelengths short with respect to the Debye length of the medium relate to fluctuations due to non-interacting Maxwellian electrons, while larger wavelengths relate to fluctuations due to collective Coulomb interactions. In the latter case, the scattered signal exhibits a spectral distribution which is characteristic of the main properties of the electron and ion gases and, therefore, provides a powerful diagnosis of the state of the ionosphere.
Scattering functions of Platonic solids
Chen, Wei-Ren; Herwig, Kenneth W; Li, Xin; Liu, Emily; Pynn, Roger; Shew, Chwen-Yang; Smith, Gregory Scott; Myles, Dean A A; He, Lilin; Meilleur, Flora
2011-01-01
In this report the single-particle scattering properties of five Platonic solids, including tetrahedron, hexahedron, octahedron, dodecahedron and icosahedron, are investigated in a systematic manner. For each given geometry, the Debye spatial autocorrelation function (r), pair distance distribution function (PDDF) p (r) and intraparticle structure factor (form factor) P (Q) are respectively calculated and compared to the corresponding scattering function of the spherical referential system. Based on our theoretical models, the empirical relationship between the dodecahedral and icosahedral structural characteristics and those of the equivalent spheres is found. Moreover, the single-particle scattering properties of the icosahedral and the spherical shells with the same volume are further investigated and the prospect of using different data analysis approaches to explore their structural difference is also presented and discussed.
Scattering functions of Platonic solids
Li, Xin; Shew, Chwen-Yang; He, Lilin; Meilleur, Flora; Myles, Dean A A; Liu, Emily; Zhang, Yang; Smith, Greg; Herwig, Kenneth W; Pynn, Roger; Chen, Wei-Ren
2011-01-01
The single-particle small-angle scattering properties of five Platonic solids, including the tetrahedron, hexahedron, octahedron, dodecahedron and icosahedron, are systematically investigated. For each given geometry, the Debye spatial autocorrelation function, pair distance distribution function and intraparticle structure factor (form factor) are calculated and compared with the corresponding scattering function of a spherical reference system. From the theoretical models, the empirical relationship between the dodecahedral and icosahedral structural characteristics and those of the equivalent spheres is found. Moreover, the single-particle scattering properties of icosahedral and spherical shells with identical volume are investigated, and the prospect of using different data analysis approaches to explore their structural differences is presented and discussed.
Positron-alkali atom scattering
NASA Technical Reports Server (NTRS)
Mceachran, R. P.; Horbatsch, M.; Stauffer, A. D.; Ward, S. J.
1990-01-01
Positron-alkali atom scattering was recently investigated both theoretically and experimentally in the energy range from a few eV up to 100 eV. On the theoretical side calculations of the integrated elastic and excitation cross sections as well as total cross sections for Li, Na and K were based upon either the close-coupling method or the modified Glauber approximation. These theoretical results are in good agreement with experimental measurements of the total cross section for both Na and K. Resonance structures were also found in the L = 0, 1 and 2 partial waves for positron scattering from the alkalis. The structure of these resonances appears to be quite complex and, as expected, they occur in conjunction with the atomic excitation thresholds. Currently both theoretical and experimental work is in progress on positron-Rb scattering in the same energy range.
Light Scattering in Exoplanet Transits
NASA Astrophysics Data System (ADS)
Robinson, Tyler D.; Fortney, Jonathan J.
2016-10-01
Transit spectroscopy is currently the leading technique for studying exoplanet atmospheric composition, and has led to the detection of molecular species, clouds, and/or hazes for numerous worlds outside the Solar System. The field of exoplanet transit spectroscopy will be revolutionized with the anticipated launch of NASA's James Webb Space Telescope (JWST) in 2018. Over the course of the design five year mission for JWST, the observatory is expected to provide in-depth observations of many tens of transiting exoplanets, including some worlds in the poorly understood 2-4 Earth-mass regime. As the quality of transit spectrum observations continues to improve, so should models of exoplanet transits. Thus, certain processes initially thought to be of second-order importance should be revisited and possibly added to modeling tools. For example, atmospheric refraction, which was commonly omitted from early transit spectrum models, has recently been shown to be of critical importance in some terrestrial exoplanet transits. Beyond refraction, another process that has seen little study with regards to exoplanet transits is light multiple scattering. In most cases, scattering opacity in exoplanet transits has been treated as equivalent to absorption opacity. However, this equivalence cannot always hold, such as in the case of a strongly forward scattering, weakly absorbing aerosol. In this presentation, we outline a theory of exoplanet transit spectroscopy that spans the geometric limit (used in most modern models) to a fully multiple scattering approach. We discuss a new technique for improving model efficiency that effectively separates photon paths, which tend to vary slowly in wavelength, from photon absorption, which can vary rapidly in wavelength. Using this newly developed approach, we explore situations where cloud or haze scattering may be important to JWST observations of gas giants, and comment on the conditions necessary for scattering to become a major
Stimulated Brillouin Scattering Microscopic Imaging
Ballmann, Charles W.; Thompson, Jonathan V.; Traverso, Andrew J.; Meng, Zhaokai; Scully, Marlan O.; Yakovlev, Vladislav V.
2015-01-01
Two-dimensional stimulated Brillouin scattering microscopy is demonstrated for the first time using low power continuous-wave lasers tunable around 780 nm. Spontaneous Brillouin spectroscopy has much potential for probing viscoelastic properties remotely and non-invasively on a microscopic scale. Nonlinear Brillouin scattering spectroscopy and microscopy may provide a way to tremendously accelerate the data aquisition and improve spatial resolution. This general imaging setup can be easily adapted for specific applications in biology and material science. The low power and optical wavelengths in the water transparency window used in this setup provide a powerful bioimaging technique for probing the mechanical properties of hard and soft tissue. PMID:26691398
Electron Scattering from Silicon 30.
1983-01-01
COMPLETING FORM I. REPORT NUMBER 2. GOVT ACCESSION NO. 3. RECIPIENT’S CATALOG NUMBER AFIT/CI/NR 83-3 T___ __ _ . 4. TITLE (and Subtitle) S . TYPE OF...REPORT & PERIOD COVERED ElectrogScattering from Silicon 30 THESIS/P AA~7Aj1AN 6. PERFORMING ORG. REPORT NUMBER 7. AUTHOR(q) S . CONTRACT OR GRANT NUMBER( s ...spectrometers. The machines used in the 1950’ s allowed electron scattering with a resolution of 4p/p f5xlO- and with currents of a few tenths of a micro
The Full Mottness: Asymptiotic Slavery
Phillips, Philip
2004-03-10
Vast progress in theoretical solid state physics has been made by constructing models which mimic the low-energy properties of solids. Essential to the success of this program is the separability of the high and low energy degrees of freedom. While it is hoped that a high energy reduction can be made to solve the problem of high temperature superconductivity in the copper oxide materials, I will show that no consistent theory is possible if the high energy scale is removed. At the heart of the problem is the mixing of all energy scales (that is, UV-IR mixing) in the copper-oxide materials. Several optical measurements will be discussed which demonstrate the slavery of high and low energy degrees of freedom. The implications of asymptotic slavery for the phase diagram of the cuprates will be discussed.
MOTT PROGRAM SUMMARIES (TITLE SUPPLIED).
ERIC Educational Resources Information Center
Flint Board of Education, MI.
THE BETTER TOMORROW FOR THE URBAN CHILD PROGRAM (BTU) ATTEMPTS TO HELP INNER-CITY CHILDREN BECOME MORE EFFECTIVE CITIZENS, BOTH EDUCATIONALLY AND SOCIALLY, THROUGH THE USE OF ADDITIONAL HUMAN AND MATERIAL RESOURCES. THE GOALS ARE TO RAISE THE LEVEL OF SCHOOL READINESS, TO DEVELOP A GREATER MOTIVATION FOR LEARNING, AND TO IMPROVE STUDENT SELF-IMAGE…
Interferometric Rayleigh Scattering Measurement System
NASA Technical Reports Server (NTRS)
Bivolaru, Daniel (Inventor); Danehy, Paul M. (Inventor); Lee, Joseph W. (Inventor)
2008-01-01
A method and apparatus for performing simultaneous multi-point measurements of multiple velocity components in a gas flow is described. Pulses of laser light are directed to a measurement region of unseeded gas to produce Rayleigh or Mie scattered light in a plurality of directions. The Rayleigh or Mie scattered light is collected from multiple directions and combined in a single collimated light beam. The Rayleigh or Mie scattered light is then mixed together with a reference laser light before it is passed through a single planar Fabry-Perot interferometer for spectral analysis. At the output of the interferometer, a high-sensitivity CCD camera images the interference fringe pattern. This pattern contains the spectral and spatial information from both the Rayleigh scattered light and the reference laser light. Interferogram processing software extracts and analyzes spectral profiles to determine the velocity components of the gas flow at multiple points in the measurement region. The Rayleigh light rejected by the interferometer is recirculated to increase the accuracy and the applicability of the method for measurements at high temperatures without requiring an increase in the laser energy.
NASA Astrophysics Data System (ADS)
Hayes, Anna
2017-01-01
Neutrino scattering cross-sections from 12C, which have been measure for pion decay-at-rest and pion decay-in-flight neutrino energies, are difficult to reproduce theoretically. In this talk I discuss the physics issues involved and show the importance of a proper treatment of the conservation of the vector current.
Electron Scattering and Nuclear Structure
ERIC Educational Resources Information Center
Trower, W. P.; Ficenec, J. R.
1971-01-01
Presents information about the nucleus gained by studies of electron scattering. Discusses what can be implied about the shape of the charge distribution, the nucleus positions, the vibrational modes of the nucleus, the momentum of the nucleus, and the granularity and core structures of the nucleus. (DS)
Pauli Principle and Pion Scattering
DOE R&D Accomplishments Database
Bethe, H. A.
1972-10-01
It is pointed out that if the Pauli principle is taken into account in the discussion of pion scattering by complex nuclei (as it ought, of course, to be) some rather implausible consequences of some earlier treatments of this problem can be avoided. (auth)
Alpha particle collective Thomson scattering in TFTR
Machuzak, J.S.; Woskov, P.P.; Rhee, D.Y.; Gilmore, J.; Bretz, N.L.; Park, H.K.; Aamodt, R.E.; Cheung, P.Y.; Russell, D.A.; Bindslev, H.
1993-11-01
A collective Thomson scattering diagnostic is being implemented on TFTR to measure alpha particle, energetic and thermal ion densities and velocity distributions. A 60 GHz, 0.1-1 kW gyrotron will be used as the transmitter source, and the scattering geometry will be perpendicular to the magnetic field in the extraordinary mode polarization. An enhanced scattered signal is anticipated from fluctuations in the lower hybrid frequency range with this scattering geometry. Millimeter wave collective Thomson scattering diagnostics have the advantage of larger scattering angles to decrease the amount of stray light, and long, high power, modulated pulses to obtain improved signal to noise through synchronous detection techniques.
Integrated Raman and angular scattering microscopy (IRAM)
NASA Astrophysics Data System (ADS)
Smith, Zachary J.; Berger, Andrew J.
2008-02-01
A microscope system has been constructed that allows simultaneous acquisition of Raman scattering spectra and elastic scattering Fourier-plane data. The Raman scattering channel reports on chemical composition of the microscopic sample while the elastic scattering channel reports on morphological information about the sample. The system has been validated by acquiring data from single polystyrene beads and analyzing the elastic scattering signal using Generalized Lorenz-Mie Theory while comparing the Raman scattering signature to other polystyrene spectra from the literature. Monocytes and neutrophils, two immune cell types, have also been studied and show clear chemical and morphological differences between cell types.
Einstein-Yang-Mills scattering amplitudes from scattering equations
NASA Astrophysics Data System (ADS)
Cachazo, Freddy; He, Song; Yuan, Ellis Ye
2015-01-01
We present the building blocks that can be combined to produce tree-level S-matrix elements of a variety of theories with various spins mixed in arbitrary dimensions. The new formulas for the scattering of n massless particles are given by integrals over the positions of n points on a sphere restricted to satisfy the scattering equations. As applications, we obtain all single-trace amplitudes in Einstein-Yang-Mills (EYM) theory, and generalizations to include scalars. Also in EYM but extended by a B-field and a dilaton, we present all double-trace gluon amplitudes. The building blocks are made of Pfaffians and Parke-Taylor-like factors of subsets of particle labels.
2004 Photon Correlation and Scattering Conference
NASA Technical Reports Server (NTRS)
Meyer, William (Editor); Smart, Anthony (Editor); Wegdam, Gerard (Editor); Dogariu, Aristide (Editor); Carpenter, Bradley (Editor)
2004-01-01
The Photon Correlation and Scattering (PCS) meeting welcomes all who are interested in the art and science of photon correlation and its application to optical scattering. The meeting is intended to enhance interactions between theory, applications, instrument design, and participants.
Multiple scattering by deep perturbed gratings
Knotts, M.E.; O`Donnell, K.A.
1994-11-01
We present measurements of the far-field scattered intensity for gratings consisting of uniform, regularly spaced, wavelength-scale grooves that have randomly fluctuating depths. The complete polarization dependence of the scattering is determined, and particular attention is given to measurements that isolate multiple scattering. For both perturbed and unperturbed gratings, effects similar to backscattering enhancement seen for randomly rough surfaces are observed, and these effects are linked to the coherent interference of reciprocal pairs of waves multiply scattered within the grooves.
Rayleigh Scattering by Helium in Stellar Atmospheres
NASA Astrophysics Data System (ADS)
Fišák, J.; Kubát, J.; Krtička, J.
2017-02-01
We study the influence of Rayleigh scattering by helium on synthetic spectra and stellar atmosphere models. Rayleigh scattering by helium is often neglected in hot star atmosphere models. This approximation is justified by the small population of helium in stars with solar composition (about 10% by number) and lower Rayleigh scattering total cross section of helium with respect to neutral hydrogen. However, for stars with large helium abundances Rayleigh scattering by helium can be a significant opacity source.
Scattering Properties of a Moving Dielectric Object
1984-12-01
rest while the medium, i.e. the scattering particle , is in general accelarated motion. However, this is not the whole story, for to be able to...very high and von,’ low refractive index on the scattering orooerties of a particle with possible ons^t of resonance scatverina. W) I JAM 71 1473...scattering properties of particles of very high and very low refractive index, with possible onset of resonance scattering. As will be seen below this
Shear Brillouin light scattering microscope
Kim, Moonseok; Besner, Sebastien; Ramier, Antoine; Kwok, Sheldon J. J.; An, Jeesoo; Scarcelli, Giuliano; Yun, Seok Hyun
2016-01-01
Brillouin spectroscopy has been used to characterize shear acoustic phonons in materials. However, conventional instruments had slow acquisition times over 10 min per 1 mW of input optical power, and they required two objective lenses to form a 90° scattering geometry necessary for polarization coupling by shear phonons. Here, we demonstrate a confocal Brillouin microscope capable of detecting both shear and longitudinal phonons with improved speeds and with a single objective lens. Brillouin scattering spectra were measured from polycarbonate, fused quartz, and borosilicate in 1-10 s at an optical power level of 10 mW. The elastic constants, phonon mean free path and the ratio of the Pockels coefficients were determined at microscopic resolution. PMID:26832263
Brillouin scattering self-cancellation
NASA Astrophysics Data System (ADS)
Florez, O.; Jarschel, P. F.; Espinel, Y. A. V.; Cordeiro, C. M. B.; Mayer Alegre, T. P.; Wiederhecker, G. S.; Dainese, P.
2016-06-01
The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon-phonon interaction, enhancing or suppressing it.
Electromagnetic scattering by impedance structures
NASA Technical Reports Server (NTRS)
Balanis, Constantine A.; Griesser, Timothy
1987-01-01
The scattering of electromagnetic waves from impedance structures is investigated, and current work on antenna pattern calculation is presented. A general algorithm for determining radiation patterns from antennas mounted near or on polygonal plates is presented. These plates are assumed to be of a material which satisfies the Leontovich (or surface impedance) boundary condition. Calculated patterns including reflection and diffraction terms are presented for numerious geometries, and refinements are included for antennas mounted directly on impedance surfaces. For the case of a monopole mounted on a surface impedance ground plane, computed patterns are compared with experimental measurements. This work in antenna pattern prediction forms the basis of understanding of the complex scattering mechanisms from impedance surfaces. It provides the foundation for the analysis of backscattering patterns which, in general, are more problematic than calculation of antenna patterns. Further proposed study of related topics, including surface waves, corner diffractions, and multiple diffractions, is outlined.
Solar Neutrinos with Exotic Scattering
NASA Astrophysics Data System (ADS)
Pulido, João
The possibility of unconventional neutrino scattering in the Sun via flavor changing neutral currents as a possible source of the solar neutrino deficit is investigated. If the effect is really significant, a resonant process will occur. Taking into account the neutrino deficit reported by the solar neutrino experiments (Kamiokande II, SAGE Gallex), one finds Δ2m21 = (0.6-1.4) × 10-5 eV2 with no vacuum mixing and 0.16 ≤ fex ≤ 0.34 where fex is the lepton violating coupling. Our understanding of the neutrino phenomenon in the Sun may be improved through accuracy improvements in experiments measuring νee- elastic scattering or others searching for exotic lepton decays.
Advanced studies of electromagnetic scattering
NASA Technical Reports Server (NTRS)
Ling, Hao
1994-01-01
In radar signature applications it is often desirable to generate the range profiles and inverse synthetic aperture radar (ISAR) images of a target. They can be used either as identification tools to distinguish and classify the target from a collection of possible targets, or as diagnostic/design tools to pinpoint the key scattering centers on the target. The simulation of synthetic range profiles and ISAR images is usually a time intensive task and computation time is of prime importance. Our research has been focused on the development of fast simulation algorithms for range profiles and ISAR images using the shooting and bouncing ray (SBR) method, a high frequency electromagnetic simulation technique for predicting the radar returns from realistic aerospace vehicles and the scattering by complex media.
Perspectives on stimulated Brillouin scattering
NASA Astrophysics Data System (ADS)
Garmire, Elsa
2017-01-01
This collection of papers describes research that goes into detail on some of the more important issues in the physics of stimulated Brillouin scattering. This perspective describes the earliest years of the physics of stimulated Brillouin scattering, along with key developments that have led to this technically and physically rich field of today’s nonlinear optics. Stimulated Brillouin has a profound effect in optical fiber communications, initially discovered by its limit on the transmitted power. By controlling SBS in fibers and making use of its phase conjugation properties in both fibers and bulk media, a wide range of applications have been enabled. Today ring Brillouin lasers in fibers, whispering gallery modes and in photonic integrated circuits provide optical delay lines and switches, pulse shapers and components for increasingly complex and important optical systems.
Brillouin scattering self-cancellation
Florez, O.; Jarschel, P. F.; Espinel, Y. A. V.; Cordeiro, C. M. B.; Mayer Alegre, T. P.; Wiederhecker, G. S.; Dainese, P.
2016-01-01
The interaction between light and acoustic phonons is strongly modified in sub-wavelength confinement, and has led to the demonstration and control of Brillouin scattering in photonic structures such as nano-scale optical waveguides and cavities. Besides the small optical mode volume, two physical mechanisms come into play simultaneously: a volume effect caused by the strain-induced refractive index perturbation (known as photo-elasticity), and a surface effect caused by the shift of the optical boundaries due to mechanical vibrations. As a result, proper material and structure engineering allows one to control each contribution individually. Here, we experimentally demonstrate the perfect cancellation of Brillouin scattering arising from Rayleigh acoustic waves by engineering a silica nanowire with exactly opposing photo-elastic and moving-boundary effects. This demonstration provides clear experimental evidence that the interplay between the two mechanisms is a promising tool to precisely control the photon–phonon interaction, enhancing or suppressing it. PMID:27283092
Scattering of Acoustic Waves from Ocean Boundaries
2014-09-30
derived reflection coefficients as a function of range along the reverberation track (right). RESULTS Analysis of Acoustic Scattering for Layered and... acoustic interaction with the ocean floor, including penetration through and reflection from smooth and rough water/sediment interfaces, scattering ...can account for the all of the physical processes and variability of acoustic propagation and scattering in ocean environments with special emphasis
Bayesian Inversion of Seabed Scattering Data
2014-09-30
Bayesian Inversion of Seabed Scattering Data (Special Research Award in Ocean Acoustics ) Gavin A.M.W. Steininger School of Earth & Ocean...Figure 1: Schematic diagram of the environmental parameterizations for the monostatic- scattering kernel and reflection- coefficient forward and inverse...frequencies. Left two columns: scattering data; right two columns: reflection- coefficient data. 3 layers, hence accounting for the uncertainty of
Scattering Tools for Nanostructure Phonon Engineering
2013-09-25
Arlington, VA 22203 AFOSR The vibrational properties of solids have crucial roles underpinning functional properties ranging from thermal conductivity... thermal diffuse scattering (TDS) techniques to nanoscale systems. With this approach we can probe phonons across the nanomaterials, phonons, x-ray...scattering, nanomembrane fabrication, flatness, large-wavevector vibrational properties, synchrotron x-rays, thermal diffuse scattering, silicon
Mathematical Model For Scattering From Mirrors
NASA Technical Reports Server (NTRS)
Wang, Yaujen
1988-01-01
Additional terms account for effects of particulate contamination. Semiempirical mathematical model of scattering of light from surface of mirror gives improved account of effects of particulate contamination. Models that treated only scattering by microscopic irregularities in surface gave bidirectional reflectance distribution functions differing from measured scattering intensities over some ranges of angles.
Multiple-scattering effects in lidar spectroscopy
NASA Astrophysics Data System (ADS)
Joelson, Brad D.; Kattawar, George W.
1996-11-01
We have performed Monte Carlo calculations to investigate the effect of multiple scattering on the frequency spectra due to Brillouin scattering in the ocean. The use of the frequency spectra to determine the speed of sound and temperature profiles and the hydrosol backscattering probability is shown to be stable in turbid multiple scattering waters.
Spectroscopy, scattering, and KK molecules
Weinstein, J.
1994-04-01
The author presents a pedagogical description of a new theoretical technique, based on the multichannel Schroedinger equation, for simultaneously applying the quark model to both meson spectroscopy and meson-meson scattering. This is an extension of an earlier analysis which led to the prediction that the f{sub o}(975) and a{sub o}(980) scalar mesons are K{bar K} molecular states.
Ultrasonic scattering from anisotropic shells
NASA Astrophysics Data System (ADS)
Mittleman, John; Thompson, R. B.; Roberts, R.
The exact differential equations for elastic wave scattering from spherical shells with spherically orthotropic properties are presently shown to be separable; the angular equations are satisfied by Legendre polynomials that are independent of material properties. The results thus obtained have been validated by exact solutions for the case with vanishing shell thickness, and that of isotropic elastic constants. Excellent agreement is thus obtained over a wide range of shell thicknesses and wave numbers.
Electron scattering from polarized tritium
Jones, C.E.
1993-11-01
the recent development of high-intensity gaseous targets of polarized hydrogen and deuterium raises the interesting possibility of developing a polarized tritium target that can operate in relatively high current electron beams. Here I discuss the feasibility of a measurement of the helicity-dependent asymmetry in {sup 3}{rvec H}({rvec e},e{prime}) inclusive quasielastic scattering with such a target.
Regional Seismograms: Attenuation and Scattering
1992-03-06
chosen because it can produce a full solution to the elastodynamic equation of motion, and unlike high frequency approximations (such as raytracing ...Lechniques such as raytracing are valid only when the size of the scatterer is large compared to a wavelength (e.g., ka > 10) (Cervenk, et al., 1982...crustal structure in southern Norway, Bull. Seismol. Soc. Am., 61, 457-471, 1971. Skolnik, M. I., Radar Handbook, McGraw-Hill Book Co., New York, 1970
Parity Violation in Electron Scattering
Beise, Elizabeth
2007-10-26
About thirty years ago, electron scattering from nucleons was used [1] to identify, and then measure, the properties of the weak interaction, the only force of nature known to violate the symmetry parity. The basic technique has not fundamentally changed, which is to look for a small asymmetry in count rate from scattering a polarized electron beam from an unpolarized target. Since then, parity-violating (PV) electron scattering has developed substantially, a result of significant improvements in polarized electron beams, accelerator advancements, and developments in cryogenic targets that make it possible to carry out experiments with much higher statistical precision. In the last decade PV experiments have focused on using the complementary electron-quark flavor coupling of the weak interaction to identify and place limits on contributions of strange quark-antiquark pairs to the charge and magnetism of the proton. This observable provides a unique window into the structure of the proton since strange quark contributions can arise only from the sea of quarks and gluons that are responsible for the vast majority of the nucleon's mass. This paper will report on recent results aimed at this goal, along with a brief overview of future directions.
Decoherence due to Scattering Atoms
NASA Astrophysics Data System (ADS)
Uys, Hermann; Perreault, John; Cronin, Alex
2004-05-01
Coherent manipulation of a quantum system is difficult because of uncontrolled interactions with the system's environment. The study of decoherence so introduced is important for progress in quantum mechanical engineering, and for understanding the transition from quantum to classical behavior. We have observed loss of fringe contrast in a Mach-Zhender atom interferometer due to scattering background gas atoms and propose that this might be interpreted as quantum decoherence. Progress will be reported on the use of a general model of decoherence incorporating a semi-classical picture of atom scattering to explain the contrast loss [1]. A formal analogy is made to decoherence due to scattering photons from atoms in an interferometer [2]. [1] S.M. Tan, D.F. Waals, ``Loss of coherence in interferometry", Phys. Rev. A 47 p.4663 (1993) [2] D.A. Kokorowski, A.D. Cronin, T.D. Roberts, and D.E. Pritchard, ``From single- to multiple-photon decoherence in an atom interferometer", Phys. Rev. Lett. 86 p. 2191 (2001)
Electron-Hydrogen Elastic Scattering
NASA Technical Reports Server (NTRS)
Bhatia, A. K.
2004-01-01
Scattering by single-electron systems is always of interest because the wave function of the target is known exactly. Various approximations have been employed to take into account distortion produced in the target. Among them are the method of polarized orbitals and the close coupling approximation. Recently, e-H and e-He+ S-wave scattering in the elastic region has been studied using the Feshbach projection operator formalism. In this approach, the usual Hartree-Fock and exchange potentials are augmented by an optical potential and the resulting phase shifts have rigorous lower bounds. Now this method is being applied to the e-H P-wave scattering in the elastic region. The number of terms in the Hylleraas-type wave function for the 1,3 P phase shifts is 84 and the resulting phase shifts (preliminary) are given. The results have been given up to five digits because to that accuracy they are rigorous lower bounds. They are in general agreement with the variational (VAR) results of Armstead, and those obtained from the intermediate energy R-matrix method (RM) of Scholz et al., and the finite element method (FEM) of Botero and Shertzer. The later two methods do not provide any bounds on phase shifts.
Deep and shallow inelastic scattering
Ray, Heather
2015-05-15
In this session we focused on the higher energy deep and shallow inelastic particle interactions, DIS and SIS. DIS interactions occur when the energy of the incident particle beam is so large that the beam is able to penetrate the nucleons inside of the target nuclei. These interactions occur at the smallest level possible, that of the quark-gluon, or parton, level. SIS interactions occur in an intermediate energy range, just below the energy required for DIS interactions. The DIS cross section formula contains structure functions that describe our understanding of the underlying parton structure of nature. The full description of DIS interactions requires three structure functions: two may be measured in charged lepton or neutrino scattering, but one can only be extracted from neutrino DIS data. There are reasons to expect that the impact of nuclear effects could be different for neutrinos engaging in the DIS interaction, vs those felt by leptons. In fact, fits by the nCTEQ collaboration have found that the neutrino-Fe structure functions appear to differ from those extracted from lepton scattering data [1]. To better understand the global picture of DIS and SIS, we chose a three-pronged attack that examined recent experimental results, data fits, and latest theory predictions. Experimental results from neutrino and lepton scattering, as well as collider experiments, were presented.
Light scattering by marine heterotrophic bacteria
NASA Technical Reports Server (NTRS)
Ulloa, Osvaldo; Sathyendranath, Shubha; Platt, Trevor; Quinones, Renato A.
1992-01-01
Mie theory is applied to estimate scattering by polydispersions of marine heterotrophic bacteria, and a simple expression is derived for the bacterial scattering coefficient. The error incurred in deriving bacterial optical properties by use of the van de Hulst approximations is computed. The scattering properties of natural bacterial assemblages in three marine environments, Georges Bank, Northeast Channel, and Sargasso Sea, are assessed by applying Mie theory to field data on bacterial size and abundance. Results are used to examine the potential contribution of bacteria to the scattering properties of seawater. The utility of using pigment data to predict the magnitude of scattering by bacteria is discussed.
Speckles in interstellar radio-wave scattering
NASA Technical Reports Server (NTRS)
Desai, K. M.; Gwinn, C. R.; Reynolds, J.; King, E. A.; Jauncey, D.; Nicholson, G.; Flanagan, C.; Preston, R. A.; Jones, D. L.
1991-01-01
Observations of speckles in the scattering disk of the Vela pulsar are presented and speckle techniques for studying and circumventing scattering of radio waves by the turbulent interstellar plasma are discussed. The speckle pattern contains, in a hologrammatic fashion, complete information on the structure of the radio source as well as the distribution of the scattering material. Speckle observations of interstellar scattering of radio waves are difficult because of their characteristically short timescales and narrow bandwidths. Here, first observations are presented, taken at 13 cm wavelength with elements of the SHEVE VLBI network, of speckles in interstellar scattering.
PREFACE: Atom-surface scattering Atom-surface scattering
NASA Astrophysics Data System (ADS)
Miret-Artés, Salvador
2010-08-01
It has been a privilege and a real pleasure to organize this special issue or festschrift in the general field of atom-surface scattering (and its interaction) in honor of J R Manson. This is a good opportunity and an ideal place to express our deep gratitude to one of the leaders in this field for his fundamental and outstanding scientific contributions. J R Manson, or Dick to his friends and colleagues, is one of the founding fathers, together with N Cabrera and V Celli, of the 'Theory of surface scattering and detection of surface phonons'. This is the title of the very well-known first theoretical paper by Dick published in Physical Review Letters in 1969. My first meeting with Dick was around twenty years ago in Saclay. J Lapujoulade organized a small group seminar about selective adsorption resonances in metal vicinal surfaces. We discussed this important issue in surface physics and many other things as if we had always known each other. This familiarity and warm welcome struck me from the very beginning. During the coming years, I found this to be a very attractive aspect of his personality. During my stays in Göttingen, we had the opportunity to talk widely about science and life at lunch or dinner time, walking or cycling. During these nice meetings, he showed, with humility, an impressive cultural background. It is quite clear that his personal opinions about history, religion, politics, music, etc, come from considering and analyzing them as 'open dynamical systems'. In particular, with good food and better wine in a restaurant or at home, a happy cheerful soirée is guaranteed with him, or even with only a good beer or espresso, and an interesting conversation arises naturally. He likes to listen before speaking. Probably not many people know his interest in tractors. He has an incredible collection of very old tractors at home. In one of my visits to Clemson, he showed me the collection, explaining to me in great detail, their technical properties
Proximity effect correction concerning forward scattering
NASA Astrophysics Data System (ADS)
Tsunoda, Dai; Shoji, Masahiro; Tsunoe, Hiroyuki
2010-09-01
The Proximity Effect is a critical problem in EB Lithography which is used in Photomask writing. Proximity Effect means that an electron shot by gun scatters by collided with resist molecule or substrate atom causes CD variation depending on pattern density [1]. Scattering by collision with resist molecule is called as "forward scattering", that affects in dozens of nanometer range, and with substrate atom is called as "backward scattering, that affects approximately 10 micrometer in 50keV acceleration voltage respectively. In conventional Proximity Effect Correction (PEC) for mask writing, we don't need to think forward scattering effect. However we should think about forward scattering because of smaller feature size. We have proposed a PEC software product named "PATACON PC-Cluster"[2], which can concern forward scattering and calculate optimum dose modulation. In this communication, we explain the PEC processing throughput when the that takes forward scattering into account. The key technique is to use different processing field size for forward scattering calculation. Additionally, the possibility is shown that effective PEC may be available by connecting forward scattering and backward scattering.
Directional light scattering from individual Au nanocup
NASA Astrophysics Data System (ADS)
Bai, Jinjun; Li, Yong; Zhao, Bo
2017-03-01
We investigate the optical scattering properties of gold nanocup with different orientation and fractional height by full vector finite element method. All of the scattering cross section, the distribution of electric field intensity, and the ability of directional light scattering are simulated, respectively. It is demonstrated that the scattering cross section of Au nanocup is a superposition of scattering spectrum of a transverse mode and an axial mode. The wavelength and the intensity of the maximum value of the scattering cross section increase initially then reduce with the fractional height increasing for transverse mode, while they increase monotonously with the fractional height increasing for axial mode. Furthermore, the calculation results show that the ability of redirecting incident light of Au nanocup mainly depends on the transverse mode. And the deflected angle of scattering increases with the fractional height of Au nanocup decreasing. These results indicate that Au nanocup has a promising application in the planar plasmon devices.
Positronium and Electron Scattering on Helium
NASA Technical Reports Server (NTRS)
DiRienzi, Joseph
2011-01-01
A recent work [1] establishes experimentally that Positronium scattering by atoms of various elements is surprisingly close in total cross-section to that of an isolated electron of the same velocity. In this work we will look at the scattering of Ps on Helium and compare it to a determination of the scattering of an e- with the same element. For both the Ps scattering and the e- scattering on He, we assume the symmetrization of the e- with the closed shell He electrons is the dominant interaction. A local effective potential employed in [2] and [3] is used to model the electron exchange and cross- sections are determined for a set of partial waves. For the Ps scattering we include as a secondary effect the Van der Waals interaction. For single e- scattering of He, we also employ a short range Coulomb potential and dispersion as contributing effects. Results of the cross-sections determined in each case are then compared
Scattering measurements on natural and model trees
NASA Technical Reports Server (NTRS)
Rogers, James C.; Lee, Sung M.
1990-01-01
The acoustical back scattering from a simple scale model of a tree has been experimentally measured. The model consisted of a trunk and six limbs, each with 4 branches; no foliage or twigs were included. The data from the anechoic chamber measurements were then mathematically combined to construct the effective back scattering from groups of trees. Also, initial measurements have been conducted out-of-doors on a single tree in an open field in order to characterize its acoustic scattering as a function of azimuth angle. These measurements were performed in the spring, prior to leaf development. The data support a statistical model of forest scattering; the scattered signal spectrum is highly irregular but with a remarkable general resemblance to the incident signal spectrum. Also, the scattered signal's spectra showed little dependence upon scattering angle.
Zhang, Lu; Chen, Xingyu; Zhang, Zhenxi; Chen, Wei; Zhao, Hong; Zhao, Xin; Li, Kaixing; Yuan, Li
2016-04-01
Scattering pulse is sensitive to the morphology and components of each single label-free cell. The most direct detection result, label free cell's scattering pulse is studied in this paper as a novel trait to recognize large malignant cells from small normal cells. A set of intrinsic scattering pulse calculation method is figured out, which combines both hydraulic focusing theory and small particle's scattering principle. Based on the scattering detection angle ranges of widely used flow cytometry, the scattering pulses formed by cell scattering energy in forward scattering angle 2°-5° and side scattering angle 80°-110° are discussed. Combining the analysis of cell's illuminating light energy, the peak, area, and full width at half maximum (FWHM) of label free cells' scattering pulses for fine structure cells with diameter 1-20 μm are studied to extract the interrelations of scattering pulse's features and cell's morphology. The theoretical and experimental results show that cell's diameter and FWHM of its scattering pulse agree with approximate linear distribution; the peak and area of scattering pulse do not always increase with cell's diameter becoming larger, but when cell's diameter is less than about 16 μm the monotone increasing relation of scattering pulse peak or area with cell's diameter can be obtained. This relationship between the features of scattering pulse and cell's size is potentially a useful but very simple criterion to distinguishing malignant and normal cells by their sizes and morphologies in label free cells clinical examinations.
Electron scattering in tantalum monoarsenide
NASA Astrophysics Data System (ADS)
Zhang, Cheng-Long; Yuan, Zhujun; Jiang, Qing-Dong; Tong, Bingbing; Zhang, Chi; Xie, X. C.; Jia, Shuang
2017-02-01
We report comprehensive studies of the single crystal growth and electrical transport properties for various samples of TaAs, the first experimentally confirmed inversion symmetry-breaking Weyl semimetal. The transport parameters for different samples are obtained through the fitting of the two-band model and the analysis of Shubnikov-de Haas oscillations. We find that the ratio factor of transport lifetime to quantum lifetime is intensively enhanced when the Fermi level approaches the Weyl node. This result is consistent with the side-jump interpretation derived from a chirality-protected shift in the scattering process for a Weyl semimetal.
Stimulated Cerenkov-Raman Scattering.
1983-12-14
Dokl. Akad. Nauk. SSSR 3,253. 11. Coleman, P., and Enderby, C. (1960). J. AppI. Phys. 31, 1695. 12. Danos , M. ( 1953 ). J. Appl. Phys. 26,2. *1f 13...made by Coleman, by Danos , by Lashinsky,13 and by Ulrich.14 In these experiments, no provision was made for feeding back the emitted radia- I tion on...latio e ted ltiple Scattering’ * Pts. Is.; Vol. 8I(2), pp. 245-248. Jan. 11, 19S2. d . Jelly, J. V., Cerefo U diation nd its A liti rgqam sess, 1953
Neutron scattering from a ferrofluid
Lin, M.Y. |; Luo, W.; Lynn, J.
1995-12-31
Small angle neutron scattering experiments were performed on a eicosane-based ferrofluid. An average size of 88 {angstrom} can be extracted from the data, in agreement with results from electron microscopy. Below the frozen temperature of eicosane, however, the particles are seen to be in larger aggregates with a fractal dimension of 2.15, similar to those formed under reaction-limited cluster aggregation (RLCA) conditions. At high concentrations, particles form larger aggregates even in the liquid state. Applying a magnetic field introduces new structure and changes the density inside the aggregates.
Hadron scattering, resonances, and QCD
Briceno, Raul
2016-12-01
The non-perturbative nature of quantum chromodynamics (QCD) has historically left a gap in our understanding of the connection between the fundamental theory of the strong interactions and the rich structure of experimentally observed phenomena. For the simplest properties of stable hadrons, this is now circumvented with the use of lattice QCD (LQCD). In this talk I discuss a path towards a rigorous determination of few-hadron observables from LQCD. I illustrate the power of the methodology by presenting recently determined scattering amplitudes in the light-meson sector and their resonance content.
Thomson scattering at general fusion
NASA Astrophysics Data System (ADS)
Young, W. C.; Parfeniuk, D.
2016-11-01
This paper provides an overview of the Thomson scattering diagnostic in use at General Fusion, including recent upgrades and upcoming plans. The plasma experiment under examination produces temperatures in the 50-500 eV range with density on the order of 1020 m-3. A four spatial point collection optics scheme has been implemented, with plans to expand to six spatial points. Recent changes to the optics of the laser beamline have reduced stray light. The system employs a frequency doubled Nd:YAG laser (532 nm), a grating spectrometer, and a photomultiplier array based detector.
Electromagnetic Scattering from Realistic Targets
NASA Technical Reports Server (NTRS)
Lee, Shung- Wu; Jin, Jian-Ming
1997-01-01
The general goal of the project is to develop computational tools for calculating radar signature of realistic targets. A hybrid technique that combines the shooting-and-bouncing-ray (SBR) method and the finite-element method (FEM) for the radiation characterization of microstrip patch antennas in a complex geometry was developed. In addition, a hybridization procedure to combine moment method (MoM) solution and the SBR method to treat the scattering of waveguide slot arrays on an aircraft was developed. A list of journal articles and conference papers is included.
Hard Scattering Studies at Jlab
Harutyun Avagyan; Peter Bosted; Volker Burkert; Latifa Elouadrhiri
2005-09-01
We present current activities and future prospects for studies of hard scattering processes using the CLAS detector and the CEBAF polarized electron beam. Kinematic dependences of single and double spin asymmetries have been measured in a wide kinematic range at CLAS with a polarized NH{sub 3} and unpolarized liquid hydrogen targets. It has been shown that the data are consistent with factorization and observed target and beam asymmetries are in good agreement with measurements performed at higher energies, suggesting that the high energy-description of the semi-inclusive DIS process can be extended to the moderate energies of JLab measurements.
Scattering of phonons by vacancies
Ratsifaritana, C.A.; Klemens, P.G.
1987-11-01
The scattering of phonons by vacancies is estimated by a perturbation technique in terms of the missing mass and the missing linkages. An argument is given why distortion effects can be disregarded. The resonance frequency of the defect is sufficiently high so that resonance effects can be disregarded for phonons in the important frequency range for thermal conduction. The theory is applied to the thermal resistance by vacancies in cases where the vacancy concentration is known: potassium chloride with divalent cations, nonstoichiometric zirconium carbide, and tin telluride.
Enhanced Forward Scattering of Ellipsoidal Dielectric Nanoparticles.
Wang, Zhonghua; An, Ning; Shen, Fei; Zhou, Hongping; Sun, Yongxuan; Jiang, Zhaoneng; Han, Yanhua; Li, Yan; Guo, Zhongyi
2017-12-01
Dielectric nanoparticles can demonstrate a strong forward scattering at visible and near-infrared wavelengths due to the interaction of optically induced electric and magnetic dipolar resonances. For a spherical nanoparticle, the first Kerker's condition within dipole approximation can be realized, where backward scattering can reach zero. However, for this type of dielectric sphere, maximum forward scattering without backward scattering cannot be realized by modulating the refractive index and particle size of this nanoparticle. In this paper, we have demonstrated that a larger directional forward scattering than the traditional spherical nanoparticle can be obtained by using the ellipsoidal nanoparticle, due to the overlapping electric and magnetic dipolar modes. For the oblate ellipsoid with a determined refractive index, there is an optimum shape for generating the suppressed backward scattering along with the enhanced forward scattering at the resonant wavelength, where the electric and magnetic dipolar modes overlap with each other. For the prolate ellipsoid, there also exist the overlapping electric and magnetic dipolar modes at the resonant wavelength of total scattering, which have much higher forward scattering than those for both oblate ellipsoid and sphere, due to the existence of the higher multipolar modes. Furthermore, we have also demonstrated the realization of the dimensional tailoring in order to make the strong forward scattering shift to the desired wavelength.
Scattering from Thin Dielectric Disks
NASA Technical Reports Server (NTRS)
Levine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.
1984-01-01
A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectric properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T is sufficiently large the disk will always be in one or the other of these regimes (T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.
Thomson scattering on inhomogeneous targets.
Thiele, R; Sperling, P; Chen, M; Bornath, Th; Fäustlin, R R; Fortmann, C; Glenzer, S H; Kraeft, W-D; Pukhov, A; Toleikis, S; Tschentscher, Th; Redmer, R
2010-11-01
The introduction of brilliant free-electron lasers enables new pump-probe experiments to characterize warm dense matter states. For instance, a short-pulse optical laser irradiates a liquid hydrogen jet that is subsequently probed with brilliant soft x-ray radiation. The strongly inhomogeneous plasma prepared by the optical laser is characterized with particle-in-cell simulations. The interaction of the soft x-ray probe radiation for different time delays between pump and probe with the inhomogeneous plasma is also taken into account via radiative hydrodynamic simulations. We calculate the respective scattering spectrum based on the Born-Mermin approximation for the dynamic structure factor considering the full density and temperature-dependent Thomson scattering cross section throughout the target. We can identify plasmon modes that are generated in different target regions and monitor their temporal evolution. Therefore, such pump-probe experiments are promising tools not only to measure the important plasma parameters density and temperature but also to gain valuable information about their time-dependent profile through the target. The method described here can be applied to various pump-probe scenarios by combining optical lasers and soft x ray, as well as x-ray sources.
Bromley, Benjamin C.; Kenyon, Scott J. E-mail: skenyon@cfa.harvard.edu
2014-12-01
As gas giant planets evolve, they may scatter other planets far from their original orbits to produce hot Jupiters or rogue planets that are not gravitationally bound to any star. Here, we consider planets cast out to large orbital distances on eccentric, bound orbits through a gaseous disk. With simple numerical models, we show that super-Earths can interact with the gas through dynamical friction to settle in the remote outer regions of a planetary system. Outcomes depend on planet mass, the initial scattered orbit, and the evolution of the time-dependent disk. Efficient orbital damping by dynamical friction requires planets at least as massive as the Earth. More massive, longer-lived disks damp eccentricities more efficiently than less massive, short-lived ones. Transition disks with an expanding inner cavity can circularize orbits at larger distances than disks that experience a global (homologous) decay in surface density. Thus, orbits of remote planets may reveal the evolutionary history of their primordial gas disks. A remote planet with an orbital distance ∼100 AU from the Sun is plausible and might explain correlations in the orbital parameters of several distant trans-Neptunian objects.
Exact Multiple Scattering XANES Calculations
NASA Astrophysics Data System (ADS)
Ravel, B.; Rehr, J. J.
1996-03-01
Ab initio calculations of X-ray absorption near-edge structure (XANES), are made by inverting the full multiple-scattering (MS) matrix G=(1-G_0t)-1G_0. Our approach uses the fast, quickly convergent Rehr-Albers(J.J. Rehr and R.C. Albers, Phys. Rev. B, 41), 8139, (1990) separable representation of the free electron propagator G0 together with atomic scattering t-matrices from the FEFF6 code,(S. I. Zabinsky, et al., Phys. Rev. B52), 2995 (1995). which are calculated within the muffin-tin approximation with overlapped atom potentials. With this technique XANES spectra and its polarization dependence can be calculated in reasonable cpu time on large clusters. Good agreement with the XANES spectra of several sample compounds is obtained. This strategy is also used to determine the local densities of states ρ(E, r ) from the full MS matrix. From ρ(E, r ) we calculate the Fermi energies and estimate charge transfer for our sample clusters. The prospect of quantitative analysis of XANES spectra and its preedge features is discussed.
Scattering from thin dielectric disks
NASA Technical Reports Server (NTRS)
Le Vine, D. M.; Schneider, A.; Lang, R. H.; Carter, H. G.
1985-01-01
A solution was obtained for scattering from thin dielectric disks by approximating the currents induced inside the disk with the currents which would exist inside a dielectric slab of the same thickness, orientation and dielectic properties. This approximation reduces to an electrostatic approximation when the disk thickness, T, is small compared to the wavelength of the incident radiation and the approximation yields a conventional physical optics solution when the dimension, A, characteristic of the geometrical cross section of the disk (e.g., the diameter of a circular disk) is large compared to wavelength. When the ratio A/T sufficiently large the disk will always be in one or the other of these regimes, T lambda or kA1. Consequently, when A/T is large this solution provides a conventional approximation for the scattered fields which can be applied at all frequencies. As a check on this conclusion, a comparison was made between the theoretical and measured radar cross section of thin dielectric disks. Agreement was found for thin disks with both large and small values of kA.
Pion scattering and nuclear dynamics
Johnson, M.B.
1988-01-01
A phenomenological optical-model analysis of pion elastic scattering and single- and double-charge-exchange scattering to isobaric-analog states is reviewed. Interpretation of the optical-model parameters is briefly discussed, and several applications and extensions are considered. The applications include the study of various nuclear properties, including neutron deformation and surface-fluctuation contributions to the density. One promising extension for the near future would be to develop a microscopic approach based on powerful momentum-space methods brought to existence over the last decade. In this, the lowest-order optical potential as well as specific higher-order pieces would be worked out in terms of microscopic pion-nucleon and delta-nucleon interactions that can be determined within modern meson-theoretical frameworks. A second extension, of a more phenomenological nature, would use coupled-channel methods and shell-model wave functions to study dynamical nuclear correlations in pion double charge exchange. 35 refs., 11 figs., 1 tab.
Spectral scattering properties of turbid waters
NASA Technical Reports Server (NTRS)
Whitlock, C. H.; Poole, L. R.; Houghton, W. M.
1980-01-01
River water samples have been examined for optical scattering properties at wavelengths between 400 and 800 nm. Scattering coefficients were calculated from measurements of beam attenuation and absorption coefficients and are observed to vary with wavelength. At a fixed wavelength, the scattering coefficient is influenced by both phytoplankton concentration (as indicated by chlorophyll a) and suspended solids concentration. Measurements of small angle volume-scattering function indicate that the phase function at an angle of 1.5 deg is not constant for turbid waters and varies with both wavelength and beam attenuation coefficient. These data differ from previously published results for relatively clear oceanic and coastal waters. Caution is required when attempting to estimate scattering coefficient values from single-angle measurements of volume-scattering function.
Stimulated Electronic X-Ray Raman Scattering
NASA Astrophysics Data System (ADS)
Weninger, Clemens; Purvis, Michael; Ryan, Duncan; London, Richard A.; Bozek, John D.; Bostedt, Christoph; Graf, Alexander; Brown, Gregory; Rocca, Jorge J.; Rohringer, Nina
2013-12-01
We demonstrate strong stimulated inelastic x-ray scattering by resonantly exciting a dense gas target of neon with femtosecond, high-intensity x-ray pulses from an x-ray free-electron laser (XFEL). A small number of lower energy XFEL seed photons drive an avalanche of stimulated resonant inelastic x-ray scattering processes that amplify the Raman scattering signal by several orders of magnitude until it reaches saturation. Despite the large overall spectral width, the internal spiky structure of the XFEL spectrum determines the energy resolution of the scattering process in a statistical sense. This is demonstrated by observing a stochastic line shift of the inelastically scattered x-ray radiation. In conjunction with statistical methods, XFELs can be used for stimulated resonant inelastic x-ray scattering, with spectral resolution smaller than the natural width of the core-excited, intermediate state.
An electrical analogy to Mie scattering
NASA Astrophysics Data System (ADS)
Caridad, José M.; Connaughton, Stephen; Ott, Christian; Weber, Heiko B.; Krstić, Vojislav
2016-09-01
Mie scattering is an optical phenomenon that appears when electromagnetic waves, in particular light, are elastically scattered at a spherical or cylindrical object. A transfer of this phenomenon onto electron states in ballistic graphene has been proposed theoretically, assuming a well-defined incident wave scattered by a perfectly cylindrical nanometer scaled potential, but experimental fingerprints are lacking. We present an experimental demonstration of an electrical analogue to Mie scattering by using graphene as a conductor, and circular potentials arranged in a square two-dimensional array. The tabletop experiment is carried out under seemingly unfavourable conditions of diffusive transport at room-temperature. Nonetheless, when a canted arrangement of the array with respect to the incident current is chosen, cascaded Mie scattering results robustly in a transverse voltage. Its response on electrostatic gating and variation of potentials convincingly underscores Mie scattering as underlying mechanism. The findings presented here encourage the design of functional electronic metamaterials.
Optical Sensors Using Stimulated Brillouin Scattering
NASA Technical Reports Server (NTRS)
Christensen, Caleb A (Inventor); Zavriyev, Anton (Inventor)
2017-01-01
A method for enhancing a sensitivity of an optical sensor having an optical cavity counter-propagates beams of pump light within the optical cavity to produce scattered light based on Stimulated Brillouin Scattering (SBS). The properties of the pump light are selected to generate fast-light conditions for the scattered light, such that the scattered light includes counter-propagating beams of fast light. The method prevents the pump light from resonating within the optical cavity, while allowing the scattered light to resonate within the optical cavity. At least portions of the scattered light are interfered outside of the optical cavity to produce a beat note for a measurement of the optical sensor. The disclosed method is particularly applicable to optical gyroscopes.
An electrical analogy to Mie scattering
Caridad, José M.; Connaughton, Stephen; Ott, Christian; Weber, Heiko B.; Krstić, Vojislav
2016-01-01
Mie scattering is an optical phenomenon that appears when electromagnetic waves, in particular light, are elastically scattered at a spherical or cylindrical object. A transfer of this phenomenon onto electron states in ballistic graphene has been proposed theoretically, assuming a well-defined incident wave scattered by a perfectly cylindrical nanometer scaled potential, but experimental fingerprints are lacking. We present an experimental demonstration of an electrical analogue to Mie scattering by using graphene as a conductor, and circular potentials arranged in a square two-dimensional array. The tabletop experiment is carried out under seemingly unfavourable conditions of diffusive transport at room-temperature. Nonetheless, when a canted arrangement of the array with respect to the incident current is chosen, cascaded Mie scattering results robustly in a transverse voltage. Its response on electrostatic gating and variation of potentials convincingly underscores Mie scattering as underlying mechanism. The findings presented here encourage the design of functional electronic metamaterials. PMID:27671003
Microscopic Imaging and Spectroscopy with Scattered Light
Boustany, Nada N.; Boppart, Stephen A.; Backman, Vadim
2012-01-01
Optical contrast based on elastic scattering interactions between light and matter can be used to probe cellular structure and dynamics, and image tissue architecture. The quantitative nature and high sensitivity of light scattering signals to subtle alterations in tissue morphology, as well as the ability to visualize unstained tissue in vivo, has recently generated significant interest in optical scatter based biosensing and imaging. Here we review the fundamental methodologies used to acquire and interpret optical scatter data. We report on recent findings in this field and present current advances in optical scatter techniques and computational methods. Cellular and tissue data enabled by current advances in optical scatter spectroscopy and imaging stand to impact a variety of biomedical applications including clinical tissue diagnosis, in vivo imaging, drug discovery and basic cell biology. PMID:20617940
An optical model for composite nuclear scattering
NASA Technical Reports Server (NTRS)
Wilson, J. W.; Townsend, L. W.
1981-01-01
The optical model of composite particle scattering is considered and compared to the accuracies of other models. A nonrelativistic Schroedinger equation with two-body potentials is used for the scattering of a single particle by an energy-dependent local potential. The potential for the elastic channel is composed of matrix elements of a single scattering operator taken between the ground states of the projectile and the target; the coherent amplitude is considered as dominating the scattering in the forward direction. A multiple scattering series is analytically explored and formally summed by the solution of an equivalent Schroedinger equation. Cross sections of nuclear scattering are then determined for He-4 and C-12 nuclei at 3.6 GeV/nucleus and O-16 projectiles at 2.1 GeV/nucleus, and the optical model approximations are found to be consistently lower and more accurate than approximations made by use of Glauber's theory.
Basin topology in dissipative chaotic scattering.
Seoane, Jesús M; Aguirre, Jacobo; Sanjuán, Miguel A F; Lai, Ying-Cheng
2006-06-01
Chaotic scattering in open Hamiltonian systems under weak dissipation is not only of fundamental interest but also important for problems of current concern such as the advection and transport of inertial particles in fluid flows. Previous work using discrete maps demonstrated that nonhyperbolic chaotic scattering is structurally unstable in the sense that the algebraic decay of scattering particles immediately becomes exponential in the presence of weak dissipation. Here we extend the result to continuous-time Hamiltonian systems by using the Henon-Heiles system as a prototype model. More importantly, we go beyond to investigate the basin structure of scattering dynamics. A surprising finding is that, in the common case where multiple destinations exist for scattering trajectories, Wada basin boundaries are common and they appear to be structurally stable under weak dissipation, even when other characteristics of the nonhyperbolic scattering dynamics are not. We provide numerical evidence and a geometric theory for the structural stability of the complex basin topology.
Relativistic Electron Beams, Forward Thomson Scattering, and ``Raman'' Scattering
NASA Astrophysics Data System (ADS)
Simon, A.
1999-11-01
Experiments at LLE (see abstract by D. Hicks at this meeting) show that surprisingly high potentials (+0.5 to 2.0 MV) develop in plasmas irradiated by high-energy lasers. The highly conducting plasma will be a near equipotential and should attract return-current electrons in a radial beam-like distribution, especially in the outer low-density regions. This will initiate the BOT instability, creating large plasma waves with phase velocities close to c. Coherent Thomson scattering of the interaction beam from these waves must occur primarily in the forward direction. This will appear to be ``backward SRS'' upon reflection from a critical surface. We will show that the resulting spectrum is fairly broad and at short wavelengths. Collisional absorption of the scattered EM wave limits the reflectivity to low values (depending on the density scale length). Thus, a distinct difference exists between the spectrum for thick targets (nc surface present) and thin targets (gasbags, etc., from which primarily a narrow absolute-SRS backward emission occurs, at the peak density). The thick-target, reflected-wave angular distribution will be concentrated in the backward direction. The corresponding plasma-wave k-vector will be a fraction of k_0. The variation of the spectrum with potential and angle will be discussed. Comparison will be made with recent results at LLE and LLNL. This work was supported by the U.S. Department of Energy Office of Inertial Confinement Fusion under Cooperative Agreement No. DE-FC03-92SF19460, UR, and NYSERDA.
Collinear scattering of photoexcited carriers in graphene
NASA Astrophysics Data System (ADS)
Trushin, Maxim
2016-11-01
We propose an explicitly solvable model for collinear scattering of photoexcited carriers in intrinsic graphene irradiated by monochromatic light. We find that the collinear scattering rate is directly proportional to the photocarrier energy and derive an analytic expression for the corresponding relaxation time. The result agrees with the recent numerical prediction [Nat. Commun. 7, 11617 (2016), 10.1038/ncomms11617] and is able to describe the photocarrier evolution at low energies, where scattering on optical phonons is strongly suppressed.
Scattering from Rock and Rock Outcrops
2014-09-30
display a currently valid OMB control number. 1. REPORT DATE 30 SEP 2014 2. REPORT TYPE 3. DATES COVERED 00-00-2014 to 00-00-2014 4. TITLE AND...outcrops are intended to address many of the open questions which exist for scattering from these types of surfaces and include increasing our basic...understanding of: 1) geoacoustic characteristics of rock relevant to scattering, 2) scattering strength versus grazing angle, and 3
Efficient Finite Element Modelling of Elastodynamic Scattering
NASA Astrophysics Data System (ADS)
Velichko, A.; Wilcox, P. D.
2010-02-01
A robust and efficient technique for predicting the complete scattering behavior for an arbitrarily-shaped defect is presented that can be implemented in a commercial FE package. The spatial size of the modeling domain around the defect is as small as possible to minimize computational expense and a minimum number of models are executed. Example results for 2D and 3D scattering in isotropic material and guided wave scattering are presented.
Laser scattering properties of rough spherical surfaces
NASA Astrophysics Data System (ADS)
Yang, Chun-ping; Wu, Jian
2007-12-01
An approximate model is developed to study the properties of laser scattering from a rough spherical surface based on a random facet model and the electromagnetic scattering theory. For actual spheres, for instance oilcan, its lateral correlation length is much longer than the incident laser wavelength, and its surface distribution is usually isotropic and conforms to Gaussian distribution. Hence, it is feasible to deal with scattering of the rough spherical surface with the random facet model. First, power scattered into a detective system can be denoted for every facet with the scattering model of a coarse plane corresponded to the isotropic Gaussian statistics. Second, total power received by the detective system should correspond to incoherent addition of power scattered into a far-field detector system by all facets. Here, an incident shadow function has been taken into account to exclude the contribution of the facets not being illuminated. Likewise, a scattering shadow function is introduced to exclude the contribution of the scattered light blocked by undulations of spherical surface. An unfolded factor has been taken into account in this model, too. Finally, to verify this model, the angular distribution of the scattering intensity in far field is calculated and analyzed under different cases. The results show that the scattering intensity is stronger in the backward than in other directions if the spherical surface is smooth, but if the spherical surface is rough to some extent, the incident laser power will be scattered to other direction and there is faint scattered intensity in forward direction concomitantly. We can use these properties to make remote sensing for spherical objects.
Shaped beam scattering by a spheroidal object
NASA Astrophysics Data System (ADS)
Zhang, Huayong
2016-12-01
A theoretical procedure is developed for the calculation of the electromagnetic fields scattered by a spheroidal object with arbitrary monochromatic illumination. The suggested solution utilizes the method of moments technique in a spheroidal coordinate system. For oblique incidence of a Gaussian beam and zero-order Bessel beam, numerical results of the normalized differential scattering cross section are presented, and the scattering characteristics are analyzed concisely.
Learning-based imaging through scattering media.
Horisaki, Ryoichi; Takagi, Ryosuke; Tanida, Jun
2016-06-27
We present a machine-learning-based method for single-shot imaging through scattering media. The inverse scattering process was calculated based on a nonlinear regression algorithm by learning a number of training object-speckle pairs. In the experimental demonstration, multilayer phase objects between scattering plates were reconstructed from intensity measurements. Our approach enables model-free sensing, where it is not necessary to know the sensing processes/models.
An Analysis of Scatterable Mine Doctrine.
1983-06-02
SOVT ACCESSION NO 3. RECIPIENT’S CATALOG NUMBER 4. TITLE (and Subtitle) S. TYPE OF REPORT & PERIOD COVERED An Analysis of Scatterable Mine Doctrine Group...smcy. AN ANALYSIS OF SCATTERABLE MINE DOCTRINE BY LIEUTENANT COLONEL (P) LARRY G. LEHOWICZ, INFANTRY MR. GEORGE W. DANEKER, SR., GS-14 COLONEL ERNEST... ANALYSIS OF SCATTERABLE MINE DOCTRINE GROUP STUDY PROJECT by Lieutenant Colonel (P) Larry G. Lehowicz, Infantry Mr. George W. Deneker, Sr. GS-14 Colonel
Circular Intensity Differential Scattering of chiral molecules
Bustamante, C.J.
1980-12-01
In this thesis a theory of the Circular Intensity Differential Scattering (CIDS) of chiral molecules as modelled by a helix oriented with respect to the direction of incidence of light is presented. It is shown that a necessary condition for the existence of CIDS is the presence of an asymmetric polarizability in the scatterer. The polarizability of the scatterer is assumed generally complex, so that both refractive and absorptive phenomena are taken into account.
Elastic scattering with weakly bound projectiles
Figueira, J. M.; Abriola, D.; Arazi, A.; Capurro, O. A.; Marti, G. V.; Martinez Heinmann, D.; Pacheco, A. J.; Testoni, J. E.; Barbara, E. de; Fernandez Niello, J. O.; Padron, I.; Gomes, P. R. S.; Lubian, J.
2007-02-12
Possible effects of the break-up channel on the elastic scattering threshold anomaly has been investigated. We used the weakly bound 6,7Li nuclei, which is known to undergo break-up, as projectiles in order to study the elastic scattering on a 27Al target. In this contribution we present preliminary results of these experiments, which were analyzed in terms of the Optical Model and compared with other elastic scattering data using weakly bound nuclei as projectile.
Radiation Transfer in the Atmosphere: Scattering
NASA Technical Reports Server (NTRS)
Mishchenko, M.; Travis, L.; Lacis, Andrew A.
2014-01-01
Sunlight illuminating the Earth's atmosphere is scattered by gas molecules and suspended particles, giving rise to blue skies, white clouds, and optical displays such as rainbows and halos. By scattering and absorbing the shortwave solar radiation and the longwave radiation emitted by the underlying surface, cloud and aerosol particles strongly affect the radiation budget of the terrestrial climate system. As a consequence of the dependence of scattering characteristics on particle size, morphology, and composition, scattered light can be remarkably rich in information on particle properties and thus provides a sensitive tool for remote retrievals of macro- and microphysical parameters of clouds and aerosols.
Geometrical effects in X-mode scattering
Bretz, N.
1986-10-01
One technique to extend microwave scattering as a probe of long wavelength density fluctuations in magnetically confined plasmas is to consider the launching and scattering of extraordinary (X-mode) waves nearly perpendicular to the field. When the incident frequency is less than the electron cyclotron frequency, this mode can penetrate beyond the ordinary mode cutoff at the plasma frequency and avoid significant distortions from density gradients typical of tokamak plasmas. In the more familiar case, where the incident and scattered waves are ordinary, the scattering is isotropic perpendicular to the field. However, because the X-mode polarization depends on the frequency ratios and the ray angle to the magnetic field, the coupling between the incident and scattered waves is complicated. This geometrical form factor must be unfolded from the observed scattering in order to interpret the scattering due to density fluctuations alone. The geometrical factor is calculated here for the special case of scattering perpendicular to the magnetic field. For frequencies above the ordinary mode cutoff the scattering is relatively isotropic, while below cutoff there are minima in the forward and backward directions which go to zero at approximately half the ordinary mode cutoff density.
Scattering of waves by the invisible lens
NASA Astrophysics Data System (ADS)
Zuzaňáková, Kateřina; Tyc, Tomáš
2017-01-01
We investigate the scattering properties of the invisible lens in two ways. First, we describe the scattering of electromagnetic waves by the invisible lens realised by a purely dielectric, purely magnetic, and impedance-matched medium, respectively, using Debye potentials. Second, we employ the Wentzel-Kramers-Brillouin method to analyse the scattering of scalar waves by the lens. We show that in all cases the scattering is negligible for a discrete set of frequencies, while for other frequencies there is a phase slip at the boundary of the lens ‘shadow’.
Coupled-channel scattering on a torus
Guo, Peng; Dudek, Jozef Jon; Edwards, Robert G.; ...
2013-07-01
Based on the Hamiltonian formalism approach, a generalized Luscher's formula for two particle scattering in both the elastic and coupled-channel cases in moving frames is derived from a relativistic Lippmann-Schwinger equation. Some strategies for extracting scattering amplitudes for a coupled-channel system from the discrete finite-volume spectrum are discussed and illustrated with a toy model of two-channel resonant scattering. This formalism will, in the near future, be used to extract information about hadron scattering from lattice QCD computations.
Hadron scattering and resonances in QCD
Dudek, Jozef J.
2016-05-01
I describe how hadron-hadron scattering amplitudes are related to the eigenstates of QCD in a finite cubic volume. The discrete spectrum of such eigenstates can be determined from correlation functions computed using lattice QCD, and the corresponding scattering amplitudes extracted. I review results from the Hadron Spectrum Collaboration who have used these finite volume methods to study pi pi elastic scattering, including the rho resonance, as well as coupled-channel pi K, eta K scattering. Ongoing calculations are advertised and the outlook for finite volume approaches is presented.
Bidirectional scattering of light from tree leaves
NASA Technical Reports Server (NTRS)
Brakke, Thomas W.; Smith, James A.; Harnden, Joann M.
1989-01-01
A laboratory goniometer consisting of an He-Ne laser (632.8 nm), vertical leaf holder, and silicon photovoltaic detector was used to measure the bidirectional scattering (both transmittance and reflectance) of red oak and red maple. The illumination angles were 0, 30, and 60 deg, and the scattering was recorded approximately every 10 deg in the principal plane. The scattering profiles obtained show the non-Lambertian characteristics of the scattering, particularly for the off-nadir illumination directions. The transmitted light was more isotropic than the reflected light.
Modeling of scattering from ice surfaces
NASA Astrophysics Data System (ADS)
Dahlberg, Michael Ross
Theoretical research is proposed to study electromagnetic wave scattering from ice surfaces. A mathematical formulation that is more representative of the electromagnetic scattering from ice, with volume mechanisms included, and capable of handling multiple scattering effects is developed. This research is essential to advancing the field of environmental science and engineering by enabling more accurate inversion of remote sensing data. The results of this research contributed towards a more accurate representation of the scattering from ice surfaces, that is computationally more efficient and that can be applied to many remote-sensing applications.
Efficient finite element modeling of elastodynamic scattering
NASA Astrophysics Data System (ADS)
Wilcox, Paul D.; Velichko, Alexander
2009-03-01
The scattering of elastic waves by defects is the physical basis of ultrasonic NDE. Although analytical models exist for some canonical problems, the general case of scattering from an arbitrarily-shaped defect requires numerical methods such as finite elements (FE). In this paper, a robust and efficient FE technique is presented that is based on the premise of meshing a relatively small domain sufficient to enclose the scatterer. Plane waves are then excited from a particular direction by a numerical implementation of the Helmholtz-Kirchhoff integral that uses an encircling array of uni-modal point sources. The scattered field displacements are recorded at the same points and the field decomposed into plane waves of different modes at different angles. By repeating this procedure for different incident angles it is possible to generate the scattering- or S-matrix for the scatterer. For a given size of scatterer, all the information in an S-matrix can be represented in the Fourier domain by a limited number of complex coefficients. Thus the complete scattering behavior of an arbitrary-shaped scatterer can be characterized by a finite number of complex coefficients, that can be obtained from a relatively small number of FE model executions.
Material-independent modes for electromagnetic scattering
NASA Astrophysics Data System (ADS)
Forestiere, Carlo; Miano, Giovanni
2016-11-01
In this Rapid Communication, we introduce a representation of the electromagnetic field for the analysis and synthesis of the full-wave scattering by a homogeneous dielectric object of arbitrary shape in terms of a set of eigenmodes independent of its permittivity. The expansion coefficients are rational functions of the permittivity. This approach naturally highlights the role of plasmonic and photonic modes in any scattering process and suggests a straightforward methodology to design the permittivity of the object to pursue a prescribed tailoring of the scattered field. We discuss in depth the application of the proposed approach to the analysis and design of the scattering properties of a dielectric sphere.
Shaped beam scattering by an anisotropic particle
NASA Astrophysics Data System (ADS)
Chen, Zhenzhen; Zhang, Huayong; Huang, Zhixiang; Wu, Xianliang
2017-03-01
An exact semi-analytical solution to the electromagnetic scattering from an optically anisotropic particle illuminated by an arbitrarily shaped beam is proposed. The scattered fields and fields within the anisotropic particle are expanded in terms of spherical vector wave functions. The unknown expansion coefficients are determined by using the boundary conditions and the method of moments scheme. For incidence of a Gaussian beam, zero-order Bessel beam and Hertzian electric dipole radiation, numerical results of the normalized differential scattering cross section are given to a uniaxial, gyrotropic anisotropic spheroid and circular cylinder of finite length. The scattering properties are analyzed concisely.
Experimental confirmation of neoclassical Compton scattering theory
Aristov, V. V.; Yakunin, S. N.; Despotuli, A. A.
2013-12-15
Incoherent X-ray scattering spectra of diamond and silicon crystals recorded on the BESSY-2 electron storage ring have been analyzed. All spectral features are described well in terms of the neoclassical scattering theory without consideration for the hypotheses accepted in quantum electrodynamics. It is noted that the accepted tabular data on the intensity ratio between the Compton and Rayleigh spectral components may significantly differ from the experimental values. It is concluded that the development of the general theory (considering coherent scattering, incoherent scattering, and Bragg diffraction) must be continued.
Scatter factor corrections for elongated fields
Higgins, P.D.; Sohn, W.H.; Sibata, C.H.; McCarthy, W.A. )
1989-09-01
Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.
Scatter factor corrections for elongated fields.
Higgins, P D; Sohn, W H; Sibata, C H; McCarthy, W A
1989-01-01
Measurements have been made to determine scatter factor corrections for elongated fields of Cobalt-60 and for nominal linear accelerator energies of 6 MV (Siemens Mevatron 67) and 18 MV (AECL Therac 20). It was found that for every energy the collimator scatter factor varies by 2% or more as the field length-to-width ratio increases beyond 3:1. The phantom scatter factor is independent of which collimator pair is elongated at these energies. For 18 MV photons it was found that the collimator scatter factor is complicated by field-size-dependent backscatter into the beam monitor.
Scatter From Optical Components: An Overview
NASA Astrophysics Data System (ADS)
Stover, John C.
1990-01-01
Although optical scatter is a source of noise, limits resolution and reduces system throughput, it is also an extremely sensitive metrology tool and is being employed in a wide variety of applications both in and out of the optics industry. This paper is intended as a brief review of the current state of this important technology as it emerges from university and government laboratories to more general industry use. The bidirectional scatter distribution function (or BSDF) has become the common format for expressing scatter data and is now used almost universally. Measurements are routinely made at several laboratories around the country from the UV to the mid-IR. Data analysis of optical component scatter has progressed to the point where a variety of analysis tools are becoming available for discriminating between the various sources of scatter. Work has progressed on the analysis of rough surface scatter and the application of these techniques to some challenging problems outside the optical industry. Scatter metrology is acquiring standards and formal test procedures. The available scatter data base is rapidly expanding as the number and sophistication of measurement facilities increases. Scatter from contaminants, which is a key issue for space optics, is continuing to be a major area of work as scatterometers appear in vacuum chambers at various laboratories across the country. The current flurry of work in this growing area of metrology can be expected to continue for several more years and expand to applications outside the optics industry.
Hadron scattering and resonances in QCD
NASA Astrophysics Data System (ADS)
Dudek, Jozef J.
2016-05-01
I describe how hadron-hadron scattering amplitudes are related to the eigenstates of QCD in a finite cubic volume. The discrete spectrum of such eigenstates can be determined from correlation functions computed using lattice QCD, and the corresponding scattering amplitudes extracted. I review results from the Hadron Spectrum Collaboration who have used these finite volume methods to study ππ elastic scattering, including the ρ resonance, as well as coupled-channel π >K, ηK scattering. Ongoing calculations are advertised and the outlook for finite volume approaches is presented.
NASA Astrophysics Data System (ADS)
Fournier, David
Les conducteurs organiques quasi-bidimensionnels kappa-ET2X presentent d'importantes similitudes avec les SCHT telles qu'une phase isolant de Mott, un regime de pseudogap et un etat supraconducteur. L'etude de leurs proprietes apparait donc complementaire. Parmi les interrogations persistantes concernant la physique de ces systemes, l'origine du (ou des) processus exotique d'appariement, responsable de la supraconductivite est le sujet suscitant l'interet le plus marque dans la communaute. L'hypothese d'un mecanisme lie a la proximite d'un etat antiferromagnetique est privilegiee. Une etape importante dans la resolution de cette problematique est l'identification de la symetrie du parametre d'ordre. D'apres de nombreux travaux sur les systemes fortement correles, la sonde ultrasonore, de par sa sensibilite aux excitations de quasiparticule a basse temperature, est consideree comme particulierement adaptee a l'etude de cette propriete. Cependant, son emploi necessite l'utilisation d'un compose metallique a basse temperature et completement supraconducteur. Le compose metallique organique kappa-ET 2Cu[N(CN)2]Br presente toutes les caracteristiques necessaires a l'etude de cette propriete. En effet, il est situe loin de la transition du premier ordre de Mott et est completement supraconducteur. De facon surprenante, ce systeme semble se coupler fortement avec le reseau ce qui augmente significativement la sensibilite de cette sonde aux proprietes du gaz electronique. Cependant, des difficultes techniques importantes, liees a la nature intrinseque de ce materiau, doivent etre surmontees pour proceder a des mesures suivant differentes polarisations. La presente etude a profondement modifie notre comprehension de ce systeme. En effet, ces mesures ont permis de constater que le kappa-ET2Cu[N(CN)2]Br est un compose qui est situe en bordure de la zone de coexistence entre la supraconductivite et le magnetisme, ce qui constitue un resultat totalement inattendu. De plus, la
Multiple magnetic scattering in small-angle neutron scattering of Nd–Fe–B nanocrystalline magnet
Ueno, Tetsuro; Saito, Kotaro; Yano, Masao; Ito, Masaaki; Shoji, Tetsuya; Sakuma, Noritsugu; Kato, Akira; Manabe, Akira; Hashimoto, Ai; Gilbert, Elliot P.; Keiderling, Uwe; Ono, Kanta
2016-01-01
We have investigated the influence of multiple scattering on the magnetic small-angle neutron scattering (SANS) from a Nd–Fe–B nanocrystalline magnet. We performed sample-thickness- and neutron-wavelength-dependent SANS measurements, and observed the scattering vector dependence of the multiple magnetic scattering. It is revealed that significant multiple scattering exists in the magnetic scattering rather than the nuclear scattering of Nd–Fe–B nanocrystalline magnet. It is considered that the mean free path of the neutrons for magnetic scattering is rather short in Nd–Fe–B magnets. We analysed the SANS data by the phenomenological magnetic correlation model considering the magnetic microstructures and obtained the microstructural parameters. PMID:27321149