Inelastic light scattering from a Mott insulator
Oosten, D. van; Dickerscheid, D.B.M.; Farid, B.; Stoof, H.T.C.; Straten, P. van der
2005-02-01
We propose to use Bragg spectroscopy to measure the excitation spectrum of the Mott-insulator state of an atomic Bose gas in an optical lattice. We calculate the structure factor of the Mott insulator taking into account both the self-energy corrections of the atoms and the corresponding dressing of the atom-photon interaction. We determine the scattering rate of photons in the stimulated Raman transition and show that by measuring this scattering rate in an experiment, in particular, the excitation gap of the Mott insulator can be determined.
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
NASA Astrophysics Data System (ADS)
Hussein, M. S.; Canto, L. F.; Donangelo, R.; Mittig, W.
2016-03-01
The scattering of identical nuclei at low energies exhibits conspicuous Mott oscillations which can be used to investigate the presence of components in the predominantly Coulomb interaction arising from several physical effects. It is found that at a certain critical value of the Sommerfeld parameter the Mott oscillations disappear and the cross section becomes quite flat. We call this effect Transverse Isotropy (TI). The critical value of the Sommerfeld parameter at which TI sets in is found to be {ηc = √{3s + 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 {η_c} is found to be {E_c = 0.40} MeV for {α + α} (s = 0), 1.2 MeV for {6}Li + {6}LI (s = 1) and 7.1 MeV for {^{10}}B + {^{10}}B (s = 3). We further found that the inclusion of the nuclear interaction induces a significant modification in the TI. We suggest measurements at these sub-barrier energies for the purpose of extracting useful information about the nuclear interaction between light heavy ions. We also suggest extending the study of the TI to the scattering of identical atomic ions.
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.
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. PMID:27081996
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)
Wray, L. Andrew; Huang, Shih-Wen; Xia, Yuqi; Hasan, M. Zahid; Mathy, Charles; Eisaki, Hiroshi; Hussain, Zahid; Chuang, Yi-De
2014-03-01
Resonant inelastic X-ray scattering (RIXS) is a powerful technique for observing the energy states of many-body quantum materials. The core hole resonance states that make RIXS possible are strongly correlated, and undergo complex time evolution that shapes scattering spectra. However, current inelastic scattering measurements cannot be converted to a time resolved picture, because techniques that determine relative phase information from elastic scattering have not been adapted to the greater complexity of inelastic spectra. We will show that inelastic scattering phases can be identified from quantum interference in sharply resolved (dE < 35meV) M-edge RIXS spectra of Mott insulators (e.g. SrCuO2 and NiO), and provide new information for identifying excitation symmetries and many-body time dynamics.
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.
Raghu, S.
2010-03-02
We consider extended Hubbard models with repulsive interactions on a honeycomb lattice, and the transitions from the semimetal to Mott insulating phases at half-filling. Because of the frustrated nature of the second-neighbor interactions, topological Mott phases displaying the quantum Hall and the quantum spin Hall effects are found for spinless and spin fermion models, respectively. The mean-field phase diagram is presented and the fluctuations are treated within the random phase approximation. Renormalization group analysis shows that these states can be favored over the topologically trivial Mott insulating states.
NASA Astrophysics Data System (ADS)
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.
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
Mott transition in granular aluminum
NASA Astrophysics Data System (ADS)
Bachar, N.; Lerer, S.; Levy, A.; Hacohen-Gourgy, S.; Almog, B.; Saadaoui, H.; Salman, Z.; Morenzoni, E.; Deutscher, G.
2015-01-01
A Mott transition in granular Al films is observed by probing the increase of the spin-flip scattering rate of conduction electrons as the nanosize metallic grains are being progressively decoupled. The presence of free spins in granular Al films is directly demonstrated by μ SR measurements. Analysis of the magnetoresistance in terms of an effective Fermi energy shows that it becomes of the order of the grains electrostatic charging energy at a room temperature resistivity ρ300 K≈50000 μ Ω cm , at which a metal to insulator transition is known to exist. As this transition is approached the magnetoresistance exhibits a heavy-fermion-like behavior, consistent with an increased electron effective mass.
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.
5 MeV Mott Polarimeter Development at Jefferson Lab
Price, J. S.; Sinclair, C. K.; Cardman, L. S.; Haanskneccht, J.; Mack, D. J.; Piot, P.; Assamagan, K. A.; Grames, J.
1997-01-01
Low energy (E{sub k}=100 keV) Mott scattering polarimeters are ill- suited to support operations foreseen for the polarized electron injector at Jefferson Lab. One solution is to measure the polarization at 5 MeV where multiple and plural scattering are unimportant and precision beam monitoring is straightforward. The higher injector beam current offsets the lower cross-sections. Recent improvements in the CEBAF injector polarimeter scattering chamber have improved signal to noise.
NASA Astrophysics Data System (ADS)
Choy, Ting-Pong
One of the leading problems in condensed matter physics is what state of matter obtain when there is a strong Coulomb repulsion between the electrons. One of the exotic examples is the high temperature superconductivity which was discovered in copper-oxide ceramics (cuprates) over twenty years ago. Thus far, a satisfactory theory is absent. In particular, the nature of the electron state outside the superconducting phase remains controversial. In analogy with the BCS theory of a conventional superconductor, in which the metal is well known to be a Fermi liquid, a complete understanding of the normal state of cuprate is necessary prior to the study of the superconducting mechanism in the high temperature superconductors. In this thesis, we will provide a theory for these exotic normal state properties by studying the minimal microscopic model which captures the physics of strong electron correlation. Even in such a simple microscopic model, striking properties including charge localization and presence of a Luttinger surface resemble the normal state properties of cuprate. An exact low energy theory of a doped Mott insulator will be constructed by explicitly integrating (rather than projecting) out the degrees of freedom far away from the chemical potential. The exact low energy theory contains degrees of freedom that cannot be obtained from projective schemes. In particular, a charge 2e bosonic field which is not made out of elemental excitations emerges at low energies. Such a field accounts for dynamical spectral weight transfer across the Mott gap. At half-filling, we show that two such excitations emerge which play a crucial role in preserving the Luttinger surface along which the single-particle Green function vanishes. We also apply this method to the Anderson-U impurity and show that in addition to the Kondo interaction, bosonic degrees of freedom appear as well. We show that many of the normal state properties of the cuprates can result from this new charge
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.
Photovoltaic effect for narrow-gap Mott insulators
NASA Astrophysics Data System (ADS)
Manousakis, Efstratios
2012-02-01
Solar cells, based on conventional band-semiconductors, have low efficiency for conversion of solar into electrical energy. The main reason is that the excess energy of the photon absorbed by an electron/hole pair beyond the band-gap becomes heat through electron-phonon scattering and phonon emission; through these processes electrons and holes relax to their band edges within a characteristic time scale of the order of 10-12-10-13 secs. We will discuss that a narrow-gap Mott insulator can produce a significant photovoltaic effect and, more importantly, if appropriately chosen it can lead to solar cells of high efficiency. In this case, a single solar photon can produce multiple electron/hole (doublon/hole) pairs, an effect known as impact ionization, faster than other relaxation processes such as relaxation through phonons. It has been proposed previously that this process could lead to an efficient solar cell using band-gap semiconductors; however, the characteristic time-scale for impact ionization is comparable to that for electron-phonon relaxation in band-gap semiconductors. The reason that a Mott insulator can behave differently is that the large Coulomb repulsion present in a Mott insulator leads to a large enhancement of the impact ionization rate. Provided that this enhancement does occur in an appropriately chosen Mott insulator, it can be demonstrated that the efficiency can improve significantly over conventional band-insulators. At present, we are doing calculations on specific transition-metal-oxide based materials believed to be Mott-insulators using extensions of the density functional theory (hybrid functionals) in combination with many-body perturbation theory. Our goal is to determine a promising candidate with suitable band structure and transition matrix elements leading to fast transition rates for impact ionization to occur in a time-scale faster than other relaxation processes.
Photoheat-induced Schottky nanojunction and indirect Mott transition in VO2: photocurrent analysis
NASA Astrophysics Data System (ADS)
Kim, Hyun-Tak; Kim, Minjung; Sohn, Ahrum; Slusar, Tetiana; Seo, Giwan; Cheong, Hyeonsik; Kim, Dong-Wook
2016-03-01
In order to elucidate a mechanism of the insulator-to-metal transition (IMT) for a Mott insulator VO2 (3d 1), we present Schottky nanojunctions and the structural phase transition (SPT) by simultaneous nanolevel measurements of photocurrent and Raman scattering in microlevel devices. The Schottky nanojunction with the monoclinic metallic phase between the monoclinic insulating phases is formed by the photoheat-induced IMT not accompanied with the SPT. The temperature dependence of the Schottky junction reveals that the Mott insulator has an electronic structure of an indirect subband between the main Hubbard d bands. The IMT as reverse process of the Mott transition occurs by temperature-induced excitation of bound charges in the indirect semiconductor band, most likely formed by impurities such as oxygen deficiency. The metal band (3d 1) for the Mott insulator is screened (trapped) by the indirect band (impurities).
Influence of spinons fluctuations near the spin liquid Mott transition
NASA Astrophysics Data System (ADS)
Lee, Tsung-Han; Florens, Serge; Dobrosavljevic, Vladimir
We investigate the metal to Mott-insulator transition (MIT) in the Hubbard-Heisenberg model using the slave-rotor technique, which allows to combine for the first time the dynamical mean field theory (DMFT) with the Resonating Valence Bond (RVB) approach. In the spin-liquid phase at large Coulomb repulsion, the system shows a RVB transition from a trivial paramagnetic Mott insulator towards a low temperature insulating state with long lived spinons, as seen by the emergence of a linear specific heat. This quenching of the entropy in the spin liquid phase provides strong modifications in the shape of the standard DMFT phase diagram for the MIT occurring at intermediate values of the Coulomb repulsion. We find that the RVB transition happens concomitantly with the first order MIT lines at low temperature. This implies that the Mott insulator always accommodates a spinon Fermi surface, even in the coexistence regime of the MIT, and that the metallic state always stays a Fermi-liquid as it rejects the presence of free spinons, due to their strong scattering onto the holons.
Phase Coherence of an Atomic Mott Insulator
Gerbier, Fabrice; Widera, Artur; Foelling, Simon; Mandel, Olaf; Gericke, Tatjana; Bloch, Immanuel
2005-07-29
We investigate the phase coherence properties of ultracold Bose gases in optical lattices, with special emphasis on the Mott insulating phase. We show that phase coherence on short length scales persists even deep in the insulating phase, preserving a finite visibility of the interference pattern observed after free expansion. This behavior can be attributed to a coherent admixture of particle-hole pairs to the perfect Mott state for small but finite tunneling. In addition, small but reproducible kinks are seen in the visibility, in a broad range of atom numbers. We interpret them as signatures for density redistribution in the shell structure of the trapped Mott insulator.
Towards Mott design by δ-doping of strongly correlated titanates
NASA Astrophysics Data System (ADS)
Lechermann, Frank; Obermeyer, Michael
2015-04-01
Doping the distorted-perovskite Mott insulators LaTiO3 and GdTiO3 with a single SrO layer along the [001] direction gives rise to a rich correlated electronic structure. A realistic superlattice study by means of the charge self-consistent combination of density functional theory with dynamical mean-field theory reveals layer- and temperature-dependent multi-orbital metal-insulator transitions. An orbital-selective metallic layer at the interface dissolves via an orbital-polarized doped-Mott state into an orbital-ordered insulating regime beyond the two conducting TiO2 layers. We find large differences in the scattering behavior within the latter. Breaking the spin symmetry in δ-doped GdTiO3 results in blocks of ferromagnetic itinerant and ferromagnetic Mott-insulating layers that are coupled antiferromagnetically.
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
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
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.
VIEW NORTHON MOTT STREETBUILDING 62 ANNEALING HOUSE EXTENSION John ...
VIEW NORTH-ON MOTT STREET-BUILDING 62 ANNEALING HOUSE EXTENSION - John A. Roebling's Sons Company & American Steel & Wire Company, South Broad, Clark, Elmer, Mott & Hudson Streets, Trenton, Mercer County, NJ
VIEW WESTON MOTT STREETBUILDING 57 FLAT SHOP NO 1 (1905) ...
VIEW WEST-ON MOTT STREET-BUILDING 57 FLAT SHOP NO 1 (1905) - John A. Roebling's Sons Company & American Steel & Wire Company, South Broad, Clark, Elmer, Mott & Hudson Streets, Trenton, Mercer County, NJ
VIEW NORTHLEFTBUILDING 51 MOTT STREET GENERATING STATION (1897) RIGHTBUILDING 57 ...
VIEW NORTH-LEFT-BUILDING 51 MOTT STREET GENERATING STATION (1897) RIGHT-BUILDING 57 FLAT SHOP NO.1 (1905) - John A. Roebling's Sons Company & American Steel & Wire Company, South Broad, Clark, Elmer, Mott & Hudson Streets, Trenton, Mercer County, NJ
Constraints on topological order in mott insulators.
Zaletel, Michael P; Vishwanath, Ashvin
2015-02-20
We point out certain symmetry induced constraints on topological order in Mott insulators (quantum magnets with an odd number of spin 1/2 moments per unit cell). We show, for example, that the double-semion topological order is incompatible with time reversal and translation symmetry in Mott insulators. This sharpens the Hastings-Oshikawa-Lieb-Schultz-Mattis theorem for 2D quantum magnets, which guarantees that a fully symmetric gapped Mott insulator must be topologically ordered, but is silent about which topological order is permitted. Our result applies to the kagome lattice quantum antiferromagnet, where recent numerical calculations of the entanglement entropy indicate a ground state compatible with either toric code or double-semion topological order. Our result rules out the latter possibility. PMID:25763971
Universality class of the mott transition.
Abdel-Jawad, M; Kato, R; Watanabe, I; Tajima, N; Ishii, Y
2015-03-13
Pressure dependence of the conductivity and thermoelectric power is measured through the Mott transition in the layer organic conductor EtMe_{3}P[Pd(dmit)_{2}]_{2}. The critical behavior of the thermoelectric effect provides a clear and objective determination of the Mott-Hubbard transition during the isothermal pressure sweep. Above the critical end point, the metal-insulator crossing, determined by the thermoelectric effect minimum value, is not found to coincide with the maximum of the derivative of the conductivity as a function of pressure. We show that the critical exponents of the Mott-Hubbard transition fall within the Ising universality class regardless of the dimensionality of the system. PMID:25815951
Holography and Mottness: A Discrete Marriage
NASA Astrophysics Data System (ADS)
Phillips, Philip
2012-02-01
Gauge-gravity duality has allowed us to solve the physics of certain strongly coupled quantum mechanical systems using gravity. I will show how a space-time consisting of a charged black hole and a bulk Pauli coupling corresponds to a boundary theory with a dynamically generated gap (with no obvious symmetry breaking) and a massive rearrangement of the spectral weight as in classic Mott systems such as VO2. In this holographic set-up, the gap opens only when discrete scale invariance is present. This raises the possibility that the elusive symmetry that might be broken in Mott insulators, in general, might pertain to scale invariance. The relevance of this claim to recent theories of Mott systems that possess massless charged bosons is explored.
Spectral Evolution in (Ca,
Ahn, J.S.; Bak, J.; Choi, H.S.; Noh, T.W.; Han, J.E.; Bang, Y.; Cho, J.H.; Jia, Q.X.
1999-06-01
We investigated optical properties of (Ca,Sr)RuO {sub 3} films on the borderline of a metal-insulator transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc limit, (ii) a U/2 excitation, and (iii) a U excitation. Also, self-consistency is exploited within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. However, low frequency behaviors of electrodynamic quantities suggest extra scattering mechanisms in addition to the Mott-Hubbard correlation. {copyright} {ital 1999} {ital The American Physical Society }
Spectral Evolution in (Ca,
Ahn, J.S.; Bak, J.; Choi, H.S.; Noh, T.W. ); Han, J.E. ); Bang, Y. ); Cho, J.H. ); Jia, Q.X. )
1999-06-01
We investigated optical properties of (Ca,Sr)RuO [sub 3] films on the borderline of a metal-insulator transition. Our results show all of the predicted characteristics for a metallic Mott-Hubbard system, including (i) a mass enhancement in dc limit, (ii) a U/2 excitation, and (iii) a U excitation. Also, self-consistency is exploited within the Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays that electron correlation should be important even in 4d materials. However, low frequency behaviors of electrodynamic quantities suggest extra scattering mechanisms in addition to the Mott-Hubbard correlation. [copyright] [ital 1999] [ital The American Physical Society
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
Electronic reconstruction of doped Mott insulator heterojunctions
NASA Astrophysics Data System (ADS)
Charlebois, M.; Hassan, S. R.; Karan, R.; Dion, M.; Senechal, D.; Tremblay, A.-M. S.
2012-02-01
Correlated electron heterostructures became a possible alternative when thin-film deposition techniques achieved structures with a sharp interface transition [1]. Soon thereafter, Okamoto & Millis introduced the concept of ``electronic reconstruction'' [2]. We study here the electronic reconstruction of doped Mott insulator heterostructures based on a Cluster Dynamical Mean Field Theory (CDMFT) calculations of the Hubbard model in the limit where electrostatic energy dominates over the kinetic energy associated with transport across layers. The grand potential of individual layers is first computed within CDMFT and then the electrostatic potential energy is taken into account in the Hartree approximation. The charge reconstruction in an ensemble of stacked planes of different nature can lead to a distribution of electron charge and to transport properties that are unique to doped-Mott insulators.[4pt] [1] J. Mannhart, D. G. Schlom, Science 327, 1607 (2010).[0pt] [2] S. Okamoto and A. J. Millis, Nature 428, 630 (2004).
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
Quantum criticality of a Bose gas in an optical lattice near the Mott transition
NASA Astrophysics Data System (ADS)
Rançon, A.; Dupuis, N.
2012-01-01
We derive the equation of state of bosons in an optical lattice in the framework of the Bose-Hubbard model. Near the density-driven Mott transition, the expression of the pressure P(μ,T) versus chemical potential and temperature is similar to that of a dilute Bose gas but with renormalized mass m* and scattering length a*. Here m* is the mass of the elementary excitations at the quantum critical point governing the transition from the superfluid phase to the Mott-insulating phase, while a* is related to their effective interaction at low energy. We use a nonperturbative renormalization-group approach to compute these parameters as a function of the ratio t/U between hopping amplitude and on-site repulsion.
Mott-superfluid transition of q-deformed bosons
NASA Astrophysics Data System (ADS)
Kopeć, T. K.
2015-10-01
The effect of q-deformation of the bosonic algebra on the Mott-superfluid transition for interacting lattice bosons described by the Bose-Hubbard model is studied using mean-filed theory. It has been shown that the Mott state proliferates and the initial periodicity of the Mott lobes as a function of the chemical potential disappears as the q-deformation increases. The ground state phase diagram as a function of the q-parameter exhibits superfluid order, which intervenes in narrow regions between Mott lobes, demonstrating the new concept of statistically induced quantum phase transition.
Dynamical electronic nematicity from Mott physics
Okamoto, Satoshi; Senechal, D.; Civelli, M.; Tremblay, A.-M.
2010-01-01
Very large anisotropies in transport quantities have been observed in the presence of very small in-plane structural anisotropy in many strongly correlated electron materials. By studying the two-dimensional Hubbard model with dynamical-mean-field theory for clusters, we show that such large anisotropies can be induced without static stripe order if the interaction is large enough to yield a Mott transition. Anisotropy decreases at large frequency. The maximum effect on conductivity anisotropy occurs in the underdoped regime, as observed in high temperature superconductors.
VIEW WEST ON MOTT STREET AT HUDSON STREET LEFTBUILDING 62 ...
VIEW WEST ON MOTT STREET AT HUDSON STREET LEFT-BUILDING 62 ANNEALING HOUSE (c.1900) CENTER-BUILDING 57 FLAT SHOP NO. 1 (c.1905) - John A. Roebling's Sons Company & American Steel & Wire Company, South Broad, Clark, Elmer, Mott & Hudson Streets, Trenton, Mercer County, NJ
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…
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
Slope-reversed Mott transition in multiorbital systems
NASA Astrophysics Data System (ADS)
Kim, Aaram J.; Choi, MooYoung; Jeon, Gun Sang
2015-09-01
We examine finite-temperature phase transitions in the two-orbital Hubbard model with different bandwidths by means of the dynamical mean-field theory combined with the continuous-time quantum Monte Carlo method. It is found that there emerges a peculiar slope-reversed first-order Mott transition between the orbital-selective Mott phase and the Mott insulator phase in the presence of Ising-type Hund's coupling. The origin of the slope-reversed phase transition is clarified by the analysis of the temperature dependence of the energy density. It turns out that the increase of Hund's coupling lowers the critical temperature of the slope-reversed Mott transition. Beyond a certain critical value of Hund's coupling the first-order transition turns into a finite-temperature crossover. We also reveal that the orbital-selective Mott phase exhibits frozen local moments in the wide orbital, which is demonstrated by the spin-spin correlation functions.
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…
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.
Dual vortex theory of doped Mott insulators
Balents, Leon; Sachdev, Subir
2007-11-15
We present a general framework for describing the quantum phases obtained by doping paramagnetic Mott insulators on the square lattice. The undoped insulators are efficiently characterized by the projective transformations of various fields under the square lattice space group (the PSG). We show that the PSG also imposes powerful constraints on the doped system, and on the effective action for the vortex and Bogoliubov quasiparticle excitations of superconducting states. This action can also be extended across transitions to supersolid or insulating states at non-zero doping. For the case of a valence bond solid (VBS) insulator, we show that the doped system has the same PSG as that of elementary bosons with density equal to the density of electron Cooper pairs. We also discuss aspects of the action for a d-wave superconductor obtained by doping a 'staggered-flux' spin liquid state.
Bose and Mott glass phases in dimerized quantum antiferromagnets
NASA Astrophysics Data System (ADS)
Thomson, S. J.; Krüger, F.
2015-11-01
We examine the effects of disorder on dimerized quantum antiferromagnets in a magnetic field, using the mapping to a lattice gas of hard-core bosons with finite-range interactions. Combining a strong-coupling expansion, the replica method, and a one-loop renormalization-group analysis, we investigate the nature of the glass phases formed. We find that away from the tips of the Mott lobes, the transition is from a Mott insulator to a compressible Bose glass, however the compressibility at the tips is strongly suppressed. We identify this finding with the presence of a rare Mott glass phase and demonstrate that the inclusion of replica symmetry breaking is vital to correctly describe the glassy phases. This result suggests that the formation of Bose and Mott glass phases is not simply a weak localization phenomenon but is indicative of much richer physics. We discuss our results in the context of both ultracold atomic gases and spin-dimer materials.
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
2015-12-15
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
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
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.; et al
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
Anomalous superconductivity near the Mott transition
NASA Astrophysics Data System (ADS)
Tremblay, Andre-Marie
2006-03-01
High-temperature superconductivity appears near an antiferromagnetic Mott insulating phase and a normal phase with a pseudogap. It was suggested early on by Anderson that the strong-coupling limit of the Hubbard model should contain the main physics. It is only recently that we have begun to have access to sufficiently accurate algorithms and powerful enough computers to begin to extract the main features of the phase diagram of high-temperature superconductors from the Hubbard model in a nearly quantitative manner. In this talk, the zero temperature phase diagram of the two-dimensional Hubbard model is discussed based on several ``quantum cluster'' approaches, mainly Variational Cluster Perturbation Theory [1] and Cellular Dynamical Mean Field Theory [2], that shall be introduced. The overall ground state phase diagram of the high-temperature superconductors as well as the asymmetric one-particle excitation spectra for both hole- and electron-doping are reproduced. The d-wave order parameter is found to assume a dome shape as a function of doping and to scale like the magnetic exchange coupling J for U comparable to the bandwidth. We stress the features of superconductivity that are non-BCS like due to the proximity to the Mott insulator. In stark contrast with BCS theory, the superconducting gap can decrease monotonically at the same time as the d-wave order parameter increases away from half-filling. Also, d-wave superconductivity is driven by a lowering of kinetic energy instead of potential energy, in conformity with experiments on cuprates. The pseudogap [3-5] and results of other approaches will also be briefly touched upon. [1] David S'en'echal, P.-L. Lavertu, M.-A. Marois, and A.- M.S. Tremblay, Phys. Rev. Lett. 94, 156404 (2005). [2] S. S. Kancharla, M. Civelli, M. Capone, B. Kyung, D. Senechal, G. Kotliar, A.-M.S. Tremblay, cond-mat/0508205. [3] B. Kyung, S.S. Kancharla, D. S'en'echal, A.-M.S. Tremblay, M. Civelli, and G. Kotliar cond-mat/0502565 [4] B
Spin liquid phases of large-spin Mott insulating ultracold bosons
NASA Astrophysics Data System (ADS)
Rutkowski, Todd C.; Lawler, Michael J.
2016-03-01
Mott insulating ultracold gases possess a unique whole-atom exchange interaction which enables large quantum fluctuations between the Zeeman sublevels of each atom. By strengthening this interaction—either through the use of large-spin atoms or by tuning the particle-particle interactions via optical Feshbach resonance—one may enhance fluctuations and facilitate the appearance of the long-sought-after quantum spin liquid phase—all in the highly tunable environment of cold atoms. To illustrate the relationship between the spin magnitude, interaction strength, and resulting magnetic phases, we present and solve a mean-field theory for bosons optically confined to the one-particle-per-site Mott state, using both analytic and numerical methods. We find on square and triangular lattices for bosons of hyperfine spin f >2 that making the repulsive s -wave scattering length through the singlet channel small—relative to the higher-order scattering channels—accesses a short-range resonating valence bond (s-RVB) spin liquid phase.
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.
A scalable neuristor built with Mott memristors.
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. PMID:23241533
Feshbach molecules from an atomic Mott insulator
NASA Astrophysics Data System (ADS)
Volz, Thomas; Syassen, Niels; Bauer, Dominik; Hansis, Eberhard; Duerr, Stephan; Rempe, Gerhard
2006-05-01
Feshbach molecules from bosonic atomic species have proven to be very unstable with respect to inelastic collisions [1]. As a result, the typical lifetime observed for a cloud of ultracold ^87Rb2 molecules stored in an optical dipole trap is limited to a few ms.Here, we report on the observation of long-lived Feshbach molecules in an optical lattice. A BEC of ^87Rb atoms is loaded into the lowest Bloch band of a 3D optical lattice operated at a wavelength of 830 nm. By ramping up the lattice depth, the atomic gas enters the Mott insulator regime. A magnetic-field ramp through the Feshbach resonance at 1007 G creates molecules [2]. Lattice sites initially occupied with more than 2 atoms experience fast inelastic collisional losses. The observed lifetime of the remaining molecules is ˜100 ms, which is much longer than for a pure molecular sample in an optical dipole trap. Similar results have recently been reported in Ref.[3]. The increased lifetime is an important step on the route to a BEC of molecules in the vibrational ground state [4].[1] T. Mukaiyama et al., Phys. Rev. Lett. 92, 180402 (2004) [2] S. D"urr et al., Phys. Rev. Lett. 92, 020406 (2004) [3] G. Thalhammer et al., cond-mat/0510755 [4] D. Jaksch et al., Phys. Rev. Lett. 89, 040402 (2002)
Thermodynamics of a Bose gas near the superfluid-Mott-insulator transition
NASA Astrophysics Data System (ADS)
Rançon, A.; Dupuis, N.
2012-10-01
We study the thermodynamics near the generic (density-driven) superfluid-Mott-insulator transition in the three-dimensional Bose-Hubbard model using the nonperturbative renormalization-group approach. At low energy, the physics is controlled by the Gaussian fixed point and becomes universal. Thermodynamic quantities can then be expressed in terms of the universal scaling functions of the dilute Bose gas universality class while the microscopic physics enters only via two nonuniversal parameters, namely, the effective mass m* and the “scattering length” a* of the elementary excitations at the quantum critical point between the superfluid and Mott-insulating phases. A notable exception is the condensate density in the superfluid phase which is proportional to the quasiparticle weight Zqp of the elementary excitations. The universal regime is defined by m*a*2T≪1 and m*a*2|δμ|≪1 or, equivalently, |n¯-n¯c|a*3≪1, where δμ=μ-μc is the chemical potential shift from the quantum critical point (μ=μc,T=0) and n¯-n¯c the doping with respect to the commensurate density n¯c of the T=0 Mott insulator. We compute Zqp, m*, and a* and find that they vary strongly with both the ratio t/U between hopping amplitude and onsite repulsion and the value of the (commensurate) density n¯c. Finally, we discuss the experimental observation of universality and the measurement of Zqp, m*, and a* in a cold-atomic gas in an optical lattice.
Nonequilibrium gap collapse near a first-order Mott transition
NASA Astrophysics Data System (ADS)
Sandri, Matteo; Fabrizio, Michele
2015-03-01
We study the nonequilibrium dynamics of a simple model for V2O3 that consists of a quarter-filled Hubbard model for two orbitals that are split by a weak crystal field. Peculiarities of this model are (1) a Mott insulator whose gap corresponds to transferring an electron from the occupied lower orbital to the empty upper one, rather than from the lower to the upper Hubbard subbands; (2) a Mott transition generically of first order even at zero temperature. We simulate by means of time-dependent Gutzwiller approximation the evolution within the insulating phase of an initial state endowed by a nonequilibrium population of electrons in the upper orbital and holes in the lower one. We find that the excess population may lead, above a threshold, to a gap collapse and drive the insulator into the metastable metallic phase within the coexistence region around the Mott transition. This result foresees a nonthermal pathway to revert a Mott insulator into a metal. Even though this physical scenario is uncovered in a very specific toy model, we argue it might apply to other Mott insulating materials that share similar features.
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.
Anderson localization effects near the Mott metal-insulator transition
NASA Astrophysics Data System (ADS)
Bragança, Helena; Aguiar, M. C. O.; Vučičević, J.; Tanasković, D.; Dobrosavljević, V.
2015-09-01
The interplay between Mott and Anderson routes to localization in disordered interacting systems gives rise to different transitions and transport regimes. Here, we investigate the phase diagram at finite temperatures using dynamical mean-field theory combined with typical medium theory, which is an effective theory of the Mott-Anderson metal-insulator transition. We mainly focus on the properties of the coexistence region associated with the Mott phase transition. For weak disorder, the coexistence region is found to be similar to that in the clean case. However, as we increase disorder, Anderson localization effects are responsible for shrinking the coexistence region, and at sufficiently strong disorder (approximately equal to twice the bare bandwidth) it drastically narrows, the critical temperature Tc abruptly goes to zero, and we observe a phase transition in the absence of a coexistence of the metallic and insulating phases. In this regime, the effects of interaction and disorder are found to be of comparable importance for charge localization.
Cluster dynamical mean field theory of the Mott transition.
Park, H; Haule, K; Kotliar, G
2008-10-31
We address the nature of the Mott transition in the Hubbard model at half-filling using cluster dynamical mean field theory (DMFT). We compare cluster-DMFT results with those of single-site DMFT. We show that inclusion of the short-range correlations on top of the on-site correlations does not change the order of the transition between the paramagnetic metal and the paramagnetic Mott insulator, which remains first order. However, the short range correlations reduce substantially the critical U and modify the shape of the transition lines. Moreover, they lead to very different physical properties of the metallic and insulating phases near the transition point. Approaching the transition from the metallic side, we find an anomalous metallic state with very low coherence scale. The insulating state is characterized by the narrow Mott gap with pronounced peaks at the gap edge. PMID:18999845
Superconducting fluctuations in organic molecular metals enhanced by Mott criticality
Nam, Moon-Sun; Mézière, Cécile; Batail, Patrick; Zorina, Leokadiya; Simonov, Sergey; Ardavan, Arzhang
2013-01-01
Unconventional superconductivity typically occurs in materials in which a small change of a parameter such as bandwidth or doping leads to antiferromagnetic or Mott insulating phases. As such competing phases are approached, the properties of the superconductor often become increasingly exotic. For example, in organic superconductors and underdoped high-Tc cuprate superconductors a fluctuating superconducting state persists to temperatures significantly above Tc. By studying alloys of quasi-two-dimensional organic molecular metals in the κ-(BEDT-TTF)2X family, we reveal how the Nernst effect, a sensitive probe of superconducting phase fluctuations, evolves in the regime of extreme Mott criticality. We find strong evidence that, as the phase diagram is traversed through superconductivity towards the Mott state, the temperature scale for superconducting fluctuations increases dramatically, eventually approaching the temperature at which quasiparticles become identifiable at all. PMID:24292063
Site-resolved imaging of a fermionic Mott insulator
NASA Astrophysics Data System (ADS)
Chiu, Christie; Greif, Daniel; Parsons, Maxwell F.; Mazurenko, Anton; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus
2016-05-01
Quantum gas microscopy of ultracold fermionic atoms in an optical lattice opens new perspectives for addressing long-standing open questions on strongly correlated low-temperature phases in the Hubbard model. Here we report on site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators with Lithium-6. For strong repulsive interactions we observe Mott insulators with more than 400 atoms and for intermediate interactions we observe a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1 . 0kB in the Mott insulator and local entropies in the band insulator as low as 0 . 5kB . Our measurements serve as a benchmark for the performance of our experiment and are a starting point for accessing the low-temperature regime of magnetic ordering. Current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
Charge dynamics in doped Mott insulators on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Ma, Xixiao; Lan, Yu; Qin, Ling; Feng, Shiping
2016-03-01
Within the framework of the fermion-spin theory, the charge transport in the doped Mott insulators on a honeycomb lattice is studied by taking into account the pseudogap effect. It is shown that the conductivity spectrum in the low-doped regime is separated by the pseudogap into a low-energy non-Drude peak followed by a broad mid-infrared band. However, the decrease of the pseudogap with the increase of doping leads to a shift of the position of the mid-infrared band towards the low-energy non-Drude peak, and then the low-energy Drude behavior recovers in the high-doped regime. The combined results of both the doped honeycomb-lattice and square-lattice Mott insulators indicate that the two-component conductivity induced by the pseudogap is a universal feature in the doped Mott insulators.
Fragmentation of Expanding Cylinders and the Statistical Theory of N. F. Mott
NASA Astrophysics Data System (ADS)
Grady, Dennis
2002-07-01
The seminal investigation of the explosive fragmentation of steel cylindrical shells by N. F. Mott in the early 1940's led to an elegant statistics-based theory of dynamic fragmentation (Mott, 1947). Experiments in which rapidly expanded metal rings undergo dynamic fragmentation provide ideal data for testing the fragment size and statistical distribution predictions of Mott's theory. In this work the theoretical development of Mott is examined and compared with expanding metal ring experimental data.
Kinetic magnetism at the interface between Mott and band insulators
NASA Astrophysics Data System (ADS)
Iaconis, Jason; Ishizuka, Hiroaki; Sheng, D. N.; Balents, Leon
2016-04-01
We show that the interplay of a high-density two-dimensional electron gas and localized electrons in a neighboring Mott insulator leads to kinetic magnetism unique to the Mott and band insulator interface. Our study is based upon a bilayer Hubbard model at U =∞ with a potential difference between the two layers. We combine analytic results with DMRG simulations to show that magnetism, and especially ferromagnetism, is greatly enhanced relative to the proximity of the two subsystems. The results are potentially relevant to recent experiments, suggesting magnetism in R TiO3 /SrTiO3 heterostructures.
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 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.
Quantum Capillary Waves at the Superfluid—Mott-Insulator Interface
NASA Astrophysics Data System (ADS)
Rath, Steffen Patrick; Spivak, Boris; Zwerger, Wilhelm
2011-10-01
We discuss quantum fluctuations of the interface between a superfluid and a Mott-insulating state of ultracold atoms in a trap. The fluctuations of the boundary are due to a new type of surface modes, whose spectrum is similar—but not identical—to classical capillary waves. The corresponding quantum capillary length sets the scale for the penetration of the superfluid into the Mott-insulating regime by the proximity effect and may be on the order of several lattice spacings. It determines the typical magnitude of the interface width due to quantum fluctuations, which may be inferred from single-site imaging of ultracold atoms in an optical lattice.
Influence of Local Moment Fluctuations on the Mott Transition
NASA Astrophysics Data System (ADS)
Janani, C.; Florens, S.; Gupta, T.; Narayanan, R.
The Mott metal to insulator transition is a remarkable phenomenon observed in strongly correlated materials, where the localization of electronic waves is driven by on-site electron-electron repulsion (see [7] for a review). Although the appearance of a Mott gap is clearly a charge-related effect, magnetism is expected to play a key role in elucidating the true nature of this phase transition. Indeed, since the Mott insulating state is purely paramagnetic, local moments are well-defined objects between their formation at high temperature (about the local Coulomb interaction ) and their ultimate ordering at the Neel temperature. This offers a window for the Mott transition to occur, in which the behavior of these local spin excitations is yet to be clearly understood. The simplest situation lies in case where the low-temperature magnetic ordering is first order, as in Cr-doped {textrm V}_2{textrm O}_3 . Accordingly magnetic fluctuations should be expected to be weak, so that many predictions can be made from a single-site approach such as the Dynamical Mean Field Theory (DMFT) [4]. In particular, the fact that a low-temperature metallic state leads upon heating to an insulating phase can be understood as a Pomeranchuk effect , where the entropy gain benefits the state with magnetic degeneracy.
Assessing the orbital selective Mott transition with variational wave functions
NASA Astrophysics Data System (ADS)
Tocchio, Luca F.; Arrigoni, Federico; Sorella, Sandro; Becca, Federico
2016-03-01
We study the Mott metal-insulator transition in the two-band Hubbard model with different hopping amplitudes t 1 and t 2 for the two orbitals on the two-dimensional square lattice by using non-magnetic variational wave functions, similarly to what has been considered in the limit of infinite dimensions by dynamical mean-field theory. We work out the phase diagram at half filling (i.e. two electrons per site) as a function of R={{t}2}/{{t}1} and the on-site Coulomb repulsion U, for two values of the Hund’s coupling J = 0 and J/U = 0.1. Our results are in good agreement with previous dynamical mean-field theory calculations, demonstrating that the non-magnetic phase diagram is only slightly modified from infinite to two spatial dimensions. Three phases are present: a metallic one, for small values of U, where both orbitals are itinerant; a Mott insulator, for large values of U, where both orbitals are localized because of the Coulomb repulsion; and the so-called orbital-selective Mott insulator (OSMI), for small values of R and intermediate Us, where one orbital is localized while the other one is still itinerant. The effect of the Hund’s coupling is two-fold: on one side, it favors the full Mott phase over the OSMI; on the other side, it stabilizes the OSMI at larger values of R.
Pressure-Induced Confined Metal from the Mott Insulator Sr3 Ir2 O7
NASA Astrophysics Data System (ADS)
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
2016-05-01
The spin-orbit Mott insulator Sr3Ir2O7 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 Sr3Ir2O7 up to 63-65 GPa at 300 K. The material becomes a confined metal at 59.5 GPa, showing metallicity in the a b 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.
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.
Pressure-Induced Confined Metal from the Mott Insulator Sr_{3}Ir_{2}O_{7}.
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
2016-05-27
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. PMID:27284666
Mott metal-insulator transition on compressible lattices.
Zacharias, Mario; Bartosch, Lorenz; Garst, Markus
2012-10-26
The critical properties of the finite temperature Mott end point are drastically altered by a coupling to crystal elasticity, i.e., whenever it is amenable to pressure tuning. Similar as for critical piezoelectric ferroelectrics, the Ising criticality of the electronic system is preempted by an isostructural instability, and long-range shear forces suppress microscopic fluctuations. As a result, the end point is governed by Landau criticality. Its hallmark is, thus, a breakdown of Hooke's law of elasticity with a nonlinear strain-stress relation characterized by a mean-field exponent. Based on a quantitative estimate, we predict critical elasticity to dominate the temperature range ΔT*/T(c)≃8%, close to the Mott end point of κ-(BEDT-TTF)(2)X. PMID:23215206
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
NASA Astrophysics Data System (ADS)
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
2016-02-01
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as a control parameter driving the second-order critical end point Tc of the metal-insulator transition down to zero at t⊥c/t ≃0.2 . Below t⊥c, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far.
Compressibility of a fermionic mott insulator of ultracold atoms.
Duarte, Pedro M; Hart, Russell A; Yang, Tsung-Lin; Liu, Xinxing; Paiva, Thereza; Khatami, Ehsan; Scalettar, Richard T; Trivedi, Nandini; Hulet, Randall G
2015-02-20
We characterize the Mott insulating regime of a repulsively interacting Fermi gas of ultracold atoms in a three-dimensional optical lattice. We use in situ imaging to extract the central density of the gas and to determine its local compressibility. For intermediate to strong interactions, we observe the emergence of a plateau in the density as a function of atom number, and a reduction of the compressibility at a density of one atom per site, indicating the formation of a Mott insulator. Comparisons to state-of-the-art numerical simulations of the Hubbard model over a wide range of interactions reveal that the temperature of the gas is of the order of, or below, the tunneling energy scale. Our results hold great promise for the exploration of many-body phenomena with ultracold atoms, where the local compressibility can be a useful tool to detect signatures of different phases or phase boundaries at specific values of the filling. PMID:25763942
Electronic Griffiths phase of the d = 2 Mott transition.
Andrade, E C; Miranda, E; Dobrosavljević, V
2009-05-22
We investigate the effects of disorder within the T = 0 Brinkman-Rice scenario for the Mott metal-insulator transition in two dimensions. For sufficiently weak disorder the transition retains the Mott character, as signaled by the vanishing of the local quasiparticle weights Z_{i} and strong screening of the renormalized site energies at criticality. In contrast to the behavior in high dimensions, here the local spatial fluctuations of quasiparticle parameters are strongly enhanced in the critical regime, with a distribution function P(Z) approximately Z;{alpha-1} and alpha --> 0 at the transition. This behavior indicates a robust emergence of an electronic Griffiths phase preceding the metal-insulator transition, in a fashion surprisingly reminiscent of the "infinite randomness fixed point" scenario for disordered quantum magnets. PMID:19519046
Mott Physics at the Boundaries of Topological Insulators
NASA Astrophysics Data System (ADS)
Medhi, Amal; Verma, Pramod Kumar; Shenoy, Vijay; Krishnamurthy, H. R.
2011-03-01
We address how the nature of linearly dispersing edge states of a topological insulating solid evolves with increasing electron-electron correlation engendered by a Hubbard like on-site repulsion. We report studies on strips (2D) and slabs (3D) of varying widths and thicknesses of topological insulators described by model Hamiltonians using an inhomogeneous slave rotor mean-field theory. Motivated by these studies, we construct variational wavefunctions with approriate Gutzwiller-Jastrow correlations and study them using the Monte-Carlo method. These studies reveal the width/thickness dependence of the critical on-site repulsion that obtains an edge Mott insulating state, and uncover the mechanism of the Mott transition in such systems. Work supported by DAE, SRC and DST, India.
Site-resolved imaging of a fermionic Mott insulator.
Greif, Daniel; Parsons, Maxwell F; Mazurenko, Anton; Chiu, Christie S; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus
2016-02-26
The complexity of quantum many-body systems originates from the interplay of strong interactions, quantum statistics, and the large number of quantum-mechanical degrees of freedom. Probing these systems on a microscopic level with single-site resolution offers important insights. Here we report site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators, using ultracold atoms in a square lattice. For strong repulsive interactions, we observed two-dimensional Mott insulators containing over 400 atoms. For intermediate interactions, we observed a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1.0 times the Boltzmann constant (k(B)). In the band insulator, we find local entropies as low as 0.5 k(B). Access to local observables will aid the understanding of fermionic many-body systems in regimes inaccessible by modern theoretical methods. PMID:26917766
Mottness-induced healing in strongly correlated superconductors
NASA Astrophysics Data System (ADS)
Tang, S.; Dobrosavljević, V.; Miranda, E.
2014-03-01
We study impurity healing effects in models of strongly correlated superconductors. We show that in general both the range and the amplitude of the spatial variations caused by nonmagnetic impurities are significantly suppressed in the superconducting as well as in the normal states. We explicitly quantify the weights of the local and the non-local responses to inhomogeneities and show that the former are overwhelmingly dominant over the latter. We find that the local response is characterized by a well-defined healing length scale, which is restricted to only a few lattice spacings over a significant range of dopings in the vicinity of the Mott insulating state. We demonstrate that this healing effect is ultimately due to the suppression of charge fluctuations induced by Mottness. We also define and solve analytically a simplified yet accurate model of healing, within which we obtain simple expressions for quantities of direct experimental relevance, such as the healing length.
Mottness-induced healing in strongly correlated superconductors
NASA Astrophysics Data System (ADS)
Tang, Shao; Miranda, E.; Dobrosavljevic, V.
2015-01-01
We study impurity healing effects in models of strongly correlated superconductors. We show that in general both the range and the amplitude of the spatial variations caused by nonmagnetic impurities are significantly suppressed in the superconducting as well as in the normal states. We explicitly quantify the weights of the local and the nonlocal responses to inhomogeneities and show that the former are overwhelmingly dominant over the latter. We find that the local response is characterized by a well-defined healing length scale, which is restricted to only a few lattice spacings over a significant range of dopings in the vicinity of the Mott insulating state. We demonstrate that this healing effect is ultimately due to the suppression of charge fluctuations induced by Mottness. We also define and solve analytically a simplified yet accurate model of healing, within which we obtain simple expressions for quantities of direct experimental relevance.
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.
Design of a Mott Multiferroic from a Nonmagnetic Polar Metal.
Puggioni, Danilo; Giovannetti, Gianluca; Capone, Massimo; Rondinelli, James M
2015-08-21
We examine the electronic properties of the newly discovered "ferroelectric metal" LiOsO3 combining density-functional and dynamical mean-field theories. We show that the material is close to a Mott transition and that electronic correlations can be tuned to engineer a Mott multiferroic state in the 1/1 superlattice of LiOsO3 and LiNbO3. We use electronic structure calculations to predict that the (LiOsO3)1/(LiNbO3)1 superlattice exhibits strong coupling between magnetic and ferroelectric degrees of freedom with a ferroelectric polarization of 41.2 μC cm(-2), Curie temperature of 927 K, and Néel temperature of 379 K. Our results support a route towards high-temperature multiferroics, i.e., driving nonmagnetic polar metals into correlated insulating magnetic states. PMID:26340204
Constitutive relations associated with the Mott-Smith distribution function
Nathenson, M.; Baganoff, D.
1973-01-01
It is shown that the distribution function assumed by Mott-Smith determines a unique relation between heat flux, stress, and fluid velocity given by q = (3/2)??u, i.e., it provides a constitutive relation for heat flux, and it also determines a simple expression for this ratio of third-order central moments Q = . These expressions allow the equation of transfer for c x2 to be cast in a form that yields a nonlinear constitutive relation for stress. The results obtained from the Mott-Smith ansatz are compared with the theory of Baganoff and Nathenson and results from a numerical solution of the Boltzmann equation for shock-wave structure obtained by Hicks and Yen.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model.
Lenz, Benjamin; Manmana, Salvatore R; Pruschke, Thomas; Assaad, Fakher F; Raczkowski, Marcin
2016-02-26
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t_{⊥} acts as a control parameter driving the second-order critical end point T_{c} of the metal-insulator transition down to zero at t_{⊥}^{c}/t≃0.2. Below t_{⊥}^{c}, the volume of the hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t_{⊥}^{c}, the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors, whose location remains elusive so far. PMID:26967431
Vanadium dioxide: a Peierls-Mott insulator stable against disorder.
Weber, Cédric; O'Regan, David D; Hine, Nicholas D M; Payne, Mike C; Kotliar, Gabriel; Littlewood, Peter B
2012-06-22
Vanadium dioxide undergoes a first order metal-insulator transition at 340 K. In this Letter, we develop and carry out state-of-the-art linear scaling density-functional theory calculations refined with nonlocal dynamical mean-field theory. We identify a complex mechanism, a Peierls-assisted orbital selection Mott instability, which is responsible for the insulating M(1) phase, and which furthermore survives a moderate degree of disorder. PMID:23004627
Sudden expansion of Mott insulators in one dimension
NASA Astrophysics Data System (ADS)
Vidmar, L.; Langer, S.; McCulloch, I. P.; Schneider, U.; Schollwöck, U.; Heidrich-Meisner, F.
2013-12-01
We investigate the expansion of bosons and fermions in a homogeneous lattice after a sudden removal of the trapping potential using exact numerical methods. As a main result, we show that in one dimension, both bosonic and fermionic Mott insulators expand with the same velocity, irrespective of the interaction strength, provided the expansion starts from the ground state of the trapped gas. Furthermore, their density profiles become identical during the expansion; the asymptotic density dynamics is identical to that of initially localized, noninteracting particles, and the asymptotic velocity distribution is flat. The expansion velocity for initial correlated Mott insulating states is therefore independent of the interaction strength and particle statistics. Interestingly, this nonequilibrium dynamics is sensitive to the interaction driven quantum phase transition in the Bose-Hubbard model; while being constant in the Mott phase, the expansion velocity decreases in the superfluid phase and vanishes for large systems in the noninteracting limit. These results are compared to the setup of a recent experiment [Ronzheimer , Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.110.205301 110, 205301 (2013)], where the trap opening was combined with an interaction quench from infinitely strong interactions to finite values. In the latter case, the interaction quench breaks the universal dynamics in the asymptotic regime and the expansion depends on the interaction strength. We carry out an analogous analysis for a two-component Fermi gas, with similar observations. In addition, we study the effect of breaking the integrability of hard-core bosons in different ways; while the fast ballistic expansion from the ground state of Mott insulators in one dimension remains unchanged for finite interactions, we observe strong deviations from this behavior on a two-leg ladder even in the hard-core case. This change in dynamics bares similarities with the dynamics in the dimensional
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.
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
Charge relaxation and recombination in photo-excited Mott insulators
NASA Astrophysics Data System (ADS)
Prelovšek, P.; Lenarčič, Z.
2016-04-01
Recent femtosecond pump-probe experiments on Mott insulators reveal charge recombination, which is in picosecond range, i.e., much faster than in clean bandgap semiconductors although excitation gaps in Mott insulators are even larger. The charge response in photo-excited insulators can be generally divided in femtosecond transient relaxation of charge excitations, which are holons and doublons, and a second slower, but still very fast, holon-doublon (HD) recombination. We present a theory of the recombination rate of the excited HD pairs, based on the two-dimensional (2D) model relevant for cuprates, which shows that such fast processes can be explained even quantitatively with the multi-magnon emission. We show that the condition for the exponential decay as observed in the experiment is the existence of the exciton, i.e., the bound HD pair. Its recombination rate is exponentially dependent on the charge gap and on the magnon energy, while the ultrafast process can be traced back to strong charge-spin coupling. We comment also fast recombination times in the one-dimensional (1D) Mott insulators, as e.g., organic salts. The recombination rate in the latter cases can be explained with the stronger coupling with phonon excitations.
Doping induced Mott transition in the two dimensional Hubbard model
NASA Astrophysics Data System (ADS)
Sordi, Giovanni; Tremblay, A.-M. S.
2010-03-01
The description of the Mott transition by single-site dynamical mean-field theory is exact in infinite dimensions but, in two dimensions, substantial deviations from those results have been found for the interaction driven transition [1]. In addition, the experimentally relevant transition for layered systems such as the high-Tc cuprates is doping driven. We thus study this transition in the two dimensional Hubbard model on the square lattice using cluster dynamical mean-field theory with continuous-time quantum Monte Carlo in the hybridization expansion [2]. We find that the Mott transition is strongly influenced by the inclusion of short-range antiferromagnetic correlations. Doping of the Mott insulating state occurs gradually in the different momentum sectors, as found in previous studies [3], but in addition we find a first order transition between an incoherent metal and an insulator or between two incoherent metals, depending on interaction strength. Short range spin correlations create a pseudogap in a doping range that increases with interaction. [1] H. Park et al., PRL 101, 186403 (2008) [2] K. Haule, PRB 75, 155113 (2007) [3] E. Gull et al., arXiv:0909.1795 (2009)
A Mott insulator of fermionic atoms in an optical lattice
NASA Astrophysics Data System (ADS)
Moritz, Henning
2009-03-01
In a solid material strong interactions between the electrons can lead to surprising properties. A prime example is the Mott insulator, where the suppression of conductivity is a result of interactions and not the consequence of a filled Bloch band. The proximity to the Mott insulating phase in fermionic systems is the origin for many intriguing phenomena in condensed matter physics, most notably high-temperature superconductivity. Compared to real materials, a fermionic quantum gas trapped in an optical lattice offers a very pure realisation of the Hubbard model, giving a new approach to understand the physics of strongly correlated systems. We report on the formation of a Mott insulator of a repulsively interacting two-component Fermi gas in an optical lattice. It is signalled by three features: a drastic suppression of doubly occupied lattice sites, a strong reduction of the compressibility inferred from the response of double occupancy to atom number increase, and the appearance of a gapped mode in the excitation spectrum. In collaboration with Robert J"ordens, Niels Strohmaier, and Daniel Greif, ETH Zurich; Kenneth G"unter, ETH Zurich, ENS Paris; Leticia Tarruell and Tilman Esslinger, ETH Zurich.
NASA Astrophysics Data System (ADS)
Ku, Wei; Yang, Fan
2015-03-01
In contrast to the current lore, we demonstrate that even the overdoped cuprates suffer from superconducting phase fluctuation in the strong binding limit. Specifically, the Mott-ness of the underlying doped holes dictates naturally a generic optimal doping around 15% and nearly complete loss of phase coherence around 25%, giving rise to a dome shape of superconducting transition temperature in excellent agreement with experimental observations of the cuprates. We verify this effect with a simple estimation using Gutzwiller approximation of the preformed pairs, obtained through variational Monte Carlo calculation. This realization suggests strongly the interesting possibility that the high-temperature superconductivity in the cuprates might be mostly described by Bose-Einstein condensation, without crossing over to amplitude fluctuating Cooper pairs. Supported by Department of Energy, Office of Basic Energy Science DE-AC02-98CH10886.
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. PMID:25603958
Are peripheral Mott cells an indication of stress or inefficient immunity?
Cotter, Paul F
2015-07-01
Atypical plasmacytes having distinctive cytoplasmic vacuoles (Mott cells) were detected in 77/1,000 (7.7%) of commercial hens housed conventionally, in aviaries, or in enriched environments. The earliest Mott positive peripheral blood samples were at placement (18 wk) from 2 consecutive commercial flocks. Additional samples obtained at 32, 48, 56, and 77 wk were positive. Most Mott cells came from hens with high total white blood cell counts as a component of leukocytosis. However, Mott cells were found in hens with low total white blood cell counts, and low heterophil/lymphocyte ratios. Phagocytosis of bacteria by some Mott cells was a remarkable feature. Many of the Mott positive hens had polymicrobial bacteremia and a few had fungemia likely accounting for the leukocytosis. In other cases, free-swimming bacteria were located near to a Mott cell. These atypical cells were in the peripheral blood samples from other poultry; a tom at slaughter (17 wk), experimental toms (10 wk), and experimental ducklings. Examples are included.As descriptions of avian Mott cells are few, the purpose of describing these cells is their contribution to hematology, immunology, and cytology. Mott cells like other atypia are sentinels, frank cytological indicators of an unusual hemogram, and consequently infer stress. Therefore, they bear directly on welfare issues. PMID:25725075
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…
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.
Mott transition in one dimension: Benchmarking dynamical cluster approaches
NASA Astrophysics Data System (ADS)
Balzer, Matthias; Hanke, Werner; Potthoff, Michael
2008-01-01
The variational cluster approach (VCA) is applied to the one-dimensional Hubbard model at zero temperature using clusters (chains) of up to ten sites with full diagonalization and the Lanczos method as cluster solver. Within the framework of the self-energy-functional theory (SFT), different cluster reference systems with and without bath degrees of freedom, in different topologies and with different sets of variational parameters, are considered. Static and one-particle dynamical quantities are calculated for half-filling as a function of U as well as for fixed U as a function of the chemical potential to study the interaction- and filling-dependent metal-insulator (Mott) transition. The recently developed Q -matrix technique is used to compute the SFT grand potential. For benchmarking purposes we compare the VCA results with exact results available from the Bethe ansatz, with essentially exact dynamical density-matrix renormalization-group data, with (cellular) dynamical mean-field theory and full diagonalization of isolated Hubbard chains. Several issues are discussed including convergence of the results with cluster size, the ability of cluster approaches to access the critical regime of the Mott transition, efficiency in the optimization of correlated-site vs bath-site parameters, and of multidimensional parameter optimization. We also study the role of bath sites for the description of excitation properties and as charge reservoirs for the description of filling dependencies. The VCA turns out to be a computationally cheap method which is competitive with established cluster approaches.
Spectral functions of 1D Peierls and Mott insulators
NASA Astrophysics Data System (ADS)
Voit, Johannes
1998-03-01
We construct the spectral function of the Luther-Emery model which describes one-dimensional Peierls and Mott insulators with a spin resp. charge gap, using symmetries and known limits and equivalences to other models. For the Peierls insulator, we find a true singularity with interaction dependent exponents on the gapped spin dispersion and a finite maximum depending on the magnitude of the spin gap, on a charge dispersion shifted by Δ_σ, as well as strong shadow bands with the same functional form as the main bands. For 1D Mott insulators, one or two singularities with universal inverse-square-root singularities are found depending on whether the charge velocity is larger or smaller than the spin velocity. The shadow band has a single singularity on the renormalized charge dispersion. These results could apply to the description of photoemission experiments in systems like K_0.3 Mo O_3, TTF-TCNQ, or Sr Cu O_2.
Mott Quantum Criticality in the Anisotropic 2D Hubbard Model
NASA Astrophysics Data System (ADS)
Lenz, Benjamin; Manmana, Salvatore R.; Pruschke, Thomas; Assaad, Fakher F.; Raczkowski, Marcin
We present evidence for Mott quantum criticality in an anisotropic two-dimensional system of coupled Hubbard chains at half-filling. In this scenario emerging from variational cluster approximation and cluster dynamical mean-field theory, the interchain hopping t⊥ acts as control parameter driving the second-order critical endpoint Tc of the metal-insulator transition down to zero at t⊥c / t ~= 0 . 2 . Below t⊥c the volume of hole and electron Fermi pockets of a compensated metal vanishes continuously at the Mott transition. Above t⊥c the volume reduction of the pockets is cut off by a first-order transition. We discuss the relevance of our findings to a putative quantum critical point in layered organic conductors whose location remains elusive so far. We acknowledge support by DFG research units FOR1807 and FOR1346, ERC Starting Grant No. 306897 and NSF Grant No. PHY11-25915, and computer support by the GWDG and Jülich Supercomputing Centre.
Mott physics and spin fluctuations: A functional viewpoint
NASA Astrophysics Data System (ADS)
Ayral, Thomas; Parcollet, Olivier
2016-06-01
We present a formalism for strongly correlated systems with fermions coupled to bosonic modes. We construct the three-particle irreducible functional K by successive Legendre transformations of the free energy of the system. We derive a closed set of equations for the fermionic and bosonic self-energies for a given K . We then introduce a local approximation for K , which extends the idea of dynamical mean-field theory (DMFT) approaches from two- to three-particle irreducibility. This approximation entails the locality of the three-leg electron-boson vertex Λ (i ω ,i Ω ) , which is self-consistently computed using a quantum impurity model with dynamical charge and spin interactions. This local vertex is used to construct frequency- and momentum-dependent electronic self-energies and polarizations. By construction, the method interpolates between the spin-fluctuation or G W approximations at weak coupling and the atomic limit at strong coupling. We apply it to the Hubbard model on two-dimensional square and triangular lattices. We complement the results of [T. Ayral and O. Parcollet, Phys. Rev. B 92, 115109 (2015), 10.1103/PhysRevB.92.115109] by (i) showing that, at half-filling, as DMFT, the method describes the Fermi-liquid metallic state and the Mott insulator, separated by a first-order interaction-driven Mott transition at low temperatures, (ii) investigating the influence of frustration, and (iii) discussing the influence of the bosonic decoupling channel.
Spin liquid phases of large spin Mott insulating ultracold atoms
NASA Astrophysics Data System (ADS)
Rutkowski, Todd C.; Lawler, Michael J.
2015-03-01
Understanding exotic forms of magnetism, primarily those driven by large spin fluctuations such as the quantum spin liquid state, is a major goal of condensed matter physics. But, the relatively small number of viable candidate materials poses a difficulty. We believe this problem can be solved by Mott insulating ultracold atoms with large spin moments that interact via whole-atom exchange. The large spin fluctuations of this exchange could stabilize exotic physics similar to condensed matter systems, all in an extremely tunable environment. We have approached the problem by performing a mean field theory for spin-f bosons in an optical lattice which is exact in the large-f limit. This setting is similar to that of SU(N) magnetism proposed for alkali-earth atoms but without the SU(N) symmetry. We find that states with long-range order, such as the spin nematic phase of f = 1 Na atoms, become highly entangled spin-liquid-like states for f = 3 Cr atoms. This is evidence that the magnetic phase diagram for Mott insulating atoms at larger spins generically contains exotic forms of magnetism.
Finite temperature quantum critical transport near the Mott transition
NASA Astrophysics Data System (ADS)
Terletska, Hanna; Dobrosavljevic, Vladimir
2010-03-01
We use Dynamical Mean-Field Theory to study incoherent transport above the critical end-point temperature Tc of the single band Hubbard model at half-filling. By employing an eigenvalue analysis for the free energy functional, we are able to precisely identify the crossover temperature T*(U) separating the Fermi liquid and the Mott insulating regimes. Our calculations demonstrate that a broad parameter range exist around the crossover line, where the family of resistivity curves displays simple scaling behavior. This is interpreted as a manifestation of quantum criticality controlled by the T=0 Mott transition, which is ``interrupted'' by the emergence of the coexistence dome at T < Tc . We argue that in situations where the critical temperature Tc is significantly reduced, so that the coexistence region is reduced or even absent (as in two-band, particle-hole asymmetric models, where this is found even in the clean d->∞ limit [1, 2]), similar critical scaling properties should persist down to much lower temperatures, resembling quantum critical transport similar to that found in a number of experiments [2]. [1] A. Amaricci, G. Sordi, and M. J. Rosenberg, Phys. Rev. Lett. 101, 146403 (2008) [2] A. Camjayi, K. Haule, V. Dobrosavljevic, and G. Kotliar, Nature Physics, 4, 932 (2008)
Scattering of twisted relativistic electrons by atoms
NASA Astrophysics Data System (ADS)
Serbo, V.; Ivanov, I. P.; Fritzsche, S.; Seipt, D.; Surzhykov, A.
2015-07-01
The Mott scattering of high-energetic twisted electrons by atoms is investigated within the framework of the first Born approximation and Dirac's relativistic equation. Special emphasis is placed on the angular distribution and longitudinal polarization of the scattered electrons. In order to evaluate these angular and polarization properties we consider two experimental setups in which the twisted electron beam collides with either a single well-localized atom or macroscopic atomic target. Detailed relativistic calculations have been performed for both setups and for the electrons with kinetic energy from 10 to 1000 keV. The results of these calculations indicate that the emission pattern and polarization of outgoing electrons differ significantly from the scattering of plane-wave electrons and can be very sensitive to the parameters of the incident twisted beam. In particular, it is shown that the angular- and polarization-sensitive Mott measurements may reveal valuable information about both the transverse and longitudinal components of the linear momentum and the projection of the total angular momentum of twisted electron states. Thus, the Mott scattering emerges as a diagnostic tool for the relativistic vortex beams.
Mott-Ioffe-Regel limit and resistivity crossover in a tractable electron-phonon model
NASA Astrophysics Data System (ADS)
Werman, Yochai; Berg, Erez
2016-02-01
Many metals display resistivity saturation—a substantial decrease in the slope of the resistivity as a function of temperature that occurs when the electron scattering rate τ-1 becomes comparable to the Fermi energy EF/ℏ (the Mott-Ioffe-Regel limit). At such temperatures, the usual description of a metal in terms of ballistically propagating quasiparticles is no longer valid. We present a tractable model of a large number N of electronic bands coupled to N2 optical phonon modes, which displays a crossover behavior in the resistivity at temperatures where τ-1˜EF/ℏ . At low temperatures, the resistivity obeys the familiar linear form, while at high temperatures, the resistivity still increases linearly, but with a modified slope (that can be either lower or higher than the low-temperature slope, depending on the band structure). The high-temperature non-Boltzmann regime is interpreted by considering the diffusion constant and the compressibility, both of which scale as the inverse square root of the temperature.
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.
Elastic collapse and avalanche criticality near a Mott transition
NASA Astrophysics Data System (ADS)
Smith, J. L.; Safarik, D. J.; Lashley, J. C.; Salje, E. K. H.; Opeil, C. P.; Riseborough, P. S.
2011-03-01
We study some dynamic aspects of a Mott transition in a rare-earth alloy Ce 0.90 Th 0.10 by resonant-ultrasound spectroscopy (RUS), electrical-transport, and thermal-expansion measurements. In the temperature range spanning the first-order transition, we observe a stiffening of the elastic response that is associated with a continuous front propagation (e . g . solitons). A defining characteristic of a mixed phase regime, slow scanning rates (0.01 K/min) show these solitons to be superimposed with jerks and avalanches in all three data sets: RUS, resistivity, and thermal expansion data. Analysis of the avalanche data give power law distributions with critical exponents P (E) =En for energy, in the case of thermal expansion data and length, in the case of electrical transport data. Work performed under the auspices of the U.S. Dept. of Energy.
Slowdown of the Electronic Relaxation Close to the Mott Transition.
Sayyad, Sharareh; Eckstein, Martin
2016-08-26
We investigate the time-dependent reformation of the quasiparticle peak in a correlated metal near the Mott transition, after the system is quenched into a hot electron state and equilibrates with an environment which is colder than the Fermi-liquid crossover temperature. Close to the transition, we identify a purely electronic bottleneck time scale, which depends on the spectral weight around the Fermi energy in the bad metallic phase in a nonlinear way. This time scale can be orders of magnitude larger than the bare and renormalized electronic hopping time, so that a separation of electronic and lattice time scales may break down. The results are obtained using nonequilibrium dynamical mean-field theory and a slave-rotor representation of the Anderson impurity model. PMID:27610867
Wannier-Mott excitons in semiconductors with a superlattice
Suris, R. A.
2015-06-15
The effect of the motion of a Wannier-Mott exciton in semiconductors with a superlattice formed by heterojunctions on the exciton binding energy and wave function is analyzed. This effect arises as a result of the fact that the dispersion laws of the electron and hole that form an exciton in a superlattice differ from the quadratic law. The investigated one-dimensional superlattice consists of alternating semiconductor layers with different energy positions of the conduction and valence bands, i.e., with one-dimensional wells and barriers. The exciton state in a superlattice consisting of quantum dots is analyzed. It is demonstrated that the closer the electron and hole effective masses, the greater the dependence of the binding energy on the exciton quasi-momentum. The possibility of replacing the tunneling excitation transfer between superlattice cells with the dipole-dipole one at certain exciton quasi-wave vector values is investigated.
A cylindrically symmetric "micro-Mott" electron polarimeter.
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 Seff (2)IIo 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. PMID:27250409
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.
First-order superfluid to Mott-insulator phase transitions in spinor condensates
NASA Astrophysics Data System (ADS)
Chen, Zihe; Jiang, Jie; Zhao, Lichao; Wang, Shengtao; Tang, Tao; Duan, Luming; Liu, Yingmei
2016-05-01
We observe evidence of first-order superfluid to Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include hysteresis effect, significant heatings across the phase transitions, and evolutions of spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory, and in addition suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid to Mott-insulator phase transitions.
First-order superfluid-to-Mott-insulator phase transitions in spinor condensates
NASA Astrophysics Data System (ADS)
Jiang, J.; Zhao, L.; Wang, S.-T.; Chen, Z.; Tang, T.; Duan, L.-M.; Liu, Y.
2016-06-01
We observe evidence of first-order superfluid-to-Mott-insulator quantum phase transitions in a lattice-confined antiferromagnetic spinor Bose-Einstein condensate. The observed signatures include the hysteresis effect, significant heatings across the phase transitions, and changes in spin populations due to the formation of spin singlets in the Mott-insulator phase. The nature of the phase transitions is found to strongly depend on the ratio of the quadratic Zeeman energy to the spin-dependent interaction. Our observations are qualitatively understood by the mean field theory and suggest tuning the quadratic Zeeman energy is a new approach to realize superfluid-to-Mott-insulator phase transitions.
Parity-time symmetry-breaking mechanism of dynamic Mott transitions in dissipative systems
NASA Astrophysics Data System (ADS)
Tripathi, Vikram; Galda, Alexey; Barman, Himadri; Vinokur, Valerii M.
2016-07-01
We describe the critical behavior of the electric field-driven (dynamic) Mott insulator-to-metal transitions in dissipative Fermi and Bose systems in terms of non-Hermitian Hamiltonians invariant under simultaneous parity (P ) and time-reversal (T ) operations. The dynamic Mott transition is identified as a PT symmetry-breaking phase transition, with the Mott insulating state corresponding to the regime of unbroken PT symmetry with a real energy spectrum. We establish that the imaginary part of the Hamiltonian arises from the combined effects of the driving field and inherent dissipation. We derive the renormalization and collapse of the Mott gap at the dielectric breakdown and describe the resulting critical behavior of transport characteristics. The obtained critical exponent is in an excellent agreement with experimental findings.
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, T; Mao, Z Q; Liu, G Q; Ke, X
2016-05-27
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. PMID:27284665
Colossal Magnetoresistance in a Mott Insulator via Magnetic Field-Driven Insulator-Metal Transition
NASA Astrophysics Data System (ADS)
Zhu, M.; Peng, J.; Zou, T.; Prokes, K.; Mahanti, S. D.; Hong, T.; Mao, Z. Q.; Liu, G. Q.; Ke, X.
2016-05-01
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 systems other than manganites, such as Mott insulators in the vicinity of the boundary between competing phases.
Pressure-induced Mott transition in an organic superconductor with a finite doping level.
Oike, H; Miyagawa, K; Taniguchi, H; Kanoda, K
2015-02-13
We report the pressure study of a doped organic superconductor with a Hall coefficient and conductivity measurements. We find that maximally enhanced superconductivity and a marginal-Fermi liquid appear around a certain pressure where mobile carriers increase critically, suggesting a possible quantum phase transition between strongly and weakly correlated regimes. This observation points to the presence of a criticality in Mottness for a doped Mott insulator with tunable correlation. PMID:25723239
Noise Correlation Spectroscopy of the Broken Order of a Mott Insulating Phase
Guarrera, V.; Fabbri, N.; Fallani, L.; Fort, C.; Stam, K. M. R. van der; Inguscio, M.
2008-06-27
We use a two-color lattice to break the homogeneous site occupation of an atomic Mott insulator of bosonic {sup 87}Rb. We detect the disruption of the ordered Mott domains via noise correlation analysis of the atomic density distribution after time of flight. The appearance of additional correlation peaks evidences the redistribution of the atoms into a strongly inhomogeneous insulating state, in quantitative agreement with the predictions.
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.
Quantum gases in optical lattices : the atomic Mott insulator
NASA Astrophysics Data System (ADS)
van Oosten, D.
2004-09-01
An optical lattice is a periodic potential for atoms, created using a standing wave pattern of light. Due to the interaction between the light and the atoms, the atoms are attracted to either the nodes or the anti-nodes of the standing wave, depending on the exact wave lenght of the light. This means that if such a lattice is loaded with a sufficiently high number of ultracold atoms, a periodic array of atoms is obtained, we an interatomic distance of a few tenths of a micrometer. In order to obtain such a high number of cold atoms, one first has to create a so-called Bose-Einstein condensate. When an optical lattice is loaded from a Bose-Einstein condensate, it is possible to create a system in which every atom is in the lowest band of the lattice and there is on average one atom in each lattice site. Because the lattice potential is created with laser light, the depth of the lattice can easily be tuned by changing the intensity of the laser. When the intensity of the laser light is low, the atoms can tunnel from one site to the next. Due to this tunneling, the gas of atoms in the lattice will remain superfluid. However, if the intensity of the laser light is increased to above a certain critical value, a quantum phase transition occurs to a so-called Mott insulator. In this state, the atoms can no longer tunnel due to the fact that the on-site interaction between atoms becomes more important then the tunneling probability. In this PhD thesis, a description is given of the experimental setup that is being constructed in our group to create these systems in our lab. Also, a theoretical description is given of these systems and several important quantities our derived, such as the gap of the Mott-insulating state. Furthermore, an experiment is proposed that can be used to accurately measure this gap.
Importance of subleading corrections for the Mott critical point
NASA Astrophysics Data System (ADS)
Tremblay, A.-M. S.; Semon, Patrick
2013-03-01
The interaction-induced metal-insulator transition should be in the Ising universality class. Experiments on layered organic superconductors suggest instead that the observed critical endpoint of the first-order Mott transition in d = 2 does not belong to any of the known universality classes for thermal phase transitions. In particular, it is found that δ = 2 . Given the quantum nature of the two phases involved in the transition, we use dynamical mean-field theory and a cluster generalization to investigate whether the new exponents could arise as transient quantum behavior preceding the asymptotic critical behavior. In the cluster calculation, a canonical transformation that minimizes the sign problem in continuous-time quantum Monte Carlo calculations allows previously unattainable precision. Our results show that there are important subleading corrections in the mean-field regime that can lead to an apparent exponent δ = 2 . Experiments on optical lattices could verify our predictions for double occupancy. P. Sémon and A.-M.S. Tremblay, Phys. Rev. B 85, 201101(R)/1-5 (2012). Supported by NSERC, Canada Research Chair, CIFAR, CFI, MELS, Calcul Quebec, Compute/Calcul Canada
Nature of strong hole pairing in doped Mott antiferromagnets.
Zhu, Zheng; Jiang, Hong-Chen; Sheng, D N; Weng, Zheng-Yu
2014-01-01
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-T(c) cuprate superconductors. PMID:24957467
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
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
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
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
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
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.
Miyake, Hirokazu; Siviloglou, Georgios A; Puentes, Graciana; Pritchard, David E; Ketterle, Wolfgang; Weld, David M
2011-10-21
We have observed Bragg scattering of photons from quantum degenerate ^{87}Rb atoms in a three-dimensional optical lattice. Bragg scattered light directly probes the microscopic crystal structure and atomic wave function whose position and momentum width is Heisenberg limited. The spatial coherence of the wave function leads to revivals in the Bragg scattered light due to the atomic Talbot effect. The decay of revivals across the superfluid to Mott insulator transition indicates the loss of superfluid coherence. PMID:22107532
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.
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).
Tunnelling into the twisted Mott insulator Sr2IrO4 with atomic resolution
NASA Astrophysics Data System (ADS)
Ansary, Armin; Nichols, John; Bray-Ali, Noah; Cao, Gang; Ng, Kwok-Wai
2014-03-01
We studied the single-layered iridate Sr2IrO4 with a scanning tunneling microscope. The finite low temperature conductance enables the electronic structure of this antiferromagnetic Mott insulator to be measured by tunneling spectroscopy. We imaged the topography of freshly cleaved surfaces and measured differential tunneling conductance at cryogenic temperatures. We found the Mott gap in the tunneling density of states to be 2 Δ = 615 meV. Within the Mott gap, additional shoulders are observed which are interpreted as inelastic loss features due to magnons. This research was supported by NSF grants DMR- 0800367, DMR-0856234 and EPS-0814194. Noah Bray- Ali acknowledges support from the National Research Council Postdoctoral Research Associateship Program.
On the gap problem for the Mott--Hubbard transition within Dynamical Mean-Field Theory
NASA Astrophysics Data System (ADS)
Noack, Reinhard M.; Gebhard, Florian
1998-03-01
Within the Dynamical Mean-Field Theory, the zero temperature Mott-Hubbard metal-to-insulator transition has been proposed to be discontinuous in the sense that the gap jumps to a finite value at the transition.(A. Georges, G. Kotliar, W. Krauth, and M. J. Rozenberg, Rev. Mod. Phys. 68), 13 (1996). We use the Random Dispersion Approximation to the Hubbard model,(F. Gebhard, The Mott Metal-Insulator Transition), Springer Tracts in Modern Physics 137 (Springer, Berlin, 1997). which becomes equivalent to the Dynamical Mean-Field Theory in the thermodynamic limit, to show that the charge gap opens continuously at the critical interaction strength which is of the size of the bandwidth. Therefore, our results support the idea^2 that the Dynamical Mean Field Theory provides a generic description of the Mott--Hubbard transition as a continuous quantum phase transition.
Quantum critical Mott transitions in a bilayer Kondo insulator-metal model system
NASA Astrophysics Data System (ADS)
Sen, Sudeshna; Vidhyadhiraja, N. S.
2016-04-01
A bilayer system comprising a Kondo insulator coupled to a simple metal (KI-M) is considered. Employing the framework of dynamical mean-field theory, the model system is shown to exhibit a surface of quantum critical points (QCPs) that separates a Kondo screened, Fermi liquid phase from a local moment, Mott insulating phase. The quantum critical nature of these Mott transitions is characterized by the vanishing of (a) the coherence scale on the Fermi liquid side, and (b) the Mott gap on the MI side. In contrast to the usual "large-to-small" Fermi surface (FS) QCPs in heavy-fermion systems, the bilayer KI-M system exhibits a complete FS destruction.
Electron-hole doping asymmetry of Fermi surface reconstructed in a simple Mott insulator
NASA Astrophysics Data System (ADS)
Kawasugi, Yoshitaka; Seki, Kazuhiro; Edagawa, Yusuke; Sato, Yoshiaki; Pu, Jiang; Takenobu, Taishi; Yunoki, Seiji; Yamamoto, Hiroshi M.; Kato, Reizo
2016-08-01
It is widely recognized that the effect of doping into a Mott insulator is complicated and unpredictable, as can be seen by examining the Hall coefficient in high Tc cuprates. The doping effect, including the electron-hole doping asymmetry, may be more straightforward in doped organic Mott insulators owing to their simple electronic structures. Here we investigate the doping asymmetry of an organic Mott insulator by carrying out electric-double-layer transistor measurements and using cluster perturbation theory. The calculations predict that strongly anisotropic suppression of the spectral weight results in the Fermi arc state under hole doping, while a relatively uniform spectral weight results in the emergence of a non-interacting-like Fermi surface (FS) in the electron-doped state. In accordance with the calculations, the experimentally observed Hall coefficients and resistivity anisotropy correspond to the pocket formed by the Fermi arcs under hole doping and to the non-interacting FS under electron doping.
'An atmosphere of cure': Frederick Mott, shell shock and the Maudsley.
Jones, Edgar
2014-12-01
Although recognized as a medical scientist, the work of Frederick Mott as a physician, educator and clinical policymaker has been overshadowed. As a late entrant to the asylum system, Mott questioned established practices of treating mentally-ill patients and campaigned for reform. During World War I, entrusted with the management of the Maudsley neurological section, he sought to raise clinical standards and experimented with a range of therapies designed to treat the most severe or intractable forms of shell shock. While Mott believed that psychiatric disorder was underwritten by inherited characteristics, he did not dismiss the impact of the environment. The diversity of his interests has led to an understatement of his contribution as a physician, not only to the design and founding of the Maudsley Hospital but also to the therapeutic regime practised there during the interwar period. PMID:25395439
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
Dean, M. P. M.; Cao, Y.; Liu, X.; Wall, S.; Zhu, D.; Mankowsky, R.; Thampy, V.; Chen, X. M.; Vale, J. G.; Casa, D.; et al
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
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.
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. PMID:27159018
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.
THz-Frequency Modulation of the Hubbard U in an Organic Mott Insulator
NASA Astrophysics Data System (ADS)
Singla, R.; Cotugno, G.; Kaiser, S.; Först, M.; Mitrano, M.; Liu, H. Y.; Cartella, A.; Manzoni, C.; Okamoto, H.; Hasegawa, T.; Clark, S. R.; Jaksch, D.; Cavalleri, A.
2015-10-01
We use midinfrared pulses with stable carrier-envelope phase offset to drive molecular vibrations in the charge transfer salt ET -F2TCNQ , a prototypical one-dimensional Mott insulator. We find that the Mott gap, which is probed resonantly with 10 fs laser pulses, oscillates with the pump field. This observation reveals that molecular excitations can coherently perturb the electronic on-site interactions (Hubbard U ) by changing the local orbital wave function. The gap oscillates at twice the frequency of the vibrational mode, indicating that the molecular distortions couple quadratically to the local charge density.
Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector
Souma, S.; Sugawara, K.; Takayama, A.; Sato, T.; Takahashi, T.
2010-09-15
We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90 deg. electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states.
Ultrahigh-resolution spin-resolved photoemission spectrometer with a mini Mott detector.
Souma, S; Takayama, A; Sugawara, K; Sato, T; Takahashi, T
2010-09-01
We have developed an ultrahigh-resolution spin-resolved photoemission spectrometer with a highly efficient mini Mott detector and an intense xenon plasma discharge lamp. The spectrometer achieves the energy resolutions of 0.9 and 8 meV for non-spin-resolved and spin-resolved modes, respectively. Three-dimensional spin-polarization is determined by using a 90° electron deflector situated before the Mott detector. The performance of spectrometer is demonstrated by observation of a clear Rashba splitting of the Bi(111) surface states. PMID:20887002
Pressure induced novel-phenomena in Mott insulator Ca2RuO4
NASA Astrophysics Data System (ADS)
Yamauchi, Yohei; Nakamura, Fumihiko; Sakaki, Mariko; Takemoto, Tetsuo; Suzuki, Takashi; Alireza, Patricia L.; Maeno, Yoshiteru
2010-12-01
In order to explore unconventional superconductivity, we have studied pressure effect on a 4d-electron Mott insulator Ca2RuO4. Pressurisation to Ca2RuO4 above 0.5 GPa transforms it from a Mott insulator to a metal with a ferromagnetic ground state. The itinerancy of the ferromagnetic state at 2 GPa is quantitatively evidenced by the magnetisation process at 2 K. Moreover, the pressure phase diagram of this system suggests the existence of a ferromagnetic quantum phase transition at ˜10 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.
Observation of a Superradiant Mott Insulator in the Dicke-Hubbard Model
NASA Astrophysics Data System (ADS)
Klinder, J.; Keßler, H.; Bakhtiari, M. Reza; Thorwart, M.; Hemmerich, A.
2015-12-01
It is well known that the bosonic Hubbard model possesses a Mott insulator phase. Likewise, it is known that the Dicke model exhibits a self-organized superradiant phase. By implementing an optical lattice inside of a high-finesse optical cavity, both models are merged such that an extended Hubbard model with cavity-mediated infinite range interactions arises. In addition to a normal superfluid phase, two superradiant phases are found, one of them coherent and hence superfluid and one incoherent Mott insulating.
Critical Slowing Down of the Charge Carrier Dynamics at the Mott Metal-Insulator Transition
NASA Astrophysics Data System (ADS)
Hartmann, Benedikt; Zielke, David; Polzin, Jana; Sasaki, Takahiko; Müller, Jens
2015-05-01
We report on the dramatic slowing down of the charge carrier dynamics in a quasi-two-dimensional organic conductor, which can be reversibly tuned through the Mott metal-insulator transition (MIT). At the finite-temperature critical end point, we observe a divergent increase of the resistance fluctuations accompanied by a drastic shift of spectral weight to low frequencies, demonstrating the critical slowing down of the order parameter (doublon density) fluctuations. The slow dynamics is accompanied by non-Gaussian fluctuations, indicative of correlated charge carrier dynamics. A possible explanation is a glassy freezing of the electronic system as a precursor of the Mott MIT.
Jeff=1 /2 Mott-Insulating State in Rh and Ir Fluorides
NASA Astrophysics Data System (ADS)
Birol, Turan; Haule, Kristjan
2015-03-01
Discovery of new transition metal compounds with large spin orbit coupling coexisting with strong electron-electron correlation among the d electrons is essential for understanding the physics that emerges from the interplay of these two effects. In this study, we predict a novel class of Jeff=1 /2 Mott insulators in a family of fluoride compounds that are previously synthesized, but not characterized extensively. First principles calculations in the level of all electron density functional theory +dynamical mean field theory indicate that these compounds have large Mott gaps and some of them exhibit unprecedented proximity to the ideal, S U (2 ) symmetric Jeff=1 /2 limit.
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.; et al
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
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
Time-dependent Mott transition in the periodic Anderson model with nonlocal hybridization
NASA Astrophysics Data System (ADS)
Hofmann, Felix; Potthoff, Michael
2016-08-01
The time-dependent Mott transition in a periodic Anderson model with off-site, nearest-neighbor hybridization is studied within the framework of nonequilibrium self-energy functional theory. Using the two-site dynamical-impurity approximation, we compute the real-time dynamics of the optimal variational parameter and of different observables initiated by sudden quenches of the Hubbard-U and identify the critical interaction. The time-dependent transition is orbital selective, i.e., in the final state, reached in the long-time limit after the quench to the critical interaction, the Mott gap opens in the spectral function of the localized orbitals only. We discuss the dependence of the critical interaction and of the final-state effective temperature on the hybridization strength and point out the various similarities between the nonequilibrium and the equilibrium Mott transition. It is shown that these can also be smoothly connected to each other by increasing the duration of a U-ramp from a sudden quench to a quasi-static process. The physics found for the model with off-site hybridization is compared with the dynamical Mott transition in the single-orbital Hubbard model and with the dynamical crossover found for the real-time dynamics of the conventional Anderson lattice with on-site hybridization.
Time and the "True Light" in Lucretia Coffin Mott's "Discourse on Woman."
ERIC Educational Resources Information Center
Zulick, Margaret D.; Leff, Michael
1995-01-01
Argues that some of the complexity and tension in Lucretia Coffin Mott's speech results from the conflicting demands of the immediate situation and the speaker's broader views on theological and social issues. Suggests the speech's inherent tensions are not fully resolved, particularly those between a typological sense of history and a progressive…
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…
ERIC Educational Resources Information Center
Sillars, Malcolm O.
1995-01-01
Suggests that the contrast between speeches by Richard Henry Dana Sr. and Lucretia Coffin Mott lies not only in their two views of the woman's place and role in society but also in the respective orientation toward Romantic idealism and Enlightenment rationalism. (TB)
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.
Spectral properties of the two-dimensional t- J model near the Mott transition
NASA Astrophysics Data System (ADS)
Kohno, Masanori
The single-particle spectral function of the two-dimensional t- J model near the Mott transition is studied using cluster perturbation theory to clarify how the spectral-weight distribution transforms to that of the Mott insulator as the doping concentration decreases. Various anomalous features observed in cuprate high-temperature superconductors are collectively explained in the two-dimensional t- J model near the Mott transition as in the two-dimensional Hubbard model. The results imply that the spectral features are primarily related to the proximity of the antiferromagnetic Mott insulator, which has a low-energy spin-wave mode but no low-energy charge excitation, and to the presence of states characterized by different energy scales rather than to the presence of double occupancy, which is completely removed in the t- J model. The results are confirmed to remain almost unchanged as the cluster size is increased from 4 ×4 to 6 ×6 sites in cluster perturbation theory by using the non-Abelian dynamical density-matrix renormalization group method.
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
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.
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. PMID:26230823
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
Mott criticality and multiferroicity in organic κ-(BEDT-TTF)2X salts
NASA Astrophysics Data System (ADS)
Lang, Michael
2014-03-01
Layered organic charge-transfer (CT) salts of the κ-(BEDT-TTF)2X family show a wealth of electronic phases resulting from the interplay of strong electron-electron correlations, reduced dimensions and magnetic frustration. Of particular interest has been the bandwidth-controlled Mott transition, separating an antiferromagnetic (afm) insulating state from a correlated metallic and superconducting state. Whereas the hydrogenated X = Cu[N(CN)2]Br salt is located on the metallic side, the deuterated variant, denoted κ-D8, is situated in splitting distance to the Mott transition, enabling the s-shaped transition line TMI to be crossed via temperature sweeps. The talk will address the following aspects: 1) Thermal expansion measurements on single crystalline κ-D8 reveal discontinuous changes of the lattice parameters on crossing the Mott transition line and a huge anomaly close to the second-order critical end point of TMI. By elaborating on a scaling theory, we found that (i) the latter effect is a consequence of an almost divergence of the Grüneisen parameter Γ at the finite- T critical end point, and (ii) that the expansivity data of are in excellent agreement with the Mott criticality lying within the 2D Ising universality class, at variance with results from conductivity measurements. Thermal expansion measurements under Helium-gas pressure are underway for providing thermodynamic information at variable pressure. 2) Surprisingly, for the isostructural X = Cu[N(CN)2]Cl salt, located close to the Mott transition on the insulating side, we found that besides the well-established afm order at TN ~ 27 K, the system also reveals a ferroelectric transition at TFE, making this material the first multiferroic CT salt. Most remarkably, the measurements reveal TFE ~TN , suggesting a close interrelation between both types of ferroic order. Work was supported by Deutsche Forschungsgemeinschaft through the Collaborative Research Centers TRR 49 and TRR 80.
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.
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.
NASA Astrophysics Data System (ADS)
Tremblay, A.-M. S.; Kyung, Bumsoo
2007-03-01
We study the Mott transition, antiferromagnetism and superconductivity in layered organic conductors using Cellular Dynamical Mean Field Theory for the frustrated Hubbard model. A d-wave superconducting phase appears between an antiferromagnetic insulator and a metal for t^'/t=0.3-0.7 , or between a nonmagnetic Mott insulator (spin liquid) and a metal for t^'/t>=0.8, in agreement with experiments on layered organic conductors including κ-(ET)2Cu2(CN)3. These phases are separated by a strong first order transition. The phase diagram gives much insight into the mechanism for d-wave superconductivity. Two predictions are made. B. Kyung and A.-M.S. Tremblay, Phys. Rev. Lett. 97, 046402 (2006)
A microscopic view on the Mott transition in chromium-doped V(2)O(3).
Lupi, S; Baldassarre, L; Mansart, B; Perucchi, A; Barinov, A; Dudin, P; Papalazarou, E; Rodolakis, F; Rueff, J-P; Itié, J-P; Ravy, S; Nicoletti, D; Postorino, P; Hansmann, P; Parragh, N; Toschi, A; Saha-Dasgupta, T; Andersen, O K; Sangiovanni, G; Held, K; Marsi, M
2010-01-01
V(2)O(3) is the prototype system for the Mott transition, one of the most fundamental phenomena of electronic correlation. Temperature, doping or pressure induce a metal-to-insulator transition (MIT) between a paramagnetic metal (PM) and a paramagnetic insulator. This or related MITs have a high technological potential, among others, for intelligent windows and field effect transistors. However the spatial scale on which such transitions develop is not known in spite of their importance for research and applications. Here we unveil for the first time the MIT in Cr-doped V(2)O(3) with submicron lateral resolution: with decreasing temperature, microscopic domains become metallic and coexist with an insulating background. This explains why the associated PM phase is actually a poor metal. The phase separation can be associated with a thermodynamic instability near the transition. This instability is reduced by pressure, that promotes a genuine Mott transition to an eventually homogeneous metallic state. PMID:21045823
NASA Astrophysics Data System (ADS)
Yin, Xinmao; Zeng, Shengwei; Das, Tanmoy; Baskaran, G.; Asmara, Teguh Citra; Santoso, Iman; Yu, Xiaojiang; Diao, Caozheng; Yang, Ping; Breese, Mark B. H.; Venkatesan, T.; Lin, Hsin; Ariando; Rusydi, Andrivo
2016-05-01
We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y0.38 La0.62 (Ba0.82 La0.18 )2Cu3 Oy films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L3 ,2 edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates.
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; et al
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
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
NASA Astrophysics Data System (ADS)
Hogan, Tom; Yamani, Z.; Walkup, D.; Chen, Xiang; Dally, Rebecca; Ward, Thomas Z.; Dean, M. P. M.; Hill, John; Islam, Z.; Madhavan, Vidya; Wilson, Stephen D.
2015-06-01
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. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state.
Correlation-driven charge order at the interface between a Mott and a band insulator.
Pentcheva, Rossitza; Pickett, Warren E
2007-07-01
To study digital Mott insulator LaTiO3 and band insulator SrTiO3 interfaces, we apply correlated band theory within the local density approximation including a Hubbard U to (n, m) multilayers, 1
STM/STS study of metal-to-Mott-insulator transitions
NASA Astrophysics Data System (ADS)
Hanaguri, T.; Kohsaka, Y.; Iwaya, K.; Satow, S.; Kitazawa, K.; Takagi, H.; Azuma, M.; Takano, M.
2004-08-01
We performed low-temperature scanning tunneling microscopy/spectroscopy (STM/STS) on Ca 2- xNa xCuO 2Cl 2 and NiS 2- xSe x, which are filling and bandwidth-controlled Mott transition systems, respectively. STM images of Ca 2- xNa xCuO 2Cl 2 show inhomogeneous patch-like corrugations which are originated from the spatial variations of the local density of states. Such an electronic inhomogeneity is absent in NiS 2- xSe x, except in the close vicinity of the metal-insulator transition (MIT). These results suggest that the change in electronic states across the MIT is different between filling- and bandwidth-controlled Mott transition systems.
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
Extended dynamic Mott transition in the two-band Hubbard model out of equilibrium
NASA Astrophysics Data System (ADS)
Behrmann, Malte; Fabrizio, Michele; Lechermann, Frank
2013-07-01
We reformulate the time-dependent Gutzwiller approximation by M. Schiró and M. Fabrizio, [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.105.076401 105, 076401 (2010)] in the framework of slave-boson mean-field theory, which is used to investigate the dynamical Mott transition of the generic two-band Hubbard model at half filling upon an interaction quench. Interorbital fluctuations lead to notable changes with respect to the single-band case. The singular dynamical transition is replaced by a broad regime of long-lived fluctuations between metallic and insulating states, accompanied by intriguing precursor behavior. A mapping to a spin model proves helpful to analyze the different regions in terms of the evolution of an Ising-like order parameter. Contrary to the static case, singlet occupations remain vital in the Mott-insulating regime with finite Hund's exchange.
Carrier doping to the organic Mott insulator by conjugating with tetrathiafulvalene
NASA Astrophysics Data System (ADS)
Takahashi, Y.; Nakagawa, Y.; Hayakawa, K.; Inabe, T.; Naito, T.
2012-09-01
The electrical conductivity of the organic Mott insulator ET-F2TCNQ (ET = bis(ethylenedithio)tetrathiafulvalene, F2TCNQ = 2,5-difluoro-7,7,8,8-tetracyanoquinodimethane) crystal was found to be enhanced by conjugation with a tetrathiafulvalene (TTF) single crystal on its surface; surface sheet resistance decreased from 5 × l05 to 2 × 103 Ω/sq. The mechanism of this decrement was investigated through optical and atomic force microscopy measurements at the interface. When TTF was conjugated to the ET-F2TCNQ crystal, electron injection from TTF and complex formation between TTF and F2TCNQ occurred. Neutral ET molecules were consequently generated at the interface, and this charge doping broke the Mott insulating state.
Yin, Xinmao; Zeng, Shengwei; Das, Tanmoy; Baskaran, G; Asmara, Teguh Citra; Santoso, Iman; Yu, Xiaojiang; Diao, Caozheng; Yang, Ping; Breese, Mark B H; Venkatesan, T; Lin, Hsin; Ariando; Rusydi, Andrivo
2016-05-13
We report the first observation of the coexistence of a distinct midgap state and a Mott state in undoped and their evolution in electron and hole-doped ambipolar Y_{0.38}La_{0.62}(Ba_{0.82}La_{0.18})_{2}Cu_{3}O_{y} films using spectroscopic ellipsometry and x-ray absorption spectroscopies at the O K and Cu L_{3,2} edges. Supported by theoretical calculations, the midgap state is shown to originate from antiferromagnetic correlation. Surprisingly, while the magnetic state collapses and its correlation strength weakens with dopings, the Mott state in contrast moves toward a higher energy and its correlation strength increases. Our result provides important clues to the mechanism of electronic correlation strengths and superconductivity in cuprates. PMID:27232036
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 Z; Dean, M P M; Hill, John; Islam, Z; Madhavan, Vidya; Wilson, Stephen D
2015-06-26
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. As the metallic state is stabilized, a weak structural distortion develops and suggests a competing instability with the parent spin-orbit Mott state. PMID:26197142
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.
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.
Site-selective Mott transition in rare-earth-element nickelates.
Park, Hyowon; Millis, Andrew J; Marianetti, Chris A
2012-10-12
A combination of density functional and dynamical mean field theory calculations are used to show that the remarkable metal-insulator transition in the rare-earth-element nickelate perovskites arises from a site-selective Mott phase, in which the d electrons on half of the Ni ions are localized to form a fluctuating moment while the d electrons on other Ni ions form a singlet with holes on the surrounding oxygen ions. The calculation reproduces key features observed in the nickelate materials, including an insulating gap in the paramagnetic state, a strong variation of static magnetic moments among Ni sites and an absence of charge order. A connection between structure and insulating behavior is documented. The site-selective Mott transition may be a more broadly applicable concept in the description of correlated materials. PMID:23102343
5f-electron localization in the actinide metals: thorides, actinides and the Mott transition
NASA Astrophysics Data System (ADS)
Lawson, A. C.
2016-03-01
For the light actinides Ac-Cm, the numbers of localized and itinerant 5f-electrons are determined by comparing various estimates of the f-electron counts. At least one itinerant f-electron is found for each element, Pa-Cm. These results resolve certain disagreements among electron counts determined by different methods and are consistent with the Mott transition model and with the picture of the 5f-electrons' dual nature.
Random Field Driven Spatial Complexity at the Mott Transition in VO2
NASA Astrophysics Data System (ADS)
Carlson, Erica; Liu, Shuo; Phillabaum, Benjamin; Dahmen, Karin; Vidhyadhiraja, Narsimhamurthy; Qazilbash, Mumtaz; Basov, Dimitri
We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system.
Microsphere plate detectors used with a compact Mott polarimeter for time-of-flight studies
Snell, G.; Viefhaus, J.; Dunning, F. B.; Berrah, N.
2000-06-01
A compact retarding-potential Mott polarimeter combined with microsphere plates (MSP) as electron detectors was built to perform spin-resolved time-of-flight electron spectroscopy. The comparison of the performance of MSP and channeltron detectors shows that the MSP detector has a better time resolution but a lower efficiency. The overall time resolution of the system was determined to be 350 ps using synchrotron radiation pulses. (c) 2000 American Institute of Physics.
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.
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.
Interacting bosons in an optical lattice: Bose-Einstein condensates and Mott insulator
Fialko, O.; Moseley, Ch.; Ziegler, K.
2007-05-15
A dense Bose gas with hard-core interaction is considered in an optical lattice. We study the phase diagram in terms of a special mean-field theory that describes a Bose-Einstein condensate and a Mott insulator with a single particle per lattice site for zero as well as for nonzero temperatures. We calculate the densities, the excitation spectrum, and the static structure factor for each of these phases.
Critical behavior near the Mott transition in the half-filled asymmetric Hubbard model
NASA Astrophysics Data System (ADS)
Hoang, Anh-Tuan; Le, Duc-Anh
2016-03-01
We study the half-filled asymmetric Hubbard model within the two-site dynamical mean field theory. At zero temperature, explicit expressions of the critical interaction Uc for the Mott transition and the local self-energy are analytically derived. Critical behavior of the quasiparticle weights and the double occupancy are obtained analytically as functions of the on-site interaction U and the hopping asymmetry r. Our results are in good agreement with the ones obtained by much more sophisticated theory.
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.
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.
Bosons with Artificial Gauge Fields and Mott Physics on the Honeycomb Lattice
NASA Astrophysics Data System (ADS)
Vidanovic, Ivana; Petrescu, Alexandru; Le Hur, Karyn; Hofstetter, Walter
2014-03-01
We study bosons in the tight-binding model on the honeycomb lattice introduced by Haldane. We analyze the ground state topology and quasiparticle properties in the Mott phase by applying bosonic dynamical mean field theory, strong-coupling perturbation theory, exact diagonalization and numerical evaluations of sample Hall conductivity. The phase diagram also contains two different superfluid phases. The quasiparticle dynamics, number fluctuations, and local currents are measurable in cold atom experiments.
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
Double Occupancy in low-energy theoreis of doped Mott insulators
NASA Astrophysics Data System (ADS)
Phillips, Philip; Pong Choy, Ting; Leigh, Robert; Sawatzky, George
2008-03-01
We review how a proper low-energy theory can be constructed for the Hubbard model by explicitly integrating over the degrees of freedom far away from the chemical potential. A surprsing feature of the exact low-energy theory is the emergence of an elementary charge 2e boson which mediates double occupancy much below the Mott scale. We show that within the standard canonical transformation formalismused to derive the t-J model from the Hubbard model, a similar feature (double occupancy below the Mott scale) appears ONLY if the electron creation and annihilation operators are properly transformed as well. By comparing precisely how the electron operators transform in both theories, we are able to show that the charge 2e boson mediates dynamical spectral weight transfer across the Mott gap. At half-filling, the interactions mediated by the charge 2e boson defeat the artificial local SU(2) symmetry found earlier in the projected t-J model. R. G. Leigh, P. Phillips and T. -P. Choy, Phys. Rev. Lett. 99 46404 (2007); arxiv:07071554 (PRB, in press).
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. PMID:25272476
Le Hur, Karyn Maurice Rice, T.
2009-07-15
Since the discovery of high-temperature superconductivity in 1986 by Bednorz and Mueller, great efforts have been devoted to finding out how and why it works. From the d-wave symmetry of the order parameter, the importance of antiferromagnetic fluctuations, and the presence of a mysterious pseudogap phase close to the Mott state, one can conclude that high-T{sub c} superconductors are clearly distinguishable from the well-understood BCS superconductors. The d-wave superconducting state can be understood through a Gutzwiller-type projected BCS wavefunction. In this review article, we revisit the Hubbard model at half-filling and focus on the emergence of exotic superconductivity with d-wave symmetry in the vicinity of the Mott state, starting from ladder systems and then studying the dimensional crossovers to higher dimensions. This allows to confirm that short-range antiferromagnetic fluctuations can mediate superconductivity with d-wave symmetry. Ladders are also nice prototype systems allowing to demonstrate the truncation of the Fermi surface and the emergence of a Resonating Valence Bond (RVB) state with preformed pairs in the vicinity of the Mott state. In two dimensions, a similar scenario emerges from renormalization group arguments. We also discuss theoretical predictions for the d-wave superconducting phase as well as the pseudogap phase, and address the crossover to the overdoped regime. Finally, cold atomic systems with tunable parameters also provide a complementary insight into this outstanding problem.
Strongly Correlated Superconductivity close to a Mott transition in orbitally degenerate models
NASA Astrophysics Data System (ADS)
Capone, Massimo; Fabrizio, Michele; Castellani, Claudio; Tosatti, Erio
2004-03-01
Recently a novel strongly correlated superconductivity (SCS) scenario has been proposed [1] which deals with the question whether and under which conditions Cooper-pairing may get enhanced by strong electron repulsion close to a Mott transition. The core of the SCS proposal is that the effective repulsion between quasiparticles vanishes close to the Mott transition, whereas any pairing attraction will remain unrenormalized if it acts inside the spin channel. This scenario was originally demonstrated through a Dynamical Mean Field Theory (DMFT) solution of a model for doped fullerenes, but it is believed to be far more general. Very recently, a twofold orbitally degenerate model with inverted Hund rule exchange has been proposed as a new candidate for SCS [2]. We report fresh DMFT work that fully confirms this expectation, and provides an extremely appealing phase diagram, where superconductivity arises by doping the Mott insulator, out of an unstable a pseudogapped metal, very much as it happens in cuprates. [1] M. Capone, M. Fabrizio, C. Castellani, and E. Tosatti, Science 296, 2364 (2002). [2] M. Fabrizio, A.F. Ho, L. De Leo, and G. Santoro, Phys. Rev. Lett., to appear; L. De Leo and M. Fabrizio, unpublished.
NASA Astrophysics Data System (ADS)
Hasunuma, Takumi; Kaneko, Tatsuya; Miyakoshi, Shohei; Ohta, Yukinori
2016-07-01
The variational cluster approximation is used to study the ground-state properties and single-particle spectra of the three-component fermionic Hubbard model defined on the two-dimensional square lattice at half filling. First, we show that either a paired Mott state or color-selective Mott state is realized in the paramagnetic system, depending on the anisotropy in the interaction strengths, except around the SU(3) symmetric point, where a paramagnetic metallic state is maintained. Then, by introducing Weiss fields to observe spontaneous symmetry breakings, we show that either a color-density-wave state or color-selective antiferromagnetic state is realized depending on the interaction anisotropy and that the first-order phase transition between these two states occurs at the SU(3) point. We moreover show that these staggered orders originate from the gain in potential energy (or Slater mechanism) near the SU(3) point but originate from the gain in kinetic energy (or Mott mechanism) when the interaction anisotropy is strong. The staggered orders near the SU(3) point disappear when the next-nearest-neighbor hopping parameters are introduced, indicating that these orders are fragile, protected only by the Fermi surface nesting.
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.
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.
NASA Astrophysics Data System (ADS)
Dean, Mark P. M.
In the iridates, competition between spin-orbit coupling, crystal field, and electronic correlation has lead to the observation of several novel states. Particularly notable is the spin-orbit Mott insulating state in Sr2IrO4 which has close analogies to the high temperature superconducting cuprates. This talk will describe the nature of the magnetic correlations in Sr2IrO4 and how the magnetic correlations can be modified by two different doping schemes. I will first describe doping via photo-excitation in which we use femtosecond infrared pulses to excite carriers across the Mott gap. After excitation, we probe the resulting magnetic state as a function of time delay using the first implementation of magnetic resonant inelastic X-ray scattering at a free electron laser. We find that the non-equilibrium state 2 ps after the excitation has strongly suppressed long-range magnetic order, but hosts photo-carriers that induce strong, non-thermal magnetic correlations. The magnetism recovers its two-dimensional in-plane Néel correlations on a timescale of a few ps, while the three-dimensional long range magnetic order is restored over a far longer, fluence-dependent timescale of a few 100 ps. In the second part of the talk I will describe chemical doping via Ir-Ru substitution. In this situation, we find that with increased Ru concentration, the dispersive magnetic excitations in the parent compound become almost momentum-independent, opening a magnetic gap > 150 meV. We attribute this gap to the combined effects of disorder and Ir-Ru interactions. Work performed at Brookhaven National Laboratory was supported by the US Department of Energy, Division of Materials Science, under Contract No. DE-AC02-98CH10886.
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)
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 NiS2
Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.
2016-05-12
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
NASA Astrophysics Data System (ADS)
Friedemann, S.; Chang, H.; Gamża, M. B.; Reiss, P.; Chen, X.; Alireza, P.; Coniglio, W. A.; Graf, D.; Tozer, S.; Grosche, F. M.
2016-05-01
One early triumph of quantum physics is the explanation why some materials are metallic whereas others are insulating. While a treatment based on single electron states is correct for most materials this approach can fail spectacularly, when the electrostatic repulsion between electrons causes strong correlations. Not only can these favor new and subtle forms of matter, such as magnetism or superconductivity, they can even cause the electrons in a half-filled energy band to lock into position, producing a correlated, or Mott insulator. The transition into the Mott insulating state raises important fundamental questions. Foremost among these is the fate of the electronic Fermi surface and the associated charge carrier mass, as the Mott transition is approached. We report the first direct observation of the Fermi surface on the metallic side of a Mott insulating transition by high pressure quantum oscillatory measurements in NiS2. Our results point at a large Fermi surface consistent with Luttinger’s theorem and a strongly enhanced quasiparticle effective mass. These two findings are in line with central tenets of the Brinkman-Rice picture of the correlated metal near the Mott insulating state and rule out alternative scenarios in which the carrier concentration vanishes continuously at the metal-insulator transition.
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
Relativistic electron scattering from a freely movable proton in a strong laser field
NASA Astrophysics Data System (ADS)
Liu, Ai-Hua; Li, Shu-Min
2014-11-01
We study the electron scattering from the freely movable spin-1/2 proton in the presence of a linearly polarized laser field in the first Born approximation. The dressed state of the electron is described by a time-dependent wave function derived from a perturbation treatment (in a laser field). With the aid of numerical results we explore the dependencies of the differential cross section (DCS) on the electron-impact energy. Due to the mobility of the target, the DCS of this process is modified compared to the Mott scattering, especially in large scattering angles.
Random Field Driven Spatial Complexity at the Mott Transition in VO2
NASA Astrophysics Data System (ADS)
Liu, Shuo; Phillabaum, B.; Carlson, E. W.; Dahmen, K. A.; Vidhyadhiraja, N. S.; Qazilbash, M. M.; Basov, D. N.
2016-01-01
We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric universal properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system.
Specific features of the hybridization of Frenkel and Wannier-Mott excitons in a microcavity
NASA Astrophysics Data System (ADS)
Dubovskii, O. A.; Agranovich, V. M.
2016-07-01
Polariton states have been investigated in a microcavity, where the energy of the Frenkel exciton in an organic quantum well and the energy of the semiconductor Wannier-Mott exciton in an inorganic quantum well are close to the microcavity optical mode. It has been shown that the interaction of each of these excitons with the microcavity optical mode leads to their interaction with each other and to the formation of mutually coupled hybrid excitations. The influence of the location of the quantum wells in a microcavity on the spectra of hybrid states with different polarizations has been analyzed.
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.
Haldane-Hubbard Mott Insulator: From Tetrahedral Spin Crystal to Chiral Spin Liquid
NASA Astrophysics Data System (ADS)
Hickey, Ciaran; Cincio, Lukasz; Papic, Zlatko; Paramekanti, Arun
Motivated by recent experimental realizations of artificial gauge fields in ultracold atoms, 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 low energy spectra, many-body Chern numbers, entanglement spectra, and modular matrices, we identify the molten state as a chiral spin liquid with gapped semion excitations.
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.
Observation of 2D Fermionic Mott Insulators of 40K with Single-Site Resolution
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence W.; Nichols, Matthew A.; Lawrence, Katherine R.; Okan, Melih; Zhang, Hao; Zwierlein, Martin W.
2016-06-01
We report on the site-resolved observation of characteristic states of the two-dimensional repulsive Fermi-Hubbard model, using ultracold 40K atoms in an optical lattice. By varying the tunneling, interaction strength, and external confinement, we realize metallic, Mott-insulating, and band-insulating states. We directly measure the local moment, which quantifies the degree of on-site magnetization, as a function of temperature and chemical potential. Entropies per particle as low as 0.99 (6 )kB indicate that nearest-neighbor antiferromagnetic correlations should be detectable using spin-sensitive imaging.
Probing spin dynamics from the Mott insulating to the superfluid regime in a dipolar lattice gas
NASA Astrophysics Data System (ADS)
de Paz, A.; Pedri, P.; Sharma, A.; Efremov, M.; Naylor, B.; Gorceix, O.; Maréchal, E.; Vernac, L.; Laburthe-Tolra, B.
2016-02-01
We analyze the spin dynamics of an out-of-equilibrium large spin dipolar atomic Bose gas in an optical lattice. We observe a smooth crossover from a complex oscillatory behavior to an exponential behavior throughout the Mott-to-superfluid transition. While both of these regimes are well described by our theoretical models, we provide data in the intermediate regime where dipolar interactions, contact interactions, and superexchange mechanisms compete. In this strongly correlated regime, spin dynamics and transport are coupled, which challenges theoretical models for quantum magnetism.
Mott variable range hopping conduction mechanism in single-phase CZTS thin film
NASA Astrophysics Data System (ADS)
Ansari, Mohd Zubair; Khare, Neeraj
2015-06-01
Single-phase Cu2ZnSnS4 (CZTS) thin film has been deposited by ultrasonic assisted chemical vapor deposition method on glass substrate at 325 °C substrate temperature. The temperature dependent of electrical conductivity of the CZTS thin film has been measured in order to identify the dominant conduction mechanism. In the high temperature range, the dominance of thermally activated band conduction is observed, whereas in the lower temperature region (70K-230K) the Mott 3D Variable Range Hopping is found to dominate.
Random Field Driven Spatial Complexity at the Mott Transition in VO(2).
Liu, Shuo; Phillabaum, B; Carlson, E W; Dahmen, K A; Vidhyadhiraja, N S; Qazilbash, M M; Basov, D N
2016-01-22
We report the first application of critical cluster techniques to the Mott metal-insulator transition in vanadium dioxide. We show that the geometric universal properties of the metallic and insulating puddles observed by scanning near-field infrared microscopy are consistent with the system passing near criticality of the random field Ising model as temperature is varied. The resulting large barriers to equilibrium may be the source of the unusually robust hysteresis phenomena associated with the metal-insulator transition in this system. PMID:26849604
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
Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2
Cho, Doohee; Cheon, Sangmo; Kim, Ki-Seok; Lee, Sung-Hoon; Cho, Yong-Heum; Cheong, Sang-Wook; Yeom, Han Woong
2016-01-01
The controllability over strongly correlated electronic states promises unique electronic devices. A recent example is an optically induced ultrafast switching device based on the transition between the correlated Mott insulating state and a metallic state of a transition metal dichalcogenide 1T-TaS2. However, the electronic switching has been challenging and the nature of the transition has been veiled. Here we demonstrate the nanoscale electronic manipulation of the Mott state of 1T-TaS2. The voltage pulse from a scanning tunnelling microscope switches the insulating phase locally into a metallic phase with irregularly textured domain walls in the charge density wave order inherent to this Mott state. The metallic state is revealed as a correlated phase, which is induced by the moderate reduction of electron correlation due to the charge density wave decoherence. PMID:26795073
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.
Nanoscale manipulation of the Mott insulating state coupled to charge order in 1T-TaS2
NASA Astrophysics Data System (ADS)
Cho, Doohee; Cheon, Sangmo; Kim, Ki-Seok; Lee, Sung-Hoon; Cho, Yong-Heum; Cheong, Sang-Wook; Yeom, Han Woong
2016-01-01
The controllability over strongly correlated electronic states promises unique electronic devices. A recent example is an optically induced ultrafast switching device based on the transition between the correlated Mott insulating state and a metallic state of a transition metal dichalcogenide 1T-TaS2. However, the electronic switching has been challenging and the nature of the transition has been veiled. Here we demonstrate the nanoscale electronic manipulation of the Mott state of 1T-TaS2. The voltage pulse from a scanning tunnelling microscope switches the insulating phase locally into a metallic phase with irregularly textured domain walls in the charge density wave order inherent to this Mott state. The metallic state is revealed as a correlated phase, which is induced by the moderate reduction of electron correlation due to the charge density wave decoherence.
Pressure-Induced Mott Transition Followed by a 24-K Superconducting Phase in BaFe2S3
NASA Astrophysics Data System (ADS)
Yamauchi, Touru; Hirata, Yasuyuki; Ueda, Yutaka; Ohgushi, Kenya
2015-12-01
We performed high-pressure study for a Mott insulator BaFe2S3 , by measuring dc resistivity and ac susceptibility up to 15 GPa. We found that the antiferromagnetic insulating state at the ambient pressure is transformed into a metallic state at the critical pressure, Pc=10 GPa , and the superconductivity with the optimum Tc=24 K emerges above Pc. Furthermore, we found that the metal-insulator transition (Mott transition) boundary terminates at a critical point around 10 GPa and 75 K. The obtained pressure-temperature (P -T ) phase diagram is similar to those of the organic and fullerene compounds; namely, BaFe2S3 is the first inorganic superconductor in the vicinity of bandwidth control type Mott transition.
NASA Technical Reports Server (NTRS)
Eby, P. B.; Morgan, S. H.; Parnell, T. A.
1978-01-01
Energy deposition due to secondary electrons is calculated as a function of distance from the axis of the track of a heavy ion. The calculation incorporates the empirical formulas of Kobetich and Katz (1968) for delta-ray energy dissipation. Both the Mott and Born-approximation expressions for the delta-ray energy distributions are used, and the results are compared. The energy deposition projected along a line perpendicular to the track is also calculated. These results are used to estimate the effect that the use of the Mott cross section would have in the interpretation of photometric measurements on emulsion tracks of trans-iron cosmic-ray particles. It is shown that the use of 50 keV as a characteristic track-formation electron energy to estimate the effect of the Mott cross section systematically overestimates charge as derived from emulsions for Z greater than 20.
Nozoe, Soichiro; Kinoshita, Nobuaki; Matsuda, Masaki
2016-04-01
By using the short-time electrocrystallization technique, phthalocyanine (Pc)-based Mott insulator Co(Pc)(CN)2 . 2CHCl3 nanocrystals were fabricated and applied to organic light-emiting diodes (OLEDs). The fabricated device having the configuration ITO/Co(Pc)(CN)2 . 2CHCl3/Alq3/Al, in which ITO is indium-tin oxide and Alq3 is tris(8-hydroxyquinolinato)aluminum, showed clear emission from Alq3, suggesting the Mott insulator Co(Pc)(CN)2 . 2CHCl3 can work as useful hole-injection and transport material in OLEDs. PMID:27451640
Hopping conduction in bismuth modified zinc vanadate glasses: An applicability of Mott's model
NASA Astrophysics Data System (ADS)
Punia, R.; Kundu, R. S.; Murugavel, S.; Kishore, N.
2012-12-01
The dc conductivity measured in a wide range of temperatures (room temperature to 533.16 K) for glass samples of compositions 50V2O5.xBi2O3.(50-x) ZnO; x = 0, 5, 10, 15, and 20, is discussed in this paper. The temperature dependent dc conductivity has been analyzed in the framework of various theoretical models, which describe the hopping conduction in disordered semiconducting systems. It has been observed that Mott's model of polaron hopping in transition metals is in good agreement with the experimental data in high as well as intermediate temperature regions. The various polaron hopping parameters have also been deduced. It has been ascertained by these estimated quantities and different approaches that the electrical conduction in present glass system is due to non-adiabatic variable range hopping of small polarons. Moreover, it has been found that Mott's and Greaves' variable range hopping models are in good agreement with the experimental data in the whole studied temperature range in the present investigation.
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.
Charge-ordering cascade with spin-orbit Mott dimer states in metallic iridium ditelluride.
Ko, K-T; Lee, H-H; Kim, D-H; Yang, J-J; Cheong, S-W; Eom, M J; Kim, J S; Gammag, R; Kim, K-S; Kim, H-S; Kim, T-H; Yeom, H-W; Koo, T-Y; Kim, H-D; Park, J-H
2015-01-01
Spin-orbit coupling results in technologically-crucial phenomena underlying magnetic devices like magnetic memories and energy-efficient motors. In heavy element materials, the strength of spin-orbit coupling becomes large to affect the overall electronic nature and induces novel states such as topological insulators and spin-orbit-integrated Mott states. Here we report an unprecedented charge-ordering cascade in IrTe2 without the loss of metallicity, which involves localized spin-orbit Mott states with diamagnetic Ir(4+)-Ir(4+) dimers. The cascade in cooling, uncompensated in heating, consists of first order-type consecutive transitions from a pure Ir(3+) phase to Ir(3+)-Ir(4+) charge-ordered phases, which originate from Ir 5d to Te 5p charge transfer involving anionic polymeric bond breaking. Considering that the system exhibits superconductivity with suppression of the charge order by doping, analogously to cuprates, these results provide a new electronic paradigm of localized charge-ordered states interacting with itinerant electrons through large spin-orbit coupling. PMID:26059464
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.
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. PMID:26601242
Orbital-selective Mott phase of Cu-substituted iron-based superconductors
NASA Astrophysics Data System (ADS)
Liu, Yang; Zhao, Yang-Yang; Song, Yun
2016-07-01
We study the phase transition in Cu-substituted iron-based superconductors with a new developed real-space Green’s function method. We find that Cu substitution has strong effect on the orbital-selective Mott transition introduced by the Hund’s rule coupling. The redistribution of the orbital occupancy which is caused by the increase of the Hund’s rule coupling, gives rise to the Mott–Hubbard metal-insulator transition in the half-filled d xy orbital. We also find that more and more electronic states appear inside that Mott gap of the d xy orbital with the increase of Cu substitution, and the in-gap states around the Fermi level are strongly localized at some specific lattice sites. Further, a distinctive phase diagram, obtained for the Cu-substituted Fe-based superconductors, displays an orbital-selective insulating phase, as a result of the cooperative effect of the Hund’s rule coupling and the impurity-induced disorder.
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
Quantum simulation of a topological Mott insulator with Rydberg atoms in a Lieb lattice
NASA Astrophysics Data System (ADS)
Dauphin, A.; Müller, M.; Martin-Delgado, M. A.
2016-04-01
We propose a realistic scheme to quantum simulate the so-far experimentally unobserved topological Mott insulator phase—an interaction-driven topological insulator—using cold atoms in an optical Lieb lattice. To this end, we study a system of spinless fermions in a Lieb lattice, exhibiting repulsive nearest- and next-to-nearest-neighbor interactions and derive the associated zero-temperature phase diagram within mean-field approximation. In particular, we analyze how the interactions can dynamically generate a charge density wave ordered, a nematic, and a topologically nontrivial quantum anomalous Hall phase. We characterize the topology of the different phases by the Chern number and discuss the possibility of phase coexistence. Based on the identified phases, we propose a realistic implementation of this model using cold Rydberg-dressed atoms in an optical lattice. The scheme, which allows one to access, in particular, the topological Mott insulator phase, robustly and independently of its exact position in parameter space, merely requires global, always-on off-resonant laser coupling to Rydberg states and is feasible with state-of-the-art experimental techniques that have already been demonstrated in the laboratory.
Mott insulating states and quantum phase transitions of correlated SU(2 N ) Dirac fermions
NASA Astrophysics Data System (ADS)
Zhou, Zhichao; Wang, Da; Meng, Zi Yang; Wang, Yu; Wu, Congjun
2016-06-01
The interplay between charge and spin degrees of freedom in strongly correlated fermionic systems, in particular of Dirac fermions, is a long-standing problem in condensed matter physics. We investigate the competing orders in the half-filled SU (2 N ) Hubbard model on a honeycomb lattice, which can be accurately realized in optical lattices with ultracold large-spin alkaline-earth fermions. Employing large-scale projector determinant quantum Monte Carlo simulations, we have explored quantum phase transitions from the gapless Dirac semimetals to the gapped Mott insulating phases in the SU(4) and SU(6) cases. Both of these Mott insulating states are found to be columnar valence bond solid (cVBS) and to be absent of the antiferromagnetic Néel ordering and the loop current ordering. Inside the cVBS phases, the dimer ordering is enhanced by increasing fermion components and behaves nonmonotonically as the interaction strength increases. Although the transitions generally should be of first order due to a cubic invariance possessed by the cVBS order, the coupling to gapless Dirac fermions can soften the transitions to second order through a nonanalytic term in the free energy. Our simulations provide important guidance for the experimental explorations of novel states of matter with ultracold alkaline-earth fermions.
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)
Bhunia, Amit; Bansal, Kanika; Datta, Shouvik; Alshammari, Marzook S.; Henini, Mohamed
In contrast to the widely reported optical techniques, there are hardly any investigations on corresponding electrical signatures of condensed matter physics of excitonic phenomena. We studied small signal steady state capacitance response in III-V materials based multi quantum well (AlGaInP) and MBE grown quantum dot (InGaAs) laser diodes to identify signatures of excitonic presence. Conductance activation by forward bias was probed using frequency dependent differential capacitance response (fdC/df), which changes characteristically with the onset of light emission indicating the occurrence of negative activation energy. Our analysis shows that it is connected with a steady state population of exciton like bound states. Calculated average energy of this bound state matches well with the binding energy of weakly confined excitons in this type of structures. Further increase in charge injection decreases the differential capacitive response in AlGaInP based diodes, indicating a gradual Mott transition of excitonic states into electron hole plasma. This electrical description of excitonic Mott transition is fully supplemented by standard optical spectroscopic signatures of band gap renormalization and phase space filling effects.
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
Nonequilibrium self-energy functional approach to the dynamical Mott transition
NASA Astrophysics Data System (ADS)
Hofmann, Felix; Eckstein, Martin; Potthoff, Michael
2016-06-01
The real-time dynamics of the Fermi-Hubbard model, driven out of equilibrium by quenching or ramping the interaction parameter, is studied within the framework of the nonequilibrium self-energy functional theory. A dynamical impurity approximation with a single auxiliary bath site is considered as a reference system, and the time-dependent hybridization is optimized as prescribed by the variational principle. The dynamical two-site approximation turns out to be useful to study the real-time dynamics on short and intermediate time scales. Depending on the strength of the interaction in the final state, two qualitatively different response regimes are observed. For both weak and strong couplings, qualitative agreement with previous results of nonequilibrium dynamical mean-field theory is found. The two regimes are sharply separated by a critical point at which the low-energy bath degree of freedom decouples in the course of time. We trace the dependence of the critical interaction of the dynamical Mott transition on the duration of the interaction ramp from sudden quenches to adiabatic dynamics and therewith link the dynamical to the equilibrium Mott transition.
NASA Astrophysics Data System (ADS)
Omori, Yukiko; Rüegg, Andreas; Sigrist, Manfred
2014-10-01
Metallic interfaces between insulating perovskites are often observed in heterostructures combining polar and nonpolar materials. In these systems, the polar discontinuity across the interface may drive an electronic reconstruction inducing free carriers at the interface. Here, we theoretically show that a metallic interface between a Mott and a band insulator can also form in the absence of a polar discontinuity. The condition for the appearance of such a metallic state is consistent with the classical Mott criterion: the metallic state is stable if the screening length falls below the effective Bohr radius of a particle-hole pair. In this case, the metallic state bears a remarkable similarity to the one found in polar/nonpolar heterostructures. On the other hand, if the screening length approaches the size of the effective Bohr radius, particles and holes are bound to each other resulting in an overall insulating phase. We analyze this metal-insulator transition, which is tunable by the dielectric constant, in the framework of the slave-boson mean-field theory for a lattice model with both on-site and long-range Coulomb interactions. We discuss ground-state properties and transport coefficients, which we derive in the relaxation-time approximation. Interestingly, we find that the metal-insulator transition is accompanied by a strong enhancement of the Seebeck coefficient in the band-insulator region in the vicinity of the interface. The implications of our theoretical findings for various experimental systems such as nonpolar (110) interfaces are also discussed.
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.
Topological Mott Insulator in Three-Dimensional Systems with Quadratic Band Touching
NASA Astrophysics Data System (ADS)
Herbut, Igor F.; Janssen, Lukas
2014-09-01
We argue that a three-dimensional electronic system with the Fermi level at the quadratic band touching point such as HgTe could be unstable with respect to the spontaneous formation of the (topological) Mott insulator at arbitrary weak long-range Coulomb interaction. The mechanism of the instability can be understood as the collision of Abrikosov's non-Fermi liquid fixed point with another, quantum critical, fixed point, which approaches it in the coupling space as the system's dimensionality d→dlow+, with the "lower critical dimension" 2
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
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).
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).
Bose-glass, superfluid, and rung-Mott phases of hard-core bosons in disordered two-leg ladders
NASA Astrophysics Data System (ADS)
Carrasquilla, Juan; Becca, Federico; Fabrizio, Michele
2011-06-01
By means of Monte Carlo techniques, we study the role of disorder on a system of hard-core bosons in a two-leg ladder with both intrachain (t) and interchain (t') hoppings. We find that the phase diagram as a function of the boson density, disorder strength, and t'/t is far from being trivial. This contrasts with the case of spinless fermions where standard localization arguments apply and an Anderson-localized phase pervades the whole phase diagram. A compressible Bose-glass phase always intrudes between the Mott insulator with zero (or one) bosons per site and the superfluid that is stabilized for weak disorder. At half-filling, there is a direct transition between a (gapped) rung-Mott insulator and a Bose glass, which is driven by exponentially rare regions where disorder is suppressed. Finally, by doping the rung-Mott insulator, a direct transition to the superfluid is possible only in the clean system, whereas the Mott phase is always surrounded by the a Bose glass when disorder is present. The phase diagram based on our numerical evidence is finally reported.
Jeff = 1/2 Mott spin-orbit insulating state close to the cubic limit in Ca4IrO6
NASA Astrophysics Data System (ADS)
Calder, S.; Cao, G.-X.; Okamoto, S.; Kim, J. W.; Cooper, V. R.; Gai, Z.; Sales, B. C.; Lumsden, M. D.; Mandrus, D.; Christianson, A. D.
2014-03-01
The Jeff = 1/2 Mott spin-orbit insulating state is manifested in systems with large cubic crystal field splitting and spin-orbit coupling that are comparable to the on-site Coulomb interaction, U. 5d transition metal oxides host parameters in this regime and recently strong evidence for this state in Sr2IrO4, and additional iridates, has been presented. All the candidates, however, have distorted octahedra, such as the elongation along the c-axis in Sr2IrO4, and consequently a non-cubic local crystal field environment. Consequently the materials form a mixed Jeff = 1/2,3/2 ground state. The lack of a material with an unmixed Jeff = 1/2 has impacted the development and testing of robust models of this novel insulating and magnetic state. We present neutron diffraction, resonant x-ray scattering and DFT calculations that not only reveal Ca4IrO6 is a new candidate Jeff = 1/2 material with long-range magnetic order, but furthermore resides close to the required cubic limit. Both our experimental and theoretical investigation indicate Ca4IrO6 is uniquely positioned to act as a canonical system to investigate of the Jeff = 1/2 state. This research was supported by the Scientific User Facilities Division and the Materials Sciences and Engineering Division, Office of Basic Energy Sciences, U.S. Department of Energy.