Showing papers on "Mott transition published in 2015"
TL;DR: This work demonstrates abrupt, reversible switching of resistance in 1T-TaS2 using dc and pulsed sources, corresponding to an insulator-metal transition between the insulating Mott and equilibrium metallic states, and suggests that the transition is facilitated by a carrier driven collapse of the Mott gap.
Abstract: In this work, we demonstrate abrupt, reversible switching of resistance in 1T-TaS2 using dc and pulsed sources, corresponding to an insulator–metal transition between the insulating Mott and equilibrium metallic states. This transition occurs at a constant critical resistivity of 7 mohm-cm regardless of temperature or bias conditions and the transition time is significantly smaller than abrupt transitions by avalanche breakdown in other small gap Mott insulating materials. Furthermore, this critical resistivity corresponds to a carrier density of 4.5 × 1019 cm–3, which compares well with the critical carrier density for the commensurate to nearly commensurate charge density wave transition. These results suggest that the transition is facilitated by a carrier driven collapse of the Mott gap in 1T-TaS2, which results in fast (3 ns) switching.
146 citations
TL;DR: In this paper, the Mott transition in three different organic insulators with triangular lattices was investigated and evidence of quantum criticality in an intermediate temperature regime was uncovered, and it was shown that triangular lattice lattices are quantum critical.
Abstract: The Mott transition is investigated in three different organic insulators with triangular lattices and evidence of quantum criticality in an intermediate temperature regime is uncovered.
119 citations
TL;DR: In this paper, a quantum impurity model with dynamical interactions in the charge and spin channels was proposed for strongly correlated electron systems which consists in a local approximation of the dynamical three-leg interaction vertex.
Abstract: We present a formalism for strongly correlated electron systems which consists in a local approximation of the dynamical three-leg interaction vertex. This vertex is self-consistently computed using a quantum impurity model with dynamical interactions in the charge and spin channels, similar to dynamical mean field theory approaches. The electronic self-energy and the polarization are both frequency and momentum dependent. The method interpolates between the spin-fluctuation or GW approximations at weak coupling and the atomic limit at strong coupling. We apply the formalism to the Hubbard model on a two-dimensional square lattice and show that as interactions are increased towards the Mott insulating state, the local vertex acquires a strong frequency dependence, driving the system to a Mott transition, while at low enough temperatures the momentum dependence of the self-energy is enhanced due to large spin fluctuations. Upon doping, we find a Fermi arc in the one-particle spectral function, which is one signature of the pseudogap state.
109 citations
TL;DR: The results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high Tc s-wave superconductivity.
Abstract: 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.
83 citations
TL;DR: BaFe_{2}S_{3} is the first inorganic superconductor in the vicinity of bandwidth control type Mott transition, and the obtained pressure-temperature (P-T) phase diagram is similar to those of the organic and fullerene compounds.
Abstract: We performed high-pressure study for a Mott insulator BaFe_{2}S_{3}, 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, P_{c}=10 GPa, and the superconductivity with the optimum T_{c}=24 K emerges above P_{c}. 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, BaFe_{2}S_{3} is the first inorganic superconductor in the vicinity of bandwidth control type Mott transition.
79 citations
TL;DR: It is shown that for the doped Mott insulator regime, the coexistence dome and the associated first-order Mott metal-insulator transition are confined to extremely low temperatures, while clear signatures of Mott quantum criticality emerge across much of the phase diagram.
Abstract: Bad-metal (BM) behavior featuring linear temperature dependence of the resistivity extending to well above the Mott-Ioffe-Regel (MIR) limit is often viewed as one of the key unresolved signatures of strong correlation. Here we associate the BM behavior with the Mott quantum criticality by examining a fully frustrated Hubbard model where all long-range magnetic orders are suppressed, and the Mott problem can be rigorously solved through dynamical mean-field theory. We show that for the doped Mott insulator regime, the coexistence dome and the associated first-order Mott metal-insulator transition are confined to extremely low temperatures, while clear signatures of Mott quantum criticality emerge across much of the phase diagram. Remarkable scaling behavior is identified for the entire family of resistivity curves, with a quantum critical region covering the entire BM regime, providing not only insight, but also quantitative understanding around the MIR limit, in agreement with the available experiments.
67 citations
01 Jan 2015
TL;DR: In this paper, the authors describe the first-principles band calculation for many-body computations in a t-J-like model with localized moments and the orbital-selective Mott transition.
Abstract: Part I Materials: Synthesis, structural properties, and phase diagrams- Bulk- Film- Part II Experiments: Characterization of Electronic and Magnetic Properties- Electron spectroscopy - ARPES- Magnetic order and dynamics - neutron scattering- Scanning Tunneling Spectroscopy- X-ray scattering and diffraction- Optics and transport- Other techniques- Properties under extreme conditions- Part III Theories- First-principles band calculation- Many-body computation- Itinerant electron model- t-J-like model with localized moments- Coexisting itinerant and localized electrons- Orbital-selective Mott transition
58 citations
TL;DR: The pressure study of a doped organic superconductor with a Hall coefficient and conductivity measurements finds that maximally enhanced superconductivity and a marginal-Fermi liquid appear around a certain pressure, suggesting a possible quantum phase transition between strongly and weakly correlated regimes.
Abstract: 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.
58 citations
TL;DR: In this article, the effect of dynamical screening in photoexcited Mott insulators was investigated using a nonequilibrium implementation of extended dynamical mean field theory in combination with a noncrossing approximation impurity solver.
Abstract: We use a nonequilibrium implementation of extended dynamical mean-field theory in combination with a noncrossing approximation impurity solver to study the effect of dynamical screening in photoexcited Mott insulators. The insertion of doublons and holes adds low-energy screening modes and leads to a reduction of the Mott gap. The coupling to low-energy bosonic modes furthermore opens new relaxation channels and significantly speeds up the thermalization process. We also investigate the effect of the energy distribution of the photo doped carriers on the screening.
40 citations
TL;DR: In this paper, the Bose-Hubbard model on a two-leg ladder under an artificial magnetic field was considered and the superfluid-to-Mott insulator transition in this setting was investigated.
Abstract: We consider the Bose-Hubbard model on a two-leg ladder under an artificial magnetic field and investigate the superfluid--to--Mott insulator transition in this setting. Recently, this system has been experimentally realized [M. Atala et al., Nature Phys. 10, 588 (2014)], albeit in a parameter regime that is far from the Mott transition boundary. Depending on the strength of the magnetic field, the single-particle spectrum has either a single ground state or two degenerate ground states. The transition between these two phases is reflected in the many-particle properties. We first investigate these phases through the Bogoliubov approximation in the superfluid regime and calculate the transition boundary for weak interactions. For stronger interactions the system is expected to form a Mott insulator. We calculate the Mott transition boundary as a function of the magnetic field and interleg coupling with mean-field theory, strong-coupling expansion, and density matrix renormalization group (DMRG). Finally, using the DMRG, we investigate the particle-hole excitation gaps of this system at different filling factors and find peaks at simple fractions, indicating the possibility of correlated phases.
36 citations
TL;DR: In this article, a half-filled extended Hubbard model on a triangular lattice strip geometry was studied and it was shown that the model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi surface.
Abstract: More than half a century after first being proposed by Sir Nevill Mott, the deceptively simple question of whether the interaction-driven electronic metal-insulator transition may be continuous remains enigmatic. Recent experiments on two-dimensional materials suggest that when the insulator is a quantum spin liquid, lack of magnetic long-range order on the insulating side may cause the transition to be continuous, or only very weakly first order. Motivated by this, we study a half-filled extended Hubbard model on a triangular lattice strip geometry. We argue, through use of large-scale numerical simulations and analytical bosonization, that this model harbors a continuous (Kosterlitz-Thouless-like) quantum phase transition between a metal and a gapless spin liquid characterized by a spinon Fermi surface, i.e., a “spinon metal.” These results may provide a rare insight into the development of Mott criticality in strongly interacting two-dimensional materials and represent one of the first numerical demonstrations of a Mott insulating quantum spin liquid phase in a genuinely electronic microscopic model.
TL;DR: In this paper, the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics are described.
Abstract: Electrical switching, manifesting itself in the nonlinear current-voltage characteristics with S- and N-type NDR (negative differential resistance), is inherent in a variety of materials, in particular, transition metal oxides Although this phenomenon has been known for a long time, recent suggestions to use oxide-based switching elements as neuristor synapses and relaxation-oscillation circuit components have resumed the interest in this area In the present review, we describe the experimental facts and theoretical models, mainly on the basis of the Mott transition in vanadium dioxide as a model object, of the switching effect with special emphasis on the emerging applied potentialities for oxide electronics
TL;DR: In this article, electron correlations in the half-filled Hubbard model on a two-dimensional Penrose lattice were investigated. And the existence of the Mott transition was clarified by calculating double occupancy and renormalization factor at each site.
Abstract: We study electron correlations in the half-filled Hubbard model on a two-dimensional Penrose lattice. Applying real-space dynamical mean-field theory to large clusters, we discuss how low-temperature properties are affected by a quasiperiodic structure. By calculating the double occupancy and renormalization factor at each site, we clarify the existence of the Mott transition. The spatially dependent renormalization characteristic of a geometrical structure is also addressed.
TL;DR: In this paper, the authors proposed a method to produce a low temperature gas by preparing it in a disordered potential and following a constant entropy trajectory to deliver the gas into a nondisordered state which exhibits these incompletely understood phases.
Abstract: Cold atomic gases have proven capable of emulating a number of fundamental condensed matter phenomena including Bose-Einstein condensation, the Mott transition, Fulde-Ferrell-Larkin-Ovchinnikov pairing, and the quantum Hall effect. Cooling to a low enough temperature to explore magnetism and exotic superconductivity in lattices of fermionic atoms remains a challenge. We propose a method to produce a low temperature gas by preparing it in a disordered potential and following a constant entropy trajectory to deliver the gas into a nondisordered state which exhibits these incompletely understood phases. We show, using quantum Monte Carlo simulations, that we can approach the Neel temperature of the three-dimensional Hubbard model for experimentally achievable parameters. Recent experimental estimates suggest the randomness required lies in a regime where atom transport and equilibration are still robust.
TL;DR: In this paper, the authors used spatially averaged infrared and visible radiations followed by spectroscopy and nanoscale imaging using x-rays to probe the same VO2 sample while controlling the ambient temperature across its hysteretic phase transitions and monitoring its electrical resistance.
Abstract: Vanadium dioxide (VO2) is a model system that has been used to understand closely-occurring multiband electronic (Mott) and structural (Peierls) transitions for over half a century due to continued scientific and technological interests. Among the many techniques used to study VO2, the most frequently used involve electromagnetic radiation as a probe. Understanding of the distinct physical information provided by different probing radiations is incomplete, mostly owing to the complicated nature of the phase transitions. Here we use transmission of spatially averaged infrared ({\lambda}=1500 nm) and visible ({\lambda}=500 nm) radiations followed by spectroscopy and nanoscale imaging using x-rays ({\lambda}=2.25-2.38 nm) to probe the same VO2 sample while controlling the ambient temperature across its hysteretic phase transitions and monitoring its electrical resistance. We directly observed nanoscale puddles of distinct electronic and structural compositions during the transition. The two main results are that, during both heating and cooling, the transition of infrared and visible transmission occur at significantly lower temperatures than the Mott transition; and the electronic (Mott) transition occurs before the structural (Peierls) transition in temperature. We use our data to provide insights into possible microphysical origins of the different transition characteristics. We highlight that it is important to understand these effects because small changes in the nature of the probe can yield quantitatively, and even qualitatively, different results when applied to a non-trivial multiband phase transition. Our results guide more judicious use of probe type and interpretation of the resulting data.
TL;DR: In this article, the authors clarified the orbital mechanism of the $sdf$ Wannier orbital basis to describe the electronic structure of cerium and used this basis to study the relative role of several orbital hoppings.
Abstract: We clarify the orbital mechanism of the $\ensuremath{\alpha}\text{\ensuremath{-}}\ensuremath{\gamma}$ transition in cerium. First we built an $sdf$ Wannier orbital basis to describe the electronic structure of cerium. Second, we use this basis to study the relative role of several orbital hoppings upon compression of cerium. Third, we use DFT + DMFT calculations to quantify the impact of these hoppings on electronic structure. Our conclusion is that upon compression of $\ensuremath{\gamma}$ cerium, the change of hybridization is due to both interatomic $ff$ and $fd$ hopping integrals. In particular, neglecting $ff$ hoppings leads to an important renormalization of both the hybridization and the quasiparticle peak. Thus, neither the Kondo volume collapse nor the Mott transition model are sufficient to describe the isostructural transition in cerium.
TL;DR: The present study reveals that a staged electron-correlation-driven Mott transition and structure-driven Peierls transition are involved in MIT of VO2.
Abstract: Unraveling the metal–insulator transition (MIT) mechanism of VO2 becomes tremendously important for understanding strongly correlated character and developing switching applications of VO2. First-principles calculations were employed in this work to map the reduced-dimension potential energy surface of the MIT of VO2. In the beginning stage of MIT, a significant orbital switching between σ-type dz2 and π-type dx2–y2/dyz accompanied by a large V–V dimerization and a slight twisting angle change opens a band gap of ∼0.2 eV, which can be attributed to the electron-correlation-driven Mott transition. After that, the twisting angle of one chain quickly increases, which is accompanied by the appearance of a larger change in band gap from 0.2 to 0.8 eV, even though orbital occupancy is maintained. This finding can be ascribed to the structure-driven Peierls transition. The present study reveals that a staged electron-correlation-driven Mott transition and structure-driven Peierls transition are involved in MIT o...
TL;DR: The full phase diagram of the extended Hubbard model of hard-core bosons on the pyrochlore lattice with partial fillings is revealed and it is demonstrated 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.
Abstract: 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.
TL;DR: In this article, the authors study the non-equilibrium 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.
Abstract: We study the non-equilibrium 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 sub-bands; (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 non-equilibrium 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 non-thermal 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.
TL;DR: It is demonstrated that THz lasing threshold in realistic structures cannot be achieved without a THz cavity, due to destruction of polaritons via excitonic Mott transition.
Abstract: The influence of the surrounding cavity on the efficiency of different types of polaritonic emitters of THz radiation has been analysed. It is demonstrated that THz lasing threshold in realistic structures cannot be achieved without a THz cavity, due to destruction of polaritons via excitonic Mott transition. Even modest values of cavity quality factor (not exceeding 50) provide significant quantum efficiency.
TL;DR: A pressure-induced isostructural Mott transition in cubic perovskite PbCrO3 is reported, which validate the scenario conceived by Mott and is fundamentally and technologically important for the study of correlated systems.
Abstract: 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.
TL;DR: It is demonstrated how the static electron-electron structure factor in warm dense matter can be obtained from density functional theory in combination with quantum Monte Carlo data.
Abstract: It is demonstrated how the static electron-electron structure factor in warm dense matter can be obtained from density functional theory in combination with quantum Monte Carlo data. In contrast to theories assuming well-separated bound and free states, this ab initio approach yields also valid results for systems close to the Mott transition (pressure ionization), where bound states are strongly modified and merge with the continuum. The approach is applied to x-ray Thomson scattering and compared to predictions of the Chihara formula whereby we use the ion-ion and electron-ion structure from the same simulations. The results show significant deviations of the screening cloud from the often applied Debye-like form.
TL;DR: In this paper, the single-particle spectral properties of the two-dimensional $t\text{\ensuremath{-}}J$ model in the parameter regime relevant to cuprate high-temperature superconductors are investigated using cluster perturbation theory.
Abstract: The single-particle spectral properties of the two-dimensional $t\text{\ensuremath{-}}J$ model in the parameter regime relevant to cuprate high-temperature superconductors are investigated using cluster perturbation theory. Various anomalous features observed in cuprate high-temperature superconductors are collectively explained in terms of the dominant modes near the Mott transition in this model. Although the behavior of the dominant modes in the low-energy regime is similar to that in the two-dimensional Hubbard model, significant differences appear near the Mott transition for the high-energy electron removal excitations which can be considered to primarily originate from holon modes in one dimension. The overall spectral features are confirmed to remain almost unchanged as the cluster size is increased from $4\ifmmode\times\else\texttimes\fi{}4$ to $6\ifmmode\times\else\texttimes\fi{}6$ sites by using a combined method of the non-Abelian dynamical density-matrix renormalization group method and cluster perturbation theory.
TL;DR: In this article, the authors reviewed the properties of elastic phase transitions of crystals and phase transitions whose order parameter couples linearly to elastic degrees of freedom with particular focus on instabilities at zero temperature.
Abstract: Elastic phase transitions of crystals and phase transitions whose order parameter couples linearly to elastic degrees of freedom are reviewed with particular focus on instabilities at zero temperature. A characteristic feature of these transitions is the suppression of critical fluctuations by long-range shear forces. As a consequence, at an elastic crystal symmetry-breaking quantum phase transition the phonon velocity vanishes only along certain crystallographic directions giving rise to critical phonon thermodynamics described by a stable Gaussian fixed point. At an isostructural solid-solid quantum critical end point, on the other hand, the complete suppression of critical fluctuations results in true mean-field critical behavior without a diverging correlation length. Whenever an order parameter couples bilinearly to the strain tensor, the critical properties are eventually governed by critical crystal elasticity. This is, for example, the case for quantum critical metamagnetism but also for the classical critical Mott end point at finite T. We discuss and compare the solid-solid end points expected close to the Mott transition in V2O3 and κ-(BEDT-TTF)2
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TL;DR: The microscopic mechanism of the metal-insulator transition is studied by orbital-resolved ^{51}V NMR spectroscopy in a prototype of the quasi-one-dimensional system V6O13, uncovering that the transition involves a site-selective d orbital order lifting twofold orbital degeneracy in one of the two VO6 chains.
Abstract: The microscopic mechanism of the metal-insulator transition is studied by orbital-resolved $^{51}\mathrm{V}$ NMR spectroscopy in a prototype of the quasi-one-dimensional system ${\mathrm{V}}_{6}{\mathrm{O}}_{13}$. We uncover that the transition involves a site-selective $d$ orbital order lifting twofold orbital degeneracy in one of the two ${\mathrm{VO}}_{6}$ chains. The other chain leaves paramagnetic moments on the singly occupied ${d}_{xy}$ orbital across the transition. The two chains respectively stabilize an orbital-assisted spin-Peierls state and an antiferromagnetic long-range order in the ground state. The site-selective Mott transition may be a source of the anomalous metal and the Mott-Peierls duality.
TL;DR: In this article, it was shown that the insulating properties of the iron selenide can be explained in terms of Mott localization in sharp contrast with the metallic behavior of FeSe and other parent compounds of iron superconductors.
Abstract: We show that the insulating character of the iron selenide $\mathrm{La}{}_{2}\mathrm{O}{}_{3}\mathrm{Fe}{}_{2}\mathrm{Se}{}_{2}$ can be explained in terms of Mott localization in sharp contrast with the metallic behavior of FeSe and other parent compounds of iron superconductors. We demonstrate that the key ingredient that makes $\mathrm{La}{}_{2}\mathrm{O}{}_{3}\mathrm{Fe}{}_{2}\mathrm{Se}{}_{2}$ a Mott insulator, rather than a correlated metal dominated by the Hund's coupling, is the enhanced crystal-field splitting, accompanied by a smaller orbital-resolved kinetic energy. The strong deviation from orbital degeneracy introduced by the crystal-field splitting also pushes this material close to an orbital-selective Mott transition. We predict that either doping or uniaxial external pressure can drive the material into an orbital-selective Mott state, where only one or a few orbitals are metallized while the others remain insulating.
TL;DR: In this article, a self-consistent equation for the electron Green γs function was derived for the repulsive Hubbard model, where terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation.
Abstract: Using the strong coupling diagram technique a self-consistent equation for the electron Green׳s function is derived for the repulsive Hubbard model. Terms of two lowest orders of the ratio of the bandwidth Δ to the Hubbard repulsion U are taken into account in the irreducible part of the Larkin equation. The obtained equation is shown to retain causality and reduces to Green׳s function of uncorrelated electrons in the limit U → 0 . Calculations were performed for the semi-elliptical initial band. It is shown that the approximation describes the Mott transition, which occurs at U c = 3 Δ / 2 . This value coincides with that obtained in the Hubbard-III approximation. At half-filling, for 0 U U c the imaginary part of the self-energy is nonzero at the Fermi level, which indicates that the obtained solution is not a Fermi liquid. At small deviations from half-filling the density of states shifts along the frequency axis without perceptible changes in its shape. For larger deviations the density of states is modified: it is redistributed in favor of the subband, in which the Fermi level is located, and for U > U c the Mott gap disappears.
TL;DR: This work uses the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and shows the competing effects of interaction, frustration and temperature on the Shastry-Sutherland lattice.
Abstract: The Shastry-Sutherland lattice, one of the simplest systems with geometrical frustration, which has an exact eigenstate by putting singlets on diagonal bonds, can be realized in a group of layered compounds and raises both theoretical and experimental interest. Most of the previous studies on the Shastry-Sutherland lattice are focusing on the Heisenberg model. Here we opt for the Hubbard model to calculate phase diagrams over a wide range of interaction parameters, and show the competing effects of interaction, frustration and temperature. At low temperature, frustration is shown to favor a paramagnetic metallic ground state, while interaction drives the system to an antiferromagnetic insulator phase. Between these two phases, there are an antiferromagnetic metal phase and a paramagnetic insulator phase (which should consist of a small plaquette phase and a dimer phase) resulting from the competition of the frustration and the interaction. Our results may shed light on more exhaustive studies about quantum phase transitions in geometrically frustrated systems.
TL;DR: The spin-fermion model can be mapped exactly with no additional constraint onto a model of free fermions coupled in a $Z_2$ gauge-invariant manner to auxiliary Ising spins in a transverse field as mentioned in this paper.
Abstract: The infinite dimensional half-filled Hubbard model can be mapped exactly with no additional constraint onto a model of free fermions coupled in a $Z_2$ gauge-invariant manner to auxiliary Ising spins in a transverse field. In this slave-spin representation, the zero-temperature insulator-to-metal transition translates into spontaneous breaking of the local $Z_2$ gauge symmetry, which is not forbidden in infinite dimensions, thus endowing the Mott transition of an order parameter that is otherwise elusive in the original fermion representation. We demonstrate this interesting scenario by exactly solving the effective spin-fermion model by dynamical mean-field theory both at zero and at finite temperature.
TL;DR: It is shown that the critical exponents of the Mott-Hubbard transition fall within the Ising universality class regardless of the dimensionality of the system.
Abstract: 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.