Showing papers on "Mott insulator published in 2023"
TL;DR: In this article , the authors demonstrate a quantum simulation of superfluid to Mott insulator transition in twisted-bilayer square lattices based on atomic Bose-Einstein condensates loaded into spin-dependent optical lattices.
Abstract: Observation of strong correlations and superconductivity in twisted-bilayer graphene1-4 has stimulated tremendous interest in fundamental and applied physics5-8. In this system, the superposition of two twisted honeycomb lattices, generating a moiré pattern, is the key to the observed flat electronic bands, slow electron velocity and large density of states9-12. Extension of the twisted-bilayer system to new configurations is highly desired, which can provide exciting prospects to investigate twistronics beyond bilayer graphene. Here we demonstrate a quantum simulation of superfluid to Mott insulator transition in twisted-bilayer square lattices based on atomic Bose-Einstein condensates loaded into spin-dependent optical lattices. The lattices are made of two sets of laser beams that independently address atoms in different spin states, which form the synthetic dimension accommodating the two layers. The interlayer coupling is highly controllable by a microwave field, which enables the occurrence of a lowest flat band and new correlated phases in the strong coupling limit. We directly observe the spatial moiré pattern and the momentum diffraction, which confirm the presence of two forms of superfluid and a modified superfluid to insulator transition in twisted-bilayer lattices. Our scheme is generic and can be applied to different lattice geometries and for both boson and fermion systems. This opens up a new direction for exploring moiré physics in ultracold atoms with highly controllable optical lattices.
5 citations
TL;DR: In this paper , a model for the spontaneous time-reversal symmetry (TRS) breaking in the charge density wave (CDW) ordered state has been proposed for vanadium-based nonmagnetic kagom-e metals.
Abstract: Recent experiments on vanadium-based nonmagnetic kagom\'e metals $A{\mathrm{V}}_{3}{\mathrm{Sb}}_{5}\phantom{\rule{4pt}{0ex}}(A=\mathrm{K},\mathrm{Rb},\mathrm{Cs})$ revealed evidence for possible spontaneous time-reversal symmetry (TRS) breaking in the charge density wave (CDW) ordered state. The long-sought-after quantum order of loop currents has been suggested as a candidate for the TRS breaking state. However, a microscopic model for the emergence of the loop-current CDW due to electronic correlations is still lacking. Here, we calculate the susceptibility of the real and imaginary bond orders on the kagom\'e lattice near van Hove filling, and reveal the importance of next-nearest-neighbor Coulomb repulsion ${V}_{2}$ in triggering the instability toward imaginary bond ordered CDW. The concrete effective single-orbital $t\text{\ensuremath{-}}{V}_{1}\text{\ensuremath{-}}{V}_{2}$ model on the kagom\'e lattice is then studied, where $t$ and ${V}_{1}$ are the hopping and Coulomb repulsion on the nearest-neighbor bonds. We obtain the mean-field ground states, analyze their properties, and determine the phase diagram in the plane spanned by ${V}_{1}$ and ${V}_{2}$ at van Hove filling. The region dominated by ${V}_{1}$ is occupied by a $2{a}_{0}\ifmmode\times\else\texttimes\fi{}2{a}_{0}$ real CDW insulator with the inverse of Star-of-David (ISD) bond configuration. Increasing ${V}_{2}$ indeed drives a first-order transition from ISD to stabilized loop-current insulators that exhibit four possible current patterns of different topological properties, leading to orbital Chern insulators. We then extend these results away from van Hove filling and show that electron doping helps the stabilization of loop currents, and gives rise to doped orbital Chern insulators with emergent Chern Fermi pockets carrying large Berry curvature and orbital magnetic moment. Our findings provide a concrete model realization of the loop-current Chern metal at the mean-field level for the TRS breaking normal state of the kagom\'e superconductors.
3 citations
TL;DR: In this paper , an atomic-scale epitaxy and photo-emission spectroscopy platform was used to realize the interface control of correlated electronic phases in atomicscale ruthenate-titanate heterostructures.
Abstract: Interfaces between dissimilar correlated oxides can offer devices with versatile functionalities, and great efforts have been made to manipulate interfacial electronic phases. However, realizing such phases is often hampered by the inability to directly access the electronic structure information; most correlated interfacial phenomena appear within a few atomic layers from the interface. Here, atomic‐scale epitaxy and photoemission spectroscopy are utilized to realize the interface control of correlated electronic phases in atomic‐scale ruthenate–titanate heterostructures. While bulk SrRuO3 is a ferromagnetic metal, the heterointerfaces exclusively generate three distinct correlated phases in the single‐atomic‐layer limit. The theoretical analysis reveals that atomic‐scale structural proximity effects yield Fermi liquid, Hund metal, and Mott insulator phases in the quantum‐confined SrRuO3. These results highlight the extensive interfacial tunability of electronic phases, hitherto hidden in the atomically thin correlated heterostructure. Moreover, this experimental platform suggests a way to control interfacial electronic phases of various correlated materials.
2 citations
TL;DR: In this article , the physics of a mobile impurity confined in a lattice, moving within a Bose-Hubbard bath at zero temperature, is studied. But the authors focus on the quantum phase transition between the superfluid and Mott insulating phases.
Abstract: We study the physics of a mobile impurity confined in a lattice, moving within a Bose-Hubbard bath at zero temperature. Within the Quantum Gutzwiller formalism, we develop a beyond-Fr\"ohlich model of the bath-impurity interaction. Results for the properties of the polaronic quasiparticle formed from the dressing of the impurity by quantum fluctuations of the bath are presented throughout the entire phase diagram, focusing on the quantum phase transition between the superfluid and Mott insulating phases. Here we find that the modification of the impurity properties is highly sensitive to the different universality classes of the transition, providing an unambiguous probe of correlations and collective modes in a quantum critical many-body environment.
2 citations
TL;DR: In this paper , it was shown that for sufficiently large interaction strengths, the quarter-filled Haldane model is a ferromagnetic topological Mott insulator with a Chern number of unity.
Abstract: While the recent advances in topology have led to a classification scheme for electronic bands described by the standard theory of metals, a similar scheme has not emerged for strongly correlated systems such as Mott insulators in which a partially filled band carries no current. By including interactions in the topologically non-trivial Haldane model, we show that a quarter-filled state emerges with a non-zero Chern number provided the interactions are sufficiently large. We first motivate this result on physical grounds and then by two methods: analytically by solving exactly a model in which interactions are local in momentum space and then numerically through the corresponding Hubbard model. All methods yield the same result: For sufficiently large interaction strengths, the quarter-filled Haldane model is a ferromagnetic topological Mott insulator with a Chern number of unity. Possible experimental realizations in cold-atom and solid state systems are discussed.
2 citations
TL;DR: In this article , an applied electric field spatially reconstructs the insulating phase that, uniquely after switching off the electric field, exhibits nanoscale stripe domains, which can be observed through high-resolution scanning transmission electron microscopy.
Abstract: The control of the Mott phase is intertwined with the spatial reorganization of the electronic states. Out-of-equilibrium driving forces typically lead to electronic patterns that are absent at equilibrium, whose nature is however often elusive. Here, we unveil a nanoscale pattern formation in the Ca2RuO4 Mott insulator. We demonstrate how an applied electric field spatially reconstructs the insulating phase that, uniquely after switching off the electric field, exhibits nanoscale stripe domains. The stripe pattern has regions with inequivalent octahedral distortions that we directly observe through high-resolution scanning transmission electron microscopy. The nanotexture depends on the orientation of the electric field; it is nonvolatile and rewritable. We theoretically simulate the charge and orbital reconstruction induced by a quench dynamics of the applied electric field providing clear-cut mechanisms for the stripe phase formation. Our results open the path for the design of nonvolatile electronics based on voltage-controlled nanometric phases.
2 citations
TL;DR: In this article , the effects of magnetic order on the Mott-Hubbard excitons were investigated in both iridates and ultracold atoms, and it was shown that the binding energy of a Mott exciton increases with increasing the Neelyel order parameter, whereas the exciton mass decreases.
Abstract: Motivated by recent experiments on Mott insulators, in both iridates and ultracold atoms, we theoretically study the effects of magnetic order on the Mott-Hubbard excitons. In particular, we focus on spin-mediated doublon-holon pairing in Hubbard materials. We use several complementary theoretical techniques: Mean-field theory to describe the spin degrees of freedom, the self-consistent Born approximation to characterize individual charge excitations across the Hubbard gap, and the Bethe-Salpeter equation to identify bound states of doublons and holons. The binding energy of the Mott exciton is found to increase with increasing the N\'eel order parameter, whereas the exciton mass decreases. We observe that these trends rely significantly on the retardation of the effective interaction, and require consideration of multiple effects from changing the magnetic order. Our results are consistent with the key qualitative trends observed in recent experiments on iridates. Moreover, the findings could have direct implications on ultracold atom Mott insulators where the Hubbard model is the exact description of the system and the microscopic degrees of freedom can be directly accessed.
2 citations
TL;DR: In this article , an increase in the electronic heat capacity at the transition from a nonmagnetic Mott insulating (NMI) state to a Fermi liquid (FL) state was studied using calorimetric measurements.
Abstract: The organic system $\ensuremath{\kappa}\text{\ensuremath{-}}{[{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{1\ensuremath{-}x}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{STF})}_{x}]}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$, showing a Mott transition between a nonmagnetic Mott insulating (NMI) state and a Fermi liquid (FL), is systematically studied using calorimetric measurements. An increase in the electronic heat capacity at the transition from the NMI state to the FL state which keeps the triangular dimer lattice demonstrates that the charge sector lost in the Mott insulating state is recovered in the FL state. We observed that the remaining low-energy spin excitations in the Mott insulating state show a unique temperature dependence and that the NMI state has a larger lattice entropy originating from the frustrated lattice, which leads to a Pomeranchuk-like effect on the electron localization. Near the Mott boundary, an unexpected enhancement and magnetic field dependence of the heat capacity are observed. This anomalous heat capacity is different from the behavior in a typical first-order Mott transition and shows similarities with quantum critical behavior. To reconcile our results with previously reported scenarios about a spin gap and the first-order Mott transition, further studies are desired.
2 citations
TL;DR: In this article , it was shown that the Mott transition evolves into a first-order transition between two metals, associated to a phase separation region ending in a quantum critical point (QCP) at finite doping.
Abstract: Strongly correlated materials often undergo a Mott metal-insulator transition, which is tipically first-order, as a function of control parameters like pressure. Upon doping, rich phase diagrams with competing instabilities are found. Yet, the conceptual link between the interaction-driven Mott transition and the finite-doping behavior lacks a clear connection with the theory of critical phenomena. In a prototypical case of a first-order Mott transition the surface associated with the equation of state for the homogeneous system is "folded" so that in a range of parameters stable metallic and insulating phases exist and are connected by an unstable metallic branch. Here we show that tuning the chemical potential the zero-temperature equation of state gradually unfolds. Under general conditions, we find that the Mott transition evolves into a first-order transition between two metals, associated to a phase separation region ending in a quantum critical point (QCP) at finite doping. This scenario is here demonstrated solving a simple multi-orbital Hubbard model relevant for the Iron-based superconductors, but its origin - the splitting of the atomic ground state multiplet by a small energy scale, here Hund's coupling - is much more general. A strong analogy with cuprate superconductors is traced.
2 citations
TL;DR: In this paper , a perturbative theory for liquid formation in strongly correlated lattice systems is proposed based on an interplay between long-range attraction and superexchange processes.
Abstract: We propose a mechanism for liquid formation in strongly correlated lattice systems. The mechanism is based on an interplay between long-range attraction and superexchange processes. As an example, we study dipolar bosons in one-dimensional optical lattices. We present a perturbative theory and validate it in comparison with full density-matrix renormalization group simulations for the energetic and structural properties of different phases of the system, i.e., self-bound Mott insulator, liquid, and gas. We analyze the nonequilibrium properties and calculate the dynamic structure factor. Its structure differs in compressible and insulating phases. In particular, the low-energy excitations in compressible phases are linear phonons. We extract the speed of sound and analyze its dependence on dipolar interaction and density. We show that it exhibits a nontrivial behaviour owing to the breaking of Galilean invariance. We argue that an experimental detection of this previously unknown quantum liquid could provide a fingerprint of the superexchange process and open intriguing possibilities for investigating non-Galilean invariant liquids.
1 citations
TL;DR: In this paper , the authors used organic $\kappa$-type salts as quasi-two-dimensional bandwidth-controlled Mott insulators and gained direct access to their charge carrier properties via magnetic quantum oscillations.
Abstract: The physics of the Mott metal-insulator transition (MIT) has attracted huge interest in the last decades. However, despite broad efforts, some key theoretical predictions are still lacking experimental confirmation. In particular, it is not clear whether the large coherent Fermi surface survives in immediate proximity to the bandwidth-controlled first-order MIT. A quantitative experimental verification of the predicted behavior of the quasiparticle effective mass, renormalized by many-body interactions, is also missing. Here we address these issues by employing organic $\kappa$-type salts as exemplary quasi-two-dimensional bandwidth-controlled Mott insulators and gaining direct access to their charge carrier properties via magnetic quantum oscillations. We trace the evolution of the effective cyclotron mass as the conduction bandwidth is tuned very close to the MIT by means of precisely controlled external pressure. We find that the sensitivity of the mass renormalization to tiny changes of the bandwidth is significantly stronger than theoretically predicted and is even further enhanced upon entering the transition region where the metallic and insulating phases coexist. On the other hand, even at its very edge of stability the metallic ground state preserves a large coherent Fermi surface with no significant enhancement of scattering.
TL;DR: In this paper , the authors present a numerical method for constructing the Hubbard Hamiltonian of non-periodic potentials without making use of Bloch's theorem and apply it to the case of an eightfold rotationally symmetric 2D optical quasicrystal that was recently realized using cold atoms.
Abstract: Quasicrystals are long-range ordered, yet not periodic, and thereby present a fascinating challenge for condensed matter physics, as one cannot resort to the usual toolbox based on Bloch's theorem. Here, we present a numerical method for constructing the Hubbard Hamiltonian of non-periodic potentials without making use of Bloch's theorem and apply it to the case of an eightfold rotationally symmetric 2D optical quasicrystal that was recently realized using cold atoms. We construct maximally localised Wannier functions and use them to extract on-site energies, tunneling amplitudes, and interaction energies. In addition, we introduce a configuration-space representation, where sites are ordered in terms of shape and local environment, that leads to a compact description of the infinite-size quasicrystal in which all Hamiltonian parameters can be expressed as smooth functions. This configuration-space picture allows one to construct arbitrarily large tight-binding graphs for numerical many-body calculations and enables new analytic arguments on the topological structure and many-body physics of these models, for instance the conclusion that this quasicrystal will host unit-filling Mott insulators in the thermodynamic limit.
TL;DR: In this paper , the angle-resolved photoemission spectroscopy and strongly correlated band structure calculations are combined to show that an unusual Mott instability exists in YbInCu4 accompanying its mysterious first-order valence transition.
Abstract: ABSTRACT Mott physics plays a critical role in materials with strong electronic correlations. Mott insulator-to-metal transition can be driven by chemical doping, external pressure, temperature and gate voltage, which is often seen in transition metal oxides with 3d electrons near the Fermi energy (e.g. cuprate superconductor). In 4f-electron systems, however, the insulator-to-metal transition is mostly driven by Kondo hybridization and the Mott physics has rarely been explored in experiments. Here, by combining the angle-resolved photoemission spectroscopy and strongly correlated band structure calculations, we show that an unusual Mott instability exists in YbInCu4 accompanying its mysterious first-order valence transition. This contrasts with the prevalent Kondo picture and demonstrates that YbInCu4 is a unique platform to explore the Mott physics in Kondo lattice systems. Our work provides important insight for the understanding and manipulation of correlated quantum phenomena in the f-electron system.
TL;DR: In this article , spin-resolved tunneling measurements on extremely underdoped Bi 2 Sr 2− x La x CuO 6+δ have been performed, showing that the antiferromagnetic order is destroyed, while at the same time an increasing density of states (DOS) peaked at around 200 meV within the charge transfer gap.
Abstract: Abstract The pairing mechanism of high-temperature superconductivity in cuprates is regarded as one of the most challenging issues in condensed matter physics. The core issue concerns how the Cooper pairs are formed. Here we report spin-resolved tunneling measurements on extremely underdoped Bi 2 Sr 2− x La x CuO 6+δ . Our data reveal that, when holes are doped into the system, the antiferromagnetic order is destroyed, while at the same time an increasing density of states (DOS) peaked at around 200 meV appears within the charge transfer gap. Meanwhile, an electronic structure with 4 a 0 × 4 a 0 basic plaquettes emerges inhomogeneously, with an area fraction that grows with hole doping. In each plaquette, there are some unidirectional bars (along the Cu-O bond) which are most pronounced at energies near peaks in the DOS around at 25 meV, with an intensity that is especially pronounced at oxygen sites. We argue that the atomically resolved low-energy DOS and related gap are closely associated with some kinds of density waves, possibly reflecting modulations of the electron density, or a pair-density wave, i.e. a modulation of the local pairing. Our work sheds new light on the doping induced electronic evolution from the “parent” insulator of the cuprate superconductors.
12 Jan 2023
TL;DR: In this article , the authors investigate the nonequilibrium electronic structure of 1 T -TaS 2 by time and angle-resolved photoemission spectroscopy and find that strong photo excitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase.
Abstract: Abstract We investigate the nonequilibrium electronic structure of 1 T -TaS 2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photo excitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change of the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy. We find that two different peak structures exhibit anti-phase oscillation with respect to each other. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flat band constructed as a result of CDW band folding survives with the collapse of the Mott gap. Our results strongly suggest the CDW phase is more robust than the Mott insulating phase, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulates the Mott gap.
TL;DR: In this paper, it is demonstrated that mean-field-like density functional theory (DFT) driven by molecular dynamics temperature evolution can describe not only the origin of the magnetically long-range ordered insulating phase (i), but also the creation of an insulating paramagnet (ii) that lacks spin-long-range order, and of a metallic paramagnetic (iii) as temperature rises.
Abstract: The YNiO$_3$ nickelate is a paradigm d-electron oxide that manifests the intriguing temperature-mediated sequence of three phases transitions from (i) magnetically ordered insulator to (ii) paramagnetic (PM) insulator and then to (iii) PM metal. Such phenomena raised the question of the nature of the association of magnetism and structural symmetry breaking with the appearance in (i) and (ii) and disappearance in (iii) of insulating band gaps. It is demonstrated here that first-principles mean-field-like density functional theory (DFT), driven by molecular dynamics temperature evolution, can describe not only the origin of the magnetically long-range ordered insulating phase (i), but also the creation of an insulating paramagnet (ii) that lacks spin-long-range order, and of a metallic paramagnet (iii) as temperature rises. This approach provides the patterns of structural and magnetic symmetry breaking at different temperatures, in parallel with band gaps obtained when the evolving geometries are used as input to DFT electronic band structure calculations. This disentangles the complex interplay among spin, charge and orbital degrees of freedom. Analysis shows that the success in describing the rise and fall of the insulating band gaps along the phase transition sequence is enabled by allowing sufficient flexibility in describing diverse local structural and magnetic motifs as input to DFT. This entails using sufficiently large supercells that allow expressing structural disproportionation of octahedra, as well as a description of PM phases as a distribution of local magnetic moments. It appears that the historic dismissal of mean-field-like DFT as being unable to describe such Mott-like transitions was premature, as it was based on consideration of averaged crystallographic unit cells, a description that washes out local symmetry-breaking motifs.
TL;DR: In this paper , the authors used scanning tunneling microscopy observations of the upper Hubbard band of the host Mott insulator to detect magnetic field dependent behavior of a quantum spin liquid.
Abstract: Recent theoretical investigations of quantum spin liquids have described phenomenology amenable to experimental observation using scanning tunneling microscopy. This includes characteristic resonances found at the edge of the upper Hubbard band of the host Mott insulator, that under certain conditions shift into the Mott gap under external magnetic field [W.-Y. He and P. A. Lee, arXiv:2212.08767]. In light of this we report scanning tunneling microscopy observations, in samples of the quantum spin liquid candidate $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, of a conductance peak at the upper Hubbard band edge and its magnetic field dependent behavior. These observations potentially represent evidence for the existence of a quantum spin liquid in $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$. We also observe samples in which such field dependence is absent, but with no observed correlate for the presence or absence of field dependence. This suggests one or more material properties controlling electronic behavior that are yet to be understood, and should help to motivate renewed investigation of the microscopic degrees of freedom in play in $1T\text{\ensuremath{-}}{\mathrm{TaS}}_{2}$, as well as the possible realization of a quantum spin liquid phase.
TL;DR: In this article , a photocarrier-doping-induced Mott-insulator-to-metal phase transition is shown in a few atomic layers of perovskite strontium ruthenate SrRuO3−δ.
Abstract: Light control of emergent quantum phenomena is a widely used external stimulus for quantum materials. Generally, perovskite strontium ruthenate SrRuO3 has an itinerant ferromagnetism with a low‐spin state. However, the phase of intermediate‐spin (IS) ferromagnetic metallic state has never been seen. Here, by means of UV‐light irradiation, a photocarrier‐doping‐induced Mott‐insulator‐to‐metal phase transition is shown in a few atomic layers of perovskite IS ferromagnetic SrRuO3−δ. This new metastable IS metallic phase can be reversibly regulated due to the convenient photocharge transfer from SrTiO3 substrates to SrRuO3−δ ultrathin films. These dynamical mean‐field theory calculations further verify such photoinduced electronic phase transformation, owing to oxygen vacancies and orbital reconstruction. The optical manipulation of charge‐transfer finesse is an alternative pathway toward discovering novel metastable phases in strongly correlated systems and facilitates potential light‐controlled device applications in optoelectronics and spintronics.
TL;DR: In this paper , a topological superconducting state is realized in the doped Mott insulators with time-reversal symmetry (TRS) by tuning the next-nearest-neighbor (NNN) electron hopping and spin interaction.
Abstract: The topological superconducting state is a highly sought-after quantum state hosting topological order and Majorana excitations. In this Letter, we explore the mechanism to realize the topological superconductivity (TSC) in the doped Mott insulators with time-reversal symmetry (TRS). Through large-scale density matrix renormalization group study of an extended triangular-lattice t−J model on the six- and eight-leg cylinders, we identify a d+id-wave chiral TSC with spontaneous TRS breaking, which is characterized by a Chern number C=2 and quasi-long-range superconducting order. We map out the quantum phase diagram with by tuning the next-nearest-neighbor (NNN) electron hopping and spin interaction. In the weaker NNN-coupling regime, we identify a pseudogaplike phase with a charge stripe order coexisting with fluctuating superconductivity, which can be tuned into d-wave superconductivity by increasing the doping level and system width. The TSC emerges in the intermediate-coupling regime, which has a transition to a d-wave superconducting phase with larger NNN couplings. The emergence of the TSC is driven by geometrical frustrations and hole dynamics which suppress spin correlation and charge order, leading to a topological quantum phase transition.Received 11 September 2022Accepted 6 March 2023Corrected 27 April 2023DOI:https://doi.org/10.1103/PhysRevLett.130.136003© 2023 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasTopological phase transitionTopological superconductorsPhysical SystemsTriangular latticeUnconventional superconductorsTechniquesDensity matrix renormalization groupCondensed Matter, Materials & Applied Physics
TL;DR: In this article , the existence at intermediate coupling of a symmetry-breaking transition to a nontopological topological insulator characterized by exciton condensation has been shown, where the correlated excitonic state corresponds to a magneto-electric insulator, which allows for direct experimental probing.
Abstract: Time-reversal symmetric topological insulators are generically robust with respect to weak local interaction unless symmetry-breaking transitions take place. Using dynamical mean-field theory, we solve an interacting model of quantum spin Hall insulators and show the existence at intermediate coupling of a symmetry-breaking transition to a nontopological insulator characterized by exciton condensation. This transition is of first order. For a larger interaction strength, the insulator evolves into a Mott one. The transition is continuous if magnetic order is prevented, and notably, for any finite Hund's exchange, it progresses through a Mott localization before the condensate coherence is lost. We show that the correlated excitonic state corresponds to a magneto-electric insulator, which allows for direct experimental probing. Finally, we discuss the fate of the helical edge modes across the excitonic transition.
TL;DR: In this paper , a new type of chiral superconducting phase can be stabilized in photodoped frustrated Mott insulators, which can exhibit a second-order supercurrent perpendicular to the field in addition to a first-order parallel response, similar to a nonlinear anomalous Hall effect.
Abstract: Recent advances in ultrafast pump-probe spectroscopy provide access to hidden phases of correlated matter, including light-induced superconducting states, but the theoretical understanding of these nonequilibrium phases remains limited. Here we report how a new type of chiral superconducting phase can be stabilized in photodoped frustrated Mott insulators. The metastable phase features a spatially varying order parameter with a $120^\circ$ phase twist which breaks both time-reversal and inversion symmetry. Under an external electric pulse, the $120^\circ$ chiral superconducting state can exhibit a second-order supercurrent perpendicular to the field in addition to a first-order parallel response, similar to a nonlinear anomalous Hall effect. This phase can be tuned by artificial gauge fields when the system is dressed by high-frequency periodic driving. The mechanism revealed in this study applies to Mott insulators on various frustrated lattices and the hidden superconducting phase can be realized in both cold-atom quantum simulators and correlated solids.
TL;DR: In this article , the López-Ruiz-Mancini-Calbet (LMC) measure of complexity is used to depict the superfluid to Mott-insulator transition.
Abstract: This work reports the different information theoretic measures, i.e., Shannon information entropy, order, disorder, complexity, and their dynamical measure for the interacting bosons in an optical lattice with both commensurate and incommensurate filling factor. We solve the many-body Schrödinger equation from first principles by multiconfigurational time-dependent Hartree method which calculates all the measures with high level of accuracy. We find for both relaxed state as well as quenched state the López-Ruiz-Mancini-Calbet (LMC) measure of complexity is the most efficient depictor of superfluid (SF) to Mott-insulator transition. In the quench dynamics, the distinct structure of LMC complexity can be used as a "figure of merit" to obtain the timescale of SF to Mott state entry, Mott holding time, and the Mott state to SF state entry in the successive cycles. We also find that fluctuations in the dynamics of LMC complexity measure for incommensurate filling clearly establish that superfluid to Mott-insulator transition is incomplete. We overall conclude that distinct structure in the complexity makes it more sensitive than the standard use of Shannon information entropy.
TL;DR: In this paper , the authors report how to tailor electronic structures of the honeycomb Mott insulator RuCl3 employing a facile and reversible single-crystal to singlecrystal intercalation process, and the resulting product (NH4)0.5RuCl3·1.5H2O forms a new hybrid superlattice of alternating RuCl 3 monolayers with NH4+ and H2O molecules.
Abstract: The core task for Mott insulators includes how rigid distributions of electrons evolve and how these induce exotic physical phenomena. However, it is highly challenging to chemically dope Mott insulators to tune properties. Herein, we report how to tailor electronic structures of the honeycomb Mott insulator RuCl3 employing a facile and reversible single-crystal to single-crystal intercalation process. The resulting product (NH4)0.5RuCl3·1.5H2O forms a new hybrid superlattice of alternating RuCl3 monolayers with NH4+ and H2O molecules. Its manipulated electronic structure markedly shrinks the Mott-Hubbard gap from 1.2 to 0.7 eV. Its electrical conductivity increases by more than 103 folds. This arises from concurrently enhanced carrier concentration and mobility in contrary to the general physics rule of their inverse proportionality. We show topotactic and topochemical intercalation chemistry to control Mott insulators, escalating the prospect of discovering exotic physical phenomena.
TL;DR: In this paper , the dielectric properties of the molecular quantum spin-liquid candidate were explored as a function of frequency, pressure, and temperature, and they showed that the pressure-dependent response is remarkably similar to the less-correlated sister compound.
Abstract: We explore the dielectric properties of the molecular quantum-spin-liquid candidate $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Ag}}_{2}{(\mathrm{CN})}_{3}$ as a function of frequency, pressure, and temperature. The transition from the incoherent semiconducting to the Mott-insulating state at the quantum Widom line yields a drop of the low-frequency dielectric constant to small positive values ${\ensuremath{\varepsilon}}_{1}\ensuremath{\approx}10$. The characteristic relaxor-type peak around $T=50$ K moves to lower temperatures when pressurized. An additional feature appears and quickly grows as the percolative first-order transition is approached with rising pressure. Above 4 kbar, it dominates the dielectric response and rapidly shifts to $T\ensuremath{\rightarrow}0$. Overall, the pressure-dependent dielectric response is remarkably similar to the less-correlated sister compound $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}{\mathrm{Cu}}_{2}{(\mathrm{CN})}_{3}$. At the Mott transition, we identify a reentrant insulating behavior at ${T}^{★}=11$ K which might indicate a low-entropy ground state --- possibly with a spin gap.
TL;DR: In this article , a terahertz pulse is used to drive the dielectric breakdown in Mott insulators, which exhibit variations in their electronic structures under carrier doping, a filling-controlled transition can be induced in the sub-picosecond time scale.
Abstract: When a semiconductor is subjected to a strong electric field, carriers are generated via quantum tunneling; this is termed as dielectric breakdown. Thus, using a terahertz pulse to drive the dielectric breakdown in Mott insulators, which exhibit variations in their electronic structures under carrier doping, a filling-controlled transition can be induced in the subpicosecond time scale. However, to generate carriers via quantum tunneling in a material with a band gap in the visible or near-infrared regions, an electric field pulse significantly exceeding $1 \mathrm{MV} {\mathrm{cm}}^{\ensuremath{-}1}$ is necessary. In this paper, using an organic molecular compound, bis(ethylenedithio)tetrathiafulvalene-difluorotetracyanoquinodimethane, which is a typical one-dimensional (1D) Mott insulator with a Mott gap of 0.7 eV, we aimed at realizing carrier generation and metallization via a strong electric field component of a terahertz pulse enhanced with an organic nonlinear optical crystal up to $2.8 \mathrm{MV} {\mathrm{cm}}^{\ensuremath{-}1}$. Even after the terahertz electric field decays, the reflectivity change caused by the terahertz pulse remains; this is different from the case involving the use of weaker electric fields. More importantly, this response indicates a threshold behavior against the electric field amplitude, which is characteristic of carrier generation via the quantum tunneling process. Furthermore, transient reflectivity spectra across the mid-infrared region could be reproduced well by numerical simulations using the Drude model, in which inhomogeneous carrier distributions are considered. The observed Drude response of the doublons and holons was ascribed to the spin-charge separation characteristic of 1D strongly correlated electron systems. We also demonstrate that the energy efficiency of such carrier generation by the terahertz pulse excitation is at least five times greater than that when using photoexcitation beyond the Mott gap. This indicates that excitation with the strong terahertz pulse is more effective for carrier doping in solids; thus, the proposed method is expected to be widely applicable for the electronic-state control of various correlated electron materials in which chemical carrier doping is currently difficult.
15 Feb 2023
TL;DR: In this article , the authors derived lattice models for the narrow moir\'e bands of the AB-stacked twisted WSe$_2$ homobilayer through continuum model and Wannier orbital construction.
Abstract: In this paper, we derive lattice models for the narrow moir\'e bands of the AB-stacked twisted WSe$_2$ homobilayer through continuum model and Wannier orbital construction. Previous work has shown that an approximate SU(4) Hubbard model may be realized by combining spin and layer because inter-layer tunneling is suppressed due to spin $S_z$ conservation. However, Rashba spin-orbit coupling (SOC) was ignored in the previous analysis. Here, we show that a Rashba SOC of reasonable magnitude can induce a finite but very small inter-layer hopping in the final lattice Hubbard model. At total filling $n=1$, we derive a spin-layer model on a triangular lattice in the large-U limit where the inter-layer tunneling contributes as a sublattice-dependent transverse Ising field for the layer pseudospin. We then show that the $n=2$ Mott insulator is also captured by an approximate SU(4) spin model, but now on honeycomb lattice. We comment on the possibility of a Dirac spin liquid (DSL) and competing phases due to SU(4) anisotropy terms.
08 May 2023
TL;DR: In this article , a single-orbital Hubbard model is constructed within a "molecular" rather than atomic basis set using ab initio constrained random phase approximation calculations and correlated electron theory.
Abstract: The Hubbard model provides an idealized description of electronic correlations in solids. Despite its simplicity, the model features a competition between several different phases that have made it one of the most studied systems in theoretical physics. Real materials usually deviate from the ideal of the Hubbard model in several ways, but the monolayer of Nb$_3$Cl$_8$ has recently appeared as a potentially optimal candidate for the realization of such a single-orbital Hubbard model. Here we show how this single orbital Hubbard model can be indeed constructed within a "molecular" rather than atomic basis set using ab initio constrained random phase approximation calculations. This way, we provide the essential ingredients to connect experimental reality with ab initio material descriptions and correlated electron theory, which clarifies that monolayer Nb$_3$Cl$_8$ is a Mott insulator with a gap of about 1 to 1.2eV depending on its dielectric environment. By comparing with an atomistic three-orbital model, we show that the single molecular orbital description is indeed adequate. We furthermore comment on the expected electronic and magnetic structure of the compound and show that the Mott insulating state survives in the low-temperature and bulk phases of the material.
TL;DR: In this paper , the authors show that the infinite-layer SCO, a topical cuprate Mott insulator in bulk form, can manifest an unexpected metallic state in the quasi-2D limit when SCO is grown on a few-layer substrate.
Abstract: Recent quasi-two-dimensional (quasi-2D) systems with judicious exploitation of the atomic monolayer or few-layer architecture exhibit unprecedented physical properties that challenge the conventional wisdom on condensed matter physics. Here we show that the infinite layer ${\mathrm{SrCuO}}_{2}$ (SCO), a topical cuprate Mott insulator in bulk form, can manifest an unexpected metallic state in the quasi-2D limit when SCO is grown on ${\mathrm{TiO}}_{2}$-terminated ${\mathrm{SrTiO}}_{3}$ (STO) substrates. The sheet resistance does not conform to Landau's Fermi liquid paradigm. Hard x-ray core-level photoemission spectra demonstrate a definitive Fermi level that resembles the hole doped metal. Soft x-ray absorption spectroscopy also reveals features analogous to those of a hole doped Mott insulator. Based on these results, we conclude that the hole doping does not occur at the interfaces between SCO and STO; instead, it comes from the transient layers between the chain-type and the planar-type structures within the SCO slab. The present work reveals a metallic state in the infinite layer SCO and invites further examination to elucidate the spatial extent of this state.
TL;DR: In this paper , it was shown that anomalous behavior is not inconsistent with Landau's Fermi liquid theory of quasiparticles at a Luttinger surface, i.e., the manifold of zeros within the Brillouin zone of the single-particle Green's function at zero frequency.
Abstract: The long search for insulating materials that possess low-energy quasiparticles carrying electron's quantum numbers except charge---inspired by the neutral spin-$1/2$ excitations, the so-called spinons, exhibited by Anderson's resonating-valence-bond state---seems to have reached a turning point after the discovery of several Mott insulators displaying the same thermal and magnetic properties as metals, including quantum oscillations in a magnetic field. Here, we show that such anomalous behavior is not inconsistent with Landau's Fermi liquid theory of quasiparticles at a Luttinger surface. That is the manifold of zeros within the Brillouin zone of the single-particle Green's function at zero frequency, and which thus defines the spinon Fermi surface conjectured by Anderson.