Showing papers on "Mott insulator published in 2009"
TL;DR: The magnetic interactions in Mott-Hubbard systems with partially filled t_{2g} levels and with strong spin-orbit coupling are studied to explain "weak" ferromagnetism, with an anomalously large ferromagnetic moment, in Sr2IrO4.
Abstract: We study the magnetic interactions in Mott-Hubbard systems with partially filled t_{2g} levels and with strong spin-orbit coupling. The latter entangles the spin and orbital spaces, and leads to a rich variety of the low energy Hamiltonians that extrapolate from the Heisenberg to a quantum compass model depending on the lattice geometry. This gives way to "engineer" in such Mott insulators an exactly solvable spin model by Kitaev relevant for quantum computation. We, finally, explain "weak" ferromagnetism, with an anomalously large ferromagnetic moment, in Sr2IrO4.
1,641 citations
TL;DR: In this article, the Mott transition between a low-temperature insulating phase and a high temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature.
Abstract: Correlated electron materials can undergo a variety of phase transitions, including superconductivity, the metal-insulator transition and colossal magnetoresistance. Moreover, multiple physical phases or domains with dimensions of nanometres to micrometres can coexist in these materials at temperatures where a pure phase is expected. Making use of the properties of correlated electron materials in device applications will require the ability to control domain structures and phase transitions in these materials. Lattice strain has been shown to cause the coexistence of metallic and insulating phases in the Mott insulator VO(2). Here, we show that we can nucleate and manipulate ordered arrays of metallic and insulating domains along single-crystal beams of VO(2) by continuously tuning the strain over a wide range of values. The Mott transition between a low-temperature insulating phase and a high-temperature metallic phase usually occurs at 341 K in VO(2), but the active control of strain allows us to reduce this transition temperature to room temperature. In addition to device applications, the ability to control the phase structure of VO(2) with strain could lead to a deeper understanding of the correlated electron materials in general.
560 citations
TL;DR: In this paper, an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO was performed, and it was shown that correlations between electrons in these materials are just as strong as in some copper oxide and ruthenate superconductors.
Abstract: When electrons experience Coulomb repulsion, their kinetic energy becomes significantly reduced. This effect has now been measured in the pnictide superconductor LaFePO, and shows that correlations between electrons in these materials are just as strong as in some copper oxide and ruthenate superconductors. In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron’s kinetic energy, leading to remarkable experimental manifestations in optical spectroscopy1. The high-transition-temperature (Tc) superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides2,3,4 puts a spotlight on the relevance of correlation effects in these materials5. Here, we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. We deduce that electronic many-body effects are important in the iron pnictides despite the absence of a Mott transition.
290 citations
TL;DR: In this paper, a two-dimensional ultracold Bose gas as it crosses the superfluid to Mott insulator transition is shown to exhibit a strong suppression in the insulator domain and suppressed density fluctuations in the Mott domain.
Abstract: The observation of the superfluid to Mott insulator phase transition of ultracold atoms in optical lattices was an enabling discovery in experimental many-body physics, providing the first tangible example of a quantum phase transition (one that occurs even at zero temperature) in an ultracold atomic gas. For a trapped gas, the spatially varying local chemical potential gives rise to multiple quantum phases within a single sample, complicating the interpretation of bulk measurements. Here we report spatially resolved, in-situ imaging of a two-dimensional ultracold atomic gas as it crosses the superfluid to Mott insulator transition, providing direct access to individual characteristics of the insulating, superfluid and normal phases. We present results for the local compressibility in all phases, observing a strong suppression in the insulator domain and suppressed density fluctuations for the Mott insulator, in accordance with the fluctuation-dissipation theorem. Furthermore, we obtain a direct measure of the finite temperature of the system. Taken together, these methods enable a complete characterization of multiple phases in a strongly correlated Bose gas, and of the interplay between quantum and thermal fluctuations in the quantum critical regime.
281 citations
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TL;DR: In this article, the density profile of a two-dimensional Mott insulator formed by ultracold atoms in an optical lattice was measured using high-resolution absorption imaging.
Abstract: We present a direct measurement of the density profile of a two-dimensional Mott Insulator formed by ultracold atoms in an optical lattice. High resolution absorption imaging is used to probe the "wedding-cake" structure of a trapped gas as it crosses the boundary from a unit-filled Mott insulating phase to the superfluid phase at finite temperature. Detailed analysis of images yields measurements of temperature and local compressibility; for the latter we observe a strong suppression deep in the Mott-insulating phase, which is recovered for the superfluid and normal phases. Furthermore, we measure spatially resolved fluctuations in the local density, showing a suppression of fluctuations in the insulator. Results are consistent with the fluctuation-dissipation theorem for insulator, superfluid and normal gas.
221 citations
TL;DR: A general mechanism for orbital-selective Mott transition, the coexistence of both itinerant and localized conduction electrons, is outlined and it is shown how it can take place in a wide range of realistic situations, even for bands of identical width and correlation.
Abstract: We outline a general mechanism for orbital-selective Mott transition, the coexistence of both itinerant and localized conduction electrons, and show how it can take place in a wide range of realistic situations, even for bands of identical width and correlation, provided a crystal field splits the energy levels in manifolds with different degeneracies and the exchange coupling is large enough to reduce orbital fluctuations. The mechanism relies on the different kinetic energy in manifolds with different degeneracy. This phase has Curie-Weiss susceptibility and non-Fermi-liquid behavior, which disappear at a critical doping, all of which is reminiscent of the physics of the pnictides.
203 citations
TL;DR: Chiral spin liquids with non-Abelian anyons may also be realizable with alkaline earth atoms and a chiral spin liquid ground state with topological order and Abelian fractional statistics is found.
Abstract: We study Mott insulators of fermionic alkaline earth atoms, described by Heisenberg spin models with enhanced SU(N) symmetry. In dramatic contrast to SU(2) magnetism, more than two spins are required to form a singlet. On the square lattice, the classical ground state is highly degenerate and magnetic order is thus unlikely. In a large-N limit, we find a chiral spin liquid ground state with topological order and Abelian fractional statistics. We discuss its experimental detection. Chiral spin liquids with non-Abelian anyons may also be realizable with alkaline earth atoms.
171 citations
TL;DR: It is shown that the stress-induced antiferromagnetic Mott insulating phase is critical in controlling the spatial extent and distribution of the insulating monoclinic and metallic rutile phases as well as the electrical characteristics of the Mott transition.
Abstract: We demonstrate that the Mott metal-insulator transition (MIT) in single crystalline VO(2) nanowires is strongly mediated by surface stress as a consequence of the high surface area to volume ratio of individual nanowires. Further, we show that the stress-induced antiferromagnetic Mott insulating phase is critical in controlling the spatial extent and distribution of the insulating monoclinic and metallic rutile phases as well as the electrical characteristics of the Mott transition. This affords an understanding of the relationship between the structural phase transition and the Mott MIT.
151 citations
TL;DR: The heart of the Mott physics such as the pseudogap, hole pockets, Fermi arcs, in-gap states, Lifshitz transitions, and non-Fermi liquids appears as natural consequences of this global interference in the frequency space.
Abstract: We study the evolution of metals from Mott insulators in the carrier-doped 2D Hubbard model using a cluster extension of the dynamical mean-field theory. While the conventional metal is simply characterized by the Fermi surface (pole of the Green function $G$), interference of the zero surfaces of $G$ with the pole surfaces becomes crucial in the doped Mott insulators. Mutually interfering pole and zero surfaces are dramatically transferred over the Mott gap, when lightly doped holes synergetically loosen the doublon-holon binding. The heart of the Mott physics such as the pseudogap, hole pockets, Fermi arcs, in-gap states, Lifshitz transitions, and non-Fermi liquids appears as natural consequences of this global interference in the frequency space.
150 citations
TL;DR: In this article, it was shown that an energy gap exists in nominally metallic carbon nanotubes and occurs in addition to the band gap in small-band-gap nanotube, indicating that carbon nanotsubes are never metallic.
Abstract: The Mott insulating state is a manifestation of strong electron interactions in nominally metallic systems. Using transport spectroscopy, we showed that an energy gap exists in nominally metallic carbon nanotubes and occurs in addition to the band gap in small–band-gap nanotubes, indicating that carbon nanotubes are never metallic. This gap has a magnitude of ~10 to 100 milli–electron volts and a nanotube radius (r) dependence of ~1/r, which is in good agreement with predictions for a nanotube Mott insulating state. We also observed neutral excitations within the gap, as predicted for this state. Our results underscore nanotubes' exceptional capabilities for use in studying correlated electron phenomena in one dimension.
145 citations
TL;DR: In this paper, the authors derived effective Hubbard-type Hamiltonians of κ-(BEDT-TTF) 2 X, using an ab initio downfolding technique, for the first time for organic conductors.
Abstract: We derive effective Hubbard-type Hamiltonians of κ-(BEDT-TTF) 2 X , using an ab initio downfolding technique, for the first time for organic conductors. They contain dispersions of the highest occupied Wannier-type molecular orbitals with the nearest neighbor transfer t ∼0.067 eV for a metal X =Cu(NCS) 2 and 0.055 eV for a Mott insulator X =Cu 2 (CN) 3 , as well as screened Coulomb interactions. It shows unexpected differences from the conventional extended Huckel results, especially much stronger onsite interaction U ∼0.8 eV ( U / t ∼12–15) than the Huckel estimates ( U / t ∼7–8) as well as an appreciable longer-ranged interaction. Reexamination on physics of this family of materials is required from this realistic basis.
TL;DR: Using the differential light shift caused by a spatially inhomogeneous far detuned light field, a "phase gradient" is imprinted across the atomic sample, resulting in controlled angular redirection of the retrieved light pulse.
Abstract: We experimentally demonstrate electromagnetically induced transparency and light storage with ultracold Rb-87 atoms in a Mott insulating state in a three-dimensional optical lattice We have observed light storage times of similar or equal to 240 ms, to our knowledge the longest ever achieved in ultracold atomic samples Using the differential light shift caused by a spatially inhomogeneous far detuned light field we imprint a ``phase gradient'' across the atomic sample, resulting in controlled angular redirection of the retrieved light pulse
TL;DR: In this paper, a field-theory approach is applied to prove the existence of multicritical curves analogous to the multicritical points of the Bose-Hubbard model, and analytical expressions for the position of these curves are provided.
Abstract: Regular arrays of electromagnetic resonators, in turn coupled coherently to individual quantum two-level systems, exhibit a quantum phase transition of polaritons from a superfluid phase to a Mott-insulating phase. The critical behavior of such a Jaynes-Cummings lattice thus resembles the physics of the Bose-Hubbard model. We explore this analogy by elaborating on the mean-field theory of the phase transition and by presenting several useful mappings which pinpoint both similarities and differences of the two models. We show that a field-theory approach can be applied to prove the existence of multicritical curves analogous to the multicritical points of the Bose-Hubbard model, and we provide analytical expressions for the position of these curves.
TL;DR: The absence of a direct quantum phase transition between a superfluid and a Mott insulator in a bosonic system with generic, bounded disorder is proved and the compressibility of the system on the superfluid-insulator critical line and in its neighborhood is proved.
Abstract: We prove the absence of a direct quantum phase transition between a superfluid and a Mott insulator in a bosonic system with generic, bounded disorder. We also prove the compressibility of the system on the superfluid--insulator critical line and in its neighborhood. These conclusions follow from a general theorem of inclusions, which states that for any transition in a disordered system, one can always find rare regions of the competing phase on either side of the transition line. Quantum Monte Carlo simulations for the disordered Bose-Hubbard model show an even stronger result, important for the nature of the Mott insulator to Bose glass phase transition: the critical disorder bound ${\ensuremath{\Delta}}_{c}$ corresponding to the onset of disorder-induced superfluidity, satisfies the relation ${\ensuremath{\Delta}}_{c}g{E}_{g/2}$, with ${E}_{g/2}$ the half-width of the Mott gap in the pure system.
TL;DR: In this article, the authors study three-dimensional systems where strong repulsion leads to an insulating state via spontaneously generated spin-orbit interactions and discuss a microscopic model where the resulting state is topological.
Abstract: We study three-dimensional systems where strong repulsion leads to an insulating state via spontaneously generated spin-orbit interactions. We discuss a microscopic model where the resulting state is topological. Such topological ``Mott'' insulators differ from their band-insulator counterparts in that they possess an additional order parameter, a rotation matrix, which describes the spontaneous breaking of spin-rotation symmetry. We show that line defects of this order are associated with protected one-dimensional modes in the strong topological Mott insulator that provides a bulk characterization of this phase. Possible physical realizations in cold-atom systems are discussed.
TL;DR: The phase diagram of the disordered three-dimensional Bose-Hubbard model at unity filling has been established in this paper, showing that the Gapless phase always intervenes between the Mott insulating and superfluid phases.
Abstract: We establish the phase diagram of the disordered three-dimensional Bose-Hubbard model at unity filling which has been controversial for many years. The theorem of inclusions, proven by Pollet et al. [Phys. Rev. Lett. 103, 140402 (2009)] states that the Bose-glass phase always intervenes between the Mott insulating and superfluid phases. Here, we note that assumptions on which the theorem is based exclude phase transitions between gapped (Mott insulator) and gapless phases (Bose glass). The apparent paradox is resolved through a unique mechanism: such transitions have to be of the Griffiths type when the vanishing of the gap at the critical point is due to a zero concentration of rare regions where extreme fluctuations of disorder mimic a regular gapless system. An exactly solvable random transverse field Ising model in one dimension is used to illustrate the point. A highly nontrivial overall shape of the phase diagram is revealed with the worm algorithm. The phase diagram features a long superfluid finger at strong disorder and on-site interaction. Moreover, bosonic superfluidity is extremely robust against disorder in a broad range of interaction parameters; it persists in random potentials nearly 50 (!) times larger than the particle half-bandwidth. Finally, we comment on the feasibility of obtaining this phase diagram in cold-atom experiments, which work with trapped systems at finite temperature.
TL;DR: The Bragg spectroscopy of interacting one-dimensional Bose gases loaded in an optical lattice across the superfluid to the Mott-insulator phase transition paves the way for a precise characterization of the state of correlated gases in optical lattices.
Abstract: We report the Bragg spectroscopy of interacting one-dimensional Bose gases loaded in an optical lattice across the superfluid to the Mott-insulator phase transition. Elementary excitations are created with a nonzero momentum and the response of the correlated 1D gases is in the linear regime. The complexity of the strongly correlated quantum phases is directly displayed in the spectra which exhibit novel features. This work paves the way for a precise characterization of the state of correlated gases in optical lattices.
TL;DR: In this paper, magnetic, electrical, and thermal measurements on single crystals of the Mott insulator reveal a giant magnetoelectric effect (GME) arising from a frustrated magnetic/ferroelectric state whose signatures are: a strongly enhanced electric permittivity that peaks near an observed magnetic anomaly at 100 K, and a large magnetodielectric shift that occurs near a metamagnetic transition.
Abstract: Our magnetic, electrical, and thermal measurements on single crystals of the ${J}_{\mathrm{eff}}=1/2$ Mott insulator, ${\text{Sr}}_{2}{\text{IrO}}_{4}$, reveal a giant magnetoelectric effect (GME) arising from a frustrated magnetic/ferroelectric state whose signatures are: (1) a strongly enhanced electric permittivity that peaks near an observed magnetic anomaly at 100 K, and (2) a large $(\ensuremath{\sim}100%)$ magnetodielectric shift that occurs near a metamagnetic transition. The GME hinges on a spin-orbit gapping of $5d$ bands rather than the magnitude and spatial dependence of magnetization, as traditionally accepted.
TL;DR: High-resolution scanning tunneling microscopy measurements of the high–transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ show that samples with different Tc values in the low doping regime follow a remarkably universal d wave low-energy excitation spectrum, indicating a doping-independent nodal gap.
Abstract: Understanding the mechanism by which d wave superconductivity in the cuprates emerges and is optimized by doping the Mott insulator is one of the major outstanding problems in condensed-matter physics. Our high-resolution scanning tunneling microscopy measurements of the high–transition temperature (Tc) superconductor Bi2Sr2CaCu2O8+δ show that samples with different Tc values in the low doping regime follow a remarkably universal d wave low-energy excitation spectrum, indicating a doping-independent nodal gap. We demonstrate that Tc instead correlates with the fraction of the Fermi surface over which the samples exhibit the universal spectrum. Optimal Tc is achieved when all parts of the Fermi surface follow this universal behavior. Increasing the temperature above Tc turns the universal spectrum into an arc of gapless excitations, whereas overdoping breaks down the universal nodal behavior.
TL;DR: In this article, the authors demonstrate spin gradient thermometry, a new general method of measuring the temperature of ultracold atoms in optical lattices, using a mixture of spins separated by a magnetic field gradient.
Abstract: We demonstrate spin gradient thermometry, a new general method of measuring the temperature of ultracold atoms in optical lattices. We realize a mixture of spins separated by a magnetic field gradient. Measurement of the width of the transition layer between the two spin domains serves as a new method of thermometry which is observed to work over a broad range of lattice depths and temperatures, including in the Mott insulator regime. We demonstrate the thermometry using ultracold rubidium atoms, and suggest that interesting spin physics can be realized in this system. The lowest measured temperature is 1 nK, indicating that the system has reached the quantum regime, where insulating shells are separated by superfluid layers.
TL;DR: Neutron spectroscopy and diffuse neutron scattering on herbertsmithite reveal the hallmark property of a quantum spin liquid: instantaneous short-ranged antiferromagnetic correlations in the absence of a time-averaged ordered moment.
Abstract: Neutron spectroscopy and diffuse neutron scattering on herbertsmithite [ZnCu3(OH)(6)Cl-2], a near-ideal realization of the s=1/2 kagome antiferromagnet, reveal the hallmark property of a quantum spin liquid: instantaneous short-ranged antiferromagnetic correlations in the absence of a time-averaged ordered moment. These dynamic antiferromagnetic correlations are weakly dependent of neutron-energy transfer and temperature, and persist up to 25 meV and 120 K. At low energy transfers a shift of the magnetic scattering to low Q is observed with increasing temperature, providing evidence of gapless spinons. It is argued that these observations provide important evidence in favor of resonating-valence-bond theories of (doped) Mott insulators.
01 Dec 2009
TL;DR: The thermometry is demonstrated using ultracold rubidium atoms, and it is suggested that interesting spin physics can be realized in this system, which has reached the quantum regime, where insulating shells are separated by superfluid layers.
Abstract: We demonstrate spin gradient thermometry, a new general method of measuring the temperature of ultracold atoms in optical lattices. We realize a mixture of spins separated by a magnetic field gradient. Measurement of the width of the transition layer between the two spin domains serves as a new method of thermometry which is observed to work over a broad range of lattice depths and temperatures, including in the Mott insulator regime. We demonstrate the thermometry using ultracold rubidium atoms, and suggest that interesting spin physics can be realized in this system. The lowest measured temperature is 1 nK, indicating that the system has reached the quantum regime, where insulating shells are separated by superfluid layers.
TL;DR: In this paper, the effect of interspecies interaction on a degenerate mixture of bosonic {sup 87}Rb and fermionic {sup 40}K atoms in a three-dimensional optical lattice potential was investigated.
Abstract: We investigate the effect of interspecies interaction on a degenerate mixture of bosonic {sup 87}Rb and fermionic {sup 40}K atoms in a three-dimensional optical lattice potential. Using a Feshbach resonance, the {sup 87}Rb-{sup 40}K interaction is tuned over a wide range. Through an analysis of the {sup 87}Rb momentum distribution, we find a pronounced asymmetry between strong repulsion and strong attraction. In the latter case, we observe a marked shift in the superfluid to Mott insulator transition, which we attribute to a renormalization of the Bose-Hubbard parameters due to self-trapping.
TL;DR: In this paper, the authors studied the conditions under which, using a canonical transformation, the phases sought after for the repulsive Hubbard model, namely, a Mott insulator in the paramagnetic and antiferromagnetic phases, and a putative $d$-wave superfluid can be deduced from observations in an optical lattice loaded with a spin-imbalanced ultracold Fermi gas with attractive interactions.
Abstract: We study the conditions under which, using a canonical transformation, the phases sought after for the repulsive Hubbard model, namely, a Mott insulator in the paramagnetic and antiferromagnetic phases, and a putative $d$-wave superfluid can be deduced from observations in an optical lattice loaded with a spin-imbalanced ultracold Fermi gas with attractive interactions, thus realizing the attractive Hubbard model We argue that the Mott insulator and antiferromagnetic phase of the repulsive Hubbard model are easier to observe in the attractive Hubbard mode as a band insulator of Cooper pairs and superfluid phase, respectively The putative $d$-wave superfluid phase of the repulsive Hubbard model doped away from half filling is related to a $d$-wave antiferromagnetic phase for the attractive Hubbard model We discuss the advantages of this approach to ``quantum simulate'' the Hubbard model in an optical lattice over the simulation of the doped Hubbard model in the repulsive regime We also point out a number of technical difficulties of the proposed approach and, in some cases, suggest possible solutions
TL;DR: In this article, the spin-order of ultracold bosons in an optical lattice was investigated by means of dynamical mean-field theory, and a rich phase diagram with anisotropic magnetic order was found, both for ground state and at finite temperatures.
Abstract: We investigate spin-order of ultracold bosons in an optical lattice by means of dynamical mean-field theory. A rich phase diagram with anisotropic magnetic order is found, both for the ground state and at finite temperatures. Within the Mott insulator, a ferromagnetic to antiferromagnetic transition can be tuned using a spin-dependent optical lattice. In addition we find a supersolid phase, in which superfluidity coexists with antiferromagnetic spin order. We present detailed phase diagrams at finite temperature for the experimentally realized heteronuclear 87Rb-41K mixture in a three-dimensional optical lattice.
TL;DR: In this article, the authors studied the zero temperature Mott transition in the two-dimensional Hubbard model on the square lattice with the variational cluster approximation, taking into account the influence of antiferromagnetic short-range correlations.
Abstract: The nature of the metal-insulator Mott transition at zero temperature has been discussed for a number of years. Whether it occurs through a quantum critical point or through a first-order transition is expected to profoundly influence the nature of the finite-temperature phase diagram. In this paper, we study the zero temperature Mott transition in the two-dimensional Hubbard model on the square lattice with the variational cluster approximation. This takes into account the influence of antiferromagnetic short-range correlations. By contrast to single-site dynamical mean-field theory, the transition turns out to be first order even at zero temperature.
TL;DR: In this article, it was shown that CrN is close to a charge transfer insulator transition and that the density of states near the Fermi level is strongly depleted by the spin separation of the states.
Abstract: Calculations using the $\text{LSDA}+\text{U}$ (local spin-density approximation corrected by Hubbard Coulomb terms for the $d$ electrons) approach show that CrN is close to a charge-transfer insulator transition. The values of $U$ are estimated in various ways, including the recently developed linear-response approach. With reasonable values of $U$ in the range of 3--5 eV it is found that the density of states near the Fermi level is strongly depleted by the spin separation of the states. In the case of the antiferromagnetic (AFM)-${[110]}_{2}$ configuration a small gap actually opens even for $U$ as small as 3 eV. Furthermore a smallest direct gap of about 1 eV can be seen in these band structures and could be responsible for the onset of strong optical absorption observed to occur at 0.7 eV. The tendency of opening the gap is found to be strongest in the actually observed AFM-${[110]}_{2}$ structure below the N\'eel temperature. The widely varying transport data in the literature are critically examined. They indicate a gap smaller than 0.1 eV, consistent with the present calculations, a strong influence of N-vacancy-induced doping carriers and possibly localization effects associated with the distortions accompanying the loss of antiferromagnetic ordering above the N\'eel temperature.
TL;DR: In this paper, the Bose-Hubbard model and a recently proposed coupled-cavity model are studied by means of quantum Monte Carlo simulations in one dimension, focusing on the parameter region around the phase transition from the Mott insulator with density one to the superfluid phase, where correlations are important.
Abstract: Spectral properties of the Bose-Hubbard model and a recently proposed coupled-cavity model are studied by means of quantum Monte Carlo simulations in one dimension. Both models exhibit a quantum phase transition from a Mott insulator to a superfluid phase. The dynamic structure factor $S(k,\ensuremath{\omega})$ and the single-particle spectrum $A(k,\ensuremath{\omega})$ are calculated, focusing on the parameter region around the phase transition from the Mott insulator with density one to the superfluid phase, where correlations are important. The strongly interacting nature of the superfluid phase manifests itself in terms of additional gapped modes in the spectra. Comparison is made to recent analytical work on the Bose-Hubbard model. Despite some subtle differences due to the polaritonic particles in the cavity model, the gross features are found to be very similar to the Bose-Hubbard case. For the polariton model, emergent particle-hole symmetry near the Mott lobe tip is demonstrated and temperature and detuning effects are analyzed. A scaling analysis for the generic transition suggests mean-field exponents, in accordance with field-theory results.
TL;DR: In this article, direct analytic continuation of the self-energy was used to determine the effect of antiferromagnetic ordering on the spectral function and optical conductivity of a Mott insulator.
Abstract: Direct analytic continuation of the self-energy is used to determine the effect of antiferromagnetic ordering on the spectral function and optical conductivity of a Mott insulator. Comparison of several methods shows that the most robust estimation of the gap value is obtained by use of the real part of the continued self-energy in the quasiparticle equation within the single-site dynamical mean-field theory of the two-dimensional square lattice Hubbard model, where, for a $U$ that is slightly greater than the Mott critical value, antiferromagnetism increases the gap by about 80%.
TL;DR: An angle resolved photoemission study of V2O3, a prototype system for the observation of Mott transitions in correlated materials, shows that the spectral features corresponding to the quasiparticle peak in the metallic phase present a marked wave vector dependence, with a stronger intensity along the GammaZ direction.
Abstract: We present an angle resolved photoemission study of V2O3, a prototype system for the observation of Mott transitions in correlated materials. We show that the spectral features corresponding to the quasiparticle peak in the metallic phase present a marked wave vector dependence, with a stronger intensity along the GammaZ direction. The analysis of their intensity for different probing depths shows the existence of a characteristic length scale for the attenuation of coherent electronic excitations at the surface. This length scale, which is larger than the thickness of the surface region as normally defined for noncorrelated electronic states, is found to increase when approaching the Mott transition. These results are in agreement with the behavior of quasiparticles at surfaces as predicted by Borghi et al.