Showing papers on "Mott insulator published in 2012"
TL;DR: In this article, the authors used high-resolution, in situ Rydberg atom imaging to measure directly strong correlations in a laser-excited, two-dimensional atomic Mott insulator.
Abstract: The ability to control and tune interactions in ultracold atomic gases has paved the way for the realization of new phases of matter. So far, experiments have achieved a high degree of control over short-range interactions, but the realization of long-range interactions has become a central focus of research because it would open up a new realm of many-body physics. Rydberg atoms are highly suited to this goal because the van der Waals forces between them are many orders of magnitude larger than those between ground-state atoms. Consequently, mere laser excitation of ultracold gases can cause strongly correlated many-body states to emerge directly when atoms are transferred to Rydberg states. A key example is a quantum crystal composed of coherent superpositions of different, spatially ordered configurations of collective excitations. Here we use high-resolution, in situ Rydberg atom imaging to measure directly strong correlations in a laser-excited, two-dimensional atomic Mott insulator. The observations reveal the emergence of spatially ordered excitation patterns with random orientation, but well-defined geometry, in the high-density components of the prepared many-body state. Together with a time-resolved analysis, this supports the description of the system in terms of a correlated quantum state of collective excitations delocalized throughout the gas. Our experiment demonstrates the potential of Rydberg gases to realize exotic phases of matter, thereby laying the basis for quantum simulations of quantum magnets with long-range interactions.
474 citations
TL;DR: In this article, the theoretical understanding and physical properties of these ''Hund's metals'' are reviewed, together with the relevance of this concept to transition-metal oxides of the 3D and 4d series (such as ruthenates), as well as to the iron-based superconductors (iron pnictides and chalcogenides).
Abstract: Strong electronic correlations are often associated with the proximity of a Mott insulating state. In recent years however, it has become increasingly clear that the Hund's rule coupling (intra-atomic exchange) is responsible for strong correlations in multi-orbital metallic materials which are not close to a Mott insulator. Hund's coupling has two effects: it influences the energetics of the Mott gap and strongly suppresses the coherence scale for the formation of a Fermi-liquid. A global picture has emerged recently, which emphasizes the importance of the average occupancy of the shell as a control parameter. The most dramatic effects occur away from half-filling or single occupancy. The theoretical understanding and physical properties of these `Hund's metals' are reviewed, together with the relevance of this concept to transition-metal oxides of the 3d, and especially 4d series (such as ruthenates), as well as to the iron-based superconductors (iron pnictides and chalcogenides).
358 citations
TL;DR: A multicomponent gas of ytterbium atoms accommodates more entropy in its spin degrees of freedom than does its two-component analogue, leading to a lower effective temperature, and an easy route for cooling ultracold fermions towards a Mott-insulating state as mentioned in this paper.
Abstract: A multicomponent gas of ytterbium atoms accommodates more entropy in its spin degrees of freedom than does its two-component analogue, leading to a lower effective temperature, and an easy route for cooling ultracold fermions towards a Mott-insulating state.
287 citations
TL;DR: The separation of the orbital degree of freedom (orbiton) is observed using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3 to resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum.
Abstract: When viewed as an elementary particle, the electron has spin and charge. When binding to the atomic nucleus, it also acquires an angular momentum quantum number corresponding to the quantized atomic orbital it occupies. Even if electrons in solids form bands and delocalize from the nuclei, in Mott insulators they retain their three fundamental quantum numbers: spin, charge and orbital1. The hallmark of one-dimensional physics is a breaking up of the elementary electron into its separate degrees of freedom2. The separation of the electron into independent quasi-particles that carry either spin (spinons) or charge (holons) was first observed fifteen years ago3. Here we report observation of the separation of the orbital degree of freedom (orbiton) using resonant inelastic X-ray scattering on the one-dimensional Mott insulator Sr2CuO3. We resolve an orbiton separating itself from spinons and propagating through the lattice as a distinct quasi-particle with a substantial dispersion in energy over momentum, of about 0.2 electronvolts, over nearly one Brillouin zone.
265 citations
TL;DR: The layered ferroelectric bismuth titanate is examined and it is demonstrated that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its bandgap can be narrowed by as much as 1 eV, while remaining strongly ferroElectric.
Abstract: Fabricating complex transition metal oxides with a tunable bandgap without compromising their intriguing physical properties is a longstanding challenge. Here we examine the layered ferroelectric bismuth titanate and demonstrate that, by site-specific substitution with the Mott insulator lanthanum cobaltite, its bandgap can be narrowed by as much as 1 eV, while remaining strongly ferroelectric. We find that when a specific site in the host material is preferentially substituted, a split-off state responsible for the bandgap reduction is created just below the conduction band of bismuth titanate. This provides a route for controlling the bandgap in complex oxides for use in emerging oxide optoelectronic and energy applications.
238 citations
TL;DR: In this article, a tight-binding model for the three-dimensional orthorhombic perovskite (Pbnm) was proposed to understand the physical origin of the metallic state and possible transitions to insulating phases.
Abstract: The two-dimensional layered perovskite Sr${}_{2}$IrO${}_{4}$ was proposed to be a spin-orbit Mott insulator, where the effect of Hubbard interaction is amplified on a narrow $J$${}_{\mathrm{eff}}=1/2$ band due to strong spin-orbit coupling. On the other hand, the three-dimensional orthorhombic perovskite (Pbnm) SrIrO${}_{3}$ remains metallic. To understand the physical origin of the metallic state and possible transitions to insulating phases, we construct a tight-binding model for SrIrO${}_{3}$. The band structure possesses a line node made of $J$${}_{\mathrm{eff}}=1/2$ bands below the Fermi level. As a consequence, instability toward magnetic ordering is suppressed, and the system remains metallic. This line node, originating from the underlying crystal structure, turns into a pair of three-dimensional nodal points on the introduction of a staggered potential or spin-orbit coupling strength between alternating layers. Increasing this potential beyond a critical strength induces a transition to a strong topological insulator, followed by another transition to a normal band insulator. We propose that materials constructed with alternating Ir- and Rh-oxide layers along the (001) direction, such as Sr${}_{2}$IrRhO${}_{6}$, are candidates for a strong topological insulator.
214 citations
TL;DR: The results for A=Sr and Ba correctly reproduce paramagnetic metals undergoing continuous transitions to insulators below the Néel temperature T(N); these compounds are classified not into Mott insulators but into Slater insulators.
Abstract: Ab initio analyses of ${A}_{2}{\mathrm{IrO}}_{4}$ ($A=\mathrm{Sr},\mathrm{Ba}$) are presented. Effective Hubbard-type models for Ir $5d$ ${t}_{2g}$ manifolds downfolded from the global band structure are solved based on the dynamical mean-field theory. The results for $A=\mathrm{Sr}$ and Ba correctly reproduce paramagnetic metals undergoing continuous transitions to insulators below the N\'eel temperature ${T}_{N}$. These compounds are classified not into Mott insulators but into Slater insulators. However, the insulating gap opens by a synergy of the N\'eel order and significant band renormalization, which is also manifested by a 2D bad metallic behavior in the paramagnetic phase near the quantum criticality.
166 citations
TL;DR: A complex mechanism, a Peierls-assisted orbital selection Mott instability, is identified, which is responsible for the insulating M(1) phase, and which furthermore survives a moderate degree of disorder.
Abstract: Vanadium dioxide undergoes a first order metal-insulator transition at 340 K. In this Letter, we develop and carry out state-of-the-art linear scaling density-functional theory calculations refined with nonlocal dynamical mean-field theory. We identify a complex mechanism, a Peierls-assisted orbital selection Mott instability, which is responsible for the insulating M(1) phase, and which furthermore survives a moderate degree of disorder.
158 citations
TL;DR: An isotropic isospin correlation that is well described by the two-dimensional S=1/2 quantum Heisenberg model is discovered that points out the weak and marginal Mott character of this spin-orbital entangled system.
Abstract: The dynamical correlations of ${J}_{\mathrm{eff}}=1/2$ isospins in the paramagnetic state of spin-orbital Mott insulator ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ were revealed by resonant magnetic x-ray diffuse scattering. We found a two-dimensional antiferromagnetic fluctuation with a large in-plane correlation length exceeding 100 lattice spacings at even 20 K above the magnetic ordering temperature. In marked contrast to the naive expectation of the strong magnetic anisotropy associated with an enhanced spin-orbit coupling, we discovered an isotropic isospin correlation that is well described by the two-dimensional $S=1/2$ quantum Heisenberg model. The estimated antiferromagnetic coupling constant as large as $J\ensuremath{\sim}0.1\text{ }\text{ }\mathrm{eV}$ that is comparable to the small Mott gap ($l0.5\text{ }\text{ }\mathrm{eV}$) points out the weak and marginal Mott character of this spin-orbital entangled system.
139 citations
TL;DR: A slave-boson theory is presented which gives insight into such intertwined spin-charge orders in the SF, and signatures of these orders in Bragg scattering, in situ microscopy, and dynamic quench experiments are discussed.
Abstract: Motivated by the experimental realization of synthetic spin-orbit coupling for ultracold atoms, we investigate the phase diagram of the Bose-Hubbard model in a non-Abelian gauge field in two dimensions. Using a strong coupling expansion in the combined presence of spin-orbit coupling and tunable interactions, we find a variety of interesting magnetic Hamiltonians in the Mott insulator (MI), which support magnetic textures such as spin spirals and vortex and Skyrmion crystals. An inhomogeneous mean-field treatment shows that the superfluid (SF) phases inherit these exotic magnetic orders from the MI and display, in addition, unusual modulated current patterns. We present a slave-boson theory which gives insight into such intertwined spin-charge orders in the SF, and discuss signatures of these orders in Bragg scattering, in situ microscopy, and dynamic quench experiments.
136 citations
TL;DR: A unified perspective of this interplay between superconductivity, pseudogap, and Mott transition is provided in the two-dimensional Hubbard model within cellular dynamical mean-field theory on a 2×2 plaquette and using the continuous-time quantum Monte Carlo method as impurity solver.
Abstract: An intricate interplay between superconductivity, pseudogap, and Mott transition, either bandwidth driven or doping driven, occurs in materials. Layered organic conductors and cuprates offer two prime examples. We provide a unified perspective of this interplay in the two-dimensional Hubbard model within cellular dynamical mean-field theory on a $2\ifmmode\times\else\texttimes\fi{}2$ plaquette and using the continuous-time quantum Monte Carlo method as impurity solver. Both at half filling and at finite doping, the metallic normal state close to the Mott insulator is unstable to $d$-wave superconductivity. Superconductivity can destroy the first-order transition that separates the pseudogap phase from the overdoped metal, yet that normal state transition leaves its marks on the dynamic properties of the superconducting phase. For example, as a function of doping one finds a rapid change in the particle-hole asymmetry of the superconducting density of states. In the doped Mott insulator, the dynamical mean-field superconducting transition temperature ${T}_{c}^{d}$ does not scale with the order parameter when there is a normal-state pseudogap. ${T}_{c}^{d}$ corresponds to the local pair formation temperature observed in tunneling experiments and is distinct from the pseudogap temperature.
TL;DR: It is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.
Abstract: The concept of spin-orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin-orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin-orbital entanglement in the $R$VO$_3$ perovskites, with $R$=La,Pr,...,Yb,Lu, where such finite temperature properties of these compounds can be understood only using entangled states: ($i$) thermal evolution of the optical spectral weights, ($ii$) the dependence of transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the $R$VO$_3$ perovskites, and ($iii$) dimerization observed in the magnon spectra for the $C$-type antiferromagnetic phase of YVO$_3$. Finally, it is shown that joint spin-orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduces topological constraints for the hole propagation and will thus radically modify transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.
TL;DR: In this paper, the pseudogap phase of a hole-doped cuprate superconductor was found to emerge in localized clusters that grow with increasing doping, and the eventual coalescence of these clusters coincides with the emergence of superconductivity.
Abstract: Scanning tunnelling microscopy images of the evolution of the pseudogap phase of a hole-doped cuprate superconductor suggest that it emerges in localized clusters that grow with increasing doping. Moreover, the eventual coalescence of these clusters coincides with the emergence of superconductivity.
TL;DR: In this article, the effects of hole doping on a Mott insulator on the honeycomb lattice where spins interact via direction-dependent Kitaev couplings and weak antiferromagnetic Heisenberg couplings was studied.
Abstract: We study the effects of doping a Mott insulator on the honeycomb lattice where spins interact via direction-dependent Kitaev couplings ${J}_{\mathrm{K}}$, and weak antiferromagnetic Heisenberg couplings $J$. This model is known to have a spin-liquid ground state and may potentially be realized in correlated insulators with strong spin -orbit coupling. The effect of hole doping is studied within a $t$-$J$-${J}_{\mathrm{K}}$ model, treated using the SU(2) slave boson formalism, which correctly captures the parent spin liquid. We find superconductor ground states with spin triplet pairing that spontaneously break time-reversal symmetry. Interestingly, the pairing is qualitatively different at low and high dopings, and undergoes a first-order transition with doping. At high dopings, it is smoothly connected to a paired state of electrons propagating with the underlying free particle dispersion. However, at low dopings the dispersion is strongly influenced by the magnetic exchange, and is entirely different from the free-particle band structure. Here the superconductivity is fully gapped and topological, analogous to spin polarized electrons with ${p}_{x}+i{p}_{y}$ pairing. These results may be relevant to honeycomb lattice iridates such as ${A}_{2}$IrO${}_{3}$ ($A$ = Li or Na) on doping.
TL;DR: The state of the art of experiments to realize and detect magnetic orderings in strongly correlated optical lattices and the low-energy spin Hamiltonian for bosons and fermions is discussed.
Abstract: We study cold atoms in an optical lattice with synthetic spin-orbit coupling in the Mott-insulator regime. We calculate the parameters of the corresponding tight-binding model using Peierls substitution and "localized Wannier states method" and derive the low-energy spin Hamiltonian for bosons and fermions. The spin Hamiltonian is a combination of Heisenberg model, quantum compass model and Dzyaloshinskii-Moriya interactions and it has a rich classical phase diagram with collinear, spiral and vortex phases. We discuss the state of the art of experiments to realize and detect magnetic orderings in strongly correlated optical lattices.
TL;DR: In this paper, the intrinsic phase diagram of antiferromagnetic magnetism and high-temperature superconductivity for a disorder-free CuO 2 plane with hole carriers was uncovered.
Abstract: High-temperature superconductivity (HTSC) in copper oxides emerges on a layered CuO 2 plane when an antiferromagnetic Mott insulator is doped with mobile hole carriers. We review extensive studies of multilayered copper oxides by site-selective nuclear magnetic resonance (NMR), which have uncovered the intrinsic phase diagram of antiferromagnetism (AFM) and HTSC for a disorder-free CuO 2 plane with hole carriers. We present our experimental findings such as the existence of the AFM metallic state in doped Mott insulators, the uniformly mixed phase of AFM and HTSC, and the emergence of d -wave SC with a maximum T c just outside a critical carrier density, at which the AFM moment on a CuO 2 plane disappears. These results can be accounted for by the Mott physics based on the t – J model. The superexchange interaction J in among spins plays a vital role as a glue for Cooper pairs or mobile spin-singlet pairs, in contrast to the phonon-mediated attractive interaction among electrons established in the Bardeen...
TL;DR: Spectroscopically investigated the thermally and doping-induced metal-insulator transitions for pyrochlore-type Nd2Ir2O7 as well as its Rh-doped analogs Nd 2(Ir(1-x)Rh(x))(2)O(7), where the spin-orbit interaction aswell as the electron correlation is effectively tuned by the doping level.
Abstract: We have spectroscopically investigated the thermally and doping-induced metal-insulator transitions for pyrochlore-type Nd2Ir2O7 as well as its Rh-doped analogs Nd2(Ir(1-x)Rh(x))(2)O(7), where the spin-orbit interaction as well as the electron correlation is effectively tuned by the doping level (x). The charge dynamics dramatically changes on an energy scale of 1 eV in the course of thermally and doping-induced metal-insulator transitions, while the insulating ground state shows a small but well-defined charge gap of 45 meV. Anomalous doping variation of the low-energy (<0.3 eV) optical-conductivity spectra at the ground state can be interpreted in terms of the phase changes among the narrow-gap Mott insulator, Weyl semimetal, and correlated metal.
TL;DR: The computed HSE lattice constants and band gaps of AnO(2) are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC.
Abstract: We present a systematic comparison of the lattice structures, electronic density of states, and band gaps of actinide dioxides, AnO2 (An=Th, Pa, U, Np, Pu, and Am) predicted by the Heyd-Scuseria-Ernzerhof screened hybrid density functional (HSE) with the self-consistent inclusion of spin-orbit coupling (SOC). The computed HSE lattice constants and band gaps of AnO2 are in consistently good agreement with the available experimental data across the series, and differ little from earlier HSE results without SOC. ThO2 is a simple band insulator (f 0), while PaO2, UO2, and NpO2 are predicted to be Mott insulators. The remainders (PuO2 and AmO2) show considerable O2p/An5f mixing and are classified as charge-transfer insulators. We also compare our results for UO2, NpO2, and PuO2 with the PBE+U, self interaction correction (SIC), and dynamic mean-field theory (DMFT) many-body approximations.
TL;DR: In this paper, the two-dimensional Kane-Mele-Hubbard model at half filling was studied by means of quantum Monte Carlo simulations and a refined phase boundary for the quantum spin liquid was presented.
Abstract: We study the two-dimensional Kane-Mele-Hubbard model at half filling by means of quantum Monte Carlo simulations. We present a refined phase boundary for the quantum spin liquid. The topological insulator at finite Hubbard interaction strength is adiabatically connected to the groundstate of the Kane-Mele model. In the presence of spin-orbit coupling, magnetic order at large Hubbard $U$ is restricted to the transverse direction. The transition from the topological band insulator to the antiferromagnetic Mott insulator is in the universality class of the three-dimensional XY model. The numerical data suggest that the spin liquid to topological insulator and spin liquid to Mott insulator transitions are both continuous.
TL;DR: The origin of anisotropic exchange interactions in a Mott insulator in the strong spin-orbit coupling regime holds the key to the various types of unconventional magnetism proposed in 5d transition metal oxides.
Abstract: Using resonant x-ray diffraction, we observe an easy c-axis collinear antiferromagnetic structure for the bilayer Sr3Ir2O7, a significant contrast to the single layer Sr2IrO4 with in-plane canted moments. Based on a microscopic model Hamiltonian, we show that the observed spin-flop transition as a function of number of IrO2 layers is due to strong competition among intra- and interlayer bond-directional pseudodipolar interactions of the spin-orbit entangled J(eff)=1/2 moments. With this we unravel the origin of anisotropic exchange interactions in a Mott insulator in the strong spin-orbit coupling regime, which holds the key to the various types of unconventional magnetism proposed in 5d transition metal oxides.
TL;DR: In this paper, the authors obtained the phase diagrams in the Hubbard model on the triangular kagome lattice as a function of interaction, temperature, and asymmetry by combining the cellular dynamical mean-field theory with the continuous time quantum Monte Carlo method.
Abstract: We obtain the rich phase diagrams in the Hubbard model on the triangular kagome lattice as a function of interaction, temperature, and asymmetry by combining the cellular dynamical mean-field theory with the continuous time quantum Monte Carlo method. The phase diagrams show the asymmetry separates the critical points in the Mott transition of two sublattices on the triangular kagome lattice and produces two novel phases called plaquette insulator with a clearly visible gap and a gapless Kondo metal. When the Coulomb interaction is stronger than the critical value U-c, a short range paramagnetic insulating state, which is a candidate for the short rang resonating valence-bond spin liquid, emerges before the ferrimagnetic order is formed independent of asymmetry. Furthermore, we discuss how to measure these phases in future experiments.
TL;DR: In this article, it was shown that the spin-orbital SU(4) symmetric Kugel-Khomskii model of Mott insulators on the honeycomb lattice is a quantum spinorbital liquid.
Abstract: The main characteristic of Mott insulators, as compared to band insulators, is to host low-energy spin fluctuations. In addition, Mott insulators often possess orbital degrees of freedom when crystal-field levels are partially filled. While in the majority of Mott insulators, spins and orbitals develop long-range order, the possibility for the ground state to be a quantum liquid opens new perspectives. In this paper, we provide clear evidence that the spin-orbital SU(4) symmetric Kugel-Khomskii model of Mott insulators on the honeycomb lattice is a quantum spin-orbital liquid. The absence of any form of symmetry breaking-lattice or SU(N)-is supported by a combination of semiclassical and numerical approaches: flavor-wave theory, tensor network algorithm, and exact diagonalizations. In addition, all properties revealed by these methods are very accurately accounted for by a projected variational wave function based on the pi-flux state of fermions on the honeycomb lattice at 1/4 filling. In that state, correlations are algebraic because of the presence of a Dirac point at the Fermi level, suggesting that the symmetric Kugel-Khomskii model on the honeycomb lattice is an algebraic quantum spin-orbital liquid. This model provides an interesting starting point to understanding the recently discovered spin-orbital-liquid behavior of Ba3CuSb2O9. The present results also suggest the choice of optical lattices with honeycomb geometry in the search for quantum liquids in ultracold four-color fermionic atoms.
TL;DR: In this article, it was shown that spin-orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions.
Abstract: The concept of spin–orbital entanglement on superexchange bonds in transition metal oxides is introduced and explained on several examples. It is shown that spin–orbital entanglement in superexchange models destabilizes the long-range (spin and orbital) order and may lead either to a disordered spin-liquid state or to novel phases at low temperature which arise from strongly frustrated interactions. Such novel ground states cannot be described within the conventionally used mean field theory which separates spin and orbital degrees of freedom. Even in cases where the ground states are disentangled, spin–orbital entanglement occurs in excited states and may become crucial for a correct description of physical properties at finite temperature. As an important example of this behaviour we present spin–orbital entanglement in the RV O3 perovskites, with R = La,Pr,…,Y b,Lu, where the finite temperature properties of these compounds can be understood only using entangled states: (i) the thermal evolution of the optical spectral weights, (ii) the dependence of the transition temperatures for the onset of orbital and magnetic order on the ionic radius in the phase diagram of the RV O3 perovskites, and (iii) the dimerization observed in the magnon spectra for the C-type antiferromagnetic phase of Y V O3. Finally, it is shown that joint spin–orbital excitations in an ordered phase with coexisting antiferromagnetic and alternating orbital order introduce topological constraints for the hole propagation and will thus radically modify the transport properties in doped Mott insulators where hole motion implies simultaneous spin and orbital excitations.
TL;DR: In this article, the quench dynamics of a one-dimensional bosonic Mott insulator were analyzed and the time evolution of density correlations was studied, and the velocity of the velocity can serve as a quantitative characteristic of the many-body Hamiltonian.
Abstract: We analyze the quench dynamics of a one-dimensional bosonic Mott insulator and focus on the time evolution of density correlations. For these we identify a pronounced propagation front, the velocity of which, once correctly extrapolated at large distances, can serve as a quantitative characteristic of the many-body Hamiltonian. In particular, the velocity allows the weakly interacting regime, which is qualitatively well described by free bosons, to be distinguished from the strongly interacting one, in which pairs of distinct quasiparticles dominate the dynamics. In order to describe the latter case analytically, we introduce a general approximation to solve the Bose-Hubbard Hamiltonian based on the Jordan-Wigner fermionization of auxiliary particles. This approach can also be used to determine the ground-state properties. As a complement to the fermionization approach, we derive explicitly the time-dependent many-body state in the noninteracting limit and compare our results to numerical simulations in the whole range of interactions of the Bose-Hubbard model.
TL;DR: In this paper, the fully frustrated Bose-Hubbard model with half a magnetic flux quantum per plaquette was studied and the phase diagram of this model was obtained on a two-leg ladder at integer filling via the density matrix renormalization group approach.
Abstract: Motivated by experiments on Josephson junction arrays, and cold atoms in an optical lattice in a synthetic magnetic field, we study the ``fully frustrated'' Bose-Hubbard model with half a magnetic flux quantum per plaquette. We obtain the phase diagram of this model on a two-leg ladder at integer filling via the density matrix renormalization group approach, complemented by Monte Carlo simulations on an effective classical XY model. The ground state at intermediate correlations is consistently shown to be a chiral Mott insulator (CMI) with a gap to all excitations and staggered loop currents which spontaneously break time-reversal symmetry. We characterize the CMI state as a vortex supersolid or an indirect exciton condensate, and discuss various experimental implications.
TL;DR: In this article, an array of superconducting islands with semiconducting nanowires in the right regime provides a macroscopic implementation of Kitaev's toy model for Majorana wires.
Abstract: An array of superconducting islands with semiconducting nanowires in the right regime provides a macroscopic implementation of Kitaev's toy model for Majorana wires. We show that a capacitive coupling between adjacent islands leads to an effective interaction between the Majorana modes. We demonstrate that, even though strong repulsive interaction eventually drives the system into a Mott insulating state, the competition between the (trivial) band insulator and the (trivial) Mott insulator leads to an interjacent topological insulating state for arbitrary strong interactions.
TL;DR: In this paper, Doublon-hole pair production in a Mott insulator subject to a strong laser or a static electric field is studied in the one-dimensional Hubbard model.
Abstract: Doublon-hole pair production, which takes place during dielectric breakdown in a Mott insulator subject to a strong laser or a static electric field, is studied in the one-dimensional Hubbard model. Two nonlinear effects cause the excitation, i.e., multiphoton absorption and quantum tunneling. Keldysh crossover between the two mechanisms occurs as the field strength and photon energy are changed. The calculation is done analytically by the Landau-Dykhne method in combination with the Bethe ansatz solution, and the results are compared with those of the time-dependent density matrix renormalization group. Using this method, we calculate the distribution function of the generated doublon-hole pairs and show that it drastically changes as we cross the Keldysh crossover line. After calculating the tunneling threshold for several representative one-dimensional Mott insulators, possible experimental tests of the theory are proposed, such as angle-resolved photoemission spectroscopy of the upper Hubbard band in the quantum tunneling regime. We also discuss the relationship of the present theory with a many-body extension of electron-positron pair production in nonlinear quantum electrodynamics, known as the Schwinger mechanism.
TL;DR: This work shows that a quantum spin liquid state in the organic Mott insulator EtMe(3)Sb[Pd(dmit)(2)](2) with two-dimensional triangular lattice has Pauli-paramagnetic-like low-energy excitations, which are a hallmark of itinerant fermions.
Abstract: Spin liquids are states of matter in which the constituent spins of a magnet are highly correlated yet fluctuate strongly down to millikelvin temperatures. Here the authors report torque magnetometry measurements of the Mott insulator EtMe3Sb[Pd(dmit)2]2 and find it displays an ungapped quantum spin liquid state.
TL;DR: In this paper, the authors considered a spinless fermions with nearest and next-to-nearest neighbor repulsive Hubbard interactions on a honeycomb lattice, and proposed and analyzed a realistic scheme for analog quantum simulation of this model with cold atoms in a two-dimensional hexagonal optical lattice.
Abstract: In this work we consider a system of spinless fermions with nearest and next-to-nearest neighbor repulsive Hubbard interactions on a honeycomb lattice, and propose and analyze a realistic scheme for analog quantum simulation of this model with cold atoms in a two-dimensional hexagonal optical lattice. To this end, we first derive the zero-temperature phase diagram of the interacting model within a mean-field theory treatment. We show that besides a semimetallic and a charge-density-wave ordered phase, the system exhibits a quantum anomalous Hall phase, which is generated dynamically, i.e., purely as a result of the repulsive fermionic interactions and in the absence of any external gauge fields. We establish the topological nature of this dynamically created Mott-insulating phase by the numerical calculation of a Chern number, and we study the possibility of coexistence of this phase with any of the other phases characterized by local order parameters. Based on the knowledge of the mean-field phase diagram, we then discuss in detail how the interacting Hamiltonian can be engineered effectively by state-of-the-art experimental techniques for laser dressing of cold fermionic ground-state atoms with electronically excited Rydberg states that exhibit strong dipolar interactions.
15 Jul 2012
TL;DR: In this paper, the authors performed a time-resolved optical study of a strongly spin-orbit coupled J_(eff) = 1/2 Mott insulator and found that upon cooling through the Neel temperature T_N, the system evolves continuously from a metal-like phase with fast (∼50 fs) and excitation density independent relaxation dynamics to a gapped phase characterized by slower ( ∼500 fs) bimolecular recombination dynamics.
Abstract: We perform a time-resolved optical study of Sr_2IrO_4 to understand the influence of magnetic ordering on the low energy electronic structure of a strongly spin-orbit coupled J_(eff) = 1/2 Mott insulator. By studying the recovery dynamics of photoexcited carriers, we find that upon cooling through the Neel temperature T_N the system evolves continuously from a metal-like phase with fast (∼50 fs) and excitation density independent relaxation dynamics to a gapped phase characterized by slower (∼500 fs) excitation density-dependent bimolecular recombination dynamics, which is a hallmark of a Slater-type metal-to-insulator transition. However our data indicate that the high energy reflectivity associated with optical transitions into the unoccupied J_(eff) = 1/2 band undergoes the sharpest upturn at TN, which is consistent with a Mott-Hubbard type metal-to-insulator transition involving spectral weight transfer into an upper Hubbard band. These findings show Sr_2IrO_4 to be a unique system in which Slater- and Mott-Hubbard-type behaviors coexist and naturally explain the absence of anomalies at T_N in transport and thermodynamic measurements.