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The ionic Hubbard model in a two-dimensional square lattice is revisited using determinant quantum Monte Carlo (DQMC) and numerical analytic continuation. From the dc conductivity extracted by stochastic maximum entropy of the DQMC data, we find that the band insulator induced by a staggered potential Δ goes through a metallic phase before entering a Mott insulator as the on-site Hubbard interaction U is increased. Moreover, we map out the phase diagram in the (Δ , U) plane, and reveal a smaller metallic region than that found in the previous studies. Our results provide a more exact location of the phase boundaries, and are an important complement to those obtained by an approximate approach. [ABSTRACT FROM AUTHOR]

Recent studies have revealed the potential of 2D moiré superlattices as a condensed matter quantum simulator. The realization of different lattice model Hamiltonians in moiré superlattices has become the focus of researches. Here, it shows that, compared to bilayer moiré superlattices where there is only one interface, the interference between moiré patterns at different interfaces in 2D multilayer structures allows the physical realization of more complicated lattice models. The concept is demonstrated by trilayer moiré superlattices (TMSLs) of MoS2, where it finds that isolated flat moiré bands appear near the valence band edge, and they can be described by the honeycomb lattice ionic Hubbard model. More importantly, the hopping strength, the on‐site Coulomb repulsion, and the staggered potential in the TMSLs are highly tunable through the control of the twist angle, the dielectric environment, and the perpendicular electric field. It is possible to achieve various transitions between distinct quantum phases in the TMSLs, spanning from weak to strong correlation regimes. Therefore, the proposed TMSLs can serve as a good platform to study the strong correlation physics in the honeycomb lattice ionic Hubbard model. [ABSTRACT FROM AUTHOR]

To address the issues of superconducting and charge properties in hydrated sodium cobalt, we investigate an extended ionic Hubbard model on the triangular lattice, which includes off-site attractions between sites with minor charges. Our quantum Monte Carlo simulations show that close to quarter filling, the off-site attractions induce a significant enhancement of d-wave and extended s-wave pairing correlations. Simultaneously, they render an increase of the charge structure factor at most of wave vectors. A combination with charge correlations in real space indicates the development of short-range finite-q charge density waves on the sites with minor charges. Our findings provide a new perspective on the superconducting mechanism in hydrated sodium cobalt based on the electronic structure which explicitly takes the effect of sodium atoms into account.

To address the issues of superconducting and charge properties in hydrated sodium cobalt, we investigate an extended ionic Hubbard model on the triangular lattice, which includes off-site attractions between sites with minor charges. Our quantum Monte Carlo simulations show that close to quarter filling, the off-site attractions induce a significant enhancement of d -wave and extended s -wave pairing correlations. Simultaneously, they render an increase of the charge structure factor at most of wave vectors. A combination with charge correlations in real space indicates the development of short-range finite- q charge density waves on the sites with minor charges. Our findings provide a new perspective on the superconducting mechanism in hydrated sodium cobalt based on the electronic structure which explicitly takes the effect of sodium atoms into account. • The hydrated sodium cobalt is studied based on an extended ionic Hubbard model. • Unconventional superconductivity is enhanced by the off-site attractions. • Short-range charge density wave is induced by the off-site attractions. [ABSTRACT FROM AUTHOR]

The quantum integrability of the 1D ionic Hubbard model (IHM) is established using two independent numerical methods, namely i) energy level spacing statistics and ii) occupation profile of one‐particle density matrix (OPDM) eigen‐values. Both methods suggest that the 1D IHM is integrable. The calculations of energy level statistics reproduce the known results for the standard Hubbard model. Upon turning on the the ionic term, the energy level spacing distribution of this model continues to obey the Poissonian distribution. Occupation patterns as extracted from OPDM indicate that quasi‐particles are sharpened upon increasing the ionic potential. This is evidenced by a larger jump in the occupation number distribution. [ABSTRACT FROM AUTHOR]

The ionic Hubbard model with spatially alternating interactions, which may be realized by cold atoms in optical lattices, is studied by mean of the coherent potential approximation. The paramagnetic phase diagram for the half-filled model at zero temperature is obtained. The possibility of enlarging an intermediate metallic region in the parameter space is addressed. [ABSTRACT FROM AUTHOR]

Motivated by the recent progress in time-resolved nonequilibrium spectroscopy in condensed matter, we study an optically excited one-dimensional ionic Hubbard model by exact diagonalization. The model is relevant to organic crystals, transition metal oxides, or ultracold atoms in optical lattices. We implement numerical pump-probe measurements to calculate time-dependent conductivity and single-particle spectral functions. In general, short optical excitation induces a metallic behavior imprinted as a Drude peak in conductivity or an in-gap density of states. In a Mott insulator, we find that the induced Drude peak oscillates at the pump frequency and its second harmonic. The former comes from the oscillation of currents, and the latter from the interference of single- and three-photon excited states. In a band insulator, the Drude peak oscillates only at the pump frequency, and quantities such as the double occupancy do not oscillate. The absence of the second harmonic oscillation is due to the degeneracy of multi-photon excited states. The in-gap density of states in both insulators correlates with the Drude weight and the energy absorption for weak pumping. Strong pumping leads to saturation of the in-gap density of states and to suppression of the Drude weight in the Mott regime. We have also checked that the above features are robust for insulators in the intermediate parameter range. Our study demonstrates the distinct natures of the multi-photon excited states in two different insulators.

We study electronic phase transitions in the half-filled ionic Hubbard model with an on-site Coulomb repulsion U and an ionic energy Δ by using the Kotliar-Ruckenstein slave-boson theory. Assuming a paramagnetic solution, we show that for any non-zero values of Δ, with increasing U the system undergoes a transition from band-insulator to Mott-insulator. Our results have implied the absence of a metallic phase between the band and the Mott insulator phases. [ABSTRACT FROM AUTHOR]

With the ionic Hubbard model (IHM) in mind, we construct a non-trivial generalization of the Bethe ansatz (BA) wave function which naturally generalizes the Lieb–Wu wave function with an ionic parameter Δ , and reduces to Lieb–Wu solution in the limit Δ → 0. The resulting two-particle scattering matrix satisfies the Yang–Baxter equation. To the extent that the unit cells with more than two electrons (Choy–Haldane issue) are avoided on average, our wave function represents an effective solution for the one-dimensional IHM. The Choy–Haldane issue limits the validity of our solution to low-filling and large U ≳ 4. This regime is attainable in cold atom realizations of the IHM. For this regime, we numerically solve the generalized Bethe equations and compute the ground state energy in the thermodynamic limit. • An extension of Lieb–Wu Bethe Ansatz wave function has been constructed. • This wave function addresses the low-filling and large U limit of the ionic Hubbard model. • Thermodynamic limit was constructed and the resulting ground state properties are compared with the Lieb–Wu solution. [ABSTRACT FROM AUTHOR]