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We investigate the ground-state phase diagram of the Hubbard model for the AB$_{N-1}$ chain with filling 1/N, where $N$ is the number of atoms per unit cell. In the strong-coupling limit, a charge transition takes place from a band insulator (BI) to a correlated insulator (CI) for increasing on-site repulsion $U$ and positive on-site energy difference $Delta$ (energy at A sites lower than at B sites). In the weak-coupling limit, a bosonization analysis suggests that for $N > 2$ the physics is qualitatively similar to the case $N = 2$ which has already been studied: an intermediate phase emerges, which corresponds to a bond-ordered ferroelectric insulator (FI) with spontaneously broken inversion symmetry. We have determined the quantum phase diagram for the cases $N = 3$ and $N = 4$ from the crossings of energy levels of appropriate excited states, which correspond to jumps in the charge and spin Berry phases, and from the change of sign of the localization parameter $z_{L}^{c}$. From these techniques we find that, quantitatively, the BI and FI phases are broader for $N > 2$ than when $N = 2$, in agreement with the bosonization analysis. Calculations of the Drude weight and $z_{L}^{c}$ indicate that the system is insulating for all parameters, with the possible exception of the boundary between the BI and FI phases.
We study the phase diagram of the ionic Hubbard model (IHM) at half-filling using dynamical mean field theory (DMFT), with two impurity solvers, namely, iterated perturbation theory (IPT) and continuous time quantum Monte Carlo (CTQMC). The physics o
The finite-temperature phase diagram of the Hubbard model in $d=3$ is obtained from renormalization-group analysis. It exhibits, around half filling, an antiferromagnetic phase and, between 30%--40% electron or hole doping from half filling, a new $t
We investigate the phases of the ionic Hubbard model in a two-dimensional square lattice using determinant quantum Monte Carlo (DQMC). At half-filling, when the interaction strength or the staggered potential dominate we find Mott and band insulators
We investigate paramagnetic metal-insulator transitions in the infinite-dimensional ionic Hubbard model at finite temperatures. By means of the dynamical mean-field theory with an impurity solver of the continuous-time quantum Monte Carlo method, we
We investigate the phase diagram of the half-filled SU(N) Hubbard-Heisenberg model with hopping t, exchange J and Hubbard U, on a square lattice. In the large-N limit, and as a function of decreasing values of t/J, the model shows a transition from a