Ground States of the Falicov-Kimball model with correlated hopping

Abstract

Two-dimensional spinless Falicov-Kimball model (FKM) with correlated hopping is studied perturbatively in the limit of large on-site Coulomb interaction $U$. In the neutral case the effective Hamiltonian in spin variables is derived up to terms proportional to $U^{-3}$. Unlike the simplest FKM case, it contains odd parity terms (resulting from the correlated hopping) in addition to even parity ones. The ground-state phase diagram of the effective Hamiltonian is examined in the $(a/t, h)$ plane, where $a/t$ is a parameter characterizing strength of the correlated hopping and $h$ is a difference of chemical potentials of two sorts of particles present in the system. It appears to be asymmetric with respect to the change $h\to -h$ and a new ordered phase is found for a certain interval of $a/t$.