Ground state phase diagram of the one-dimensional t-J model with pair hopping terms

The t-J model is a standard model of strongly correlated electrons, often studied in the context of high-Tc superconductivity. However, most studies of this model neglect three-site terms, which appear at the same order as the superexchange J. As these terms correspond to pair-hopping, they are expected to play an important role in the physics of superconductivity when doped sufficiently far from half-filling. In this paper we present a density matrix renormalisation group study of the one-dimensional t-J model with the pair hopping terms included. We demonstrate that that these additional terms radically change the one-dimensional ground state phase diagram, extending the superconducting region at low fillings, while at larger fillings, superconductivity is completely suppressed. We explain this effect by introducing a simplified effective model of repulsive hardcore bosons.