Superfluid-insulator transitions of two-species Bosons in an optical lattice

TL;DR

This paper investigates the superfluid-insulator transition in a two-species bosonic Hubbard model, revealing complex phase behaviors and transitions influenced by interspecies interactions, with results supported by mean-field and quantum Monte Carlo methods.

Contribution

It provides a detailed phase diagram for odd filling cases, including novel transition types and the impact of quantum fluctuations, using a combined mean-field and Monte Carlo approach.

Findings

Superfluid-insulator transition can be first order in large phase diagram regions.

Distinct transition scenarios depending on filling and species coexistence.

Quantum fluctuations significantly affect the phase boundaries.

Abstract

We consider a realization of the two-species bosonic Hubbard model with variable interspecies interaction and hopping strength. We analyze the superfluid-insulator (SI) transition for the relevant parameter regimes and compute the ground state phase diagram for odd filling at commensurate densities. We find that in contrast to the even commensurate filling case, the superfluid-insulator transition occurs with (a) simultaneous onset of superfluidity of both species or (b) coexistence of Mott insulating state of one species and superfluidity of the other or, in the case of unit filling, (c) complete depopulation of one species. The superfluid-insulator transition can be first order in a large region of the phase diagram. We develop a variational mean-field method which takes into account the effect of second order quantum fluctuations on the superfluid-insulator transition and corroborate the mean-field phase diagram using a quantum Monte Carlo study.