Strongly Interacting Two-component Coupled Bose Gas in Optical Lattices

TL;DR

This paper investigates a two-component Bose gas in a 1D optical lattice, revealing how coupling alters spin phases, induces new phase transitions, and showcases complex spin correlations through advanced computational methods.

Contribution

It introduces a new effective spin Hamiltonian for coupled Bose gases and demonstrates the impact of coupling on spin phase transitions using exact diagonalization and VMC methods.

Findings

Coupling changes the nature of spin phase transitions from first-order to second-order.

Emergence of two spin phases with second-order transition for comparable interactions.

Enhanced understanding of spin correlations beyond mean-field approximations.

Abstract

Two-component coupled Bose gas in a 1D optical lattice is examined. In addition to the postulated Mott insulator and superfluid phases, multiple bosonic components manifest spin degrees of freedom. Coupling of the components in the Bose gas leads to substantial change in the previously observed spin phases, giving rise to new effective spin Hamiltonian and unraveling remarkable spin correlations. The system exhibiting ferromagnetic and non-ferromagnetic spin phases for on-site intra-component interaction stronger than inter-component interaction switches from first-order to second-order phase transition between the spin phases upon introduction of coupling, on which is dependent the transition width. For comparable on-site inter- and intra- component interaction, with coupling, instead of one, two spin phases emerge with a second-order phase transition. Exact diagonalization and Variational Monte Carlo (VMC) with stochastic minimization on Entangled Plaquette State (EPS) bestow a unique and enhanced perspective into the system beyond the scope of a mean-field treatment.