Phase diagram of two-component bosons on an optical lattice

TL;DR

This paper develops a new theoretical framework to analyze the phase diagram of two-component bosons in optical lattices, revealing complex phase transitions influenced by spin interactions and fluctuations.

Contribution

A novel formalism that simultaneously treats spin interactions in Mott and superfluid phases, enabling detailed phase boundary mapping and prediction of first-order transitions.

Findings

Spin exchange can be very large near the transition, aiding experimental realization.

Spin and quantum fluctuations can induce first-order phase transitions.

Competition between exchange and on-site interactions leads to additional spin-ordered phases.

Abstract

We present a theoretical analysis of the phase diagram of two--component bosons on an optical lattice. A new formalism is developed which treats the effective spin interactions in the Mott and superfluid phases on the same footing. Using the new approach we chart the phase boundaries of the broken spin symmetry states up to the Mott to superfluid transition and beyond. Near the transition point, the magnitude of spin exchange can be very large, which facilitates the experimental realization of spin-ordered states. We find that spin and quantum fluctuations have a dramatic effect on the transition making it first order in extended regions of the phase diagram. For Mott states with even occupation we find that the competition between effective Heisenberg exchange and spin-dependent on--site interaction leads to an additional phase transition from a Mott insulator with no broken symmetries into a spin-ordered insulator.