Eur. Phys. J. B (2012) 85: 169
https://doi.org/10.1140/epjb/e2012-30055-9

Regular Article

Finite temperature phase diagram of spin-1/2 bosons in two-dimensional optical lattice

¹ INLN, Université de Nice-Sophia Antipolis, CNRS, 1361 route des Lucioles, 06560 Valbonne, France
² Department of Physics and Astronomy, Louisiana State University, Bâton Rouge, 70803 Louisiana, USA
³ Institut Universitaire de France, 103 boulevard Saint Michel, 75005 Paris, France
⁴ Centre for Quantum Technologies, National University of Singapore, 2 Science Drive 3, 117542 Singapore, Singapore

^a e-mail: frederic.hebert@inln.cnrs.fr

Received: 22 January 2012
Published online: 28 May 2012

Abstract

We study a two-species bosonic Hubbard model on a two-dimensional square lattice by means of quantum Monte Carlo simulations and focus on finite temperature effects. We show in two different cases, ferro- and antiferromagnetic spin-spin interactions, that the phase diagram is composed of a superfluid phase and an unordered phase that can be separated into weakly compressible Mott insulators regions and compressible Bose liquid regions. The superfluid-liquid transitions are of the Berezinsky-Kosterlitz-Thouless type whereas the insulator-liquid passages are crossovers. We analyse the pseudo-spin correlations that are present in the different phases, focusing particularly on the existence of a polarization in this system.