Ferromagnetic phase in the polarized two-species bosonic Hubbard Model

TL;DR

This paper investigates a polarized two-species bosonic Hubbard model, revealing a stable ferromagnetic phase with phase separation and Mott behavior, characterized by finite size scaling consistent with 2D Ising universality, and discusses its experimental relevance.

Contribution

It introduces the existence of a broad-range, fully phase-separated ferromagnetic phase in a polarized two-species bosonic Hubbard model, supported by quantum Monte Carlo simulations.

Findings

Discovery of a stable ferromagnetic phase with phase separation.

Finite size scaling indicates 2D Ising universality class.

Higher entropy of this phase suggests experimental observability.

Abstract

We recently studied a doped two-dimensional bosonic Hubbard model with two hard-core species, with different masses, using quantum Monte Carlo simulations [Phys. Rev. B 88, 161101(R) (2013)]. Upon doping away from half-filling, we find several distinct phases, including a phase-separated ferromagnet with Mott behavior for the heavy species and both Mott insulating and superfluid behaviors for the light species. Introducing polarization, an imbalance in the population between species, we find a fully phase-separated ferromagnet. This phase exists for a broad range of temperatures and polarizations. By using finite size scaling of the susceptibility, we find a critical exponent which is consistent with the two-dimensional Ising universality class. Significantly, since the global entropy of this phase is higher than that of the ferromagnetic phase with single species, its experimental observation in cold atoms may be feasible.