Phase separation versus supersolid behavior in frustrated antiferromagnets

TL;DR

This paper explores the competition between spin-supersolidity and phase separation in a frustrated antiferromagnetic model, identifying conditions for stable supersolid phases and challenging previous findings on phase separation at strong frustration.

Contribution

It introduces a new criterion for distinguishing supersolid order from phase separation and maps the phase diagram using effective models and cluster mean-field methods.

Findings

Phase separation dominates at strong frustration.

Stable supersolid phase exists at intermediate frustration.

The results challenge previous claims of phase separation in the strong frustration limit.

Abstract

We investigate the competition between spin-supersolidity and phase separation in a frustrated spin-half model of weakly coupled dimers. We start by considering systems of hard-core bosons on the square lattice, onto which the low-energy physics of the herein investigated spin model can be mapped, and devise a criterion for gauging the interplay between supersolid order and domain wall formation based on strong coupling arguments. Effective bosonic models for the spin model are derived via the contractor renormalization (CORE) algorithm and we propose to combine a self-consistent cluster mean-field solution with our criterion for the occurrence of phase separation to derive the phase diagram as a function of frustration and magnetic field. In the limit of strong frustration, the model is shown to be unstable toward phase separation, in contradiction with recently published results. However, a region of stable supersolidity is identified for intermediate frustration, in a parameter range not investigated so far and of possible experimental relevance.