Supersolidity, entropy and frustration

TL;DR

This paper investigates the phase diagram of a hard-core boson model on a triangular lattice, revealing novel supersolid phases, phase transitions, and entropic effects due to geometric frustration, with implications for optical lattice experiments.

Contribution

It provides the first detailed analysis of supersolid phases and phase transitions in the t-t'-V model on a triangular lattice, including the effects of temperature and frustration.

Findings

Identification of a supersolid phase with (x,x,-2x') ordering

Discovery of a first-order transition from SS A to SS C supersolid

Observation of a Pomeranchuk-like effect where superfluidity turns into solid with increasing temperature

Abstract

We study the properties of t-t'-V model of hard-core bosons on the triangular lattice that can be realized in optical lattices. By mapping to the spin-1/2 XXZ model in a field, we determine the phase diagram of the t-V model where the supersolid characterized by the ordering pattern (x,x,-2x') ("ferrimagnetic" or SS A) is a ground state for chemical potential \mu >3V. By turning on either temperature or t' at half-filling \mu =3V, we find a first order transition from SS A to the elusive supersolid characterized by the (x,-x,0) ordering pattern ("antiferromagnetic" or SS C). In addition, we find a large region where a superfluid phase becomes a solid upon raising temperature at fixed chemical potential. This is an analog of the Pomeranchuk effect driven by the large entropic effects associated with geometric frustration on the triangular lattice.