Temperature-induced spontaneous time-reversal symmetry breaking on the honeycomb lattice

TL;DR

This paper demonstrates that on the honeycomb lattice, increasing temperature can induce a stable, uniform metallic phase with broken time-reversal symmetry due to thermally excited intraband particle-hole pairs, challenging conventional expectations.

Contribution

It provides an exact mean-field expression for the equation of state at low temperatures and reveals a novel temperature-induced symmetry-breaking phase transition.

Findings

Thermally excited intraband particle-hole pairs can stabilize time-reversal symmetry breaking.

A closed-form mean-field equation of state is derived for low temperatures.

Temperature can induce a non-trivial metallic phase on the honeycomb lattice.

Abstract

Phase transitions involving spontaneous time-reversal symmetry breaking are studied on the honeycomb lattice at finite hole-doping with next-nearest-neighbor repulsion. We derive an exact expression for the mean-field equation of state in closed form, valid at temperatures much less than the Fermi energy. Contrary to standard expectations, we find that thermally induced intraband particle-hole excitations can create and stabilize a uniform metallic phase with broken time-reversal symmetry as the temperature is "raised" in a region where the groundstate is a trivial metal.