Interaction Driven Quantum Phase Transitions in Fractional Topological Insulators

TL;DR

This paper investigates the phase transitions in fractional topological insulators with two fermion species under magnetic fields, revealing stable FTI phases, phase separation, superfluidity, and the nature of the phase transition.

Contribution

It provides a detailed phase diagram and characterizes the FTI-superfluid transition as a (2+1)D XY universality class using effective field theory.

Findings

FTI phase stable against moderate inter-species interactions

Strong inter-species repulsion causes phase separation

Strong inter-species attraction induces superfluid phase

Abstract

We study two species of (or spin-1/2) fermions with short-range intra-species repulsion in the presence of opposite (effective) magnetic field, each at Landau level filling factor 1/3. In the absence of inter-species interaction, the ground state is simply two copies of the 1/3 Laughlin state, with opposite chirality, representing the fractional topological insulator (FTI) phase. We show this phase is stable against moderate inter-species interactions. However strong enough inter-species repulsion leads to phase separation, while strong enough inter-species attraction drives the system into a superfluid phase. We obtain the phase diagram through exact diagonalization calculations. The FTI-superfluid phase transition is shown to be in the (2+1)D XY universality class, using an appropriate Chern-Simons-Ginsburg-Landau effective field theory.