Persistence of phase boundaries between a topological and trivial Z2 insulator

TL;DR

This paper reveals that phase boundaries between topological and trivial insulators can persist without time reversal symmetry, forming gapless regions and enclosing Chern phases, which are robust to disorder and interactions.

Contribution

It demonstrates the persistence of phase boundary regions without time reversal symmetry and explains their topological origin through quantized charge pumping.

Findings

Gapless regions from phase boundaries persist without time reversal symmetry.

Enclosed Chern insulating phases of finite extent appear at the phase boundaries.

The effect is robust against disorder and interactions.

Abstract

When time reversal symmetry is present there is a sharp distinction between topological and trivial band insulators which ensures that, as parameters are varied, these phases are separated by a phase transition at which the bulk gap closes. Surprisingly we find that even in the absence of time reversal symmetry, gapless regions originating from the phase boundaries persist. Moreover the critical line generically opens up to enclose Chern insulating phases that are thin but of finite extent in the phase diagram. We explain the topological origin of this effect in terms of quantized charge pumping, showing in particular that it is robust to the effect of disorder and interactions.