Disordered topological metals

TL;DR

This paper investigates how disorder affects topological insulators, revealing that they can become gapless yet retain topological features, leading to a new phase called disordered topological metal with unique edge states and topological indices.

Contribution

It derives conditions for gaplessness in disordered topological insulators and demonstrates the survival of edge states and topological indices in the gapless phase, including in Mott topological insulators.

Findings

Edge states survive as resonances in the gapless phase

Disordered topological metals have a finite, non-quantized topological index

A phase exists where the Mott topological insulator remains ordered but gapless

Abstract

Topological behavior can be masked when disorder is present. A topological insulator, either intrinsic or interaction induced, may turn gapless when sufficiently disordered. Nevertheless, the metallic phase that emerges once a topological gap closes retains several topological characteristics. By considering the self-consistent disorder-averaged Green function of a topological insulator, we derive the condition for gaplessness. We show that the edge states survive in the gapless phase as edge resonances and that, similar to a doped topological insulator, the disordered topological metal also has a finite, but non-quantized topological index. We then consider the disordered Mott topological insulator. We show that within mean-field theory, the disordered Mott topological insulator admits a phase where the symmetry-breaking order parameter remains non-zero but the gap is closed, in complete analogy to 'gapless superconductivity' due to magnetic disorder.