Topological Phase Transitions in Disordered Electric Quadrupole Insulators

TL;DR

This paper explores how disorder can induce topological phase transitions in electric quadrupole insulators, highlighting the role of chiral symmetry in maintaining topological invariants despite broken crystalline symmetries.

Contribution

It demonstrates that chiral symmetry protects quadrupole moment quantization and enables disorder-induced topological phases in insulators.

Findings

Chiral symmetry preserves quadrupole moment quantization under disorder.

Disorder can induce nontrivial topological phases from trivial insulators.

Extended boundary states signal topological phase transitions in disordered systems.

Abstract

We investigate disorder-driven topological phase transitions in quantized electric quadrupole insulators. We show that chiral symmetry can protect the quantization of the quadrupole moment $q_{xy}$, such that the higher-order topological invariant is well-defined even when disorder has broken all crystalline symmetries. Moreover, nonvanishing $q_{xy}$ and consequent corner modes can be induced from a trivial insulating phase by disorder that preserves chiral symmetry. The critical points of such topological phase transitions are marked by the occurrence of extended boundary states even in the presence of strong disorder. We provide a systematic characterization of these disorder-driven topological phase transitions from both bulk and boundary descriptions.