Scattering theory of higher order topological phases

TL;DR

This paper develops a scattering theory approach to detect higher order topological phases by analyzing flux-dependent reflection matrices, overcoming previous limitations related to symmetry and geometry.

Contribution

It introduces a symmetric scattering geometry and flux-based spectral flow method to identify higher order topological phases, extending the bulk--edge correspondence framework.

Findings

Flux dependence of reflection matrix signals higher order topology

Spectral flow of flux line indicates topological phase

Applicable to topological insulators and superconductors with disorder

Abstract

The surface states of intrinsic higher order topological phases are protected by the spatial symmetries of a finite sample. This property makes the existing scattering theory of topological invariants inapplicable because the scattering geometry is either incompatible with the symmetry or does not probe the bulk topology. We resolve this obstacle by using a symmetric scattering geometry that probes transport from the inside to the outside of the sample. We demonstrate that the intrinsic higher order topology is captured by the flux dependence of the reflection matrix. Our finding follows from identifying the spectral flow of a flux line as a signature of higher order topology. We show how this scattering approach applies to several examples of higher order topological insulators and superconductors. Our theory provides an alternative approach for proving bulk--edge correspondence in intrinsic higher order topological phases, especially in presence of disorder.