Topological modes and spectral flows in inhomogeneous PT-symmetric continuous media

TL;DR

This paper demonstrates that topological modes in inhomogeneous PT-symmetric media are connected to bulk topology despite non-Hermiticity, with applications to magnetized plasma wave phenomena.

Contribution

It develops a theoretical framework linking topological modes to bulk topology in PT-symmetric non-Hermitian systems, extending topological concepts beyond Hermitian media.

Findings

Topological Alfvén-sound wave identified in magnetized plasmas.

Topological modes persist at interfaces despite non-Hermiticity.

Framework applies to classical continuous media with PT symmetry.

Abstract

In classical Hermitian continuous media, the spectral-flow index of topological modes is linked to the bulk topology via index theorem. However, the interface between two bulks is usually non-Hermitian due to the inhomogeneities of system parameters. We show that the connection between topological modes and bulk topology still exists despite the non-Hermiticity at the interface if the system is endowed with PT symmetry. The theoretical framework developed is applied to the Hall magnetohydrodynamic model to identify a topological mode called topological Alfv\'{e}n-sound wave in magnetized plasmas.