Probing topological invariants in the bulk of a non-Hermitian optical system

TL;DR

This paper demonstrates a method to probe topological invariants directly in the bulk of a non-Hermitian optical system, bypassing surface measurements, which could be applicable to various physical systems.

Contribution

It introduces an experimental approach to detect topological transitions using bulk properties in non-Hermitian systems, expanding the tools for topological characterization.

Findings

Successful demonstration of bulk-based topological transition detection

Utilization of non-Hermiticity to access bulk topological properties

Potential applicability to other physical systems with challenging surface probing

Abstract

Topological insulators are insulating in the bulk but feature conducting states on their surfaces. Standard methods for probing their topological properties largely involve probing the surface, even though topological invariants are defined via the bulk band structure. Here, we utilize non-hermiticy to experimentally demonstrate a topological transition in an optical system, using bulk behavior only, without recourse to surface properties. This concept is relevant for a wide range of systems beyond optics, where the surface physics is difficult to probe.