Wavefront dislocations reveal the topology of quasi-1D photonic insulators

TL;DR

This paper experimentally demonstrates that wavefront dislocations in 1D microwave insulators serve as topological markers, linking wavefront phase singularities to the topological classification of insulators.

Contribution

It introduces the observation of wavefront dislocations as a topological indicator in quasi-1D photonic insulators, bridging wavefront singularities with topological phases.

Findings

Wavefront dislocations appear at topological phase transitions.

The change in interference fringes reveals the topological index.

Experimental evidence links phase singularities to topological properties.

Abstract

Phase singularities appear ubiquitously in wavefields, regardless of the wave equation. Such topological defects can lead to wavefront dislocations, as observed in a humongous number of classical wave experiments. Phase singularities of wave functions are also at the heart of the topological classification of the gapped phases of matter. Despite identical singular features, topological insulators and topological defects in waves remain two distinct fields. Realising 1D microwave insulators, we experimentally observe a wavefront dislocation - a 2D phase singularity - in the local density of states when the systems undergo a topological phase transition. We show theoretically that the change in the number of interference fringes at the transition reveals the topological index that characterises the band topology in the insulator.