Partial chiral symmetry-breaking as a route to spectrally isolated topological defect states in two-dimensional artificial materials

TL;DR

This paper demonstrates how partial breaking of chiral symmetry in two-dimensional artificial materials can create spectrally isolated topological defect states, verified through microwave experiments on a dimerized Lieb lattice.

Contribution

It introduces a natural reduction of chiral symmetry to isolate topological defect states in 2D systems, supported by experimental microwave realizations.

Findings

Spectrally isolated zero modes are achieved by coupling sites on the majority sublattice.

Topological defect states are supported by the minority sublattice.

Topological mode selection is demonstrated via sublattice-staggered absorption.

Abstract

Bipartite quantum systems from the chiral universality classes admit topologically protected zero modes at point defects. However, in two-dimensional systems these states can be difficult to separate from compacton-like localized states that arise from flat bands, formed if the two sublattices support a different number of sites within a unit cell. Here we identify a natural reduction of chiral symmetry, obtained by coupling sites on the majority sublattice, which gives rise to spectrally isolated point-defect states, topologically characterized as zero modes supported by the complementary minority sublattice. We observe these states in a microwave realization of a dimerized Lieb lattice with next-nearest neighbour coupling, and also demonstrate topological mode selection via sublattice-staggered absorption.