Probing chiral symmetry with a topological domain wall sensor

TL;DR

This paper demonstrates how topological defects can reveal broken chiral symmetry in materials with spectral symmetry, using high-resolution STM/STS to observe spectral imbalances at domain walls in topological crystalline insulators.

Contribution

It introduces a method to differentiate chiral symmetry breaking from spectral symmetry preservation via topological defect analysis in condensed matter systems.

Findings

Spectral imbalance in Landau levels indicates chiral symmetry breaking.

Topological defects induce shifts in Landau orbital guiding centers.

Chiral flow of spectral density observed at step edges.

Abstract

Chiral symmetry is a fundamental property with profound implications for the properties of elementary particles, that implies a spectral symmetry (i.e. E => -E ) in their dispersion relation. In condensed matter physics, chiral symmetry is frequently associated with superconductors or materials hosting Dirac fermions such as graphene or topological insulators. There, chiral symmetry is an emergent low-energy property, accompanied by an emergent spectral symmetry. While the chiral symmetry can be broken by crystal distortion or external perturbations, the spectral symmetry frequently survives. As the presence of spectral symmetry does not necessarily imply chiral symmetry, the question arises how these two properties can be experimentally differentiated. Here, we demonstrate how a system with preserved spectral symmetry can reveal underlying broken chiral symmetry using topological defects. Our study shows that these defects induce a spectral imbalance in the Landau level spectrum, providing direct evidence of symmetry alteration at topological domain walls. Using high-resolution STM/STS we demonstrate the intricate interplay between chiral and translational symmetry which is broken at step edges in topological crystalline insulator Pb$_{1-x}$Sn$_x$Se. The chiral symmetry breaking leads to a shift in the guiding center coordinates of the Landau orbitals near the step edge, thus resulting in a distinct chiral flow of the spectral density of Landau levels. This study underscores the pivotal role of topological defects as sensitive probes for detecting hidden symmetries, offering profound insights into emergent phenomena with implications for fundamental physics.