STM observation of the hinge-states of bismuth nanocrystals

TL;DR

This study uses scanning tunneling spectroscopy to observe hinge-states in bismuth nanocrystals, confirming their classification as second-order topological insulators and exploring how shape and symmetry influence these states.

Contribution

First direct observation of hinge-states in bismuth nanocrystals, confirming their second-order topological insulator nature and analyzing their spatial distribution.

Findings

Hinge-states are present at facet intersections in bismuth nanocrystals.

Hinge-states are likely tunnel-coupled across nanometer-sized facets.

Bismuth nanocrystals exhibit topology-imposed hinge-states consistent with second-order topological insulators.

Abstract

The recent application of topological quantum chemistry to rhombohedral bismuth established the non-trivial band structure of this material. This is a 2$^{nd}$order topological insulator characterized by the presence of topology-imposed hinge-states. The spatial distribution of hinge-states and the possible presence of additional symmetry-protected surface-states is expected to depend on the crystal shape and symmetries. To explore this issue, we have grown bismuth nanocrystals in the tens of nanometers on the $(110)$ surface of InAs. By scanning tunneling spectroscopy, we mapped the local density of states on all facets and identified the presence of the hinge-states at the intersection of all facets. Our study confirm the classification of bulk bismuth as a 2$^{nd}$order topological insulator. We propose that the ubiquitous presence of the hinge-states result from their tunnel-coupling across the nanometer-sized facets.