Visualizing topological edge states of single and double bilayer Bi supported on multibilayer Bi(111) films

TL;DR

This study combines microscopy and calculations to visualize and understand the topological edge states in Bi(111) thin films on NbSe2, clarifying their topological nature and how edge modifications influence these states.

Contribution

It provides a systematic analysis of edge states in Bi(111) films supported on NbSe2, revealing their topological origin and tunability through edge structure modifications.

Findings

Persistent edge states observed in both single and double bilayer Bi islands

Different edge structures exhibit distinct energy and spatial distributions of edge states

Clarification of the topological nature of Bi(111) thin films

Abstract

Freestanding single-bilayer Bi(111) is a two-dimensional topological insulator with edge states propagating along its perimeter. Given the interlayer coupling experimentally, the topological nature of Bi(111) thin films and the impact of the supporting substrate on the topmost Bi bilayer are still under debate. Here, combined with scanning tunneling microscopy and first-principles calculations, we systematically study the electronic properties of Bi(111) thin films grown on a NbSe2 substrate. Two types of non-magnetic edge structures, i.e., a conventional zigzag edge and a 2x1 reconstructed edge, coexist alternately at the boundaries of single bilayer islands, the topological edge states of which exhibit remarkably different energy and spatial distributions. Prominent edge states are persistently visualized at the edges of both single and double bilayer Bi islands, regardless of the underlying thickness of Bi(111) thin films. We provide an explanation for the topological origin of the observed edge states that is verified with first-principles calculations. Our paper clarifies the long-standing controversy regarding the topology of Bi(111) thin films and reveals the tunability of topological edge states via edge modifications.