Tunable topological edge states in black phosphorus-like Bi(110)

TL;DR

This study demonstrates that manipulating surface atom buckling in ultrathin Bi(110) films can control topological phase transitions, revealing robust edge states and paving the way for topological superconductor applications.

Contribution

It provides experimental validation and theoretical analysis of how surface buckling controls topological phases in Bi(110) films, with implications for quantum device engineering.

Findings

Robust edge states observed at 3- and 4-BL Bi(110) films.

Surface buckling decreases with increasing film thickness.

Transition from trivial to non-trivial topological phase occurs beyond 2 layers.

Abstract

We have investigated the structures and electronic properties of ultra-thin Bi(110) films grown on an s-wave superconductor substrate using low-temperature scanning tunneling microscopy and spectroscopy. Remarkably, our experimental results validate the theoretical predictions that the manipulation of Bi(110) surface atom buckling can control the topological phase transition. Notably, we have observed robust unreconstructed edge states at the edges of both 3-bilayer (BL) and 4-BL Bi(110) films, with the 4-BL film displaying stronger edge state intensity and a smaller degree of atomic buckling. First-principle calculations further substantiate these findings, demonstrating a gradual reduction in buckling as the film thickness increases, with average height differences between two Bi atoms of approximately 0.19 {\AA}, 0.10 {\AA}, 0.05 {\AA}, and 0.00 {\AA} for the 1-BL, 2-BL, 3-BL, and 4-BL Bi(110) films, respectively. When Bi films are larger than 2 layers, the system changes from a trivial to a non-trivial phase. This research sets the stage for the controlled realization of topological superconductors through the superconducting proximity effect, providing a significant platform for investigating Majorana zero modes and fabricating quantum devices.