Visualizing the in-gap states in domain boundaries of ultra-thin topological insulator films

TL;DR

This study investigates the in-gap states at domain boundaries in ultra-thin topological insulator films, revealing their role in forming conduction channels that affect transport properties.

Contribution

It provides direct visualization and analysis of in-gap bound states at domain boundaries in ultra-thin topological insulators, highlighting their impact on electronic transport.

Findings

Large rotation angle boundaries host pronounced in-gap bound states.

In-gap states form one-dimensional conduction channels.

Domain boundaries significantly degrade transport properties.

Abstract

Ultra-thin topological insulators provide a platform of realizing many exotic phenomena such a Quantum spin Hall effect, Quantum anomalous Hall effect, etc. These effects or states are characterized by quantized transport behavior of edge states. Experimentally, although these states have been realized in various systems, the temperature for the edge states to be the dominating channel in transport is extremely low, contrary to the fact that the bulk gap is usually in the order of a few tens of milli-electron volts. There must be other in-gap conduction channels that won't freeze out till a much low temperature. Here we grow ultra-thin topological insulator Bi2Te3 and Sb2Te3 films by molecular beam epitaxy and investigate the structures of domain boundaries in these films. By scanning tunneling microscopy and spectroscopy we find that the domain boundaries with large rotation angles have pronounced in-gap bound states, through which one dimensional conduction channels are suggested to form as visualized by spatially resolved spectroscopy. Our work indicates the critical role played by domain boundaries in degrading the transport properties.