# Dimensional crossover and topological nature of the thin films of a three-dimensional topological insulator by band gap engineering

## TL;DR

This study explores how band gap engineering via In alloying in (Bi1-xInx)2Se3 thin films induces a dimensional crossover and topological phase transition, providing insights for topological device applications.

## Contribution

It offers a comprehensive phase diagram and experimental demonstration of topological phase control in (Bi1-xInx)2Se3 films through alloying and thickness variation.

## Key findings

- Identified phases with distinct topological properties.
- Demonstrated dimensional crossover from 3D to 2D topological insulators.
- Showed topological phase transition from insulator to normal semiconductor.

## Abstract

Identification and control of topological phases in topological thin films offer great opportunity for fundamental research and the fabrication of topology-based devices. Here, combining molecular beam epitaxy, angle-resolved photoemission spectroscopy and ab-initio calculations, we investigate the electronic structure evolution in (Bi1-xInx)2Se3 films with thickness from 2 to 13 quintuple layers. We identify several phases with their characteristic topological nature and evolution between them, i.e., dimensional crossover from a three-dimensional topological insulator with gapless surface state to its two-dimensional counterpart with gapped surface state, and topological phase transition from topological insulator to a normal semiconductor with increasing In concentration x. Furthermore, by introducing In alloying as an external knob of band gap engineering, we experimentally demonstrated the trivial topological nature of Bi2Se3 thin films (below 6 quintuple layers) as two-dimensional gapped systems, in consistent with our theoretical calculations. Our results provide not only a comprehensive phase diagram of (Bi1-xInx)2Se3 and a route to control its phase evolution, but also a practical way to experimentally determine the topological properties of a gapped compound by topological phase transition and band gap engineering.

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Source: https://tomesphere.com/paper/1905.06776