Electric Field Tuning of the Surface Band Structure of Topological Insulator Sb2Te3 Thin Films

TL;DR

This study demonstrates electric field control over the surface state spectrum of Sb2Te3 thin films, revealing a tunable topological phase transition and a surface band gap in ultra-thin films, advancing topological insulator research.

Contribution

It provides experimental evidence of electric field tuning of surface states and topological phase transitions in Sb2Te3 thin films, with a detailed theoretical explanation.

Findings

Gate electric fields shift the Fermi level in Sb2Te3 films.

A gap opens at the Dirac point in films thinner than four quintuple layers.

The top surface state band gap is tunable by back gate in three quintuple layer films.

Abstract

We measured the response of the surface state spectrum of epitaxial Sb2Te3 thin films to applied gate electric fields by low temperature scanning tunneling microscopy. The gate dependent shift of the Fermi level and the screening effect from bulk carriers vary as a function of film thickness. We observed a gap opening at the Dirac point for films thinner than four quintuple layers, due to the coupling of the top and bottom surfaces. Moreover, the top surface state band gap of the three quintuple layer films was found to be tunable by back gate, indicating the possibility of observing a topological phase transition in this system. Our results are well explained by an effective model of 3D topological insulator thin films with structure inversion asymmetry, indicating that three quintuple layer Sb2Te3 films are topologically nontrivial and belong to the quantum spin Hall insulator class.