Topological electronic states in Sb and Bi films by STS measurements and DFT calculations

Abstract

In this thesis, we combine the scanning tunneling spectroscopy (STS) and density functional theory (DFT) calculations to reveal the electronic properties in Sb and Bi films. The experiments and calculation results prove that the quantum confinement effect can help to open a bulk gap in Sb, Bi and Bi(1-x)Sb(x) films. At the same time, when the film thickness is decreased, an inter-surface coupling between upper and lower surface states cannot be neglected when the thickness of sample is reduced to nanometers. It provides limits of thickness for topological materials to preserve their topological properties. Compared with the surface states of Sb(111) film, the surface states of Bi(111) and Bi(1-x)Sb(x)(111) films have lower penetration depth. Moreover, according to the DFT and tight-binding calculation, the bulk energy gap is also tunable with the composition of Bi(1-x)Sb(x) film, which provides a greater possibility to optimize the properties of topological insulators.