Tailoring the topological surface state in ultrathin $\alpha$-Sn (111) films

TL;DR

This study investigates the electronic structure of ultrathin $ ext{α}$-Sn (111) films, revealing tunable topological surface states and hybridization gaps that depend on film thickness, with implications for topological edge states.

Contribution

It provides direct experimental observation and theoretical analysis of topological surface states in ultrathin $ ext{α}$-Sn films, highlighting the effects of film thickness on their electronic properties.

Findings

Topological surface states observed between valence and conduction bands.

Dirac point located 200 meV below Fermi level in 10-nm films.

Hybridization gap opens at the Dirac point in thinner films.

Abstract

We report on the electronic structure of $\alpha$-Sn films in the very low thickness regime grown on InSb(111)A. High-resolution low photon energies angle-resolved photoemission (ARPES) allows for the direct observation of the linearly dispersing 2D topological surface states (TSSs) that exist between the second valence band and the conduction band. The Dirac point of this TSS was found to be 200meV below the Fermi level in 10-nm-thick $\alpha$-Sn films, which enables the observation of the hybridization gap opening at the Dirac point of the TSS for thinner films. The crossover to a quasi-2D electronic structure is accompanied by a full gap opening at the Brillouin zone center, in agreement with our density functional theory calculations. We further identify the thickness regime of $\alpha$-Sn films where the hybridization gap in TSS coexists with the topologically non-trivial electronic structure and one can expect the presence of a 1D helical edge states.