Observation of oscillatory relaxation in the Sn-terminated surface of epitaxial rock-salt SnSe $\{111\}$ topological crystalline insulator

TL;DR

This study demonstrates that the Sn-terminated surface of epitaxial rock-salt SnSe {111} thin films exhibits oscillatory relaxation and hosts a high-velocity Dirac surface state, revealing new possibilities for tuning topological surface properties.

Contribution

It provides conclusive evidence of a stable Sn-terminated surface in epitaxial SnSe {111} films and links surface relaxation to the properties of Dirac surface states.

Findings

Sn-terminated surface is stable and undergoes structural relaxation.

Dirac surface state exhibits high Fermi velocity.

Surface configuration influences topological surface states.

Abstract

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe $\{111\}$ thin films. Previous studies have suggested that the Se-terminated surface of this thin film with hydrogen passivation, has a reduced surface energy and is thus a preferred configuration. In this paper, synchrotron-based angle-resolved photoemission spectroscopy, along with density functional theory calculations, are used to demonstrate conclusively that a rock-salt SnSe $\{111\}$ thin film epitaxially-grown on \ce{Bi2Se3} has a stable Sn-terminated surface. These observations are supported by low energy electron diffraction (LEED) intensity-voltage measurements and dynamical LEED calculations, which further show that the Sn-terminated SnSe $\{111\}$ thin film has undergone a surface structural relaxation of the interlayer spacing between the Sn and Se atomic planes. In sharp contrast to the Se-terminated counterpart, the observed Dirac surface state in the Sn-terminated SnSe $\{111\}$ thin film is shown to yield a high Fermi velocity, $0.50\times10^6$m/s, which suggests a potential mechanism of engineering the Dirac surface state of topological materials by tuning the surface configuration.