# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1704.02928