Electronic Structure of the Metastable Epitaxial Rock-Salt SnSe {111} Topological Crystalline Insulator

Topological crystalline insulators have been recently predicted and observed in rock-salt structure SnSe f111g 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, is used to demonstrate that a rock-salt SnSe f111g thin film epitaxially grown on 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 f111g 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 f111g thin film is shown to yield a high Fermi velocity, 0.50 × 106 m=s, which suggests a potential mechanism of engineering the Dirac surface state of topological materials by tuning the surface configuration.