Thickness Dependence of the Energy Band Structure and Topological Property of Topological Crystalline Insulator SnTe Films

A topological crystalline insulator (TCI) is characterized by gapless surface states that are protected by the crystalline symmetry. For an enough thin film of three-dimensional TCI, the top and bottom surface states hybridize, opening up an energy gap at the Dirac surface states. According to theoretical prediction, the quantum spin Hall (QSH) phase may occur in such a film of certain thickness, and the topological phase diagram is dependent on the electrical field perpendicular to the film plane. Here we present a systematic angle-resolved photoemission spectroscopy (ARPES) study on molecular beam epitaxy-grown TCI SnTe (111) films with different thicknesses and on different substrates. A thickness-dependent oscillation of the surface state gap was observed in the films and was found to strongly depend on the substrate used. The origin of the oscillation and its relationship with topological phase transitions were discussed.