Unlike time-reversal topological insulators, surface metallic states with Dirac cone dispersion in the recently discovered topological crystalline insulators (TCIs) are protected by crystal symmetry. To date, TCI behaviors have been observed in SnTe and the related alloys Pb1−xSnxSe/Te, which incorporate heavy elements with large spin-orbit coupling (SOC). Here, by combining first-principles and {\it ab initio} tight-binding calculations, we report the formation of a TCI in the relatively lighter rock-salt SnS and SnSe. This TCI is characterized by an even number of Dirac cones at the high-symmetry (001), (110) and (111) surfaces, which are protected by the reflection symmetry with respect to the (1ˉ10) mirror plane. We find that both SnS and SnSe have an intrinsically inverted band structure and the SOC is necessary only to open the bulk band gap. The bulk band gap evolution upon volume expansion reveals a topological transition from an ambient pressure TCI to a topologically trivial insulator. Our results indicate that the SOC alone is not sufficient to drive the topological transition.
@article{arxiv.1308.5657,
title = {Rock-salt SnS and SnSe: Native Topological Crystalline Insulators},
author = {Yan Sun and Zhicheng Zhong and Tomonori Shirakawa and Cesare Franchini and Dianzhong Li and Yiyi Li and Seiji Yunoki and Xing-Qiu Chen},
journal= {arXiv preprint arXiv:1308.5657},
year = {2015}
}