Observation of nontrivial topological electronic structure of orthorhombic SnSe

Topological electronic structures are key to the topological classification of quantum materials and play an important role in their physical properties and applications. Recently, SnSe has attracted great research interest due to its superior thermoelectric performance. However, its topological nature has long been ignored. In this work, by combining synchrotron-based angle-resolved photoemission spectroscopy and ab initio calculations, we systematically investigate the topological electronic structure of orthorhombic SnSe. By identifying the continuous gap in the valence bands due to the band inversion and the topological surface states on its (001) surface, we establish SnSe as a strong topological insulator. Furthermore, we study the evolution of the topological electronic structure and propose the topological phase diagram in SnSe1-xTex. Our work reveals the topological nontrivial nature of SnSe and provides understandings of its intriguing transport properties.