Topological insulator materials for advanced optoelectronic devices

Topological insulators are quantum materials that have an insulating bulk state and a topologically protected metallic surface state with spin and momentum helical locking and a Dirac-like band structure [1-3]. Two-dimensional (2D) topological insulators are associated with gapless edge states, and three-dimensional (3D) topological insulators with gapless surface states [4]. A variety of compounds have been identified as 2D or 3D topological insulators, including HgTe/CdTe, Bi2Se3, Bi2Te3, Sb2Te3, BiTeCl, Bi1.5Sb0.5Te1.8Se1.2, SmB6 and so on [5-8]. The topological surface (edge) states in these materials have been mainly investigated by first-principle theoretical calculation, electronic transport, angle-resolved photoemission spectroscopy (ARPES), and scanning tunneling microscopy (STM) [6]. Unique and fascinating electronic properties, such as the quantum spin Hall effect, quantum anomalous Hall effect, topological magnetoelectric effect, magnetic monopole image, and Majorana fermions, have been observed in the topological insulator materials [9, 10]. With these unique properties, topological insulator materials have great potential applications in spintronics and quantum information processing, as well as magnetoelectric devices with higher efficiency and lower energy consumption [11, 12].