Evidence for topological surface states in amorphous Bi₂Se₃

Crystalline symmetries and classification schemes have played a central role in the identification of topological materials [1-3]. We address whether amorphous topological materials, which lie beyond this classification, exist in the solid state [4]. Amorphous Bi₂Se₃ thin films show a metallic behavior and an increased bulk resistance. The low field magnetoresistance due to weak antilocalization reveals a significant number of two-dimensional surface conduction channels. Angle-resolved photoemission spectroscopy data is consistent with a dispersive two-dimensional surface state with a distinct node. Spin resolved photoemission spectroscopy shows this state has an anti-symmetric spin-texture resembling that of the surface state of crystalline Bi₂Se₃. Experimental results are consistent with an amorphous tight-binding model that utilizes a realistic amorphous structure. Evidence of amorphous materials with topological properties uncovers topological matter outside the current classification scheme, enabling materials discovery and scalable topological devices.
[1] T. Zhang, et al., Nature 566, 475 (2019)
[2] M. G. Vergniory, et al., Nature 566, 480 (2019)
[3] F. Tang, et al., Nature 566, 486 (2019)
[4] P. Corbae, et al., submitted (2019)