- Corbae, Paul;
- Ciocys, Samuel;
- Varjas, Dániel;
- Kennedy, Ellis;
- Zeltmann, Steven;
- Molina-Ruiz, Manel;
- Griffin, Sinéad M;
- Jozwiak, Chris;
- Chen, Zhanghui;
- Wang, Lin-Wang;
- Minor, Andrew M;
- Scott, Mary;
- Grushin, Adolfo G;
- Lanzara, Alessandra;
- Hellman, Frances
Crystalline symmetries have played a central role in the identification and understanding of quantum materials. Here we investigate whether an amorphous analogue of a well known three-dimensional strong topological insulator has topological properties in the solid state. We show that amorphous Bi2Se3 thin films host a number of two-dimensional surface conduction channels. Our angle-resolved photoemission spectroscopy data are consistent with a dispersive two-dimensional surface state that crosses the bulk gap. Spin-resolved photoemission spectroscopy shows this state has an anti-symmetric spin texture, confirming the existence of spin-momentum locked surface states. We discuss these experimental results in light of theoretical photoemission spectra obtained with an amorphous topological insulator tight-binding model, contrasting it with alternative explanations. The discovery of spin-momentum locked surface states in amorphous materials opens a new avenue to characterize amorphous matter, and triggers the search for an overlooked subset of quantum materials outside of current classification schemes.