Atypical Highly-Dispersive Band Structure in Putative Amorphous Topological Insulator*

In typical amorphous and highly disordered materials, Anderson Localization guarantees flat valence bands. This effect is so dramatic and pervasive in the amorphous field of study that the density of states is assumed to be momentum-independent, serving as the full characterization of an amorphous system's electronic structure. In this work, we discover an exception to this rule in amorphous Bi₂Se₃ films. Angle-resolved photoemission spectroscopy uncovers an amorphous surface-state band structure with strong momentum-dependence and spin-momentum locking. We observe a Fermi surface with repeated annuli and reveal a spherically-parameterized momentum-space picture that warrants a re-evaluation of amorphous band structure on the most fundamental level.