Revealing Dispersive Amorphous Electronic States on the Surface of a Glassy Topological Insulator*

The typical description of amorphous electronic structure assumes that a lack of translational symmetry ensures that momentum is ill-defined. This description is so 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 uncover a highly dispersive, spin-momentum locked topological surface state in amorphous Bi₂Se₃ using Angle Resolved Photoemission Spectroscopy. We observe a Fermi surface with repeated annuli suggesting Bloch-like repetition and analogous Brillouin-like zones. We argue that amorphous structures conserve real-space length-scales, allowing for the existence of well-defined momentum-space length-scales, warranting a re-evaluation of amorphous band structure on the most fundamental level.