Realization of Majorana Zero Modes within a Topological Hinge State

Higher order topological insulators (HOTI) host helical edge modes along its hinges that are protected by crystal and time-reversal symmetry. Proximity induced superconductivity on these hinge states is predicted to be topological in nature and provides a platform for the realization of Majorana zero modes (MZM). Theoretical modeling shows the emergence of MZMs in the hinge states at an interface where they are influenced by superconductivity and magnetism. Recently, bismuth was identified as a HOTI where scanning tunneling microscopy (STM) studies revealed the existence of hinge states on its surface (1). To realize this MZM platform, we grow bismuth thin films and iron clusters on a niobium surface. Using high-resolution spectroscopic mapping and spin-polarized STM, we characterize the influence of superconductivity and magnetism on the hinge states. Our measurements show the presence of localized zero energy states at the interface between superconducting hinge states and the iron clusters. Comparing various measurements with theoretical models, we will discuss how our observations are consistent with the presence of MZM.

(1) F. Schindler et al., Nature Phys. 14, 918-924 (2018)