Monolayer superconductivity and tunable topological electronic structure at the Fe(Te,Se)/Bi 2 Te 3 interface.

The interface between two-dimensional topological Dirac states and an s-wave superconductor is expected to support Majorana bound states that can be used for quantum computing applications. Realizing these novel states of matter and their applications requires control over superconductivity and spin-orbit coupling to achieve spin-momentum locked topological surface states which are simultaneously superconducting. While signatures of Majorana bound states have been observed in the magnetic vortex cores of bulk FeTe 0.55 Se 0.45 , inhomogeneity and disorder from doping makes these signatures unclear and inconsistent between vortices. Here we report superconductivity in monolayer FeTe 1-y Se y (Fe(Te,Se)) grown on Bi 2 Te 3 by molecular beam epitaxy. Spin and angle resolved photoemission spectroscopy directly resolves the interfacial spin and electronic structure of Fe(Te,Se)/Bi 2 Te 3 heterostructures. We find that for y = 0.25 the Fe(Te,Se) electronic structure overlaps with the topological Bi 2 Te 3 interfacial states and the desired spin-momentum locking is not observed. In contrast, for y = 0.1 we find reduced inhomogeneity measured by scanning tunneling microscopy and a smaller Fe(Te,Se) Fermi surface with clear spin-momentum locking in the topological states. Hence, we demonstrate the Fe(Te,Se)/Bi 2 Te 3 system is a highly tunable platform for realizing Majorana bound states where reduced doping can improve characteristics important for Majorana interrogation and potential applications. This article is protected by copyright. All rights reserved.