Commensurate Magnetic and Superconducting Transitions in a Candidate Topological Superconductor

We propose to understand the interplay between superconductivity and magnetism in the candidate topological superconductor heterostructure system composed of Cr-doped (Bi,Sb)2Te3 (CBST) and FeTe. CBST is a magnetic topological insulator while FeTe is an antiferromagnetic analogue of the well-know superconductor FeSe. Individually non-superconducting, these elements manifest an emergent interfacial superconductivity when interfaced. Our preliminary muon spin relaxation (µSR) data and scanning tunneling microscopy indicates that magnetism and topologically nontrivial surface states are preserved in the superconducting state. The combination of magnetism, superconductivity, topologically protected chiral surface states makes these systems ideal candidates for realizing Majorana physics. Even more interesting, our µSR data suggests that a transition to a henceforce unknown magnetic ground state in the FeTe is critical for supporting the superdoncutivity, raising the possibility that CBST/FeTe is a spin-triplet superconductor. It is of course critical to understand the magnetic transition revealed by µSR, and we consequently propose to perform thin film neutron diffraction on WISH to precisely identify how the magnetic ground state evolves across the superconducting transition.