Coexistence and Competition between topological superconducting phases in FeSe_0.45Te_0.55

Identifying the microscopic origin of topological superconductivity in FeSe_0.45Te_0.55 has remained an open question. This origin was initially proposed to arise from a band-inversion involving the bulk p_z and d_xz-bands -- rendering FeSe_0.45Te_0.55 a 3D topological insulator -- and the gapping of the ensuing surface Dirac cone by proximity induced superconductivity (the 3DTI mechanism) However, recent ARPES and quantum sensing experiments have reported strong evidence for the existence of ferromagnetism on the surface of FeSe_0.45Te_0.55. This has opened a new path to the emergence of topological surface superconductivity in FeSe_0.45Te_0.55 as arising from the interplay of ferromagnetism, a superconducting gap of s_±-wave symmetry, and a Rashba spin-orbit interaction. In this talk, I will discuss the physical properties and topological phases that arise from the coexistence and competition between the two potential mechanisms. In particular, I will demonstrate that their coupling can lead to a suppression of the topological phase arising from the 3DTI mechanism, and will discuss the experimental signatures of such suppression.