Competing topological superconducting phases in FeSe_0.45Te0.55

We demonstrate that recent angle-resolved photoemission spectroscopy experiments provide strong evidence for the existence of two competing topological superconducting phases in FeSe0.45Te0.55. The coupling of their underlying microscopic mechanisms-one based on a three-dimensional topological insulator, one based on two-dimensional superconductivity-stabilizes topological superconductivity over a wide range of parameters, and gives rise to two disjoint topological regions in the phase diagram of FeSe0.45Te0.55. We show that the topological origin of these regions can be identified by considering the form of Majorana edge modes at domain walls.