Competing topological superconducting phases in FeSe0.45Te0.55

We demonstrate that recent angle-resolved photoemission spectroscopy experiments provide strong evidence for the existence of two competing topological superconducting phases in ${\mathrm{FeSe}}_{0.45}{\mathrm{Te}}_{0.55}$. 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 ${\mathrm{FeSe}}_{0.45}{\mathrm{Te}}_{0.55}$. We show that the topological origin of these regions can be identified by considering the form of Majorana edge modes at domain walls.