Topological superconductivity facilitated by exchange interaction on the surface of FeTe_0.5Se_0.5

FeTe_1-xSe_xis a family of iron-based superconductors with a well-known critical temperature (T _c) of 14.5 K for x = 0.45. Also well-established is the presence of topological surface states of FeTe_0.55Se_0.45in which topological superconductivity sets in. By using density functional calculations and the Bardeen-Cooper-Schrieffer (BCS) theory for traditional superconductors we calculated the T _cof the surface layers of FeTe_0.5Se_0.5with the exchange interaction as the source of attractive force to form the Cooper pairs. The estimated T _cis in reasonable agreement with the experimental value and suggests that the exchange interaction is behind the topological superconductivity on the surface of FeTe_0.55Se_0.45