Statistics of the subgap states of s± superconductors

There is strong support in favor of an unusual s(+/-) superconducting state in the recently discovered iron-based superconductors in which the gap parameter has opposite signs in different bands. In this case, scattering between different bands by impurities has a pair-breaking effect and introduces states inside the gap. We studied the statistics of disorder-induced subgap states in s(+/-) superconductors due to collective effects of impurities. Numerically solving the two-band Bogolyubov equations, we explored the behavior of the density of states and localization length. We located the mobility edge separating the localized and delocalized states for the three-dimensional case and the crossover between the weak and strong localization regimes for the two-dimensional case. We found that the widely used self-consistent T-matrix approximation is not very accurate in describing subgap states.