Statistics and localization of subgap states in superconductors with sign-changing order parameter

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Date/Time:Thursday, 15 Apr 2010 from 4:10 pm to 5:00 pm
Location:Physics 5
Phone:515-294-0849
Channel:Condensed Matter Physics
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Dr. Alexei Koshelev (Argonne National Laboratory, US DOE)

There is strong theoretical reasoning in favor of an unusual s+- superconducting state in recently discovered iron-based superconductors. The order parameter in such a state has different signs in the electron and hole Fermi pockets. In this situation scattering between different pockets by impurities has 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 for the two-dimensional and three-dimensional
models, we computed the precise density of states and explored its dependence on concentration of impurities and strengths of the interband and intraband scattering. We also explored behavior of the localization length and located mobility edge separating the localized and delocalized states (3D case) or an abrupt crossover between the weak and strong localization regimes (2D case). For 3D case at certain impurity concentrations depending on scattering parameters, the mobility edge reaches zero energy and all states become delocalized. We found that the widely used self-consistent T-matrix
approximation is incomplete and not very accurate in describing subgap states.