 
Summary: Statistics of the subgap states of są superconductors
A. Glatz and A. E. Koshelev
Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, USA
Received 8 June 2010; published 21 July 2010
There is strong support in favor of an unusual s superconducting state in the recently discovered ironbased
superconductors in which the gap parameter has opposite signs in different bands. In this case, scattering
between different bands by impurities has a pairbreaking effect and introduces states inside the gap. We
studied the statistics of disorderinduced subgap states in s superconductors due to collective effects of
impurities. Numerically solving the twoband 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 threedimensional case and the crossover between the weak and strong localization regimes for the
twodimensional case. We found that the widely used selfconsistent Tmatrix approximation is not very
accurate in describing subgap states.
DOI: 10.1103/PhysRevB.82.012507 PACS number s : 74.20. z, 74.62.En, 74.70.Xa
The recent discovery of hightemperature superconductiv
ity in the iron arsenide LaFeAsO1xFx Ref. 1 followed by
the discovery of several classes of superconducting
materials2
led to a major breakthrough in the field of super
conductivity. The Fermi surface of these materials is com
