Superfluid density and penetration depth in the iron pnictides

We consider the superfluid density rho(s)(T) in a two-band superconductor with sign-changing extended s-wave symmetry (s(+)) in the presence of nonmagnetic impurities and apply the results to Fe-pnictides. We show that the behavior of the superfluid density is essentially the same as in an ordinary s-wave superconductor with magnetic impurities. We show that, for moderate to strong interband impurity scattering, rho(s)(T) behaves as a power law T(n) with n approximate to 1.6/2 over a wide range of T. We argue that the power-law behavior is consistent with recent experiments on the penetration depth lambda(T) in doped BaFe(2)As(2) but disagrees quantitatively with the data on LaFePO.