Superfluid density and penetration depth in the iron pnictides

Abstract

We consider the superfluid density ${\ensuremath{\rho}}_{s}(T)$ 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, ${\ensuremath{\rho}}_{s}(T)$ behaves as a power law ${T}^{n}$ with $n\ensuremath{\approx}1.6\textdiv{}2$ over a wide range of $T$. We argue that the power-law behavior is consistent with recent experiments on the penetration depth $\ensuremath{\lambda}(T)$ in doped ${\text{BaFe}}_{2}{\text{As}}_{2}$ but disagrees quantitatively with the data on LaFePO.