London penetration depth and strong pair breaking in iron-based superconductors

Abstract

The low-temperature variation in the London penetration depth for a number of iron-pnictide and iron-chalcogenide superconductors is nearly quadratic, $\ensuremath{\Delta}\ensuremath{\lambda}(T)=\ensuremath{\beta}{T}^{n}$ with $n\ensuremath{\approx}2$. The coefficient in this dependence shows a robust scaling, $\ensuremath{\beta}\ensuremath{\propto}1/{T}_{c}^{3}$ across different families of these materials. We associate the scaling with a strong pair breaking. The same mechanism has recently been suggested to explain the scalings of the specific-heat jump, $\ensuremath{\Delta}C\ensuremath{\propto}{T}_{c}^{3}$ [Bud'ko et al., Phys. Rev. B 79, 220516(R) (2009)], and the slopes of the upper critical field, $d{H}_{c2}/dT\ensuremath{\propto}{T}_{c}$ in these materials [Kogan, Phys. Rev. B 80, 214532 (2009)]. This suggests that thermodynamic and electromagnetic properties of the iron-based superconductors can be described within a strong pair-breaking scenario (this work).