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

The low-temperature variation in the London penetration depth for a number of iron-pnictide and iron-chalcogenide superconductors is nearly quadratic, Delta lambda(T) = beta T(n) with n approximate to 2. The coefficient in this dependence shows a robust scaling, beta proportional to 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, Delta C proportional to T(c)(3) [Bud'ko et al., Phys. Rev. B 79, 220516 (R) (2009)], and the slopes of the upper critical field, dH(c2)/dT proportional to 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).