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

Abstract

The low temperature variation of the London penetration depth for a number of iron-pnictide and iron-chalcogenide superconductors is nearly quadratic, $\hat{I}”\hat{I}»(T)={\hat{I}}^2{T}^n$ with $n\approx 2$. The coefficient in this dependence shows a robust scaling, ${\hat{I}}^2\propto 1/T_c^3$ across different families of these materials. We associate the scaling with a strong pair-breaking. The same mechanism have recently been suggested to explain the scalings of the specific heat jump, $\hat{I}”C\propto T_c^3$, and of the slopes of the upper critical field, $d{H}_{c2}/dT\propto T_c$ in these materials. This suggests that thermodynamic and electromagnetic properties of the iron-based superconductors can be described within a strong pair-breaking scenario.