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

## TL;DR

This paper investigates the low-temperature behavior of the London penetration depth in iron-based superconductors, revealing a universal quadratic dependence linked to strong pair-breaking effects that influence various thermodynamic and electromagnetic properties.

## Contribution

It demonstrates a universal scaling law for the penetration depth coefficient and links it to strong pair-breaking, providing a unified explanation for multiple superconducting properties.

## Key findings

- The penetration depth varies as approximately T^2 at low temperatures.
- The coefficient scales as 1/T_c^3 across different materials.
- Strong pair-breaking explains multiple thermodynamic and electromagnetic scalings.

## Abstract

The low temperature variation of the London penetration depth for a number of iron-pnictide and iron-chalcogenide superconductors is nearly quadratic, $\Delta \lambda(T) = \beta T^n$ with $n\approx 2$. The coefficient in this dependence shows a robust scaling, $\beta \propto 1/T_c^3$ 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, $\Delta C \propto T_c^3$, and of the slopes of the upper critical field, $dH_{c2}/dT\propto T_c$ in these materials. This suggests that thermodynamic and electromagnetic properties of the iron-based superconductors can be described within a strong pair-breaking scenario.