Mutual independence of critical temperature and superfluid density under pressure in optimally electron-doped superconducting LaFeAsO$_{1-x}$F$_{x}$

TL;DR

This study shows that in optimally electron-doped LaFeAsO$_{1-x}$F$_{x}$, applying pressure increases superfluid density without affecting the critical temperature, highlighting the role of impurity scattering in multi-band superconductivity.

Contribution

It demonstrates the mutual independence of $T_{c}$ and superfluid density under pressure and introduces a model considering impurity effects on multi-band superconductivity.

Findings

Superfluid density increases by ~30% under pressure.

Critical temperature remains unchanged despite pressure.

Impurity scattering influences multi-band superconductivity.

Abstract

The superconducting properties of LaFeAsO$_{1-x}$F$_{x}$ in conditions of optimal electron-doping are investigated upon the application of external pressure up to $\sim 23$ kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature $T_{c}$ and the low-temperature saturation value for the ratio $n_{s}/m^{*}$ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of $\sim 30$ % is reported for $n_{s}/m^{*}$ at the maximum pressure value while $T_{c}$ is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of non-magnetic impurities on multi-band superconductivity into account. In particular, the unique possibility to modify the ratio between intra-band and inter-bands scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model.