The superconducting properties of ${\mathrm{LaFeAsO}}_{1-x}{\mathrm{F}}_x$ under conditions of optimal electron doping are investigated upon the application of external pressure up to $\sim 23\mathrm{kbar}$. 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 nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model.

• Received 28 January 2015
• Publisher error corrected 19 June 2015

DOI:https://doi.org/10.1103/PhysRevLett.114.247004