The superconducting properties of LaFeAsO1−xFx in conditions of
optimal electron-doping are investigated upon the application of external
pressure up to ∼23 kbar. Measurements of muon-spin spectroscopy and dc
magnetometry evidence a clear mutual independence between the critical
temperature Tc and the low-temperature saturation value for the ratio
ns/m∗ (superfluid density over effective band mass of Cooper pairs).
Remarkably, a dramatic increase of ∼30 % is reported for ns/m∗ at
the maximum pressure value while Tc 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.Comment: 8 pages (Main text: 5 pages. Paper merged with supplemental
information), 5 figure