Mutual independence of T_c and superfluid density under pressure in optimally-doped LaFeAsO_1-xF_x

We report on the effect of nearly-hydrostatic pressure P ≤ 23 kbar in an optimally-doped LaFeAsO_1-xF_x sample. Our results of muon spin rotation show no dependence of T_c on P and, at the same time, a remarkable enhancement of the superfluid density (n_s). This is a dramatic effect, the saturation value of n_s being increased by ∝ 30 % at the maximum P value. We provide evidence from density-functional theory (DFT) calculations that this increase should not be associated to an induced change in the fermiology of LaFeAsO_1-xF_x. Accordingly, we suggest that the experimental data can be explained by assuming a modification of the ratio between intra- and inter-band impurity scattering, only possible in multi-band SC.