Scanning SQUID characterization of extremely overdoped La 2 − x Sr x CuO 4

When a scanning SQUID susceptometer -- a mesoscopic quantum version of a mutual inductance sensor -- hovers over a superconductor, it sees its own magnetic image reflected with a strength proportional to the density of the Cooper pairs. Here, a scanning SQUID was used to corroborate previous reports that the superfluid density in an extremely overdoped cuprate behaves unusually compared to conventional superconductors. The results obtained show the superfluid density is homogenous in space and linear with temperature, confirming that these characteristics are intrinsic electronic effects.