The nature of the overdoped state in high T_c superconductors

We correlate the non-monotonic doping dependence of the penetration depth λ obtained on La2-xSrxCuO4 thin films, with the doping dependence of the 63Cu Knight shift, and the electronic specific heat coefficient γ obtained on bulk compounds. These data suggest that the increase of λ in the overdoped regime is related to a decrease of the superfluid density and that the carriers induced beyond optimum doping do not condense into pairs, but contribute to decrease the superfluid density which was present at optimum doping.