Effects of carrier concentration on the superfluid density of high-Tc cuprates

The absolute values and temperature, T, dependence-Of the in-plane magnetic penetration depth of La2-xSrxCuO4 and HgBa2CuO4+delta have been measured as a function of carrier concentration. We find that the superfluid density rho(s) changes substantially and systematically with doping. The values of rho(s)(0) are closely linked to the available low-energy spectral weight as determined by the electronic entropy just above T-c, and the magnitude of the initial slope of [rho(s)(T)/rho(s)(0)] increases rapidly with carrier concentration. The results are discussed in the context of a possible relationship between-rho(s) and the normal-state (or pseudo)energy gap. [S0163-1829(99)04546-4].