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

Abstract

The absolute values and temperature, T, dependence of the in-plane magnetic penetration depth, $\hat{I}{»}_{ab}$, of La_{2-x}Sr_xCuO_4 and HgBa_2CuO_{4+δ} have been measured as a function of carrier concentration. We find that the superfluid density, $\ddot{I}{}_s$, changes substantially and systematically with doping. The values of $\ddot{I}{}_s(0)$ are closely linked to the available low energy spectral weight as determined by the electronic entropy just above T_c and the initial slope of $\ddot{I}{}_s(T)/\ddot{I}{}_s(0)$ increases rapidly with carrier concentration. The results are discussed in the context of a possible relationship between $\ddot{I}{}_s$ and the normal-state (or pseudo) energy gap.

4 pages and 5 figures, submitted to Phys. Rev. Lett