c-Axis Superfluid Response and Pseudogap in High-Tc Superconductors

Abstract

To gain insight into the out-of-plane electrodynamics of high-$T_c$ superconduct ors we have measured the absolute values and temperature dependence of the c-a xis magnetic penetration depth $\hat{I}{»}_c(T)$ for two typical single layer high -$T_c$ cuprates, La${}_{2-x}$Sr${}_x$CuO${}_4$ and HgBa${}_2$CuO${}_{4+x}$ as a function o f doping. A distinct change in the behaviour of $\hat{I}{»}_c$ is observed near 0. 20 holes/Cu, which is related to the opening of the normal state pseudogap. The variation of $\hat{I}{»}_c$ with doping is qualitatively similar to that of the in -plane component, $\hat{I}{»}_{ab}$, which suggests that the c-axis superfluid r esponse is mainly governed by the superconducting condensation energy. The stron g doping dependence of $\hat{I}{»}_c(0)$ for p<0.20 provides an explanation for the discrepancies in the literature.

4 pages, 2 figures