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

TL;DR

This study measures the c-axis magnetic penetration depth in high-Tc cuprates to understand out-of-plane electrodynamics and its relation to the pseudogap, revealing doping-dependent behavior linked to superconducting properties.

Contribution

It provides the first detailed doping-dependent measurements of $\lambda_c(T)$ in single-layer cuprates, connecting c-axis superfluid response to the pseudogap and in-plane properties.

Findings

$\lambda_c$ changes near 0.20 holes/Cu, indicating pseudogap opening.

$\lambda_c$ variation is similar to $\lambda_{ab}$, linking c-axis response to superconducting condensation energy.

Strong doping dependence of $\lambda_c(0)$ explains literature discrepancies.

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 $\lambda_c(T)$ 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 $\lambda_c$ is observed near 0. 20 holes/Cu, which is related to the opening of the normal state pseudogap. The variation of $\lambda_c$ with doping is qualitatively similar to that of the in -plane component, $\lambda _{ab}$, which suggests that the c-axis superfluid r esponse is mainly governed by the superconducting condensation energy. The stron g doping dependence of $\lambda_c(0)$ for p<0.20 provides an explanation for the discrepancies in the literature.