Anomalously Sharp Superconducting Transitions in Overdoped $La_{2-x}Sr_{x}CuO_{4}$ Films

TL;DR

This study investigates the superconducting properties of overdoped La2-xSrxCuO4 films, revealing unexpectedly sharp transitions and suggesting a homogeneous d-wave superconducting state with enhanced elastic scattering, challenging previous inhomogeneity models.

Contribution

It provides new insights into the nature of the overdoped regime, showing sharp superconducting transitions and supporting a homogeneous superconducting state contrary to phase separation theories.

Findings

Superconducting transition sharpens dramatically beyond x=0.22

Transition temperature Tc decreases with overdoping

Upward curvature appears in lambda^{-2}(T)

Abstract

We present measurements of $ab$-plane resistivity $\rho_{ab}(T)$ and superfluid density [$\propto \lambda^{-2}$, $\lambda$ = magnetic penetration depth] in $La_{2-x}Sr_{x}CuO_{4}$ films. As Sr concentration $x$ exceeds about 0.22, the superconducting transition sharpens dramatically, becoming as narrow as 200 mK near the super-to-normal metal quantum critical point. At the same time, $\rho_{ab}(T)$, $\lambda^{-2}(T)$, and transition temperature $T_c$ decrease, and upward curvature develops in $\lambda^{-2}(T)$. Given the sharp transitions, we interpret these results in the context of a homogeneous d-wave superconducting state, with elastic scattering that is enhanced relative to underdoped LSCO due to weaker electron correlations. This interpretation conflicts with the viewpoint that the overdoped state is inhomogeneous due to phase separation into superconducting and normal metal regions.