Magnetic-field-induced enhancement of the vortex pinning in the overdoped regime of La$_{2-x}$Sr$_x$CuO$_4$ : Relation to the microscopic phase separation

TL;DR

This study reveals enhanced vortex pinning and signs of microscopic phase separation in overdoped La$_{2-x}$Sr$_x$CuO$_4$, suggesting inhomogeneity in the superconducting state through magnetic susceptibility and magnetization measurements.

Contribution

It provides evidence of microscopic phase separation in overdoped cuprates by analyzing magnetic susceptibility and vortex behavior, a novel insight into their inhomogeneous superconductivity.

Findings

Plateau in magnetic susceptibility indicating stable vortex pinning.

Appearance of a second peak in magnetization curves.

Evidence of microscopic phase separation in overdoped regime.

Abstract

In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high-$T_{\rm c}$ cuprates, we have measured the magnetic susceptibility, $\chi$, of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) single crystals in the overdoped regime in magnetic fields parallel to the c-axis up to 7 T on warming after zero-field cooling. It has been found for $x$ = 0.198 and 0.219 that the temperature dependence of $\chi$ in 1 T shows a plateau, that is, $\chi$ is almost independent of temperature in a moderate temperature-range in the SC state. Moreover, a so-called second peak in the magnetization curve has markedly appeared in these crystals. These results indicate an anomalous enhancement of the vortex pinning and strongly suggest the occurrence of a $microscopic$ phase separation into SC and normal-state regions in the overdoped high-$T_{\rm c}$ cuprates.