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

Abstract

In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high-$T_{\mathrm{c}}$ 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-$T_{\mathrm{c}}$ cuprates.

4 pages, 4 figures

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