Abstract
In order to investigate the inhomogeneity of the superconducting (SC) state in the overdoped high- T c cuprates, we have measured the magnetic susceptibility, χ, 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 χ in 1 T shows a plateau, that is, χ 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 c cuprates.
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