Possible stripe ordering at x = 0.21 in La_2-xSr_xCu_1-yZn_yO₄

Anomalies, which we have recently discovered at x = 0.21 in La_2-xSr_xCu_1-yZn_yO₄ single crystals, are reviewed. In the 1% Zn-substituted crystal with x = 0.21, the resistivity exhibits an upturn at low temperatures below about 80 K and the superconductivity (SC) is markedly suppressed. The muon-spin-relaxation (μSR) measurements have revealed the existence of a static ordered state of Cu spins in this crystal at low temperatures below 2 K. From the elastic neutron-scattering experiment, incommensurate magnetic peaks around (π, π) have been observed in this crystal at low temperatures below 20 K. Even in the Zn-free crystal with x = 0.21, the SC is a little suppressed and the magnetic correlation has been found from the μSR measurements to be enhanced at low temperatures below about 0.8 K. These results strongly suggest that the dynamical stripe correlations of spins and holes tend to become static singularly at x = 0.21 and are pinned by a small amount of Zn at x = 0.21, leading to the static stripe-order and the marked suppression of SC, as in the case of x = 0.115.