Anomalous slowing down of Cu-spin fluctuations observed by muon spin relaxation in the Zn-substituted Bi₂Sr₂Ca_1-xY_x(Cu_1-yZn_y)2O_8+δ system around the hole concentration of 1/8 per Cu

Muon spin relaxation (μSR) measurements were applied to a partially Zn-substituted Bi-2212 system, Bi₂Sr₂Ca_1-xY_x(Cu_1-yZn_y)2O_8+δ, to study a possibility of the existence of the so-called “1/8 effect” which has been established in La systems. The muon spin depolarization rate has been found to increase with decreasing temperature below 10 K in Zn-substituted samples around the hole concentration p=1/8 per Cu where the high-T_c superconductivity is anomalously suppressed. It has been revealed that the enhancement of the muon spin depolarization rate is attributed to the slowing down of the Cu-spin fluctuations and that both Zn substitution and p=1/8 per Cu are essential for the slowing down of the Cu-spin fluctuations. Although no three-dimensional long-range coherent ordering of the Cu spins appeared down to 0.30 K, the present μSR results support the existence of the 1/8 effect in a Bi-2212 system also.