Cu spin dynamics in the overdoped regime of La2-x Srx Cu1-y Zny O4 probed by muon spin relaxation

Muon-spin-relaxation measurements have been performed for partially Zn-substituted La2-x Srx Cu1-y Zny O4 with y=0-0.10 in the overdoped regime up to x=0.30. In the 3% Zn-substituted samples up to x=0.27, exponential-like depolarization of muon spins has been observed at low temperatures, indicating a Zn-induced slowing down of the Cu spin fluctuations. The depolarization rate decreases with increasing x, and almost no fast depolarization of muon spins has been observed for x=0.30 where superconductivity disappears. The present results suggest that there is no quantum critical point at x∼0.19. These results are discussed in terms of the stripe-pinning model and the phase-separation model.