μSR study on slowing-down behavior of the Cu-spin fluctuations at high temperatures in La_2-xSr_xCuO₄

Zero-field muon-spin-relaxation measurements have been carried out in order to investigate changes of the Cu-spin fluctuations in a wide hole-concentration range of La_2-x Sr_x CuO₄. An increase of the muon-spin depolarization rate with decreasing temperature has been observed between about 70 K and 140 K in the underdoped samples. The characteristic temperature, where the muon-spin depolarization rate starts to increase with decreasing temperature, has been found to decrease with increasing x and seems to vanish around x=0.15 after showing a local maximum around x=0.115. The present results are discussed in terms of the dynamical stripe and the pseudogap.