Change of the dynamics of internal fields in the normal state of La _2-xSr_xCuO₄ observed by muon-spin-relaxation

Zero-field and longitudinal-field muon-spin-relaxation measurements have been carried out in order to investigate the electronic and magnetic states in La_2-xSr_xCuO₄ over a wide range of hole concentration from x = 0.024 to 0.15. It has been found that the dynamic depolarization rate of muon spins in zero field starts to increase monotonically with decreasing temperature at a high temperature around 100 K. This effect is enhanced around the hole concentration of 1/8 per Cu but easily suppressed by the application of a small external field of a couple of ten gauss. The present study suggests that the dynamics of fluctuating internal fields at the muon site in the normal state of La_2-xSr_xCuO₄ changes at a high temperature around 100K and is correlated with the mobility of holes. Possible relationships with spin-hole stripes and the spin-gap state in the normal state are discussed.