Precise measurements of the dynamics of local fields in the underdoped regime of La_2-xSr_xCuO₄ by μsR

Precise zero-field (ZF) and longitudinal-field (LF) muon spin relaxation (μSR) measurements have been carried out on La_2-xSr _xCuO₄ in the underdoped regime of 0.024 ≤ x ≤ 0.15 to investigate the dynamics of local fields in the normal state. ZF-μSR time spectra show the Gaussian shape, indicating that muon spins depolarize mainly by nuclear dipole fields which are randomly distributed at the muon site. A slight deviation of the shape of the ZF-μSR time spectrum from the Gaussian shape has been observed with decreasing temperature. This deviation is due to a change of the dynamic depolarization rate of the muon-spin polarization. From LF-μSR measurements, it has been found that a small and quasi-static local field exists at the muon site even in the normal state around 100 K. The change of the muon-spin depolarization rate observed in ZF is due to a change of the magnitude of the small and quasi-static local field at the muon site.