Anomalous spin excitation in the metallic state of La2-xSrxCuO4 observed by Cu NQR

We have measured the temperature dependence of the planar Cu-63 nuclear spin-lattice relaxation rate, 1/T-1, up to 700 K in underdoped La2-xSrxCuO4 (x = 0.08, 0.10, 0.12), The observed 1/T1T for those samples show Curie-Weiss like behaviour at high temperatures as previously reported. However, we can extract a characteristic temperature, T*, below which the data deviate from the high temperature Curie-Weiss law for each sample. The hole concentration dependence of T* is discussed from a viewpoint of the pseudo spin-gap in this single layer system, We have also found an anomalous behaviour in which the copper relaxation rate, 1/T-1, depends on the NQR frequency especially in under-doping region. In this system, it is important to recognize microscopic disorder of the CuO2 planes which modifies the intrinsic spin dynamics.