Pseudo-spin-gap and slow spin fluctuation in La2-xSrxCuO4 (x=0.13 and 0.18) via 63Cu and 139La nuclear quadrupole resonance -: art. no. 184503

We analyzed nonexponential Cu-63 nuclear spin-lattice relaxation curves for Cu-63-enriched high-T-c superconductors: La2-xSrxCuO4 with x=0.13 (slightly underdoped) and 0.18 (slightly overdoped), and studied the applicability of an impurity-induced nuclear spin-lattice relaxation theory. We found a remnant of pseudo-spin-gap effect on the host Cu-63 nuclear spin-lattice relaxation time and slow inhomogeneous spin fluctuation via the impurity-induced relaxation time. The effect of slow spin dynamics was also observed in La-139 nuclear spin-lattice relaxation. The inhomogeneous electron-spin fluctuation, which is associated with randomly distributed staggered moments on the CuO2 plane, smears the pseudo-spin-gap. The fact that the optimal T(c)similar to38 K is smaller than T(c)similar to96 K of HgBa2CuO4+delta can be attributed to the depairing effect due to the slow spin fluctuation.