Nuclear spin-spin coupling in La2-alpha Sr alpha CuO4 studied by stimulated echo decay

We have performed copper nuclear quadrupole resonance experiments in high-t emperature superconductors YBa2Cu4O8, YBa2Cu3O7, and La2-xSrxCuO4 (x=0.12 a nd x=0.15), using the stimulated echo technique which utilizes the rf-pulse sequence pi/2-(tau)-pi/2-(T-tau)-pi/2. The tau and T dependences of the st imulated echo intensity is analyzed by a model that includes the spin-latti ce relaxation process (T, process) and the fluctuating local field due to n uclear spin-spin coupling. The model gives quantitative account of the expe rimental results in YBa2Cu4O8 and YBa2Cu3O7, using the known values of 1/T- 1 and 1/T-2G, the Gaussian decay rate of the spin-echo intensity. The same model applied to La2-xSrxCuO4 enables us to extract the value of T-2G Our r esults indicate that T1T/T-2G(z) shows significant temperature dependence f or z=2 but is approximately independent of temperature for z=1. This implie s that the dynamic exponent is close to one in La2-xSrxCuO4.