THEORY OF NUCLEAR-SPIN-LATTICE RELAXATION IN LA2CUO4 AT HIGH-TEMPERATURES

The nuclear spin-lattice relaxation in La2CuO4 is reexamined in connection with the recent measurements of the NQR relaxation rate for temperatures up to 900 K [T. Imai, C.P. Slichter, K. Yoshimura, and K. Kosuge, Phys. Rev. Lett. 70, 1002 (1993)]. We use an approach based on the exact diagonalization for the Heisenberg model to calculate the short-wavelength contribution to the relaxation rate in the high-temperature region, T greater than or similar to J/2. It is shown that the spin diffusion accounts for approximately 10% of the total relaxation rate at 900 K and would become dominant for T > J. The calculated 1/T1 is in good agreement with the experiment both in terms of the absolute value and temperature dependence.