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

The nuclear spin-lattice relaxation in La2CuO4 is reexamined in connec tion with the recent measurements of the NQR relaxation rate for tempe ratures up to 900 K [T. Imai, C.P. Slichter, K. Yoshimura, and K. Kosu ge, 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-temperatur e 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 i n good agreement with the experiment both in terms of the absolute val ue and temperature dependence.