Spin diffusion of the t-J model.

The spin-diffusion constant of the two-dimensional {ital t}-{ital J} model is calculated using an analytical approach at high temperatures and a recently developed numerical method based on the Lanczos technique combined with random sampling in the intermediate temperature regime. A simple relation, {sigma}={ital D}{sub {ital s}}{chi}, between spin conductivity and spin diffusion is established and used to calculate the latter. In the high-temperature and low-doping limit, the calculated diffusion constant agrees with known results for the Heisenberg model. At small hole doping, {ital D}{sub {ital s}} increases approximately linearly with doping, which leads us to an important conclusion that hopping processes enhance spin diffusion at high temperatures. At modest hole doping, {delta}{similar_to}0.25, diffusion exhibits a nonmonotonic temperature dependence, which indicates anomalous spin dynamics at small frequencies.