Lawrence Berkeley National Laboratory

We consider the isotropic S=1 Heisenberg chain with a finite Haldane gap Δ and use state-of-the-art numerical techniques to investigate its dynamical properties at finite temperature, focusing on the nuclear spin-lattice relaxation rate 1/T1 measured in nuclear magnetic resonance (NMR) experiments, for instance. In particular, we analyze the contributions from modes with momenta close to q≈0 and q≈π as a function of temperature. At higherature we observe spin diffusion, while at lowerature we argue that a simple activated behavior 1/T1exp(-Δ/T) can be observed only at temperatures much smaller than the gap Δ.