Spin Transport Properties of the Quantum One-Dimensional Non-Linear Sigma Model: an Application to Haldane Gap Systems

Spin transport properties of the quantum one-dimensional non-linear sigma model are studied based upon the Bethe ansatz exact solution for the O(3) sigma model and the 1/N-expansion approach for the O(N) sigma model. It is shown that the spin transport at finite temperatures is ballistic and there is no spin diffusion in this system. A possible mechanism for the spin diffusion observed in the NMR experiment of the Haldane gap system AgVP_2S_6 by Takigawa et al. [Phys. Rev. Lett.{ 76}, 2173 (1996)] is also discussed. The inclusion of the spin-phonon interaction accounts for the experimental results qualitatively.