Spin transport properties of the quantum one-dimensional non-linear sigma model : an application to Haldane gap systems

TL;DR

This paper investigates the spin transport in the quantum one-dimensional non-linear sigma model, revealing ballistic transport at finite temperatures and discussing mechanisms for observed spin diffusion in Haldane gap systems.

Contribution

It provides a theoretical analysis of spin transport properties using Bethe ansatz and 1/N-expansion, explaining experimental observations in Haldane gap materials.

Findings

Spin transport is ballistic at finite temperatures.

No spin diffusion occurs in the ideal model.

Spin-phonon interactions can explain experimental spin diffusion.

Abstract

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.{\bf 76}, 2173 (1996)] is also discussed. The inclusion of the spin-phonon interaction accounts for the experimental results qualitatively.