Finite Temperature Drude Weight of the One-Dimensional Spin-1/2Heisenberg Model

Using the Bethe ansatz method, the zero frequency contribution (Drude weight) to the spin current correlations is analyzed for the easy plane antiferromagnetic Heisenberg model. The Drude weight is a monotonically decreasing function of temperature for all $0\le \Delta \le 1$; it approaches the zero temperature value with a power law and appears to vanish for all finite temperatures at the isotropic $\Delta =1\mathrm{}$ point.