title: Spin transport in the XXZ chain at finite temperature and momentum.
abstract: We investigate the role of momentum for the transport of magnetization in the spin-1/2 Heisenberg chain above the isotropic point at finite temperature and momentum. Using numerical and analytical approaches, we analyze the autocorrelations of density and current and observe a finite region of the Brillouin zone with diffusive dynamics below a cutoff momentum, and a diffusion constant independent of momentum and time, which scales inversely with anisotropy. Lowering the temperature over a wide range, starting from infinity, the diffusion constant is found to increase strongly while the cutoff momentum for diffusion decreases. Above the cutoff momentum diffusion breaks down completely.
authors.affiliation: Institute for Theoretical Physics, Technical University Braunschweig, D-38106 Braunschweig, Germany. r.steinigeweg@tu-bs.de
authors.forename: Robin
authors.initials: R
authors.lastname: Steinigeweg
authors.forename: Wolfram
authors.initials: W
authors.lastname: Brenig