title: Projection operator approach to spin diffusion in the anisotropic Heisenberg chain at high temperatures.
abstract: Spin transport in the anisotropic Heisenberg chain is typically investigated theoretically with respect to the finiteness of transport coefficients only. Assuming their finiteness at high temperatures, we develop a concrete quantitative picture of the diffusion constant/(dc-)conductivity as a function of both the anisotropy parameter Δ and the spin quantum number s, going beyond the most commonly considered case s=1/2. Using this picture, we enable the comparison of finite transport coefficients from complementary theoretical methods on a quantitative level, having more significance than the finiteness alone. Our method is essentially based on an application of the time-convolutionless projection operator technique to current autocorrelations. This technique, although being a perturbation theory in Δ, is found to be applicable, even if Δ is not small. This finding supports the applicability to a wider class of strongly interacting many-particle quantum systems.
authors.affiliation: Institute for Theoretical Physics, Technical University Braunschweig, Mendelsohnstr. 3, D-38106 Braunschweig, Germany. r.steinigeweg@tu-bs.de
authors.forename: Robin
authors.initials: R
authors.lastname: Steinigeweg
authors.forename: Roman
authors.initials: R
authors.lastname: Schnalle