  Magnetization transport in a one-dimensional isotropic spin 1/2 Heisenberg
model is studied. It is shown that in a nonequilibrium steady state at high
temperature and constant small driving the magnetization current depends on the
system length L as 1/L^{0.5}, meaning that the diffusion constant diverges as
L^{0.5}. Spectral properties of a superoperator governing the relaxation
towards a nonequilibrium steady state are also discussed.
