Spin transport in long-range interacting one-dimensional chain

We numerically study spin transport and nonequilibrium spin-density profiles in a clean one-dimensional spin-chain with long-range interactions, decaying as a power-law,$r^{-\alpha}$ with distance. We find two distinct regimes of transport: for $\alpha<1/2$, spin excitations relax instantaneously in the thermodynamic limit, and for $\alpha>1/2$, spin transport combines both diffusive and superdiffusive features. We show that while for $\alpha>3/2$ the spin diffusion coefficient is finite, transport in the system is never strictly diffusive, contrary to corresponding classical systems.