A class of states supporting diffusive spin dynamics in the isotropic Heisenberg model

The spin transport in the isotropic Heisenberg model in the sector with zero magnetization is generically super-diffusive. Despite that, we here demonstrate that for a specific set of domain-wall-like initial product states it can instead be diffusive. We theoretically explain the time evolution of such states by showing that in the limiting regime of weak spatial modulation they are approximately product states for very long times, and demonstrate that even in the case of larger spatial modulation the bipartite entanglement entropy grows only logarithmically in time. In the limiting regime we derive a simple closed equation governing the dynamics, which in the continuum limit and for the initial step magnetization profile results in a solution expressed in terms of Fresnel integrals.