Exact solutions of domain wall and spiral ground states in Hubbard   models
  We construct a set of exact ground states with a localized ferromagnetic domain wall and an extended spiral structure in a deformed flat-band Hubbard model. In the case of quarter filling, we show the uniqueness of the ground state with a fixed magnetization. We discuss more realistic situation given by a band-bending perturbation, which can stabilize these curious structures. We study the scattering of a conduction electron by the domain wall and the spiral spins. 
Makoto Homma and Chigak Itoi