Phases of the 2D Hubbard model at low doping

We study the equilibrium spin configuration of the 2D Hubbard model for a low degree of doping, x, when a long-range magnetic order is still present. We show that the conventional planar spiral phase has negative bosonic modes and is therefore unstable. The novel equilibrium state that we find at low doping is incommensurate and non-coplanar with the inverse pitch of the spiral varying as square root x; nevertheless this state has a dominant peak in the susceptibility at ( pi , pi ).