The Hubbard model on a two-dimensional square lattice is investigated within an unrestricted, inhomogeneous Hartree-Fock approximation. Vortexlike states discussed by Verge´s et al. [Phys. Rev. B 43, 6099 (1991)] are studied in detail. They are found to be unstable against transverse spin fluctuations. Doping of holes does not suppress these fluctuations strongly enough to stabilize the vortex states.

• Received 14 April 1993

DOI:https://doi.org/10.1103/PhysRevB.48.6680