New skyrmions in the attractive Hubbard model with broken SO(4)symmetry

The coexistence of superconducting and charge-density-wave order in the hal f-filled attractive Hubbard model is interpreted as a consequence of the ps eudospin SU(2) symmetry spontaneously broken to a 'hidden' subgroup U(1). B y topological arguments we show that there must exist new skyrmion textures associated with this symmetry breakdown. This fact is illustrated via a no n-linear sigma-model. Unlike the spin textures previously known in an antif erromagnetic background, doping the model away from half-filling leads the new skyrmions to unwrap. (C) 1999 Published by Elsevier Science B.V. All ri ghts reserved.