  The repulsive one-dimensional Hubbard model with bond-charge interaction
(HBC) in the superconducting regime is mapped onto the spin-1/2 XY model with
transverse field. We calculate correlations and phase boundaries, realizing an
excellent agreement with numerical results. The critical line for the
superconducting transition is shown to coincide with the analytical
factorization line identifying the commensurate-incommensurate transition in
the XY model.

Strongly Correlated Electrons;Superconductivity;Quantum Physics