Crossover in the attractive one-dimensional Hubbard model for general electron concentrations

The crossover and the ground-state properties in the attractive Hubbard mod el are studied using the exact Bethe-ansatz equations and the self-consiste nt held (SCF) approach with renormalized chemical potential. The exact and the SCF results for the ground-state energy, the concentration of double oc cupied sites D, the chemical potential mu and the kinetic energy are in goo d agreement for all band fillings n and a wide range of the coupling streng th - U/t. The SCF theory in one dimension suggests a smooth crossover from the BCS superconductivity to the superfluidity of local pairs under Variati on of - U/t and n. We found a simple relationship between D, n and the BCS order parameter. (C) 1999 Elsevier Science B.V. All rights reserved.