SUPERCONDUCTING CORRELATIONS IN HUBBARD CHAINS WITH CORRELATED HOPPING

We consider an extended one-dimensional Hubbard model in which the magnitude of the hopping between two sites for particles with given spin depends on the occupation of the states with opposite spin at both sites. Diagonalizing exactly finite-size chains, and using known results of conformal field theory we delimit the regions of parameters for which two particles bind and the pair superconducting correlation functions are the dominant ones at large distances. For Coulomb repulsion U smaller than a critical density-dependent value Uc and any density, there are ranges of the ratios of the hopping parameters for which the superconducting fluctuations dominate. At half filling, for parameters within this range, a transition from a regime with dominant superconducting correlations to an insulating state takes place as a function of U. We also study the model for parameters near a recently found exactly solvable limit in which the number of doubly occupied sites is conserved. © 1994 The American Physical Society.