Effect of correlated hopping on the superconductivity of the one-dimensional t-J model

We have studied by exact diagonalization the phase diagram of a ring described by the t-J model supplemented by a next-nearest-neighbor hopping combined with a nearest-neighbor spin hip t ''. The sign of t '' is taken opposite to that derived from a strong-coupling limit of the Hubbard model, and corresponds to that obtained from a systematic low-energy reduction of the three-band Hubbard model for CuO2 planes for large O-O hopping. We have calculated several correlation functions and the phase diagram. For doping levels realistic for the cuprates, the effect of t '' is to shift the region for which superconducting correlations become dominant, to significantly lower (more realistic) values of J.