  The ground-state phase diagram is numerically studied for an electronic model
consisting of the spin exchange term (J) and the correlated hopping term (t_3:
the three-site term). This model has no single-particle hopping and the ratio
of the two terms is controlled by a parameter \alpha \equiv 4 t_3 / J. The case
of \alpha=1 corresponds to complete suppression of single-particle hopping in
the strong-coupling limit of the Hubbard model. In one dimension, phase
separation takes place below a critical value \alpha_c = 0.36-0.63 which
depends on the electron density. Spin gap opens in the whole region except the
phase-separated one. For \alpha \gsim 1.2 and low hole densities,
charge-density-wave correlations are the most dominant, whereas singlet-pairing
correlations are the most dominant in the remaining region. The possibility of
superconductivity in the two-dimensional case is also discussed, based on
equal-time pairing correlations.
