ONE-DIMENSIONAL T-J AND HUBBARD MODELS IN A STAGGERED FIELD

The influence of the staggered magnetic field h on properties of the o ne-dimensional t-J and Hubbard models with nearly half-filled bands ar e studied. Using the exact diagonalization method for small systems as well as analytical approaches possible in the anisotropic model and f or h >> t, we determine the phase diagram of the t-J-h model at low do ping, which displays three different regimes: the phase with repelling holes for J < J(c), the phase with paired holes for J(c) < J < J(s) a nd the phase separation for J > J(s). Employing for h not-equal 0 the analogy with the universal behavior of one-dimensional interacting fer mions within the Luther-Emery regime, we calculate the charge exponent K(rho), which can be K(rho) > 1 in the pairing regime, indicating dom inant superconducting fluctuations. An analogous analysis, in particul ar the perturbation expansion in t/h, performed for the Hubbard t-U-h model shows a phase of stable hole pairs for U < U(c). Again K(rho) se ems to approach a nonuniversal value at half-filling.