HOLE MOTION IN THE T-J AND HUBBARD MODELS - EFFECT OF A NEXT-NEAREST-NEIGHBOR HOPPING

Using exact diagonalization techniques, we study one dynamical hole in the two-dimensional t-J and Hubbard models on a square lattice including a next-nearest-neighbor hopping t. We present the phase diagram in the parameter space (J/t,t/t), discussing the ground-state properties of the hole. At J=0, a crossing of levels exists at some value of t separating a ferromagnetic from an antiferromagnetic ground state. For nonzero J, at least four different regions appear where the system behaves like an antiferromagnet or a (not fully saturated) ferromagnet. We study the quasiparticle behavior of the hole, showing that for small values of -t- the previously presented string picture is still valid. We also find that, for a realistic set of parameters derived from the Cu-O Hamiltonian, the hole has momentum (/2,/2), suggesting an enhancement of the p-wave superconducting mode due to the second-neighbor interactions in the spin-bag picture. Results for the t-t-U model are also discussed with conclusions similar to those of the t-t-J model. In general we found that t=0 is not a singular point of these models. © 1990 The American Physical Society.