Showing papers by "William G. Macready published in 1993"

Hubbard model in the strong-coupling approximation.

Abstract: We report numerical results for the two-dimensional Hubbard model in the strong-coupling approximation, including the three-site terms omitted in the [ital t]-[ital J] model, for a 4[times]4 system with periodic boundary conditions. We study the one- and two-hole band structures, the root-mean-square hole-hole separation, and the hole-hole binding energy for both the [ital t]-[ital J] and the strong-coupling models. In the physical parameter region (8[lt][ital U]/[ital t][lt]40) believed appropriate for the high-temperature superconductors, the three-site terms enhance the hole mobility, increasing the one- and two-hole bandwidths and decreasing the binding energy, but changing the hole-hole separation only slightly; quantitative differences between the models range up to 40%. The transition (at large [ital U]/[ital t]) to the ferromagnetic Nagaoka state is sharper in the strong-coupling model; our results do not support a transition through all intermediate [ital S] values in the bulk.