Enhanced bound-state formation in two dimensions via stripelike hopping anisotropies - art. no. 100506

We investigate two-electron bound-state formation in a square two-dimension al t-J-U model with hopping anisotropies for zero-electron density; these a nisotropies are introduced to mimic the hopping energies similar to those e xpected in the stripelike arrangements of holes and spins found in various transition metal oxides. We provide complete analytical solutions to this p roblem, and thus demonstrate that bound-state formation occurs at a critica l exchange coupling, J(c), that decreases to zero in the limit of extreme h opping anisotropy t(y)/t(x)-->0. This behavior is found to be qualitatively identical to that of two electrons on a two-leg ladder in the limit of t(i nterchain)/t(intrachain)-->0. Using the latter result as guidance, we have determined that this bound state corresponds to one electron moving along o ne chain, with the second electron moving along the opposite chain, similar to two electrons confined to move along parallel neighboring metallic stri pes. Further, we have found that similar behavior is found in systems doped with two holes away from half filling.