GROUND-STATE PROPERTIES AND DYNAMICS OF THE BILAYER T-J MODEL

We present an exact diagonalization study of bilayer clusters of the t-J model. Our results indicate a crossover between two markedly different regimes which occurs when the ratio J(perpendicular to)/J between interlayer and intralayer exchange constants increases: for small J(perpendicular to)/J the data suggest the development of three-dimensional antiferromagnetic correlations without appreciable degradation of the intralayer spin order and the d(x2-y2) hole pairs within the planes persist. For larger values of J(perpendicular to)/J local singlets along the interlayer bonds dominate, leading to an almost complete suppression of the intralayer spin correlation and the breaking of the intralayer hole pairs. The ground state with two holes in this regime has s-like symmetry. We present data for static spin correlation function, magnetic structure factor and spin gap. We calculate the momentum distribution and electronic spectral function of the ''local singlet state'' realized for large J(perpendicular to)/J, and show that it deviates markedly from that of a single layer, making it an implausible candidate for modeling high-temperature superconductors.