QUASI-PARTICLE STRUCTURE AND COHERENT PROPAGATION IN THE T-J(Z)-J(PERPENDICULAR-TO) MODEL

Numerical studies, from variational calculation to exact diagonalizati on, all indicate that the quasiparticle generated by introducing one h ole into a two-dimensional quantum antiferromagnet has the same nature as a string state in the t-J(z) model. Based on this observation, we attempt to visualize the quasiparticle formation and subsequent cohere nt propagation at low energy by studying the generalized t-J(z)-J(perp endicular to) model in which we first diagonalize the t-J(z) model and then perform a degenerate perturbation in J(perpendicular to). We con struct the quasiparticle state and derive an effective Hamiltonian des cribing the coherent propagation of the quasiparticle and its interact ion with the spin wave excitations in the presence of the Neel order. We expect that qualitative properties of the quasiparticle remain inta ct when analytically continuing J(perpendicular to) from the anisotrop ic J(perpendicular to)<J(z) to the isotropic J(perpendicular to)= J(z) limit, despite the fact that the spin wave excitations change from ga pful to gapless. Extrapolating to J(perpendicular to)=J(z), our quasip article dispersion and spectral weight compare well with the exact num erical results for small clusters.