CHARGE AND SPIN DYNAMICS IN THE ONE-DIMENSIONAL T-J(Z) AND T-J MODELS

The impact of the spin-flip terms on the (static and dynamic) charge a nd spin-correlations in the Luttinger-liquid ground state of the one-d imensional (ID) t-J model is assessed by comparison with the same quan tities in the 1D t-J(z) model, where spin-flip terms are absent. We em ploy the recursion method combined with a weak-coupling or a strong-co upling continued-fraction analysis. At J(z)/t=0(+) we use the Pfaffian representation of dynamic spin correlation's. The changing nature of the dynamically relevant charge and spin excitations on approach of th e transition to phase separation is investigated in detail. At the tra nsition point, the t-J(z) ground state has zero (static) charge correl ations and very short-ranged (static) spin correlations, whereas the t -J ground state is critical. The t-J(z) charge excitations (but not th e spin excitations) at the transition have a single-mode nature, where as charge and spin excitations have a complicated structure in the t-J model. A major transformation of the t-J spin excitations takes place between two distinct regimes within the Luttinger-liquid phase, while the t-J(z) spin excitations are found to change much more gradually. In the t-J(z) model, phase separation is accompanied by Neel long-rang e order, caused by the condensation of electron clusters with an alrea dy existing alternating up-down spin configuration (topological long-r ange order). In the t-J model, by contrast, the spin-flip processes in the exchange coupling are responsible for continued strong spin fluct uations(dominated by two-spinon excitations) in the phase-separated st ate.