DYNAMIC SPIN AND CHARGE SUSCEPTIBILITIES IN THE T-J MODEL

Based on the spin-rotation-invariant formulation of the Kotliar Rucken stein slave-boson representation, the paramagnetic spin and charge sus ceptibilities in the t-J model are calculated. Analyzing the static sp in susceptibility, the instability of the paraphase towards incommensu rate magnetic order is in agreement, with the saddle-point phase diagr am recently obtained by some of the authors. The spin dynamics at arbi trary frequencies, wave vectors and band fillings is calculated, where the Fermi-surface and correlation effects are studied. The magnetic i nstability region is investigated with respect to the formation of a c ollective spin-fluctuation mode. Near the transition point, a kinetic gap and a sharp peak in the spectral weight ((1,0) paramagnon) are obt ained.