EVOLUTION OF SPIN DYNAMICS WITH DOPING IN COPPER-OXIDE SUPERCONDUCTORS WITHIN THE T-T'-J MODEL - THE DOPED AF STATE

The spin dynamics in the doped AF state of high-T(c) copper oxide superconductors has been investigated within the t-t'-J model. We have shown that a small amount of doped holes affects the spin dynamics in CuO2 planes so strongly, that above a very small hole concentration, n(c)=0.027, the 2D AF ground state becomes unstable. We have also predicted a great change of the spin excitation spectrum in the doped AF state, particularly, the existence of the regime of overdamped softened magnons. Analyzing the imaginary part of the spin susceptibility, chi''(q, omega), we have discovered, in addition to the spin-wave part, also an incoherent band associated with electron-hole excitations. The relative contribution of the band increases with increasing n and dominates near the critical point even for the smallest q.