THEORY OF SPIN DYNAMICS IN HIGH-T-C COPPER-OXIDE SUPERCONDUCTORS - APPLICATION TO NEUTRON-SCATTERING

A theory of spin dynamics in copper oxide superconductors is developed . The theory is based on the t-t'-J model and the diagrammatic techniq ue for Hubbard operators. The dynamic spin susceptibility calculated f or metallic hole concentrations includes two different contributions. The ''localized'' contribution arises from the subsystem of localized Cu spins with quantum short-range correlations. The ''itinerant'' cont ribution arises from the subsystem of propagating carrier quasiparticl es. As a result of their competition, the spin dynamics evolves contin uously within the metallic state from normal-metal behavior at high do ping (overdoped regime) to quantum spin-liquid-type dynamics with magn onlike excitations at low doping through non-Fermi-liquid behavior in all intermediate regimes. Based on the theory, a detailed analysis of momentum and energy dependences of the dynamic spin susceptibility for different doping regimes is performed in order to compare the theoret ical predictions with the experimental results discovered by inelastic neutron scattering. We are able to understand the strange shape of Im (c)hi versus omega and its exotic evolution with doping, the existence of the resonance peak, the gap and pseudogap effects, and many other unusual features observed for YBa2Cu3O6+x as well as the incommensurat e and ''gapless'' behavior for La2-xSrxCuO4.