INVESTIGATION OF THE SPIN DYNAMICS IN YBA2CU3O6+X BY INELASTIC NEUTRON-SCATTERING

Inelastic neutron scattering experiments have been carried out on YBa2Cu3O6+x single crystals to investigate the spin dynamics in the pure AF-state (x = 0.15, T(N) = 410 K), in the doped AF-state (x = 0.37, T(N) = 180 K), in the metallic weakly doped superconducting state (x = 0.45, T(c) = 37 K; x = 0.51, T(c) = 47 K) and in the T(c) = 60 K superconducting phase (x = 0.69, T(c) = 59 K). The main results are summarized: the two dimensional character of the spin-wave spectrum in the AF-stat, strong renormalization of low-energy excitations and overdamping of in-plane spin fluctuations in the doped AF-state, dynamical AF correlations in the superconducting state, evidence for a pseudo-gap induced by superconductivity and existence of superconducting correlations above T(c).