ZINC-INDUCED MODIFICATION OF THE DYNAMICAL MAGNETIC-SUSCEPTIBILITY INTHE SUPERCONDUCTING STATE OF YBA2CU3O6-SCATTERING(X AS REVEALED BY INELASTIC NEUTRON)

Inelastic-neutron-scattering measurements have been performed to deter mine the imaginary part of the dynamical susceptibility, chi ''(Q,omeg a), of a YBa2(Cu1-yZny)(3)O-6.97 sample exhibiting a superconducting t ransition at T-c = 69 K. Zinc substitution induces striking modificati ons of the energy dependence of chi ''(Q,omega) but magnetic fluctuati ons remain peaked at the antiferromagnetic wave vector, Q(AF), at all investigated energies. In the superconducting state of the zinc-free c ompound, chi ''(Q,omega) is restricted to a narrow energy range, HBAR omega = 33-47 meV, displaying a spin gap at E(G) = 33 meV and a resona nt enhancement at E(tau) = 39 meV, both features vanishing upon heatin g up above T-c. In the y = 0.02 substituted sample in the superconduct ing state, there is still an energy band in the range 32-47 meV but no clear resonance, and a signal is now observed in the low energy range , though the line shape of chi ''(Q,omega) indicates some reminiscence of the spin gap of the pure compound.