Zinc-induced modification of the dynamical magnetic susceptibility in the superconducting state of YBa2Cu3O6+x as revealed by inelastic neutron scattering

Inelastic-neutron-scattering measurements have been performed to determine the imaginary part of the dynamical susceptibility, chi ''(Q,omega), of a YBa2(Cu1-yZny)(3)O-6.97 sample exhibiting a superconducting transition at T-c = 69 K. Zinc substitution induces striking modifications of the energy dependence of chi ''(Q,omega) but magnetic fluctuations remain peaked at the antiferromagnetic wave vector, Q(AF), at all investigated energies. In the superconducting state of the zinc-free compound, 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 resonant enhancement at E(tau) = 39 meV, both features vanishing upon heating up above T-c. In the y = 0.02 substituted sample in the superconducting 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.