Local-moment fluctuations in the optimally doped high-Tc superconductor YBa2Cu3O6.95

We present results of neutron scattering experiments on YBa(2)Cu(3)O(6.95) (YBCO) (T(c)=93 K). Our results indicate that magnetic collective modes due to correlated local moments are present both above and below T(c) in optimally doped YBCO. The magnon-like modes are robust and not overdamped by itinerant particle-hole excitations. We compare the experimental results to predictions of the Fermi-liquid (FL) theory in the random phase approximation.