q-dependent neutron-scattering measurements of the dynamic susceptibility χ"(q,ω) in superconducting YBa2Cu3O6.6 are presented. The observed magnetic scattering near the antiferromagnetic zone center has a nontrivial, approximately flat-topped q dependence. A separable model of the susceptibility, χ"(q,ω)=χ"(ω)F(q), is found to describe this scattering at all energies in the range 2 meV ≤Latin small letter h with strokeω≤40 meV. Measurements at temperatures above and below Tc=46 K indicate that the q-dependent "shape" function, F(q), is the same in both the superconducting and normal states. A phenomenological expression for F(q) is presented and the physical significance of its parametrization is discussed. These results are compared with current theories in the literature.
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