Energy Scales in the Local Magnetic Excitation Spectrum of YBCO

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The wave-vector integrated dynamical spin susceptibility chi₂D(omega) of YBCO cuprates is considered. chi₂D is calculated in the superconducting state from a renormalized mean-field theory of the t-t'-J-model, based on the slave-boson formulation. Besides the well-known 41 meV resonance a second, much broader peak (`hump') appears in Im chi₂D. It is caused by particle-hole excitations across the maximum gap Delta⁰. In contrast to the resonance, which moves to lower energies when the hole filling is reduced from optimal doping, the position of this `hump' at approx. 2 Delta⁰ stays almost unchanged. The results are in reasonable agreement with inelastic neutron-scattering experiments.