Energy Scales in the Local Magnetic Excitation Spectrum of YBCO

Abstract

The wave-vector integrated dynamical spin susceptibility chi_{2D}(omega) of YBCO cuprates is considered. chi_{2D} 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 chi_{2D}. It is caused by particle-hole excitations across the maximum gap Delta^0. 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 Delta^0 stays almost unchanged. The results are in reasonable agreement with inelastic neutron-scattering experiments.