Energy Scales in the Local Magnetic Excitation Spectrum of YBCO
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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.
8pp including figures. To appear in the Festschrift on the occasion of P. Woelfle's 60th birthday, to be published in J. Low Temp. Physics
8pp including figures. To appear in the Festschrift on the occasion of P. Woelfle's 60th birthday, to be published in J. Low Temp. Physics