The neutron peak in the extended saddle point model of high temperature superconductors

An explanation is proposed for the maximum at 41 meV in the inelastic spin- flip neutron scattering from YBa2Cu3O7-delta, based on the extended saddle point model developed by the author in his previous works. It is shown that , for appearance of the maximum in the imaginary part of the spin susceptib ility, close proximity of the Fermi energy to the extended saddle point is necessary. The energy of the maximum is then close to 2 Delta(max), in agre ement with experiment. Theoretical and experimental evidence concerning the energy of the extended saddle point (Rat region) is discussed. Different l imiting cases are calculated. A proof is given within the present model tha t interaction in the Final state is small, and hence no collective modes ar e formed. A general discussion of the experimental situation is presented. (C) 1998 Elsevier Science Ltd. All rights reserved.