Dynamic nesting and the incommensurate magnetic response in superconducting YBa_2Cu_3O_(6+y)

摘要

The dynamic magnetic susceptibility #chi#~n(q,#omega#) of the t-t'-J-model for YBCO compounds is studied in slave-boson mean-field theory. Within a renormalized random-phase approximation #chi#~n is compared for different fixed energies #omega# in the superconducting state. At the energy #omega# = #omega#_0, where #chi#~n((#pi#,#pi#),#omega#) shows a sharp peak (the '41 meV resonance'), the response is commensurate in wave vector space. At lower energies around #omega#_i = 0.7#omega#_0, however, we find four peaks at q = (#pi# +- #delta#, #pi#) and (#pi#, #pi# +- #delta#). The results are in agreement with inelastic neutron scattering experiments, in particular with the incommensurate response recently observed in YBa_2Cu_3O_(6.6) by Mook et al. We argue that dynamic nesting in the dispersion of quasi particles causes this effect.