Novel neutron resonance mode in $d_{x^2-y^2}$ superconductors

Abstract

We show that a new resonant magnetic excitation at incommensurate momenta, observed recently by inelastic neutron scattering experiments on YBa${}_2$Cu${}_3$O${}_{6.85}$ and YBa${}_2$Cu${}_3$O${}_{6.6}$, is a {\it spin exciton}. Its location in the magnetic Brillouin zone and its frequency are determined by the momentum dependence of the particle-hole continuum. We identify several features that distinguish this novel mode from the previous resonance mode observed near $\mathbf{Q}=(\pi ,\pi )$, such as its intensity maximum which occurs in a different part of the magnetic Brillouin zone.

4 pages, 4 figures