Polarized neutron determination of the magnetic excitations in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$

Polarization analysis has been used to identify the magnetic excitations in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$. The dominant feature in the spectra is a peak at the (π,π) reciprocal lattice position and centered at 41 meV. The behavior of the peak is shown to change dramatically at ${\mathit{T}}_{\mathit{c}}$, so that the magnetic excitations responsible for the peak must be strongly coupled to the superconductivity. Below an energy of about 35 meV, superconductivity suppresses the continuum scattering found in addition to the 41-meV peak.