A critical examination of the spin dynamics in high-$T_C$ cuprates

A critical examination of the spin dynamics in high-$T_C$ cuprates is made on the light of inelastic neutron scattering results obtained by different groups. Recent neutron data show that incommensurate magnetic peaks in YBCO belong to the same excitation as the resonance peak observed at $(\pi \mathrm{/}a,\pi \mathrm{/}a)$. Being only observed in the superconducting state, the incommensurability is then rather difficult to reconcile with a stripe picture. We also discuss the link between the resonance peak spectral weight and the superconducting condensation energy.