We study the evolution of the neutron cross section with variable frequency $\omega$ and fixed T below $T_c$ in two different cuprate families. Our calculations, which predominantly probe the role of d-wave pairing, lead to generic features, independent of Fermi-surface shapes. Among our findings, reasonably consistent with experiment, are (i) for $\omega$ near the gap energy $\Delta ,$ both optimal ${\mathrm{La}}_{0.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4$ and slightly underdoped ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{6.6}$ exhibit (comparably) incommensurate peaks, (ii) peak sharpening below $T_c$ is seen in LaSrCuO, and (iii) quite generically, a frequency evolution from incommensurate to commensurate and then back to incommensurate structure is found with increasing $\omega .$ Due to their narrow $\omega$ regime of stability, commensurate peaks in LaSrCuO should be extremely difficult to observe.

• Received 23 August 1999

DOI:https://doi.org/10.1103/PhysRevB.61.R11898