Frequency evolution of neutron peaks below T-c: Commensurate and incommensurate structure in La0.85Sr0.15CuO4 and YBa2Cu3O6.6

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 calcula tions, which predominantly probe the role of d-wave pairing, lend to generi c features, independent of Fermi-surface shapes. Among our findings, reason ably consistent with experiment, are (i) for omega near the gap energy Delt a, both optimal LaO0.85Sr0.15CuO4 and slightly underdoped YBa2Cu3O6.6 exhib it (comparably) incommensurate peaks, (ii) peak sharpening below T-c is See n in LaSrCuO, and (iii) quite generically, a frequency evolution from incom mensurate to commensurate and then back to incommensurate structure is foun d with increasing omega. Due to their narrow omega regime of stability, com mensurate peaks in LaSrCuO should be extremely difficult to observe.