Frequency Evolution of Neutron Peaks Below Tc: Commensurate and Incommensurate Structure in LaSrCuO and YBaCuO

Abstract

We study the evolution of the neutron cross-section with variable frequency $ω$ 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 $ω$ near the gap energy $Δ$, both optimal {LaSrCuO} and slightly underdoped YBCO exhibit (comparably) incommensurate peaks (ii) peak sharpening below $T_c$ is seen in {LaSrCuO}, (iii) quite generically, a frequency evolution from incommensurate to commensurate and then back to incommensurate structure is found with increasing $ω$. Due to their narrow $ω$ regime of stability, commensurate peaks in {LaSrCuO} should be extremely difficult to observe.

RevTex 5pages, 4figures; Manuscript rewritten, figures revised, and direct comparisons with experiments added