Comparison of spin dynamics in YBa2Cu3O7−δ and La2−xSrxCuO4: Effects of Fermi-surface geometry

Abstract

Neutron experiments have indicated that the structure factor S(q,ω) for the two cuprates ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ and ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ has a different q dependence. Commensurate peaks at (π/a,π/a) are observed in the former case, whereas clearly incommensurate peaks are seen in the latter, for metallic hole concentrations. We attribute this contrasting q dependence to differences in the Fermi-surface geometry, obtained in band-structure approaches, and (for the YBaCuO system) also corroborated by photoemission experiments. Using a large Coulomb-U, Fermi-liquid-based scheme, we present results for the q,ω and temperature dependence of the neutron cross section as well as for the temperature dependence of the NMR relaxation, in both cuprate families at various hole concentrations. When antiferromagnetic quasiparticle interactions of moderate strength are included, these calculations compare favorably with experiment. It should be stressed that the Fermi-surface shape must be accurately represented in both systems in order to produce this good agreement with the neutron data. We conclude that the close correspondence found, thus far, between band-structure-derived spin dynamics and the detailed fermiology of both cuprates provides support for Fermi-liquid-based schemes.