Spin fluctuations in a two-dimensional marginal Fermi liquid

Abstract

We use a simple two-dimensional band-structure model for ${\mathrm{La}}_{2\mathrm{-}\mathit{x}}$ ${\mathrm{Sr}}_{\mathit{x}}$ ${\mathrm{CuO}}_4$ incorporating marginal-Fermi-liquid self-energy corrections to calculate the spin-fluctuation spectrum at low energies. Features in the band structure lead to peaks in the structure factor at incommensurate wave vectors. The frequency and temperature dependence of these peaks is controlled by the quasiparticle lifetimes. Comparison with both neutron-scattering data and NMR or NQR relaxation rates suggests a modest mass enhancement, and indicates neither strong magnetic-exchange interactions nor a separate non-Fermi-surface contribution to the polarizability. We compare our results with conventional Fermi-liquid behavior, and with a model of magnetic fluctuations with a long correlation length.