Excitations in a spin-polarized two-dimensional electron gas

A remarkably long-lived spin plasmon may exist in two-dimensional electron liquids with imbalanced spin up and spin down population. Predictions for this interesting mode by Agarwal et al. [Phys. Rev. B 90, 155409 (2014)] are based on the random phase approximation. We here show how to account for spin dependent correlations from known ground state pair correlation functions and study the consequences on the various spin dependent longitudinal response functions. The spin plasmon dispersion relation and its critical wave vector for Landau damping by minority spins turn out to be significantly lowered. We further demonstrate that spin dependent effective interactions imply a rich structure in the excitation spectrum of the partially spin-polarized system. Most notably, we find a "magnetic antiresonance", where the imaginary part of both, the spin-spin as well as the density-spin response function vanish. The resulting minimum in the double-differential cross section is awaiting experimental confirmation.