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 lower. 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.

Pragmatic ways of including lifetime broadening of collective modes in the electron liquid are critically compared. Special focus lies on the impact of the damping parameter onto the dispersion. It is quantitatively exemplified for the two-dimensional case, for both, the charge (`sheet'-)plasmon and the spin-density plasmon. The predicted deviations fall within the resolution limits of advanced techniques.Comment: 6 pages, 4 figure

Correlations, highly important in low-dimensional systems, are known to decrease the plasmon dispersion of two?dimensional electron liquids. Here we calculate the plasmon properties, applying the ?Dynamic Many-Body Theory?, accounting for correlated two-particle-two-hole fluctuations. These dynamic correlations are found to significantly lower the plasmon's energy. For the data obtained numerically, we provide an analytic expression that is valid across a wide range both of densities and of wave vectors. Finally, we demonstrate how this can be invoked in determining the actual electron densities from measurements on an AlGaAs quantum well.