Longitudinal collective modes in asymmetric charged-particle bilayers

We have analysed the dispersion of longitudinal collective modes in classical asymmetric charged-particle bilayer liquids in the strong coupling regime. The theoretical analysis is based on a dielectric matrix calculated in the quasi-localized charge approximation (QLCA). The matrix elements are expressed as integrals over inter-layer and intra-layer pair correlation function data that we have generated by molecular dynamics (MD) simulations. At the same time, MD simulations of density and current fluctuation spectra were analysed to infer the collective mode dispersion. The long-wavelength finite frequency (energy) gap, brought about by strong inter-layer correlations, is a monotonically increasing function of the density ratio, n2/n1, and, for the smallest value of the inter-layer spacing considered, the gap reaches its maximum value when the two layer densities are equal. It appears that it stays at that value for n2/n1 > 1