Collective excitations of a system of coupled relativistic and   non-relativistic two-dimensional electron gases
  We study collective excitations of a two-dimensional electron system consisting of two kinds of charge carriers: relativistic or Dirac electrons with linear dispersion and non-relativistic electrons with parabolic dispersion. We find that the strength of the interaction between the different charge carriers, i.e., the inter-species interaction, plays a significant role in determining the number of plasmon modes as well as their dispersions in certain parameter regimes. 
Ajit C. Balram, Jimmy A. Hutasoit, and Jainendra K. Jain
cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.str-el