Plasmons and Coulomb drag in Dirac-Schrödinger hybrid electron systems

We show that the plasmon spectrum of an ordinary two-dimensional electron gas (2DEG) hosted in a GaAs heterostructure is significantly modified when a graphene sheet is placed on the surface of the semiconductor in close proximity to the 2DEG. Long-range Coulomb interactions between massive electrons and massless Dirac fermions lead to a set of optical and acoustic intrasubband plasmons. Here we compute the dispersion of these coupled modes within the random phase approximation, providing analytical expressions in the long-wavelength limit that shed light on their dependence on the Dirac velocity and Dirac-fermion density. We also evaluate the resistivity in a Coulomb-drag transport setup. These Dirac-Schr\"odinger hybrid electron systems are experimentally feasible and open research opportunities for fundamental studies of electron-electron interaction effects in two spatial dimensions.