Dynamic polarization of graphene by moving external charges: Comparison with 2D electron gas

We calculate the stopping and image forces on a point charge moving over a single-layer graphene grown on an SiC substrate, and compare them with forces arising when a charge moves over a two-dimensional electron gas (2DEG) in an Ag monolayer on a Si substrate. Given that both these systems constitute a one-atom thick 2DEG, major differences are found in the velocity and distance dependencies of the two forces owing to different electronic structures of the respective 2DEG. Within the massless Dirac fermion picture of graphene’s π electron bands, the inter-band single particle excitations are found to affect the stopping and image forces at high speeds in a substantial way, whereas such excitations are absent in the 2DEG of the metallic layer described by a single parabolic band.