Energy-loss rates of heavy and light charged particles in a two-dimensional electron gas

Energy-loss rates for charged external particles moving in two-dimensional electron gas of zero temperature are calculated. The transition probability per unit time for excitations in the host system is determined by using weak coupling, i.e., linear-response theory. Contributions arising from electron-hole and collective excitations to the total loss rate are separated at the levels of the random-phase approximation and a generalized mean-field approach for the linear-response function. Substantial phase-space reduction in the excitations of the fermion system is demonstrated for light external particles and interpreted as the effect of recoil. The results obtained for heavy external particles an compared with recent strong-scattering predictions based on the kinetic theory of the energy-loss process. A kinematical effect that influences the high-velocity form of the loss rate for different masses of the projectiles is pointed out.