NONLINEAR DOPPLER-SHIFT OF THE PLASMON RESONANCE IN A GRATING-COUPLEDDRIFTING 2DEG

We report experimental measurements and computer calculations of the p lasmon resonances of two dimensional electron gases in the far-infrare d which show the effects of laterally drifting the 2DEG. Coupling to r adiation is achieved using an overlaid metal grating of submicron peri od, and its periodic screening effect splits the plasmon into upper an d lower energy modes. For a symmetric gating profile the higher energy mode is non-radiative for a stationary 2DEG and a splitting is not ob servable, but when the 2DEG is laterally drifted under the grating, co upling to both modes can occur, and their Doppler shifts produce an ob servable splitting which increases with drift velocity. These Doppler shifts are not linear with drift velocity for low velocities, but appr oach asymptotically the expected linear shift with increasing drift ve locity. Experimental results on 2DEGs at GaAs/AlGaAs heterojunctions c ompare well with theoretical calculations.