BERNSTEIN MODES IN GRATING-COUPLED 2DEGS

Calculations and experimental data are reported on the optical couplin g to the Bernstein modes of a two-dimensional electron gas (2DEG) in a perpendicular magnetic field using an overlaid grating coupler. The B ernstein modes are harmonics of the cyclotron resonance and are observ ed indirectly through their interaction with the 2DEG magnetoplasmon. The optical response of a grating-heterojunction structure is calculat ed using a modal expansion technique, with the Bernstein modes include d semiclassically through non-local corrections to the 2DEG conductivi ty tenser. Dispersion curves deduced from the calculated spectra show the expected anticrossing behaviour at magnetic fields for which the B ernstein and magnetoplasmon modes have similar frequencies. This calcu lated dispersion behaviour is in excellent agreement with experimental data on a GaAs/AlGaAs heterojunction sample, underlining the importan ce of using the full electromagnetic response of the structure, includ ing the periodic screening effects of the coupling grating, in compari sons between theory and experiment. The strength of the coupling to th e Bernstein modes is also extremely well modelled.