DISTORTION OF FERMI-SURFACE INDUCED BY PARALLEL MAGNETIC-FIELD IN A 2-DIMENSIONAL ELECTRON-GAS

We have investigated the anisotropy of Fermi surface of two-dimensiona l electron gas in GaAs/AlGaAs heterostructures induced by a strong par allel magnetic held. By means of a magnetic electron focusing effect, the anisotropy of the cyclotron diameter, that is, the anisotropy of t he Fermi surface, is directly determined. The anisotropy of Fermi surf ace increases by 5-10% with increasing parallel magnetic field up to 6 T. It is found that the anisotropy is enlarged with increasing carrie r density by illumination, while the anisotropy increases with decreas ing carrier density by the gate voltage. (C) 1998 Elsevier Science B.V . All rights reserved.