We demonstrate a severe Fermi contour anisotropy induced by the application
of a parallel magnetic field to high-mobility electrons confined to a
30-nm-wide (001) GaAs quantum well. We study commensurability oscillations,
namely geometrical resonances of the electron orbits with a unidirectional,
surface-strain-induced, periodic potential modulation, to directly probe the
size of the Fermi contours along and perpendicular to the parallel field. Their
areas are obtained from the Shubnikov-de Haas oscillations. Our experimental
data agree semi-quantitatively with the results of parameter-free calculations
of the Fermi contours but there are significant discrepancies.Comment: 5 pages, 5 figure
