Exchange enhancement of the spin splitting in a GaAs-GaxAl1−xAs heterojunction

The spin splitting in a GaAs-${\mathrm{Ga}}_{\mathrm{x}}$ ${\mathrm{Al}}_{1\mathrm{-}\mathrm{x}}$As heterojunction has been studied by using the coincidence technique, where the Shubnikov–de Haas oscillations of the conductivity are measured in tilted magnetic fields, and by measurements of the activation energy associated with spin-split conductivity minima. The spin splitting is found to be very strongly enhanced by exchange interactions, and values for the effective g factor as high as 6.2 have been found. The coincidence measurements were made at 0.37 K, and required the use of tilt angles in the range 85°–89°. These show evidence of oscillatory spin splitting determined by the relative spin-population difference within the Landau levels. The activation energy was also studied as a function of tilt angle, and shows that the spin splitting is primarily determined by the perpendicular component of magnetic field for well-resolved levels. The dependence upon total field is sublinear and shows a saturation behavior at high tilt angles.