Exchange enhancement of the spin splitting in a GaAs-GaxAl

Abstract

The spin splitting in a GaAs-${\mathrm{Ga}}_{\mathrm{x}}$${\mathrm{Al}}_{1\mathrm{\ensuremath{-}}\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\ifmmode^\circ\else\textdegree\fi{}--89\ifmmode^\circ\else\textdegree\fi{}. 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.