PHONON-DRAG MAGNETOTHERMOPOWER OSCILLATIONS IN GAAS/ASXGA1-XAS HETEROJUNCTIONS

The tensor M over arrow pointing both left and right which determines the heat flux U=M over arrow pointing both left and right E in a weak electric field E is calculated for a two-dimensional electron gas in a perpendicular magnetic field B. The dominant phonon-drag contribution is calculated using Boltzmann transport, allowing for the two-dimensional (2D) character of the electron gas. The Landau levels are taken to have Gaussian line shapes with the rms level width gamma=CB1/2 where C is the only adjustable parameter. Setting C=0.5 meV T-1/2 gives good agreement with new experimental values of M(yx). obtained for GaAs/AlxGa1-xAs heterojunctions when B varies between 2 and 10 T and the temperature varies between 1 and 5 K. M(yx) is negative and contains strong magneto-oscillations in phase with the density of states at the Fermi level. The model also predicts M(xx)=0, whereas experiment gives peak values of \M(xx)\ up to 60% of those of \M(yx)\. We demonstrate that setting M(xx)=0 in the calculation has little effect on the predicted thermopower component S(xx) but yields poor approximations to the experimental values of S(yx).