Diffusion thermopower of a silicon inversion layer at low magnetic fields

We have investigated the longitudinal and transverse thermopowers, Sₓₓ and Syx, of an electron inversion layer in a Si-metal-oxide-semiconductor field-effect transistor at low magnetic fields in the temperature range ~0.5--4K. We show that a single theoretical model, based on the Mott relation for diffusion, gives a good account of both the quantum oscillations and the smooth background at low temperatures where phonon drag can be ignored. An anomalous nonoscillatory component, possibly due to phonon drag, is found in Syx at higher temperatures.