  The response of two-dimensional electron gas to temperature gradient in
perpendicular magnetic field under steady-state microwave irradiation is
studied theoretically. The electric currents induced by temperature gradient
and the thermopower coefficients are calculated taking into account both
diffusive and phonon-drag mechanisms. The modification of thermopower by
microwaves takes place because of Landau quantization of electron energy
spectrum and is governed by the microscopic mechanisms which are similar to
those responsible for microwave-induced oscillations of electrical resistivity.
The magnetic-field dependence of microwave-induced corrections to phonon-drag
thermopower is determined by mixing of phonon resonance frequencies with
radiation frequency, which leads to interference oscillations. The transverse
thermopower is modified by microwave irradiation much stronger than the
longitudinal one. Apart from showing prominent microwave-induced oscillations
as a function of magnetic field, the transverse thermopower appears to be
highly sensitive to the direction of linear polarization of microwave
radiation.
