Theory of magnetothermoelectric phenomena in high-mobility two-dimensional electron systems under microwave irradiation

Abstract

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.

Microwave-Induced Magneto-Oscillations and Signatures of Zero-Resistance States in Phonon-Drag Voltage in Two-Dimensional Electron Systems

“…Under MW irradiation the dissipative resistivity ρ xx is strongly modified while the Hall one, ρ xy , remains unchanged. The coefficients β yy and β xy are not modified by microwaves as strongly as ρ xx [24]. Thus, the terms in α xy no longer compensate each other, and the voltage developing in the direction perpendicular to the phonon flux should have an oscillating component proportional to the MW-induced part of dissipative resistivity.…”

“…The ballistic phonon model is reliable because of large (1 mm) mean free path lengths of phonons in GaAs at low T [26]. Using the basic formalism for calculation of thermoelectric response in quantizing magnetic field [24] in application to this model [25], one may represent the PDV between the contacts i and j in the form…”

Magnetocapacitance oscillations and thermoelectric effect in a two-dimensional electron gas irradiated by microwaves

“…The thermoinduced current in GaAs quantum wells is dominated by phonon drag contribution. In general, this current is modified in the presence of microwave irradiation [25], but the effect is small compared to the influence of microwaves on the resistivity and will be neglected in the following. Using the model of bulk phonons with a three-dimensional wave vector Q = (q, q z ) and taking into account that the scattering of electrons by phonons is quasi-elastic because of the smallness of the phonon energies compared to Fermi energy, one gets [25]…”

“…The function C λQ is the squared matrix element of the electron-phonon interaction in the bulk, comprising deformation-potential and piezoelectric-potential mechanisms (the detailed expression can be found, for example, in Ref. 25). The squared overlap integral I qz is defined as I qz = | dze iqz z F 2 (z)| 2 , where F (z) is the ground-state wavefunction describing confinement of electrons in the quantum well.…”

“…In this case,B is the thermoelectric tensorβ; see Ref. 25 for the theory of phonon-drag thermoelectric effect in a quantizing magnetic field. Both B d and B H contain classical (nonoscillating) and quantum (oscillating with B) contributions, the latter include the magnetophonon oscillations.…”