Phonon-drag thermopower of lateral superlattices: the role of anisotropic scattering

Abstract

We have measured the phonon-drag thermopower of a periodically modulated two-dimensional electron gas, and report on a complex series of oscillations developing in the presence of a perpendicular magnetic field. At low electron density these oscillations are in phase with the commensurability resistance oscillations, however they become increasingly antisymmetrical with respect to B at higher electron density. We are able to explain this magnetic field dependence by proposing that the periodic potential lowers the symmetry of electron-phonon interaction. We calculate the thermopower by solving the Boltzmann equation given an electron-phonon scattering term with two-fold symmetry. Our fit of the experimental curves shows that the Brillouin zone folding enhances the electron-phonon scattering rate by a factor of two along the periodic potential and that a small misalignment (6 • ) of the heat gradient with the direction of the periodic potential is sufficient to explain the antisymmetrical oscillations. Our experiment demonstrates phonon drag as a very sensitive tool to probe the electronic and vibronic anisotropy in mesoscopic systems.

Signature of phonon drag thermopower in periodically modulated structures

“…7 is that the dominant contribution to the thermopower now arises from the phonon drag acting on the 2DEG rather than from the diffusion of hot electrons. 8,9 A series of magneto-drag thermopower oscillations were reported 10 that cannot be explained within the current theoretical framework that only extends to unmodulated systems. [11][12][13] We shall show that the potential modulation lowers the symmetry of the Fermi surface and we shall calculate its influence on the phonon drag acting on the 2DEG.…”