Thermopower of a 2D electron gas in suspended AlGaAs/GaAs heterostructures

We present thermopower measurements on a high electron mobility two-dimensional electron gas (2DEG) in a thin suspended membrane.We show that the small dimension of the membrane substantially reduces the thermal conductivity compared to bulk material so that it is possible to establish a strong thermal gradient along the 2DEG even at a distance of few micrometers. We find that the zero-field thermopower is significantly affected by the micro patterning. In contrast to 2DEGs incorporated in a bulk material, the diffusion contribution to the thermopower stays dominant up to a temperature of 7 K until the phonon-drag becomes strong and governs the run of the thermopower. We also find that the coupling between electrons and phonons in the phonon-drag regime is due to screened deformation potentials, in contrast to piezoelectric coupling found with bulk phonons.Comment: 7 page

Missing 2k_F Response for Composite Fermions in Phonon Drag

The response of composite Fermions to large wavevector scattering has been studied through phonon drag measurements. While the response retains qualitative features of the electron system at zero magnetic field, notable discrepancies develop as the system is varied from a half-filled Landau level by changing density or field. These deviations, which appear to be inconsistent with the current picture of composite Fermions, are absent if half-filling is maintained while changing density. There remains, however, a clear deviation from the temperature dependence anticipated for 2k_F scattering.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. Let