Thermopower measurements of the coupling of phonons to electrons and composite fermions

Abstract

The thermopower of electrons at zero magnetic field and composite fermions ͑CF's͒ at high fields in GaAs/Ga 1Ϫx Al x As heterojunctions has been measured in the temperature range 0.1-1.2 K. In both cases the data are completely consistent with phonon drag being the only visible contribution. The results have been used to evaluate the phonon-limited mobility of electrons and CF's as a function of temperature. The electron mobility is in good agreement with calculation and with previous results deduced directly from the resistivity, but the CF mobility is not. We have previously reported that the thermopowers at filling factors ϭ 3 2 and 1 2 are identical. New data at fields up to 30 T show that this is also true for ϭ 3 4 and 1 4 . The effect of the substrate crystallographic orientation on phonon drag thermopower is reported.

Anisotropic Corbino magnetothermopower in a quantum Hall system

“…18 Phonon focusing in the ͑100͒ plane has fourfold symmetry, in contrast to Fig. 2͑c͒, and can thus be excluded as a cause.…”

Diffusion Thermopower of a Two-Dimensional Hole Gas in SiGe in a Quantum Hall Insulating State

“…In order to eliminate any spurious voltage caused by the bias current, the signal was measured both with and without temperature gradient, keeping the average temperature of the sample constant [13,14]. Data in swept magnetic fields were obtained with an ac lock-in technique detecting at 4 Hz [15]. The factor used to convert the ac data to absolute thermopower was determined by comparing ac and dc measurements at zero field.…”

Thermoelectric Power in Graphene

“…(43) gives S g μ p = -v s ΛT -1 [62] so that Herring's law is validated even in 2D graphene, in which 2D electrons with linear dispersion interact with 2D phonons with ω q ~ q. This relation can, therefore, be used to determine, as in 2D GaAs system [105], a value for μ p, from the measured S g . It may be mentioned here that for the 2D phonons with ω q ~ q 2 (flexural modes) in semiconducting thin films, Herring's law is shown to be invalidated [106].…”