Thermopower and Nernst measurements in a half-filled lowest Landau level

TL;DR

This study investigates thermopower and Nernst effects in a half-filled Landau level, revealing non-zero Nernst signals and temperature-dependent behaviors that challenge existing theoretical predictions.

Contribution

First experimental measurement of Nernst signals at v=1/2 showing deviations from theoretical models, especially in the electron-diffusion dominant region.

Findings

Nernst signals Sxy are non-zero at v=1/2.

Sxx thermopower is consistent with previous results.

Sxy decreases faster than linear with temperature in the diffusion region.

Abstract

Motivated by recent proposal by Potter et al. [Phys. Rev. X 6, 031026 (2016)] concerning possible thermoelectric signatures of Dirac composite fermions, we perform a systematic experimental study of thermoelectric transport of an ultrahigh-mobility GaAs/AlxGa1-xAs two dimensional electron system at filling factor v = 1/2. We demonstrate that the thermopower Sxx and Nernst Sxy are symmetric and anti-symmetric with respect to B = 0 T, respectively. The measured properties of thermopower Sxx at v = 1/2 are consistent with previous experimental results. The Nernst signals Sxy of v = 1/2, which have not been reported previously, are non-zero and show a power law relation with temperature in the phonon-drag dominant region. In the electron-diffusion dominant region, the Nernst signals Sxy of v = 1/2 are found to be significantly smaller than the linear temperature dependent values predicted by Potter et al., and decreasing with temperature faster than linear dependence.