Measurement of diffusion thermopower in the quantum Hall systems

TL;DR

This study measures diffusion thermopower in a two-dimensional electron gas at very low temperatures across various magnetic fields, revealing agreement with theoretical models at low fields and novel behaviors in the quantum Hall regime.

Contribution

It introduces a new experimental setup with a Hall bar device and metallic gate for precise thermopower measurements in quantum Hall systems.

Findings

Thermopower agrees with Mott formula at low magnetic fields.

Thermopower appears only in resistive regions in the quantum Hall regime.

Anomalous gate-voltage dependence observed above 1.8 T due to spin-splitting.

Abstract

We have measured diffusion thermopower in a two-dimensional electron gas at low temperature ($T$=40 mK) in the field range 0 $<B<$ 3.4 T, by employing the current heating technique. A Hall bar device is designed for this purpose, which contains two crossing Hall bars, one for the measurement and the other used as a heater, and is equipped with a metallic front gate to control the resistivity of the areas to be heated. In the low magnetic field regime ($B\leq$ 1 T), we obtain the transverse thermopower $S_{yx}$ that quantitatively agrees with the $S_{yx}$ calculated from resistivities using the generalized Mott formula. In the quantum Hall regime ($B\geq$ 1T), we find that $S_{yx}$ signal appears only when both the measured and the heater area are in the resistive (inter-quantum Hall transition) region. Anomalous gate-voltage dependence is observed above $\sim$1.8 T, where spin-splitting in the measured area becomes apparent.