Measurement of diffusion thermopower in the quantum Hall systems

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 ≤ 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 ≥ 1 T ), 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 ∼ 1.8 T , where spin-splitting in the measured area becomes apparent.