Dresden 2003 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 26: Transport im hohen Magnetfeld/Quanten-Hall-Effekt

HL 26.2: Vortrag

Dienstag, 25. März 2003, 15:30–15:45, BEY/154

Direct measurement of the diffusion thermopower in a GaAs 2DEG — •Michael Gbordzoe, Serguei Maximov, Hartmut Buhmann, and Laurens W Molenmkamp — Physikalisches Institut der Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

The diffusion thermopower of a micro-scale ballistic Hall-bar structure (4×8 µm) defined by four quantum point contacts (QPCs), with an adjoining 2 µm electron heating channel, has been experimentally studied at low temperatures. The magnetic field dependence of the thermopower both parallel to the temperature gradient (magneto-thermopower) and perpendicular to the temperature gradient (Nernst-Ettinghausen effect) were investigated for different channel heating currents and for different depletion states of the QPCs.

For low heating currents, we have observed thermopower oscillations for magnetic field values up to 7.2 T, whereas for high heating currents thermopower oscillations are absent for magnetic fields up to 2 T. At high magnetic fields and for all heating currents up to 100 µA, the periods of the oscillations in thermopower correspond approximately to the periods of the Shubnikov-de Haas (SdH) oscillations in the unheated 2DEG.

Our results have been compared with those of Tieke et al. [1] obtained for a standard Hall-bar with direct heating of the sample and show some substantial differences. However, our measurement has the advantage that only the electrons in the narrow channel are heated, thus minimizing the influence of phonon drag.

[1] B. Tieke et al., Phys. Rev. Lett. 78, 4621 (1997).