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HL: Halbleiterphysik
HL 9: Poster I
HL 9.105: Poster
Montag, 27. März 2006, 15:15–17:45, P3
De Haas-van Alphen effect in a two-dimensional electron system with variable carrier density and mobility — •N. Ruhe, J. I. Springborn, M. A. Wilde, Ch. Heyn, and D. Grundler — Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung der Universität Hamburg, Jungiusstraße 11, 20355 Hamburg, Germany
We have studied simultaneously the de Haas-van Alphen (dHvA) and the quantum Hall effect in a gated two-dimensional electron system (2DES) at temperatures down to 300 mK. The 2DES was formed in a modulation-doped GaAs/AlGaAs heterostructure and integrated into a micromechanical cantilever. Using a fiber-optics interferometer we measured the quantum oscillatory behavior of the magnetization in a magnetic field B up to 14.5 T. The high sensitivity of 4.5 · 10−16 J/T at B=10 T allowed us to measure the dHvA oscillations for carrier densities nS ranging from 5 to 33· 1010 cm−2. Leads were integrated to measure simultaneously the zero-field mobility µe. It was found to vary by a factor of five between 1 and 5· 105 cm2/Vs. Unexpectedly we observed that the sawtooth like dHvA amplitude per electron did not depend on nS and µe for even integer filling factors ν at fixed B. The behavior is consistent within a density-independent quantum scattering time of 7· 10−13 s. For the dHvA amplitude at ν = 1 we find a characteristic dependence on B and nS which we explain by exchange enhancement.
The authors thank D. Heitmann and A. Schwarz for continuous support and the Deutsche Forschungsgemeinschaft for financial support via SFB 508 and GR 1640/1.