Levée de dégénérescence de spin dans le régime Hall quantique

Abstract : Spin splitting in the integer quantum Hall effect is investigated for a series of AlGaAs/GaAs heterojunctions and quantum wells. Magnetoresistance measurements are performed at mK temperature to characterize the electronic density of states and estimate the strength of manybody interactions. The exchange interaction magnitude is found to be essentially controlled by the electron density, increasing smoothly with decreasing density in the range (1.10^11-1.10^12cm^-2). A simple model with no free parameters correctly predicts the magnetic field required to observe spin splitting, showing that the appearance of spin splitting is a result of a competition between the disorder induced energy cost of flipping spins and the exchange energy gain associated with the polarized state. In this model, the single particle Zeeman energy plays no role, so that the appearance of this quantum Hall ferromagnet in the highest occupied Landau level can also be thought of as a magnetic field induced Stoner transition. The case of non-zero Zeeman energy, adressed by introducing an additionnal in-plane magnetic field, can be described using the same model with no free parameters, confirming the validity of this approach.
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Benjamin Piot. Levée de dégénérescence de spin dans le régime Hall quantique. Matière Condensée [cond-mat]. Université Joseph-Fourier - Grenoble I, 2006. Français. ⟨tel-00125776⟩

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