Magnetisierungsmessungen an tunnelgekoppelten niedrigdimensionalen Elektronensystemen (English shop)

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In this work, the magnetization of tunnel-coupled low-dimensional electron systems was investigated experimentally by means of micromechanical cantilever magnetometry. The magnetization is a thermodynamic state variable which, at low temperatures, reflects the thermodynamic ground state of the electrons. The electron systems were realized in modulation-doped AlGaAs/GaAs heterostructures. These consist of two two-dimensional electron systems (2DES) separated from each other by a barrier only a few nanometres thick.

The magnetization of the tunnel-coupled systems can be divided into two regimes. At low magnetic fields, a characteristic beating pattern can be observed in the oscillations of the magnetization data. This is consistent with the tendency of the tunnel-coupled 2DES to occupy a symmetric as well as an antisymmetric subband. The comparison of the experimental data in this field range with calculations in a single-particle model, which is based on a modelled density of states, yields good agreement. In particular, the magnetization data can be calculated without varying the energetic splitting ∆SAS between the symmetric and the antisymmetric subband. This changes when magnetization data at high magnetic fields, or at a magnetic field in the plane of the tunnel-coupled 2DES, are compared with calculations in the single-particle model. The magnetic-field-dependent charge transfer between the tunnel-coupled 2DES is used to explain this deviation. In angle-dependent magnetization measurements, an oscillation of the amplitudes of the magnetization at even filling factors can be observed. Up to an in-plane magnetic field at which a magnetic breakdown occurs, this can be explained qualitatively by a decrease of the energetic splitting. At higher in-plane magnetic fields, the properties of the interacting total system emerge more strongly. Magnetization measurements at high magnetic fields >20 T make it possible to investigate possible phase transitions at a filling factor v=2.