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Correlated two-dimensional electrons in quantum Hall systems

Ziel

The objective of the project is experimental and theoretical study of strongly correlated electron liquids at high magnetic field and the nature of excitations in them, such as composite fermions, skyrmions, charge and spin density waves in the regimes of Integer and Fractional QHE. Using a broad range of magneto-optical and transport techniques combined with the FIR and NMR methods, the results listed below are expected to be obtained:
1. Fermi-energy of composite fermions and their effective mass will be measured from the magnetic field and temperature dependence of the electronic spin polarization, which will be derived from the degree of circular polarization of time-resolved luminescence. Novel inelastic light scattering technique with wave-vector resolution will be applied in order to study possible magnetoplasmon modes of composite fermions. The effective mass of composite fermions will also be measured by this alternative method. Spin splitting of composite fermions and its enhancement due to interaction between composite fermions will be measured from the temperature dependence of the electron spin polarization for different Fractional Quantum Hall Effect states. Experimental results will be compared with corresponding theoretical calculations;
2. Spin coupling between 2D-electrons and optically spin-oriented nuclei will be studied experimentally and used for an enhancement and a suppression of the Zeeman energy. Spin orientation of nuclear spins both along and against the external magnetic field will be performed by circularly polarized light. A dynamics of skyrmion motion, kinetics of their formation, annihilation of skyrmion-antiskyrmion pair and a manifestation of these effects in luminescence spectrum will be analysed theoretically. The ground state of ferromagnetic QHE liquid in the limit of a vanishing Zeeman energy will be studied and the effect of spin-orbital coupling in the electron energy will be taken into account. Optical detection of the Nuclear Magnetic Resonance will be realized in order to measure directly the electron spin-polarization from the Knight shift;
3. The system of 2D-electrons coupled to the magnetic environment will investigate in CdMnTe/CdMgTe quantum wells using interband and far-infrared magneto-optical techniques. The goal is to determine the electronic and magnetic properties of this system, particularly in the range of odd filling factors (electron spin density waves coupled to manganese spins) and in the limit of low magnetic fields and low temperatures (magnetism mediated by 2D-electrons). Spin dynamics of 2D-electrons and excitons will be studied by use of ultra-fast time-resolved technique and spin-relaxation mechanisms as well as time evolution of the energetic structure will be analysed. The experimental results will be compared with theoretical calculations. Optical detection of the manganese ions EPR will be realized in order to measure the electron spin-polarization from the equivalence of the Knight shift for the EPR signal;
4. Modification of the electronic energy spectrum due to electron-electron interaction in coupled 2D-channels will be studied in InAs and GaAs double quantum wells by far-infrared spectroscopic technique. Both interaction and spin related phenomena would be investigated.

Possible formation of charged multiexcitonic complexes with a large number of excitons (which can be considered as a condensation into a novel excitonic liquid) will be experimentally investigated in a weakly doped single quantum wells. The corresponding binding energies will be measured. The experimental results will be compared with theoretical calculations.

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Koordinator

Centre National de la Recherche Scientifique
EU-Beitrag
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Adresse
Avenue des Martyrs, 25
38042 Grenoble
Frankreich

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Beteiligte (7)