UBC Theses and Dissertations
Electrical measurement of spin-dependent resistivity in GaAs/AlGaAs two-dimensional electron gas Ebrahimnejad Rahbari, Seyed Hadi
The electrical transport in the semiconductor two-dimensional electron gases (2DEGs) in the presence of magnetic fields have been the subject of extensive experimental and theoretical studies. Whereas the experiments generally focus on the total magnetotransport of the spin-up and spin-down electrons, the problem of how individual spin components contribute to the sum has been mostly remained untouched. Due to the Zeeman splitting of the Fermi velocities, spin-up and spin-down electrons face different resistivities against their flow. In this thesis, this problem is addressed based on electrical generation and detection of nonequilibrium spin polarization in a narrow conducting channel of 2DEG in a GaAs/AlGaAs heterostructure. It makes use of narrow quasi-one-dimensional constrictions, known as quantum point contacts (QPCs), at a high magnetic field as the injector and detector of the spin polarization. We also simulate the problem based on an one-dimensional spin diffusion model and it turns out that it numerically agrees with the measurements using an electron spin susceptibility which is enhanced compared to that of bare GaAs. Such enhancements are generally linked with the electron-electron interactions which become important for electrons in confined geometries. The first section reviews the general characteristic properties of 2DEGs in GaAs/AlGaAs semiconductor heterostructures, gate-defined structures and quantized electrical transport through QPCs. The second chapter reviews the main results of electronic transport measurements on 2DEGs in the presence of in-plane magnetic fields, and the third chapter includes our spin polarization measurement results in a narrow channel of 2DEG and how they help to account for the effect of spin orientation on the electrical resistivity.
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