| Summary: | 碩士 === 國立臺灣大學 === 物理研究所 === 92 === In the thesis, I shall report the transport properties in a high-mobility GaAs two-dimensional electron gas (2DEG). I will introduce them in the following two parts.
1. Spin-splitting in a GaAs two-dimensional electron gas
We have measured the low-temperature electron transport properties in a GaAs/AlGaAs heterostructure. In our system, the enhanced effective g-factor of 9.28 is measured from activation experiments at Landau-level filling factors 1, 3, 5 and 7. We also observe collapse of spin-splitting in which the spin gap approaches 0 at a critical magnetic field of 1.48 T. According to the critical magnetic field , we can expect that the energy caused by the disorder broadening is of 0.79 meV. It is consistent with what we expect from the uncertainty principle.
2. Huge quasi-classical positive magnetoresistance in a high-mobility GaAs two-dimensional electron gas
I shall report observation of huge positive magnetoresistance (PMR) in a high-mobility GaAs 2DEG. The PMR persists up to 80K, demonstrating its quasi-classical origin. We find that where ?1.08-0.85 over the measurement range 10K K with increasing T, ?decreases, showing that electron-phonon scattering becomes stronger at higher temperatures. Our experimental results can be explained in terms of a recent theory by Polyakov et al.. In their work, it has been demonstrated that the interplay of a short-range impurity potential and a long-range correlated random potential can give rise to positive non-saturating MR in a perpendicular magnetic field.
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