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The thesis describes the low temperature magnetotransport properties in a GaAs two-dimensional electron gas containing self-assembled InAs quantum dots. This thesis comprises the following two parts.
1. Localization, Landau quantization, and insulator-quantum Hall transition at low magnetic fields
We present a magnetotransport study of a two-dimensional electron system. Shubnikov-de Haas (SdH) oscillations are observed in the insulator, indicating that Landau quantization can modulate the density of states without causing the formation of the QH liquid. With increasing the perpendicular magnetic field, from our study the insulator-quantum Hall (I-QH) transition from the low-B insulator to a filling factor ν which is greater than or equal to 3 QH state does occur as Landau bands become well-separated while the Hall and longitudinal resistivities may be different at the transition point. We can estimate the quantum mobility according to the expression of SdH oscillations. At the transition point, the relation μB ~ 1 is still valid, which represents a necessity of well-separated Landau bands in the energy spectrum.
2. Temperature driven flow lines and “phase” transitions in a GaAs two-dimensional electron system containing InAs quantum dots
We have constructed temperature driven flow lines from the longitudinal and transverse conductivities (σxx , σxy) in a gated two-dimensional GaAs electron gas containing InAs quantum dots, which allowed us to study the phase transition in our system. The flow lines could be realized theoretically from the effect of the renormalization-group functions. In the spin-degenerate regime, the separatrix σxy = me2/h ( m is an odd integer) separates a quantum Hall state from another. Moreover, the merging into these quantum Hall states with decreasing temperature appears to deviate from a semicircle relation. This could be due to the fact that the presence of inelastic scatterings (electron-phonon, electron-electron, etc.) is known to affect the localization effect.
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