Nonequilibrium magnetotransport in gallium arsenide and aluminum gallium arsenide based two dimensional electron systems

This thesis is on experimental investigations of nonequilibrium magneto-transport in GaAs/AlGaAs-based two-dimensional electron systems (2DES). In Chapter 1 magnetotransport in 2DES is reviewed and the background of the research is presented. Experimental techniques are described in Chapter 2. Chapter 3 is on dc (Hall field)-induced resistance oscillations (HIRO) observed in 2DES subject to dc current. Studies of HIRO in high mobility samples revealed conditions for maxima and minima which are qualitatively different from earlier studies. In addition, dramatic resistance suppression in the regime of separated Landau levels (LLs) and weak dc excitation was observed. The main observations can be explained by a simple model based on impurity-scattered electron transitions between Hall field-tilted LLs. Chapter 4 is on magnetotransport of 2DES subject simultaneously to ac (microwave) and dc excitations. This study was motivated by the current domain model proposed by Andreev et al. explaining microwave-induced zero-resistance states (ZRS) and predicting that dc current should destroy current domains and ZRS. Despite apparent simplicity of such an experiment, it will be seen that its interpretation is not straightforward due to dc-induced effects without microwave. It was found that photoresistance maxima (minima) evolve into minima (maxima) and back under dc excitation, reflecting strong coupling and interplay of ac and dc-induced effects. Chapter 5 is on phonon-induced resistance oscillations (PIRO) observed in 2DES at elevated temperatures. It was observed that dc electric field strongly modifies phonon resonances, transforming resistance maxima into minima and back into maxima. Further, phonon resonances are enhanced dramatically in the nonlinear response and can be detected even at low temperatures. Most of the observations can be explained in terms of dc-induced (de)tuning of resonant acoustic phonon scattering and its interplay with inter-LL impurity scattering.