Microwave-induced Resistance Oscillations Research Articles

ABSORPTION AND REFLECTION EXPERIMENTS ON HIGH-MOBILITY 2DEGs IN THE REGIME OF MICROWAVE-INDUCED RESISTANCE OSCILLATIONS

We have performed microwave absorption and near-field reflection experiments on a high mobility GaAs / AlGaAs heterostructure for the same conditions for which Microwave-Induced Resistance Oscillations (MIROs) are observed. It is shown that the electrodynamic aspect of the problem is important in these experiments. In the absorption experiments a broad CR line was observed due to a large reflection from the highly conductive electron gas. There were no additional features observed related to absorption at harmonics of the cyclotron resonance. In near-field reflection experiments a very different oscillation pattern was revealed when compared to MIROs. The oscillation pattern observed in the reflection experiments is probably due to plasma effects occurring in a finite-size sample. The whole microscopic picture of MIROs is more complicated than simply a resonant absorption at harmonics of the cyclotron resonance. Nevertheless, the experimental observations are in good agreement with the model by Durst et al. involving the photo-assisted scattering in the presence of a crossed magnetic field and dc bias. The observed damping factor of MIROs may be attributed to a change in the electron mobility as a function of temperature. MIROs may be considered as a light-induced drift effect, a broad class of phenomena associated with a light-induced asymmetry in the velocity distribution function.

Microwave Absorption/Reflection and Magneto-Transport Experiments on High-Mobility Electron Gas

We have performed simultaneous measurements of microwave absorption/reflection and magneto-transport characteristics of a high-mobility two-dimensional electrons in GaAs-AlGaAs heterostructure in the regime of microwave-induced resistance oscillations (MIROs). It is shown that the electrodynamic aspect of the problem is important in these experiments. In the absorption experiments, a broad cyclotron resonance line was observed due to a large reflection from the highly conductive electron gas. There were no additional features observed related to absorption at harmonics of the cyclotron resonance. In near-field reflection experiments, a very different oscillation pattern was revealed when compared to MIROs. The oscillation pattern observed in the reflection experiments is probably due to plasma effects occurring in a finite-size sample. The whole microscopic picture of MIROs is more complicated than simply a resonant absorption at harmonics of the cyclotron resonance. Nevertheless, the experimental observations are in good agreement with the model by Ryzhii et al. involving the photo-assisted scattering in the presence of a crossed magnetic field and dc bias. The observed damping factor of MIROs may be attributed to a change in the electron mobility as a function of temperature.

Period and phase of microwave-induced resistance oscillations and zero-resistance states in two-dimensional electron systems

We present phenomenological analysis of the period and the phase of microwave-induced resistance oscillations (MIRO) and ``zero-resistance'' states (ZRS) recently observed in two-dimensonal electron systems. While MIRO are found to be well described by a ``1/4-cycle shift,'' we find that as MIRO evolve into ZRS with increasing magnetic field B, the phase becomes progressively smaller, decreasing roughly as $1/B.$ As a result, both maxima and minima in the ZRS regime form periodic in $1/B$ sequences, without a 1/4-cycle shift. A simple model based on oscillatory density of states is found to provide a unified description of the period/phase of MIRO/ZRS and leads to an interpretation of previously reported fine structures in terms of multiphoton processes.