Date of Award

Summer 8-10-2021

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics and Astronomy

First Advisor

Vadym Apalkov

Abstract

Illuminating high mobility GaAs/AlGaAs samples with microwaves has revealed interesting radiation and matter coupling properties. Many studies have been carried out to perceive the microwave-induced oscillatory behavior in diagonal resistance of GaAs/AlGaAs 2D electron systems placed in an external magnetic field. Bichromatic Microwave excitation of high mobility 2D electron systems provides an extra tool to identify the physical mechanisms behind the microwave-induced zero resistance states. Here, we study the oscillatory behavior of diagonal resistance as a function of magnetic field under dual radiation excitement when the system is illuminated with microwave radiation with two different frequencies. The behavior of diagonal resistance is analyzed both experimentally and theoretically. We have photo-excited the GaAs/AlGaAs Hall bar high mobility sample at cryogenic temperatures with microwave radiation at two frequencies with different combinations of high and low frequencies. The intensities of microwave radiation from both sources have been also systematically changed to study their effect on the Microwave induce magnetoresistance behavior. To enhance the sensitivity of experimental results, a technique using two Lock-in amplifiers was implemented to extract the derivative of the diagonal magnetoresistance. Our theoretical simulations were based on the radiation-driven electron orbit model. The main outcome of our research is that for bichromatic microwave excitations, the induced oscillatory behavior of magnetoresistance at low magnetic field is determined by lower-frequency microwave radiation, while at large magnetic field, the magnetoresistance is mainly affected by the higher-frequency component. Our theoretical simulations have supported this experimental observation.

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