Microwave reflection study of ultra-high mobility GaAs/AlGaAs 2D-electron system at large filling factors
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Microwave reflection study of ultra-high mobility GaAs/AlGaAs 2D-electron system at large filling factors Tianyu Ye1, Ramesh Mani1 and Werner Wegscheider2 1 Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303, USA. 2 Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zurich, Switzerland. ABSTRACT The microwave-induced magnetoresistance oscillations are exhibited by the GaAs/AlGaAs two dimensional electron system (2DES) under microwave and terahertz photoexcitation at liquid helium temperatures. Such oscillations are presently understood in terms of various theories. In order to identify the relative physical contributions, we have concurrently examined magnetotransport and microwave reflection from the 2DES. For the reflection measurements, a sensitive microwave detector was assimilated into the standard experimental setup. Here, we correlate changes in reflection with the concurrent transport response of the photo-excited 2DES. INTRODUCTION Microwave and terahertz excitation of the GaAs/AlGaAs two dimensional electron gas at liquid helium temperatures and large filling factors reveals the radiation-induced zero resistance state (RIZRS) and the ¼-cycle-shifted radiation-induced magnetoresistance oscillations (RIMRO).[1] These effects can potentially be used for microwave and terahertz detection, because of its huge and accurate response to centimeter and millimeter waves.[2] The radiation-induced magnetoresistance oscillations (RIMROs) are presently understood on the basis of several different models:[3-6] The displacement model[3,4] describes microwave excited inter- and intra-Landau level transitions of electrons and the scattering by impurities/phonons in the lattice. The inelastic model[5] describes a microwave radiation induced non-equilibrium electron distribution. The radiation driven electron orbit model[6] describes microwave driven oscillating electron orbits. The experimentally observed zeroresistance states, according to the theory, result from instability in the uniform current distribution and concomitant current domain formation when the diagonal resistivity becomes negative at the oscillatory minima.[7] Another more recent model appeals to the accumulation/depletion of carriers at the contacts. [8]. In order to better understand the physics behind RIZRS and RIMROs, different experiments have been carried out and these include: radiation frequency dependence measurements,[1] temperature dependence measurements,[1] magnetic field tilt angle dependence measurements,[9] applied current dependence measurements,[1] phase studies of MRIMOs,[10] microwave power dependence measurements,[11,12] microwave polarization dependence measurements[13], etc. These previous studies changed external parameters and directly measured the electrical transport response of the sample. On the other hand, there are only a few indirect studies of this regime that rely on the microwave reflection[14,15] and absorption[16,17] from GaAs/AlGaAs. Thus, this study combines a standard magnetotransport
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