Linear Polarization Rotation Study of the Microwave-Induced Magnetoresistance Oscillations in the GaAs/AlGaAs System
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Linear Polarization Rotation Study of the Microwave-Induced Magnetoresistance Oscillations in the GaAs/AlGaAs System A. N. Ramanayaka1, Tianyu Ye1, H-C. Liu1, R. G. Mani1, W. Wegscheider2 1 Department of Physics and Astronomy, Georgia State University, Atlanta, GA 30303 U.S.A. 2 Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich, Switzerland. ABSTRACT Microwave-induced zero-resistance states appear when the associated B-1-periodic magnetoresistance oscillations grow in amplitude and become comparable to the dark resistance of the two-dimensional electron system (2DES). Existing theories have made differing predictions regarding the influence of the microwave polarization in this phenomenon. We have investigated the effect of rotating, in-situ, the polarization of linearly polarized microwaves relative to long-axis of Hall bars. The results indicate that the amplitude of the magnetoresistance oscillations is remarkably responsive to the relative orientation between the linearly polarized microwave electric field and the current-axis in the specimen. At low microwave power, P, experiments indicate a strong sinusoidal variation in the diagonal resistance Rxx vs. θ at the oscillatory extrema of the microwave-induced magnetoresistance oscillations. Interestingly, the phase shift θ0 for maximal oscillatory Rxx response under photoexcitation is a strong function of the magnetic field, the extremum in question, and the magnetic field orientation. INTRODUCTION In the recent past, low-B transport studies under microwave irradiation in the 2DES uncovered the possibility of eliminating backscattering by photo-excitation, without concurrent Hall quantization.[1, 2] The experimental realization of such radiation-induced zero-resistance states and associated B−1-periodic radiation-induced magneto-resistance oscillations expanded the experimental [1-14] and theoretical [15-28] investigations of light-matter coupling in lowdimensional electronic systems. Microwave-induced zero-resistance states appear when the associated B−1-periodic magnetoresistance oscillations grow in amplitude and become comparable to the dark resistance of the 2DES. Such oscillations are now understood via the displacement model [15, 16, 18, 25] the non-parabolicity model [17] the inelastic model [19] and the radiation driven electron orbit model [20, 22]. A distinguishing feature between these theories is the role of the microwave-polarization. Here, the displacement model indicates that the oscillation amplitude is influenced by whether the microwave electric field, Eω where ω=2πf, is parallel or perpendicular to the dc-electric field, Edc [16]. In contrast, the inelastic model suggests polarization insensitivity of the radiationinduced magneto-resistance oscillations [19]. The radiation-driven electron orbit model indicates a polarization immunity that depends upon the damping factor, γ, exceeding the microwave frequency, f [21, 22]. Finally, the non-parabolicity model suggests distinct polarization sensitivity for linearly polarized microwaves [17]
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