A small and narrow negative-magnetoresistance (MR) effect that appears about null magnetic field over the interval −0.025 ≤ B ≤ 0.025 T in magnetotransport studies of the GaAs/AlGaAs 2D system with μ ≈ 107cm2/Vs is experimentally examined as a function of the sample temperature, T. The temperature dependent magnetoresistance data were fit using the Hikami et al. theory, without including the spin-orbit correction, to extract the inelastic length, li, which decreases rapidly with increasing temperature. It turns out that li < le, where le is the elastic length, for all T. Thus, we measured the single particle lifetime, τs, and the single particle mean free path ls = vFτs. A comparison between li and ls indicates that li > ls. The results suggest that the observed small and narrow magnetoresistance effect about null magnetic field could be a manifestation of coherent backscattering due to small angle scattering from remote ionized donors in the high mobility GaAs/AlGaAs 2DES.
We examined the influence of microwave radiation on both the amplitude of Shubnikov-de Haas (SdH) oscillations and the null field longitudinal magnetoresistance at liquid helium temperatures, in GaAs/AlGaAs Hall bar devices. Microwave radiation over the frequency range 25 ≤ f ≤ 50 GHz with source power 0 ≤ P ≤ 4 mW served to photo-excite the high mobility (10 7 cm 2 /V s) 2D electron system (2DES) as magnetoresistance traces were obtained as a function of the microwave power P and temperature T. Lineshape study of SdH oscillations has been carried out over the span 2.3 < ωc/ω ≤ 5.2, where ωc = eB/m * , ω = 2πf , B is the magnetic field, m * is the effective mass and f is the microwave frequency. Here, fits of the SdH lineshape served to determine the electron temperature (Te) as a function of P and T. Theory has proposed that, in the ωc/ω ≥ 1 regime, both the electron temperature and radiation energy absorption rate (Sp) exhibit relatively small response, while in the ωc/ω ≤ 1 regime, both Te and Sp are enhanced and exhibit oscillatory behavior. We compare the experimental results with these theoretical predictions, and comment upon relative role of electron heating in the microwave photo-excited high mobility 2DES.
Millimeter wave radiation-induced magneto-resistance oscillations are examined in the GaAs/AlGaAs 2D electron system under bichromatic excitation in order to study the evolution of the oscillatory diagonal magnetoresistance, Rxx as the millimeter wave intensity is changed systematically for various frequency combinations. The results indicate that at low magnetic fields, the lower frequency millimeter wave excitation sets the observed Rxx response, as the higher frequency millimeter wave component determines the Rxx response at higher magnetic fields. The observations are qualitatively explained in terms of the order of the involved transitions. The results are also modeled using the radiation-driven electron orbit theory.
In addition to the photo-excited zero-resistance states and radiation-induced magnetoresistance oscillations, which can be observed in the high-quality GaAs/AlGaAs two-dimensional electron system (2DES), magnetotransport studies of this 2DES also exhibit interesting dark magnetoresistance effects. Here, a narrow negative magnetoresistance (MR) effect that appears around zero field, and spans over about À0.02 T B 0.02 T is examined. This experimental work aims to study the influence of microwave (MW) photoexcitation on this narrow negative-MR effect in high-mobility GaAs/AlGaAs 2DES. Experimental data exhibit that the observed negative magnetoresistance effect disappears with increasing MW power. For example, the change in magnetoresistance (ΔR xx ) due to the narrow negative-MR effect drops by %50% upon increasing the source power up to about 8 mW. Further analysis shows that the zero-field resistance monotonically increases with increasing the power, suggesting that electron heating due to the energy absorbed from the radiation field accounts for the observed quenching of the narrow negative-MR effect.
The magnetotransport properties of the high mobility GaAs/AlGaAs two-dimensional electron gas systems have been examined to determine the influence of the ac current bias on the carrier temperature. The changes in the line shape of Shubnikov-de Haas oscillations in the longitudinal magnetoresistance ([Formula: see text]) were followed as a function of the ac current bias in the temperature range of [Formula: see text] in order to determine the carrier heating effect due to the ac bias. The lineshape analysis of these oscillations indicates that the carrier temperature of the two-dimensional electron system is linearly proportional to the ac bias current.
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