Microwave resonance in a high-quality GaAs/AlGaAs two-dimensional electron system in the low-density and low-mobility condition

R. G. Mani, A. Kriisa, C. Reichl, and W. Wegscheider

Phys. Rev. B 100, 155301 – Published 4 October 2019

Abstract

Radiation induced magnetoresistance oscillations are well known and readily observable in the high-quality two-dimensional (2D) electron system. Here, we report unexpected photoexcited transport, under a low-carrier density, low-mobility condition, in the high-quality GaAs/AlGaAs devices that exhibit the above-mentioned oscillations. This study reveals enhanced nonresonant magnetoresistance as well as microwave resonance that appear unrelated to the above-mentioned radiation-induced magnetoresistance oscillations. The positions of the resonance along the $B$ axis depends on the microwave power, the microwave frequency, and the direction of sweep of the magnetic field, as the photoexcited diagonal resistance is prominently enhanced over the dark value. Most remarkably, the observed microwave-induced resonance becomes unobservable below a characteristic cutoff frequency. These features suggest a bulk magnetoplasmon origin for the observed resonances. A picture including bottlenecks in transport within 2D electron systems and microwave modified tunneling at bottlenecks is suggested to help understand some aspects of experiment.

Received 14 May 2019
Revised 17 July 2019

DOI:https://doi.org/10.1103/PhysRevB.100.155301

Physics Subject Headings (PhySH)

Electrical conductivity Landau levels Magnetotransport Optical & microwave phenomena Photoconductivity

Heterostructures III-V semiconductors Two-dimensional electron system

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

R. G. Mani¹, A. Kriisa¹, C. Reichl², and W. Wegscheider²

¹Department of Physics and Astronomy, Georgia State University, Atlanta 30303, USA
²Laboratorium für Festkörperphysik, ETH-Zürich, Zürich 8093, Switzerland

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Vol. 100, Iss. 15 — 15 October 2019

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Images

Figure 1
(a) The dark and photoexcited diagonal resistance $R_{x x}$ in a GaAs/AlGaAs heterostructure in the high-mobility ( $14.5 \times 10^{6} {cm}^{2} / V s$ ), high-carrier density ( $n = 2.3 \times 10^{11} {cm}^{- 2}$ ) condition. The red (blue) traces correspond to the upsweep (downsweep) conditions. (b) The photoexcited traces of $R_{x x}$ in the low-mobility ( $5.6 \times 10^{6} {cm}^{2} / V s$ ), low-density ( $n = 1.34 \times 10^{11} {cm}^{- 2}$ ) condition. Notice the large hysteresis effect. The photoexcited traces in both (a) and (b) were obtained with $f = 44 - GHz$ photoexcitation. $B_{f} = 2 π f m^{*} / e$ is the characteristic field for the radiation-induced magnetoresistance oscillations. Note that in (a) a $B_{f}$ lies next to a node in the radiation-induced magnetoresistance oscillations.
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Figure 2
(a) The dark and photoexcited magnetoresistance traces with $f = 45$ -GHz photoexcitation. Note the hysteresis in the photoexcited $R_{x x}$ traces. (b) This panel demonstrates reproducibility in the hysteresis observed in the photoexcited $R_{x x}$ traces at $f = 45$ GHz.
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Figure 3
(a) The dark and photoexcited magnetoresistance traces with $f = 35$ -GHz photoexcitation. (b) The dark and photoexcited magnetoresistance traces with $f = 68$ -GHz photoexcitation. Note that the dark traces lie well below the photoexcited traces. Further, substantial hysteresis appears in $R_{x x}$ under photoexcitation.
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Figure 4
(a) The photoexcited magnetoresistance $R_{x x}$ under $f = 43.5$ -GHz photoexcitation. (b) The downsweep photoexcited magnetoresistance under $f = 43.5 - GHz$ photoexcitation at various radiation source-power ( $P$ ) levels as shown. Notice that the largest peak in $R_{x x}$ shifts to higher magnetic field with increased power $P$ . (c) This panel shows the position of the largest peak in $R_{x x}$ in (b) as a function of $P$ . The peak shifts approximately as $P^{0.5}$ , as indicated by the fit line.
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Figure 5
The vanishing power, i.e., $P \to 0$ , resonance peak positions, see Fig. 4, is exhibited as a function of the radiation frequency $f$ . Note that the fit curve, shown in red, intercepts the abscissa at $B \approx 35$ GHz.
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Figure 6
This figure shows the diagonal magnetoresistance $R_{x x}$ vs $B$ at $B$ -sweep rates. Top: 0.0027 T/s; center: 0.0020 T/s; bottom: 0.0010 T/s. Note that the shift in the locations of the major peak on the upsweep and downsweep traces is sensitive to the sweep rate. In addition, the magnitude of the hysteresis between the upsweep and downsweep traces depends also on the sweep rate. In these experiments, the hold time at $B = 0.3 T$ was the same for all three measurements.
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