Interference oscillations of microwave photoresistance in double quantum wells

Abstract

We observe oscillatory magnetoresistance in double quantum wells under microwave irradiation. The results are explained in terms of the influence of subband coupling on the frequency-dependent photoinduced part of the electron distribution function. As a consequence, the magnetoresistance demonstrates the interference of magneto-intersubband oscillations and conventional microwaveinduced resistance oscillations. 73.43.Qt, 73.50.Pz The phenomenon of microwave-induced resistance oscillations 1−3 (MIRO) in two-dimensional (2D) electron systems under perpendicular magnetic fields has attracted much interest. 4 These oscillations are periodic in the inverse magnetic field with a period determined by the ratio of the microwave radiation frequency ω to the cyclotron frequency ω c and survive at high temperatures. Basically, the observed oscillatory photoconductivity is caused by the Landau quantization of electron states, though different microscopic mechanisms of this phenomenon are still under discussion.The influence of microwave irradiation on the magnetotransport properties is currently under investigation in quantum wells with a single occupied subband. In our paper, we underline the importance of similar studies for the systems with two occupied 2D subbands, where the magnetotransport shows special new features as compared to the single-subband case. Apart from the commonly known Shubnikov-de Haas oscillations (SdHO), there exist the magneto-intersubband (MIS) oscillations of resistivity caused by periodic modulation of the probability of intersubband transitions by the magnetic field 5,6 (see Ref. 7 for more references). These oscillations survive at high temperatures, because they are not related to the position of the Landau levels with respect to the Fermi surface. Our recent observation 7 of large-amplitude MIS oscillations at magnetic fields below 1 T in high-mobility double quantum wells (DQWs) has established that these oscillations are a well-reproducible feature of magnetotransport in such systems. The present measurements, supported by a theoretical analysis, suggest that the behavior of oscillating magnetoresistance in DQWs under microwave irradiation is caused by an interference of the physical mechanisms responsible for the MIS oscillations and con- * Permanent address: Institute of Semiconductor Physics, Prospekt Nauki 45, 03028, Kiev, Ukraine † Permanent address: Institute of Semiconductor Physics, Novosibirsk 630090, Russia ventional MIRO. We have studied dependence of the resistance of symmetric balanced GaAs DQWs with wells widths of 14 nm and different barrier widths d b = 1.4, 2, and 3 nm on the magnetic field B in the presence of microwave irradiation of different frequencies and at different temperatures and intensities of radiation. 0.1 0.2 0.3 0.4 0.9

Microwave-induced Hall resistance in bilayer electron systems

“…It should be noticed that for lower MW frequencies, see also Ref. 8, MIS oscillations show a more complicated behavior compared to high frequencies where several MIS peaks are strongly enhanced but they can be successfully described by the model used in Ref. 8.…”

“…Microwave-induced resistance oscillations have been found in bilayer and trilayer systems, 8,9 and high-mobility bilayers with two occupied 2D subbands exhibit ZRS. 10 The specific features in magnetoresistance in bilayers and multilayers are caused by an interference of magneto-intersubband (MIS) oscillations 11 with MIRO's, when MW irradiation enhances, suppresses, or inverses the MIS oscillations.…”

Evidence for zero-differential resistance states in electronic bilayers

“…The minima of these oscillations evolve into zero-resistance states (ZRS) for high electron mobility and elevated microwave power [2]. The MIROs have been found also in bilayer and trilayer electron systems [3], where they interfere with magneto-intersubband (MIS) oscillations [4] because of the presence of more than one populated subband. Recently, it has been demonstrated [5] that ZRS exist in bilayer systems despite of additional intersubband scattering.…”

“…Next, we applied the theoretical [9] estimate τ in ≃ ε F /T 2 e , where ε F is the Fermi energy and T e is the electron temperature. Heating of electron gas by the current is taken into account by considering energy loss due to electron-phonon interaction [3,20] (for I DC = 50 µA the heating is appreciable only at low temperatures, at T = 1.4 K we find T e ≃ 1.6 K). To describe elastic collisions, we used the model of long-range scattering potential, w(q) ∝ exp(−l c q) (where l c ≫ 1/k F is the correlation length), which produces τ tr = τ 0 (1 + χ)/χ with χ = 1/(k F l c ) 2 and γ(ζ) ≃ (τ tr /τ 0 )/ 1 + χζ 2 [14].…”

Evolution of the linear-polarization-angle-dependence of the radiation-induced magnetoresistance-oscillations with microwave power

“…3 The amplitude of the radiation-induced magnetoresistance oscillations (RiMOs) depends on factors such as radiation frequency [4][5][6] ; temperature 7 , radiation power 8 , linear polarization direction 9,10 , angle between magnetic field and sample normal 11 and current through sample 12 . All these factors have been examined both experimentally [13][14][15][16][17][18][19][20][21][22][23] and theoretically . However, there are still open questions, two of which are the microwave power dependence and microwave polarization dependence of RiMOs.…”