Nonlinear AC and DC Conductivities in a Two-Subband n -GaAs/AlAs Heterostructure
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Nonlinear AC and DC Conductivities in a Two-Subband n-GaAs/AlAs Heterostructure I. L. Drichkoa, *, I. Yu. Smirnova, A. K. Bakarovb, A. A. Bykovb, A. A. Dmitrievc, and Yu. M. Galperina, d a Ioffe
b
Institute, Russian Academy of Sciences, St. Petersburg, 194021 Russia Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, 630090 Russia c ITMO University, St. Petersburg, 197101 Russia d Department of Physics, University of Oslo, P. O. Box 1048 Blindern, Oslo, 0316 Norway *e-mail: [email protected] Received April 30, 2020; revised May 19, 2020; accepted May 19, 2020
The DC and AC conductivities of the n-GaAs/AlAs heterostructure with two filled size quantization levels are studied within a wide magnetic field range. The electron spectrum of such heterostructure is characterized by two subbands (symmetric S and antisymmetric AS), separated by the band gap Δ12 = 15.5 meV. It is shown that, in the linear regime at the applied magnetic field B > 3 T, the system exhibits oscillations corresponding to the integer quantum Hall effect. A quite complicated pattern of such oscillations is well interpreted in terms of transitions between Landau levels related to different subbands. At B < 1 T, magneto-intersubband resistance oscillations (MISOs) are observed. An increase in the conductivity with the electric current flowing across the sample or in the intensity of the surface acoustic wave (SAW) in the regime of the integer quantum Hall effect is determined by an increase in the electron gas temperature. In the case of intersubband transitions, it is found that nonlinearity cannot be explained by heating. At the same time, the decrease in the AC conductivity with increasing SAW electric field is independent of frequency, but the corresponding behavior does not coincide with that corresponding to the dependence of the DC conductivity on the Hall voltage Ey. DOI: 10.1134/S0021364020130068
SdH oscillations [1]. Magneto-intersubband oscillations were actively studied both theoretically [1, 3–5] and experimentally in single and double GaAs quantum wells [6, 7]. Recently, they were detected in a HgTe quantum well with two filled spin subbands [8]. In quantizing magnetic fields, two-subband systems exhibit not only the integer and fractional quantum Hall effects [2, 9] but also collective electronic states caused by the anticrossing of Landau levels of different subbands [10, 11].
1. INTRODUCTION The electron spectrum of semiconductor heterostructures including two quantum wells, wide quantum wells, or two size quantization bands with bottoms below the Fermi level has two subbands separated by a band gap Δ12. Coupling between these subbands significantly affects the main characteristics of such twosubband systems, giving rise to a number of new magnetotransport phenomena [1, 2], which are absent in single-subband systems. For example, in a two-subband system, the 1/B dependence of the conductivity exhibits not only periodic Shubnikov–de Haas (SdH) oscillations whos
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