Electron localization in sound absorption oscillations in the quantum Hall effect regime

Abstract

The absorption coefficient for surface acoustic waves in a piezoelectric insulator in contact with a GaAs/AlGaAs heterostructure (with two-dimensional electron mobility µ = 1.3 × 10 5 cm 2 /V · s) at T =4.2K) via a small gap has been investigated experimentally as a function of the frequency of the wave, the width of the vacuum gap, the magnetic field, and the temperature. The magnetic field and frequency dependencies of the high-frequency conductivity (in the region 30-210 MHz) are calculated and analyzed. The experimental results can be explained if it assumed that there exists a fluctuation potential in which current carrier localization occurs. The absorption of the surface acoustic waves in an interaction with two-dimensional electrons localized in the energy "tails" of Landau levels is discussed.

Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure

“…7 presented are the magnetic field dependence of both DC conductivity from [1], and that of the real part, σ 1 , of the AC conductivity at T = 1.7 K. As one can conclude observing the figure, the curves at T = 1.7 K practically coincide up to B =2.1 T, and then σ 1 exceeds σ DC xx and the difference between these values grows with the growth of the magnetic field. In relatively week magnetic field the carriers are delocalized σ DC xx =σ 1 and σ 2 =0 [8], the conductivity mechanisms for DC and AC are the same. With the increase of the magnetic field the holes in the SdH oscillation minima became localized, and the conductivity turns to be hopping.…”

Nonlinearity of acoustic effects and high-frequency electrical conductivity in GaAs/AlGaAs heterostructures under conditions of the integer quantum Hall effect

“…The heterostructures were grown by molecular-beam epitaxy and involved a spacer layer 4 × 10 −6 cm in width. The experimental procedure was described in detail elsewhere 15 . Here, we only note that the structure with 2D electron gas was grown on the piezoelectric (lithium niobate) surface over which the SAWs propagated.…”

Interaction of surface acoustic waves with a two-dimensional electron gas in the presence of spin splitting of the Landau bands

“…The GaAs/AlGaAs heterostructures were fabricated by molecular-beam epitaxy with carrier densities n = (1.3 − 2.8) × 10 11 cm −2 and mobilities µ = (1 − 2) × 10 5 cm 2 /(V · s). The density and mobility of 2D electrons were determined by a contactless acoustical method [8].…”

“…The gap a can be determined from the solution of (3). If we assume that in relatively weak magnetic fields, where electrons are delocalized [8], the quantity σ xx = σ 1 = σ dc xx does not depend on the frequency, while σ 2 = 0 and 4πσ xx /ε s V ≫ 1, we then have Γ ∼ 1/σ xx ; we now infer from (2) that the ratio of the absorption coefficients in these fields at two different frequencies for the same sample mounting (i.e., for the same gap) can be written in the form…”