Acoustic studies of ac conductivity mechanisms inn-GaAs/AlxGa1−

Abstract

In case of a of the heterostructure n-GaAs/AlGaAs with sheet density n = 2 × 10 11 cm −2 and mobility µ ≈ 2 × 10 6 cm 2 /V·s with integer and fractional quantum Hall effect (IQHE and FQHE, respectively) we demonstrate the wide applicability of acoustic methods for determining the general conduction parameters of a two dimensional electron gas. We also examine the mechanisms of lowtemperature conductivity in the minima of oscillations of high frequency conductivity in the IQHE and FQHE regimes. In the magnetic field region where electrons are delocalized, the parameters determined by the acoustic technique do not differ from those determined by a direct current. However, the acoustic measurements do not require Hall bars and electrical contacts to be fabricated. In the minima of IQHE and FQHE oscillations electrons are localized, and ac conductivity turns to be via hopping. An analysis of the high frequency conductivity in the QHE regime has been carried out within a "two site" model. Furthermore, measurements of acoustoelectric effects in a tilted magnetic field provided the dependence of the activation energy on magnetic field in the fractional quantum Hall effect regime at ν=2/3. PACS numbers: 73.23.-b, 73.43.Qt arXiv:1112.0743v2 [cond-mat.mes-hall] 7 Dec 2011 FIG. 1. Sketches of the (a) acoustic experiment setup and (b) sample.

Crossover between localized states and pinned Wigner crystal in high-mobilityn-GaAs/AlGaAs heterostructures near filling factorν=1

“…(6) of Ref. 22. The dependences σ 1 (E) are qualitatively similar to the dependences σ 1 (T ) shown in Fig.…”

“…18) around integer values of the filling factor. 11,[19][20][21][22] These sharp wings have not been ever observed in low-mobility systems. Numerous microwave studies of real part, σ 1 (ω), of the complex conductance, σ(ω) ≡ σ 1 (ω) − iσ 2 (ω), close to integer ν revealed resonances at frequencies of 0.4-3 GHz, which were ascribed to pinned modes of the Wigner crystal.…”

“…34 Assuming that the electron system can be characterized by an effective temperature, T e , and performing analysis similar to the one described in Ref. 22 for ν = 1.1 we conclude that the heat released is proportional to (T noting that when the temperature (or the SAW intensity) increases the behavior of the complex conductance can be interpreted as manifestation of WC melting.…”

Acoustoelectric effects in very high-mobility p-SiGe/Ge/SiGe heterostructure at low temperatures in high magnetic fields

“…12; ε 1 , ε 0 and ε s are the dielectric constants of LiNbO 3 , of vacuum, and of the semiconductor, respectively; b and t are functions of a, d, ε 1 , ε 0 and ε s . The magnetic field dependence of σ 1 , i.e., the real part of the complex high-frequency conductivity, obtained from the SAW measurements at different temperatures is shown in Fig.…”

Surface Acoustic Waves Probe of the Spin Phase Transition at v=2/3 in n-GaAs/AlGaAs structure

“…This spin phenomenon has been investigated in numerous papers by different methods [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In Fig.…”