Nonlinearity of Acoustic Effects and High-Frequency Electrical   Conductivity in GaAs/AlGaAs Heterostructures under Conditions of the Integer   Quantum Hall Effect
  The absorption coefficient for surface acoustic wave $\Gamma$ and variation in the wave velocity $\Delta V/V$ were measured in GaAs/AlGaAs heterostructures; the above quantities are related to interaction of the wave with two-dimensional electron gas and depend nonlinearly on the power of the wave. Measurements were performed under conditions of the integer quantum Hall effect (IQHE), in which case the two-dimensional electron gas was localized in a random fluctuation potential of impurities. The dependences of the components $\sigma_1(E)$ and $\sigma_2(E)$ of high-frequency conductivity $\sigma=\sigma_1 - i\sigma_2$ on the electric field of the surface wave were determined. In the range of the conductivity obeying the Arrhenius law ($\sigma_1 \gg \sigma_2$), the results obtained are interpreted in terms of the Shklovskii theory of nonlinear percolation-based conductivity, which makes it possible to estimate the magnitude of the fluctuation potential of impurities. The dependences $\sigma_1(E)$ and $\sigma_2(E)$ in the range of high-frequency hopping electrical conductivity, in which case ($\sigma_1 \ll \sigma_2$) and the theory of nonlinearities has not been yet developed, are reported. 
I. L. Drichko (a), A. M. Diakonov (a), I. Yu. Smirnov (a), and A. I.   Toropov (b) (a - A.F.Ioffe PTI of RAS, b - SPI of SD RAS)