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Surface acoustic waves and the magnetoconductivity of a two-dimensional electron gas

The frequency- and wavevector-dependent conductivity tensor of a two-dimensional electron gas is determined within a semiclassical model containing two different characteristic times, a transport time and a lifetime. The velocity shift of a surface acoustic wave, caused by the piezoelectric coupling, is calculated as a function of magnetic field. The results are applicable under conditions where the frequency of the surface acoustic wave is comparable to the cyclotron frequency. The calculated velocity shift is compared to that observed for composite fermions in the quantum Hall regime near half-filling.