Abstract:
We present the theory of the effect of exciton dragging by a Rayleigh surface acoustic wave at temperatures above the condensation temperature of the exciton gas and at zero temperature, where the effects of the Bose–Einstein condensation of the exciton gas are most pronounced. The magnitude of the acoustic drag flux in the exciton gas at high temperatures has been calculated taking into account the exciton-exciton interaction. It has been shown that the drag flux at typical experimental parameters (at a given intensity of the surface acoustic wave (SAW)) is independent of the frequency of the acoustic wave, whereas the interaction between excitons leads to screening of the SAW-induced perturbation, which results in an exponentially fast decrease in the drag flux with an increase in the exciton density. At low temperatures, in the presence of a condensate, the drag flux of condensate particles exhibits a resonance character when the velocity of Bogoliubov excitations approaches the velocity of the acoustic wave and the magnitude of the flux is linear in the SAW frequency. The drag flux of the above-condensate particles has a threshold character: the above-condensate particles are dragged by the wave at a velocity of the acoustic wave higher than the bogolon velocity. The magnitude of the above-condensate flux is inversely proportional to the SAW frequency.
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