Frictional drag between spatially separated two-dimensional electron   gases mediated by virtual phonon exchange
  We have calculated the frictional drag between spatially separated quantum wells with parallel two-dimensional electron gases due to interlayer electron-electron interaction mediated by virtual exchange of acoustic phonons due to piezoelectric and deformation potential interaction. It is shown that the frictional drag is dominated by the piezoelectric coupling. According to our calculations temperature dependence of the drag scattering rate divided by squared temperature T exhibits a pronounced peak which for the experimental situation and in agreement with the finding of T. J. Gramila, et al., Phys. Rev. B 47, (1993) 12957 is obtained at about T=2.1 K. We ascribe the appearance of this peak to a change from small to large angle scattering in the virtual phonon exchange. 
Samvel M. Badalyan and Ulrich Roessler