High-frequency transport in $p$-type Si/Si$_{0.87}$Ge$_{0.13}$   heterostructures studied with surface acoustic waves in the quantum Hall   regime
  The interaction of surface acoustic waves (SAW) with $p$-type Si/Si$_{0.87}$Ge$_{0.13}$ heterostructures has been studied for SAW frequencies of 30-300 MHz. For temperatures in the range 0.7$<T<$1.6 K and magnetic fields up to 7 T, the SAW attenuation coefficient $\Gamma$ and velocity change $\Delta V /V$ were found to oscillate with filling factor. Both the real $\sigma_1$ and imaginary $\sigma_2$ components of the high-frequency conductivity have been determined and compared with quasi-dc magnetoresistance measurements at temperatures down to 33 mK. By analyzing the ratio of $\sigma_1$ to $\sigma_2$, carrier localization can be followed as a function of temperature and magnetic field. At $T$=0.7 K, the variations of $\Gamma$, $\Delta V /V$ and $\sigma_1$ with SAW intensity have been studied and can be explained by heating of the two dimensional hole gas by the SAW electric field. Energy relaxation is found to be dominated by acoustic phonon deformation potential scattering with weak screening. 
I. L. Drichko, A. M. Diakonov, I. Yu. Smirnov, G. O. Andrianov, O. A.   Mironov, M. Myronov, D. R. Leadley, T. E. Whall