Frictional Drag between Two Dilute Two-Dimensional Hole Layers
  We report drag measurements on dilute double layer two-dimensional hole systems in the regime of r_s=19~39. We observed a strong enhancement of the drag over the simple Boltzmann calculations of Coulomb interaction, and deviations from the T^2 dependence which cannot be explained by phonon-mediated, plasmon-enhanced, or disorder-related processes. We suggest that this deviation results from interaction effects in the dilute regime. 
R. Pillarisetty, Hwayong Noh, D. C. Tsui, E. P. De Poortere, E. Tutuc,   and M. Shayegan