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 $r_s=19\mathrm{}–39$. 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.