title: Anomalous Coulomb Drag in Electron-Hole Bilayers due to the Formation of Excitons.
abstract: Several recent experiments have reported an anomalous temperature dependence of the Coulomb drag effect in electron-hole bilayers. Motivated by these puzzling data, we study theoretically a low-density electron-hole bilayer, where electrons and holes avoid quantum degeneracy by forming excitons. We describe the ionization-recombination crossover between the electron-hole plasma and exciton gas and calculate both the intralayer and drag resistivity as a function of temperature. The latter exhibits a minimum followed by a sharp upturn at low temperatures, in qualitative agreement with the experimental observations [see, e.g., J. A. Seamons et al., Phys. Rev. Lett. 102, 026804 (2009)]. Importantly, the drag resistivity in the proposed scenario is found to be rather insensitive to a mismatch in electron and hole concentrations, in sharp contrast to the scenario of electron-hole Cooper pairing.
authors.affiliation: Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland, College Park, Maryland 20742-4111, USA.
authors.forename: Dmitry K
authors.initials: DK
authors.lastname: Efimkin
authors.affiliation: Joint Quantum Institute and Condensed Matter Theory Center, University of Maryland, College Park, Maryland 20742-4111, USA.|School of Physics, Monash University, Melbourne, Victoria 3800, Australia.
authors.forename: Victor
authors.initials: V
authors.lastname: Galitski