Measurement of electron-hole friction in an n-doped GaAs/AlGaAs quantum   well using optical transient grating spectroscopy
  We use phase-resolved transient grating spectroscopy to measure the drift and diffusion of electron-hole density waves in a semiconductor quantum well. The unique aspects of this optical probe allow us to determine the frictional force between a two-dimensional Fermi liquid of electrons and a dilute gas of holes. Knowledge of electron-hole friction enables prediction of ambipolar dynamics in high-mobility electron systems. 
Luyi Yang, J. D. Koralek, J. Orenstein, D. R. Tibbetts, J. L. Reno,   and M. P. Lilly
cond-mat.mes-hall