We report single layer resistivities of 2-dimensional electron and hole gases in an electron-hole bilayer with a 10nm barrier. In a regime where the interlayer interaction is stronger than the intralayer interaction, we find that an insulating state
($drho/dT < 0$) emerges at $Tsim1.5{rm K}$ or lower, when both the layers are simultaneously present. This happens deep in the $$metallic regime, even in layers with $k_{F}l>500$, thus making conventional mechanisms of localisation due to disorder improbable. We suggest that this insulating state may be due to a charge density wave phase, as has been expected in electron-hole bilayers from the Singwi-Tosi-Land-Sjolander approximation based calculations of L. Liu {it et al} [{em Phys. Rev. B}, {bf 53}, 7923 (1996)]. Our results are also in qualitative agreement with recent Path-Integral-Monte-Carlo simulations of a two component plasma in the low temperature regime [ P. Ludwig {it et al}. {em Contrib. Plasma Physics} {bf 47}, No. 4-5, 335 (2007)]
We report Coulomb drag measurements on GaAs-AlGaAs electron-hole bilayers. The two layers are separated by a 10 or 25nm barrier. Below T$approx$1K we find two features that a Fermi-liquid picture cannot explain. First, the drag on the hole layer show
s an upturn, which may be followed by a downturn. Second, the effect is either absent or much weaker in the electron layer, even though the measurements are within the linear response regime. Correlated phases have been anticipated in these, but surprisingly, the experimental results appear to contradict Onsagers reciprocity theorem.
