Towards the ground state of an electron–hole bilayer

Transport measurements down to 50 mK have been performed on independently contacted electron–hole bilayers (EHBL) with a 10 nm barrier, close to the excitonic Bohr radius of the system (View the MathML source). Coulomb drag measured reveals a departure from that expected for two Fermi liquids, exhibiting an upturn that may be followed by a downturn or even a sign-reversal at the lowest temperatures. Concurrently an insulating state in the single-layer resistivities has been found for low sheet resistances (ρ≪h/e2), well away from where the metal–insulator transition has been previously observed in two-dimensional systems. We can unambiguously show that this insulating state is caused by the interlayer interaction, as opposed to disorder. We consider the possibility of excitonic and collective mode driven phases that have been anticipated in EHBLs.