Interlayer coherent composite Fermi liquid phase in quantum Hall bilayers

Composite fermions have played a seminal role in understanding the quantum Hall effect, particularly the formation of a compressible composite Fermi liquid' (CFL) at filling factor nu = 1/2. Here we suggest that in multi-layer systems interlayer Coulomb repulsion can similarly generate metallic’ behavior of composite fermions between layers, even if the electrons remain insulating. Specifically, we propose that a quantum Hall bilayer with nu = 1/2 per layer at intermediate layer separation may host such an interlayer coherent CFL, driven by exciton condensation of composite fermions. This phase has a number of remarkable properties: the presence of bonding' and antibonding’ composite Fermi seas, compressible behavior with respect to symmetric currents, and fractional quantum Hall behavior in the counterflow channel. Quantum oscillations associated with the Fermi seas give rise to a new series of incompressible states at fillings nu = p/[2(p \pm 1)] per layer (p an integer), which is a bilayer analogue of the Jain sequence.