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Interlayer Coherent Composite Fermi Liquid in Quantum Hall Bilayers and Beyond


Composite fermions have played a seminal role in advancing our understanding of the quantum Hall effect, particularly the formation of a compressible composite Fermi liquid (CFL) at filling factor nu = 1/2.  Motivated by experiments on systems ranging from quantum Hall bilayers to 3D bismuth, I will discuss a new kind of multi-layer CFL, wherein interlayer Coulomb repulsion generates `metallic' behavior of composite fermions between layers.  Such `interlayer coherent CFLs' raise the intriguing possibility that composite fermions may emerge in higher dimensions.  As a concrete example, I will propose that quantum Hall bilayers with nu = 1/2 per layer at intermediate layer separation may host an interlayer coherent CFL, driven by exciton
condensation of composite fermions.  I will discuss the rather remarkable properties of this state, and describe a new sequence of incompressible quantum Hall states that emerge from it at nearby filling factors.  Future experimental and theoretical work will also be discussed, in particular a generalization of this phase to three dimensions.