Pairing in bilayer quantum Hall systems

Among the peculiar quantum Hall states that have been observed in Coulomb-coupled bilayer quantum Hall systems, there are a number whose origin depends on some type of pairing between constituent fermions.  For example, a fractional quantized state observed in a double layer of graphene separated by insulating hBN, at Landau-level filling 3/7 in each layer, requires pairing between electron-like composite fermions in one layer and hole-like composite fermions in the other. The interlayer coherent quantum Hall state observed in GaAs double quantum wells and in graphene double layers, at total Landau-level filling 1, may be variously understood as arising from pairing between electrons in one layer and holes in the other, as p-wave pairing of composite fermions in opposite layers, or as s-wave pairing between electron composite fermions in one layer and hole composite fermions in the other. I will discuss these concepts in the context of recent experimental observations and  theoretical developments concerning these systems.[1-4]