  Pairing interaction between fermionic particles leads to composite Bosons
that condense at low temperature. Such condensate gives rise to long range
order and phase coherence in superconductivity, superfluidity, and other exotic
states of matter in the quantum limit. In graphene double-layers separated by
an ultra-thin insulator, strong interlayer Coulomb interaction introduces
electron-hole pairing across the two layers, resulting in a unique superfluid
phase of interlayer excitons. In this work, we report a series of emergent
fractional quantum Hall ground states in a graphene double-layer structure,
which is compared to an expanded composite fermion model with two-component
correlation. The ground state hierarchy from bulk conductance measurement and
Hall resistance plateau from Coulomb drag measurement provide strong
experimental evidence for a sequence of effective integer quantum Hall effect
states for the novel two-component composite fermions (CFs), where CFs fill
integer number of effective LLs (Lambda-level). Most remarkably, a sequence of
incompressible states with interlayer correlation are observed at half-filled
Lambda-levels, which represents a new type of order involving pairing states of
CFs that is unique to graphene double-layer structure and beyond the
conventional CF model.
