Coexistence of Composite Bosons and Composite Fermions inν=12+12Quantum Hall Bilayers

In bilayer quantum Hall systems at filling fractions near $\nu =1/2+1/2$, as the spacing $d$ between the layers is continuously decreased, intralayer correlations must be replaced by interlayer correlations, and the composite fermion (CF) Fermi seas at large $d$ must eventually be replaced by a composite boson (CB) condensate or “111 state” at small $d$. We propose a scenario where CBs and CFs coexist in two interpenetrating fluids in the transition. Trial wave functions describing these mixed CB-CF states compare very favorably with exact diagonalization results. A Chern-Simons transport theory is constructed that is compatible with experiment.