Role of density imbalance in an interacting bilayer hole system

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We study interacting GaAs hole bilayers in the limit of zero tunneling. When the layers have equal densities, we observe a phase coherent bilayer quantum Hall (QH) state at total filling factor ν=1, flanked by insulating phases at nearby fillings which suggest the formation of a pinned, bilayer Wigner crystal. As we transfer charge from one layer to another, the insulating phases disappear while, surprisingly, the ν=1 QH state becomes stronger. Concomitantly, a pronounced hysteresis develops in the longitudinal magnetoresistance at higher fillings, indicative of a first-order quantum phase transition.