Giant frictional drag in strongly interacting bilayers near filling factor one

We study the frictional drag in high mobility, strongly interacting GaAs bilayer hole systems in the vicinity of the filling factor ν=1 quantum Hall state (QHS) at the same fillings where the bilayer resistivity displays a re-entrant insulating phase. Our measurements reveal a very large longitudinal drag resistivity (ρ xx D) in this regime, exceeding 15 kΩ/□ at filling factor ν=1.15. ρ xx D shows a weak temperature dependence and appears to saturate at a finite, large value at the lowest temperatures. Our observations are consistent with theoretical models positing a phase separation, e.g., puddles of ν=1 QHS embedded in a different state, when the system makes a transition from the coherent ν=1 QHS to the weakly coupled ν=2 QHS.