Hall resistance of the reentrant insulating phase around the 1/5 fractional quantum Hall liquid

We report a systematic study of the low-temperature Hall resistance ρxy in the reentrant insulating phase (IP) around the 1/5 fractional quantum Hall (FQH) liquid. At filling factors {ν}=1/5 and {ν}=2/9, ρxy=5h/e² down to 22 mK and ρxy=9h/2e² down to 40 mK, respectively. In the reentrant IP for {ν}>1/5, and for {ν}1/5 near the 1/5 FQH liquid, ρxy is normal (=B/ne) and independent of T. Our experimental findings directly imply that σₓₓ{→}0 and σxy{→}0, but ρxy{→}B/ne as T{→}0 in these IP regions. We discuss implications of the findings with regard to the various theoretically proposed ground states for the IP.