7/3 fractional quantum Hall state in GaAs double quantum wells

We observed the fractional quantum Hall effect at a total filling factor of 7/3 in the Hall resistance, accompanied by a single minimum in longitudinal magnetoresistance in uncoupled, bilayer electron gases formed in GaAs double quantum well systems. When the density of the top electron gas is varied, the total 7/3 (1+4/3) state can be tuned such that while the Hall plateau value essentially remains unchanged, the associated longitudinal magnetoresistance develops into a double minimum. When Zeeman energy is introduced by tilting the applied magnetic field, the two minima respond differently; one remains essentially unchanged, while the other deepens, consistent with the differing spin dependences of the integer and fractional gaps. Our results demonstrate that the detailed evolution of the 7/3 plateau probes layer-resolved incompressibility, interlayer charge redistribution, and spin-dependent gap behavior in a nontunneling bilayer system.