New fractional quantum Hall state in double-layer two-dimensional electron systems

Transport studies on bilayer two-dimensional electron systems in GaAs double quantum wells have revealed a new fractional quantum Hall state that has no known counterpart in a single-layer 2D system. At total filling fraction =1/2 we observe a deep minimum in the diagonal resistivity and a flat Hall plateau within 1.5% of 2h/e2. Studies of this new state in several samples with varying densities and layer separations strongly suggest this new state arises from interlayer Coulomb correlations. The data also suggest that the =1 quantum Hall effect seen in these samples has a similar origin.