Observation of even-denominator fractional quantum Hall states at ν = 3/4 and 5/4 in wide GaAs quantum wells

Two-dimensional electron systems (2DESs) confined to wide GaAs quantum wells provide a unique platform to study exotic fractional quantum Hall states (FQHSs) because the 2DES has a bilayer charge distribution with significant interlayer tunneling. Precise control over the 2DES density allows the tuning of the interlayer tunneling over a wide range. Here, we present our discovery of new even-denominator FQHSs in the lowest Landau level (orbital index N = 0) at filling factors v = 3/4 and 5/4 in an ultrahigh-quality 2DES confined to a 72.5-nm-wide GaAs quantum well. When the interlayer tunneling is sufficiently reduced at large 2DES density, the ground states at v = 3/4 and 5/4 evolve from composite fermion Fermi seas to FQHSs. These even-denominator FQHSs are easily destabilized by introducing a layer imbalance of about 2%, further elucidating their two-component nature. The v = 3/4 and 5/4 FQHSs can be interpreted using a generalization of the well known, two-component Halperin state.