7/3 fractional quantum Hall state in bilayer electron systems

The Fractional Quantum Hall Effect (FQHE) is a remarkable demonstration of quantum physics observed in the two-dimensional electron gas (2DEG) under a strong magnetic field. In the FQHE regime, free electrons form bound states influenced by magnetic flux quanta, leading to correlated many-body states. In the present work, we investigated the 7/3 FQH state in bilayer electron systems (BES) formed in a GaAs double quantum well, which offers a platform distinct from single-layer systems. The wide barrier (30 nm) separating the two electron layers prohibits tunnelling between them. In this system, we observed the FQHE at a total filling factor of 7/3 (1+4/3). When the density of the top electron gas is varied, the combined 7/3 state can be tuned such that the plateau representing it almost doubles, accompanied by a double minimum in longitudinal magnetoresistance, indicating the emergence of an additional state. A strong interaction between them results in the merging of two states into a single state depending on carrier density.