Strongly coupled edge states and frequency doubling in a graphene quantum Hall interferometer

Electronic interferometers using chiral, one-dimensional (1D) edge channels of the quantum Hall effect (QHE) can demonstrate a wealth of fundamental phenomena including quasiparticle exchange statistics. When multiple edge channels are involved, FP interferometers in past works have also exhibited Aharonov-Bohm (AB) interference frequency doubling, suggesting pairing of elementary charges to form 2e quasiparticles. Here, following our recent report we discuss measurements in a highly tunable graphene-based QHE FP interferometer that elucidates the connection between interferometer phase jump and AB frequency doubling. By tuning the electron density from the QHE filling factors ν < 2 to ν > 7, we observe continuously modulating periodic interference phase jumps leading to apparent AB oscillation frequency doubling. These results reveal that repulsive Coulomb coupling between the spin-split, copropagating edge channels can explain aspects of this novel strongly coupled regime, where a perfect anti-correlation exists between the two channels. These results expand the understanding of edge state coupling in multichannel QHE interferometers and provide an informative framework for future multi-edge interference experiments.