Interaction-induced interference in the integer quantum Hall effect

A recent experiment with a Fabry-Perot interferometer (FPI), operating in the integer quantum Hall effect regime, revealed that the period of the Aharonov-Bohm (AB) oscillations drops by a half at bulk fillings $\nu_B>2.5$, accompanied by an interfering charge $e^*=2e$. Although charge e is observed when the visibility is low, the single-particle interference is invariably fully dephased. Counterintuitively, the interference periodicity is determined by the area enclosed by the second-inner edge channel, separating the $\nu = 1$ and $\nu = 2$ regions, and not by the area within the outermost interfering channel. Such pairing is not observed in a Mach-Zehnder interferometer (MZI). A combination of an MZI and an FPI elucidates the role of the second-inner edge mode, as well as the formation of paired-electrons quasiparticles. The results suggest that a neutral chiral edge mode plays a crucial role in the pairing phenomenon. Our findings reveal that the observed pairing is not a curious isolated phenomenon, but one of many manifestations of unexpected edge physics in the quantum Hall regime.