Patterns in paired electron additions to fractional quantum Hall edge states in large GaAs quantum dots

In vertical tunneling into a large and low disorder 2D GaAs quantum dot, we observe electrons entering edge states and an unusual and unpredicted pair tunneling of electrons into the dot’s quantum Hall edge states, with double-height capacitance peaks and a coincident h/2e periodicity in magnetic flux through the dot. Remarkably, results from interferometry experiments[1] at similar Landau level filling fractions also show this h/2e periodicity over the nearly the same filling factor range where it is observed in these dot experiments. Thus, in increasing the magnetic field through the dot by one flux quantum, we observe that 4 electrons are added to the edge (2 double height peaks). While we observe such pairing everywhere in the filling factor range from v = 2 to v = 5, the h/2e periodicity applies near filling factor 5/2. Away from 5/2, the double-height peaks are not uniformly spaced in magnetic field but instead themselves group into pairs. Fourier transforms of the data reveal different unusual periodicities other than h/e and h/2e, particularly in the tunneling rates for the peaks.
[1]Choi et al. Nat. Comm. 6, 7435 (2015)