Paired Electron Additions to Fractional Quantum Hall Edge States in Large GaAs Quantum Dots*

We measure capacitance signals from additions of single electrons to a large (0.8 μm) 2D GaAs quantum dot and thereby determine the energies required to add electrons to the dot. The dot is sandwiched inside of a “tunnel capacitor” in which electrons can tunnel from the dot to a nearby capacitor electrode. We observe single electron capacitance peaks to edge states over a wide range of filling factors. As a function of magnetic flux through the dot, between filling factors v = 1 and v = 2, these edge state peaks are regularly spaced, with periodicity h/e. Surprisingly, over the range v = 2 to v = 5, the peaks have double-height, and the periodicity is halved to h/2e. The pairing cannot be explained in the Coulomb blockade picture, in which the two electrons in a pair would instead be separated by a charging energy, and models involving electron rearrangements fail because they predict a suppression of tunneling rates that we do not observe. Instead the sequence of successive paired tunneling events behaves in the same way as tunneling of electrons into superconducting quantum dots.