Pairing and Pair Tunneling of Electrons at the Edge of a GaAs Quantum Dot Two-Dimensional Electronic System

We have large (diameter ~0.8 μm) ultra-clean quantum dots that act as mini-2D electron systems and studied their single electron addition spectra at ~45 mK using capacitive sensing. Single electrons tunnel from an n+ GaAs electrode across an AlGaAs tunnel barrier into an otherwise electrically floating quantum dot. We measured the magnetic field dependence of electron addition energies from a completely empty dot, up to dot occupancies of ~2000 electrons. Here, we report the observation in the addition spectra of individually localized states, incompressible Landau gaps, and isolated tunneling to edge states. We see electron additions to the edge states between filling factors ν = 1 and ν = 2 with single flux quantum (h/e) periodicity in magnetic field. Remarkably, between filling factors ν = 2 and ν = 5, we observe the pairing of electron additions to states at the edges of the quantum dots with a corresponding 2e charge tunneling and with (h/2e) periodicity in magnetic field. These results are consistent with interferometry work from the group of Heiblum[1] showing an unexpected h/2e periodicity around the same filling factors, and they suggest that the same correlated electron physics is creates a novel pair tunneling effect.
Choi et al. Nat. Comm. 6, 7435 (2015)