Quantum limitation on Coulomb blockade observed in a 2D electron system

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Abstract
The evolution of the Coulomb blockade of conduction through a small 2D electron island of large density of states, realized in a GaAs/Ga(Al)As heterojunction, is studied from the weak tunnel coupling to the Ohmic regime. Cotunneling arising from quantum charge fluctuations is identified, at low voltage, by its dependence on the product of junction conductances, and the current at threshold voltage is well described by a nonperturbative model. Small Coulomb conductance oscillations are found to persist even when both junctions exceed the conductance quantum.