Observation of Coulomb-blockade oscillations by the back gate with subattofarad mutual capacitance

A quantum dot is formed in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs using the split-gate method. First the characteristics of the point contact, which determine the electron transport in the quantum dot, are investigated. Quantized conductance peculiar to the one-dimensional subband is observed. Next the transport properties of the quantum dot are studied by changing the voltage of the back gate, which is placed about 360 μm from the dot. Coulomb-blockade oscillations are observed before the current is completely pinched off. The charging energy of the dot is estimated to be about 0.6 meV based on the temperature dependence and source-drain voltage dependence of the oscillations. It is clarified experimentally that only the mutual capacitance between the back gate and the dot determines the oscillation period.