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(a) Linear conductance as a function of gate voltage of the QPC. Conductance plateaus appear near 1.2 and , with several resonances before the QPC is pinched off. (b) Grayscale plot of nonlinear differential conductance . In addition to clear Coulomb diamonds, transport through excited levels appears as extra lines outside the diamonds (white arrows).
(Color online) Linear conductance vs the gate voltage of the SET. Clear Coulomb oscillations are observed. Inset (a): Electron micrograph of the SET. The coupling between the 2D reservoirs and the quantum dot can be tuned by controlling the voltages on gates , , and . By varying the voltage on the plunger gate , the potential of the quantum dot is modified and the energy for adding an electron to the quantum dot is shifted into and out of resonance with the Fermi level of the 2D reservoirs. A peak in conductance occurs when the addition energy is aligned to the Fermi level so that an electron can tunnel onto and off of the quantum dot. All the data shown in this letter are measured by varying the plunger gate , with gates , , and fixed at constant voltages. Inset (b): A conductance peak fit to the line shape expected in the classical Coulomb blockade regime (multilevel transport), (Ref. 3), where is the peak conductance, is the conversion ratio from gate voltage to energy, and is the location in gate voltage of the conductance peak. The three fit parameters are , , and .
(Color online) (a) Coulomb oscillations at three different temperatures. From bottom to top: 0.314, 1, and . (b) The fitting parameter as a function of temperature. The line is the least squares fit to the data excluding the two lowest temperature points. The slope is equal to , yielding an estimate .
(Color online) (a) Differential conductance as a function of plunger gate voltage and source-drain bias . Stable and uniform Coulomb diamonds are observed. (b) Energy spacing between successive adjacent peaks. The average spacing is with a fluctuation of tens of .
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