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The undoped SET is embedded in a measurement set-up capable of simultaneous rf and dc measurements. The 2DEG is induced by applying a voltage to the TG, with current passed between the source (S) and drain (D). The SET is controlled by applying voltage to L, R, and PG gates via 10 kΩ rf-chokes (L was kept grounded due to strong coupling with the PG). Inset: A SEM image of the SET, the darker regions are where the top-gate has been etched away. The scale bar is 500 nm.
4 K characterisation of the SET. (a) The measured dependence of rf reflectance S 11 on frequency (f) is shown for different top-gate voltages corresponding to electron densities (n) of , respectively. S 11 starts at −17 dB due to losses in the lines from the top of the rf dip-station to the sample stage at room temperature. The dashed black line is the result of a lumped-element circuit model 17 for VTG = 1.020 V. (b) The rf reflectometry circuit is at resonance (487 MHz). We plot S 11 as a function of the four-terminal resistance of the dot, where R 4 T is varied by changing the plunger gate voltage VPG . Measurements were performed for , where . 8
Millikelvin measurements of the CB oscillations (left axis) in the two-terminal conductance g (series resistance subtracted 19 ). The rf-reflectance S 11 (right axis) traces out the CB oscillations when the transfer function is sensitive to the dot. We apply −50 dBm at 447 MHz to the source. Losses in the lines, from the top of the dilution fridge to the sample stage at room temperature, are −37 dB marking the upper limit of S 11. The inset shows the spectrum of the reflected power for a small (0.09 erms .) 890 Hz sine wave on the top plunger-gate.
Rapid gated measurements of CB oscillations. The SET is biased to sit on the side of a CB peak and a 15 mV triangle-wave is applied at 110 Hz to the top plunger-gate. (a) S 11 monitors the changing occupation number of the SET as indicated by the smaller peaks, and (b) shows the triangle wave applied to the top plunger-gate.
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