Non-equilibrium charge stability diagrams of a silicon double quantum dot
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(Color online) (a) Schematic cross-section of the device. (b) Top-down SEM image of the depletion gates. (c) Example of the charge sensor current IAB as a function of VPL . The derivative dIAB /dVPL shows the quantum dot charging events as clear spikes on a smaller background. (d) Charge sensor current as a function of voltages VPL and VPR . Numbers (N, M) indicate regions of voltage space where the equilibrium configuration is with N electrons on the left dot and M electrons on the right dot.
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(Color online) (a) Differential charge sensor current at one inter-dot transition point in the stability diagram. (b) A cut along the red line in (a), integrated and scaled so that it shows the steepness of the transition. The black line is a fit to a theoretical model as described in the text. (c) and (e) Forward bias, VD = −0.27 mV. (d) and (f) Reverse bias, VD = +0.27 mV. Parts (e) and (f) show the same data as (c) and (d), respectively, with additional lines drawn to indicate energy levels of the system. At right electrochemical potential diagrams illustrate the configuration of each quantum dot at various points labeled in (e) and (f). A solid line indicates the electrochemical potential level of a dot when the opposite dot is unoccupied, a dashed line indicates the level when the opposite dot is occupied. Curved arrows in the diagrams for points A′ and F′ indicate the co-tunneling process described in the text.
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