Direct control of the tunnel splitting in a one-electron double quantum dot

Quasistatic transport measurements are employed on a laterally defined tunnel-coupled double quantum dot. A nearby quantum point contact allows us to track the charge as added to the device. If charged with only up to one electron, the low-energy spectrum of the double quantum dot is characterized by its quantum mechanical interdot tunnel splitting. We directly measure its magnitude by utilizing particular anticrossing features in the stability diagram at finite source-drain bias. By modification of gate voltages defining the confinement potential, as well as by variation of a perpendicular magnetic field, we demonstrate the tunability of the coherent tunnel coupling.

Figure 1

(Color online) (a) Scanning electron microscopy image of the gate electrodes used for defining a DQD and a QPC. The approximate geometry of the DQD (white area) and electron flow (arrows) are indicated. (b) Stability diagram of the DQD plotting the transconductance $d{I}_{\mathrm{QPC}}∕d{U}_{\mathrm{gL}}$ through the QPC. A background signal has been subtracted. The open circles indicate local maxima of current through the DQD at constant $U_{\mathrm{gR}}$. The bars $(\Sigma ,\Delta )$, each corresponding to $1\mathrm{meV}$, illustrate the axis directions, the box the plot range of Figs. 2, 3.

Figure 2

(Color online) (a) Measurement of the SET current through a one-electron DQD at $U_{\mathrm{SD}}=-0.75\mathrm{mV}$ and $U_{\mathrm{gC}}=-1.47\mathrm{V}$ (logarithmic scale), including model lines for strong interdot coupling [see (b)]. (b) Corresponding model expectations for SET transport features at finite source-drain bias in the two cases of weak (dashed lines) versus strong (solid and dotted lines) interdot coupling.

Figure 3

(Color online) (a) Differential conductance $d{I}_{\mathrm{DQD}}∕d{U}_{\mathrm{SD}}$ through the DQD corresponding to the current measurement shown in Fig. 2a (identical parameters, logarithmic scale). (b) The corresponding differential transconductance $d{I}_{\mathrm{QPC}}∕d{U}_{\mathrm{gL}}$ through a nearby QPC (linear scale). For both plots, the model lines are identical to those in Fig. 2.

Figure 4

(Color online) (a) Tunnel splitting $2t_0$ of the one-electron DQD and charging energy for the second electron $E_2$ in dependence on gate voltage $U_{\mathrm{gC}}$. (b) $E_2$ and $2t_0$ plotted as function of a perpendicular magnetic field.