Voltage Fluctuation to Current Converter with Coulomb-Coupled Quantum Dots

We study the rectification of voltage fluctuations in a system consisting of two Coulomb-coupled quantum dots. The first quantum dot is connected to a reservoir where voltage fluctuations are supplied and the second one is attached to two separate leads via asymmetric and energy-dependent transport barriers. We observe a rectified output current through the second quantum dot depending quadratically on the noise amplitude supplied to the other Coulomb-coupled quantum dot. The current magnitude and direction can be switched by external gates, and maximum output currents are found in the nA region. The rectification delivers output powers in the pW region. Future devices derived from our sample may be applied for energy harvesting on the nanoscale beneficial for autonomous and energy-efficient electronic applications.

Figure 1

(a) Schematic operating principle. Top: Designation of system components. Center: Asymmetric configuration with charge current flow to the right. Bottom: Asymmetric configuration with charge current flow to the left. For details see main text. (b) Electron microscopy image of the sample. The top, current carrying part of the system is shaded in blue, the bottom part, where the voltage fluctuations are supplied, in red. The respective QDs ${\text{QD}}_t$ and ${\text{QD}}_b$ are highlighted in dark blue and dark red. (c) Equivalent circuit with corresponding capacitances. The current through the upper part is measured via a picoamperemeter. The two upper side gates and their voltages $V_{\mathrm{gl}}$ and $V_{\mathrm{gr}}$ control the conductances of the left and right channel, whereas $V_{\mathrm{gb}}$ influences both channels almost equally and shifts the QD’s energy levels. $V_{\text{noise}}$ can be added to $V_{\mathrm{gb}}$ and provides the fluctuations which the device is able to rectify.

Figure 2

(a) Differential conductance traces for $V_{\mathrm{gb}}$ from 3.5 to 6 V against $V_{lr}$. Dark regions where the traces lie close to each other signify stable conductances. (b) Conductance asymmetry $g_{\mathrm{as}}$ against $V_{\mathrm{gb}}$ for $V_{lr}$ ranging from 0 to 10 mV.

Figure 3

(a) Experimental results of the noise rectification. The output current is plotted against $V_{\mathrm{gl}}=-V_{\mathrm{gr}}$ (push-pull) for noise amplitudes varied from 7.6 to 144 mV in steps of 15 mV. $V_{lr}=0\mathrm{V}$, $V_{\mathrm{gb}}=4.7\mathrm{V}$. ${\sigma }_{\text{noise}}$ controls the maximum current amplitude, while the side gates are able to influence the current flow’s direction. The insets show the current maxima $I_{\max }$ in dependence on ${\sigma }_{\text{noise}}$ up to 150 mV. (b) Simulated current rectification. $I$ versus $V_{\mathrm{gl}}=-V_{\mathrm{gr}}$ (push-pull) for different noise amplitudes.

Figure 4

(a) Output powers $P$ versus $V_{lr}$ for different ${\sigma }_{\text{noise}}$ increasing from 7.6 to 150 mV in steps of 15 mV. $V_{\mathrm{gl}}=-V_{\mathrm{gr}}=-0.75\mathrm{V}$ [cf. Fig. 3]. The power curves feature a parabolic shape, are zero at $V_{lr}=0\mathrm{V}$ and at $V_{lr}=V_{\mathrm{st}}$, and reach their maxima at $V_{lr}=V_{\mathrm{st}}/2$. (b) Maximum output powers $P_{\max }$ against ${\sigma }_{\text{noise}}$ at $V_{\mathrm{gl}}=-V_{\mathrm{gr}}=-0.75\mathrm{V}$. $P_{\max }$ exhibits a quadratic dependence on ${\sigma }_{\text{noise}}$. (c) Output powers $P$ versus $V_{lr}$ for different ${\sigma }_{\text{noise}}$ increasing from 7.6 to 150 mV in steps of 15 mV. $V_{\mathrm{gl}}=-V_{\mathrm{gr}}=0.55\mathrm{V}$. (d) Maximum output powers $P_{\max }$ against ${\sigma }_{\text{noise}}$ at $V_{\mathrm{gl}}=-V_{\mathrm{gr}}=0.55\mathrm{V}$. $V_{\mathrm{gb}}=4.7\mathrm{V}$ for all figures. The side gate voltage configurations used here are displayed in Fig. 3 via two small black arrows.