Anomalous single-electron transfer in common-gate quadruple-dot single-electron devices with asymmetric junction capacitances

Abstract

In this paper, anomalous single-electron transfer in common-gate quadruple-dot turnstile devices with asymmetric junction capacitances is revealed. That is, the islands have the same total number of excess electrons at high and low gate voltages of the swing that transfers a single electron. In another situation, two electrons enter the islands from the source and two electrons leave the islands for the source and drain during a gate voltage swing cycle. First, stability diagrams of the turnstile devices are presented. Then, sequences of single-electron tunneling events by gate voltage swings are investigated, which demonstrate the above-mentioned anomalous single-electron transfer between the source and the drain. The anomalous single-electron transfer can be understood by regarding the four islands as "three virtual islands and a virtual source or drain electrode of a virtual triple-dot device". The anomalous behaviors of the four islands are explained by the normal behavior of the virtual islands transferring a single electron and the behavior of the virtual electrode.

Single-electron pumping in single-common-gate quadruple-dot devices with asymmetric gate capacitances

“…The structure of a single-common-gate quadruple-dot SE device has been explained in our previous work. 25) The equivalent circuit of the quadruple-dot device is shown in Fig. 1.…”

“…The CB condition for T ij is denoted by CB ij . The CB conditions CB k(k+1) and CB (k+1)k , which correspond to tunneling events towards the drain and source, respectively, are expressed as follows 25) according to the orthodox theory:…”

“…where C T(k+1)k for 0 ⩽ k ⩽ 4 are the total capacitances between neighboring nodes (k + 1) and k. By replacing C T(k+1)k , V k+1 and V k with their solutions, the CB conditions can be expressed as linear inequalities of V, V g , and n 1 to n 4 with coefficients including combined capacitances consisting of C g1 to C g4 and C 10 to C 54 , as presented in appendix B in Ref. 25. Furthermore, the CB conditions can be rewritten using normalized voltages and capacitances in order to simplify them.…”

“…We have analytically investigated common-gate triple-dot and quadruple-dot SE devices and have demonstrated discrete SE transfer. [21][22][23][24][25] Furthermore, by introducing asymmetric gate capacitance (C g ) distributions into the common-gate triple-dot SE devices, we have demonstrated that SE pumping can be achieved by only one alternating gate voltage where an additional constant gate voltage is unnecessary. 26) In Ref.…”

“…We have already studied the quadruple-dot devices by an analytical approach 25) by using the orthodox theory 1,[14][15][16][17][18]31,32) and acquired explicit CB conditions within five tunnel junctions at zero temperature. In this paper, with the help of the established formulas, the stability diagrams for various C g distributions are drawn on the V′ g −V′ plane in order to confirm SE pumping where V′ g and V′ are the normalized gate and biasing voltages, respectively.…”