Electron pump in multiple-tunnel junctions

We present measurements of an electron pump based on the Coulomb blockade in two multiple-tunnel junctions (MTJ's) connected in series, utilizing a single source of radio-frequency signal. The electron pump realizes both forward and reverse electron flow. In the reverse flow, the electrons move from the drain to the source in an opposite direction to the bias-voltage polarity. Moreover, the current polarity due to the electron pump can be switched by the two dc side-gate voltages. The bidirectional electron pump is attributed to asymmetric Coulomb blockade gaps at positive and negative sides in the current-voltage characteristics of the MTJ's.