Coulomb Blockade Ratchet

We investigate the transport properties of a new class of ratchets. The device is constructed by applying an ac voltage to the metallic single electron tunneling transistor, and a net transport current is induced by the time-dependent bias-voltage, although the voltage value is on the average zero. The mechanism underlying this phenomenon is the Coulomb blockade of the single electron tunneling. The directions and the values of the induced net currents can be well controlled by the gate-voltage. A net transport current has also been observed even in the absence of the external bias-voltages, which is attributed to the noise in the circuit.