Quantum Point Contact Switches

By repeatedly bringing a sharpened nickel wire in contact with a gold surface, switching behavior between electron tunneling and ballistic transport states is demonstrated. To an accuracy of 1%, the high conductivity, ballistic state has a quantized resistance of h/2e**2= 12.9 k Omega. Switching is accomplished by moving the electrodes with a piezoelectric actuator over a distance of 2 angstroms. The two electrodes and the electromechanical actuator form a three-terminal device that is demonstrated to be a useful and reliable digital as well as analog switch. It shows a discrimination of about 20 between high and low states and possesses the important property of power gain. The conductance channel is most likely only one atom wide and possibly consists of altogether only a single atom.