A voltage difference is created across a junction of two wires held at different temperatures. This phenomenon, called thermoelectric effect, has been widely studied and used in various applications such as thermoelectric power generators, thermoelectric refrigerators, and temperature measurement. When the cross section of the junction contact is reduced to a few atoms, quantum-mechanical effects or, specifically, quantum interferences among electrons affect the transport of electrons across the junction. These interferences are strongly dependent on the structure, including minute defects, of the atomic-scale contact and surrounding material, which determine electrical properties such as conductance and thermoelectric voltage. So far, quantum interference effect in atomic-scale metal contacts has not found much application, because of the difficulty in precisely controlling atomic structures.
Akira Aiba, Manabu Kiguchi and their colleagues at Tokyo Tech experimentally demonstrated that the magnitude and sign of the thermoelectric voltage across atomic-scale gold junctions can be controlled by applying a mechanical strain to deform the contact minutely and accurately while the structure of the surrounding material remains unaffected. Minute deformations were performed through bending of the junction's substrate by using a piezoelectric transducer and by maintaining a low-temperature environment so that the atoms do not gain sufficient kinetic energy to vibrate strongly and cause random deformations of the structure. As the contact was elongated, the conductance decreased in a step-wise manner, and the thermoelectric voltage varied sharply with changes in sign. Remarkably, these changes were perfectly reversible: the electrical properties were restored to their initial values when the contact was compressed back to its initial structure.Invest in MEM. To read more, click here.