Atomic and single-molecule junctions represent the ultimate limit to the miniaturization of electrical circuits. They are also ideal platforms for testing quantum transport theories that are required to describe charge and energy transfer in novel functional nanometer-scale devices. Recent work has successfully probed electric and thermoelectric phenomena in atomic-scale junctions. However, heat dissipation and transport in atomic-scale devices remain poorly characterized owing to experimental challenges. An international team of researchers at the University of Michigan (USA), the Universidad Autónoma de Madrid (Spain), and the University of Konstanz (Germany), involving Jun.-Prof. Fabian Pauly, could provide an important contribution to these topics. They used custom-fabricated scanning probes with integrated nanoscale thermocouples to investigate heat dissipation in the electrodes of single-molecule (‘molecular’) junctions. They found that if the junctions had transmission characteristics that were strongly energy dependent, this heat dissipation was asymmetric — that is, unequal between the electrodes — and also dependent on both the bias polarity and the identity of the majority charge carriers (electrons versus holes). In contrast, junctions consisting of only a few gold atoms (‘atomic junctions’) whose transmission characteristics showed weak energy dependence did not exhibit appreciable asymmetry. Their results unambiguously relate the electronic transmission characteristics of atomic-scale junctions to their heat dissipation properties, establishing a framework for understanding heat dissipation in a range of mesoscopic systems where transport is elastic — that is, without exchange of energy in the contact region. The techniques established in their work will enable the study of Peltier effects at the atomic scale, a field that has been barely explored experimentally despite interesting theoretical predictions. Furthermore, the experimental advances described in their article might enable the study of heat transport in atomic and molecular junctions — an important and challenging scientific and technological goal that has remained elusive.
W. Lee, K. Kim, W. Jeong, L. A. Zotti, F. Pauly, J. C. Cuevas, and P. Reddy
Nature 498, 209 (2013)
Press release University of Konstanz