Electrons at the nanoscale behave quite differently from those in the bulk as their wavelength starts to be relevant. As an example, individual molecular and atomic vibrational modes dominate in the differential conductance of nanoscale materials, and the discrete character of the charges manifests itself as white noise (“shot noise”). Experimentalists can study features of the white noise to gather information on transport characteristics in nanoscale junctions and constrictions.
Writing in Physical Review Letters, Manohar Kumar, at Leiden University in the Netherlands, and co-workers present results from a study on a mechanically controlled break junction—a deliberately severed atomic contact between two gold wires. The team looked at an inelastic scattering contribution to shot noise in several configurations of nanowires. The sign of this contribution, which had been predicted but not observed, changes with the magnitude of the transmission through the conduction channel. It is positive for high transmission values but negative for low ones, a property that the authors ascribe to coherent two-electron processes mediated by electron-phonon scattering as well as the Pauli exclusion principle. These results should provide more quantitative answers to how atomic vibrations and electronic noise affect molecular electronics. – Daniel Ucko