Local ionic and electron heating in single-molecule junctions

A basic aim in molecular electronics is to understand transport through a single molecule connected to two electrodes. Substantial progress towards this goal has been made over the past decade as a result of advances in both experimental techniques and theoretical methods. Nonetheless, a fundamental and technologically important issue, current-induced local heating of molecules, has received much less attention. Here, we report on a combined experimental and theoretical study of local heating in single molecules (6-, 8- and 10-alkanedithiol) covalently attached to two gold electrodes as a function of applied bias and molecular length. We find that the effective local temperature of the molecular junction first increases with applied bias, and then decreases after reaching a maximum. At fixed bias, the effective temperature decreases with increasing molecular length. These experimental findings are in agreement with hydrodynamic predictions, which include both electron-phonon and electron-electron interactions.