Thermal conductance of single-molecule junctions

Single-molecule junctions have been extensively used to probe properties as diverse as electrical conduction1–3, light emission4, thermoelectric energy conversion5,6, quantum interference7,8, heat dissipation9,10 and electronic noise11 at atomic and molecular scales. But a quantity of considerable current interest—the thermal conductance of a single-molecule junction—has eluded direct experimental determination, reflecting the considerable challenge of detecting minute heat currents at the picowatt level. Here we show that, when used in conjunction with a time-averaging measurement scheme to increase the signal-to-noise ratio, the custom-developed probes that enabled thermal conductance measurements of single-metal-atom junctions12 can also quantify the much lower thermal conductance of single-molecule junctions. Our experiments on prototypical Au–alkanedithiol–Au junctions, where the number of carbon atoms was varied from two to ten, confirm that thermal conductance is to a first approximation independent of molecular length, consistent with detailed ab initio simulations. We anticipate that our approach will enable systematic exploration of thermal transport in many other one-dimensional systems, such as short molecules and polymer chains, for which computational predictions of thermal conductance13–16 have remained experimentally inaccessible.