Probing the limits of heat flow

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Science  17 Mar 2017:
Vol. 355, Issue 6330, pp. 1125-1126
DOI: 10.1126/science.aam9362

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The existence of universal upper bounds (limits) for the rates of transport of electricity and thermal energy is a striking manifestation of quantum mechanics. These fundamental bounds can be revealed in low-dimensional constrictions defining a single transport channel. The discrete unit (quantum) of electrical conductance G0 has been observed in many experiments dating back to 1988 (1, 2), but the quantum of thermal conductance G0,Th has been much more challenging to probe. Unlike tiny electrical currents, it is much harder to measure minute heat currents in a reproducible manner. On page 1192 of this issue, Cui et al. (3) conquer this challenge by developing an experimental platform for studying quantum thermal transport at the atomic limit. Their work reveals that thermal conductance can be quantized even at room temperature, as well as the fundamental relation between the thermal and electrical conductances. This study paves the way for investigations of thermal phenomena in individual molecular devices, with technological ramifications for controlling energy transport in nanoscale electronic circuitry.