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Nanotechnology

Heat flow through nanobridges

Nature volume 404, pages 943–944 (2000)Cite this article

When a sample of material is heated on one side, energy will flow to the cold end. In solid material, heat can be carried either by mobile electrons or by atoms vibrating around their fixed, equilibrium positions. Insulating materials do not contain mobile electrons so only atomic vibrations can transport heat in insulators. These vibrations are not random: the atoms move collectively so that together they form waves, called phonons. Objects in everyday life, such as a ceramic cooking pot, contain many different types of phonons with varying wavelengths, which carry heat from the hot to the cold end. But by making objects smaller and smaller, today's trend in physics and engineering, properties of phonons emerge that are not evident in large materials. On page 974 of this issue, Schwab et al.1 report an experiment involving an extremely narrow (nanometre-scale) bridge for phonons. A nanometre is a billionth of a metre, making the bridges about 500 atoms wide. The authors find that the amount of heat that can flow across the nanobridge is bound by an upper limit, set by the laws of quantum mechanics.

Many types of phonons with different wavelengths and characters can exist. Each leads to a specific mode of wave-like motion in an object, such as twisting or bending in a wire. In the centre of the device created by Schwab et al.1, various phonons are generated by heating ( Fig. 1b). But only specific phonon modes can couple into the narrow wires attached at each corner. One of these possible modes is shown in colour. Because only specific modes are allowed, the phonon spectrum is quantized in these nanobridges. Similarly, oscillations in the wires of the nanoharp (Fig. 1a) can occur only at a particular set of discrete frequencies, much as the strings in a full-sized harp are restricted to resonate at certain frequencies. In the nanoharp, these frequencies form the quantized spectrum of allowed wavelengths.

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Figure 1: The nanoscale world.

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Authors and Affiliations

  1. Department of Applied Physics, Delft University of Technology, PO Box 5046, GA Delft, 2600, The Netherlands

    Leo P. Kouwenhoven & Liesbeth C. Venema

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  1. Leo P. Kouwenhoven
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  2. Liesbeth C. Venema
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Correspondence to Leo P. Kouwenhoven.

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Kouwenhoven, L., Venema, L. Heat flow through nanobridges. Nature 404, 943–944 (2000). https://doi.org/10.1038/35010251

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