Ballistic Phonons in Ultrathin Nanowires

Daniel Vakulov, Subash Gireesan, Milo Y. Swinkels, Ruben Chavez, Tom Vogelaar, Pol Torres, Alessio Campo, Marta De Luca, Marcel A. Verheijen, Sebastian Koelling, Luca Gagliano, Jos E.M. Haverkort, F. Xavier Alvarez, Peter A. Bobbert, Ilaria Zardo, Erik P.A.M. Bakkers (Corresponding author)

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According to Fourier's law, a temperature difference across a material results in a linear temperature profile and a thermal conductance that decreases inversely proportional to the system length. These are the hallmarks of diffusive heat flow. Here, we report heat flow in ultrathin (25 nm) GaP nanowires in the absence of a temperature gradient within the wire and find that the heat conductance is independent of wire length. These observations deviate from Fourier's law and are direct proof of ballistic heat flow, persisting for wire lengths up to at least 15 μm at room temperature. When doubling the wire diameter, a remarkably sudden transition to diffusive heat flow is observed. The ballistic heat flow in the ultrathin wires can be modeled within Landauer's formalism by ballistic phonons with an extraordinarily long mean free path.

Original languageEnglish
Pages (from-to)2703-2709
Number of pages7
JournalNano Letters
Issue number4
Publication statusPublished - 8 Apr 2020


  • ballistic phonons
  • GaP
  • heat transport
  • Nanowires
  • Raman spectroscopy


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