Observation of superdiffusive phonon transport in aligned atomic chains

• Published in: Nature nanotechnology Vol. 16; no. 7; pp. 764 - 768
• Main Authors: Yang, Lin, Tao, Yi, Zhu, Yanglin, Akter, Manira, Wang, Ke, Pan, Zhiliang, Zhao, Yang, Zhang, Qian, Xu, Ya-Qiong, Chen, Renkun, Xu, Terry T., Chen, Yunfei, Mao, Zhiqiang, Li, Deyu
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-07-2021; Nature Publishing Group
• Subjects: 639/766/119/544; 639/925/357/1016; Anharmonicity; Chains; Chemistry and Materials Science; Current carriers; Energy charge; Heat conductivity; Heat transfer; Heat transport; Lattices; Letter; Materials Science; Mechanical properties; Modulus of elasticity; Nanotechnology; Nanotechnology and Microengineering; Nanowires; Phonons; Power law; Room temperature; Size effects; Stiffening; Superconductors; Thermal conductivity
• ISSN: 1748-3387; 1748-3395
• DOI: 10.1038/s41565-021-00884-6

Fascinating phenomena can occur as charge and/or energy carriers are confined in one dimension
1
–
4
. One such example is the divergent thermal conductivity (
κ
) of one-dimensional lattices, even in the presence of anharmonic interatomic interactions—a direct consequence of the Fermi–Pasta–Ulam–Tsingou paradox proposed in 1955
5
. This length dependence of
κ
, also known as superdiffusive phonon transport, presents a classical anomaly of continued interest
6
–
9
. So far the concept has remained purely theoretical, because isolated single atomic chains of sufficient length have been experimentally unattainable. Here we report on the observation of a length-dependent
κ
extending over 42.5 µm at room temperature for ultrathin van der Waals crystal NbSe
3
nanowires. We found that
κ
follows a 1/3 power law with wire length, which provides experimental evidence pointing towards superdiffusive phonon transport. Contrary to the classical size effect due to phonon-boundary scattering, the observed
κ
shows a 25-fold enhancement as the characteristic size of the nanowires decreases from 26 to 6.8 nm while displaying a normal–superdiffusive transition. Our analysis indicates that these intriguing observations stem from the transport of one-dimensional phonons excited as a result of elastic stiffening with a fivefold enhancement of Young’s modulus. The persistent divergent trend of the observed thermal conductivity with sample length reveals a real possibility of creating novel van der Waals crystal-based thermal superconductors with
κ
values higher than those of any known materials.
A 1/3 power law between thermal conductivity and length of a NbSe
3
nanowire is observed, pointing towards a superdiffusive heat transport regime.