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
Department of Mechanical Engineering, Vanderbilt University, Nashville, TN, USA.
School of Mechanical Engineering and Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, Southeast University, Nanjing, P. R. China.
Nat Nanotechnol. 2021 Jul;16(7):764-768. doi: 10.1038/s41565-021-00884-6. Epub 2021 Apr 15.
Fascinating phenomena can occur as charge and/or energy carriers are confined in one dimension. 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. This length dependence of κ, also known as superdiffusive phonon transport, presents a classical anomaly of continued interest. 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 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.
当电荷和/或能量载流子被限制在一维空间时，会出现一些引人入胜的现象。一个这样的例子是一维晶格的热导率（κ）发散，即使存在非谐原子间相互作用——这是1955年提出的费米-帕斯塔-乌拉姆-钦古悖论的直接结果。κ的这种长度依赖性，也被称为超扩散声子输运，是一个一直备受关注的经典反常现象。到目前为止，这个概念一直纯粹是理论上的，因为实验上无法获得足够长度的孤立单原子链。在这里，我们报告了在室温下对超薄范德华晶体NbSe纳米线的热导率κ随长度变化的观测结果，其长度范围超过42.5微米。我们发现κ随线长遵循1/3幂律，这为超扩散声子输运提供了实验证据。与声子边界散射导致的经典尺寸效应相反，当纳米线的特征尺寸从26纳米减小到6.8纳米时，观测到的κ增强了25倍，同时呈现出正常-超扩散转变。我们的分析表明，这些有趣的观测结果源于由于杨氏模量提高五倍而导致的弹性硬化所激发的一维声子的输运。观测到的热导率随样品长度持续发散的趋势揭示了创造κ值高于任何已知材料的新型范德华晶体基热超导体的真正可能性。
