The research group of Associate Professor Ni Yuxiang, who is a Eyas-Scholar from School of Physical Science and Technology, has recently made a series of progress in the research on the regulation mechanism of nanostructures on phonon heat conduction in materials, and has published two papers in Physical Review B. Physical Review B, published by American Physical Society (APS), is one of the most influential and authoritative journals in condensed matter theory and one of the 82 top journals in the world included in The Nature Index.
Thermal conductivity is concerned as one of the important physical properties of materials. Associate Professor Ni Yuxiang’s research team used molecular dynamics simulation methods and the wave-particle duality of phonons to propose a new physical mechanism for inhibiting the heat conduction of nanowires, providing new ideas and theoretical basis on the structural design of high-temperature insulation materials and thermoelectric materials
Starting from the volatility of phonons, the research group proposed a novel surface threaded resonator to reduce the thermal conductivity of silicon nanowires. The results of molecular dynamics simulation show that the thermal conductivity and phonon transmission spectrum of silicon nanowires decrease with the increase of the periodic density of surface threads. When the periodic density of surface threads is large, the thermal conductivity of silicon nanowires can be reduced by 35.8% that is far greater than the thermal conductivity reduction effect of the traditional phonon resonator nanowall (11.9%) and nanopillar (14.9%). The phonon transmission spectrum shows that the transmission of phonons is hindered in the entire frequency range. The phonon dispersion relationship, the group velocity and the spatial distribution of phonon energy all confirm that the phonon resonance effect occurs in the surface-threaded silicon nanowire. The spiral thread wraps around the nanowire, whose structure is similar to the "Golden Dragon Pillar" in ancient Chinese architecture, has an important impact on its thermal conductivity. See article:https://journals.aps.org/prb/abstract/10.1103/PhysRevB.101.205418.
Starting from the particle nature of phonons, the influence of screw dislocations on phonon transport in silicon-germanium superlattice nanowires was explored. This work is an extension of Associate Professor Ni Yuxiang's previous work [Phys. Rev. Lett. 113, 124301 (2014)]. Studies have shown that screw dislocations have varying degrees of suppression on the phonon transmission of superlattice nanowires with different period lengths, and its effect depends on the relative size of the coherent phonon wave packet width and the superlattice period length. Compared with single-component nanowires, in superlattice nanowires, screw dislocations can cause interface atomic slippage, leading to changes in bonding at the interface, thereby reducing the group velocity of phonons. See article: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.100.075432
The above-mentioned research was funded by the National Natural Science Foundation of China, the Sichuan International Science and Technology Cooperation and Exchange Research and Development Project, and the basic operating expenses of central universities. Master students Hu Song and Sun Bo, doctoral student Zhang Honggang are the first authors of the paper, and Associate Professor Ni Yuxiang is the corresponding author of the paper. The school of Physics of Southwest Jiaotong University is the first unit of the paper.
