On 29 April, Professor Chen Jie's team at the Centre for Phononics in the School of Physical Sciences and Engineering and his collaborators published a research paper entitled "How coherence is governing diffuson heat transfer in amorphous solids" online in npj Computational Materials, developing an important theory to describe heat transport in amorphous materials.Figure 1. (a) Atomic structure diagram of amorphous silicon. (b) Amorphous silicon thermal conductivity prediction based on coherent thermal transport theory and comparison with other results, where p(particle-like) is based on particle images and w(wave-like) is based on fluctuation images.Thermal transport in amorphous materials has remained one of the fundamental questions in solid state physics while involving a very large field of applications. Using a heat conduction theory incorporating coherence, we demonstrate that the strong phase correlation between local and non-propagating modes, commonly named diffusons in the terminology of amorphous systems, triggers the conduction of heat. By treating the thermal vibrations as collective excitations, the significant contribution of diffusons, predominantly relying on coherence, further reveals interesting temperature and length dependences of thermal conductivity. The propagation length of diffuson clusters is found to reach the micron, overpassing the one of propagons. The explored wavelike behavior of diffusons uncovers the unsolved physical picture of mode correlation in prevailing models and further provides an interpretation of their ability to transport heat. This work introduces a framework for understanding thermal vibrations and transport in amorphous materials, as well as an unexpected insight into the wave nature of thermal vibrations.npj Computational Materials is an English-language journal about computational physics and computational materials published by the Shanghai Institute of Ceramics, Chinese Academy of Sciences in collaboration with Nature Publishing Group, and was selected as one of the "Most Influential Chinese Academic Journals" in 2020. Dr. Zhongwei Zhang, a postdoctoral fellow at the University of Tokyo, is the first author of the paper, and Prof. Jie Chen and Prof. Sebastian Volz of CNRS are the co-corresponding authors. Dr. Zhongwei Zhang will soon join Prof. Jie Chen 's group as an Assistant Professor..This project is also supported in part by the grants from the National Natural Science Foundation of China, Science and Technology, and so on.Link: https://doi.org/10.1038/s41524-022-00776-w

北京时间2022年4月22日，《现代物理评论》(Reviews of Modern Physics)在线发表题为“Interfacial Thermal Resistance: Past, Present and Future”的长篇综述(50页)。作者分别是同济大学物理科学与工程学院/声子学与热能科学中心陈杰教授和徐象繁教授，南京师范大学量子输运和热能科学中心周俊教授，南方科技大学材料科学与工程系、物理系李保文教授。对于诸多微纳元器件，不管是电子元器件还是光电元器件，散热问题决定了该器件的工作性能和稳定性。高密度元器件在高速工作过程中产生大量热量，如果不能及时将热量疏导出去，就会导致元器件因局部温度过高(即通常所说的热点)而导致性能降低甚至被烧坏。如何将过多的热量传导出去,使得元器件在相对低温环境下运行是现代半导体工业面临的普遍问题。目前已知大部分电子器件均为半导体或金属，其热能的主要载体为声子或电子，因此研究微纳元器件中的散热问题便成为声子热传输和电子热传输等研究领域的关键物理问题。在集成电路中，热量从元器件扩散到封装外壳需要通过无数个半导体-半导体、半导体-金属界面。因此，器件散热问题涉及到物理及工程学上最基本的科学问题：热量(声子、电子)如何通过各种界面？ 电子-声子耦合、声子-声子耦合如何影响界面热阻？由于界面两侧材料组分和结构的差异，热载流子在穿过界面时会受到散射使得界面两端在微纳尺度下产生温度跳变，由此可以定义界面热阻。物理学家傅里叶(J. B. J. Fourier)最早于1822年发现了界面处的温度跳变。他发现从固体表面流失到周围气体中的热量与温差有一定关系，并提出了“外导率”(External conducibility)的概念。之后物理学家泊松(Poisson)于1835年提出通过界面的总热量与两边温差成正比，并定义了界面热阻。波兰科学家斯莫鲁超夫斯基(M. Smoluchowski)和前苏联科学家卡皮查(P. L. Kapitza)分别于1898年和1941年定量测量了固体-气体和固体-液体的界面热阻。本文为《现代物理评论》上发表的第三篇关于界面热阻的长篇综述文章。前两篇分别发表于1969年和1989年。Pollack在1969年发表的文章中着重阐述了固体-液体界面特别是液氦的界面热阻，并详细讨论了声子失配模型AMM及液氦温度下界面热阻测量的实验方法；Swartz和Pohl等人于1989年发表的文章阐述了固体-固体界面和固体-液体界面，并讨论了AMM和扩散失配模型DMM在低温下的适用性。需要指出的是，前两篇文章都集中于讨论宏观材料及宏观界面的传热问题。普遍采用的界面热阻理论，如AMM和DMM，都是简单地假设声子以弹道传输或者扩散传输的形式通过界面，因此两个模型预测的结果与实验结果都有数量级的偏差。同时，由于测量手段的匮乏以及实验难度过大，前期界面热导实验研究工作也相对落后。随着纳米技术的发展以及纳米制备工艺的完善，同时得益于现代大型计算机的运用，界面热阻研究在近三十年来取得了长足的发展。鉴于此，本文从理论模型和实验技术进展角度全面介绍了近三十年来该领域的长足发展，讨论了固体-固体界面、固体-液体界面及固体-气体界面热阻的研究进展及存在问题，重点阐述了界面及温度的定义、界面热阻几何效应、界面热阻调控等问题，并讨论了AMM、DMM及两温度模型的适用性。该工作在线发表在：Reviews of Modern Physics, 94, 025002 (2022)，得到了基金委重大项目/重点项目/面上项目，科技部重点专项，广东省重点领域研发计划和上海市科委的资助。RMP是物理领域最权威的综述期刊，主要邀请物理学权威学者对领域进行评述和展望。RMP创刊于1929年，至今以中国大陆科研机构为第一单位的论文不超过15篇。该论文的发表表明了同济大学团队在微纳尺度界面传热这一国际科技前沿领域的深厚积累和引领地位。参考文献：1. J. Chen, X.F. Xu, J. Zhou and B. Li, Interfacial Thermal Resistance: Past, Present and Future, Reviews of Modern Physics 94, 025002 (2022), https://doi.org/10.1103/RevModPhys.94.025002 2. G. L. Pollack, Kapitza Resistance, Reviews of Modern Physics 41, 48-81 (1969), https://doi.org/10.1103/RevModPhys.41.48 3. E. T. Swartz and R. O. Pohl, Thermal boundary resistance, Reviews of Modern Physics 61, 605-668 (1989), https://doi.org/10.1103/RevModPhys.61.605 4. X.F. Xu, J. Chen, J. Zhou and B. Li, Thermal Conductivity of Polymers and Their Nanocomposites, Advanced Materials 30, 1705544 (2018), https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201705544 5. Z. Zhang, Y. Ouyang, Y. Cheng, J. Chen, N. Li, and G. Zhang, Size-dependent phononic thermal transport in low-dimensional nanomaterials, Physics Reports, 860, 1-26 (2020), https://doi.org/10.1016/j.physrep.2020.03.001

On 22 April 2022, Reviews of Modern Physics published online a full-length review entitled "Interfacial Thermal Resistance: Past, Present and Future". A full-length review (50 pages). The authors are Prof. Jie Chen and Prof. Xiangfan Xu from the School of Physical Science and Engineering/Centre for Phononics and Thermal Sciences, Tongji University, Prof. Jun Zhou from the Centre for Quantum Transport and Thermal Sciences, Nanjing Normal University, and Prof. Baowen Li from the Department of Materials Science and Engineering and the Department of Physics, Southern University of Science and Technology, respectively.When two materials with different temperatures are put into contact, heat will flow from the high-temperature one to low temperature one. This phenomenon seems simple but is far more complicated than we thought. There are many interesting fundamental questions to be understood both from a physicist’s point of view, such as how the heat carriers (phonons, electrons, etc.) are transported across the interface (boundary) between these two materials, and from an engineering application point of view, such as how to efficiently remove heat from microelectric devices, batteries, quantum devices, etc.Interfacial thermal resistance (ITR) is the main obstacle for heat flows from one material to another. Understanding ITR becomes essential for the removal of redundant heat from fast and powerful electronic and photonic devices, batteries, etc. In this review, a comprehensive examination of ITR is conducted. Particular focus is placed on the theoretical, computational, and experimental developments in the 30 years after the last review given by Swartz and Pohl in 1989. To be self-consistent, the fundamental theories, such as the acoustic mismatch model, the diffuse mismatch model, and the two-temperature model, are reviewed. The most popular computational methods, including lattice dynamics, molecular dynamics, the Green’s function method, and the Boltzmann transport equation method, are discussed in detail. Various experimental tools in probing ITR, such as the time-domain thermoreflectance, the thermal bridge method, the 3ω method, and the electron-beam self-heating method, are illustrated. This review covers ITR (also known as the thermal boundary resistance or Kapitza resistance) of solid-solid, solid-liquid, and solid-gas interfaces. Such fundamental challenges as how to define the interface, temperature, etc. when the materials scale down to the nanoscale or atomic scale and the opportunities for future studies are also pointed out.This work is published online in Reviews of Modern Physics, 94, 025002 (2022) and has been supported by by the National Natural Science Foundation of China, the National Natural Science Foundation of China ,the Science and TechnologyCommission of Shanghai Municipality, the Key-Area Research andDevelopment Program of Guangdong Province and so on.RMP is the most authoritative review journal in the field of physics, inviting leading physics scholars to review and provide perspectives on the field. rMP was founded in 1929, and to date no more than 15 papers have been published with a mainland Chinese research institution as the first unit. The publication of this paper demonstrates the profound accumulation and leading position of the Tongji University team in the international science and technology frontier of interfacial heat transfer at the micro and nano scale.REFERENCES1. J. Chen, X.F. Xu, J. Zhou and B. Li, Interfacial Thermal Resistance: Past, Present and Future, Reviews of Modern Physics 94, 025002 (2022), https://doi.org/10.1103/RevModPhys.94.0250022. G. L. Pollack, Kapitza Resistance, Reviews of Modern Physics 41, 48-81 (1969), https://doi.org/10.1103/RevModPhys.41.483. E. T. Swartz and R. O. Pohl, Thermal boundary resistance, Reviews of Modern Physics 61, 605-668 (1989), https://doi.org/10.1103/RevModPhys.61.6054. X.F. Xu, J. Chen, J. Zhou and B. Li, Thermal Conductivity of Polymers and Their Nanocomposites, Advanced Materials 30, 1705544 (2018), https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.2017055445. Z. Zhang, Y. Ouyang, Y. Cheng, J. Chen, N. Li, and G. Zhang, Size-dependent phononic thermal transport in low-dimensional nanomaterials, Physics Reports, 860, 1-26 (2020), https://doi.org/10.1016/j.physrep.2020.03.001

2022年4月4日，物理科学与工程学院声子学与热能科学研究中心陈杰教授课题组在期刊Physical Review B 上发表了题为“Enhancement of the lattice thermal conductivity of two-dimensional functionalized MXenes by inversion symmetry breaking”的研究论文。（2022级博士生鲁爽为论文第一作者，陈杰教授为论文通讯作者。近年来，研究人员发现晶体的对称性对材料的热输运具有重要影响。例如由于镜面对称性的存在限制了石墨烯ZA模式的三声子散射，使得石墨烯的ZA模式对热导率的贡献超过80%。在双层的砷化硼中类似的现象也被观测到，对称性引起的散射定则使得ZA模式对其热导率起着主导作用。然而，对称性的破坏同时也会影响材料本身的稳定性。对于共价键结合的材料例如石墨烯，双层砷化硼等体系，对称性的改变对体系本身的稳定性影响比较弱，但是对于离子键结合的材料，对称性导致的散射定则是否会显著影响热导率缺乏足够的探索。最近有研究发现表面功能化的MXene存在两种相，一种具有中心对称性（高对称相），另一种则没有中心对称性（非对称相），同时，这两种相都是离子键为主导。本工作以Ta2CS2 的两种相为例，本工作通过结合第一性计算与求解玻尔兹曼输运方程，发现高对称相的Ta2CS2的热导率比低对称相的Ta2CS2的热导率低一个量级，这与通常的认知相反。通过分析两种材料的简谐性质和非谐性质，我们发现中心对称性的破坏几乎不影响材料的简谐性质，但是显著影响了其非谐性质，导致两种相的声子寿命存在量级的差异。进一步的分析表明电荷在原子间的重新分布是非谐性改变的主要原因，对称性的改变导致不同偏振的声子之间耦合程度的改变也是导致这一现象出现的原因。这项工作表明，对于离子键结合的材料，对称性引起的散射定则对热导率影响比较弱，非谐性质的改变是其热导率变化的主要因素，这与共价键结合的材料有着明显区别。同时，表面功能化的MXene具有铁电性，外电场可以诱导其相变，其两种相之间的热导率的巨大差异有望使得其可以作为一种热开关。该项工作得到了国家自然科学基金，国家重点研究发展计划和上海市科学技术委员会的支持。论文链接：https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.165301图(a) (b) 不同对称性的Ta2CS2的结构示意图；图(c) 高对称相的Ta2CS2与低对称相的Ta2CS2在不同温度下的热导率；图(d) 高对称相的Ta2CS2与低对称相的Ta2CS2不同支的声子寿命的比较。

On 4 April 2022, Professor Jie Chen's group at the Centre for Research in Acoustics and Thermal Energy in the School of Physical Sciences and Engineering published a paper entitled "Enhancement of the lattice thermal conductivity of two-dimensional functionalized MXenes by inversion symmetry breaking" was published in Physical Review B. (Shuang Lu, a 2022 PhD student, is the first author of the paper, and Prof. Jie Chen is the corresponding author）Crystal symmetry plays a critical role in thermal transport in solids. One example is mirror symmetry in monolayer graphene that promotes thermal transport by forbidding certain phonon scattering channels. Here, we show an interesting counterexample in monolayer Ta2CS2 that inversion symmetry breaking can abnormally enhance lattice thermal conductivity of two-dimensional (2D) functionalized MXenes based on the phonon Boltzmann transport theory combined with first-principles calculations. We find inversion symmetry breaking not only affects scattering channels but also redistributes the charge and changes the anharmonic phonon properties. Both atomic vibrations in real space and phonon scattering rates in the reciprocal space confirm the significantly reduced lattice anharmonicity in an asymmetric Ta2CS2 sheet, leading to substantially enhanced thermal conductivity after inversion symmetry breaking. The physical origin for the variation of anharmonic properties induced by symmetry is discussed in detail. In this paper, we provide insight into the complex role of symmetry on thermal transport in 2D functionalized MXenes.This project is supported in part by grants from the National Natural Science Foundation of China, the Science and Technology Commission of Shanghai Municipality, and the Fundamental Research Funds for the Central Universities.Link: https://journals.aps.org/prb/abstract/10.1103/PhysRevB.105.165301(a) The side and top views of asymmetric Ta2CS2 and (b)symmetric Ta2CS2. (c) Thermal conductivity of asymmetric Ta2CS2 and symmetric Ta2CS2.（d）Anharmonic scattering rates in symmetric Ta2CS2 (filled symbols) and asymmetric Ta2CS2 (empty symbols).

陈杰教授课题组最近在《PHYSICAL REVIEW B》杂志上发表题为“Accurate description of high-order phonon anharmonicity and lattice thermal conductivity from molecular dynamics simulations with machine learning potential”的研究论文。如何经济、快速、准确地预测纳米结构的热输运性质是计算凝聚态物理中的重要问题。探究纳米材料的热物性可以为电子器件散热和热电材料开发提供理论依据。考虑声子非谐效应，特别是高阶非谐声子散射，对准确预测热导率至关重要。在本工作中，我们采用机器学习势函数结合分子动力学（MD）模拟克服了基于微扰理论在考虑声子高阶非谐效应以及温度效应所需巨大计算资源的问题。我们以立方砷化硼（BAs）和diamond为例，分别构建了能够准确描述其原子相互作用的机器学习势函数MTP。在只考虑三声子散射的情况下，相比于实验测量值，微扰理论方法只能很好地预测diamond的热导率，显著地高估了BAs的热导率。相反，MTP结合MD模拟对两者热导率的预测都能很好地与实验测量值吻合，如图1所示。声子频率能量密度分析表明MTP能够有效地捕获由温度引起的声子模式软化及声子散射线宽。同时，我们在不同温度下对BAs和diamond进行了含时动态演化，进一步分析了两种材料的原子位移分布，给出了BAs中强非谐性的起因。这些为进一步理解材料的声子信息提供了直观的物理图像，为解释宏观热性质提供了微观机理，这对于微扰理论来说是很难实现的。我们的工作表明，在对声子非谐效应没有任何先验知识的前提下，机器学习势函数结合MD模拟是一种非常有效的工具去考虑所有阶声子散射过程以及温度效应对热导率的影响。相关结果发表在期刊Physical Review B 105, 115202 (2022)。图1.（a）（b）分别表示来自计算（实心图标）与实验测量（空心图标）BAs和Diamond的热导率。DFT_3ph：通过DFT计算力常数，考虑三声子时的热导率。MTP_3ph：通过MTP计算力常数，考虑三声子时的热导率。DFT_3ph+4ph：通过DFT计算三阶和四阶力常数获得的热导率。（c）（d）表示用Green-Kubo方法计算BAs和Diamond的热导率与自相关时间的关系。其中（c）中包含BAs在300 K和500 K时的热导率，（d）中包含Diamond在300 K和 500 K的热导率。蓝色实线和黑色虚线代表具有不同初始速度分布时30个独立模拟的平均热导率，红色阴影区域代表相应的偏差。

Professor Jie Chen's group recently published a paper entitled "Accurate description of high-order phonon anharmonicity and lattice thermal conductivity from molecular dynamics simulations with machine learning potential".Phonon anharmonicity is critical for accurately predicting the material’s thermal conductivity (κ). However, its calculation based on the perturbation theory is a difficult and time-consuming task, especially for the high-order phonon scattering process. In this work, using cubic boron arsenide (BAs) and diamond as examples, we combine the machine learning potential (MLP) with molecular dynamics simulations to predict κ and assess the effect of anharmonicity on thermal transport properties. A MLP based on the matrix tensor algorithm is developed in this work, which can accurately describe lattice dynamics behaviors in both BAs and diamond. The phonon spectral energy density analysis reveals that MLP can effectively capture both the phonon mode softening and the linewidth broadening induced by the anharmonicity at finite temperatures in both materials. Compared to diamond, BAs exhibits a stronger anharmonicity revealed by the larger deviation from equilibrium position and more pronounced phonon broadening effect, especially at high temperatures. Furthermore, based on the phonon Boltzmann transport equation and three-phonon scattering process, our calculation results demonstrate that the accuracy of the MLP in predicting the κ is comparable to that of density-functional theory calculations for both diamond and BAs. However, this framework can only predict κ of diamond in agreement with experimental measurements, but significantly overestimates the κ of BAs compared to the experimental results, due to the significant impact of high-order phonon scattering process in BAs. In contrast, the κ values predicted by equilibrium molecular dynamics simulations combined with MLP agree well with experimental values for both BAs and diamond. Our study suggests that molecular dynamics simulation combined with MLP is a reliable and computationally efficient tool to account for full orders of anharmonicity and provide accurate predictions of material’s thermal conductivity without any a priori knowledge of the importance of high-order phonon anharmonicity.FIG. 1. Lattice thermal conductivity κ of BAs and diamond. (a) and (b) show, respectively, κ of BAs and diamond vs temperature from theoretical predictions (solid symbols) and experimental measurements (empty symbols). (c) and (d) show the predicted thermal conductivity by Green-Kubo method with MTP vs integration time for BAs and diamond, respectively. The solid and dashed lines represent the averaged thermal conductivity over 30 independent simulations, and the shadowed area represents the corresponding deviation.

7月31日，第六届全国统计物理与复杂系统学术会议暨海峡两岸统计物理会议开幕式在吉林大学中心校区鼎新大讲堂举行。吉林大学校长、中国科学院院士张希参加开幕式并致辞。开幕式由吉林大学物理学院院长马琰铭主持。

根据2017年10月27日中国计量测试学会热物性专业委员会第一次会议的决定，拟每三年召开一次全国性的热物性学术会议，旨在交流我国热物性测试技术与理论表征方法的最新成果。由西安交通大学承办，陕西理工大学和隐身技术航空科技重点实验室协办的第一届中国热物性学术会议已于2018年10月在陕西汉中胜利召开。第二届中国热物性学术会议拟定于2021年5月21日至5月24日在上海召开。

Sebastian Volz 教授 实验室外方合作教授，国家高端外专邮箱：volz@iis.u-tokyo.ac.jpCNRS, University of TokyoLIMMS directorGoogle scholarProfessor Volz is now the Director of the Laboratory for Integrated Micro Mechatronic Systems(LIMMS) at CNRS/University of Tokyo. He obtained his Ph.D. from University of Poitiers in1996. After working at University of California Los Angeles as a postdoctoral fellow withProfessor Gang Chen (now at MIT), he became an associate Professor at the National EngineeringSchool of Mechanics and Aerotechnics (ENSMA) in 1998. He joined CNRS in 2002 as a researchfellow at Ecole Centrale Paris, and became senior research fellow in 2010. He is the winner of theBronze Medal of CNRS in 2004, and International Thermoelectric Society Scientific Award in2009. He is the head of the CNRS European Network “Thermal Nanosciences andNanoengineering”. In addition, he has served as the chairman in numerous internationalconferences related to nanoscale heat transport, the active reviewer in more than 20 journals, andthe editor of three books. So far, he has published over 480 communications, including 10chapters, 215 articles in peer-reviewer journals, and 75 invited conferences. His publications haveover 10100 citations (Google), and his current H-index is 50 (Google)