新型拓扑声子效应与拓扑声子材料的理论探索

Recently physical concepts of topological states of quantum matter have been introduced into phononic systems, leading to the emergence of a new research direction—topological phononics, which utilizes novel quantum degrees of freedom (like Berry phase, pseudospin and topology) for controlling phonons in unprecedentedly new ways. The research of this emerging field is of crucial importance to develop fundamental theory and practical applications for future phononics. However, despite some early preliminary findings, only very limited types of topological phononic states have been discovered until now. Moreover, current research predominately focused on studying theoretical models, but little progress has been achieved in finding desirable real materials for experimental research. In this context, our project is aim to solve the above key scientific problems of the cutting-edge field, based on our own previous progresses of this field. We plan to perform theoretical works on the following three aspects: 1) Explore novel topological quantum states of phononic systems, especially those phononic states with no need of breaking time reversal symmetry, protected by crystalline symmetries, easily realized in real solid-state materials, and characterized by two- or three-dimensional nontrivial topological invariants (e.g. topological insulator-like states, topological Dirac or Weyl semimetal-like states); 2) Study the interplay of symmetry and topological phonons together with the influence of symmetry breaking, explore exotic topological quantum effects of phonons and further try to design promising device applications; 3) In combination with first-principles material simulation, predict real material systems that host topologically nontrivial phononic states, and provide useful guidance for following experiments and applications.

拓扑量子物态的物理概念最近被引入声子体系，由此演生出一个新兴研究方向—拓扑声子学，即利用Berry相位、赝自旋、拓扑等新奇量子自由度实现全新的声子操控，对未来声子学基础理论与器件应用的发展有重要意义。目前已被发现的拓扑声子态种类还很有限，且当前研究以理论模型为主，缺少相应的实际材料用于后续实验。基于我们已有的前期工作积累，本项目将针对上述前沿领域中的关键科学问题开展如下三方面的理论工作：1）探索声子体系中的新奇拓扑量子物态，特别是无需破坏时间反演对称、受晶格对称保护且易于在实际固体材料中实现、具有二维或三维非平庸拓扑特性的声子态（如拓扑绝缘态、拓扑Dirac或Weyl半金属态）；2）探讨对称性与声子拓扑的相互作用以及对称性破缺对声子特性的调制，探索新型的拓扑声子量子效应，并设计潜在的器件应用；3）结合第一性原理材料计算，预测具有非平庸拓扑声子态的实际材料体系，为后续实验与应用研究提供指导。

本项目针对拓扑声子学这一新兴研究方向开展基础理论研究，即利用Berry相位、赝自旋、拓扑等新奇量子自由度实现全新的声子操控，聚焦新型拓扑声子效应与拓扑声子材料的理论探索。主要研究内容包括：1）探索声子体系中的新奇拓扑量子物态，特别是无需破坏时间反演对称、受晶格对称保护且易于在实际固体材料中实现、具有二维或三维非平庸拓扑特性的声子态；2）探讨对称性与声子拓扑的相互作用以及对称性破缺对声子特性的调制，探索新型的拓扑声子量子效应，并设计潜在的器件应用；3）结合第一性原理材料计算，预测具有非平庸拓扑声子态的实际材料体系，为后续实验与应用研究提供指导。.重要的研究进展包括：预言了多种具有非平庸拓扑表面态的拓扑声子绝缘体和拓扑声子半金属，揭示了由赝自旋-轨道耦合效应及其诱导的异常量子输运特性；预言了以硅为代表的一大类拓扑声子材料，可供后续实验与应用研究；发展了多种基于深度学习的第一性原理计算方法，为未来探索电子、声子相关的材料与器件提供了强有力的研究手段；发表了多篇研究综述，概括了领域的研究进展，并对未来学科发展做展望。.本项目共发表学术论文28篇，均发表在本领域最主要的学术刊物上。相关工作成果被大量引用，受到了国内外同行的高度认可。项目负责人也多次受邀在国际、国内重要学术会议作邀请报告。除此之外，项目还培养博士生毕业生6名，项目负责人在项目执行期间获国家杰出青年科学基金资助。

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