A tango between magnons and phonons in 2D van der Waals insulating magnets

非技术性：磁子和声子分别是自旋波和晶格振动的量子，代表了凝聚态物质中的两种基本集体激发。一般来说，磁子和声子是分开研究的。然而，在具有强烈自旋-晶格相互作用的磁性固体中，磁振子-声子耦合在决定磁性和热学性质方面起着关键作用。到目前为止，范德华磁体中磁振子-声子耦合的实验研究是发现新物理现象的肥沃乐园，在很大程度上仍然是一个未被探索的研究前沿。本项目利用中子散射和热输运技术研究范德华绝缘磁体中的磁振子-声子耦合。该项目为年轻研究人员利用尖端设施进行量子材料科学研究提供了极好的教育体验。除了培训研究生和本科生外，该项目还通过吸引K-12学生、吸引代表性不足的学生参与研究和开发研讨会来支持科学研究活动。重要的是，该项目作为培训下一代中子散射科学家的平台，因此扩大了国家实验室尖端设施的用户群体。技术：本项目研究范德华绝缘磁体中的磁振子-声子耦合，以了解磁子、声子和磁振子-声子耦合对这些系统的热输运和热力学的作用。具体地说，这项工作利用中子散射和热输运技术解决了下列关键科学问题：(I)磁振子-声子耦合如何依赖于磁基态的对称性？(Ii)自旋-晶格相互作用如何依赖于磁性过渡金属离子d轨道上的电子占有率，这对磁振子-声子耦合有什么影响？(Iii)磁振子-声子耦合如何随着自旋-轨道相互作用的变化而变化？(4)磁振子-声子耦合如何影响材料的热输运和热力学性质？这些问题的答案提供了关于磁子和声子之间的耦合以及它们对范德华材料热性质的影响的前所未有的知识，这对于这些材料在自旋热电子学和磁振子自旋电子学中的应用是必不可少的。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical:Magnons and phonons, which are quanta of spin waves and lattice vibrations respectively, represent two fundamental collective excitations in condensed matter. In general, magnons and phonons are studied separately. Nevertheless, in magnetic solids with strong spin-lattice interactions, magnon-phonon coupling plays a key role in determining magnetic and thermal properties. Thus far, experimental studies of magnon-phonon coupling in van der Waals magnets, which emerge as a fertile playground for the discovery of novel physical phenomena, remain a largely unexplored research frontier. This project studies the magnon-phonon coupling in van der Waals insulating magnets by utilizing neutron scattering and thermal transport techniques. This project offers an excellent educational experience for young researchers to utilize cutting-edge facilities for scientific research on quantum materials. In addition to training graduate and undergraduate students, this project also supports scientific research activities by engaging K-12 students, attracting underrepresented students to research, and developing workshops. Importantly, this project serves as a platform to train the next-generation of neutron scattering scientists and therefore grows the user community of cutting-edge facilities in national laboratories. Technical:This project studies magnon-phonon coupling in van der Waals insulating magnets to understand the roles of magnons, phonons, and magnon-phonon coupling on thermal transport and thermodynamics of these systems. Specifically, the work addresses the following key scientific questions with neutron scattering and thermal transport techniques: (i) how does the magnon-phonon coupling depend on the symmetry of magnetic ground states? (ii) how does the spin-lattice interaction depend on the electron occupancy on d orbitals of magnetic transition-metal ions, and what is the impact of this on the magnon-phonon coupling? (iii) How does the magnon-phonon coupling vary with the spin-orbit interaction? (iv) How does the magnon-phonon coupling affect materials’ thermal transport and thermodynamics properties? The answers to these questions provide unprecedented knowledge about the coupling between magnons and phonons as well as their impact on thermal properties of van der Waals materials, which are essential for applications of these materials in spin caloritronics and magnon spintronics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.