Spin-lattice coupling in magnetic 2D van der Waals and topological materials

低维磁学是理论和实验物理学中功能最强大、发展最快的研究领域之一：二维磁体有望成为可访问的、可工程的、可集成到新兴异质结构中的，用于以前未实现的特性和应用，如用于超紧凑自旋电子学、片上光通信和量子计算的原子薄磁光和磁电器件。在这些材料中，范德华磁体，如反铁磁拓扑绝缘体MnBi4Te7或铁磁体Cr2Ge2Te6，除了对各向异性高度敏感的铁磁或反铁磁交换相互作用外，共同具有层状结构和复杂的磁竞争相，这些各向异性敏感地依赖于键角。对于硫系化合物，如V2P2S6、Ni2P2S6和Fe2P2S6，这些材料中磁性、强电子相关性和莫特物理的存在为探索二维和器件物理提供了新的途径。其中一个主要的开放问题是，考虑到这些材料中的磁相互作用对结构的强敏感性，磁弹性耦合的作用是什么？这是一把钥匙，可以帮助揭开这些材料的磁性机制。在这个项目中，通过物理压力研究（流体静力和单轴施加压力）和膨胀测量法，对选定的二维材料中的自旋-晶格耦合进行了彻底的研究。单轴压力下的磁化研究有望深入了解其与拓扑秩序的关系和/或控制。此外，将广泛探讨通过压力调节磁交换的可能性问题，以及在掺杂实验中直接比较静水压力和化学压力诱导的磁相互作用变化。关于范德瓦尔斯材料α - rucl3和Cr2Ge2Te6的初步有趣结果已经表明了膨胀法和静水压力研究的可行性，以及二维体系体单晶性质研究可能产生的信息的丰富性。

Low-dimensional magnetism is one of the most functional and rapidly developing area of research in theoretical and experimental physics: 2D magnets promise to be accessible, engineerable, and integrable into emergent heterostructures for previously unachieved properties and applications such as atomically thin magneto-optical and magnetoelectric devices for ultracompact spintronics, on-chip optical communications, and quantum computing. Among these materials, van der Waals magnets like the antiferromagnetic topological insulator MnBi4Te7 or the ferromagnet Cr2Ge2Te6 have in common a layered structure plus complex magnetic competing phases besides ferromagnetic or antiferromagnetic exchange interactions highly sensitive to the anisotropy, which sensitively depend on bond angles. In the case of chalcogenides like V2P2S6, Ni2P2S6 and Fe2P2S6 the presence of magnetism, strong electron correlations and Mott physics in these materials offer new avenues to explore in 2D and device physics. One of the main open questions is, given the strong sensitivity of the magnetic interactions in these materials to the structure, what is the role of magnetoelastic coupling? This is a key that could help unveiling the mechanism of the magnetism in these materials. In this project, a thorough investigation of the spin-lattice coupling in selected 2D materials through physical pressure studies (hydrostatic and uniaxial applied pressure) and dilatometry is proposed. Magnetization investigations under uniaxial pressure anticipate to be promising in giving insights on its relation with and/or control of the topological order. Furthermore, the question on the possibility of tuning the magnetic exchange via pressure will be extensively explored, as well as direct comparison of changes in the magnetic interactions induced by hydrostatic pressure with the ones induced by chemical pressure in doping experiments. Preliminary interesting results on the van-der-Waals materials alpha-RuCl3 and Cr2Ge2Te6 already show both the feasibility of dilatometry and hydrostatic pressure studies, and the richness of the information which may arise from the study of bulk single-crystal properties of 2D systems.