Influence of interlayer interaction on the charge and lattice dynamics in layered transition-metal chalcogenides

层状过渡金属硫族化合物由于相互竞争的相关效应和拓扑结构，表现出大量有趣的物理性质和奇异相，如电荷密度波、莫特绝缘体、超导性、反铁磁拓扑绝缘体、Weyl半金属和铁磁节线半金属。此外，它们为实现具有独特性能的原子薄范德华晶体提供了理想的平台，具有良好的新应用前景。为了理解这些新型二维晶体的物理性质，表征和理解它们的整体物理性质是至关重要的第一步，也是本项目的主题。决定二维层状材料物理性质的一个关键方面是层间相互作用。特别是，通过改变层间间距而引起的层间相互作用的变化极大地影响了它们的物理性质，并诱发了相变，出现了奇异相。系统地研究和理解层间相互作用对层状过渡金属硫族化物中电荷和晶格动力学的影响是本项目的目标。外部压力是调节层间间距和层间相互作用的最有效方法。因此，本项目将应用外部压力系统地研究层间相互作用对电荷和晶格动力学的影响。利用压力相关红外光谱和拉曼光谱可以在调整层间相互作用的同时研究层状材料中的电荷和晶格动力学。通过这种方法，可以对压力引起的电子变化和具有新出现的奇异电子相的相变进行详细的监测和表征，并具有高能量分辨率。作为本研究的模型系统，选择了几种层状过渡金属硫族化合物，一方面在环境压力下已经显示出有趣的物理性质，如Weyl半金属或磁性拓扑相，另一方面对压力应用非常敏感。

Layered transition-metal chalcogenides exhibit a plethora of interesting physical properties and exotic phases due to competing correlation effects and topology, such as charge-density wave, Mott insulator, superconductivity, antiferromagnetic topological insulator, Weyl semimetal, and ferromagnetic nodal-line semimetal. Furthermore, they provide an ideal platform for realizing atomically thin, van der Waals crystals with unique properties and excellent prospects for novel applications. For the understanding of the physical properties of these novel 2D crystals, the characterization and understanding of their bulk physical properties is crucial as a preliminary step and is the subject of this project.One key aspect determining the physical properties of two-dimensional, layered materials is the interlayer interaction. In particular, the variation of the interlayer interaction by changing the van der Waals interlayer spacing greatly affects their physical properties and induces phase transitions with emerging exotic phases. The systematic study and understanding of the influence of the interlayer interaction on the charge and lattice dynamics in layered transition-metal chalcogenides are the goal of this project. External pressure is the most effective way for tuning the interlayer spacing and hence the interlayer interaction in a controlled manner. Hence, external pressure will be applied within this project to systematically investigate the influence of interlayer interaction on the charge and lattice dynamics. By pressure-dependent infrared and Raman spectroscopy the charge and lattice dynamics can be studied while tuning the interlayer interaction in layered materials. This way, the pressure-induced electronic changes and phase transitions with emerging exotic electronic phases can be monitored and characterized in detail and with a high energy resolution.As model systems for this study several layered transition-metal chalcogenides are chosen, which on the one hand show interesting physical properties already at ambient pressure such as Weyl semimetal or magnetic topological phase, and on the other hand are very sensitive regarding pressure application.