置于极性半导体衬底上的二维单层材料中多声子拉曼散射的理论研究

The study of the basic properties of the monolayer materials/polar substrates heterostructures is a hot spot in scientific research. Especially, the surface optical (SO) phonons induced by the polar substrates plays a key role for the potential applications of the heterostructures consisted of the monolayer material and semiconductor substrates. This project mainly intends to focus on these heterostructures that are consisted of the graphene and several like-graphene materials and the semiconductor substrates. In the frames of the perturbation theory and the lattice relaxation model, we will study the multiphonons Raman scattering assisted by the SO phonons in these monolayer materials. Both the multiphonons processes via single SO phonon mode and the SO phonon mode combined with other phonon modes are considered. Firstly, we will study the multiphonons resonance Raman scattering between the quantized Landau levels in these monolayer materials. Then we will study the multiphonons Raman scattering assisted by the exciton as the medium states in the monolayer transition metal dichalcogenides. We will discuss the relations of the multiphonons Raman scattering with the polarization strength of the substrates, the distance between the monolayer material and substrates, temperature and the strength of the magnetic field. We will compare these multiphonons processes we obtained in this project with the corresponding experimental measurements. We hope that these theoretical results of this project are helpful and meaningful for these heterostructures in many potential applications in future.

由单层材料与半导体衬底材料构成的新型异质结构是当前科学研究的热点问题，特别是对极性半导体衬底诱导的表面光学（SO）声子效应的研究是开发这类新型异质结构在多方面应用的关键问题。本课题拟针对石墨烯和类石墨烯材料与极性半导体衬底构成的异质结构，采用多级微扰理论方法结合晶格弛豫模型，深入研究单层材料中SO声子辅助的多声子拉曼散射过程。不仅考虑单一SO模式的多声子过程，而且考虑SO模与其他声子模式的组合态多声子过程。一方面，将针对单层材料在磁场作用下的朗道能级间的多声子共振拉曼散射进行探讨。另一方面，针对单层过渡金属硫族化合物明显的激子效应，对激子态为媒介态的多声子拉曼散射机制进行探讨。我们将主要分析这些多声子拉曼过程与半导体衬底的极性、衬底与单层材料的间距、外磁场强度和外界温度的依赖关系。进一步结合相关实验数据进行对比分析，力争得出对多声子拉曼散射实验有重要指导意义的理论结果。

单层材料与半导体衬底材料构筑的多种类型范德瓦尔斯异质结构的基本特性的研究是当前多科学研究的热点问题。本项目特别关注了极性半导体衬底诱导的表面光学声子效应对这些新型异质结构基本光学性质的影响。我们主要针对石墨烯和单层过渡金属硫族化合物分别与极性半导体衬底构成的异质结构，采用多级微扰理论方法结合晶格弛豫的Huang-Rhys模型，深入研究了这些结构中多声子拉曼散射过程。一方面，我们针对磁场作用下的石墨烯中朗道能级间的多声子共振拉曼散射进行探讨。在理论推导得出多声子共振拉曼散射的模型下，通过数值模拟发现：朗道量子化石墨烯是验证单一模式和组合模式多声子共振拉曼散射的非常理想的载体。另一方面，采用变分法，针对不同单层过渡金属硫族化合物间垂直堆垛构筑的范德瓦尔斯异质结构中的层内和层间激子效应进行了系统的研究。理论预测了激子-声子的耦合作用对激子的结合能有着大幅的修正影响。进一步以这两类激子态为媒介的多声子拉曼散射机制进行探讨，首次给出了该体系材料中多声子拉曼散射过程,理论结果为精细分析拉曼光谱的奠定了基础。最后，我们拓展研究了这些结构中由于电子-声子强耦合作用所导致的极化子效应及其光吸收过程，为充分理解和开发二维材料体系提供了前期的理论支持，丰富和充实了该项目的研究内容。