强磁场下石墨烯和拓扑绝缘体的晶格弛豫相关现象研究

In recent years, the appearing of novel low-dimensional materials graphene and topological insulator, because of its many peculiar properties are expected to have potential applications in new generation of optoelectronics and quickly become the hot spots in interdisciplinary research. The study of low-dimensional systems in presence of magnetic field not only can observe some novel physical phenomenon, but also is a very important way for understanding of the basic characteristics of materials. This project mainly intends to focus on the graphene and topological insulator system. In frames of Huang-Rhys's non-radiation transition model, we will study the quantum transitions related to the lattice relaxation under strong magnetic field by considering the charge carrier-phonon interaction. Our goal is that obtaining the relations of the relaxation time with the magnetic field, temperature and carrier density for the transitions between the Landau levels (LLs) in the multi-phonon transition and Auger processes and laying a foundation for the effective control of non-radiation recombination. We also discuss the mechanism of line-width and effects of temperature for the radiation transitions between LLs and give the comparisons between the relaxation time of radiation and non-radiation transitions in details. Based on what we have studied above and the Boltzmann transport theory, we will further discuss the influence of the lattice relaxation on the basic transport physical quantities, such as hall mobility, magnetic photoconductive and so on. The study of this project is helpful and meaningful for the graphene and topological insulator in application of optoelectronic devices in future.

近年来发现的新型低维材料石墨烯和拓扑绝缘体，由于其奇特的物理特性有望在未来光电子器件中有重大应用而迅速成为研究的热点。在强磁场作用下研究这些体系，是深刻认识其基本物性的一种重要方法。因此本课题拟针对这两种新型材料，在考虑载流子与多支频率声子作用的基础上，采用黄-里斯（Huang-Rhys）非辐射跃迁理论方法，深入研究强磁场下晶格弛豫效应对朗道能级间量子跃迁相关现象的影响。主要目标是通过对多声子弛豫和俄歇过程中晶格弛豫效应的研究，得出载流子非辐射跃迁机制的弛豫时间与磁场强度、载流子浓度、温度的依赖关系，为深入理解和有效控制非辐射过程奠定基础。同时，对辐射跃迁过程由于晶格弛豫效应所导致的展宽机制和温度依赖性也将重点研究，并对辐射和非辐射跃迁过程的相互竞争关系进行全面分析。在上述研究的基础上，结合玻尔兹曼输运理论，进一步研究晶格弛豫效应对载流子的霍尔迁移率、磁光导等基本输运物理量的影响。

近年来发现的新型低维材料石墨烯和拓扑绝缘体，由于其奇特的物理特性有望在未来光电子器件中有重大应用而迅速成为研究的热点。我们采用了晶格弛豫理论方法分别针对这两种新型材料体系，在强磁场作用下系统研究了朗道能级间的辐射和无辐射跃迁过程。首先在量子点体系中通过考虑载流子与多支频率声子作用的基础上，研究强磁场下晶格弛豫效应对朗道能级间单光学声子及其与声学声子的组合双声子过程。得出了这些弛豫过程与外磁场、温度的依赖关系。进一步结合自旋-轨道耦合机制讨论了朗道能级间这些多声子跃迁辅助的自旋守恒和自旋翻转弛豫过程进行系统的研究，发现两类过程的弛豫时间相差3个数量级。在考虑晶格弛豫效应的基础上，我们提出了有效声子频率模型，具体研究了石墨烯朗道能级间的磁光跃迁过程和光谱展宽的温度依赖性，建议了电注入的朗道能级激光器模型。将此模型进一步应用到单层过渡金属硫族化合物。在考虑载流子与衬底诱导的表面光学声子耦合的基础上，提出了石墨烯带隙打开的光学极化子机制，为现有的实验结果提供了很好的理论解释。最后，针对磁场的下的拓扑绝缘体，我们给出了朗道能级间的磁光跃迁过程和双声学声子的弛豫过程，讨论了弛豫过程对载流子的迁移率、光导的影响。并对拓扑绝缘体中的极化子态问题进行了初步的分析。