Ultrafast THz- and Infrared-Spectroscopy of Strongly Bound Excitons in GaN, ZnO and Transition-Metal-Dichalcogenides

我们提出了飞秒光泵太赫兹探测和光泵红外探测实验（THz/IR-PP）来研究GaN、ZnO和过渡金属二硫族化合物（TMDC）中强束缚激子的超快动力学。在本计画的第一部分，将研究氮化镓与氧化锌中施主与受主束缚激子的弛豫动力学。在这里，超快太赫兹和中红外光谱可以提供访问强结合对的内部激子能级之间的跃迁-洞察对动力学在大动量，这是只能间接访问带间方法。此外，我们将通过共振激子产生后在0.8 THz至11.5 THz范围内的激子内跃迁来寻找受激THz发射。在第二个项目部分的过程中，我们将研究激子和自由载流子在单层和多层的TMDC二硫化钼（MoS 2）和二硒化钨（WSe 2），沿着的光诱导动力学的低能量激发在二硒化钛（TiSe 2），其有趣的低温相已与激子绝缘体相的发展。由于它们的直接带隙，TMDC单层MoS 2和WSe 2不仅对基本的多粒子相互作用的研究感兴趣，而且在新兴的自旋和谷电子学领域中，也是实现双稳态晶体管和光电器件的有前途的材料系统。自旋和谷效应的动力学将通过时间分辨克尔和法拉第旋转光谱来研究。最后，1 T-TiSe 2在临界温度TC以下经历电荷密度波（CDW）不稳定性，其特征在于2 × 2 × 2实空间超结构。人们假设CDW是由激子绝缘体状态引起的，但激子关联和晶格畸变的相对影响仍有争议。在这里，我们将调查的CDW间隙动力学以及太赫兹频率的声子激发光谱洞察这些低能量的自由度在1 T-TiSe 2的相互作用的时间尺度上的相互耦合。

We propose femtosecond optical-pump-THz-probe and optical-pump-IR-probe experiments (THz/IR-PP) to investigate the ultrafast dynamics of strongly bound excitons in GaN, ZnO and transition-metal dichalcogenides (TMDC). In the first part of the project, the relaxation dynamics of donor- and acceptor-bound excitons in GaN and ZnO will be investigated. Here, ultrafast THz and mid-IR spectroscopy can provide access to transitions between internal exciton levels of the strongly bound pairs - for insight into pair dynamics at large momenta which are only indirectly accessible in interband methods. Furthermore, we will search for stimulated THz-emission via intra-excitonic transitions in the range of 0,8 THz to 11,5 THz after resonant exciton generation. In the course of the second project part, we will study the dynamics of excitons and free carriers in mono- and multi-layers of the TMDCs molybdenum disulfide (MoS2) and tungsten diselenide (WSe2), along with the photo-induced dynamics of low-energy excitations in titanium diselenide (TiSe2) whose intriguing low-temperature phase has been associated with the development of an excitonic insulator phase. Due to their direct band gap, the TMDC monolayers MoS2 and WSe2 are not only of interest for the study of fundamental many-particle interactions but are also promising material systems for the realization of ultrathin transistors and optoelectronic devices in the burgeoning fields of spin- and valleytronics. The dynamics of spin and valley effects will be investigated by time-resolved Kerr and Faraday rotation spectroscopy. Finally, 1T-TiSe2 undergoes a charge density wave (CDW) instability characterized by a 2 × 2 × 2 real-space superstructure beneath a critical temperature TC . It is assumed that the CDW is caused by an excitonic insulator state, but the relative influence of excitonic correlations and lattice distortions is under debate. Here, we will investigate the CDW gap dynamics as well as the THz-frequency phonon excitation spectrum for insight into the mutual coupling of these low-energy degrees of freedom in 1T-TiSe2 on their natural interaction timescales.