Control of light-matter interaction in 2D transition metal dichalcogenides via strain engineering

继在过渡金属二硫属化物（TMD）单层中观察到明亮的发光之后，过去十年见证了这类新的光学活性材料中出现的特殊物理。关于室温激子，高稳定的单光子发射和许多谷相关的异常的报道一直吸引着这些新的二维材料的巨大科学兴趣。在这方面，认识到独特的谷结构需要相干特性，这导致在低温下的（部分）线性偏振发射，毫无疑问，反映了一个真正杰出的例子，在TMD中遇到的显着的物理。这种现象被称为谷相干，在研究界引起了极大的兴奋，尤其是由于它在量子计算中的应用潜力。利用这些有希望的发展技术应用现在需要足够的外部控制光和物质之间的关键相互作用。在不同的方法中，二维晶格中的工程应变目前正在成为一个非常强大的工具。在这方面，TMD提供了比更刚性的经典半导体无可匹敌的优势：据报道，它们可以承受晶格晶胞的极端变形（高达10%），然后变形变成非弹性，材料被永久损坏。利用这种特殊的机械性能，通过应变工程来控制TMD中的各种轻物质相互作用，这是该项目的目标。首先，我们将探讨不同的实验平台，例如奈米结构的基板，或是利用原子力显微镜的针尖来控制压痕。虽然应变对系统的光学性质的影响将通过标准的光学光谱学进行监测和表征，但是能够对单层的形态进行成像的不同显微镜技术可以应用于量化应变区域的程度。补充的光谱学的结果，这一见解将作为理论模型的发展，以估计应变对激子态和能带结构的影响的基础。在建立了纳米级应变的实验平台后，该项目将专注于应变，激子函数和量子发射体形成之间的相互作用以及应变对Valley Coherence特性的影响。

Following the observation of bright luminescence in single layers of transition metal dichalcogenides (TMDs), the past decade has witnessed the emergence of exceptional physics in this new class of optically active materials. Reports about room temperature excitonics, highly stable single photon emission and numerous valley-related anomalies keep attracting enormous scientific interest in these new two-dimensional materials. In this regard, the realization that the unique valley structure entails coherence properties, which result in a (partially) linearly polarized emission at cryogenic temperatures, beyond doubt reflects a truly outstanding example of the remarkable physics encountered in TMDs. This phenomenon, termed Valley Coherence, has triggered profound excitement in the research community, not the least due to its potential for applications in quantum computation. Harnessing these promising developments for technological applications now demands sufficient external control over the key interactions between light and matter. Amidst the different approaches, engineering strain in the two-dimensional lattices is currently emerging as a very powerful tool. Here, TMDs offer an unrivaled advantage over the more rigid, classical semiconductors: They have been reported to withstand extreme deformations of the lattice unit cell, up to 10%, before the deformations become inelastic and the material is permanently damaged.Utilizing this exceptional mechanical property to control various light-matter interactions in TMDs via strain engineering is the goal of this project. At the beginning, different experimental platforms for the implementation of nanoscale strain in TMDs, such as nanostructured substrates, or the controlled indention by an AFM tip will be explored. While the impact of strain on the optical properties of the system will be monitored and characterized through standard optical spectroscopy, different microscopy techniques capable of imaging the morphology of single layers can be applied to quantify the extent of strained regions. Complementing the results of the optical spectroscopy, this insight will serve as a basis for the development of theoretical models to estimate the effects of strain on the excitonic states and the band structure. Having established an experimental platform for nanoscale strain, the project will focus on the interplay between strain, exciton funneling and the formation of quantum emitters and the impact of strain on Valley Coherence properties.