TWIST-NANOSPEC: Development of Advanced Optical Nano-spectroscopy Techniques for Twistronics

Twistronics利用了一种新的可调原子晶格周期性，称为摩尔超晶格（mSL）在几个原子厚的货车的范德华异质结构，这是显示和预测不仅是重要的基础物理对高度可调的量子相位在凝聚态物质，但也有希望为未来的光电和量子技术的应用。尽管极大的兴趣和高潜力的双电子，有限的表征工具存在，可以直接应用于详细调查的mSL在纳米尺度上，迄今阻碍了进展，在这个充满活力的新兴领域。在这里，我们的目标是开发新的纳米成像技术，直接观察扭曲的过渡金属双硫属化合物双层中的mSL（由相对于彼此旋转的两个单层构成），包括使用配备有激光器的散射型扫描近场光学显微镜实现的线性和非线性光学光谱学，近红外和中红外。莫尔激子，半导体mSL中的基本激发将在线性区域以及对激子态和异质双层原子晶格的对称性敏感的共振二次和三次谐波产生实验中进行探测。此外，我们的技术将能够在具有封装的电介质或导电层的样品中“看到表面以下”，这是表面扫描技术无法达到的特征。随着我们开发的技术，mSL有望在室温下可视化，具有高对比度，非接触和高分辨率的优点。我们新开发的纳米成像和纳米光谱学方法将为独特但可能非常广泛的扭曲异质结构的行为提供全新的见解，并且也将适用于其他纳米材料系统（如钙钛矿），其中纳米成像和纳米级光谱学也非常理想。

Twistronics exploits a new tunable atomic lattice periodicity called moiré superlattices (mSL) in few-atom-thick van der Waals heterostructures, which is shown and predicted not only to be important in fundamental physics towards highly tunable quantum phases in the condensed matter but also promising for future optoelectronic and quantum technology applications. Despite the great interest and high potential of twistronics, limited characterisation tools exist that can be directly applied for detailed investigation of mSLs on the nanoscale thus far impeding progress in this vibrant emerging field. Here, we aim to develop new nano-imaging techniques to directly observe mSLs in twisted transition metal dichalcogenides bilayers (built from two monolayers rotated with respect to each other) by utilizing several optical methods, including the linear and nonlinear optical spectroscopy realised using scattering-type scanning near-field optical microscope equipped with lasers enabling spectroscopy in a wide range of wavelengths in the visible, near-infrared and mid-infrared. Moiré excitons, a fundamental excitation in semiconducting mSLs will be probed in the linear regime as well as in the resonant second- and third-harmonic generation experiments sensitive to the symmetry of the excitonic states and the heterobilayer atomic lattice. Furthermore, our techniques will enable to "see below the surface" in samples with encapsulated dielectric or conducting layers, a feature unaccessible for surface scanning techniques. With our developed techniques, the mSL is expected to be visualised with advantages of high contrast, non-contact, and high resolution at room temperature. Our newly developed approaches for nano-imaging and nano-spectroscopy will provide fundamentally new insights in the behaviour of a unique but potentially very extended class of twisted heterostructures and will also be applicable in other nano-materials systems (such as perovskites), where nano-imaging and spectroscopy on the nanoscale are also highly desirable.