Collaborative Research: Probing quasiparticle excitations in TMDC Moiré superlattices for revealing and understanding novel two-dimensional correlated phases

非技术摘要：由于二维(2D)原子晶体的发展，研究人员成功地创造了一种新的周期晶格，这种晶格是由两个垂直堆叠的2D原子晶格干涉而产生的。这种所谓的“莫尔超晶格”的存在，已经从理论上得到了预测，并在实验上得到了证明。在这个合作项目中，研究小组研究了一类由过渡金属二卤化物(TMDC)制成的莫尔超晶格。该团队的目标是通过探索这些TMDC堆叠结构中的周期晶格、电荷载流子和磁矩的动力学，来了解半导体TMDC单分子层在垂直堆叠在一起时如何变成非传统的绝缘体、磁体甚至超导体的关键问题。该项目进一步与教育和外联活动相结合，以招募和指导代表性不足的学生和第一代学生，向K-12学生提供演示实验和教程，并向公众介绍合作研究的背景和结果。这些活动涉及广泛的参与者，并在K-12学生和公众中促进科学、技术和工程。技术摘要：通过两个原子薄晶体之间的晶格失配或角度失配形成莫尔超晶格已被实验证明是设计和设计2D系统电子性质的一种强有力的方法。一个特别突出的例子是小扭曲角度的TMDC莫尔超晶格，它显示出丰富的强关联电子相，这些相在组成TMDC单分子膜中是缺失的。在这个合作项目中，研究目标是对TMDC莫尔超晶格中出现的这些关联相进行全面的理解。重点是用光学光谱实验和第一性原理理论方法研究了这些关联相的集体声子、电荷和磁振子激发。具体地说，研究小组制作了TMDC莫尔超晶格，使用时间分辨和拉曼光谱进行了时间和频域的动态测量，并进行了理论计算来指导实验设计和解释实验结果。这个项目的成功不仅为更好地理解2D系统中的新兴关联物理学开辟了一条新的途径，而且还扩展了探索强关联物理学的一般平台。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstract:Thanks to the development of two-dimensional (2D) atomic crystals, researchers have managed to create a new kind of periodic lattice that arises from the interference of two vertically stacked 2D atomic lattices. The existence of this so called "moire superlattice", has been theoretically predicted and experimentally demonstrated. In this collaborative project, the research team studies a family of such moire superlattices made from transition metal dichalcogenides (TMDC). The team aims at understanding the key questions of how semiconducting TMDC monolayers turn into unconventional insulators, magnets, or even superconductors when stacked together vertically, by probing the dynamics of the periodic lattices, the charge carriers, and the magnetic moments in these TMDC stacked structures. The project is further integrated with education and outreach activities to recruit and mentor underrepresented and first-generation students, present demo experiments and tutorials to K-12 students, and introduce the background and results from collaborative research to the general public. These activities involve a wide group of participants and promote science, technology, and engineering among K-12 students and the public.Technical abstract:The formation of moire superlattice by either lattice mismatch or angular misalignment between two atomically thin crystals has been experimentally demonstrated as a powerful way to design and engineer electronic properties of 2D systems. One particular outstanding example is the small twist-angle TMDC moire superlattices, showing a wealth of strongly correlated electronic phases that are absent in the individual composing TMDC monolayers. In this collaborative project, the research goal is to develop a comprehensive understanding on these emergent correlated phases in TMDC moire superlattices. The focus is to investigate the collective phonon, charge, and magnon excitations of these correlated phases by using an integrated optical spectroscopy experiment and first-principles theory method. Specifically, the research team fabricates TMDC moire superlattices, performs time- and frequency-domain dynamic measurements using time-resolved and Raman optical spectroscopy, and carries out theoretical calculations to guide the experimental design and interpret the experimental results. The success of this project not only opens a new pathway to better understand emergent correlated physics in 2D systems, but also expands the platform to explore strongly correlated physics in general.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.