Exploring electrodynamics of correlated 2D transition metal dichalcogenides using on-chip terahertz spectroscopy

非技术性描述：正如我们可以通过电磁波看到世界一样，人们可以通过测量固体的电磁响应来了解固体中电子态的性质。然而，这些测量有时在由诸如石墨烯和过渡金属二硫属化物（TMD）的原子薄晶体堆叠形成的材料中具有挑战性。这些材料的性质可以产生许多电子的新量子态，但这些状态的特征频率通常落入电磁波波长远远超过可能的样本大小的范围内。在这个项目中，PI开发了先进的片上太赫兹光谱与集成的亚波长波导研究这些新的状态在TMD异质结构的电磁响应。这项研究可以推进我们对相互作用电子的基本理解，并导致新的功能THz器件。它还可以为研究生和本科生提供一个积极的学习环境，以获得跨学科的技能。本项目旨在研究二维过渡金属二硫族化物（TMD）异质结构中相关量子相（如平带金属、相关绝缘体和维格纳晶体）的太赫兹电动力学响应。这些高度可调的异质结构已经成为研究由相互作用的电子形成的新状态的领先平台之一。然而，尽管有很大的兴趣，这些国家在其特征频率尺度的电动力学性质仍然在很大程度上未知。在这个项目中，PI开发了先进的片上太赫兹光谱来研究这些特性。具体而言，PI在该项目中探索了三个研究方向：（1）研究频率超过单电子-空穴衰减上限的平坦带中的新型2D等离子体。这样的等离子体激元可以具有增强的寿命，并且表现出反映潜在的相关相的性质。(2)测量异质结构中频率相关电导率的全掺杂演化，类似于三角晶格哈伯德模型，相关电子的范例模型。(3)研究维格纳和广义维格纳晶体中的电子振动模式，以及它们在这些电子晶体的量子和热熔化过程中的演化。该项目的提出可以促进我们对TMD异质结构和长期存在的相关电子问题的基本理解。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

Nontechnical description: Just as we can see the world via electromagnetic waves, one can learn the properties of electronic states in solids by measuring their electromagnetic responses. However, these measurements are sometimes challenging in materials formed by stacks of atomically-thin crystals such as graphene and transition metal dichalcogenides (TMDs). The properties of these materials can give rise to novel quantum states of many electrons, but the characteristic frequencies of such states often fall into the range where the electromagnetic wavelength far exceeds the possible sample size. In this project, the PI develops advanced on-chip THz spectroscopy with integrated sub-wavelength waveguide to study the electromagnetic response of these novel states in TMD heterostructures. The research can advance our fundamental understanding of interacting electrons and lead to new functional THz devices. It can also provide an active learning environment for graduate and undergraduate students to gain interdisciplinary skills. The project engages undergraduate students at UC Berkeley, especially those from underrepresented groups, to drive the frontier of science and technology in the future.Technical description:This project aims to investigate the terahertz electrodynamic responses of correlated quantum phases, such as flat-band metals, correlated insulators, and Wigner crystals, in two-dimensional (2D) transition metal dichalcogenide (TMD) heterostructures. These highly tunable heterostructures have emerged as one of the leading platforms for studying novel states formed by interacting electrons. However, despite the great interest, the electrodynamic properties of these states at their characteristic frequency scales remain largely unknown. In this project, the PI develops advanced on-chip terahertz spectroscopy to study these properties. Specifically, the PI explores three research directions in the project: (1) Studying a new type of 2D plasmon in flat bands with frequency exceeding the upper bound for single electron-hole decay. Such plasmons may have enhanced lifetimes and exhibit properties reflecting the underlying correlated phases. (2) Measuring the full doping evolution of the frequency-dependent conductivity in heterostructures resembling the triangular-lattice Hubbard model, a paradigmatic model of correlated electrons. (3) Investigating the electron vibration modes in Wigner and generalized Wigner crystals, as well as their evolutions across the quantum and thermal melting of these electron crystals. The proposed project can advance our fundamental understanding of the TMD heterostructures and the long-standing correlated electron problem. It also provides an interdisciplinary learning environment for graduate and undergraduate students.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.