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

非技术描述：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电子状态的性质。然而，在石墨烯和过渡金属二硫化物（TMDs）等由原子级薄晶体堆叠而成的材料中，这些测量有时是具有挑战性的。这些材料的特性可以产生许多电子的新量子态，但是这种状态的特征频率通常落在电磁波长远远超过可能的样品尺寸的范围内。在这个项目中，PI开发了先进的片上太赫兹光谱，集成了亚波长波导，研究TMD异质结构中这些新状态的电磁响应。这项研究可以促进我们对相互作用电子的基本理解，并导致新的功能太赫兹器件。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。该项目吸引加州大学伯克利分校的本科生，特别是那些来自代表性不足群体的学生，以推动未来科学和技术的前沿。技术描述：本项目旨在研究二维（2D）过渡金属二硫化物（TMD）异质结构中相关量子相（如平带金属、相关绝缘体和Wigner晶体）的太赫兹电动力学响应。这些高度可调谐的异质结构已经成为研究电子相互作用形成的新状态的主要平台之一。然而，尽管有很大的兴趣，这些状态在其特征频率尺度上的电动力学特性在很大程度上仍然未知。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在项目中探索了三个研究方向：(1)研究一种新型二维平面等离子体，其频率超过单电子空穴衰变的上界。这样的等离子体可能具有延长的寿命，并表现出反映底层相关相位的特性。(2)测量了类似三角晶格Hubbard模型的异质结构中频率相关电导率的完整掺杂演化，这是一种相关电子的范例模型。(3)研究了Wigner晶体和广义Wigner晶体中的电子振动模式，以及它们在这些电子晶体的量子熔化和热熔化过程中的演变。提出的项目可以促进我们对TMD异质结构和长期存在的相关电子问题的基本认识。它还为研究生和本科生提供了一个跨学科的学习环境。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识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.