Coherent Quantum Dynamics of Indirect Excitons and Valley Pseudospins in Atomically Thin Semiconductor Heterostructures

非技术摘要：近四十年来，科学家们一直在探索通过将电子运动限制在较低维度来控制材料特性的方法。这些量子材料已经改进了发光器件，如发光二极管和激光器，以及信息处理和通信设备（例如计算机和手机），改变了我们的生活。现在可以制造出只有一个原子厚的物质层。这些被称为单层材料的非线性材料代表了二维（2D）材料的最终厚度极限。这个项目询问我们如何通过将两个或几个这样的图纸堆叠在一起来创建更好，更复杂的2D材料。超快激光脉冲类似于快门速度非常快的相机，用于探测堆叠结构并捕获材料中电子的运动。最终，这些研究教会我们如何通过操纵单个电子来控制材料的性质。对这些新型材料的新见解指导了新能源收集和信息处理技术的发展。 该项目还为年轻研究人员提供了宝贵的培训机会，这些领域对维持国家的技术竞争力至关重要。技术摘要：由原子级薄层组成的异质结构代表了极限厚度的二维量子材料。 通过堆叠两个单层过渡金属二硫属化物（TMD），形成半导体垂直异质结构（VHS）。由于在TMD VHS中通常发现的II型能带排列，电子和空穴在光激发后迅速转移到不同的层，导致层间激子的形成。该研究小组使用称为二维傅里叶变换光谱的强大非线性光谱工具，研究了TMD VHS中与层间激子和谷赝自旋相关的相干量子动力学。理解这些赝自旋的相干性质（即，激子和谷指数）指导基于这些新型二维材料的量子器件的开发，从而对信息通信和处理技术产生变革性影响。该项目还为年轻研究人员提供了宝贵的培训机会，使美国在新兴的量子技术市场中处于全球竞争地位。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。

Non-Technical Abstract: Scientists have been exploring methods of controlling material properties by confining electron motions to lower dimensions for nearly four decades. These quantum materials have led to improved light emitting devices, such as light emitting diodes and lasers, and information processing and communication devices (e.g. computers and cell phones) that have transformed our lives. It is now possible to create a sheet of matter just a single atom thick. These ultrathin materials, known as monolayer materials, represent the ultimate thickness limit of two dimensional (2D) materials. This project asks how we may create better and more complex 2D materials by stacking two or several of these ultrathin sheets together. Ultrafast laser light pulses, akin to a camera with very fast shutter speed, are used to probe the stacked structures and capture the motion of electrons in the materials. Ultimately, these studies teach us how to control the properties of materials by manipulating individual electrons. New insights on these novel materials guide the development of new energy harvesting and information processing technologies. This project also provides valuable training opportunities for young researchers in areas critical to sustaining the nation's technological competitiveness. Technical Abstract: An emerging class of heterostructures consisting of atomically thin layers represents two-dimensional quantum materials in the ultimate thickness limit. By stacking two monolayer transition metal dichalcogenides (TMD), a semiconducting vertical heterostructure (VHS) is formed. Because of the type II band alignment typically found in TMD VHSs, electrons and holes rapidly transfer to different layers following optical excitation, leading to the formation of interlayer excitons. The research group investigates coherent quantum dynamics associated with interlayer excitons and valley pseudospins in a TMD VHS using a powerful nonlinear spectroscopy tool known as two-dimensional Fourier transform spectroscopy. Understanding the coherent properties of these pseudospins (i.e., excitons and valley index) guides the development of quantum devices based on these novel two-dimensional materials, enabling transformative impacts on information communication and processing technologies. This project also provides valuable training opportunities for young researchers as future workforce, placing the U.S. in a globally competitive position in the emerging market of quantum technology.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.