The Many-Particle Physics of Lasing in Two-Dimensional Transition-Metal Dichalcogenides

非技术性总结该奖项支持由二维半导体制成的新型激光系统物理学的理论研究和教育。激光和发光二极管在日常生活中无处不在，从为互联网供电的通信网络到交通信号灯。激光器发出的光与发光二极管发出的光有很大不同。激光发出的光是相干的，这意味着光波在空间中以锁定的步伐传播，类似于军乐队中的音乐家，所有人都在一致地行走。相干性是激光的一个重要特性，它的起源往往是一个复杂的物理过程。激光是自发产生的，因此，没有任何东西可以充当乐队指挥的角色。最近，人们努力使激光晶体化，使其在与电光信息处理有关的更多应用中发挥作用，这涉及到二维材料的使用。这些材料实际上只有一个或两个原子层厚。这些材料与传统激光器中使用的材料非常不同，它们的物理特性直到现在才被发现。PI和他的团队将专注于电子和光学工艺。 对这些过程的详细了解最终将有助于通过控制和优化光发射特性（包括相干性和激光作用），使基于二维材料的激光器在技术上更加成熟。PI和他的团队还旨在阐明二维材料和其他自发形成相干性的系统中的激光之间的相似性和差异，例如，超导体的相干性与光发射无关，而是与电子的集体量子力学状态有关。该奖项还支持PI致力于指导本科生，以及在大学和高等教育中与美国原住民学生进行联系。学校水平。该项目还支持编写一本研究生水平的教科书，介绍非线性半导体光学，重点是凝聚态物理学的先进理论技术。技术概述该奖项支持由二维半导体制成的新型激光系统物理学的理论研究和教育。半导体的相干光发射可以被视为非线性半导体物理学的结果。平衡相变到具有破缺的相位对称性的状态，这导致半导体的极化的非零期望值。对于这种系统发射相干光有各种概念，范围从常规激光器到激子激光器，到与费米边缘奇点相关的发射，以及激子和激子-极化激元的Bardeen-Cooper-Schrieffer态和玻色-爱因斯坦凝聚体（BEC）。 这些稳态非平衡态与平衡态的相似程度各不相同：例如，激子BEC通常被认为与平衡态BEC非常相似，而传统激光器没有直接的平衡态类似物。 半导体中这种有趣的非平衡多粒子态是通过电子和空穴之间的强库仑相互作用产生的，例如，通过电或光泵浦产生。过渡金属二硫属化合物（TMDs）是一类二维材料，近年来引起了人们的广泛关注。这些材料是具有非常强的库仑相互作用效应的半导体。库仑效应决定了纳米激光器和高质量微腔等TMD系统的相干辐射。该项目的主要目标是回答这些系统中的基本物理问题，研究非常规激光过程的可能性，如激子激光，玻色子和费米子极化激元激光以及BCS类极化激元激光，并发展理论理解，将微观效应与二维TMD材料相关。该项目的目标还包括可测试的预测实验可达到的发射/激光特性。所使用的理论方法是基于非平衡绿色函数的方法，结合相关的时间相关的运动方程的数值解。该奖项还支持PI的努力，从事本科生辅导，以及推广到美国土著学生在大学和高中一级。该项目还支持编写一本研究生水平的教科书，介绍非线性半导体光学，重点是非平衡绿色函数和费曼图。该奖项反映了NSF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 SUMMARYThis award supports theoretical research and education on the physics of novel laser systems made of two-dimensional semiconductors.Lasers and light-emitting diodes are ubiquitous in everyday life, from communication networks powering the internet to traffic lights. The light emitted from lasers is very different compared to that from light-emitting diodes. The light from a laser is coherent, meaning that the waves of light propagate through space in lock step, similar to musicians in a marching band, all walking in unison. Coherence is an important characteristic of lasers; its origin is often a complex physical process. It occurs spontaneously so, there is nothing that plays the role of the band leader directing the march.Recent efforts to miniaturize lasers, to make them useful in more applications related to electro-optical information processing, involve the use of two-dimensional materials. These materials are effectively only one or two atomic layers thick. These materials are very different from those used in conventional lasers, and their physical properties are only now being uncovered. The PI and his team will focus on electronic and optical processes. A detailed understanding of these processes should ultimately help make lasers based on two dimensional materials technologically more mature by controlling and optimizing light emission characteristics, including coherence and laser action. The PI and his team also aim to elucidate similarities and differences between lasing in two-dimensional materials and other systems where coherence forms spontaneously, for example superconductors where coherence is not related to light emission but to a collective quantum mechanical state of electrons.This award also supports the PI's efforts to engage in undergraduate student mentoring as well as outreach to Native American students at the college and high school level. The project also supports writing a graduate-student-level text book, an introduction to nonlinear semiconductor optics with an emphasis on advanced theoretical techniques of condensed matter physics.TECHNICAL SUMMARYThis award supports theoretical research and education on the physics of novel laser systems made of two-dimensional semiconductors.Coherent light emission from semiconductors can be viewed as a result of a non-equilibrium phase transition to a state with broken phase symmetry which leads to a non-zero expectation value of the semiconductor's polarization. There are various concepts for such systems to emit coherent light, ranging from conventional lasers, to exciton lasers, to emission related to Fermi-edge singularities, and to Bardeen-Cooper-Schrieffer states and Bose-Einstein condensates (BEC) of excitons and exciton-polaritons. The degree to which these stationary non-equilibrium states are analogous to their equilibrium counterparts varies: an exciton BEC, for example, is often assumed to be very similar to an equilibrium BEC, while a conventional laser has no direct equilibrium analogue. This interesting variety of non-equilibrium many-particle states in a semiconductor arise through strong Coulomb interactions between the electrons and holes, which are created, for example, through electrical or optical pumping. Two-dimensional materials such as monolayer transition-metal dichalcogenides (TMDs) have attracted much attention. These materials are semiconductors with very strong Coulomb interaction effects. The Coulomb effects determine the coherent emission from TMD systems, such as nanolasers and high-quality microcavities. The primary objective of this project is to answer fundamental physics questions in these systems, to study the possibility of unconventional lasing processes such as exciton lasing, bosonic and fermionic polariton lasing as well as BCS-like polariton lasing, and to develop theoretical understanding that incorporates microscopic effects that are relevant in two-dimensional TMD materials. The project objectives also include testable predictions for experimentally accessible emission/laser characteristics. The theoretical approach to be used is based on the method of non-equilibrium Green's functions, combined with numerical solutions of the relevant time-dependent equations of motion. This award also supports the PI's efforts to engage in undergraduate student mentoring as well as outreach to Native American students at the college and high school level. The project also supports writing a graduate-student-level text book, an introduction to nonlinear semiconductor optics with an emphasis on non-equilibrium Green's functions and Feynman diagrams.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.