EFRI NewLAW: Magnetic Field Free Magneto-optics and Chiral Plasmonics with Dirac Materials

大多数自然现象都遵循“时间反转对称”，即如果时间方向颠倒，那么光波在前进和后退方向上的传播是相同的。但是光传输只允许光单向通过，被称为“非互反传播”，这对于降低通信能耗和抑制噪声至关重要。非互易的产生需要打破时间反转对称性，通常可以通过法拉第效应在磁光材料中实现（光通过材料受到外部磁场的影响，从而改变光波的方向）。外部磁场的这一基本要求对器件小型化和片上集成造成了重大限制。本项目研究了一种新的材料平台“间隙狄拉克材料”，其固有的贝里曲率是其能带结构的一个关键和新认识的性质，可以作为有效的磁场，从而产生独特的手性边缘等离子体共振，可以促进光的非互易传播。这项研究的结果将使光通信和量子信息处理的紧凑，无磁场（因此重量轻且节能）可调谐非互易器件成为可能。该项目将在多学科环境中培养毕业生和代表性不足的学生；通过“教师研究体验”、“即席科学”公开讲座、以中学生为对象的“拓宽视野”等活动，向公众提供服务；并在开源许可下开发和分发分析工具和代码。本项目探索了基于Dirac材料（如过渡金属二硫系单层）的磁光学和无磁场非互易光输运的新前沿，其中反转对称性的破坏和大自旋-轨道耦合导致谷自旋锁定。这些材料的本征贝里曲率进一步作为动量空间中的有效磁场，在谷不平衡下可以产生手性等离子体模式，使中红外和太赫兹频率的非互易光传播。在这些间隙Dirac材料中，谷极化将通过三种方式产生：1)掺杂过渡金属杂质；2)接近层状磁性过渡金属磷三硫化物；3)电自旋注入。在选定的单层和异质结构中进行Berry曲率、磁光效应和手性等离子体的电磁建模和计算，将为分子束外延和化学气相沉积的材料合成，以及自旋分辨扫描隧道显微镜/光谱、角度分辨光发射光谱和偏振选择性光致发光的原子尺度表征提供指导。以及远场光学表征和近场扫描光学显微镜成像。通过综合实验-理论方法，该项目旨在展示中红外到太赫兹范围内的导波手性等离子体，以实现无磁场光学器件，如非倒数法拉第隔离器和可调谐光循环器。

Most natural phenomena obey "time-reversal symmetry", which states that if the direction of time is reversed, for example, the propagation of light waves is the same in both forward and backward directions. But optical transport that only lets light pass one-way, termed "non-reciprocal propagation", is vital for energy reduction and noise suppression in telecommunications. The generation of non-reciprocity requires breaking time-reversal symmetry, and typically can be realized in magneto-optical materials via the Faraday effect (where light passing through a material is subject to an external magnetic field, thus changing the light wave orientation). This fundamental requirement of an external magnetic field places significant limitations on device miniaturization and on-chip integration. This program researches a new material platform "gapped Dirac materials" whose intrinsic Berry curvature, a key and newly-recognized property of their energy band structure, can act as an effective magnetic field - thus giving rise to unique chiral edge plasmon resonances that can facilitate non-reciprocal light propagation. The outcome of this research will enable compact, magnetic-field-free (and thus lightweight and energy-efficient) tunable nonreciprocal devices for optical communications and quantum information processing. This project will train graduate and under-represented students in STEM in a multidisciplinary environment; provide outreach to the public through programs such as Research Experience for Teachers, "Science on Tap" public lectures, and "Broaden the Horizon" that focuses on middle school female students; and develop and distribute analysis tools and codes under open source licenses.This project explores a new frontier in magneto-optics and magnetic-field-free non-reciprocal light transport based on Dirac materials such as transition-metal dichalcogenide monolayers, where the breaking of inversion symmetry and large spin-orbit coupling lead to valley-spin locking. The intrinsic Berry curvature of these materials further acts as an effective magnetic field in momentum space, which under a valley imbalance can give rise to chiral plasmon modes that enable non-reciprocal light propagation at mid infrared and terahertz frequencies. Valley polarization in these gapped Dirac materials will be induced through three approaches: 1) doping with transition-metal impurities; 2) proximity to layered magnetic transition-metal phosphorous trichalcogenides; and 3) electrical spin injection. Electromagnetic modeling and calculations of the Berry curvature, magneto optical effects, and chiral plasmons in selected monolayers and heterostructures will provide guidance for material synthesis by molecular beam epitaxy and chemical vapor deposition, and atomic scale characterization with spin-resolved scanning tunneling microscopy/spectroscopy, angle-resolved photoemission spectroscopy, and polarization selective photoluminescence, as well as far-field optical characterization and near-field scanning optical microscopy imaging. Through an integrated experimental-theoretical approach, this project aims to demonstrate wave guiding chiral plasmons in the mid-infrared to terahertz range to enable magnetic-field-free optical devices such as non-reciprocal Faraday isolators and tunable optical circulators.