EFRI 2-DARE Proposal: Spin-Valley Coupling for Photonic and Spintronic Devices

非技术：目前关键的固态技术，如发光二极管、太阳能电池和其他电光元件的性能和能力，最终受到硅和砷化镓等传统半导体的基本特性的限制。层状过渡金属二硫属化物（分子式MX2，如MoS 2和WSe 2）的单层最近被发现是一种有效地在原子薄极限的新型半导体。它们具有截然不同的基本性质，可以克服以前的限制，允许观察和发现新的物理现象，并为前所未有的固态设备提供可能性。MX2的基本新特性包括电子自旋之间的关系，“谷指数”指定电子在2D晶格中占据两个等效动量状态中的哪一个，以及“层指数”指定当两个单层形成双层时电子处于哪一层。这种材料中的自旋、谷和层量子数是相互联系的，可以联合操纵，研究人员已经在理论和实验上证明了这一点。拟议的工作旨在研究这种“自旋谷层耦合”的各个方面，从它在电传输中的作用到它与光学腔的相互作用，以期实现新颖而实用的电，磁和光学控制器件技术。这项工作将由物理和工程师的混合团队完成，并将为大量的研究生和本科生提供跨学科的研究教育。技术：在单层MX 2中，强自旋-轨道耦合将带边缘的真实的自旋锁定到谷指数，产生自旋-谷耦合。同时，谷，因此自旋，是可寻址的使用圆偏振光学选择规则。此外，在双层和异质结构中，对于给定的谷指数，谷指数进一步耦合到层指数，导致新的磁电效应。因此，MX2提供了第一个固态系统，其中可以对谷赝自旋和真实的自旋进行电和动力控制，从而开辟了大量混合自旋和谷器件的可能性。拟议的工作的重点是研究独特的自旋，谷和层赝自旋耦合MX2单层，双层和异质结构与光子和自旋电子器件的应用铭记。具体目标和方法如下：（1）发展自旋-谷-电荷耦合输运的微观理论，以指导和模拟单层、双层、异质结构和混合系统的实验工作和合成：（2）发展具有可控电荷和磁性掺杂剂的高质量、大面积晶体生长;（3）结合联合收割机对本征自旋和谷特性的电学和光学研究，确定混合自旋谷电子学中各种器件几何结构中单层和双层的基本参数;（4）研究和证明在异质结构和混合光子器件中对自旋和谷极化的操纵，混合光子器件将MX 2与诸如光子晶体腔的结构相结合，解决包括跨界面的自旋-谷-电荷传输、层间激子物理、集成腔结构中的激子-极化激元的方面，以及纳米腔内强的光子-谷激子相互作用;以及（5）开发MX2横向结器件，用于高效的、可控的以及自旋和谷特定的光发射器、调制器和检测器。

Non-Technical: The performance and capabilities of key present solid-state technologies, such as light-emitting diodes, solar cells, and other electro-optic components, are ultimately constrained by the fundamental properties of conventional semiconductors such as silicon and gallium arsenide. Monolayers of the layered transition-metal dichalcogenides (with formula MX2, such as MoS2 and WSe2) have recently been discovered to be a new class of semiconductors effectively at the atomically thin limit. They have dramatically different fundamental properties which can defy previous constraints, allowing observation and discovery of new physical phenomena and offering potential for unprecendented solid-state device possibilities. Fundamentally new properties in MX2 include the relationship between electron spin, the "valley index" specifying which of two equivalent momentum states the electron occupies in the 2D lattice, and the "layer index" specifying which layer the electron is in when two monolayers form a bilayer. The spin, valley and layer quantum numbers in this material are linked and can be manipulated jointly, as has already been demonstrated theoretically and experimentally by the investigators. The proposed work aims to study all aspects of this "spin-valley-layer coupling", ranging from its role in electrical transport to its interplay with optical cavities, with a view to novel yet practical device technologies with electrical, magnetic, and optical control. The work will be done by a mixed team of physics and engineers and will provide interdisciplinary research education to a large number of graduate and undergraduate students.Technical: In monolayer MX2 the strong spin-orbit coupling locks the real spin at the band edges to the valley index to produce spin-valley coupling. At the same time the valleys, and hence spins, are addressable using circularly polarized optical selection rules. Additionally, in bilayers and heterostructures the valley index is further coupled to the layer index for a given valley index, leading to new magnetoelectric effects. MX2s thus provide the first solid-state system in which electric and dynamical control of combined valley pseudospin and real spin are possible, opening up a wealth of hybrid spin and valley device possibilities. The focus of the proposed work is on the studying the unique spin, valley and layer pseudospin couplings in MX2 monolayers, bilayers and heterostructures with photonic and spintronic device applications in mind. The specific goals and methods are as follows: (1) develop microscopic theories for coupled spin-valley-charge transport to guide and model the experimental efforts and synthesis of monolayers, bilayers, heterostructures, and hybrid systems; (2) develop highest quality, large-area crystal growth with controllable charged and magnetic dopants; (3) combine electrical and optical investigation of intrinsic spin and valley properties to determine the fundamental parameters of monolayers and bilayers in various device geometries for hybrid spin-valleytronics; (4) investigate and demonstrate manipulation of spin and valley polarizations in heterostructures and hybrid photonic devices combining MX2s with structures such as photonic-crystal cavities, addressing aspects including spin-valley-charge transport across interfaces, interlayer exciton physics, exciton-polaritons in integrated cavity structures, and strong photon-valley exciton interactions within a nanocavity; and (5) develop MX2 lateral junction devices for efficient, controllable, and spin and valley specific light emitters, modulators and detectors.