Spin Dependent Transport in Materials with Multivalley Band Structures

该奖项支持基础理论研究和教育，以了解电子自旋在材料中的行为，为可能的未来电子设备的基础做出贡献，这些设备通过操纵电子自旋及其电荷发挥作用。除了携带电荷外，电子在某种意义上也像一个旋转的陀螺，它的行为符合量子力学的规则。电子有两种自旋的感觉，探索使用电子来物理地表示信息是很自然的，就像数字电子学中熟悉的“0”和“1”一样。自旋电子学研究的目的是利用材料中电子自旋与其环境之间的相互作用，将量子力学自旋引入电子器件。由于基于电荷的场效应晶体管正迅速接近其物理极限，自旋电荷计算方案近年来成为一个活跃的研究前沿。PI将开发理论模型，量化材料中的自旋输运，这些材料包括元素周期表中垂直高于或低于硅的硅元素。PI还将研究本质上是单层原子的晶体，例如由元素周期表中过渡金属块的原子和元素周期表中垂直低于氧的元素组成的过渡金属二硫族化合物。该模型旨在通过应变工程和适当的外电场的应用来延长操作和处理信息所需时间的自旋电子器件的设计。主要的研究重点将是量化掺杂材料中的自旋弛豫时间，其中电导率可以通过有意添加向主晶体提供/接受电子的外来原子或通过施加门电压将载流子从周围材料引入原子薄材料来提高。这个项目提出了许多吸引学生的想法。通过材料科学，物理和工程研究生的合作，每个人都从量子力学或器件功能的概念中学习。PI将通过提供互动讲座/演示，在K-12学生中积极推广这项研究，突出未来技术在设备中的应用。PI旨在利用这项研究的社会影响潜力，帮助吸引代表性不足群体的学生参与该项目。对金属材料系统中电子自旋与其固态环境之间相互作用的理解，促进了信息存储技术的巨大发展。与金属相反，硅对逻辑电路具有完全的支配作用。幸运的是，这种材料和其他IV组材料是自旋电子逻辑器件的有希望的候选材料，因为它们的晶体反转对称性可以抑制随机变化的本征磁场的自旋进动，并且它们的天然丰富的同位素的零核自旋可以通过超精细相互作用抑制自旋弛豫。该项目的一个主要目标是填补硅和锗等多谷半导体中自旋弛豫过程理论的长期空白。这些材料的自旋弛豫表现出很强的依赖于给体原子的身份。通过调用解析和数值方法，PI将通过建立与自旋轨道耦合引起的施主基态变化的联系来量化施主驱动的自旋弛豫。该效应将作为应变、温度、供体浓度和供体身份的函数进行研究。除了IV族材料外，单层过渡金属二硫族化合物和氧化物是另一类可能用于自旋电子学的重要材料。这些二维单层半导体将奇异电荷、自旋和谷电子现象结合在一起。电子和空穴之间的强结合，在真正的二维系统中阻碍库仑筛选的结果，使异常强烈的光-物质相互作用持续到室温。PI将系统地量化二维晶体（如石墨烯和过渡金属二硫化物）中电子-声子相互作用引起的动量散射和自旋弛豫。输运效应将包括通过压电和栅极电压的对称破缺的电场特征。PI还将从弛豫的角度分析二维晶体中经常讨论的拓扑绝缘体相。PI的目标是招募合格的本科生参与研究，并教授一门关于自旋电子学的新课程，该课程解释了量子力学和磁学如何应用于新的逻辑和存储架构。PI将努力招募麦克奈尔的学者，并将与罗切斯特大学的卡恩斯中心合作，吸引未被充分代表的少数民族的学生参与这项研究。

NONTECHNICAL SUMMARYThis award supports fundamental theoretical research and education to understand how electron spin behaves in materials contributing to the foundations of possible future electronic devices which function by manipulating electron spin as well as its charge. In addition to carrying an electric charge, an electron is also in a sense like a spinning top that behaves according to the rules of quantum mechanics. There are two senses of spin to an electron and it is natural to explore using the electron to physically represent information, like the familiar '0' and '1' in digital electronics. Spintronics research aims to introduce the quantum mechanical spin into electronic devices by making use of the interactions between the electron spin and its environment in a material. Because charge-based field effect transistors are rapidly approaching their physical limits, the spin-charge computation scheme has recently become an active research frontier.The PI will develop theoretical models that quantify spin transport in materials that include silicon and elements vertically above and below silicon in the periodic table of elements. The PI will also investigate crystals that are essentially a single layer of atoms such as transition-metal dichalcogenides which are made of atoms from the transition-metal block of the periodic table and elements from the periodic table vertically below oxygen. This modeling is aimed to enable the design of spintronic devices in which the time needed for manipulating and processing information is prolonged by strain engineering and proper application of external electric fields. The primary research focus will be on quantifying this spin relaxation time in doped materials where the conductivity is improved either by intentionally adding foreign atoms that donate/accept electrons to/from the host crystal, or by applying a gate-voltage that brings charge carriers into atomically thin materials from surrounding materials. This project presents ideas that are fascinating to a wide range of students. Through collaboration of materials science, physics and engineering graduate students, each learns from the other concepts of quantum mechanics or device function. The PI will actively promote this research among K-12 students by delivering interactive lectures/demos that highlight the use of future technology in devices. The PI aims to utilize the potential of this research for societal impact to help attract students from under-represented groups to the project.TECHNICAL SUMMARYUnderstanding of the interactions between the electron's spin and its solid-state environment in metallic material systems has spurred immense development in information storage technologies. Contrary to metals, silicon holds complete sway over logic circuits. Fortunately, this and other group IV materials are promising candidates for spintronic logic devices owing to their crystalline inversion symmetry which suppresses precession of spins about randomly changing intrinsic magnetic fields, and the zero nuclear spin of their naturally abundant isotopes which suppresses spin relaxation by hyperfine interactions. A major objective in this project will be to fill a longstanding gap in the theory of spin relaxation processes in multi-valley semiconductors such as silicon and germanium. The spin relaxation in these materials shows a strong dependence on the identity of the donor atom. By invoking analytical and numerical methods, the PI will quantify the donor-driven spin relaxation by establishing a connection with the induced changes in the donor ground state due to the spin orbit coupling. The effect will be investigated as a function of strain, temperature, donor concentration, and donor identity. Apart from group IV materials, monolayer transition-metal dichalcogenides and oxides present another important class of materials potentially useful for spintronics. These two-dimensional monolayer semiconductors put together exotic charge, spin and valley electronic phenomena. The strong binding between electrons and holes, a result of the impeded Coulomb screening in genuine 2D systems, enables exceptionally strong light-matter interaction that persists up to room temperature.The PI will systematically quantify the momentum scattering and spin relaxation due to electron-phonon interaction in two-dimensional crystals such as graphene and transition-metal dichalcogenides. Transport effects will include signatures of electrical fields via piezoelectricity and symmetry breaking by the gate voltage. The PI will also analyze the often-discussed topological insulator phase in two-dimensional crystals from the perspective of relaxation.The PI aims to recruit qualified undergraduate students to participate in the research, and teach a new course on spintronics which explains how quantum mechanics and magnetism can be applied into new logic and memory architectures. The PI will try to recruit McNair scholars and will work with the Kearns Center at the University of Rochester to attract students from under-represented minorities to this research.