石墨烯自旋调控和无序效应的理论研究

Spintronics, the science for processing and control of electron spins, which makes use of both charge and spin, is considered a promising avenue for future computing and communication technologies. How to introduce the local spins with strong coupling in graphene, how to effectively inject spin into graphene and enhance the polarizing efficiency of spin transport, and how to numerically obtain the exact results of the self-energy of disordered graphene to explore the disordered effect on the quasi-particles behaviors and transport properties are three central scientific themes of graphene spintronics. In this project, we adopt several theoretical methods including first-principles calculation, non-equilibrium Green’s function technique, tight-binding model, mean-filed theory as well as Monte Carlo simulation. Our activities include the following three parts: (i). to explore the mechanism of synergistic effect of several kinds of manipulation of local spin and their coupling in graphene. (ii). to enhance the spin-orbital coupling in graphene, to successfully inject spin into graphene and enhance the polarizing efficiency of spin transport through introducing the proximity effect of topological insulators and half-metallicity of Huesker alloys combined with the doping, inserting the tunnel barrier and tuning the interlayer distance. (iii). to apply and develop the accurate moment-space Lanczos numerical method, and then to exactly describe the quasi-particle behaviors and transport properties of disordered graphene based on the exact results of self-energy. These theoretical results and predictions will be helpful and useful for graphene spintronics in near future.

自旋电子学是一门前沿交叉学科，其研究核心是自旋调控。将石墨烯应用于自旋电子器件的三个关键科学问题是如何使得石墨烯获得强耦合的局域自旋、如何实现石墨烯的有效自旋注入和提升石墨烯自旋输运的极化率、以及如何描述无序效应对体系准粒子行为和输运性质的微观调制机理。本项目采用第一性原理方法、非平衡格林函数技术、紧束缚模型、平均场理论及蒙特卡罗模拟，探讨石墨烯和石墨烯纳米结构局域自旋和其耦合作用多种调控途径的协同效应及其微观机理；借助半金属性Huesker合金和拓扑绝缘体的近邻效应，通过掺杂、插层、边界等途径来增强异质结中石墨烯自旋-轨道耦合、有效注入自旋和提升自旋输运的极化率；应用和发展动量空间的的Lanczos数值模拟方法使之适用于各种无序石墨烯，基于自能的精确计算，研究无序效应如何影响石墨烯的准粒子行为和输运性质，为石墨烯应用于自旋电子学等领域的实验研究和应用提供有指导意义的理论依据和科学基础。

按研究计划执行，团队成员采用第一性原理计算、非绝热分子动力学模拟、非平衡格林函数方法、紧束缚近似等对含石墨烯在内的二维材料的理论预测、电子结构、磁性、自旋极化输运特性以及无序效应等开展理论研究，取得的主要研究成果包括：(1) 基于自主研发的结构搜索程序(AISP)，筛选出了一种新型二维类石墨烯-含四元环的金属型二维碳同素异形体Thgraphene, 第一性原理计算表明此材料具有优异的HER/OER 电催化活性，也可应于钾离子电池负极材料 (J. Mater. Chem, A 2022)；与实验课题组合作，提出一种富勒烯形成新机制-自驱动单原子碳注入法 (PNAS 2022)；(2) 揭示面内磁化、外加门压和载流子掺杂有效调控二维材料和单分子体系的自旋极化输运特性机理 (Nano Lett. 2020, J. Phys. Chem. C 2019)；在双极性二维有机框架半导体材料中，发现载流子掺杂产生铁磁 (Phys. Rev. B 2022)；提出了双极磁性分子 (bipolar magnetic molecules, 简称BMMs) 概念, 通过外加不同极性的门压能实现自旋极化通道的可逆调控 (Angew. Chem. Int. Ed. 2022)。(3) 研究了无序效应对二维费米体系(包括石墨烯)量子特性的影响，可以解释实验上石墨烯电导率对载流子浓度和温度的依赖关系等 (Phys. Rev. B 2019 & 2020)。这些研究工作为石墨烯等低维材料应用于自旋电子学等领域的实验研究和应用提供一些有指导意义的理论依据和科学基础，已在Phys. Rev. B、J. Mater. Chem. A、J. Phys. Chem. Lett.、PNAS、Angew. Chem. Int. Ed.和Nano Lett.等国内外学术期刊发表致谢SCI论文25篇。团队成员在项目执行期间参加国内外学术交流和研讨会6人次，培养博士5名，硕士3名。