新型sd2杂化二维材料电子结构的理论计算研究

Graphene is a planar sheet of carbon atoms arranged in a two-dimensional (2D) hexagonal crystal lattice. Its unique properties originate from the sp2 hybridization involving the 2s, 2px and 2py orbitals of carbon, which leaves 2pz orbital hybridized into π state, producing two Dirac bands in electronic structures. Recently, a novel 2D material, sd2 graphene was reported, which has attracted considerable interest in physics and materials science communities. sd2 graphene is made of sd2 hybridized transition metal atoms in a hexagonal lattice, involving the s and dxy, dx2-y2 orbitals of transition metal hybridized into σ state, and its electronic structures are characterized with bond-centered electronic hopping, which transforms the apparent atomic hexagonal lattice into the physics of a kagome lattice. Compared with graphene, sd2 hybridized material has many advantages, including non-zero band gap, magnetism, strong spin-orbit coupling and many-body effect, among many others. In this project, we will focus on such sd2 hybridized materials, with special attention paid to transition metal atoms arranged in hexagonal pattern that are supported on semiconductor substrates. We will calculate their geometry, stability, charge distributions, band structures, density of states, topological phase transition and electron transport in order to demonstrate their electronic, magnetic and topological properties. We also aims to control their physical properties, e.g. via pressure and/or electric field for different applications. We expect this study to shed light on future exploration and application of 2D material with sd2 hybridization.

石墨烯是由碳原子构成的二维六角晶格，其电子结构源于碳2s与2px、2py轨道之间的sp2杂化，剩下的2pz轨道杂化成π键，形成狄拉克能带结构。最近发现的一种全新材料－基于sd2杂化的二维材料，引起了物理、材料领域科学家的广泛关注。与石墨烯不同，sd2杂化材料是基于过渡金属元素s与dxy,dx2-y2轨道的sd2杂化，形成平面内的σ键，其能带结构可用一条拓扑非平庸的平带加两条狄拉克带来描述。它有许多优异的物理特性，例如自旋轨道耦合强, 可有能隙、磁性以及多体效应等。本项目将利用理论计算研究这种新颖的sd2杂化二维材料，特别是基于半导体衬底支撑的过渡金属六角晶格体系。通过计算几何、稳定性、电荷布局、能带、电子态密度、拓扑相变、电荷输运等分析其物理性质，着重研究一些体系电子结构的微观调控，揭示宏观电、磁、拓扑性质与结构、成份和电子组态之间的关联，为sd2杂化二维材料的实验研究及应用提供理论依据。

石墨烯由于sp2轨道杂化形成的独特的能带结构引起了人们的广泛关注，其发现也促进了对其他类石墨烯二维材料的研发。该项目主要关注新型类石墨烯二维结构的设计和电子结构调控的基础理论研究。我们研究的类石墨烯系统包括sd2杂化石墨烯、（px，py）类石墨烯及其他二维六角晶格结构。通过计算材料的结构稳定性、能带、态密度、电荷布局、光学和拓扑性质，我们发现轨道杂化在结构-性质内在关联中扮演重要角色。同时，通过衬底选择，外加电场、应力等条件，能对这些类石墨烯结构进行有效的微观调控，甚至产生拓扑相变。这些结果为相关实验研究提供了理论依据，并为材料在新型电子器件、拓扑计算、能源、环保等领域的潜在应用奠定了初步的理论基础。依托该项目，发表包括JCP、PCCP、JMCC、Nanoscale、npj Computational Materials、Advanced Materials在内的SCI论文15篇。在项目的支持下，培养了六名硕士和一名博士毕业生，还有四名硕士和三名博士在读。