| 转角石墨烯体系的拓扑特性和轨道磁性 |
| |
| 引用本文： | 刘健鹏,戴希.转角石墨烯体系的拓扑特性和轨道磁性[J].物理学报,2020(14):10-22. |
| |
| 作者姓名： | 刘健鹏 戴希 |
| |
| 作者单位： | 上海科技大学物质科学与技术学院;香港科技大学物理系 |
| |
| 基金项目： | 香港研究资助局(批准号:GRF16300918);上海科技大学启动经费资助的课题. |
| |
| 摘 要： | 本文介绍了转角双层石墨烯和多层石墨烯中的电子结构、拓扑性质以及轨道磁性.在转角双层石墨烯中,由于两层石墨烯之间的相对旋转会形成具有长周期的摩尔条纹.由转角产生的摩尔势场会在摩尔超元胞中产生方向相反的赝磁场,与两层的石墨烯中的狄拉克电子耦合,从而产生赝朗道能级.而魔角石墨烯中的每个谷和自旋自由度的两条平带就等价于两个具有相反陈数的零赝朗道能级.这样的赝朗道能级表示可以很自然地解释一系列"魔角"的来源,也对理解魔角双层石墨烯中观测到的关联绝缘态和量子反常霍尔效应具有重要意义.本文进一步讨论了转角多层石墨烯,并发现转角多层石墨烯体系中普遍存在具有非平庸拓扑性质的平带.这些拓扑平带通常具有非零的谷陈数,并且在一定近似下可以由一个普适的规律描述.本文还讨论了转角石墨烯体系中的拓扑平带所具有的轨道磁性.如果时间反演对称性自发破缺,转角石墨烯体系会处于一个谷极化的基态.这样的谷极化基态是一个在摩尔尺度上的轨道磁性态,在摩尔超胞中具有纳米尺度的环状电流分布.之前的理论提出在转角双层石墨烯体系中观测到的关联绝缘态的本质就是一种净磁矩为零的"摩尔轨道反铁磁态".当体系的C2z对称性被氮化硼衬底破坏时,转角石墨烯中的谷极化基态则变成了一种"摩尔轨道铁磁态",它不仅具有(量子)反常霍尔效应,也具有新奇的磁光效应和非线性光学响应.
|
| 关 键 词： | 转角石墨烯 能带拓扑 轨道磁性 |
Topological properties and orbital magnetism in twisted graphene systems |
| |
| Liu Jian-Peng,Dai Xi.Topological properties and orbital magnetism in twisted graphene systems[J].Acta Physica Sinica,2020(14):10-22. |
| |
| Authors: | Liu Jian-Peng Dai Xi |
| |
| Affiliation: | (School of Physical Science and Technology,Shanghai Tech University,Shanghai 201210,China;Department of Physics,Hong Kong University of Science and Technology,Hong Kong,China) |
| |
| Abstract: | We review and discuss the electronic structures,topological properties and orbital magnetism in twisted bilayer(TBG)and multilayer graphene systems.Moirépattern is formed in twisted bilayer graphene due to the mutual twist of the two graphene layers.The moirépotential induced by the twist can generate opposite pseudo magnetic fields in the Moirésupercell,which are coupled with the Dirac fermions and generate two sets of pseudo Landau levels with opposite Chern numbers ±1.The two flat bands for each valley each spin of TBG are equivalent to the two zeroth pseudo Landau levels with opposite Chern numbers and opposite sublattice polarizations.Such a pseudo-Landau-level representation has significant implications on the quantum anomalous Hall states observed at integer fillings of the flat bands in TBG at the magic angle.The origin of the magic angle can also be naturally explained by using the pseudo-Landau-level picture.We further discuss twisted multilayer graphene systems,and show that topological flat bands generally exist in the twisted multilayer graphene systems.These topological flat bands have nonzero valley Chern numbers,which can be described by a succinct formula under certain approxmations.These topological flat bands in twisted bilayer and multilayer graphene systems are associated with orbital magnetism.A valley polarized state in the twist graphene system is an orbital magnetic state with nontrivial current-loop pattern in the moirésupercell.The experimentally observed correlated insulating states at ±1/2 fillings and at charge neutrality point of magic-angle TBG can be valley polarized states,which are associated with compensating current loops and induce staggered orbital magnetizations on the moirélength scale.If C2z symmetry is broken due to the alignment of hexagonal boron nitride substrate,then a valley-polarized ground state would be a moiréorbital ferromagnetic state,which exhibits not only(quantum)anomalous Hall effect,but also novel magneto-optical and nonlinear optical responses. |
| |
| Keywords: | twisted graphene systems band topology orbital magnetism |
| 本文献已被 CNKI 维普 等数据库收录！ |
| 点击此处可从《物理学报》浏览原始摘要信息 |
|
点击此处可从《物理学报》下载免费的PDF全文 |
|
