Topological flat bands in twisted trilayer graphene  

转角三层石墨烯中的拓扑平带

作　　者：Zhen Ma Shuai Li Ya-Wen Zheng Meng-Meng Xiao Hua Jiang Jin-Hua Gao X.C.Xie 马振;李帅;郑雅文;肖萌萌;江华;高锦华;谢心澄(School of Physics and Wuhan National High Magnetic Field Center,Huazhong University of Science and Technology,Wuhan 430074,China;School of Physical Science and Technology,Soochow University,Suzhou 215006,China;International Center for Quantum Materials,School of Physics,Peking University,Beijing 100871,China;Collaborative Innovation Center of Quantum Matter,Beijing 100871,China;CAS Center for Excellence in Topological Quantum Computation,University of Chinese Academy of Sciences,Beijing 100190,China)

机构地区：[1]School of Physics and Wuhan National High Magnetic Field Center,Huazhong University of Science and Technology,Wuhan 430074,China [2]School of Physical Science and Technology,Soochow University,Suzhou 215006,China [3]International Center for Quantum Materials,School of Physics,Peking University,Beijing 100871,China [4]Collaborative Innovation Center of Quantum Matter,Beijing 100871,China [5]CAS Center for Excellence in Topological Quantum Computation,University of Chinese Academy of Sciences,Beijing 100190,China

出　　处：《Science Bulletin》2021年第1期18-22,M0003,共6页科学通报（英文版）

基　　金：the National Natural Science Foundation of China(11534001,11874160,11274129,11874026,and 61405067);the National Key Research and Development Program of China(2017YFA0403501);the Fundamental Research Funds for the Central Universities(HUST:2017KFYXJJ027);the National Basic Research Program of China(2015CB921102).

摘　　要：Twisted trilayer graphene(TLG)may be the simplest realistic system so far,which has flat bands with nontrivial topology.Here,we give a comprehensive calculation about its band structures and the band topology,i.e.,valley Chern number of the nearly flat bands,with the continuum model.With realistic parameters,the magic angle of twisted TLG is about 1.12°,at which two nearly flat bands appears.Unlike the twisted bilayer graphene,a small twist angle can induce a tiny gap at all the Dirac points,which can be enlarged further by a perpendicular electric field.The valley Chern numbers of the two nearly flat bands in the twisted TLG depends on the twist angleθand the perpendicular electric field E⊥.Considering its topological flat bands,the twisted TLG should be an ideal experimental platform to study the strongly correlated physics in topologically nontrivial flat band systems.And,due to its reduced symmetry,the correlated states in twisted TLG should be quite different from that in twisted bilayer graphene and twisted double bilayer graphene.本文基于连续模型方法系统地计算了转角三层石墨烯(单层+双层)的电子能带结构以及能带的拓扑性质.计算结果表明转角三层石墨烯在魔角(约1.12°)附近存在谷陈数非零的拓扑平带.与转角双层石墨烯不同,小角度的扭转可以在转角三层石墨烯的狄拉克点打开一个小的能隙,通过施加垂直方向的外电场,可以进一步扩大狄拉克点的能隙.因此,转角三层石墨烯中存在的是两条孤立的平带.同时,这两条平带的谷陈数可以通过扭转角度和外加电场来进一步调控.拓扑平带的存在表明转角三层石墨烯是一个研究拓扑能带中关联效应的理想平台.考虑到转角三层石墨烯较低的对称性,作者预期转角三层石墨烯中的关联电子态会显著不同于转角双层石墨烯和转角双两层石墨烯.

关 键 词：Twisted trilayer graphene Moire heterostructure Valley Chern number Topological flat bands 

分 类 号：TQ127.11[化学工程—无机化工]