转角双层-双层石墨烯中同位旋极化的C=4陈绝缘态  

Isospin polarized Chern insulator state of C=4 in twisted double bilayer graphene

作　　者：刘义俊 陈以威 朱雨剑 黄焱 安冬冬 李庆鑫 甘祺康 朱旺 宋珺威 王开元 魏凌楠 宗其军 刘硕涵 李世伟 刘芝 张琪 徐瑛海[1,2] 曹新宇 杨奥 王浩林 杨冰 Andy Shen 于葛亮 王雷 Liu Yi-Jun;Chen Yi-Wei;Zhu Yu-Jian;Huang Yan;An Dong-Dong;Li Qing-Xin;Gan Qi-Kang;Zhu Wang;Song Jun-Wei;Wang Kai-Yuan;Wei Ling-Nan;Zong Qi-Jun;Liu Shuo-Han;Li Shi-Wei;Liu Zhi;Zhang Qi;Xu Ying-Hai;Cao Xin-Yu;Yang Ao;Wang Hao-Lin;Yang Bing;Andy Shen;Yu Ge-Liang;Wang Lei(National Laboratory of Solid State Microstructures,School of Physics,Nanjing University,Nanjing 210093,China;Collaborative Innovation Center of Advanced Microstructures,Nanjing University,Nanjing 210093,China;School of Advanced Materials and Nanotechnology,Xidian University,Xi’an 710126,China;Hubei Jiufengshan Laboratory,Wuhan 430206,China)

机构地区：[1]南京大学物理学院,固体微结构物理国家重点实验室,南京210093 [2]南京大学,人工微结构科学与技术协同创新中心,南京210093 [3]西安电子科技大学先进材料与纳米科技学院,西安710126 [4]湖北九峰山实验室,武汉430206

出　　处：《物理学报》2023年第14期1-8,共8页Acta Physica Sinica

基　　金：江苏省杰出青年基金(批准号:BK20220066);国家自然科学基金(批准号:12074173);江苏省创新人才、企业家项目(批准号:JSSCTD202101);中央高校基本科研业务费(批准号:ZYTS23090)资助的课题.

摘　　要：范德瓦耳斯材料相对扭转到特定角度时,会出现几乎零色散的莫尔平带,从而产生一系列关联电子物态,例如非常规超导、关联绝缘态和轨道磁性等.在转角双层-双层石墨烯(TDBG)体系中,能带带宽和拓扑性质可以通过栅极施加的电位移场原位调控,使该体系成为良好的研究拓扑相变和强关联物理的量子模拟平台.在一定的电位移场作用下,TDBG中C_(2x)对称性破缺,中性点附近的导带和价带会获得有限的陈数.能带的拓扑性质与强相互作用驱动的对称性破缺使得可以在低磁场下实现并调控陈绝缘态.本工作通过制备高质量TDBG器件,在有限磁场下,在莫尔原胞填充因子ν=1处发现了陈数为4的陈绝缘态.同时还发现纵向电阻出现电阻峰并随平行磁场或温度升高而增强的现象,这类似于^(3)He中的Pomeranchuk效应,推测ν=1处的陈绝缘态或许源于同位旋的极化.A flat band with nearly zero dispersion can be created by twisting the relative orientation of van der Waals materials,leading to a series of strongly correlated states,such as unconventional superconductivity,correlated insulating state,and orbital magnetism.The bandwidth and topological property of electronic band structure in a twisted double bilayer graphene are tunable by an external displacement field.This system can be an excellent quantum simulator to study the interplay between topological phase transition and strong electron correlation.Theoretical calculation shows that the C_(2x) symmetry in twisted double bilayer graphene(TDBG)can be broken by an electric displacement field,leading the lowest conduction and valence band near charge neutrality to obtain a finite Chern number.The topological properties of the band and the symmetry breaking driven by the strong interaction make it possible to realize and regulate the old insulation state at low magnetic fields.Hence Chern insulator may emerge from this topological non-trivial flat band under strong electron interaction.Here,we observe Chern insulator state with Chern number 4 at filling factor v=1 under a small magnetic field on twisted double bilayer graphene with twist angle 1.48°.Moreover,the longitudinal resistance shows a peak under a parallel magnetic field and increases with temperature or field rising,which is similar to the Pomeranchuk effect in ^(3)He.This phenomenon indicates that Chern insulator at v=1 may originate from isospin polarization.

关 键 词：转角双层-双层石墨烯 陈绝缘态 电子关联 

分 类 号：O613.71[理学—无机化学] O469[理学—化学]