Rashba自旋轨道耦合下square-octagon晶格的拓扑相变  

Topological phase transitions in square-octagon lattice with Rashba spin-orbit coupling

作　　者：杨圆 陈帅 李小兵 Yang Yuan;Chen Shuai;Li Xiao-Bing(Zhangjiagang Campus,Jiangsu University of Science and Technology,Zhangjiagang 215600,China;National Laboratory of Solid State Microstructures,Nanjing University,Nanjing 210093,China)

机构地区：[1]江苏科技大学张家港校区,张家港215600 [2]南京大学固体微结构物理国家重点实验室,南京210093

出　　处：《物理学报》2018年第23期190-198,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11647145);南京大学固体微结构物理国家重点实验室开放课题(批准号:M31024);江苏省高校自然科学研究项目(批准号:16KJB430012)资助的课题~~

摘　　要：本文研究了各向同性square-octagon晶格在内禀自旋轨道耦合、Rashba自旋轨道耦合和交换场作用下的拓扑相变,同时引入陈数和自旋陈数对系统进行拓扑分类.系统在自旋轨道耦合和交换场的影响下会出现许多拓扑非平庸态,包括时间反演对称破缺的量子自旋霍尔态和量子反常霍尔态.特别的是,在时间反演对称破缺的量子自旋霍尔效应中,无能隙螺旋边缘态依然能够完好存在.调节交换场或者填充因子的大小会导致系统发生从时间反演对称破缺的量子自旋霍尔态到自旋过滤的量子反常霍尔态的拓扑相变.边缘态能谱和自旋谱的性质与陈数和自旋陈数的拓扑刻画完全一致.这些研究成果为自旋量子操控提供了一个有趣的途径.Motivated by the square-octagon lattice which supports topological phases over a wide range of parameters and a number of interesting quantum phase transitions in the phase diagram when considering the intrinsic spin-orbit coupling, we investigate the topological phase transitions in the isotropic square-octagon lattice combining the effects of both spin-orbit couplings and exchange field.The inversion symmetry and time-reversal symmetry are broken when both Rashba spin-orbit coupling and exchange field are present.The Z2index is not applicable for quantum spin Hall systems without time-reversal symmetry,but the spin Chern number remains valid even in the absence of time-reversal symmetry. Therefore,we use the Chern number and spin Chern number to describe the topological properties of the system.We explore that a variety of topologically nontrivial states appear with changing the exchange field,including time-reversalsymmetry-broken quantum spin Hall states and quantum anomalous Hall states.The phase transition between these topological phases is accompanied by the closing of band gaps.Interestingly,the quantum spin Hall effect described by nonzero spin Chern number is found to remain intact when the time-reversal symmetry is broken.Furthermore,the variation of the amplitude of the exchange field and filling factor drive interesting topological phase transitions from the time-reversal-symmetry-broken quantum spin Hall phase to spin-filtered quantum anomalous Hall phase.A spin-filtered quantum anomalous Hall phase is characterized by the presence of edge states with only one spin component,which provides an interesting route towards quantum spin manipulation.We also present the band structures,edge state wave functions,and spin polarizations of the different topological phases in the system.It is demonstrated that the energy spectra of edge states are in good agreement with the topological characterization based on the Chern number and spin Chern number.In particular,we observe that gapless edge states can appear

关 键 词：量子自旋霍尔效应 自旋轨道耦合 拓扑相变 

分 类 号：O469[理学—凝聚态物理]