石墨烯线缺陷的电子valley滤波特性的数值模拟研究

Numerical Simulation Study of Valley Filter Property of Graphene Electron by Line Defect

基于紧束缚近似哈密顿模型,运用波包动力学方法,数值模拟研究了石墨烯电子穿越线缺陷的输运性质和相应的透射率,着重探讨线缺陷对于电子Valley赝自旋的滤波特性.模拟结果表明:(1)石墨烯线缺陷对于电子valley赝自旋具有半透性;(2)电子的透射率与入射角度和能量都有关;(3)在某个临界角度θc,透射率出现峰值,其大小随着能量的增加而增大,而|θc|的绝对值却随能量的增加而减小;(4)当入射角|θ|大于|θc|时,透射率将急剧地降为0.进一步的理论分析指出,这是由于透射率能量关系中的非线性项所造成的.最后,我们的数值模拟结果进一步地证明了石墨烯线缺陷未来作为valley赝自旋滤波器件的实用可能性.

Graphene is a promising nanostructure material used in the field of materials science,electronics and nanotechnology because of its unique geometric structure and amazing physical and chemical properties.In addition to the conventional spatial and spin degrees of freedom,the electrons in graphene have another degree of freedom,called as the valley pseudospin,making it possible to develop the specific valleytronics devices by the graphene,which are very similar to those in the spintronics.However,the pristine graphene is a zero-gap semiconductor,which brings a great difficulty to the control of graphene electron and limits its potential applications in the field of nano-electronic devices.In order to solve this problem,the method to produce some defects in the grapheme is often used.Recently,the topological defects in graphene, such as the grain boundary and line defect,have been observed in experiments,which will have a big effect on its electronic transport properties,e.g.,changing the moving direction of electron wave packet or filtering the electron’s valley degree of freedom.Based upon the tight-binding Hamiltonian and wave packet dynamics,we have used the KPM approach to calculate the evolution operator.The transport properties of graphene electron,passing through the line defect in graphene,have been studied by a real-space simulation,in which more attention is paid to the valley filtering property of the line defect.An electron wave packet,approaching the line defect at its energy E and angle of incidenceθand scattering off it,has been＆amp;nbsp;simulated dynamically in the real space.Our obtained results show that：（1 ）The graphene line defect is semitransparent for the graphene electron with valley degree of freedom.（2 ）The transmission probability depends not only the angle of incidence,but also the electron’s energy.（3 ）A peak of transmission probability appears at a critical angle of incidenceθc , whose absolute value｜θc｜decreases with increasing the electron’s energy,in contrast to the increase of peak value.（4）The transmission probability will drastically decrease to 0 when the absolute value of incidence angle｜θ｜is greater than｜θc｜, which is found to be caused by the nonlinear terms in the relation of the transmission probability with electron’s energy,as indicated by further theoretical analysis.Finally,our numerical simulation results further prove the practical applicability of the graphene line defect used as a valley pseudospin filter device in future.