石墨烯带正常-超导结的量子输运  

Quantum transport through normal-superconducting graphene nanoribbons

作　　者：王斌[1] 李健伟[1] 卫亚东[1] 王健[2] 

机构地区：[1]深圳大学物理科学与技术学院,深圳大学计算凝聚态物理研究所,深圳518060 [2]香港大学物理系,中国香港

出　　处：《深圳大学学报（理工版）》2014年第2期111-118,共8页Journal of Shenzhen University(Science and Engineering)

基　　金：国家自然科学基金资助项目(11304205,11374246)~~

摘　　要：基于非平衡格林函数(non-equilibrium Green's function,NEGF)和密度泛函理论(density functional theory,DFT),从第一性原理出发研究Armchair型和Zigzag型的石墨烯带正常-超导结的电子输运性质,计算了缺陷对这两种正常-超导结输运性质的影响.计算表明,对无缺陷正常-超导石墨烯带,在超导能隙内,Andreev反射系数TA恰好等于正常石墨烯带的电子透射系数TN.当石墨烯带存在缺陷时,Andreev反射系数TA不再是一个常数,而在超导能隙边缘出现两个尖锐的峰,其峰值大于正常系统的电子透射系数.在超导能隙之外,Andreev反射系数TA逐渐减小为0,准粒子的正常隧穿几率T1逐渐增大,且趋于无超导下的正常系统的电子透射系数TN.不同缺陷构型对石墨烯带中载流子的输运过程影响不同.如果缺陷的存在对正常石墨烯带电子散射过程影响越大,则其对正常-超导体系中的Andreev反射和准粒子散射影响也越大.The first principles calculation has been carried out to investigate the quantum transport properties of normal-superconducting graphene nanoribbons （ GNRs） within the combination of non-equilibrium Green’s function （ NEGF） and density functional theory （ DFT） . The Andreev reflection coefficient TA and quasi-particle transmission probability T1 of normal-superconducting system of a series of defective configurations were investigated in detail. As a comparison, the electric transmission coefficient TN of normal system was also calculated. In the pristine graphene nanoribbons, The Andreev reflection coefficient TA is a constant and exactly equals to electric transmission coefficient TN of the normal system in the superconducting energy gap, which indicates that the Andreev conductance is twice of the normal electric conductance. In the defective configurations of graphene nanoribbons, TA shows two sharp peaks at E =＆#177; Δ, and the peak values are larger than the electric conductance of normal system. Outside the superconducting energy gap, Andreev conductance decays to zero, and quasi-particle transmission probability＆amp;nbsp;increases to the normal electric transmission coefficient gradually. Different defective configurations give different influence to the Andreev reflection of the normal-superconducting graphene nanoribbons.

关 键 词：凝聚态物理 石墨烯带 正常-超导结 ANDREEV反射 非平衡格林函数 密度泛函理论 

分 类 号：O469[理学—凝聚态物理]