报告题目：Inflfluence of antichiral edge states on Andreev reflflection in graphene-superconductor junction

报告人：宋俊涛教授   河北师范大学物理学院

报告时间：2021年 5月 21 日　下午 20:00-21:00

报告邀请人：江华

报告地点：致远楼 304室

报告摘要：Using the tight-binding model and the nonequilibrium Green’s function method, we study Andreev reflflection in a graphene-superconductor junction, where graphene has two nonequal Dirac cones split in energy and therefore time-reversal symmetry is broken. Due to the antichiral edge states of the current graphene model, an incident electron traveling along the edges makes a distinct contribution to Andreev reflflections. In a two-terminal device, because Andreev retroreflflection is not allowed for just the antichiral edges, in this case the mutual scattering between edge and bulk states is necessary, which leads to the coeffificient of Andreev retroreflflection always being symmetrical about the incident energy. In a four-terminal junction, however, the edges are parallel to the interface of superconductor and graphene, so at the interface an incident electron traveling along the edges can be retroreflflected as a hole into bulk modes, or specularly reflflected as a hole into antichiral edge states again. It is noted that the coeffificient of specular Andreev reflflection keeps symmetric as to the incident energy of electrons, which is consistent with the reported results before; however, the coeffificient of Andreev retroreflflection shows an unexpected asymmetrical behavior due to the presence of antichiral edge states. Our results present some ideas to study the antichiral edge modes and Andreev reflflection for a graphene model with the broken time-reversal symmetry.

报告人简介：宋俊涛，教授，博导。2003年河北师范大学物理学院毕业，2009年获中国科学院物理研究所理学博士。2012-2014年在美国Yeshiva大学做研究工作。现为河北师范大学副教授。近年来共发表40余篇SCI论文，其中2篇Phys. Rev. Lett., 9篇Phys. Rev. B.，主要研究方向有自旋电子学，石墨烯、介观纳米体系的量子输运理论，凝聚态体系拓扑效应及拓扑相变的理论研究。曾荣获河北省拔尖人才，河北省新世纪“三三三人才工程”等荣誉称号。先后主持河北省杰出青年基金、国家基金委青年基金、国家基金委面上项目2项、教育部新教师基金等。

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