Influence of antichiral edge states on Andreev reflection in graphene-superconductor junction
Influence of antichiral edge states on Andreev reflection in graphene-superconductor junction
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反手性边缘态对石墨烯-超导结中Andreev反射的影响
DOI：
10.1103/physrevb.101.045407
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发表时间：
2019-04
影响因子：
3.7
通讯作者：
Yu-Xian Li
中科院分区：
文献类型：
--
作者：
Chao Wang;Lin Zhang;Peipei Zhang;Juntao Song;Yu-Xian Li
利用紧束缚模型和非平衡绿色函数方法，研究了石墨烯-超导体结中的Andreev反射，其中石墨烯有两个能量不等的Dirac锥分裂，因此时间反演对称性被破坏.由于当前石墨烯模型的反手性边缘状态，沿着边缘沿着行进的入射电子对Andreev反射做出明显贡献。在二端器件中，由于Andreev逆反射不允许仅用于反手征边缘，在这种情况下，边缘和体态之间的相互散射是必要的，这导致Andreev逆反射系数总是关于入射能量对称的。然而，在四端结中，边缘平行于超导体和石墨烯的界面，因此在界面处，沿着边缘沿着行进的入射电子可以作为空穴被逆反射到体模中，或者作为空穴再次被镜面反射到反手性边缘状态中。结果表明，镜面Andreev反射系数与电子入射能量保持对称，这与文献报道的结果一致，但由于反手征边缘态的存在，Andreev逆反射系数表现出意想不到的不对称行为.我们的结果为研究时间反转对称性破缺的石墨烯模型的反手征边缘模和Andreev反射提供了一些新的思路。
Using the tight binding model and the non-equilibrium Green function method, we study Andreev reflection in graphene-superconductor junction, where graphene has two nonequal Dirac Cones split in energy and therefore time reversal symmetry is broken. Due to the anti-chiral edge states of the current graphene model, an incident electron travelling along the edges makes distinct contribution to Andreev reflections. In a two-terminal device, because Andreev retro-reflection is not allowed for just the anti-chiral edges, in this case the mutual scattering between edge and bulk states is necessary, which leads that the coefficient of Andreev retro-reflection is always 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 travelling along the edges can be retro-reflected as a hole into bulk modes, or specularly reflected as a hole into anti-chiral edge states again. It is noted that, the coefficient of specular Andreev reflection keeps symmetric as to the incident energy of electron which is consistent with the reported results before, however the coefficient of Andreev retro-reflection shows an unexpected asymmetrical behavior due to the presence of anti-chiral edge states. Our results present some new ideas to study the anti-chiral edge modes and Andreev reflection for a graphene model with the broken time reversal symmetry.
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