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arXiv 2306.00529cond-mat.supr-concond-mat.mes-hall
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带隙双层石墨烯-超导体结中的安德烈夫反射和正常反射

Andreev and normal reflections in gapped bilayer graphene-superconductor junctions

Panch Ram, Detlef Beckmann, Romain Danneau, Wolfgang Belzig

AI总结:

本研究通过散射理论和BTK形式主义,分析了带隙双层石墨烯-超导体结中的安德烈夫与正常反射,发现位移场调控反射类型,并首次预测正常逆行反射的可实验验证特征。

摘要:

我们研究了双层石墨烯-超导体结中的安德烈夫反射和正常反射过程——包括逆行反射和镜面反射,其中对顶层和底层施加相等且相反的位移场以诱导带隙。通过采用带隙双层石墨烯-超导体结的狄拉克-博戈留波夫-德热纳方程,我们在散射理论方法中计算了反射概率。在布隆德-廷卡姆-克拉普维克框架下计算的亚隙电导显示了当施加的偏置电压低于(高于)费米能量时安德烈夫逆行反射(镜面反射)的贡献。值得注意的是,在存在位移场的情况下,逆行反射和镜面反射都被修改,并且当位移场相对较小时,逆行到镜面的交叉被放大。通过调整费米能量,它们可以进一步调谐为镜面或逆行安德烈夫反射。此外,我们的研究揭示了当位移场变得与层间耦合强度相当时,双安德烈夫反射和双正常反射同时存在。在双层石墨烯-超导体结中正常逆行反射过程的存在是一个新发现,它显示了电导中一个独特的特征,可以通过实验验证。

英文摘要:

We study the Andreev and normal reflection processes -- retro as well as specular -- in a bilayer graphene-superconductor junction where equal and opposite displacement fields are applied for the top and bottom layers to induce a band gap. By employing the Dirac-Bogoliubov-de Gennes equation for the gapped bilayer graphene-superconductor junction, we calculate the reflections probabilities within the scattering theory approach. The subgap conductance, calculated in the framework of Blonder-Tinkham-Klapwijk formalism, shows the contribution from the Andreev retro-reflection (specular-reflection) when the applied bias voltage is below (above) the Fermi energy. Notably, both retro and specular reflections are modified in the presence of the displacement field, and the retro-to-specular crossover gets amplified when the displacement field is relatively small. They can be further tuned to either specular or retro Andreev reflection by adjusting the Fermi energy. Furthermore, our study reveals the simultaneous existence of double Andreev reflections and double normal reflections when the displacement field becomes comparable to the interlayer coupling strength. The existence of the normal retro-reflection process in a bilayer graphene-superconductor junction is a new finding which shows a distinctive feature in the conductance that can be experimentally verified.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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