Wang Da, Telford Evan J, Benyamini Avishai, Jesudasan John, Raychaudhuri Pratap, Watanabe Kenji, Taniguchi Takashi, Hone James, Dean Cory R, Pasupathy Abhay N
Department of Physics, Columbia University, New York, New York 10027, United States.
Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States.
Nano Lett. 2021 Oct 13;21(19):8229-8235. doi: 10.1021/acs.nanolett.1c02020. Epub 2021 Sep 27.
Hybrid superconductor/graphene (SC/g) junctions are excellent candidates for investigating correlations between Cooper pairs and quantum Hall (QH) edge modes. Experimental studies are challenging as Andreev reflections are extremely sensitive to junction disorder, and high magnetic fields are required to form QH edge states. We fabricated low-resistance SC/g interfaces, composed of graphene edge contacted with NbN with a barrier strength of ≈ 0.4, that remain superconducting under magnetic fields larger than 18 T. We establish the role of graphene's Dirac band structure on zero-field Andreev reflections and demonstrate dynamic tunability of the Andreev reflection spectrum by moving the boundary between specular and retro Andreev reflections with parallel magnetic fields. Through the application of perpendicular magnetic fields, we observe an oscillatory suppression of the 2-probe conductance in the ν = 4 Landau level attributed to the reduced efficiency of Andreev processes at the NbN/g interface, consistent with theoretical predictions.
混合超导体/石墨烯（SC/g）结是研究库珀对与量子霍尔（QH）边缘模式之间相关性的理想候选者。由于安德列夫反射对结无序极其敏感，且需要高磁场来形成QH边缘态，因此实验研究具有挑战性。我们制备了低电阻SC/g界面，该界面由石墨烯边缘与NbN接触组成，势垒强度约为0.4，在大于18 T的磁场下仍保持超导。我们确定了石墨烯狄拉克能带结构在零场安德列夫反射中的作用，并通过用平行磁场移动镜面和逆安德列夫反射之间的边界，证明了安德列夫反射光谱的动态可调性。通过施加垂直磁场，我们观察到在ν = 4朗道能级中2探针电导的振荡抑制，这归因于NbN/g界面处安德列夫过程效率的降低，与理论预测一致。
