Tunnelling spectroscopy of Andreev states in graphene
Tunnelling spectroscopy of Andreev states in graphene
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DOI：
10.1038/nphys4110
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发表时间：
2017-08-01
期刊：
影响因子：
19.6
通讯作者：
Jarillo-Herrero, Pablo
中科院分区：
文献类型：
--
作者：
Bretheau, Landry;Wang, Joel I-Jan;Jarillo-Herrero, Pablo
一个正常的导体放置在与超导体良好接触可以继承其显着的电子特性（1，2）。这种邻近效应在微观上起源于导体中纠缠电子-空穴态的形成，称为Andreev态（3-8）。Andreev态的光谱研究只在少数系统中进行过（9-13）。石墨烯（14，15）独特的几何形状、电子结构和高迁移率使其成为研究二维Andreev物理的新型平台。在这里，我们使用一个完整的货车德瓦尔斯异质结构进行隧道光谱测量的邻近效应在超导体-石墨烯-超导体结。测量的能谱，这取决于超导体之间的相位差，揭示了Andreev束缚态的连续存在。此外，我们的器件异质结构几何形状和材料使我们能够测量作为石墨烯费米能的函数的Andreev谱，显示出不同介观制度之间的过渡。此外，通过实验引入一个新的概念，超电流谱密度，我们确定的超导相位关系的隧道实验，从而建立在有限能量的Andreev物理和约瑟夫森效应之间的联系。这项工作为探索混合超导狄拉克材料中物质的奇异拓扑相开辟了新的途径（16-18）。
A normal conductor placed in good contact with a superconductor can inherit its remarkable electronic properties(1,2). This proximity effect microscopically originates from the formation in the conductor of entangled electron-hole states, called Andreev states(3-8). Spectroscopic studies of Andreev states have been performed in just a handful of systems(9-13). The unique geometry, electronic structure and high mobility of graphene(14,15) make it a novel platform for studying Andreev physics in two dimensions. Here we use a full van der Waals heterostructure to perform tunnelling spectroscopy measurements of the proximity effect in superconductor-graphene-superconductor junctions. The measured energy spectra, which depend on the phase difference between the superconductors, reveal the presence of a continuum of Andreev bound states. Moreover, our device heterostructure geometry and materials enable us to measure the Andreev spectrum as a function of the graphene Fermi energy, showing a transition between different mesoscopic regimes. Furthermore, by experimentally introducing a novel concept, the supercurrent spectral density, we determine the supercurrent-phase relation in a tunnelling experiment, thus establishing the connection between Andreev physics at finite energy and the Josephson effect. This work opens up new avenues for probing exotic topological phases of matter in hybrid superconducting Dirac materials(16-18).