Institut Néel, CNRS-UJF-INP, BP 166, 38042 Grenoble cedex 9, France.
Nat Mater. 2012 May 20;11(7):590-4. doi: 10.1038/nmat3335.
Graphene is a sturdy and chemically inert material exhibiting an exposed two-dimensional electron gas of high mobility. These combined properties enable the design of graphene composites, based either on covalent or non-covalent coupling of adsorbates, or on stacked and multilayered heterostructures. These systems have shown tunable electronic properties such as bandgap engineering, reversible metal-insulating transition or supramolecular spintronics. Tunable superconductivity is expected as well, but experimental realization is lacking. Here, we show experiments based on metal-graphene hybrid composites, enabling the tunable proximity coupling of an array of superconducting nanoparticles of tin onto a macroscopic graphene sheet. This material allows full electrical control of the superconductivity down to a strongly insulating state at low temperature. The observed gate control of superconductivity results from the combination of a proximity-induced superconductivity generated by the metallic nanoparticle array with the two-dimensional and tunable metallicity of graphene. The resulting hybrid material behaves, as a whole, like a granular superconductor showing universal transition threshold and localization of Cooper pairs in the insulating phase. This experiment sheds light on the emergence of superconductivity in inhomogeneous superconductors, and more generally, it demonstrates the potential of graphene as a versatile building block for the realization of superconducting materials.
石墨烯是一种坚固且化学惰性的材料，具有高迁移率的二维暴露电子气。这些综合特性使基于吸附物的共价或非共价耦合，或基于堆叠和多层异质结构的石墨烯复合材料的设计成为可能。这些系统表现出可调谐的电子特性，如能带工程、可逆的金属-绝缘转变或超分子自旋电子学。可调谐超导性也有望实现，但实验实现仍缺乏。在这里，我们展示了基于金属-石墨烯杂化复合材料的实验，实现了一系列锡超导纳米粒子在宏观石墨烯片上的可调谐近邻耦合。这种材料允许在低温下将超导性完全电控制到强绝缘状态。观察到的超导性的栅极控制源自由金属纳米粒子阵列产生的近邻诱导超导性与石墨烯的二维和可调谐金属性的组合。整体而言，所得的杂化材料表现为像一个颗粒超导体，在绝缘相中显示出普遍的跃迁阈值和库珀对的局域化。该实验揭示了非均匀超导体中超导性的出现，更广泛地说，它展示了石墨烯作为实现超导材料的多功能构建块的潜力。
