Electrical Control of the Superconducting-to-Insulating Transition in   Graphene/Metal Hybrids
  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 either based on covalent or non- covalent coupling of adsorbates, or on multilayered structures. These systems have exhibited novel 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 me tal/graphene hybrid composites, enabling the control of proximity coupling of an array of superconducting nanoparticles onto a macroscopic graphene sheet. This material allows at low temperature to tune the superconductivity down to a strongly insulating state. It results from the combination of a proximity-induced superconductivity generated by the metallic nanoparticles array with the two-dimensional and tunable metallicity of graphene. The resulting hybrid material behaves, as a whole, like a granular 2D 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 superconduc- tors, and more generally it demonstrates the potential of graphene as a versatile building-block for the realization of novel superconducting materials. 
Adrien Allain, Zheng Han and Vincent Bouchiat
cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.supr-con