Superconducting Proximity Effect in Multilayer Graphene

Abstract

Since the experimental discovery of graphene (single layer of graphite) in 2004, the research of single and multi-layer graphene has attracted much attention both theoretically and experimentally. In this article, from the experimental point of view, we describe the simple and special preparation of single and multi-layer graphene devices and report our recent stydy on superconducting proximity effect in multilayer graphene. As the gate voltage is swept, the proximity-induced superconductivity in multilayer graphene shows the bipolar behavior, from the hole supercurrent to the electron supercurrent. The following unusual facts are found: (1) for an arbitrary normal state resistance, the electron critical supercurrent is larger than the hole critical supercurrent, indicating the breakdown of the electron-hole symmetry. (2) The temperature dependence of the critical supercurrent cannot be explained by the standard theory for the superconducting proximity effect.