Superconducting proximity effect in graphene – Supergraph

In graphene, a single layer of carbon atoms arranged in a two-dimensional honeycomb lattice, charge carriers obey Dirac’s linear energy dispersion. Its electronic properties can therefore be described by relativistic massless fermionic excitations. When connected to a superconductor, unprecedented phenomena are predicted such as a specular Andreev reflection due to the interplay between superconductivity and relativistic quantum dynamics. However, in order to evidence this unique superconducting proximity effect, high quality crystals where charge carriers undergo quasi-ballistic motion are required. This is the reason why the project will explore new fabrication techniques of suspended graphene and transfer processes of graphene grown by CVD on a metal in order to get rid of uncontrolled environment issues brought by the substrate or by lithographic residues.
The project aims at understanding by the experiment the superconducting proximity effect in graphene through transport measurements and by local spectroscopy performed with a scanning tunneling microscope. Two different geometries for the samples will be considered where the superconducting correlations are is either injected by the superconducting contacting electrodes or induce by a networks of superconducting nanoparticles evaporated on top of the graphene surface. The first situation realizes the classical normal-superconductor junction and will allow studying the intrinsic properties of graphene by making the superconductor as little invasive as possible. By taking advantage of the possibility to realize good contacts between graphene and high critical magnetic field superconductors, the observation of superconductivity in the Quantum Hall Effect regime will be within reach. Moreover superconducting proximity effect in clean systems will also be studied thanks to the efforts made towards the fabrication of ballistic samples. Local and global signatures of quantum chaos in Andreev billiards will be looked for. In the second type of devices, the network of superconducting islands induces superconducting correlations in the whole graphene sheet and can be tuned with the help of an electrostatic voltage applied on a back-gate. Such a hybrid system will constitute a playground for fundamental studies of the two dimensional quantum transition and form the basic brick to design new type of devices. Finally, we will apply our know-how in making suspended graphene for studying the electron-phonon coupling and developing efficient Micro-Electro-Mechanical Systems.