Tunable Klein-like tunnelling of high-temperature superconductor pairs into graphene

Abstract

Superconductivity can be induced in a normal material via the ‘leakage’ of superconducting pairs of charge carriers from an adjacent superconductor. This so-called proximity e ect is markedly influenced by graphene’s unique electronic structure, both in fundamental and technologically relevant ways. These include an unconventional form1,2 of the ‘leakage’ mechanism— the Andreev reflection3—and the potential of supercurrent modulation through electrical gating4 . Despite the interest of high-temperature superconductors in that context5,6 , realizations have been exclusively based on low-temperature ones. Here we demonstrate a gate-tunable, high-temperature superconducting proximity e ect in graphene. Notably, gating e ects result from the perfect transmission of superconducting pairs across an energy barrier—a form of Klein tunnelling7,8 , up to now observed only for non-superconducting carriers9,10— and quantum interferences controlled by graphene doping. Interestingly, we find that this type of interference becomes dominant without the need of ultraclean graphene, in stark contrast to the case of low-temperature superconductors11. These results pave the way to a new class of tunable, high-temperature Josephson devices based on large-scale graphene.