Josephson Junctions in Graphene Constrictions in the Quantum Hall Regime*

Several groups have recently reported on samples made of encapsulated graphene with superconducting contacts in the quantum Hall (QH) regime. Here, we study ballistic graphene Josephson devices based on ~100nm constrictions between superconducting molybdenum-rhenium electrodes in the QH regime. A robust supercurrent has been observed up to 2.5 T, well above the onset of the Hall quantization. We demonstrate that the supercurrent is conducted by the states within the short and narrow channel confined on each side by the gapped graphene bulk. This situation is different from our previous observation of supercurrent.