Exceptional Superconducting Interfaces between Graphene and Atomic Chains in A15-MoRe
Realizing highly transparent and magnetic-field-resilient superconducting contacts is a critical bottleneck for the advancement of two-dimensional (2D) quantum devices. Molybdenum-rhenium (MoRe) alloys have been empirically favored as they uniquely yield ballistic, highly transparent contacts to graphene that survive in high-magnetic-field regimes; however, the microscopic origin of this anomalous transparency has remained a long-standing puzzle. Here, we resolve this paradox by revealing that pristine graphene/MoRe interfaces are governed by the classical A15 superconducting phase. Combining low-temperature transport, X-ray diffraction, and atomic-resolution electron microscopy, we demonstrate that as-deposited MoRe spontaneously forms the A15 phase in direct contact with graphene, whereas thermal annealing triggers a phase transition to a hexagonal close-packed (hcp) structure that severely degrades the Josephson transparency. Crucially, the one-dimensional (1D) transition-metal atomic chains unique to the A15 structure exhibit a near-perfect lattice match (mismatch < 1%) with graphene edges. First-principles calculations further prove that the d-orbitals of these historically renowned 1D chains possibly hybridize with graphene's Dirac cone near the K point. These findings not only uncover the structural and electronic origins of optimal MoRe contacts but also establish A15-phase superconductors as a geometrically ideal, universal platform for realizing robust quantum electronics based on 2D materials.