Probing Superconductivity in Magic Angle Twisted Trilayer Graphene with Josephson Junctions Part 1

The superconductivity in magic angle twisted bilayer graphene (TBG) has been both fascinating and puzzling since its discovery. Despite intense study, its exact nature and relationship to the correlated phases remain unclear. Recently, alternating angle twisted trilayer graphene (TTG) emerged as a new system for studying moire superconductivity. TTG is more tunable as the band structure is modified by the displacement field. Multiple phenomena also point to the possibility of unconventional superconductivity in TTG, including: the superconducting phase being tightly tied with interaction driven symmetry breaking phases; Pauli limit violation; and possible evidence for nodes in the superconducting gap from STM measurements. We report our efforts to probe the nature of the superconducting state by interfacing the TTG superconductors with a conventional s-wave superconductor, niobium nitride (NbN). We have fabricated highly transparent contacts between these two materials as evidenced by conduction enhancement of the junction due to Andreev reflection when TTG is tuned to the normal state and supercurrent when TTG is superconducting. Here we will discuss the fabrication and basic properties of these new tunable junctions between 2D and 3D superconducting states.