2D-Superconductivity Beyond the Pauli-Limit in Bulk InNb₂S_7.6

Two-dimensional superconductivity has been well established in bulk crystals but remains rare in natural transition metal dichalcogenide (TMD) crystals. Here, we report a novel van der Waals structure type that can exhibit such 2D superconductivity. The orthorhombic structure is a variation of the 4H TMD structure, with a four-layer unit cell composed of Nb-centered trigonal prism layers alternated with indium-centered octahedra layers. This phase is distinct from the previously reported hexagonal InNbS₂. The indium phase, InNb₂S_7.6, is a superconductor, while the tin and lead phases, SnNb₂S_7.6 and Pb_0.8Nb₂S_7.6, show a metal to insulator transition at low temperatures. Further transport investigation revealed InNb₂S_7.6 to exhibit anisotropic two-dimensional superconductivity beyond the Pauli-limit. These phases may provide a unique platform of comparison for the study of quantum phenomena, like 2D superconductivity.