Enhanced Superconductivity in Th₂Mo₂Ru₂Si₄C with a Collapsed Intergrowth Structure

We report the discovery of bulk superconductivity in a new quinary intermetallic compound Th₂Mo₂Ru₂Si₄C, which crystallizes in a collapsed 22241-type structure. This structure is characterized as an intergrowth of ThMo₂Si₂C and ThRu₂Si₂ units, interconnected by equivalent Si-Si bondings that enhance inter-sublattice coupling. The refined lattice parameters are a = 4.2212(1) Å and c = 20.3899(7) Å. Electrical resistivity and magnetic susceptibility measurements on both polycrystalline and single-crystal samples consistently demonstrate bulk superconductivity with a transition temperature T_c~6.0 K, significantly higher than those of the constituent compound ThMo₂Si₂C and related analogs. The superconducting state exhibits nearly isotropic behavior under magnetic fields, attributable to strong covalent interlayer coupling. First-principles calculations reveal a substantial contribution from Mo-d orbitals near the Fermi level, which exhibits several band crossing points. The enhancement in T_c can be explained by a synergistic combination of a valence electron concentration and an inter-sublattice self-doping effect between the Ru₂Si₂ and Mo₂Si₂C layers.