Enhanced Superconductivity in Th₂Mo₂Ru₂Si₄C with a Collapsed Intergrowth Structure

We report the discovery of bulk superconductivity in a new quinary intermetallic compound Th₂Mo₂Ru₂Si₄C, crystallized in a collapsed 22241-type structure. This structure is characterized by the intergrowth of ThMo₂Si₂C and ThRu₂Si₂ units interconnected by equivalent Si-Si bonds 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 of 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 its related analogs. Under magnetic fields, the superconducting state exhibits a nearly isotropic behavior, which is attributed to strong covalent interlayer coupling. First-principles calculations reveal a substantial contribution from the Mo-d orbitals near the Fermi level, which exhibit several band-crossing points. The enhancement in T_C can be attributed to the synergistic combination of the valence electron concentration and the inter-sublattice self-doping effect between the Ru₂Si₂ and Mo₂Si₂C layers.