Superconductivity in scandium borocarbide with orbital hybridization

Abstract Exploration of superconductivity in light element compounds has drawn considerable attention because those materials can easily realize the high T _C superconductivity, such as LnNi ₂ B ₂ C ( T _C = 17 K), MgB ₂ ( T _C = 39 K), and very recently super-hydrides under pressure ( T _C = 250 K). Here we report the discovery of bulk superconductivity at 7.8 K in scandium borocarbide Sc ₂₀ BC ₂₇ with a tetragonal lattice which structure changes based on the compound of Sc ₃ C ₄ with very little B doping. Magnetization and specific heat measurements show bulk superconductivity. An upper critical field of H _c2 (0) ∼ 8 T is determined. Low temperature specific-heat shows that this system is a BCS fully gapped s-wave superconductor. Electronic structure calculations demonstrate that compared with Sc ₃ C ₄ there are more orbital overlap and hybridization between Sc 3 d electrons and 2 p electrons of C-C(B)-C fragment in Sc ₂₀ BC ₂₇ , which form a new electric conduction path of Sc-C(B)-Sc. Those changes influence the band structure at the Fermi level and may be the reason of superconductivity in Sc ₂₀ BC ₂₇ .