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 ${\mathrm{LnNi}}_2{\mathrm{B}}_2\mathrm{C}$ ($T_c$ =17 K), $\mathrm{Mg}{\mathrm{B}}_2$ ($T_c$ =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 ${\mathrm{Sc}}_{20}\mathrm{B}{\mathrm{C}}_{27}$ with a tetragonal lattice which structure changes based on the compound of ${\mathrm{Sc}}_3{\mathrm{C}}_4$ with very little B doping. Magnetization and specific heat measurements show bulk superconductivity. An upper critical field of Hc2(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 ${\mathrm{Sc}}_3{\mathrm{C}}_4$ there are more orbital overlap and hybridization between Sc 3d electrons and 2p electrons of C-C(B)-C fragment in ${\mathrm{Sc}}_{20}\mathrm{B}{\mathrm{C}}_{27}$, 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 ${\mathrm{Sc}}_{20}\mathrm{B}{\mathrm{C}}_{27}$.

13 pages, 6 figures