Superconductivity in Carbon-Boron Clathrates

We report experimental and computational results for superconductivity in carbon–boron clathrate structures. For the case of SrB₃C₃ in the bipartite sodalite structure, in situ electrical transport measurements, facilitated by a novel experimental design compatible with extreme synthesis conditions (i.e., >3000 K at 50 GPa), show non-hysteretic resistivity drops that track the calculated magnitude and pressure dependence of T_c calculated using the Allen-Dynes modified McMillan equation with Coulomb pseudopotential values (μ^*) near 0.15. The superconducting nature of the transition (T_c ≈ 20 K) was confirmed via electrical transport measurements collected under applied magnetic fields up to 18 T. Carbon-boron clathrates thus represent a new class of superconductors that are similar to covalent metals like MgB₂ and doped fullerenes. Carbon clathrates share structures similar with superconducting superhydrides, but covalent C–B bonds allow metastable persistence at ambient conditions. Different guest atom substitution schemes in various carbon clathrate structure types may enable conventional superconductivity with T_c approaching 100 K.