Superconductivity in SrB3 C3 clathrate

We predict superconductivity for the carbon-boron clathrate SrB3C3 with Tc=27-43K for Coulomb pseudopotential (μ∗) values between 0.17 and 0.10 using first-principles calculations with conventional electron-phonon coupling. Electrical transport measurements, facilitated by an in situ experimental design compatible with extreme synthesis conditions (>3000K at 50 GPa), show nonhysteretic resistivity drops that track the calculated magnitude and pressure dependence of superconductivity for μ∗≈0.15, and transport measurements collected under applied magnetic fields indicate superconductivity with an onset Tc of approximately 20 K at 40 GPa. Carbon-based clathrates thus represent a class of superconductors similar to other covalent metals like MgB2 and doped fullerenes. Carbon clathrates share structures similar to superconducting superhydrides with wide potential for tunable properties, and covalent C-B bonds allow metastable persistence at ambient conditions.