Superconductivity in SrB₃C₃ clathrate

We predict superconductivity for the carbon--boron clathrate SrB₃C₃ with Tc=27--430.28em0exK 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 (>30000.28em0exK 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.