We predict superconductivity for the carbon-boron clathrate SrB3C3 at 27-43 K for Coulomb pseudopotential (mu*) values between 0.17 and 0.10 using first-principles calculations with conventional electron-phonon coupling. Electrical transport measurements, facilitated by a novel in situ experimental design compatible with extreme synthesis conditions (>3000 K at 50 GPa), show non-hysteretic resistivity drops that track the calculated magnitude and pressure dependence of superconductivity for mu*=0.15, and transport measurements collected under applied magnetic fields confirm superconductivity with an onset Tc of approximately 20 K at 40 GPa. Carbon-based clathrates thus represent a new class of superconductors similar to other covalent metals like MgB2 and doped fullerenes. Carbon clathrates share structures similar to superconducting superhydrides, but covalent C-B bonds allow metastable persistence at ambient conditions.
@article{arxiv.1708.03483,
title = {Superconductivity in SrB3C3 clathrate},
author = {Li Zhu and Hanyu Liu and Maddury Somayazulu and Yue Meng and Piotr A. Guńka and Thomas B. Shiell and Curtis Kenney-Benson and Stella Chariton and Vitali B. Prakapenka and Hyeok Yoon and Jarryd A. Horn and Johnpierre Paglione and Roald Hoffmann and R. E. Cohen and Timothy A. Strobel},
journal= {arXiv preprint arXiv:1708.03483},
year = {2021}
}