Superconductivity in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>SrB</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">C</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:mrow></mml:math> clathrate
Li Zhu, Hanyu Liu, Maddury Somayazulu, Yue Meng, Piotr A. Guńka, Thomas B. Shiell, Curtis Kenney‐Benson, Stella Chariton, Vitali B. Prakapenka, Hyeok Yoon, Jarryd A. Horn, Johnpierre Paglione, Roald Hoffmann, R. E. Cohen, Timothy A. Strobel
Abstract
We predict superconductivity for the carbon--boron clathrate ${\mathrm{SrB}}_{3}{\mathrm{C}}_{3}$ with ${T}_{c}=27\text{--}43\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ for Coulomb pseudopotential (${\text{\ensuremath{\mu}}}^{*}$) 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 ($>3000\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ at 50 GPa), show nonhysteretic resistivity drops that track the calculated magnitude and pressure dependence of superconductivity for ${\text{\ensuremath{\mu}}}^{*}\ensuremath{\approx}0.15$, and transport measurements collected under applied magnetic fields indicate superconductivity with an onset ${T}_{c}$ of approximately 20 K at 40 GPa. Carbon-based clathrates thus represent a class of superconductors similar to other covalent metals like ${\mathrm{MgB}}_{2}$ 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.