Direct Observation of Superconductivity in Calcium-Intercalated Bilayer Graphene by in situ Electrical Transport Measurements

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We report the superconductivity in Ca-intercalated bilayer graphene C₆CaC₆, the thinnest limit of Ca graphite intercalation compound. We performed in situ electrical transport measurements on pristine bilayer graphene, C₆LiC₆ and C₆CaC₆ fabricated on SiC substrate under zero and non-zero magnetic field. While both bilayer graphene and C₆LiC₆ show non-superconducting behavior, C₆CaC₆ exhibits the superconductivity with transition temperature (T c) of 4.0 K. The observed T c in C₆CaC₆ and the absence of superconductivity in C₆LiC₆ show a good agreement with the theoretical prediction, suggesting the importance of a free-electron-like metallic band at the Fermi level to drive the superconductivity.