Phys. Rev. Lett. 95, 237002 (2005) [4 pages]Theoretical Explanation of Superconductivity in C6CaReceived 3 June 2005; published 30 November 2005 Using density functional theory, we demonstrate that superconductivity in C6Ca is phonon mediated with λ=0.83 and phonon frequency ⟨ω⟩log=24.7 meV. The calculated isotope exponents are α(Ca)=0.24 and α(C)=0.26. Superconductivity is due mostly to C vibrations perpendicular and Ca vibrations parallel to the graphite layers. Since the electron-phonon couplings of these modes are activated by the presence of an intercalant Fermi surface, the occurrence of superconductivity in graphite intercalated compounds requires a noncomplete ionization of the intercalant. © 2005 The American Physical Society URL:
http://link.aps.org/doi/10.1103/PhysRevLett.95.237002
DOI:
10.1103/PhysRevLett.95.237002
PACS:
74.70.Ad, 71.15.Mb, 74.25.Kc, 74.25.Jb
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