Superconductivity in C6Ca

TL;DR

This paper uses density functional theory to show that superconductivity in C6Ca is phonon-mediated, driven by specific vibrational modes, and depends on the intercalant's electronic state, providing insights into graphite intercalated compounds.

Contribution

It demonstrates the phonon-mediated mechanism of superconductivity in C6Ca and highlights the role of intercalant Fermi surface in activating electron-phonon coupling.

Findings

Electron-phonon coupling constant of 0.83

Phonon-frequency logarithmic-average of 24.7 meV

Isotope exponents of 0.24 (Ca) and 0.26 (C)

Abstract

Using density functional theory we demonstrate that superconductivity in C6Ca is due to a phonon-mediated mechanism with electron-phonon coupling 0.83 and phonon-frequency logarithmic-average 24.7 meV. The calculated isotope exponents are 0.24 for Ca and 0.26 for C. Superconductivity is mostly due 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 non complete ionization of the intercalant.