Intercalant-Driven Superconductivity in YbC$_{6}$ and CaC$_{6}$

TL;DR

This paper investigates the superconductivity in YbC$_{6}$ and CaC$_{6}$, suggesting intercalant phonons play a key role and explaining the difference in critical temperatures through isotope effects based on atomic masses.

Contribution

It provides first-principles calculations indicating intercalant phonons are crucial for superconductivity in these compounds, contrasting with alkaline-intercalated variants, and explains T_c differences via isotope effects.

Findings

Intercalant phonons are likely responsible for superconductivity in YbC$_6$ and CaC$_6$.

The difference in T_c is attributed to isotope effects related to atomic mass differences.

Superconductivity mechanism differs from previously known intercalated graphites.

Abstract

Recently deiscovered superconductivity in YbC$_6$ and CaC$_6$ at temperatures substantially higher than previously known for intercalated graphites, raised several new questions: (1) Is the mechanism considerably different from the previously known intercalated graphites? (2) If superconductivity is conventional, what are the relevant phonons? (3) Given extreme similarity between YbC$_6$ and CaCa$_6$, why their critical temperatures are so different? We address these questions on the basis of first-principles calculations and conclude that coupling with intercalant phonons is likely to be the main force for superconductivity in YbC$_6$ and CaC$_6$, but not in alkaline-intercalated compounds, and explain the difference in $T_c$ by the ``isotope effect'' due to the difference in Yb and Ca atomic masses.