Superconductivity in graphite intercalation compounds

TL;DR

This paper reviews the history, structure, and experimental findings of superconductivity in graphite intercalation compounds, highlighting recent discoveries and ongoing questions about their superconducting mechanisms.

Contribution

It provides a comprehensive overview of experimental and theoretical insights into superconductivity in graphite intercalation compounds, emphasizing recent developments and unresolved issues.

Findings

Superconductivity in CaC6 and YbC6 supports a BCS-like mechanism.

Experimental evidence on energy gaps and lattice dynamics is summarized.

Open questions remain about electronic states and phonon roles in superconductivity.

Abstract

The field of superconductivity in the class of materials known as graphite intercalation compounds has a history dating back to the 1960s. This paper recontextualizes the field in light of the discovery of superconductivity in CaC6 and YbC6 in 2005. In what follows, we outline the crystal structure and electronic structure of these and related compounds. We go on to experiments addressing the superconducting energy gap, lattice dynamics, pressure dependence, and how this relates to theoretical studies. The bulk of the evidence strongly supports a BCS superconducting state. However, important questions remain regarding which electronic states and phonon modes are most important for superconductivity and whether current theoretical techniques can fully describe the dependence of the superconducting transition temperature on pressure and chemical composition.