Superconductivity in the Intercalated Graphite Compounds C6Yb and C6Ca

TL;DR

This paper reports the discovery of superconductivity in C6Yb and C6Ca, two graphite intercalation compounds with higher transition temperatures and more isotropic properties than previously known, expanding understanding of superconductivity in layered materials.

Contribution

It is the first demonstration of superconductivity in C6Yb and C6Ca, revealing higher transition temperatures and increased isotropy compared to other graphite intercalates.

Findings

Superconductivity observed at 6.5K in C6Yb and 11.5K in C6Ca.

These compounds are more isotropic than pure graphite.

Transition temperatures are significantly higher than other similar compounds.

Abstract

In this letter we report the discovery of superconductivity in the isostructural graphite intercalation compounds C6Yb and C6Ca, with transition temperatures of 6.5K and 11.5K respectively. A structural characterisation of these compounds shows them to be hexagonal layered systems in the same class as other graphite intercalates. If we assume that all the outer s-electrons are transferred from the intercalant to the graphite sheets, then the charge transfer in these compounds is comparable to other superconducting graphite intercalants such as C8K 1,2 . However, the superconducting transition temperatures of C6Yb and C6Ca are up to two orders of magnitude greater. Interestingly, superconducting upper critical field studies and resistivity measurements suggest that these compounds are significantly more isotropic than pure graphite. This is unexpected as the effect of introducing the intercalant is to move the graphite layer further apart.