Superconductivity in Heavy Alkaline-Earths Intercalated Graphites

TL;DR

This paper reports the discovery of superconductivity in Sr-intercalated graphite SrC6 below 1.65 K, highlighting its anisotropic properties and comparing it to CaC6, with no superconductivity observed in BaC6.

Contribution

The study provides the first observation of superconductivity in SrC6 and analyzes its anisotropic superconducting gap and pressure effects compared to CaC6.

Findings

Superconductivity in SrC6 below 1.65 K

Reduced anisotropy of upper critical fields in SrC6

No superconductivity observed in BaC6 down to 0.3 K

Abstract

We report the discovery of superconductivity below 1.65(6) K in Sr-intercalated graphite SrC6, by susceptibility and specific heat (Cp) measurements. In comparison with CaC6, we found that the anisotropy of the upper critical fields for SrC6 is much reduced. The Cp anomaly at Tc is smaller than the BCS prediction indicating an anisotropic superconducting gap for SrC6 similar to CaC6. The significantly lower Tc of SrC6 as compared to CaC6 can be understood in terms of "negative" pressure effects, which decreases the electron-phonon coupling for both in-plane intercalant and the out-of-plane C phonon modes. We observed no superconductivity for BaC6 down to 0.3 K.