Far-infrared signature of the superconducting gap in intercalated graphite CaC6

TL;DR

This study uses terahertz reflectance spectra to identify an anisotropic superconducting gap in CaC6, aligning experimental results with theoretical predictions and confirming BCS-like behavior below 11K.

Contribution

First direct observation of the superconducting gap in CaC6 using terahertz spectroscopy, demonstrating anisotropy and matching density functional theory calculations.

Findings

Superconducting gap observed below 11K

Gap shows anisotropic distribution

Temperature dependence consistent with BCS theory

Abstract

Terahertz reflectance spectra of the Ca-intercalated graphite CaC6 reveal a superconducting gap below 11K. The gap signature lacks a sharp onset to full reflectivity at 2Delta, but rather shows a distribution of gap values consistent with an anisotropic gap. The experimental data were successfully fitted to the gap distribution obtained from density functional calculations by Sanna et al. (Phys.Rev. B75, 020511, 2007). The temperature dependence of the superconducting gap is characteristic for a BCS type superconductor.