Muon spin rotation study of the magnetic penetration depth in the intercalated graphite superconductor CaC6

TL;DR

This study uses muon spin rotation to investigate the magnetic penetration depth in CaC6, revealing it as a fully gapped BCS superconductor with a consistent superfluid density and penetration depth across various conditions.

Contribution

It provides detailed measurements of the magnetic penetration depth and superfluid density in CaC6, confirming its behavior as a clean limit BCS superconductor.

Findings

Field independent in-plane magnetic penetration depth of 72 nm

Superfluid density matches the clean limit BCS model

CaC6 exhibits a fully gapped superconducting state

Abstract

We report temperature- and magnetic field-dependent bulk muon spin rotation measurements in a c-axis oriented superconductor CaC6 in the mixed state. Using both a simple second moment analysis and the more precise analytical Ginzburg-Landau model, we obtained a field independent in-plane magnetic penetration depth {\lambda}ab (0) = 72(3) nm. The temperature dependencies of the normalized muon spin relaxation rate and of the normalized superfluid density result to be identical, and both are well represented by the clean limit BCS model with 2\Delta/kB Tc = 3.6(1), suggesting that CaC6 is a fully gapped BCS superconductor in the clean limit regime.