Muon spin rotation study of the magnetic penetration depth in the   intercalated graphite superconductor CaC6
  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. 
D. Di Castro, A. Kanigel, A. Maisuradze, A. Keren, P. Postorino, D.   Rosenmann, U. Welp, G. Karapetrov, H. Claus, D.G. Hink...