Scanning Tunneling Spectroscopy on the novel superconductor CaC6
  We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC$_6$. The tunneling conductance spectra, measured between 3 K and 15 K, show a clear superconducting gap in the quasiparticle density of states. The gap function extracted from the spectra is in good agreement with the conventional BCS theory with $\Delta(0)$ = 1.6 $\pm$ 0.2 meV. The possibility of gap anisotropy and two-gap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows to deduce a coherence length in the ab plane $\xi_{ab}\simeq$ 33 nm. 
N. Bergeal, V. Dubost, Y. Noat, W. Sacks, D. Roditchev, N. Emery, C.   Herold, J-F. Mareche, P. Lagrange, G. Loupias