Scanning Tunneling Spectroscopy on the Novel Superconductor CaC6
Résumé
We present scanning tunneling microscopy and spectroscopy of the newly discovered superconductor CaC6. The tunneling conductance spectra, measured between 3 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±0.2 meV. The possibility of gap anisotropy and twogap superconductivity is also discussed. In a magnetic field, direct imaging of the vortices allows us to deduce a coherence length in the ab plane Eab~=33 nm.