Low-energy electrodynamics of superconducting diamond

Heavily boron-doped, diamond films can become superconducting with critical temperatures Tc well above 4 K. Here we first measure the reflectivity of such a film down to 5cm-1, by also using coherent synchrotron radiation. We thus determine the optical gap 2?, the field penetration depth ?, the range of action of the Ferrell-Glover-Tinkham sum rule, and the electron-phonon spectral function ?2F(?). We conclude that diamond behaves as a dirty BCS superconductor. © 2006 The American Physical Society.