Terahertz Spectroscopy of Superconductors

We show how synchrotron radiation (SR) in the terahertz (THz) region provides the possibility to measure the properties of conventional and exotic superconductors in their superconducting state. Indeed, through the coupling of SR and a conventional Michelson interferometer, one can obtain in the THz range a signal-to-noise ratio up to 103. We review the application of this technique to superconductors with a different degree of complexity: the single-gap boron-doped diamond BCS isotropic material; CaAlSi, a superconductor isostructural to MgB2 with a slight anisotropy between the gap in the hexagonal planes and that along the orthogonal c axis; and isotropic V3Si, where superconductivity opens two gaps at the Fermi energy.