We show how coherent synchrotron radiation (CSR) allows one to measure the slight increase in the reflectivity of a BCS superconductor as it is cooled below T-c. In fact, by CSR coupled to a conventional interferometric apparatus, one can obtain a signal-to-noise ratio similar to 10(3) in the sub-THz range. We apply this technique to the measurement of the optical gap in boron-doped diamond and in CaAlSi, a superconductor isostructural to MgB2. In the latter compound we are also able to determine a slight anisotropy between the gap in the hexagonal planes and that along the orthogonal c axis. (c) 2007 Elsevier B.V. All rights reserved.
Study of the optical gap in novel superconductors by coherent THz radiation / Calvani, Paolo; Lupi, Stefano; Ortolani, Michele; Baldassarre, Leonetta; Mirri, Chiara; Sopracase, Rodolphe; U., Schade; Y., Takano; T., Tamegai. - In: INFRARED PHYSICS & TECHNOLOGY. - ISSN 1350-4495. - STAMPA. - 51:5(2008), pp. 429-432. (Intervento presentato al convegno 4th International Workshop on Infrared Microscopy and Spectroscopy with Accelerator Based Sources tenutosi a Awaji Isl, JAPAN nel SEP 25-29, 2007) [10.1016/j.infrared.2007.12.022].