Superconductivity in doped clathrates, diamond and silicon

We review in the present article recent work pertaining to the superconducting transition in boron-doped silicon and diamond in their well-known ambient pressure and temperature cubic diamond structure. Thanks to recent developments in chemical vapor deposition techniques, high-temperature-high-pressure experiments, or laser assisted non-equilibrium doping approaches, it is indeed now possible to dope these standard semiconductors and insulators up to the few percent range, that is way beyond the impurity solubility limit and the insulator-metal transition doping threshold. We discuss in particular the microscopic origin of the superconducting transition, emphasizing the role of first-principles calculations in directing the interpretation to a phonon-mediated scenario for these degenerate compounds with no impurity band. A large variety of ab initio calculations predict superconducting transition temperatures larger than that of MgB2 if diamond doping can be increased up to about 30%. The case of intercalated semiconducting clathrates is discussed, not only as a precursor to the superconductivity in silicon, but also as a prototype system offering directions to significantly increase T-C is doped diamond and silicon. (c) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.