Dependence of the superconducting transition temperature on the doping   level in single crystalline diamond films
  Homoepitaxial diamond layers doped with boron in the 10^20-10^21 /cm3 range are shown to be type II superconductors with sharp transitions (~0.2K) at temperatures increasing from 0 to 2.1 K with boron contents. The critical concentration for the onset of superconductivity is about 5-7 10^20 /cm3, close to the metal-insulator transition. The H-T phase diagram has been obtained from transport and a.c. susceptibility measurements down to 300mK. These results bring new quantitative constraints on the theoretical models proposed for superconductivity in diamond. 
Etienne Bustarret (LEPES), Jozef Kacmarcik (CLTP IEP, SPSMS DRFMC),   Christophe Marcenat (SPSMS DRFMC), Etienne Gheeraert (...