Dependence of the superconducting transition temperature on the doping level in single-crystalline diamond films

The impact of superconducting transition temperature on the doping level in single-crystalline diamond films was investigated. It was observed that the critical concentration for the onset of superconductivity in those 001-oriented single-crystalline films is about 5-7 10²⁰ cm^-3. The transition width remains relatively small up to ∼1 T and rapidly increases for larger fields. The H-T phase diagrams were obtained from transport and ac-susceptibility measurements down to 300 mK.