B11-NMR study in boron-doped diamond films

We have investigated an origin of the superconductivity discovered in boron (B)-doped diamonds by means of B11-NMR on heteroepitaxially grown (111) and (100) films and polycrystalline film. The characteristic difference of B-NMR spectral shape for the (111) and (100) thin films is demonstrated as arising from the difference in the concentration (nB(1)) of boron substituted for carbon. It is revealed from a scaling between a superconducting transition temperature Tc and nB(1) that the holes doped into diamond via the substitution of boron for carbon are responsible for the onset of superconductivity. The result suggests that the superconductivity in boron-doped diamond is mediated by the electron-phonon interaction brought about a high Debye temperature ∼1860K characteristic for the diamond structure.