¹¹B-NMR study in boron-doped diamond films

We have investigated an origin of the superconductivity discovered in boron (B)-doped diamonds by means of ¹¹B-NMR on heteroepitaxially grown (1 1 1) and (1 0 0) films and polycrystalline film. The characteristic difference of B-NMR spectral shape for the (1 1 1) and (1 0 0) thin films is demonstrated as arising from the difference in the concentration (n_{B (1)}) of boron substituted for carbon. It is revealed from a scaling between a superconducting transition temperature T_c and n_{B (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 ∼ 1860 K characteristic for the diamond structure.