Microscopic evidence for evolution of superconductivity by effective carrier doping in boron-doped diamond: B11 -NMR study

We have investigated the superconductivity discovered in boron-doped diamonds by means of $^{11}\mathrm{B}\text{\ensuremath{-}}\mathrm{NMR}$ on heteroepitaxially grown (111) and (100) films. $^{11}\mathrm{B}\text{\ensuremath{-}}\mathrm{NMR}$ spectra for all of the films are identified to arise from the substitutional B(1) site as single occupation and lower symmetric B(2) site substituted as $\text{boron}+\text{hydrogen}$ $(\mathrm{B}+\mathrm{H})$ complex, respectively. Clear evidence is presented that the effective carriers introduced by B(1) substitution are responsible for the superconductivity, whereas the charge neutral B(2) sites does not offer the carriers effectively. The result is also corroborated by the density of states deduced by $1∕{T}_{1}T$ measurement, indicating that the evolution of superconductivity is driven by the effective carrier introduced by substitution at B(1) site.