T. Takenouchi

Origin of the metallic properties of heavily boron-doped superconducting diamond

The physical properties of lightly doped semiconductors are well described by electronic band-structure calculations and impurity energy levels. Such properties form the basis of present-day semiconductor technology. If the doping concentration n exceeds a critical value nc, the system passes through an insulator-to-metal transition and exhibits metallic behaviour; this is widely accepted to occur as a consequence of the impurity levels merging to form energy bands. However, the electronic structure of semiconductors doped beyond nc have not been explored in detail. Therefore, the recent observation of superconductivity emerging near the insulator-to-metal transition in heavily boron-doped diamond has stimulated a discussion on the fundamental origin of the metallic states responsible for the superconductivity. Two approaches have been adopted for describing this metallic state: the introduction of charge carriers into either the impurity bands or the intrinsic diamond bands. Here we show experimentally that the doping-dependent occupied electronic structures are consistent with the diamond bands, indicating that holes in the diamond bands play an essential part in determining the metallic nature of the heavily boron-doped diamond superconductor. This supports the diamond band approach and related predictions, including the possibility of achieving dopant-induced superconductivity in silicon and germanium. It should also provide a foundation for the possible development of diamond-based devices.

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

Low-energy electrodynamics of superconducting diamond.

^{11}\mathrm{B}\text{\ensuremath{-}}\mathrm{NMR}

Observation of a superconducting gap in boron-doped diamond by laser-excited photoemission spectroscopy

on heteroepitaxially grown (111) and (100) films.

Holes in the Valence Band of Superconducting Boron-Doped Diamond Film Studied by Soft X-ray Absorption and Emission Spectroscopy

^{11}\mathrm{B}\text{\ensuremath{-}}\mathrm{NMR}

11B-NMR study in boron-doped diamond films

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

Scanning tunneling microscopy and spectroscopy studies of superconducting boron-doped diamond films

\text{boron}+\text{hydrogen}

Acoustic and optical phonons in metallic diamond

(\mathrm{B}+\mathrm{H})

Laser-excited photoemission spectroscopy study of superconducting boron-doped diamond

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