Professor Hiroshi Kawarada of the Waseda University School of Science and Engineering and Mr. Tomohiro Takenouchi of the School of Science and Engineering, together with Professor Takayoshi Yokoya of Okayama University Graduate School of Natural Science and Technology, researchers Tetsuya Nakamura、Tomohiro Matsushita and Takayuki Muro of the Japan Synchrotron Radiation Research Institute (JASRI), Research Fellow Masanori Nagao, and Senior Scientist Yoshihiko Takano of the National Institute for Materials Science (NIMS) and Professor Tamio Oguchi of Hiroshima University have made a world breakthrough, being the first to succeed in elucidating the electronic structure3 of electric conductive heavy boron-doped2 diamond which shows superconductivity1 at cryogenic temperatures.
Semiconductor materials, when doped with a minute amount of an impure substance, display electric conductivity. In this case, the new energy level (impurity level4) created by the impurities is thought to play an important role in the electric conductivity of the material. However, when higher concentrations of impure substances were doped, it was not clear in what ways the electron structure of the material contributed to its conductivity.
On this occasion a diamond thin film sample was used and heavily doped with boron as the impurity, and experimentation was undertaken using Soft X-ray Spectroscopy of Solid’s (BL25SU) high resolution soft x-ray, angle resolved photoemission equipment5 at the large scale Spring-8 radiation facility. As a result, it was found that for the high concentration impurity dope sample, the electron holes7 generated in the diamond band6 play an important role in electrical conductivity.
This resolution of the electron structure of heavily boron doped diamond will both assist in the understanding of the superconductive features of heavily boron-doped diamond as well as greatly contributing to the development of environmentally-friendly, energy-saving diamond devices using superconductors.
This research was undertaken with the support of Grant-in-Aid for Scientific Research.
These results appeared in the December 1 issue of England’s Scientific Journal ‘Nature’ (article entitled “Origin of the metallic properties of heavily boron-doped superconducting diamond”). In addition, a lecture is planned for the International Workshop on Superconductivity in Diamond and Related Materials to be held in Tsukuba City December 7th -9th.
