Useful properties of solids (functionalities) are often related to their electronic strucutures or their spin states. On the other hand, surface or interface of solids, as well as thin films, often show interesting properties that can never appear in bulk. It becomes more and more important to understand the microscopic origin of such properties to develop new functionalities. Our main purpose of research is to look for new functionalities in solids, surface, interface, or thin films, and to understand the origin of functionalities from the observation of electronic stuructures or spin states.
To grow and develop new functional materials, we employ Chemical Vapor Deposition (CVD) or Pulsed Laser Deposition (PLD) techniques. To study their electronic structures, we mainly use photoemission spectroscopy with lights of wide energy range, from few electron volts to several thousands electron volts. Photoemission spectroscopy utilizes 'photoelectric effect'; measuring energy and momentum of electrons photoemitted from solids, we can determine their electronic structure directly. Our experiments take place at various synchrotron facilities, such as SPring-8, Photon Factory, or HiSOR. We also perform experiments employing laser photoemission spectroscopy at the Institute of Solid State Physics, The University of Tokyo. When necessary, other experimental techniques (suc as XAS, MCD, PEEM, XES, AES, LEED, or STM/STS) will be used.
Our tagets of research are new functional materials (novel superconductor, magnetic materials, semiconduxtors) and known materials whose origin of functionality is still unknown. For example, the figure below shows the experimental band structure of superconducting diamond, probed by angle-resolved photoemission spectrometer at SPring-8. In the figure, bright part indicates the experimentaly-obtained band dispersions, and white lines are the result of theoretical calculations. We show for the first time that doping of boron causes the Fermi level crossing of valence-band top, and the resultant hole is responsible for the metalic property of superconducting diamond.
The following projects are also in progress.
- Electronic structure of heavily-doped dimamond
- Superconductivity in doped semiconductors
- Electronic Structure of novel superconductors or novel magnetic materials
- Spectrocopy other than phoemission
- Synthesis and evaluation of thin films that shows metal-insulator transition
- Study of hollandite-type mangenese oxides
- Development of hot filament CVD appratus
- Synthesis of high-quality magnetic thin film
- Study of hollandite-type titanium oxides