Yoshihisa Harada Group
Group of Solid State Physics (The Institute for Solid State Physics) [Laser and Synchrotron]
From interests in light itself to its interaction with matter
I believe research quality depends on how it can broaden one’s interests.
We recognize a material’s color by detecting a visible light which, in the case of a leaf, we call green, yellow or red. This depends on the absorption or transmission property of the light reflecting complex interaction between the light and the material. When a material is illuminated by a light called "soft X-ray", we see another "color" which provides a lot of information about the origin of the electronic and magnetic property, as well as local bond coordination, local symmetry and so on.
We are currently developing soft X-ray emission spectroscopy, a tool to detect such soft X-ray "color" with an intense and well organized (color, size, polarization, position, time-structure and so on) soft X-ray light source called synchrotron radiation. With only a slight advance in the sample handling, we can extend the target of this noble spectroscopy and obtain new information that cannot be made available by other methods. For example, pure liquid water, which is completely transparent in the visible light region, looks inhomogeneous in terms of the energy distribution of valence electrons responsible for hydrogen bond formation when observed by soft X-rays. Four years ago, we reported the inhomogeneity of liquid water, which became a subject of discussions all over the world and is still much debated in water-related international conferences and on journal papers. Soft X-ray emission spectroscopy is such a powerful technique which provides us a chance to explore new fields.
Associate Professor Yoshihisa Harada
He graduated from the University of Tokyo and got a Ph.D. degree (2000) under the supervision of Professor Shik Shin. He was a fellow of Japan Society for the Promotion of Science (JSPS) and then moved to RIKEN/SPring-8 as a postdoctoral researcher (2000-2007). He was appointed as project lecturer (2007-2009) and project associate professor (2009-2011) at the University of Tokyo. He was promoted to Associate Professor at ISSP, the University of Tokyo in 2011. In the same year, he established his research group.
Introduction of the study
We can explore the origin of the electronic structure of materials responsible for their electronic, magnetic, and optical properties using extremely intense X-rays with a desired energy and high energy resolution that can be obtained using synchrotron radiation. Our home ground is SPring-8, one of the highest brilliant synchrotron facilities in the world; it is where we have developed noble and original spectroscopies for material science in 'soft' X-ray region in-between vacuum ultraviolet rays and X-rays. In particular, we are leading the world in soft X-ray emission spectroscopy, a kind of light scattering, promising for electronic structure analyses of liquids and operand spectroscopy of a variety of catalysts. Our studies include:
*observation of elementary excitations (crystal field excitation, spinon, magnon, charge density wave, orbiton etc.) in strongly correlated materials like Mott insulators and noble high temperature superconductors
*electronic structure analysis of aqueous solutions to study microheterogeneity and interaction at solid-liquid interfaces
*development of in situ soft X-ray spectroscopy for surface reaction of fuel cell catalysts, electrochemical reaction, and photocatalytic reaction
*electronic structure analysis of reaction center in metalloproteins
*basic study on ultrahigh energy resolution optics for soft X-ray emission and time-resolved spectroscopy
Message from a senior
Prof. Harada is considering further beyond the trend of our research fields to perform pioneering works. He frequently exchanges information with researchers and initiates collaboration in a variety of fields upon mutual cooperation. Recently, the rapid increase in the energy resolution of soft X-ray emission spectroscopy has boosted the use of this method, paving the way to more and more impact studies to be explored. In SPring-8, several laboratories share a workplace with a pleasant and relaxed but stimulating atmosphere. We can work together on a study that nobody has explored before; let’s start here.