| Career Summary |
1993-98: Research Associate, Graduate School of Science, The University of Tokyo
1996: Doctor of Science from The University of Tokyo
1998-99: Postdoctoral Fellow, Materials Research Center, University of Gronigen
1999- : Associate Professor, Graduate School of Frontier Sciences, The University of Tokyo
2001-05: Researcher, light and control, PRESTO-JST
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| Educational Activities |
Graduate school: Strongly Correlated Electron Systems, Complex Condensed Matter Physics
Undergraduate school: Modern Experimental Physics 1
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| Research Activities |
Photoelectrons are emitted from solid surfaces onto which ultraviolet or x-rays are directed. By measuring the energy and momentum of photoelectrons, we can study occupied states of the solid (photoemission spectroscopy). Or, we can study unoccupied states of the solid by detecting light emitted from surfaces of the solid onto which electrons are directed (inverse-photoemission spectroscopy).
We have been developing a high-energy-resolution inverse-photoemission system based on dispersion matching of light and electron. Using photoemission and inverse-photoemission experiments, we have been studying the electronic structure of bulk and surface of various solids.
In particular, we are interested in transition-metal compounds that show rich physical properties such as ferromagnetism, superconductivity, valence transition, and metal-insulator transition. In transition-metal compounds, d-electrons with spin, charge and orbital degrees of freedom are affected by complicated lattice distortions, and show interesting electric and magnetic properties. We have been studying the relationship between the physical properties and electronic structure of transition-metal compounds using experimental methods such as photoemission and inverse-photoemission spectroscopy and theoretical methods such as unrestricted Hartree-Fock calculation.
Dispersion matching for inverse-photoemission spectroscopy
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Literature
1) D. Asakura, J.W.Quilty, K. Takubo, S. Hirata, T. Mizokawa, Y. Muraoka, Z. Hiroi: Photoemission study of YBa2Cu3Oy thin films under light illumination, Physical Review Letters 93, 247006 (2004).
2) K.Takubo, S.Hirata, J.-Y.Son, J.W.Quilty, T.Mizokawa, N.Matsumoto, S.Nagata: X-Ray Photoemission Study of CuIr2S4: Ir3+-Ir4+ Charge Ordering and the Effect of Light Illumination, Physical Review Letters 95, 246401 (2005).
3) D. I. Khomskii and T. Mizokawa: Orbitally-driven Peielrs state in spinels, Physical Review Letters 94, 156402 (2005).
4) J.W. Quilty, A. Shibata, J.-Y. Son, K. Takubo, T. Mizokawa, H. Toyosaki, T. Fukumura, M. Kawasaki:Signature of Carrier-Induced Ferromagnetism in Ti1-xCoxO2-d: Exchange Interaction between High-Spin Co2+ and the Ti 3d Conduction Band, Physical Review Letters 96, 027202 (2006).
5) K. Takubo, T. Mizokawa, J.-Y. Son, Y. Nambu, S. Nakatsuji, Y. Maeno: Unusual superexchange pathways in an NiS2 triangular lattice with negative charge-transfer energy, Physical Review Letters 99, 037203 (2007).
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| Other Activities |
The Physical Society of Japan (JPS)
The Japanese Society for Synchrotron Radiation Research (JSSRR)
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| Future Plan |
Regarding new aspects of transition-metal compounds, an interesting question is what kind of new electronic states are realized when d-electrons are confined at solid surface/interface. Another interesting question is how confined d-electrons behave when perturbed by photons. We are trying to answer these questions by studying thin films and nano particles of various transition-metal compounds under laser illumination. Hopefully, the research projects along this line would contribute to the development of new optical and energy devices.
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| Messages to Students |
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As a physicist and as a member of Department of Complexity Science and Engineering, I have enjoyed working with researchers in diverse fields such as computer science, earth science, and life science. I expect that, based on these interactions, we can develop novel and significant research findings.
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