QUANTUM CONDENSED MATTER SCIENCE
HIROSHI OKAMOTO LAB.
INTRODUCTION OF LABORATORY
A photoinduced phase transition is a phenomenon, in which an electronic and crystal structures are changed by a photoirradiation.
In our laboratory, we are exploring various photoinduced phase transitions and clarifying their mechanisms by using ultra-short laser pulses with a temporal width of 100～7 fs (fs＝10-15 s). For example, a Mott insulator of copper oxide can be converted to a metal by a laser pulse irradiation via the melting of the electron order formed by electron-electron Coulomb repulsions (Fig. 1).
We are also aiming to control electronic structures of solids by using a light (electromagnetic Field) pulse in the infrared region. Figure 2 shows a conceptual diagram of a metallization when a Mott insulator is irradiated with a monocyclic terahertz pulse having a large electric Field amplitude ETHz. In this phenomenon, the bands are tilted by the electric Field pulse, and a metallization is triggered by carrier generations through quantum tunneling processes. The right panel of Fig. 3 shows time evolutions of absorption changes in the infrared region appearing when a Mott insulator consisting of organic ET molecules (the left part of Fig. 3) is irradiated with a terahertz pulse. The results provide information on the dynamics of metallization. Recently, we are trying to observe a new nonequilibrium steady state called Floquet state, which is produced by the interaction between an oscillating light electric Field and an electronic system when a solid is irradiated with a mid-infrared pulse, and to control the electronic structure using this state (Fig. 4). We are studying the nature of Floquet state using a subcycle spectroscopy, in which we can detect electronic state changes along an oscillating light electric Field via the changes of optical constants for a probe pulse shorter than the period of the mid-infrared pump pulse
光励起により金属化する銅酸化物（二次元モット絶縁体）
テラヘルツパルスの強電場で引き起こされるモット絶縁体－金属転移
有機モット絶縁体であるκ型ET塩の構造（左）とテラヘルツ電場による金属化を示す赤外領域の吸収変化ΔOD（右）
中赤外パルスの電場波形に沿った物質の電子状態化を測定するサブサイクル分光（左）と光の振動電場によって生成する光ドレスト・フロッケ状態の概念図（右）
MESSAGE
SET HIGH GOALS AND DO YOUR RESEARCHES TO ACHIEVE YOUR OWN DREAM.
Our research is to clarify and control electronic properties of condensed matter by using various kinds of laser lights with different frequencies and temporal widths. By utlizing unique features of correlated electron and low-dimensional electron systems in transition metal compounds and organic molecular materials, we expect to achieve the Final goal of making next-generation optical devices, which show the higher peformance than those based upon convential semiconductors.
In just the past thirty years, the optical technology has been extensively improved. Thirty years ago, we did not imagine that we could detect directly dynamics of electrons, spins, atoms and molecules in solids, but now we can do that by using ultra-short laser pulses.
We hope that students set high goals and make researches to achieve their dreams. In our laboratoy, a lot of students have thus far made fascinating discoveries. We believe that all the new students will be able to experience their own discoveries, each of which is the world’s First one.
keyword
Photo-induced phase transition / Strongly correlated systems / Electron lattice interaction / Terahertz pulse / Optical switch / Optical properties / Transition metal complexes / Photo-induced absorption / Solitons / Halogen-bridged metal complexes / Mid-infrared pulse / Strongly correlated electron systems / Femtosecond Laser spectroscopy / Terahertz spectroscopy / Ultrafast spectroscopy / Insulator-metal transition / Mott transition / Strongly correlated electronics / Molecular solids / Strongly correlated electronic systems / Nonlinear optical response / Electronic correlation / Exciton / Photoconduction / Polaron / Mid-infrared light / Terahertz light / Nonlinear optics / Later / Electric field-induced phase transition / Infrared spectroscopy / Felt second laser spectroscopy /Magnetism / Optical switching / Correlated electronics / Optical properties in solids / Charge transfer absorption / Organic charge transfer complexes / Switching phenomena / Magnetism / Third harmonic generation / Transition metal oxides / Copper oxides / Third order nonlinear susceptibility / Nonlinear optical effect / Nonlinear optical constants / Strong phase relationship / Third-order nonlinear susceptibility / Third harmonic generation / Copper oxide / Third-order nonlinear susceptibility / Nonlinear optical effect / Organic ferroelectrics / Terahertz electromagnetic waves / Dielectric physical properties / Femtosecond laser / Laser spectroscopy / Carbon Nanotubes / Laser photoelectron spectroscopy / Molecular conductors / Charge transfer complexes / Pump-probe spectroscopy / Molecular crystals / Phase transition / Nonlinear optical constants / SDW / CDW / Halogen-bridged transition metal complexes / Spin susceptibility / Magneto-optical effect / Pseudo-first order Original halogen-bridged metal complexes / polarized reflection spectra / X-ray photoelectron spectroscopy / one-dimensional Heisenberg spin system / halogen-bridged Ni complexes / photoelectron spectroscopy
PROFILE : Professor Hiroshi Okamoto
1983 Graduated, Faculty of Engineering, Univ. of Tokyo
1985 Doctor of Engineering, Univ. of Tokyo
1988 Research Associate, Institute for Molecular Science
1988 Lecturer, RISM, Tohoku University
1992 Associate Professor, RISM, Tohoku University
1995 Associate Professor, Faculty of Engineering, Univ. of Tokyo
1992 Associate Professor, Faculty of Frontier Sciences, Univ. of Tokyo
1995 Professor, Faculty of Frontier Sciences, Univ. of Tokyo
STUDENT VOICE : GUO ZIJING
Light is a very powerful tool for investigating physical properties of materials. At Okamoto Lab, you can carry out your researches using the latest laser spectroscopy equipment by yourself. Prof. Okamoto is a kind, reliable professor who is very easy to talk to and always caring. Other lab members are also excellent people. I am learning a lot from them while enjoying research with them. At Okamoto Lab, you will be given full and careful supports from all aspects such as how to proceed with the experiments and prepare for the presentations. Through doing research with all these supports, I feel that I have been achieving huge personal growth.
APPLIED PHYSICS
Developing new optical properties and optical functionality
Graduate School of Frontier Sciences,
The University of Tokyo
Kashiwanoha 5-1-5,
Kashiwa,Chiba 277-8561, Japan
+81-4-7136-3771（Okamoto）
okamotoh@k.u-tokyo.ac.jp
The Goal of Applied Physics
The goal of Applied Physics is to develop a stage = “new material” that can manipulate undeveloped degrees of freedom, to explore unknown phenomena created from that stage and to bring out excellent functions, and to bring out its excellent functions. The purpose is to contribute to the development of human society by elucidating the mechanisms and developing application fields for these phenomena and functions.
AMS (Advanced Materials Science)
Department Office
AMS (Advanced Materials Science),
Graduate School of Frontier Sciences,
The University of Tokyo
Kashiwanoha 5-1-5, Kashiwa, Chiba 277-8561, Japan
Email : ams-office(at)ams.k.u-tokyo.ac.jp
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