Mikio IIZUKA

The goal of my research is to develop large-scale simulation technologies to understand complex phenomenon in diverse areas of science. Needless to say, sophisticated simulation techniques are crucial for the study of complex multi-scale phenomena, such as plasma excitation of superconductor devices, earthquakes. The research of developing simulation techniques is exigent, also challenging because the simulation has several issues to be overcome; being ill, stiff conditions and multi-scale. My efforts have been focused on the discovery and understanding of complex phenomenon in plasma excitation of superconductor devices and earthquake, using a large-scale simulation. The example of research is illustrated below, exemplifying "Superconductor device".

Study of high Tc superconductor device generating the continuous terahertz waves using large-scale simulation
Terahertz region (0.3THz - 10THz) of the electromagnetic spectrum is laid between the millimeter wave and the optical regions. The terahertz waves in 0.3-10 THz, which are characterized as resonance with vibration of molecule and penetrability into medium, are applicable for next-generation technologies; carrier waves for broad-band communication, detecting devices of plastic explosive and contaminant in food, sensing devices of air pollution and ozone depletion. (Fig. 1)
On the other hand, quantum cascade laser is said to be one of effective light sources for analysis and detection. However, as it's emission power is 1 to 4THz, relatively low for practical use to the measurement and the analysis tools, a new light source of high power (mW level) with frequencies tunable is needed (Fig. 2).
In my research, I study the high Tc superconductor device generating the continuous terahertz waves, using large-scale simulation(Fig. 4, Fig. 5), based on the theory in which the Josephson plasma oscillations are excited and continuous terahertz waves are generated when impressing a direct current on the high temperature superconductor in magnetic field. (Fig. 3). Up to the present, the following results are obtained;
- The oscillation mechanism (Fig. 6)
- Oscillation condition of terahertz wave
- Characteristic of terahertz wave radiated by element (Fig. 7)
It is imperative to make full use of large-scale simulation analysis and define the ideal condition for oscillation, in order to effectively apply new technologies to meet requirements of next-generation devices.

Figure-1:Availability of continuous terahertz waves

A more expanded frequency range promises further advancement in communication technologies. The results of the research are expected to contribute dramatically to our daily life in healthcare and new technologies issues.

Figure-2:Issue of continuous terahertz waves for allpications

Several oscillation methods of terahertz wave such as an organic nonlinear optical crystal system were developed and put into practical use. However, all of them came up against the need to meet a more reliable output requirement, and the problem was left open for investigation of terahertz wave applications. It was needed to develop a new oscillation method which emits continuous coherent terahertz waves.

Figure-3:Simulation model of high Tc superconductor device generating the continuous terahertz waves

In 1994, under this background, Tachiki et al. has proposed a unique theory which shows a possibility that continuous terahertz waves could be generated by a high-temperature superconductor, in which the strongly superconducting layer of CuO2 and insulating layer of Bi2Sr2Ca Cu2O8+δ, with the thickness of 3, 12Å each, are alternatively stacked along the c axis, placed in magnetic field and impressed with direct current, as shown in Fig. 5. To establish an oscillation method based on the Tachiki theory, experimental trial and errors were far from useful, due to the fact that the oscillation conditions are too complex to be produced by the experiment. Then, a simulation approach was taken to evaluate the theory. The scale of the simulation was very large such as covering the scale from 10Å to hundreds µm, the time space from 10as to several ns with 108 time steps and millions of cells, as shown in Fig 3, and the simulation became enabling approach only after the operation of the Earth Simulator which is able to simulate well such a large-scale complex phenomena.

Figure-4:Schematic diagram of high Tc superconductor device

A high temperature superconductor is in a crystal structure, consisting of a superconducting layer and insulator layer. These layers form a multiple Josephson junction as called the intrinsic Josephson junction (IJJ). I study on the Josephson effect which is the phenomenon of current flow across two superconductors weakly coupled, separated by a very thin insulating barrier. The unique properties of the Josephson junction can be useful for diverse detecting tools in the terahertz range. To reveal its mechanism, a physical and mathematical non-linear model has been developed, and simulated.

Figure-5:Basic equations of IJJ phnomena

The basic equations governing the dynamics of the Josephson effects are shown in Fig. 5.

Figure-6:Terahertz oscillation mechanism

As the result of consideration with obtained data from the simulated model, the terahertz oscillation mechanism was elucidated. (Fig. 6)

Figure-7:characteristic of terahertz ‚—ave radiated from high-Tc superconductors

Furthermore, characteristic of terahertz wave radiated from high-Tc superconductors were ascertained using obtained data. (Fig. 7)

Figure-8:Availability of large-scale simulation

From the beginning of this research project, with the objective of revealing the mechanism of terahertz wave emission, the simulation software has been designed to run efficiently on the Earth Simulator. The optimization has been repeatedly provided with accordance of the model structure, in order to gain more efficiency in parallel computing. The time of calculation was extremely reduced after further tuning and iterative optimization. With the model based on the coupling analysis of superconducting equation and Maxwell equation, the computation time reached only 12 hours for calculating a 1-case process by using 160 parallel processors. The vector ratio achieved 98.99%, and the resulting efficiency is approximately 17 % of the peak performance.

Large-scale simulation of complex phenomena
The goal of my research is to develop large-scale simulation technologies to understand complex phenomenon in diverse areas of science. Needless to say, sophisticated simulation techniques are crucial for the study of complex multi-scale phenomena, such as plasma excitation of superconductor devices, earthquakes. The research of developing simulation techniques is exigent, also challenging because the simulation has several issues to be overcome; being ill, stiff conditions and multi-scale. My efforts have been focused on the discovery and understanding of complex phenomenon in plasma excitation of superconductor devices and earthquake, using a large-scale simulation. The example of research is illustrated below, exemplifying "Superconductor device". Study of high Tc superconductor device generating the continuous terahertz waves using large-scale simulation Terahertz region (0.3THz - 10THz) of the electromagnetic spectrum is laid between the millimeter wave and the optical regions. The terahertz waves in 0.3-10 THz, which are characterized as resonance with vibration of molecule and penetrability into medium, are applicable for next-generation technologies; carrier waves for broad-band communication, detecting devices of plastic explosive and contaminant in food, sensing devices of air pollution and ozone depletion. (Fig. 1) On the other hand, quantum cascade laser is said to be one of effective light sources for analysis and detection. However, as it's emission power is 1 to 4THz, relatively low for practical use to the measurement and the analysis tools, a new light source of high power (mW level) with frequencies tunable is needed (Fig. 2). In my research, I study the high Tc superconductor device generating the continuous terahertz waves, using large-scale simulation(Fig. 4, Fig. 5), based on the theory in which the Josephson plasma oscillations are excited and continuous terahertz waves are generated when impressing a direct current on the high temperature superconductor in magnetic field. (Fig. 3). Up to the present, the following results are obtained; - The oscillation mechanism (Fig. 6) - Oscillation condition of terahertz wave - Characteristic of terahertz wave radiated by element (Fig. 7) It is imperative to make full use of large-scale simulation analysis and define the ideal condition for oscillation, in order to effectively apply new technologies to meet requirements of next-generation devices. Figure-1:Availability of continuous terahertz waves A more expanded frequency range promises further advancement in communication technologies. The results of the research are expected to contribute dramatically to our daily life in healthcare and new technologies issues. Figure-2:Issue of continuous terahertz waves for allpications Several oscillation methods of terahertz wave such as an organic nonlinear optical crystal system were developed and put into practical use. However, all of them came up against the need to meet a more reliable output requirement, and the problem was left open for investigation of terahertz wave applications. It was needed to develop a new oscillation method which emits continuous coherent terahertz waves. Figure-3:Simulation model of high Tc superconductor device generating the continuous terahertz waves In 1994, under this background, Tachiki et al. has proposed a unique theory which shows a possibility that continuous terahertz waves could be generated by a high-temperature superconductor, in which the strongly superconducting layer of CuO2 and insulating layer of Bi2Sr2Ca Cu2O8+δ, with the thickness of 3, 12Å each, are alternatively stacked along the c axis, placed in magnetic field and impressed with direct current, as shown in Fig. 5. To establish an oscillation method based on the Tachiki theory, experimental trial and errors were far from useful, due to the fact that the oscillation conditions are too complex to be produced by the experiment. Then, a simulation approach was taken to evaluate the theory. The scale of the simulation was very large such as covering the scale from 10Å to hundreds µm, the time space from 10as to several ns with 108 time steps and millions of cells, as shown in Fig 3, and the simulation became enabling approach only after the operation of the Earth Simulator which is able to simulate well such a large-scale complex phenomena. Figure-4:Schematic diagram of high Tc superconductor device A high temperature superconductor is in a crystal structure, consisting of a superconducting layer and insulator layer. These layers form a multiple Josephson junction as called the intrinsic Josephson junction (IJJ). I study on the Josephson effect which is the phenomenon of current flow across two superconductors weakly coupled, separated by a very thin insulating barrier. The unique properties of the Josephson junction can be useful for diverse detecting tools in the terahertz range. To reveal its mechanism, a physical and mathematical non-linear model has been developed, and simulated. Figure-5:Basic equations of IJJ phnomena The basic equations governing the dynamics of the Josephson effects are shown in Fig. 5. Figure-6:Terahertz oscillation mechanism As the result of consideration with obtained data from the simulated model, the terahertz oscillation mechanism was elucidated. (Fig. 6) Figure-7:characteristic of terahertz ‚—ave radiated from high-Tc superconductors Furthermore, characteristic of terahertz wave radiated from high-Tc superconductors were ascertained using obtained data. (Fig. 7) Figure-8:Availability of large-scale simulation From the beginning of this research project, with the objective of revealing the mechanism of terahertz wave emission, the simulation software has been designed to run efficiently on the Earth Simulator. The optimization has been repeatedly provided with accordance of the model structure, in order to gain more efficiency in parallel computing. The time of calculation was extremely reduced after further tuning and iterative optimization. With the model based on the coupling analysis of superconducting equation and Maxwell equation, the computation time reached only 12 hours for calculating a 1-case process by using 160 parallel processors. The vector ratio achieved 98.99%, and the resulting efficiency is approximately 17 % of the peak performance.
	Mikio IIZUKA Research organization for Information Science & Technology(RIST) Division of Computational Science and Technology, Director 7F, RIKKOKAI building, 2-32-3, kitashinagawa, shinagawa-ku, Tokyo, 140-0001, Japan TEL: +81-3-6433-0670 FAX: +81-3-6433-0673 Query on this homepage, please mail to iizuka@tokyo.rist.or.jp Education: University of Tokyo Refereed paper Mikio Iizuka, Hiroshi Okuda and Genki Yagawa, Nonlinear Structural Subsystem of GeoFEM for Fault Zone Analysis, Pure Appl. Geophys. 157, 2105-2124, 2000. Mikio Iizuka, Daigo Sekita, Hisashi Suito, Mamoru Hyodo, Kazuro Hirahara, David Place, Peter Mora, Osamu Hazama, and Hiroshi Okuda, Parallel simulation system for earth quake generation: Nonlinear fault analysis modules and parallel coupling analysis, Concurrency Computation.: Pract. Exper. 2002, 14, 499-519. [co-Author] Suito, H., Iizuka, M., and Hirahara, K. (2001) 3D viscoelastic FEM modeling of crustal deformation in Northeast Japan, Pure Appl. Geophys., 159, 2239-2259. Tachiki, M., Iizuka M., Minami, K., Tejima, S., and Nakamura H., Emission of continuous coherent terahertz waves with tunable frequency by intrinsic Josephson junctions, Phys. Rev. B 71, (2005), 134515. Tachiki, M., Iizuka, M., Minami, K., Tejima, S., and Nakamura H., Emission of continuous terahertz waves by high Tc superconductor, Physica C., (2005), 426-431. Conference paper Mikio IIZUKA, GeoFEM: Multi-Purpose Parallel FEM for Solid Earth(4) Complex Earth Structure Analysis,@Proceedings of the Conference on Computational Engineering and Science, JSCES,@Vol.3, No.1, 97-98, 1998. Mikio IIZUKA, Kazuteru GARATANI, Kengo NAKAJIMA, Hisashi NAKAMURA, Hiroshi OKUDA, Genki YAGAWA, GeoFEM: High-Performance Parallel FEM Geophysical Applications, ISHPC99, Second@Intenational Symposium Proceedings, High Performance Computing, Lecture Notes in Computer Science 1615, 292-303, 1999. Tejima, S., Noejung, P., Miyamoto, Y., Minami, K., Iizuka, M., Nakamura, N., and Tomanek, D., Large scale simulations for carbon nanotubes, High Performance Computing and Grid in Asia Pacific Region, Japan (2004), 502. M. Iizuka, H. Nakamura, M. Tachiki, Large scale simulation for the generating mechanism of continuous terahertz waves through the nano-scale high-temperature-superconductor device, SC2004 Workshop Friday, November 12. My patent right: 1 RIST Webpage