– Theory –
Nonequilibrium Physics [R Lab]
Kunimasa MIYAZAKI (Professor)
Takeshi KAWASAKI (Assistant Professor)
We study physical and mathematical theories of nonlinear phenomena by means of analytical and numerical methods. Present subjects of investigation include the following:
(1) Chaos in Hamiltonian systems : phase space structure, invariant sets and their relation to flow in the phase space; slow dynamics such as Arnold diffusion, Nekhoroshev theorem and Boltzmann-Jeans theory; motion of charged particle in non-uniform magnetic field; dynamics of multiple pendulum and its phase space structure
(2) Dynamics of nonlinear spatial structures such as solitons, vortices and patterns
(3) Development and application of singular perturbation methods
(4) Computational geomorphology : understanding geomorphology by physical modeling and computation
(5) Dynamics of chain-type systems : active motion of chain-end particles
Condensed Matter Theory [S Lab]
Hiroshi KONTANI, Hiroshi KOHNO (Professor)
Akito KOBAYASHI, John WOJDYLO (Associate Professor)
Youichi YAMAKAWA, Ai YAMAKAGE (Assistant Professor)
We examine theoretically the fundamental problems in condensed matter physics and statistical physics.
(1) In the high density quantum systems such as high-Tc superconductors, strong electron-electron correlations are considered to play a crucial role in the appearance of superconductivity. Starting with this assumption, we are currently developing a new theory of superconductivity beyond the BCS theory.
(2) We probe quantum fluctuations inherent to superconducting states, charge density wave states, and spin-density wave states of low-dimensional organic conductors.
(3) We are also investigating the dynamical phenomena related to crystal growth and non-equilibrium pattern formation at interfaces.
Computational Biophysics [B Lab]
Florence TAMA (Professor)
Tetsuro NAGAI (Assistant Professor)
Biological complexes, structured ensembles of proteins and nucleic acids, perform many vital cellular functions and dysfunctions of those result in severe diseases. In order to understand diseases and develop treatments, the functional mechanisms of these biological complexes need to be elucidated. A crucial step in this process is the characterization of the structure and dynamics of these complexes. Our goal is to develop computational methods to obtain atomic level description of the functional states of biological complexes. Such methods will rely on the integration of computational simulations with various experimental data such as high resolution X-ray crystallography, lower resolution cryo-EM and X-ray Free Electron Lasers.
The research in the lab is interdisciplinary. We use physics, chemistry, and computational science to study biological systems. More specifically, to describe the dynamics and energetics of biological molecules, we use empirical force fields based on the physico-chemical properties of atoms or, to reduce complexity, we also use coarse-grained models. Then methods such as molecular dynamics simulations/normal mode analysis are used to obtain structural models by incorporating experimental data into the modeling procedure, where numerical optimizations techniques, such as Monte Carlo and gradient following techniques, need to be implemented in programs.
Theoretical Biophysics [TB Lab]
Yuko OKAMOTO (Professor)
Takahisa YAMATO (Associate Professor)
Akihiro KIMURA (Assistant Professor)
Protein folding problem and protein structure predictions are long-standing unsolved problems in theoretical biophysics. Even with the fastest supercomputer available, it is extremely difficult to succeed in folding even the smallest protein into its native structure by computer simulations. We study these problems by powerful molecular simulation techniques. We are also studying the molecular mechanisms which allow biomoleuces to carry out efficiently their biological functions such as photosynthesis and vision. We examine these mechanisms by means of electronic state theories and molecular simulations. Non-equilibrium phenomena such as electron transfer reactions and solvation dynamics in polar solutions are also investigated and compared with equivalent real biological systems, both using computer simulations and analytical theory.
Protein folding in water, photoenergy conversion, and photosignal transduction
– Experiment –
Condensed Matter Nuclear Magnetic Resonance [I Lab]
Masayuki ITOH (Professor)
Yoshiaki KOBAYASHI (Associate Professor)
Yasuhiro SHIMIZU (Lecturer)
Our research group specializes in nuclear magnetic resonance (NMR) spectroscopy, which is a powerful probe for studying microscopically magnetic and electronic properties of solids. Recently our activities have focused on strongly correlated electron systems in transition metal oxides and low-dimensional quantum spin systems. The goal of our research is to understand a variety of exotic quantum phenomena that the spin, charge, and orbital degrees of freedom of the electrons yield in novel solids. In particular, our current efforts are directed towards understanding the metal-insulator and spin-state transitions, as well as charge and orbital ordering in transition metal oxides. The superconducting mechanism in iron-based superconductors is also investigated by the NMR technique.
Superconducting magnet for NMR experiments
Low-Temperature Physics of Quantum Fluids and Solids [L Lab]
Nobuo WADA (Professor)
Taku MATSUSHITA (Lecturer)
At temperatures down to sub-mK, we explore superfluidity and degenerate states of 4He (Boson) and 3He (Fermion) in restricted geometries with the nanoscale, where novel quantum fluids with various dimensionalities can be realized. We also investigate ground states of quantum spin systems such as frustrated antiferromagnets and electronic states of new materials at low temperatures.
Heavy Fermion Physics [M Lab]
Noriaki SATO (Professor)
Kazuhiko DEGUCHI (Lecturer)
Keiichiro INURA (Assistant Professor)
Some of rare-earth and actinide compounds, known as "heavy fermions" exhibit a great number of interesting quantum states such as quantum criticality, unconventional superconductivity at the border of magnetism-nonmagnetism, and coexistence between magnetism and superconductivity. It is believed that these phenomena arise from "duality" of strongly correlated electrons. To explore this novel nature of electrons, we synthesize single crystals of good quality and measure the specific heat, magnetic susceptibility, and thermal expansion at extreme conditions, i.e. low temperatures down to 100 mK and high pressures up to 25 kbar. Our goal is to create a unified picture of the heavy fermions.
A snapshot of single crystal growth of a uranium-based heavy-fermion superconductor.
Condensed-matter physics of functional materials [V Lab]
Ichiro TERASAKI (Professor)
Hiroki TANIGUCHI (Associate Professor)
Kenji TANABE (Assistant Professor)
V-laboratory is interested in the physical properties of "interesting and useful materials" in strongly correlated systems. In a strongly correlated system, conduction electrons affect with each other through the strong Coulomb repulsion, and move together in a "correlated" manner. As a result, a conventional band picture is seriously broken down, and new phenomena can arise beyond the prediction of a band theory. In this respect, such materials are prime examples for "More is different". We are mainly studying on large thermopower in Co oxides and nonlinear conduction in organic conductors at present.
The schematic picture of the layered cobalt oxide NaxCoO2. This material can convert heat into electricity with a performance as high as other thermoelectric materials.
Biomolecular Dynamics and Function [D Lab]
Takayuki UCHIHASHI (Professor)
Midori MURAKAMI (Lecturer)
Proteins are inherently dynamic molecules that undergo structural changes and interactions with other molecules over a wide timescale range, from nanoseconds to milliseconds or longer. Furthermore, protein motions play an important biological role in the assembly into protein complexes, ligand binding and enzymatic reactions. Therefore, understanding the dynamic behaviour of a protein is a requisite for gaining insight into their function mechanisms. We develop novel methods for directly observing protein's dynamics based on high-speed atomic force microscopy (AFM), which is one of scanning probe microscopy, and exploit new paradigm of dynamic structural biology. Also we analyze structural dynamics of rhodopsin at atomic resolution using X-ray crystallographic technics for understanding the molecular mechanism and creating new functional GPCRs.
Photo-Bioenergetics [G Lab]
Takumi NOGUCHI (Professor)
Hiroyuki MINO (Associate Professor)
Yuki KATO (Assistant Professor)
Photosynthesis performed by plants and cyanobacteria is a highly elaborate natural system of light energy conversion, in which carbon dioxide and water are converted into sugars and molecular oxygen. We are studying the molecular mechanism of photosynthesis, especially that of water oxidation (oxygen evolution), proton-coupled electron transfer, and excitation energy transfer, using various physicochemical methods such as Fourier transform infrared spectroscopy (FTIR), electron spin resonance (ESR), ultrafast time-resolved spectroscopy, thermoluminescence (TL) and delayed luminescence (DL), and quantum chemical calculations. Understanding the photosynthesis mechanism provides important basis for solving the energy and environment problems that confront the human race today.
The structure of photosystem II (left) and its electron transfer pathway (right). Photosystem II, which is embedded in thylakoid membranes of plants and cyanobacteria, is a multisubunit protein complex that has a function of light-driven water oxidation to evolve molecular oxygen.
Biophysics of Cellular Signaling [K Lab]
Kosuke MAKI (Associate Professor)
Naoya SUZUKI (Assistant Professor)
Our research is aimed at understanding the mechanisms of information transfer in biological systems. Our interests include the investigation of protein folding at the molecular level. We focus primarily on characterizing events which occur during folding reactions by means of experimental techniques such as spectroscopy, kinetic methods and protein engineering, with the goal of understanding the molecular mechanisms of protein folding. Another area of interest is the mechanisms of intracellular signaling at the cellular level. We study various presynaptic processes of synaptic transmission, especially modulation of transmitter release and dynamics of divalent cations, by means of electrophysiological and fluorescence imaging techniques.