Koichi Nakamura
Professor, Ph.D. in Engineering
- nakamura.koichi
- Areas of Research
- Quantum Materials Science, Quantum Chemistry, Quantum Physics, Theory of Electronic States, Theory of Materials Properties, Nanomaterials
- Profile
- Research
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Dr. Koichi Nakamura obtained his M.Sc. and Ph.D. degrees in Engineering from Kyoto University, Japan in 1996 and 2000, respectively. After finishing his doctoral course, he worked at Kyoto University and Ritsumeikan University in the field of quantum chemistry and physics for group IV semiconductors (including silicon carbides), III-V semiconductors, high-k gate dielectric oxides, carbon nanomaterials, etc. – towards the application to sensing elements and electronic devices.
Since 2011, Dr. Nakamura has been part of a JICA project for the foundation of the Egypt-Japan University of Science and Technology (E-JUST) as a Japanese professor, staying in Alexandria, Egypt for more than seven years. At E-JUST, he was in charge of many courses regarding semiconductors, crystallography, electronic properties of materials, atomistic simulation, and mathematics for graduate students belonging to the Department of Materials Science and Engineering, in addition to carrying out research supervisions for them.
At KUAS, he will take over all engineering mathematics courses in the Faculty of Engineering. Dr. Nakamura’s research interests are relativistic electronic-state simulation for material systems and theoretical approaches to thermoelectric and electromechanical properties in post-graphene 2D nanomaterials and high-entropy alloys.
In his spare time, Dr. Nakamura enjoys playing shogi (Japanese chess), and he is also interested in the ecology of cats ever since he began raising quadruplet feral kittens (two brown tabby girls, a black/white masked girl, and a gray tabby boy) born at his laboratory in Egypt.
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Theory of Relativity Meets Mechanical and Electrical Systems
A material is the aggregate of its atoms, which accordingly consist of many electrons. The behavior of these electrons determines the various properties or characteristics of a material.
Quantum mechanics, which was initiated in the early 20th century, has been a strong tool for clarifying the behavior of electrons. In particular, the Schrödinger equation has been core concept as the fundamental equation in quantum mechanics theory, because the behavior of electrons can be described by finding an approximate solution to the Schrödinger equation, and various material characteristics including mechanical, electrical, magnetic, optical, thermal, and chemical properties can be derived from the techniques employed in quantum physics and quantum chemistry.
On the other hand, the Schrödinger equation is just a non-relativistic limit in quantum mechanics; namely, no relativistic effects are included in the information obtained from the Schrödinger equation. Some physical and chemical characteristics cannot be practically described via non-relativistic treatment. For example, the equilibrium distance of metal dimer, the chemical shift of nuclear magnetic resonance, and that the photoelectron spectrum cannot be evaluated quantitatively for some systems without considering the relativistic effect are all well-known.
In Dr. Nakamura’s Quantum Materials Physics and Chemistry (QMPC) Laboratory at KUAS, researchers are studying not only analysis of the electronic processes in chemical reactions but multiplex topics related to their material properties. For example, thermoelectric and electromechanical properties are important research targets from the viewpoint of quantum mechanics. Piezoresistivity is a typical electromechanical property in materials representing a change in the electrical resistivity when mechanical strain or stress is applied, and it is a widely utilized principle for mechanical sensors such as accelerometers and gyroscopes. The sensing element of piezoresistors is generally silicon, the most fundamental semiconductor material, but the behavior of holes (that is, the lack of electrons) in positively doped silicon cannot be exactly expressed via the non-relativistic Schrödinger equation due to the spin-orbit coupling at the valence-band top introduced naturally from relativistic quantum mechanics. Thus, for some material systems, the exact mechanism of piezoresistive sensors cannot be clarified without considering Einstein’s theory of relativity.
In these cases, the Dirac equation is available for use as the fundamental equation in quantum mechanics expanded to the theory of special relativity. Relativistic quantum mechanics based on the Dirac equation in material systems can derive material properties that non-relativistic techniques cannot explain. More qualitative and quantitative analysis of sensor mechanisms and of material properties can be achieved through novel techniques with relativistic quantum mechanics introduced by the QMPC Lab. For example, the Dirac equation is generally described with a 4-component spinor that consists of two of the large components representing the electronic state principally and two of the small components representing the positronic state principally. The 4-component spinor requires too much of a higher computational cost compared to a general wave function under the Schrödinger equation for application to large atomistic models corresponding to material systems. Thus, Dr. Nakamura has introduced the relativistic 2-component Dirac-Kohn-Sham theory for material systems via the combination of the density functional theory and the elimination of the small component method. For the application of this relativistic quantum-mechanical technique, transition-metal dichalcogenides become the most important research targets for the QMPC Lab members as post-graphene 2-dimensional materials with effective spin-orbit couplings, leading to giant piezoresistivity and other important material properties.
