Research Topics

  In addition to ferromagnetic materials, which have macroscopic magnetization and exhibit magnetic properties, there are various other types of magnetic materials, such as ferrimagnetism, chiral magnetism, and alternating magnetism, depending on the microscopic magnetization distribution inside the material, which cause various physical phenomena that differ from those of ferromagnetic materials. Under what conditions do these phenomena occur? How can we bring out more powerful phenomena? We investigate the properties of magnetic materials from various angles using theory and simulation, studying the relationship with functionality as a material and the possibility of new phenomena.

  Spin-orbit coupling, which is introduced into quantum mechanics as a relativistic correction for electron motion, causes a symmetry lowering in the electronic states of materials by coupling real space and spin space, which obey different symmetry rules, and is the origin of various physical phenomena. However, it is difficult to obtain a clear physical picture of the physical properties brought about by the coupling of spin, a resident of the quantum mechanical world, with real space, and in particular, the relationship with electric and magnetic ordering, including magnetism and superconductivity, is still a field of research where many mysteries remain. Our research group is studying the physical phenomena induced by spin-orbit coupling by making full use of mathematical science and first-principles calculations.

  The properties of a material are determined by the states of the electrons and atomic nuclei, which are its fundamental building blocks, within the material. Understanding the electronic state of material is essential to understanding the origin of macroscopic measurements such as electrical conduction, specific heat, and magnetization measurements, as well as experimental observations such as photoemission spectroscopy, nuclear magnetic resonance (NMR), and quantum osciration. The properties of electronic states can be investigated from many angles by analyzing band structures, density of states, Fermi surfaces, Berry phases, etc. Information on single-electron states obtained from first-principles calculations can also be used to calculate many physical quantities observed in experiments. Through collaborations with various experimental groups, our research group is working to understand unknown physical phenomena obtained experimentally.

  In many antiferromagnets, a highly symmetric magnetic structure is realized. In our research, we have shown that highly symmetric magnetic structures can be automatically generated for a given crystal structure by utilizing the multipole theory and group theory. We have shown that these theories can be combined with first-principles calculations to predict stable magnetic structures without the use of experimental information, and we are now working on the prediction of physical properties through simulations of magnetic structures. We are also engaged in research on physical properties using machine learning, a statistical analysis method that is the basis of artificial intelligence, and have proposed theoretical methods for converting magnetic structures into machine learning features.

  Rare-earth and actinide compounds that contain f-electron systems are called heavy-electron systems. It is known that the prediction accuracy of electronic states by first-principles calculations is significantly reduced for the f-electron system. In addition, some heavy fermion systems form multipole orders by using large orbital degrees of freedom of f-electrons, and it is important to understand the electronic states under complex electric/magnetic order formation by first-principles calculations. Our research group is studying electronic states in strongly correlated electron systems through the development of first-principles calculation methods and analytical theory.