Japanese

Hayami-Oiwa Group

One of the major attractions of materials science lies in its diversity, where different physical properties—such as magnetism, superconductivity, and dielectric behavior—emerge depending on the choice of constituent elements, their composition ratios, and crystal structures. In particular, in strongly correlated electron systems, electrons in solids are strongly influenced by Coulomb interactions, making not only charge degrees of freedom but also internal degrees of freedom such as spin and orbital play essential roles. These internal degrees of freedom become intertwined through various mechanisms, including spin–orbit coupling and lattice distortions, leading to fascinating properties that cannot be realized in conventional metals or semiconductors.
In our research group, we study these rich and intriguing phenomena in strongly correlated electron systems by employing simplified models that incorporate only the essential ingredients. We combine theoretical analysis based on quantum statistical mechanics with numerical simulations in a complementary manner. Furthermore, to quantitatively clarify the correspondence with real materials, we utilize first-principles calculations based on density functional theory, extending our research toward understanding the properties of real materials and the exploration and design of novel functional materials. In addition, we have recently been developing new theoretical methods and applying machine learning–based data analysis to advance the understanding of complex phenomena and to promote efficient materials discovery. Through these efforts, we aim not only to uncover and understand novel quantum states and physical phenomena, but also to provide a theoretical foundation for next-generation technologies.
Our recent research subjects include
  • Classification of electronic physical properties based on microscopic augmented multipoles
  • Development and application of symmetry-adapted closest Wannier modeling based on complete multipole basis set
  • Cross-correlated phenomena over electric, magnetic, elastic, heat, and light
  • Development of systematic analysis method for nonlinear response tensors
  • Understanding physical phenomena induced by toroidal orderings
  • Novel off-diagonal response caused by ferro-axial moment
  • Emergent spin-orbit interaction in magnetic systems without the relativistic spin-orbit coupling
  • Magnetic skyrmion crystals by itinerant frustration
  • Generation of skyrmion crystals by using multi-layer structures
  • Search for novel topological magnetic phases in itinerant magnets
  • Peculiar electronic and magnetic states in spin-charge coupled systems
  • Stabilization mechanism and dynamics in magnetic skyrmion and vortex in localized spin system
  • Photo-induced quantum states of matter and physical phenomena
  • Microscopic mechanism of nonreciprocal magnon excitations
  • Search for functional materials toward antiferromagnetic spintronics
  • Novel magnetic states by geometrical frustration
  • Analysis of unconventional electronic orderings and physical phenomena discovered in real materials

    • Our group welcomes new members, collaborations, and visitors. Application of graduate students is here. Postdoc application for JSPS fellowship is here. If you are interested in our research, please contact hayami_at_phys.sci.hokudai.ac.jp for more information.