Encountering Unknown Physical Phenomena and Creating Future Electronics Technology

With the development of AI and IoT, a new society is emerging where the physical world and digital space are highly integrated. The global volume of data traffic is expected to reach thousands of times its current level in 30 years, and ultra-high-speed, ultra-low-power information processing technology is essential to handle this exponential growth. At the same time, energy management technology to efficiently control and reuse the enormous amount of heat generated in the process has become an important issue. The key to such technological innovation lies in the discovery of unknown physical phenomena based on a deep understanding of material properties, and the development of innovative electronic materials and devices that utilize them.

The electrical, thermal, optical, and magnetic properties of materials are deeply related to the state and motion of electrons within them. Differences in electrical conduction properties—such as metals, semiconductors, and insulators—as well as various functions like magnetism, thermoelectric effects, and optical responses, arise from the energy states occupied by electrons, their response to external fields, and their connection to degrees of freedom such as spin. One of the important concepts for understanding these is the band structure, which represents the relationship between the energy and momentum of electrons in a crystal. In recent years, in addition to the control of band gaps that has traditionally been emphasized, attention has also been focused on band dispersion, band crossings, spin-split bands, and the geometric and topological properties of electron wave functions in momentum space. By controlling these electronic states through material design, it becomes possible to bring out new functions not found in conventional materials.

In our laboratory, we are working to create new electronic materials called "quantum functional materials" by fully utilizing the quantum mechanical degrees of freedom of electrons—charge, spin/orbital angular momentum, and phase—and through material design based on band and magnetic structures and the exploration of novel electronic functions. With these materials, we aim to complement and expand the functions of semiconductors and magnets that have been the core of conventional electronics, and to realize electronic materials and devices that support next-generation information processing, sensing, and energy conversion. As a representative achievement, we have demonstrated magnetic information writing and reading functions in "antiferromagnets"—magnetic materials with properties different from the ferromagnets known as magnets—which will lead to the realization of ultra-high-speed, ultra-low-power non-volatile memory. Furthermore, we are progressing with the fabrication of thin films of "topological semimetals," substances that show a large response to heat and electricity due to their characteristic band structure, and have succeeded in developing high-performance transverse thermoelectric conversion devices that utilize these characteristics.

Designing and fabricating materials, measuring and understanding physical properties, and then expanding into device development—through this series of research, we aim to connect the knowledge accumulated by physics to electrical and information technology. An encounter with a physical phenomenon that does not yet have a name may be a small discovery at first. However, by deeply understanding its principles and giving it form as a material or device, it holds great potential to grow into a foundational technology for information processing, sensing, and energy conversion.