Topological Materials Design Research Unit

Principal Investigator

PI Name Motoaki Hirayama
Degree Ph.D.
Title Unit Leader
Brief Resume
2013 Ph.D., Department of Applied Physics, University of Tokyo
2013 Postdoctoral Researcher, Nanosystem Research Institute, AIST,
2015 Project Assistant Professor, Department of Physics, Tokyo Institute of Technology
2017 Research Scientist, First-Principles Materials Science Research Team, RIKEN Center for Emergent Matter Science
2020 Unit Leader, Topological Materials Design Research Unit, RIKEN Center for Emergent Matter Science (-present)
2020 Project Associate Professor, Quantum-Phase Electronics Center, The University of Tokyo (-present)


In our unit, we explore novel materials and their properties using first-principles calculations, which are numerical methods for realistic materials. In particular, we focus on the topological properties of the electronic band structure and search for topological materials with non-trivial properties. We investigate the properties and applications of these unique electronic states. We also include superconducting states and propose the emergence of Majorana fermions. In addition, we develop ab initio methods to treat correlation effects and design a wide range of materials including strongly correlated systems and magnetic systems. We design materials across a wide range of fields, including materials in the chemical and materials fields, such as electrides.

Research Fields

Physics, Materials Science


First-principles calculations
Theoretical materials design
Topological materials
Majorana fermions and parafermions
Spin-orbit interaction


Electrides as a New Platform of Topological Materials

Our unit propose e lectrides as a new platform of topological materials. Electrides are a group of materials in which electron e- exists in the interstitial region and stabilizes the structure as an anion. Electrides are being studied in the field of catalysis because of their small work function. For example, in the layered material Sc2C (Fig. (a)), electrons enter the cavities between the layers and exhibit insulating properties as shown in Fig. (b). The charge density of [Sc2C]2+2e extends to interlayer positions that are significantly displaced from the Sc2C layer due to the anionic electrons 2e, resulting in a non-trivial system with a quantized large polarization. Reflecting the bulk topology, a topologically-protected metallic state appears on the Sc2C surface (Fig. (c)). The metallic surface state originates from the interstitial electron, and therefore floats above the Sc2C surface (Fig. (d)). This electron cloud has a small work function, making it possible to use Sc2C as a topological substrate for high-density electron doping. For example, one electron per Mo site can be doped for MoS2 (Fig. (e)). We have discovered a variety of topological electrides including relativistic systems, which will lead to the development of topological properties across scientific fields.


(a) Crystal structure of the topological electride [Sc2C]2+2e, (b) band structure of Sc2C, (c) band structure of the Sc2C (111) surface, (d) floating topological surface state, (e) topological carrier doped to MoS2


Motoaki Hirayama

Unit Leader motoaki.hirayama[at]


  1. T. Yu, R. Arita, and M. Hirayama

    Interstitial-Electron-Induced Topological Molecular Crystals

    Adv. Phys. Res. 2, 2200041 (2022)
  2. M. Hirayama, T. Tadano, Y. Nomura, and R. Arita

    Materials design of dynamically stable d9 layered nickelates

    Phys. Rev. B 101, 75107 (2020)
  3. M. Hirayama, S. Matsuishi, H. Hosono, and S. Murakami

    Electrides as a New Platform of Topological Materials

    Phys. Rev. X 8, 031067 (2018)
  4. M. Hirayama, R. Okugawa, T. Miyake, and S. Murakami

    Topological Dirac nodal lines and surface charges in fcc alkaline earth metals

    Nat. Commun. 8, 14022 (2017)
  5. M. Hirayama, R. Okugawa, S. Ishibashi, S. Murakami, and T. Miyake

    Weyl Node and Spin Texture in Trigonal Tellurium and Selenium

    Phys. Rev. Lett. 114, 206401 (2015)


Main Research Building 149, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan

TEL:+81-(0)48-462-1111 (ext. 3168)