A research group led by Associate Professor Junji Haruyama of Aoyama Gakuin University (at the time of research: Institute for Solid State Physics, University of Tokyo), Professor Shingo Katsumoto, and Professor Ruqian Wu of the University of California succeeded in transforming graphene into a topological insulator.
Graphene is a sheet-like substance composed of only carbon and having only one atom, which is extremely durable and has good electrical conductivity, and can be controlled by an externally applied voltage, so it is attracting attention as a next-generation electronic device material. ..On the other hand, topological insulators are substances in which a metallic state appears only at the interface, and are expected to be applied to spintronics.
Graphene is a model material for which a topological insulator was predicted for the first time in theory, but in reality, it does not have the strong spin-orbit interaction required for a topological insulator because its constituent atoms are light.Therefore, in this study, we attempted to introduce spin-orbit interaction by distributing ultrafine particles composed of heavy atoms such as bismuth and tellurium on graphene in a small amount.Since it is a very small amount of fine particles, the band structure derived from graphene remains, but a spin-orbit interaction is introduced between the carbon lattice and the fine particles through the quantum tunneling effect, and the topological insulator state is expressed by controlling the voltage applied from the outside. To do.
As a result of verifying this by electrical conduction measurement, density of states measurement, and first-principles calculation, it was confirmed for the first time that a topological insulator state occurred in graphene.
Since this result was able to impart topological properties to graphene, which is also useful for electronic devices, it is expected that the possibilities of application will greatly expand in the future, including spintronics and valleytronics.