Hokkaido University, Center of Education & Research for Topological Science & Technology

Topological materials

We aim to create novel materials with novel general spatial topologies and to discover new phenomena woven by geometric phases. To date, we have created topological materials that show macroscopic quantum order (charge density wave: CDW), such as the NbSe3 ring, and Möbius and figure eight crystals. Utilizing mathematical surface theory, we will develop a new field of topological crystallography and crystal growth, and elucidate the relationships between macroscopic quantum order and topology in view of their CDW properties. We also try to comprehend the relationships between symmetry and topology in view of the physical properties of quasicrystals with fivefold symmetry. In relation to general spatial topology, we will also create copper-oxide high-temperature superconductors and rings of heavy electron materials, and carry out electron wave interference tests on these topological materials.

NbSe3 ring, and Möbius and figure eight crystals
Tanda et al., Nature 417 (2002) 397.

In this project, we also aim to elucidate general system properties from the properties of topological defects found in superconductors, liquid crystals, and various other materials. We have observed a new topological defect order in the copper-oxide high-temperature superconductor La2-xSrxCuO4 magnetic flux line (typical topological defect) lattice, and found that its characteristics correspond to the spatial symmetry of high-temperature superconducting order parameters. This is a good example demonstrating that local typological defects introduced into the system are closely related to the general properties of that system. We will investigate high-temperature superconductivity from the viewpoint of topological defects. We will also study the topology of superconducting order parameters and quantum transport phenomena, another interesting subject of study from a topological perspective.

We will also try to develop topological devices in cooperation with the Novel topology-related technologies project.

A magnetic flux line square lattice observed in the La2-xSrxCuO4 neutron diffraction test
- corresponding to d-wave symmetric superconducting order -
Gilardi et al., PRL 88 (2002) 217003 (collaborative research with Swiss PSI)