Objectives of the project

Focusing on topological nature of materials, we aim to explore novel quantum phenomena driven by interaction, symmetry of crystals and nanostructure of semiconductors, and search for exotic quasiparticles inherent in the topological quantum phenomena, thereby elucidating the underlying physics behind them.

Recent years have seen a tremendous growth of interest in topological quantum phenomena. However, quite a few issues still remain unexplored. In particular, (1) clarifying effects of interactions between electrons which would lead to diversity and functionality of materials, (2) exploring topological materials based on symmetry of crystals, and (3) systematic control of artificial topological phases in nanostructured systems, are indispensable for developing novel materials and establishing the fundamental concepts. This project systematically studies these issues at the frontiers of materials science.

This project consists of four core projects:
A: Topology and Correlation
B: Topology and Symmetry
C: Topology and Nanoscience
D: Topology and New Concepts

The core projects A, B and C respectively investigate strongly correlated systems, semiconductor systems and nanostructured systems. The core project D, theory group, aims to develop new concepts and stimulates collaborations among A-C. We also have some theorists in A-C, who will do research in intimate collaboration with experimentalists.

Research issue A: Topology and Symmetry

The purpose of this core project is to investigate topologically non-trivial quantum condensates and quantum phase transitions in superconductors, insulators, semimetals, etc. with strong interactions between electrons (strongly correlated electron systems), and thereby deepen and develop the research in topological materials science.

In this core project, we choose transition metal oxides and heavy electron compounds as the main stages of correlated materials, and investigate topological quantum phenomena in systems including artificial superlattices, nanostructures, and junctions. Through this research, we attempt to re-examine the conventional classification of "unconventional superconductivity" from the new viewpoint of topological superconductivity. In addition, we will create and control novel topological phases emerging from Mott insulators and semimetals, and clarify the roles of electron correlations. We will conduct these researches utilizing active collaborations with other core research projects as well as with open-solicitation projects.

Research issue B: Topology and Symmetry

This project aims to find new types of topological materials which originate from the spin-orbit interaction and symmetry, such as topological insulators, Dirac semimetals, Weyl semimetals, and topological superconductors. We also elucidate characteristics of novel topological quantum phenomena and exotic quasiparticles expected in such systems. By establishing intimate collaboration between state-of-the-art spectroscopy and high-quality-crystal-growth techniques, we investigate the electronic states of these topological materials in great details. We also stimulate mutual collaborations in the project to contribute research progress on, e.g., topological semimetals and topological superconductors.

Research issue C: Topology and Nanoscience

This core project aims to investigate novel topological quantum phenomena and exotic quasiparticles in transport characteristics of nanostructured topological materials including semiconductor heterostructures, low-dimensional nanostructures, and hybrid structures with superconductors and ferromagnetic materials. We explore synergistic effects of symmetry, interaction, and proximity effects of the systems under topological and low-dimensional constraints. This would provide deep understanding of quantum phenomena with emergent quasiparticles as well as developing novel nanostructured topological-material devices. We also stimulate mutual collaborations in the project to contribute research progress on topological quantum phase transitions, topological superconductors, Weyl semimetals, and Majorana quasiparticles.

Research issue D: Topology and New Concepts

This core project aims to theoretically clarify fundamental properties of topological quantum phases and emergent exotic quasiparticles. To this end, we explore universal phenomena and laws that do not depend on the detail of each material and thus establish the basic concepts from a broader viewpoint. In particular, we carry out theoretical research with special emphasis on "correlation", "symmetry" and "nanoscience", which play key roles in pioneering a new field of topological materials science. We also aim at stimulating mutual collaborations among the core projects A01, B01 and C01. In this project, we particularly put emphasis on nurturing young researchers, who can pioneer a new stage of science in interdisciplinary areas.