2019 Fiscal Year Final Research Report

Investigation of novel topological phases based on symmetry

Planned Research

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Project Area	Frontiers of materials science spun from topology
Project/Area Number	15H05853
Research Category	Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
Allocation Type	Single-year Grants
Review Section	Science and Engineering
Research Institution	Tohoku University
Principal Investigator	Takafumi Sato 東北大学, 材料科学高等研究所, 教授 (10361065)
Co-Investigator(Kenkyū-buntansha)	瀬川耕司京都産業大学, 理学部, 教授 (20371297) 柏谷聡名古屋大学, 工学研究科, 教授 (40356770) 塚崎敦東北大学, 金属材料研究所, 教授 (50400396) 田仲由喜夫名古屋大学, 工学研究科, 教授 (40212039)
Project Period (FY)	2015-06-29 – 2020-03-31
Keywords	トポロジカル絶縁体 / 対称性 / 電子状態
Outline of Final Research Achievements	We have explored novel topological materials based on crystal symmetry and investigated emergent quantum phenomena and exotic quasiparticles associated with the topological properties of such materials. By combining state-of-the-art bulk-crystal-growth / molecular-beam-epitaxy techniques and advanced spectroscopies such as spin-ARPES and tunneling microscopy, we established controllability of Dirac fermions at the surface and interface of topological insulators. Moreover, we discovered several new types of topological semimetals, as represented by noncentrosymmetric Weyl semimetals, topological semimetals with new chiral fermions, and line-node semimetals protected by the nonsymmorphic symmetries of crystal. We have also conducted experiments on superconducting hybrids/junctions to pin down pairing symmetry, and found several new topological-superconductor candidates. By introducing the concept of topology, new insights in the physics of odd-frequency Cooper pairing were also obtained.
Free Research Field	トポロジカル物性
Academic Significance and Societal Importance of the Research Achievements	本研究において実現した、結晶の対称性に基づいたトポロジカル半金属の提案と実証、トポロジカル物質に内包される新しい準粒子の発見、接合系におけるトポロジカル超伝導候補物質の提案などは、トポロジカル物質探索における新しい方向性を示すものであり、固体物理学だけに留まらず、化学・工学分野なども含む広い意味での物質科学においてその概念が共有できると期待される。また、本成果に基づいてトポロジカル物質の機能性を更に向上させることで、スピントロニクス素子や量子計算などの分野におけるデバイス開発のための研究も進展すると期待される。