Topological magnets studied by extreme light source photoemission spectroscopy

2021 Fiscal Year Final Research Report

• Project/Area Number: 18H01165
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 13030:Magnetism, superconductivity and strongly correlated systems-related
• Research Institution: The University of Tokyo
• Principal Investigator: Takeshi Kondo 東京大学, 物性研究所, 准教授 (40613310)
• Co-Investigator(Kenkyū-buntansha): 黒田 健太 広島大学, 大学院先進理工系科学研究科, 准教授 (00774001)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 光電子分光

Outline of Final Research Achievements

Rare-earth compounds exhibit rich phenomena induced by the interplay between localized f orbitals and conduction electrons. However, since the energy scale of the crystal-electric-field splitting is only a few millielectronvolts, the nature of the mobile electrons accompanied by collective crystal-electric-field excitations has not been unveiled. Here, we examine the low-energy electronic structures of CeSb through the anomalous magnetostructural transitions below the Neel temperature, ~17 K, termed the ‘devil’s staircase’, using laser angle-resolved photoemission spectroscopy. We report another type of electron-boson coupling between mobile electrons and quadrupole crystal-electric-field excitations of the 4f orbitals, which renormalizes the Sb 5p band prominently, yielding a kink at ~7 meV. This coupling strength is strong and exhibits anomalous step-like enhancement during the devil’s staircase transition, unveiling a new type of quasiparticle, named the ‘multipole polaron’.

Free Research Field

固体物性

Academic Significance and Societal Importance of the Research Achievements

CeSb の「悪魔の階段」では、伝導電子と局在4f結晶場励起が電子-ボゾン結合することで「多極子ポーラロン」という新しい準粒子が形成されていることが解明された。さらに、この電子-ボゾン結合は「悪魔の階段」の秩序配列に敏感に反応し、相互作用の強さを自在に変化させていることも明らかになった。この結果は、温度・圧力・磁場などの条件でCeSbの長周期磁気配列を制御することにより、電気輸送特性を劇的に変化させることが可能であることを示している。このような機構を今後さらに研究することで、スピトロニクデバイスへ向けた磁性材料設計の新たな展開が期待される。