2026-04-28 東京大学
図1（左）積層ハニカム-カゴメ格子上に配置されたCo原子による波動関数の干渉効果の模式図。（右）遍歴フラットバンドの角度分解光電子分光（ARPES）による観測結果と理論計算。赤色の面が理論計算による遍歴フラットバンド、赤丸とカラーマップがARPESにより得られた遍歴フラットバンドを表す。
＜関連情報＞
- https://www.s.u-tokyo.ac.jp/ja/press/11128/
- https://advanced.onlinelibrary.wiley.com/doi/10.1002/adma.202517521
大きな横方向応答を生み出す遍歴強磁性フラットバンドの証拠 Evidence for Itinerant Ferromagnetic Flat Bands Producing Large Transverse Responses
Susumu Minami, Yangming Wang, Seigo Souma, Hiroto Nakamura, Akito Sakai, Takumi Osumi, Hang Su, Hikaru Watanabe, Shun’ichiro Kurosawa, Rikuto Oiwa, Daisuke Nishio-Hamane, …
Advanced Materials Published: 27 April 2026
DOI:https://doi.org/10.1002/adma.202517521
ABSTRACT
Interference of electronic wavefunctions may result in the emergence of a flat band, and trigger nontrivial correlated phenomena and phase formations when the flat band crosses the Fermi energy EF. To date, such an itinerant flat band at EF has been reported for electronic states without symmetry breaking. If a flat band arises at EF even with broken symmetry, the ordered state may offer a distinct platform for studying novel phases and spontaneous responses. Here we report experimental and theoretical evidence for itinerant ferromagnetic flat bands formed by spin-polarized d-electron orbitals on a stacked honeycomb–kagome lattice, hosting the alternating stack of honeycomb and kagome sublattices. Our theory together with angle-resolved photoemission spectroscopy and magneto–thermoelectric measurements finds multiple topological flat bands at EF generating large Berry curvature in the ferrimagnet GdCo5 below its Curie temperature of 940 K. We observe large transverse responses, in particular, gigantic anomalous Nernst effect producing the largest transverse thermoelectric conductivity over 10 A m-1K-1 at room temperature. Our study paves a path for developing itinerant magnetic flat bands and to their spintronic and thermoelectric applications.
