電子の地図が決めていた、“渦”のサイズ ～世界最小スキルミオンの誕生メカニズムを解明～

2025-05-09 東京大学,大阪大学,東京都立大学,北海道大学

「電子の地図」に刻まれた伝導電子の運動量によって、スキルミオンのサイズが決まる

＜関連情報＞

• https://www.issp.u-tokyo.ac.jp/maincontents/news2.html?pid=27110
• https://www.issp.u-tokyo.ac.jp/news/wp-content/uploads/2025/05/0509_skyrmion_web.pdf
• https://www.science.org/doi/10.1126/science.adj7710

フェルミ面のネスティングによって誘起される擬ギャップとフェルミ・アークが中心対称性スキルミオン磁石に誘起される Pseudogap and Fermi arc induced by Fermi surface nesting in a centrosymmetric skyrmion magnet

Yuyang Dong, Yuto Kinoshita, Masayuki Ochi, Ryu Nakachi, […] , and Takeshi Kondo
Science  Published:8 May 2025

Editor’s summary

Skyrmions, whirlpools of magnetic spin that hold promise for spintronics applications, usually occur in materials that lack a center of symmetry. They have also been observed in centrosymmetric materials, where they can be as small as a few nanometers, but the mechanism for their formation is not well understood. Dong et al. used photoemission measurements to access the electronic structure of GdRu₂Si₂, a centrosymmetric material featuring a skyrmion phase. The researchers focused on the ground state from which the skyrmion phase arises. Photoemission revealed the emergence of the so-called Fermi arcs, as well as a pseudogap. These findings will help to distinguish between the various theories of skyrmion formation in this class of materials and may also lead to practical applications. —Jelena Stajic

Abstract

Skyrmions in noncentrosymmetric materials are believed to occur due to the Dzyaloshinskii-Moriya interaction. By contrast, the skyrmion formation mechanism in centrosymmetric materials remains elusive. Here, we reveal the intrinsic electronic structure of the centrosymmetric GdRu₂Si₂ by selectively measuring magnetic domains using angle-resolved photoemission spectroscopy (ARPES). We found robust Fermi surface (FS) nesting, consistent with the magnetic modulation q-vector detected by the previous resonant x-ray scattering measurements. The pseudogap opens at the nested FS portions, which vary for different magnetic domains. The anomalous pseudogap disconnects the FS to generate Fermi arcs with twofold symmetry. These results indicate that the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction plays a decisive role in generating the screw spin modulation responsible for the skyrmion formation in GdRu₂Si₂. Furthermore, we demonstrate the flexible nature of magnetism in GdRu₂Si₂ by manipulating magnetic domains with magnetic field and temperature cyclings, providing potential future applications for data storage and processing devices.