Altermagnetic polar metallic phase in ultrathin epitaxially strained RuO2 films

• 成果类型: Article
• 署名作者: Jeong, Seung Gyo; Choi, In Hyeok; Nair, Sreejith; Buiarelli, Luca; Pourbahari, Bita; Oh, Jin Young; Lin, Bonnie Y. X.; LeBeau, James M.; Bassim, Nabil; Hirai, Daigorou; Seo, Ambrose; Choi, Woo Seok; Fernandes, Rafael M.; Birol, Turan; Zhao, Liuyan; Lee, Jong Seok; Jalan, Bharat
• 署名单位: University of Minnesota System; University of Minnesota Twin Cities; Gwangju Institute of Science & Technology (GIST); McMaster University; McMaster University; McMaster University; Sungkyunkwan University (SKKU); Massachusetts Institute of Technology (MIT); Nagoya University; University of Kentucky; University of Minnesota System; University of Minnesota Twin Cities; University of Illinois System; University of Illinois Urbana-Champaign; University of Michigan System; University of Michigan
• 刊物名称: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
• ISSN/ISSBN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.2526641123
• 发表日期: 2026-03-10
• 页码: e2526641123
• 关键词: altermagnetism; RuO2 thin film; strain; optical second harmonic generation; magneto-optics; SUSCEPTIBILITY MEASUREMENTS

摘要

Altermagnetism refers to a wide class of magnetic orders featuring magnetic sublattices with opposite spins related by rotational symmetries, resulting in nontrivial spin splitting and magnetic multipoles. However, the direct observation of the altermagnetic transition remains elusive. Here, by combining theoretical analysis, electrical transport, X-ray, and optical spectroscopies, we establish a phase diagram in hybrid molecular beam epitaxy-grown RuO2/TiO2 (110) films, mapping symmetries along with altermagnetic/ electronic/structural phase transitions as functions of film thickness and temperature. This features an altermagnetic metallic polar phase in epitaxially strained 2 nm films, suggesting a potential link between polar metals and altermagnetic materials. Such a clear signature of a magnetic phase transition at similar to 500 K is observed exclusively ultrathin strained films, unlike in bulk RuO2 single crystals. These results highlight the power of epitaxial heterostructure engineering to induce altermagnetism in systems initially nonmagnetic, opening avenues for realizing emergent quantum phases with multifunctional properties.