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Fermi Surface of RuO2 Measured by Quantum Oscillations

Zheyu Wu1, Mengmeng Long1, Hanyi Chen1, Shubhankar Paul2,3, Hisakazu Matsuki2, Oleksandr Zheliuk4, Uli Zeitler4, Gang Li5,6, Rui Zhou5,6 et al.

Zengwei Zhu7, Dave Graf8, Theodore I. Weinberger1, F. Malte Grosche1, Yoshiteru Maeno2,*, and Alexander G. Eaton1,†

  • *Contact author: maeno.yoshiteru.b04@kyoto-u.jp
  • †Contact author: alex.eaton@phy.cam.ac.uk
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Phys. Rev. X 15, 031044 – Published 18 August, 2025

DOI: https://doi.org/10.1103/5js8-2hj8

Abstract

The metallic oxide RuO2 has emerged as a promising altermagnet candidate, owing to reports of this material hosting antiferromagnetic ordering accompanied by a spin-split electronic band structure characteristic of time-reversal symmetry breaking. However, recent studies have robustly questioned this scenario. Here we map the Fermi surface of pristine single-crystalline RuO2. By measuring magnetic quantum oscillations of a bulk thermodynamic property, our study resolves the electronic structure present in the bulk of RuO2. Several Fermi sheets are discerned, with a range of effective quasiparticle masses up to 5 times that of the bare electron mass. We compare our measurements with the predictions for altermagnetic and nonmagnetic Fermi surfaces deduced from density functional theory calculations. The quantum oscillatory frequency spectra correspond very poorly to the profile expected for the case of altermagnetism; by contrast, they correspond well to the nonmagnetic scenario. Our findings place significant constraints on the bulk magnetic properties of RuO2 and strongly suggest that this material is an itinerant electron paramagnet.

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Popular Summary

Altermagnets are a newly proposed class of magnetic materials that have generated excitement for their potential to combine magnetic behavior with zero net magnetization—an appealing trait for future spintronic technologies. Among the leading candidates has been ruthenium dioxide (RuO2), a metallic oxide believed to exhibit this unusual magnetic order. However, recent experimental results have cast doubt on whether RuO2 truly behaves as an altermagnet. In this study, we use quantum oscillation measurements of ultrapure single crystals of RuO2 to investigate its Fermi surface, which serves as a detailed map of its electronic structure.

Unlike surface-sensitive techniques, quantum oscillations of a thermodynamic quantity such as the magnetization probe deep into the bulk of the material, providing a clearer and more reliable picture. Our measurements reveal a multisheet Fermi surface that aligns with expectations for a nonmagnetic, paramagnetic metal. These findings directly contradict several features predicted by altermagnetic models and provide strong evidence against bulk altermagnetism in RuO2.

Our results fundamentally change how we view RuO2, indicating that previously reported magnetic signals likely stem from surface effects rather than true bulk magnetism. This work resolves a key debate in the field and highlights the necessity of using bulk-sensitive tools when characterizing candidate altermagnets. Looking ahead, our study sets a higher standard for identifying genuine altermagnetic materials and will help steer the search for new systems that can power the next generation of spintronic technologies.

Article Text

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Phys. Rev. X 15, 031044– Published 18 August, 2025
  • Received 8 April 2025
  • Revised 13 June 2025
  • Accepted 10 July 2025
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

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