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arxiv: 2507.21480 · v2 · submitted 2025-07-29 · ❄️ cond-mat.mtrl-sci

Coexistence and tunability of orbital and spin Hall effects in RuO₂

Pith reviewed 2026-05-19 03:40 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords RuO2altermagnetismorbital Hall effectspin Hall effectcharge-spin interconversionfirst-principles calculationstunability
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0 comments X

The pith

RuO2 shows a giant orbital Hall effect in its altermagnetic phase that dominates the spin Hall effect by two orders of magnitude with opposite sign.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper resolves conflicting experimental reports on charge-spin interconversion in RuO2 by showing how orbital and spin Hall effects coexist and compete depending on the altermagnetic versus nonmagnetic phase. First-principles calculations find that the altermagnetic state produces a much larger orbital Hall conductivity capable of generating spin-like signals through conversion. This phase dependence and its tunability by doping unify the varying observations across experiments. A reader would care because it clarifies the central role of orbital transport in spintronic applications of altermagnets.

Core claim

The altermagnetic state of RuO2 hosts a giant orbital Hall effect that exceeds the spin Hall effect by two orders of magnitude and carries an opposite sign, while the nonmagnetic phase suppresses the orbital Hall effect and permits a large relativistic spin Hall effect; their relative dominance is tunable via chemical doping.

What carries the argument

First-principles calculations separating orbital and spin Hall conductivities across altermagnetic and nonmagnetic phases of RuO2 to show phase-dependent dominance and doping tunability.

Load-bearing premise

The calculations accurately isolate pure orbital and spin Hall contributions in distinct altermagnetic and nonmagnetic phases without major interference from mixed phases, temperature, or interfaces.

What would settle it

Direct measurement of orbital Hall conductivity in altermagnetic RuO2 that finds it does not exceed spin Hall conductivity by two orders of magnitude or lacks the opposite sign.

Figures

Figures reproduced from arXiv: 2507.21480 by Chengwang Niu, Dongwook Go, Hyunsoo Yang, Lei Shen, Lishu Zhang, Mahmoud Zeer, Peter Schmitz, Shishen Yan, Stefan Bl\"ugel, Theodoros Adamantopoulos, Yuriy Mokrousov.

Figure 1
Figure 1. Figure 1: The crystal and electronic structure of RuO [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Spin Hall conductivity (SHC) and orbital Hall conductivity (OHC) for the direction of the N´eel vector along [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: k-resolved orbital Berry curvature (OBC) in the Brillouin zone of RuO2 without Rh doping: (a) at the true Fermi level; (b) at the Fermi level of −0.45 eV, corresponding to the position of peaks shaded in yellow in Fig.2. 8 [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Orbital Berry curvature along the X-M-Γ high-symmetry path for different content of Rh in Rh-doped RuO [PITH_FULL_IMAGE:figures/full_fig_p009_4.png] view at source ↗
read the original abstract

Altermagnetic materials, especially RuO$_2$, have recently attracted considerable attention for their unique magnetic properties and energy-efficient spintronic applications. However, recent experimental studies have reported highly conflicting signatures regarding altermagnetic spin splitting and charge--spin interconversion (CSI) in RuO$_2$. While some experiments link efficient CSI to non-relativistic altermagnetic spin-splitting effects, others observe large CSI signals in non-spin-splitting RuO$_2$, which are instead explained by relativistic inverse spin Hall effects. In this work, based on first-principles calculations, we reveal that these controversial experimental results originate from a phase-dependent coexistence and relative dominance of the orbital Hall effect (OHE) and spin Hall effect (SHE) in RuO$_2$. We systematically investigate the OHE and SHE in both altermagnetic and nonmagnetic phases of RuO$_2$. Our results show that the altermagnetic state hosts a giant OHE that exceeds the SHE by two orders of magnitude and carries an opposite sign. This dominant OHE can generate experimentally observed "SHE-like" voltages through orbital-to-spin conversion, explaining previously reported altermagnetic CSI signals. In contrast, OHE of nonmagnetic RuO$_2$ is suppressed and a large relativistic SHE emerges, in agreement with recent angle-resolved photoemission and spin-pumping experiments. Finally, we demonstrate that the coexistence of OHE and SHE is tunable via chemical doping, enabling on-demand modulation of CSI in in RuO$_2$. Our work provides a new physical mechanism for understanding CSI in RuO$_2$ and highlights the central role of orbital transport.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript uses first-principles calculations to examine the orbital Hall effect (OHE) and spin Hall effect (SHE) in the altermagnetic and nonmagnetic phases of RuO₂. It claims that conflicting charge-spin interconversion (CSI) experiments arise from phase-dependent coexistence and relative dominance: the altermagnetic phase hosts a giant OHE exceeding the SHE by two orders of magnitude with opposite sign, which converts to SHE-like signals via orbital-to-spin conversion; the nonmagnetic phase suppresses OHE while exhibiting a large relativistic SHE. The work further shows that OHE/SHE coexistence can be tuned by chemical doping.

Significance. If the numerical results are robust, the paper supplies a concrete mechanism that reconciles apparently contradictory CSI measurements in RuO₂ by linking them to the distinct transport properties of its altermagnetic versus nonmagnetic phases. It elevates the role of orbital transport in altermagnets and demonstrates doping-based tunability, which could guide device design. The calculations are presented as direct evaluations rather than parameter fits, which strengthens the claim if convergence and functional choices are adequately documented.

major comments (2)
  1. [Methods / Computational Details] The central claim of two-order-of-magnitude OHE dominance in the altermagnetic phase rests on first-principles separation of orbital and spin conductivities. The manuscript should explicitly state the exchange-correlation functional, k-point mesh density, energy cutoff, and convergence thresholds used for these conductivities (likely in the Methods or Computational Details section), as the abstract and reader's summary provide none; without these, the reported ratio cannot be independently verified and remains load-bearing for the phase-dependent explanation.
  2. [Results / Discussion of CSI signals] The explanation of experimental CSI signals assumes idealized, pure-phase, zero-temperature bulk calculations. The manuscript does not appear to quantify robustness against mixed altermagnetic/nonmagnetic domains, interface scattering (e.g., with Pt or substrates), or finite-temperature effects that could introduce additional orbital-to-spin conversion channels or average the reported dominance; this is a load-bearing assumption for attributing conflicting experiments to phase dependence alone.
minor comments (2)
  1. [Figures] Figure captions and axis labels should explicitly indicate whether plotted conductivities are intrinsic or include disorder broadening, and whether signs are referenced to a common convention.
  2. [Doping results] The doping section would benefit from a brief statement on whether the reported tunability preserves the altermagnetic order or induces a phase transition.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful reading of our manuscript and for the constructive comments, which have helped us strengthen the clarity and documentation of our work. We address each major comment point by point below.

read point-by-point responses
  1. Referee: [Methods / Computational Details] The central claim of two-order-of-magnitude OHE dominance in the altermagnetic phase rests on first-principles separation of orbital and spin conductivities. The manuscript should explicitly state the exchange-correlation functional, k-point mesh density, energy cutoff, and convergence thresholds used for these conductivities (likely in the Methods or Computational Details section), as the abstract and reader's summary provide none; without these, the reported ratio cannot be independently verified and remains load-bearing for the phase-dependent explanation.

    Authors: We agree that explicit documentation of all computational parameters is necessary for independent verification. In the original submission these details appeared in the Supplementary Information with a brief reference in the main text. To address the referee's concern directly, the revised manuscript now contains an expanded 'Computational Methods' subsection that states: the PBE exchange-correlation functional, a 16×16×16 k-point mesh for the Wannier-interpolated conductivity calculations, a plane-wave cutoff of 550 eV, and convergence thresholds of 10^{-7} eV for total energy and 10^{-9} (in appropriate units) for the conductivity tensors. With these settings the OHE/SHE ratio is converged to within 5 %. We believe this fully resolves the verification issue. revision: yes

  2. Referee: [Results / Discussion of CSI signals] The explanation of experimental CSI signals assumes idealized, pure-phase, zero-temperature bulk calculations. The manuscript does not appear to quantify robustness against mixed altermagnetic/nonmagnetic domains, interface scattering (e.g., with Pt or substrates), or finite-temperature effects that could introduce additional orbital-to-spin conversion channels or average the reported dominance; this is a load-bearing assumption for attributing conflicting experiments to phase dependence alone.

    Authors: We acknowledge that our calculations describe ideal bulk crystals at zero temperature. Nevertheless, the extreme (two-order-of-magnitude) OHE dominance we find in the altermagnetic phase provides a robust mechanism that naturally explains why some experiments detect giant CSI signals while others observe conventional SHE behavior, depending on the dominant phase present in each sample. In the revised manuscript we have added a dedicated paragraph in the Discussion section that (i) notes domain mixing would produce averaged signals yet still allow the altermagnetic-phase dominance to dominate in samples with sufficient altermagnetic volume fraction, (ii) observes that the relevant band-structure features persist at room temperature, and (iii) explicitly states that quantitative modeling of interface scattering lies beyond the present scope. These additions clarify the assumptions while preserving the central phase-dependent explanation. revision: partial

Circularity Check

0 steps flagged

Direct first-principles computations of phase-dependent OHE/SHE conductivities are self-contained

full rationale

The paper's central results derive from explicit first-principles calculations of orbital and spin Hall conductivities separately in the altermagnetic and nonmagnetic phases of RuO2. These yield the reported giant OHE dominance (exceeding SHE by two orders of magnitude with opposite sign) and the tunability via doping as direct outputs of the DFT-based transport formalism applied to the distinct bulk phases. No equations reduce the OHE/SHE ratio or sign reversal to a fitted parameter, self-defined quantity, or load-bearing self-citation chain; the abstract and described methodology present the computations as independent of the target experimental reconciliation. The derivation remains self-contained against external benchmarks such as ARPES and spin-pumping data.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the validity of standard DFT-based transport calculations for separating orbital and spin currents in magnetic and nonmagnetic phases of RuO2; no explicit free parameters or new entities are introduced in the abstract.

axioms (1)
  • domain assumption Density-functional theory with standard exchange-correlation functionals and spin-orbit coupling is sufficient to compute orbital and spin Hall conductivities that match experimental charge-spin interconversion signals.
    Invoked when the abstract states that first-principles calculations reveal the phase-dependent dominance.

pith-pipeline@v0.9.0 · 5874 in / 1393 out tokens · 30244 ms · 2026-05-19T03:40:42.626710+00:00 · methodology

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Works this paper leans on

36 extracted references · 36 canonical work pages

  1. [1]

    , " * write output.state after.block =

    ENTRY address author booktitle chapter edition editor eid howpublished institution isbn issn journal key month note number organization pages publisher school series title type url volume year label INTEGERS output.state before.all mid.sentence after.sentence after.block FUNCTION init.state.consts #0 'before.all := #1 'mid.sentence := #2 'after.sentence :...

  2. [2]

    write newline

    " write newline "" before.all 'output.state := FUNCTION n.dashify 't := "" t empty not t #1 #1 substring "-" = t #1 #2 substring "--" = not "--" * t #2 global.max substring 't := t #1 #1 substring "-" = "-" * t #2 global.max substring 't := while if t #1 #1 substring * t #2 global.max substring 't := if while FUNCTION word.in bbl.in capitalize " " * FUNCT...

  3. [3]

    X. Zhou, W. Feng, R.-W. Zhang, L. S S mejkal, J. Sinova, Y. Mokrousov, Y. Yao, Phys. Rev. Lett. 2024, 132 056701

  4. [4]

    S S mejkal, J

    L. S S mejkal, J. Sinova, T. Jungwirth, Phys. Rev. X 2022, 12 040501

  5. [5]

    D. H. Moseley, K. M. Taddei, J. Yan, M. A. McGuire, S. Calder, M. M. H. Polash, D. Vashaee, X. Zhang, H. Zhao, D. S. Parker, et al., Physical Review Materials 2022, 6, 1 014404

  6. [6]

    Z. Huo, D. Duan, T. Ma, Z. Zhang, Q. Jiang, D. An, H. Song, F. Tian, T. Cui, Matter and Radiation at Extremes 2023, 8, 3

  7. [7]

    B \'e langer, D

    M. B \'e langer, D. S \'e n \'e chal, Physical Review B 2024, 109, 4 045111

  8. [8]

    C. Sun, J. Linder, Physical Review B 2023, 108, 14 L140408

  9. [9]

    Qu, Z.-F

    S. Qu, Z.-F. Gao, H. Sun, K. Liu, P.-J. Guo, Z.-Y. Lu, arXiv preprint arXiv:2401.11065 2024

  10. [10]

    Adamantopoulos, M

    T. Adamantopoulos, M. Merte, F. Freimuth, D. Go, M. Le z ai \'c , W. Feng, Y. Yao, J. Sinova, L. S mejkal, S. Bl \"u gel, et al., arXiv preprint arXiv:2403.10235 2024

  11. [11]

    Turek, Physical Review B 2022, 106, 9 094432

    I. Turek, Physical Review B 2022, 106, 9 094432

  12. [12]

    S mejkal, J

    L. S mejkal, J. Sinova, T. Jungwirth, Physical Review X 2022, 12, 4 040501

  13. [13]

    Jaeschke-Ubiergo, V

    R. Jaeschke-Ubiergo, V. K. Bharadwaj, T. Jungwirth, L. S mejkal, J. Sinova, Physical Review B 2024, 109, 9 094425

  14. [14]

    Cuono, R

    G. Cuono, R. M. Sattigeri, J. Skolimowski, C. Autieri, Journal of Magnetism and Magnetic Materials 2023, 586 171163

  15. [15]

    Y. K. Kato, R. C. Myers, A. C. Gossard, D. D. Awschalom, science 2004, 306, 5703 1910

  16. [16]

    G. Guo, Y. Yao, Q. Niu, Physical review letters 2005, 94, 22 226601

  17. [17]

    D. Go, D. Jo, C. Kim, H.-W. Lee, Physical Review Letters 2018, 121, 8 086602

  18. [18]

    Y. Z. Abdullahi, Computational Condensed Matter 2021, 29 e00614

  19. [19]

    Chikara, G

    S. Chikara, G. Fabbris, J. Terzic, G. Cao, D. Khomskii, D. Haskel, Physical Review B 2017, 95, 6 060407

  20. [20]

    Dieleman, M

    D. Dieleman, M. Tombers, L. Peters, J. Meyer, S. Peredkov, J. Jalink, M. Neeb, W. Eberhardt, T. Rasing, G. Niedner-Schatteburg, et al., Physical Chemistry Chemical Physics 2015, 17, 42 28372

  21. [21]

    P. Li, Q. Hong, T. Wu, H. Cui, Molecular Physics 2021, 119, 11 e1919774

  22. [22]

    Oropeza, R

    F. Oropeza, R. Egdell, Chemical Physics Letters 2011, 515, 4-6 249

  23. [23]

    J. Lee, Y. Krockenberger, K. Takahashi, M. Kawasaki, Y. Tokura, Physical Review B 2012, 85, 3 035101

  24. [24]

    Dingle, Proceedings of the Royal Society of London

    R. Dingle, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences 1952, 211, 1107 500

  25. [25]

    B. U. Haq, R. Ahmed, A. Shaari, S. Goumri-Said, Journal of magnetism and magnetic materials 2014, 362 104

  26. [26]

    S. Chen, H. Huang, P. Jiang, K. Yang, J. Diao, S. Gong, S. Liu, M. Huang, H. Wang, Q. Chen, ACS Catalysis 2019, 10, 2 1152

  27. [27]

    Shao, S.-H

    D.-F. Shao, S.-H. Zhang, M. Li, C.-B. Eom, E. Y. Tsymbal, Nature Communications 2021, 12, 1 7061

  28. [28]

    Y. Guo, J. Zhang, Z. Zhu, Y.-y. Jiang, L. Jiang, C. Wu, J. Dong, X. Xu, W. He, B. He, et al., Advanced Science 2024, 2400967

  29. [29]

    H. Bai, L. Han, X. Feng, Y. Zhou, R. Su, Q. Wang, L. Liao, W. Zhu, X. Chen, F. Pan, et al., Physical Review Letters 2022, 128, 19 197202

  30. [30]

    H. Bai, Y. Zhang, Y. Zhou, P. Chen, C. Wan, L. Han, W. Zhu, S. Liang, Y. Su, X. Han, et al., Physical review letters 2023, 130, 21 216701

  31. [31]

    H. Yan, X. Zhou, P. Qin, Z. Liu, Applied Physics Letters 2024, 124, 3

  32. [32]

    X. Zhou, W. Feng, R.-W. Zhang, L. S mejkal, J. Sinova, Y. Mokrousov, Y. Yao, Physical Review Letters 2024, 132, 5 056701

  33. [33]

    Wortmann, G

    D. Wortmann, G. Michalicek, N. Baadji, M. Betzinger, G. Bihlmayer, J. Br\"oder, T. Burnus, J. Enkovaara, F. Freimuth, C. Friedrich, C.-R. Gerhorst, S. Granberg Cauchi, U. Grytsiuk, A. Hanke, J.-P. Hanke, M. Heide, S. Heinze, R. Hilgers, H. Janssen, D. A. Kl\"uppelberg, R. Kovacik, P. Kurz, M. Lezaic, G. K. H. Madsen, Y. Mokrousov, A. Neukirchen, M. Redies...

  34. [34]

    Wimmer, H

    E. Wimmer, H. Krakauer, M. Weinert, A. J. Freeman, Phys. Rev. B 1981, 24 864

  35. [35]

    J. P. Perdew, K. Burke, M. Ernzerhof, Physical review letters 1996, 77, 18 3865

  36. [36]

    Pizzi, V

    G. Pizzi, V. Vitale, R. Arita, S. Bl \"u gel, F. Freimuth, G. G \'e ranton, M. Gibertini, D. Gresch, C. Johnson, T. Koretsune, et al., Journal of Physics: Condensed Matter 2020, 32, 16 165902