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arxiv: 2509.18590 · v1 · submitted 2025-09-23 · ❄️ cond-mat.mtrl-sci · cond-mat.str-el

Large Anomalous and Topological Hall Effect and Nernst Effect in a Dirac Kagome Magnet Fe3Ge

Chunqiang Xu , Shuvankar Gupta , Hengxin Tan , Hyeonhu Bae , Olajumoke Oluwatobiloba Emmanuel , Mingyu Xu , Yan Wu , Xiaofeng Xu
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Pengpeng Zhang Weiwei Xie Binghai Yan Xianglin Ke
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Pith reviewed 2026-05-18 15:00 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci cond-mat.str-el
keywords kagome magnetanomalous Hall effecttopological Hall effectanomalous Nernst effectBerry curvatureDirac gapsFe3Getransverse thermoelectric conductivity
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The pith

Fe3Ge kagome crystals produce an anomalous transverse thermoelectric conductivity of 4.6 A m^{-1} K^{-1} from Berry curvature in massive Dirac gaps.

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

The paper examines the magnetic, electronic, and thermoelectric behavior of Fe3Ge single crystals in which iron atoms form a slightly distorted kagome lattice. It reports a large anomalous Hall effect together with an anomalous Nernst effect whose transverse thermoelectric conductivity reaches approximately 4.6 A m^{-1} K^{-1}, a value larger than those found in conventional ferromagnets and most topological ferromagnets. First-principles calculations attribute these responses chiefly to intrinsic Berry curvature generated by massive Dirac gaps in momentum space. The authors also record a topological Hall resistivity near 0.9 microOhm cm and a topological Nernst coefficient of 1.2 microvolt K^{-1}, which they link to the Berry phase of field-induced scalar spin chirality. The combined momentum-space and real-space Berry phases are presented as the origin of the observed transport phenomena and as the basis for potential room-temperature transverse thermoelectric uses.

Core claim

Fe3Ge exhibits a large anomalous Hall effect and anomalous Nernst effect with an anomalous transverse thermoelectric conductivity of about 4.6 A m^{-1} K^{-1}. First-principles calculations show that these responses are governed primarily by intrinsic mechanisms arising from Berry curvature in massive Dirac gaps. A topological Hall resistivity of about 0.9 microOhm cm and topological Nernst coefficient of 1.2 microvolt K^{-1} are observed and attributed to the Berry phase associated with field-induced scalar spin chirality, establishing the combined influence of Berry phases in momentum and real space.

What carries the argument

Berry curvature generated by massive Dirac gaps in momentum space, together with the Berry phase from field-induced scalar spin chirality in real space.

If this is right

  • The transport responses remain largely intrinsic even at room temperature.
  • Fe3Ge combines anomalous and topological Hall and Nernst signals in a single kagome material.
  • The magnitude of the anomalous transverse thermoelectric conductivity exceeds most reported values for topological ferromagnets.
  • Field-induced scalar spin chirality produces measurable topological Nernst and Hall responses alongside the momentum-space contributions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Materials with similarly distorted kagome lattices may be screened for comparable or larger thermoelectric responses by tuning the Dirac gap size.
  • The coexistence of momentum-space and real-space Berry phases could be exploited to design devices that respond to both magnetic field and temperature gradients.
  • If the intrinsic mechanism holds, modest chemical substitution or strain might further enlarge the Dirac gaps and increase the Nernst conductivity without introducing strong disorder.

Load-bearing premise

First-principles calculations can isolate the intrinsic Berry curvature contribution without significant mixing from extrinsic scattering or sample defects, and the topological signals can be cleanly assigned to scalar spin chirality rather than other magnetic textures.

What would settle it

High-resolution angle-resolved photoemission spectroscopy that fails to detect the calculated massive Dirac gaps near the Fermi level, or transport measurements on cleaner samples showing dominant temperature or disorder dependence inconsistent with intrinsic Berry curvature, would challenge the central mechanism.

read the original abstract

The search for kagome magnets with unconventional magnetic and electronic properties has gained significant attention in recent years. We report the magnetic, electronic, and thermoelectric properties of Fe3Ge single crystals, where the Fe atoms form a slightly distorted kagome lattice. Fe3Ge exhibits a large anomalous Hall effect and anomalous Nernst effect. The anomalous transverse thermoelectric conductivity reaches about 4.6 A m^-1 K^-1, exceeding values reported for conventional ferromagnets and most topological ferromagnets. First-principles calculations indicate that these transport responses are primarily governed by intrinsic mechanisms, highlighting the dominant role of Berry curvature arising from massive Dirac gaps in momentum space. In addition, we observe a topological Hall resistivity of about 0.9 microOhm cm and a topological Nernst coefficient of 1.2 microvolt K^-1, which are attributed to the Berry phase associated with field-induced scalar spin chirality. These findings demonstrate the combined influence of Berry phases in both momentum and real space, establishing Fe3Ge as a promising candidate for room-temperature transverse thermoelectric applications.

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 reports magnetic, electronic, and thermoelectric measurements on Fe3Ge single crystals with a slightly distorted kagome Fe lattice. It finds a large anomalous Hall effect and anomalous Nernst effect, with the anomalous transverse thermoelectric conductivity reaching ~4.6 A m^{-1} K^{-1}. First-principles calculations attribute the responses primarily to intrinsic Berry curvature arising from massive Dirac gaps. The paper also reports a topological Hall resistivity of ~0.9 μΩ cm and topological Nernst coefficient of ~1.2 μV K^{-1}, attributed to field-induced scalar spin chirality, indicating combined momentum-space and real-space Berry phases.

Significance. If the intrinsic mechanism holds, the results position Fe3Ge as a promising room-temperature transverse thermoelectric material, with the reported anomalous Nernst conductivity exceeding many conventional and topological ferromagnets. The explicit combination of single-crystal transport data with first-principles calculations that tie the signals to Berry curvature from Dirac gaps provides concrete experimental and theoretical grounding. The additional observation of topological signals linked to real-space chirality illustrates multi-scale Berry-phase effects in a kagome magnet.

major comments (2)
  1. [§4 (First-principles section)] §4 (First-principles section): The central claim that the anomalous and topological responses are primarily governed by intrinsic Berry curvature from massive Dirac gaps requires explicit checks against extrinsic mechanisms. The manuscript should include residual-resistivity-ratio dependence of the Hall/Nernst signals or disorder-averaged calculations to demonstrate that skew-scattering and side-jump contributions remain sub-dominant to the computed intrinsic term for the measured 4.6 A m^{-1} K^{-1} value.
  2. [§3 (Experimental transport)] §3 (Experimental transport): The isolation of the topological Hall resistivity (~0.9 μΩ cm) and topological Nernst coefficient (~1.2 μV K^{-1}) from the total signals needs a clearer description of the subtraction protocol, including how ordinary and anomalous components are removed and why other possible magnetic textures or inhomogeneities can be ruled out in favor of field-induced scalar spin chirality.
minor comments (2)
  1. [Abstract] Abstract and main text: The reported values are given as 'about 4.6' and 'about 0.9'; adding uncertainties or error bars would allow readers to assess the precision of the claimed exceedance over other ferromagnets.
  2. [Figures] Figure captions and text: Ensure consistent notation for units (e.g., μΩ cm vs microOhm cm) and clarify any scaling factors applied to the Nernst data.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the positive overall assessment and for the constructive major comments, which help strengthen the presentation of our results. We respond to each point below and indicate the revisions made to the manuscript.

read point-by-point responses

  1. Referee: [§4 (First-principles section)] The central claim that the anomalous and topological responses are primarily governed by intrinsic Berry curvature from massive Dirac gaps requires explicit checks against extrinsic mechanisms. The manuscript should include residual-resistivity-ratio dependence of the Hall/Nernst signals or disorder-averaged calculations to demonstrate that skew-scattering and side-jump contributions remain sub-dominant to the computed intrinsic term for the measured 4.6 A m^{-1} K^{-1} value.

    Authors: We appreciate the referee’s emphasis on rigorously separating intrinsic and extrinsic contributions. Our first-principles calculations already yield an intrinsic anomalous Nernst conductivity that matches the experimental value of ~4.6 A m^{-1} K^{-1} within the reported precision, supporting the dominance of Berry curvature from the massive Dirac gaps. In the revised manuscript we have added a paragraph in §4 that discusses the scaling of the anomalous Hall and Nernst conductivities with longitudinal conductivity; the observed behavior is consistent with the intrinsic regime expected for our relatively clean single crystals. However, a systematic residual-resistivity-ratio study or disorder-averaged calculations would require new sample batches and substantial additional computational work that lies outside the scope of the present study. We therefore regard the close theory–experiment agreement as sufficient evidence for the intrinsic mechanism while acknowledging that future work could further quantify any residual extrinsic terms. revision: partial

  2. Referee: [§3 (Experimental transport)] The isolation of the topological Hall resistivity (~0.9 μΩ cm) and topological Nernst coefficient (~1.2 μV K^{-1}) from the total signals needs a clearer description of the subtraction protocol, including how ordinary and anomalous components are removed and why other possible magnetic textures or inhomogeneities can be ruled out in favor of field-induced scalar spin chirality.

    Authors: We agree that the subtraction procedure should be described more explicitly. In the revised §3 we now provide a step-by-step account: the ordinary Hall resistivity is extracted from the high-field linear slope and subtracted; the anomalous Hall component is scaled to the measured magnetization curve; the remaining field-dependent signal is assigned to the topological Hall effect. An analogous procedure is applied to the Nernst data. We have also added a paragraph arguing that alternative explanations (e.g., magnetic inhomogeneities or other spin textures) are unlikely, citing the absence of hysteresis in the extracted topological signals, the smooth field dependence consistent with scalar spin chirality, and the lack of corresponding features in the longitudinal resistivity or magnetization that would indicate phase separation. revision: yes

standing simulated objections not resolved
  • A comprehensive residual-resistivity-ratio dependence or disorder-averaged calculations to quantify possible extrinsic contributions, as these would require new crystal growth campaigns and extensive additional first-principles work not available in the current dataset.

Circularity Check

0 steps flagged

No significant circularity; experimental transport data and first-principles Berry curvature calculations are independent

full rationale

The paper reports independent experimental measurements of anomalous Hall/Nernst effects and topological signals in Fe3Ge crystals. First-principles calculations of band structure and Berry curvature are performed separately via standard DFT methods to interpret the data, without the transport quantities being used as inputs to fit or define the computed intrinsic contributions. Attribution of topological Hall/Nernst to field-induced scalar spin chirality follows from magnetic structure analysis rather than reducing to a self-referential fit or self-citation chain. No self-definitional steps, fitted inputs renamed as predictions, or ansatz smuggling via prior self-citations appear in the derivation; the computational results provide external support rather than tautological equivalence to the measured values.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard density-functional theory approximations for band structure and Berry curvature, plus the assumption that measured transport coefficients can be directly compared to intrinsic calculations without large extrinsic corrections.

axioms (1)
  • domain assumption Density functional theory with standard exchange-correlation functionals accurately reproduces the electronic band structure and Berry curvature near the Fermi level in Fe3Ge.
    Invoked when the paper states that first-principles calculations indicate the transport responses are governed by intrinsic mechanisms from massive Dirac gaps.

pith-pipeline@v0.9.0 · 5781 in / 1391 out tokens · 43820 ms · 2026-05-18T15:00:46.081146+00:00 · methodology

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Reference graph

Works this paper leans on

3 extracted references · 3 canonical work pages

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    Here, we report magnetic, electronic and thermoelectric properties of Fe3Ge single crystals with Fe atoms forming a slightly distorted Kagome lattice

    1 Large Anomalous and Topological Hall Effect and Nernst Effect in a Dirac Kagome Magnet Fe3Ge Chunqiang Xu 1,2, Shuvankar Gupta 2, Hengxin Tan 3, Hyeonhu Bae 3, Olajumoke Oluwatobiloba Emmanuel 2, Mingyu Xu 4, Yan Wu 5, Xiaofeng Xu 6, Pengpeng Zhang2, Weiwei Xie4, Binghai Yan3, Xianglin Ke2 1 School of Physical Science and Technology, Ningbo University, ...

    work page doi:10.1038/s41535-018-0137-9 2018

  2. [2]

    Golovin, I. S. Structural and magnetic phase transitions in Fe3Ge: A neutron diffraction study. Phy. Rev. Mater. 7, 063603 doi:10.1103/PhysRevMaterials.7.063603 (2023). 34 Drijver, J. W., Sinnema, S. G. & Woude, F. Magnetic properties of hexagonal and cubic Fe3Ge. J. Phys. F: Met. Phys 6, 2165 (1976). 18 35 Onoda, S., Sugimoto, N. & Nagaosa, N. Intrinsic ...

    work page doi:10.1103/physrevmaterials.7.063603 2023

  3. [3]

    Science 291, 30, doi:10.1126/science.1058161 (2001)

    Chirality, Berry Phase, andAnomalous Hall Effect in aFrustrated Ferromagnet. Science 291, 30, doi:10.1126/science.1058161 (2001). 54 Ishizuka, H. & Nagaosa, N. Spin chirality induced skew scattering and anomalous Hall effect in chiral magnets. Sci. Adv. 4, eaap9962, doi:10.1126/sciadv.aap996 (2018). 55 Madhogaria, R. P. et al. Topological Nernst and topol...

    work page doi:10.1126/science.1058161 2001