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arxiv: 2605.23755 · v1 · pith:E7MSXI5Wnew · submitted 2026-05-22 · ❄️ cond-mat.str-el · cond-mat.supr-con

Kondo singlet from ferromagnetic coupling: an analog of Anderson-Morel superconductivity in the magnetic channel

Ewan Scott , Yaqi Chen , Michael Turaev , Tarkan Yzeiri , Chris Hooley , Krzysztof P. W\'ojcik , Micha{\l} P. Kwasigroch This is my paper

Pith reviewed 2026-05-25 03:04 UTC · model grok-4.3

classification ❄️ cond-mat.str-el cond-mat.supr-con
keywords Kondo effectferromagnetic exchangeheavy Fermi liquidmagnetic impuritiesAnderson-Morel analogysinglet ground statemode-dependent coupling
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The pith

Mode-dependent ferromagnetic exchange between impurities and conduction electrons produces Kondo singlets and stable heavy Fermi liquids.

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

The paper establishes that magnetic impurities coupled to a conduction sea by a fully isotropic ferromagnetic spin-exchange interaction can still develop the standard Kondo effect when the coupling strength varies with the participating electron modes. In the single-impurity setting this produces a screened singlet ground state at low temperature. On a lattice the same mechanism favors a heavy Fermi liquid over magnetic order across a wide parameter range. The construction is presented as the magnetic-channel counterpart to Anderson-Morel superconductivity, where repulsive bare interactions are overcome by mode selectivity.

Core claim

A fully isotropic but mode-dependent ferromagnetic spin-exchange term between impurities and conduction electrons yields a conventional Kondo singlet ground state in the single-impurity case and, for a lattice of impurities, a heavy Fermi liquid that is energetically preferred over magnetic ordering in a broad parameter window; these outcomes constitute an analog of Anderson-Morel superconductivity realized in the spin channel.

What carries the argument

The mode-dependent ferromagnetic spin-exchange interaction, whose variation with conduction-electron modes permits effective low-energy antiferromagnetic scattering despite overall ferromagnetic sign.

If this is right

  • Kondo screening occurs at low temperature even though the bare interaction is ferromagnetic.
  • A lattice of such impurities stabilizes a heavy Fermi liquid over long-range magnetic order.
  • The low-energy physics is controlled by an effective antiferromagnetic coupling generated by the mode selectivity.
  • The construction supplies a concrete route to heavy-fermion behavior without requiring antiferromagnetic bare exchange.

Where Pith is reading between the lines

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

  • Materials with momentum- or orbital-selective exchange could realize this regime experimentally.
  • Transport and thermodynamic signatures of the heavy Fermi liquid should appear without accompanying magnetic order.
  • The same mode-selectivity idea might be applied to other interaction channels beyond the spin-exchange case.

Load-bearing premise

The strength of the ferromagnetic exchange is allowed to depend on which conduction-electron modes participate in the scattering, creating an effective antiferromagnetic channel at low energies.

What would settle it

A calculation or simulation in which the mode dependence is removed entirely, showing that the singlet ground state and the energetic preference for the heavy Fermi liquid both disappear.

Figures

Figures reproduced from arXiv: 2605.23755 by Chris Hooley, Ewan Scott, Krzysztof P. W\'ojcik, Michael Turaev, Micha{\l} P. Kwasigroch, Tarkan Yzeiri, Yaqi Chen.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Schematic illustration of an electron with momen [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: (b), shown for representative parameters. At high temperatures, the RG flow is very similar to the J1 = J2 case. However, below the scale W, it deviates and flows toward the strong-coupling spectrum at the scale cor￾responding to TK. Motivated by the perturbative RG results, we estimate the Kondo temperature by standard Kondo form taken at D˜ = W. This gives TK ≈ W exp  − D α(J1 − J ∗ 1 )  , (6) where J … view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Mean-field solution for the lattice case: (a) A [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Illustration of effective NRG Hamiltonians: (a) con [PITH_FULL_IMAGE:figures/full_fig_p007_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. The Kondo temperature as a function of [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
read the original abstract

We consider magnetic impurities coupled to a conduction sea via a fully isotropic ferromagnetic spin-exchange term, the strength of which depends on the conduction-electron modes involved in the scattering. In the single-impurity case we show both analytically and numerically that there exists a parameter regime in which the conventional Kondo effect develops at low temperatures, leading to a singlet ground state. In the case of a lattice of impurities, we show that this leads to a heavy Fermi liquid state that is energetically favored over magnetic ordering in a broad parameter range. We argue that these effects are analogs of Anderson-Morel superconductivity, and discuss routes to their experimental realization.

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

0 major / 2 minor

Summary. The paper considers magnetic impurities coupled to conduction electrons via a fully isotropic but mode-dependent ferromagnetic spin-exchange interaction. It claims that in the single-impurity case there exists a parameter regime where the conventional Kondo effect develops at low T, producing a singlet ground state, supported by both analytic and numeric arguments. For a lattice of impurities, the same mechanism is argued to stabilize a heavy Fermi liquid that is energetically preferred over magnetic ordering over a broad parameter range. The effects are presented as magnetic-channel analogs of Anderson-Morel superconductivity.

Significance. If the central claims hold, the work would demonstrate a route to Kondo screening and heavy-fermion behavior starting from ferromagnetic coupling, provided the exchange is allowed to depend on the participating conduction-electron modes. This would enlarge the set of microscopic mechanisms capable of producing singlet formation and coherent heavy quasiparticles, and could motivate searches for analogous physics in engineered or natural systems with momentum-dependent exchange.

minor comments (2)
  1. The abstract states that both analytic and numeric support exist for the single-impurity regime, but the manuscript should make explicit the form of the mode-dependent J(k,k') and the cutoff or regularization used in the analytic treatment so that the claimed parameter regime can be reproduced.
  2. For the lattice case, the energetic comparison between the heavy Fermi liquid and magnetic ordering should be quantified with explicit energy scales or variational parameters rather than left at the level of a qualitative argument.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their report, which accurately summarizes the manuscript and notes its potential significance if the central claims are substantiated. The recommendation is listed as uncertain, but the report contains no specific major comments to address.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper's central claims rest on explicit analytical derivations and numerical evidence for a Kondo singlet regime arising from mode-dependent ferromagnetic exchange, followed by a lattice extension to a heavy Fermi liquid. No load-bearing step reduces by construction to a fitted parameter, self-definition, or self-citation chain; the mode dependence is introduced as an explicit modeling choice that permits effective antiferromagnetic scattering at low energies, and the singlet/FL outcomes are computed outcomes rather than definitional equivalences. The derivation chain is therefore self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The central claim rests on the introduction of a mode-dependent ferromagnetic exchange term whose functional form is not fixed by prior literature; this term is the key modeling ingredient that enables the reported effect.

free parameters (1)
  • mode-dependent exchange function J(k,k')
    The strength of the ferromagnetic coupling is stated to depend on the conduction-electron modes; the specific functional form is a free modeling choice required for the effect to appear.
axioms (1)
  • domain assumption The exchange interaction is fully isotropic and ferromagnetic.
    Explicitly stated in the abstract as the form of the coupling.

pith-pipeline@v0.9.0 · 5665 in / 1272 out tokens · 28142 ms · 2026-05-25T03:04:20.759255+00:00 · methodology

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Reference graph

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