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arxiv: 2507.09870 · v3 · pith:RWJVYT3Znew · submitted 2025-07-14 · ❄️ cond-mat.str-el

Intertwined charge, spin, and orbital degrees of freedom under electronic correlations in the one-dimensional Fe³⁺ chalcogenide chain

Yang Zhang , Pontus Laurell , Gonzalo Alvarez , Adriana Moreo , Thomas A. Maier , Ling-Fang Lin , Elbio Dagotto This is my paper

Pith reviewed 2026-05-19 05:26 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords Fe3+ chalcogenide chainorbital-selective Mott phasecharge fluctuationsthree-orbital Hubbard modelantiferromagnetic couplingone-dimensional iron systemselectronic correlations
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The pith

In the intermediate correlation regime, the Fe3+ chalcogenide chain develops an orbital-selective Mott phase where localized and itinerant electrons coexist, with no detectable pairing tendency.

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

The paper studies electronic correlations in a one-dimensional Fe3+ chalcogenide chain motivated by similar structures in Fe2+ systems. First-principles calculations yield a comparable electronic structure, leading to a three-orbital Hubbard model that is solved with the density matrix renormalization group method. In the intermediate U/W regime the model exhibits orbital-selective behavior in charge fluctuations, indicating a Mott phase that mixes localized and itinerant electrons. A robust antiferromagnetic coupling appears along the chain direction. No pairing correlations emerge in the same parameter window where ladders had shown them, implying that superconductivity is unlikely to appear in Fe3+ chains.

Core claim

In the intermediate electronic correlation U/W region, an orbital-selective Mott phase with the coexistence of localized and itinerant electrons is found based on orbital-selective behavior in charge fluctuations. A robust antiferromagnetic coupling is present along the chain. No obvious pairing tendency is observed, in contrast to iron ladders, indicating that superconductivity is unlikely to emerge in the Fe3+ systems.

What carries the argument

Three-orbital Hubbard model derived from first-principles calculations and solved by density matrix renormalization group, whose orbital-selective charge fluctuations signal the coexistence of localized and itinerant electrons.

If this is right

  • Antiferromagnetic order remains robust along the chain direction across the studied correlation range.
  • The Fe3+ chain shares the electronic structure of the Fe2+ chain but lacks the pairing instability reported for iron ladders.
  • Superconductivity is disfavored in Fe3+ chalcogenide chains relative to related ladder compounds.
  • The orbital-selective Mott regime separates localized and itinerant electrons without generating pairing.

Where Pith is reading between the lines

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

  • Material searches could target compounds whose effective U/W falls outside the intermediate window to test whether pairing can be recovered.
  • Comparison of measured spin and charge responses in real Fe3+ chains would directly test whether the model's orbital selectivity survives beyond the Hubbard approximation.
  • The absence of pairing suggests that dimensional or orbital differences between chains and ladders control the emergence of superconductivity more than the Fe valence alone.

Load-bearing premise

The three-orbital Hubbard model taken from first-principles calculations faithfully represents the low-energy physics of the real Fe3+ chain.

What would settle it

Experimental measurement of charge fluctuations or spectral functions that shows all orbitals behaving identically rather than selectively, or direct observation of pairing correlations in the intermediate U/W window.

Figures

Figures reproduced from arXiv: 2507.09870 by Adriana Moreo, Elbio Dagotto, Gonzalo Alvarez, Ling-Fang Lin, Pontus Laurell, Thomas A. Maier, Yang Zhang.

Figure 1
Figure 1. Figure 1: FIG. 1. (a) Schematic crystal structure of BaFe [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. (a) Density of states near the Fermi level of BaFe [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. (a) The non-interacting tight-binding band structure [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. (a) Orbital-resolved occupation number [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5. (a) Orbital-resolved occupation number [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. The calculated binding energy vs electronic correlation [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. (a) Spin-spin correlation [PITH_FULL_IMAGE:figures/full_fig_p009_7.png] view at source ↗
read the original abstract

Motivated by recent developments in the study of quasi-one-dimensional iron systems with Fe$^{2+}$, we comprehensively study the Fe$^{3+}$ chalcogenide chain system. Based on first-principles calculations, the Fe$^{3+}$ chain has a similar electronic structure as discussed before in the iron 2+ chain, due to similar Fe$X_4$ ($X$ = S or Se) tetrahedron chain geometry. Furthermore, a three-orbital electronic Hubbard model for this chain was constructed by using the density matrix renormalization group method. A robust antiferromagnetic coupling was unveiled in the chain direction. In addition, in the intermediate electronic correlation $U/W$ region, we found an interesting orbital-selective Mott phase with the coexistence of localized and itinerant electrons ($U$ is the on-site Hubbard repulsion, while $W$ is the electronic bandwidth) {\color{blue}based on the orbital-selective behavior observed in the charge fluctuations}. Furthermore, we do not observe any obvious pairing tendency in the Fe$^{3+}$ chain in the electronic correlation $U/W$ region, where superconducting pairing tendencies were reported before in iron ladders. This suggests that superconductivity is unlikely to emerge in the Fe$^{3+}$ systems. Our results establish with clarity the similarities and differences between Fe$^{2+}$and Fe$^{3+}$ iron chains, as well as iron ladders.

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

1 major / 1 minor

Summary. The manuscript studies the electronic correlations in one-dimensional Fe^{3+} chalcogenide chains. First-principles calculations are used to derive a three-orbital Hubbard model for the FeX_4 tetrahedron chain geometry, which is then solved with DMRG. The work reports robust antiferromagnetic coupling along the chain direction and, in the intermediate U/W regime, an orbital-selective Mott phase with coexistence of localized and itinerant electrons, identified via orbital-selective charge fluctuations. No significant pairing tendencies are observed, in contrast to Fe^{2+} chains and iron ladders, leading to the conclusion that superconductivity is unlikely in Fe^{3+} systems.

Significance. If the orbital-selective Mott phase is robustly established beyond charge-fluctuation diagnostics, the work clarifies distinctions between Fe^{3+} and Fe^{2+} chains and between chains and ladders, adding to the understanding of orbital-selective physics in quasi-1D iron chalcogenides. The first-principles model construction combined with DMRG provides a reproducible workflow and falsifiable predictions for correlation-driven phases.

major comments (1)
  1. Abstract and the section describing the orbital-selective Mott phase: the identification rests on orbital-selective suppression of charge fluctuations. However, the variance <n(1-n)> can decrease in correlated metals or Luttinger liquids without a charge gap when inter-orbital Hund coupling and hopping are present, as is the case in the three-orbital d^5 model. Orbital-resolved spectral functions, compressibility, or momentum distribution functions demonstrating selective insulation and integer filling are required to confirm true Mott localization and the claimed coexistence of localized and itinerant electrons.
minor comments (1)
  1. Explicit tabulation of all first-principles-derived hopping and interaction parameters (including Hund's J) would improve reproducibility of the DMRG results.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and the constructive comment on the identification of the orbital-selective Mott phase. We address the point below.

read point-by-point responses

  1. Referee: Abstract and the section describing the orbital-selective Mott phase: the identification rests on orbital-selective suppression of charge fluctuations. However, the variance <n(1-n)> can decrease in correlated metals or Luttinger liquids without a charge gap when inter-orbital Hund coupling and hopping are present, as is the case in the three-orbital d^5 model. Orbital-resolved spectral functions, compressibility, or momentum distribution functions demonstrating selective insulation and integer filling are required to confirm true Mott localization and the claimed coexistence of localized and itinerant electrons.

    Authors: We appreciate the referee's observation that suppression of charge fluctuations alone does not unambiguously establish a charge gap or Mott localization, particularly in the presence of inter-orbital Hund coupling within the three-orbital d^5 model. In our calculations, the orbital-selective reduction in <n(1-n)> occurs alongside other indicators, including the formation of local moments and the evolution of spin correlations that are consistent with localized behavior in two orbitals and itinerant character in the third. Nevertheless, we agree that additional diagnostics would strengthen the claim. In the revised manuscript we will expand the relevant section to include orbital occupancies (which approach integer values in the localized orbitals), a brief discussion of the limitations of the charge-fluctuation diagnostic, and references to analogous diagnostics employed in prior studies of orbital-selective Mott phases. We will also explore the feasibility of adding orbital-resolved spectral functions or momentum distributions for representative parameter values. revision: partial

Circularity Check

0 steps flagged

No circularity: results follow from independent first-principles model solved numerically

full rationale

The paper derives a three-orbital Hubbard model from first-principles calculations on the Fe3+ chain geometry, then applies DMRG to obtain charge fluctuation diagnostics across U/W values. The orbital-selective Mott phase identification is presented as an observation of selective suppression in those fluctuations, not as a quantity fitted to or defined by the same data. No equations reduce the output to the input by construction, no self-citation chain carries the central claim, and no ansatz or uniqueness theorem is invoked to force the result. This is a standard model-construction-plus-simulation workflow whose diagnostics remain independent of the target interpretation.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on the domain assumption that the FeX4 tetrahedron geometry produces an electronic structure sufficiently similar to the Fe2+ case to justify reusing the same three-orbital model form; no new free parameters or invented entities are introduced in the abstract.

axioms (1)
  • domain assumption The Fe3+ chain has a similar electronic structure to the Fe2+ chain due to similar FeX4 tetrahedron chain geometry.
    Explicitly stated as the basis for constructing the three-orbital Hubbard model.

pith-pipeline@v0.9.0 · 5814 in / 1332 out tokens · 68172 ms · 2026-05-19T05:26:58.366623+00:00 · methodology

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  • IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear
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    in the intermediate electronic correlation U/W region, we found an interesting orbital-selective Mott phase with the coexistence of localized and itinerant electrons based on the orbital-selective behavior observed in the charge fluctuations

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