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REVIEW 2 major objections 2 minor 36 references

Tuning topological phase and Dirac point position via Pb and Sb substitution in Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$

T0 review · 2 major / 2 minor · reviewed 2026-07-01 · grok-4.3

Pith's one-line read Pb concentration alone determines the bulk band gap in Mn1-xPbx(Bi1-ySby)2Te4 and closes it at 40-50 percent Pb to drive a topological phase transition.

desk verdict Pb concentration alone closes the gap at 40-50% while the Pb/Sb ratio sets Dirac point position, giving independent tuning in this family. read the letter →

arxiv 2606.31525 v1 pith:MNBY5TJZ submitted 2026-06-30 cond-mat.mtrl-sci

classification cond-mat.mtrl-sci
keywords topologicalphasetransitionmagneticinsulatorbandgaptuningDiracpointpositionPbsubstitutionSbMnBi2Te4
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The study maps a wide range of Pb and Sb substitutions in MnBi2Te4 crystals. Measurements show the bulk gap size tracks Pb content only, vanishing between 40 and 50 percent Pb and crossing from a topological to a trivial phase. The Dirac point energy inside the gap is fixed by the Pb-to-Sb ratio instead of the absolute Sb amount. Magnetism weakens as Pb dilutes the Mn layers but shows little response to Sb. Dual substitution therefore separates control of the topological character from the Fermi-level position.

What carries the argument

Dual substitution of Pb on the Mn site to set gap size and topological phase, paired with Sb on the Bi site to shift the Dirac point without changing the gap.

What would settle it

A bulk-sensitive measurement showing the gap remaining open or closing outside the 40-50 percent Pb window would contradict the claim that gap size depends exclusively on Pb concentration.

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Extended reading notes

Core claim

The value of the bulk band gap is determined exclusively by the Pb concentration and it closes at Pb 40-50 %, which corresponds to a topological phase transition. The position of the Dirac point is determined by the Pb/Sb ratio, rather than the absolute Sb content. The magnetic properties depend on the dilution of the Mn sublattice by Pb and are weakly sensitive to Sb. Simultaneous substitution of Mn and Bi allows independent control of the topological phase and the position of the Fermi level.

Load-bearing premise

Spectroscopic measurements accurately capture bulk electronic changes driven only by the substitution levels without dominant surface states, defects, or compositional variation that could mimic the reported Pb-only dependence.

Editorial extensions

If this is right

  • The topological phase can be switched by changing only the Pb fraction.
  • The Dirac point can be placed at a chosen energy by adjusting the Pb/Sb ratio at fixed Pb.
  • Magnetic ordering strength is set mainly by how much Pb dilutes the Mn lattice.
  • Device designs can target a desired topological state and Fermi level alignment independently.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • The same two-site substitution approach could be tested in related magnetic topological families to achieve decoupled tuning.
  • Transport or optical experiments at the critical Pb concentration could check whether the gap closure produces the expected change in bulk conductivity.
  • Careful surface versus bulk separation in future probes would be needed to confirm that the Pb dependence is truly intrinsic.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 2 minor

Summary. The manuscript reports a systematic experimental study of Mn_{1-x}Pb_x(Bi_{1-y}Sb_y)_2Te_4 single crystals over x = 10-60% and y = 5-60%. It claims that the bulk band gap depends exclusively on Pb concentration and closes at 40-50% Pb, corresponding to a topological phase transition; the Dirac point position tracks the Pb/Sb ratio rather than absolute Sb content; and magnetic properties are governed by dilution of the Mn sublattice by Pb with weak sensitivity to Sb. The dual substitution is presented as enabling independent control over the topological phase and Fermi level position.

Significance. If the reported concentration dependences hold, the work demonstrates a practical route to decouple topological phase tuning (via Pb) from Dirac-point/Fermi-level positioning (via Pb/Sb ratio) in the MnBi2Te4 family. This is potentially useful for realizing desired alignments between the Dirac point and Fermi level in magnetic topological insulators. The wide concentration range explored and the observation that magnetism tracks Mn dilution are internally consistent with the substitution strategy.

major comments (2)
  1. [Results (gap extraction and concentration series)] The central claim that the bulk gap is determined exclusively by Pb concentration (and independent of y at fixed x) is load-bearing for the topological-phase-transition conclusion, yet the manuscript provides insufficient detail on data quality, error bars, or sample-to-sample variability in the ARPES or transport measurements used to extract the gap values. Without these, it is difficult to confirm that apparent independence from Sb lies outside experimental uncertainty.
  2. [Results (Dirac point vs. composition)] The assertion that Dirac-point position depends only on the Pb/Sb ratio (rather than absolute Sb) requires explicit demonstration that, at fixed Pb/Sb, varying total substitution level produces no shift; the current presentation does not include a dedicated control series or statistical test for this independence.
minor comments (2)
  1. [Methods / ARPES section] Clarify the precise method (e.g., fitting procedure, photon energy, or surface vs. bulk sensitivity) used to extract the bulk gap values reported in the abstract.
  2. [Experimental methods] Add a table or supplementary figure summarizing the actual measured compositions (via EDX or similar) for each nominal (x,y) point to allow readers to assess deviation from target stoichiometry.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments and positive recommendation for minor revision. We address the two major comments point by point below.

read point-by-point responses
  1. Referee: [Results (gap extraction and concentration series)] The central claim that the bulk gap is determined exclusively by Pb concentration (and independent of y at fixed x) is load-bearing for the topological-phase-transition conclusion, yet the manuscript provides insufficient detail on data quality, error bars, or sample-to-sample variability in the ARPES or transport measurements used to extract the gap values. Without these, it is difficult to confirm that apparent independence from Sb lies outside experimental uncertainty.

    Authors: We agree that additional details on data quality and uncertainties would strengthen the presentation. In the revised manuscript we will add error bars to all extracted gap values (from both ARPES and transport), derived from multiple scans per sample and from independent batches. A new supplementary section will quantify sample-to-sample variability at fixed x across different y, showing that the observed gap independence from Sb remains within the stated experimental uncertainty. revision: yes

  2. Referee: [Results (Dirac point vs. composition)] The assertion that Dirac-point position depends only on the Pb/Sb ratio (rather than absolute Sb) requires explicit demonstration that, at fixed Pb/Sb, varying total substitution level produces no shift; the current presentation does not include a dedicated control series or statistical test for this independence.

    Authors: The existing data set contains multiple compositions sharing similar Pb/Sb ratios at different absolute substitution levels, with Dirac-point positions that are consistent within resolution. To address the request for explicit demonstration, the revision will include a supplementary figure that isolates fixed-ratio series and reports a statistical test (regression slope consistent with zero) confirming the absence of systematic shift with total substitution. revision: yes

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity; experimental study with direct measurements

full rationale

The paper is a systematic experimental investigation of crystal substitutions, reporting measured band gaps, Dirac point positions, and magnetic properties as functions of Pb and Sb concentrations. No derivations, equations, theoretical models, or predictions are present that could reduce to inputs by construction. Claims rest on ARPES, transport, and magnetization data from synthesized samples, with no self-citation chains, fitted parameters renamed as predictions, or ansatzes. This matches the default case of self-contained empirical results carrying negligible circularity burden.

Assumptions & free parameters 0 free parameters · 0 assumptions · 0 invented entities

Experimental study; central claims rest on interpretation of measured band structures and magnetic data from flux-grown or Bridgman crystals. No mathematical axioms, free parameters, or new postulated entities are introduced.

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Cite this review

Pith. "Pith review of Tuning topological phase and Dirac point position via Pb and Sb substitution in Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$." pith.science (2026). https://pith.science/paper/MNBY5TJZ

@misc{pith2026260631525,
  author       = {Pith},
  title        = {Pith review of: Tuning topological phase and Dirac point position via Pb and Sb substitution in Mn$_1-x$Pb$_x$(Bi$_1-y$Sb$_y$)$_2$Te$_4$},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/MNBY5TJZ}},
  note         = {Machine review of arXiv:2606.31525}
}
abstract

This study presents a systematic investigation of Mn$_{1-x}$Pb$_{x}$(Bi$_{1-y}$Sb$_{y}$)$_{2}$Te$_{4}$ crystals over a wide range of concentrations (x = 10-60%, y = 5-60%). It was found that the value of the bulk band gap is determined exclusively by the Pb concentration and it closes at Pb 40-50 %, which corresponds to a topological phase transition. The position of the Dirac point is determined by the Pb/Sb ratio, rather than the absolute Sb content. The magnetic properties depend on the dilution of the Mn sublattice by Pb and are weakly sensitive to Sb. We show that the simultaneous substitution of Mn and Bi allows independent control of the topological phase and the position of the Fermi level.

Figures

Figures reproduced from arXiv: 2606.31525 by the authors.

Figure 1
Figure 1. The dispersion relations for Mn1−xPbx(Bi1−ySby)2Te4 samples with varying Pb-values and Sb-values (hν = 21.2 eV). The molar fractions of Pb and Sb are shown at the top of the panels. The Pb concentration increases from left to right, and the Sb concentration increases from top to bottom. enhancement of Rashba-like states is most noticeable at low Sb concentrations (∼ 7%). As Sb increases (> 20%), the Rashba-like stat… view at source ↗
Figure 2
Figure 2. (a) Dependence of the bulk band gap value on Pb [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗
Figure 3
Figure 3. The dispersion relations for Mn1−xPbx(Bi1−ySby)2Te4 samples with varying Pb and Sb concentration (hν = 6.3 eV). The molar fractions of Pb and Sb are shown at the top of the panels. in red and blue) [32]. Thus, CD-ARPES allows one to distinguish TSS from bulk states; however, it does not provide direct information about the spin structure [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figures from the paper (2 more)
Figure 4
Figure 4. Figure 4: Circular dichroism ARPES spectra of Mn1−xPbx(Bi1−ySby)2Te4 at various Pb and Sb concentrations. properties, the samples were grouped into two pairs based on their Pb content (left and right halves of [PITH_FULL_IMAGE:figures/full_fig_p007_4.png]
Figure 5
Figure 5. Figure 5: Temperature dependencies of the magnetic susceptibility [PITH_FULL_IMAGE:figures/full_fig_p008_5.png]

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Reference graph

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