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REVIEW 3 major objections 4 minor 44 references

Strong antisymmetric spin-orbit coupling and superconducting properties: The case of noncentrosymmetric LaPtSi

T0 review · 3 major / 4 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read Strong spin-orbit coupling fails to break s-wave pairing in LaPtSi.

desk verdict First deep-penetration-depth data for LaPtSi show a robust fully gapped response, but the dirty-s-wave and spin-singlet-dominance conclusions are more qualitative than the abstract claims. read the letter →

arxiv 1908.08828 v1 pith:U4ZBTXHB submitted 2019-08-23 cond-mat.supr-con

S. Palazzese , J. F. Landaeta , D. Subero , E. Bauer , I. Bonalde This is my paper · ORCID
classification cond-mat.supr-con
keywords noncentrosymmetricsuperconductorsantisymmetricspin-orbitcouplingmagneticpenetrationdepthdirtys-wavesuperconductivityBCSenergygaptopologicalLaPtSi
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 paper sets out to settle the gap structure of the noncentrosymmetric superconductor LaPtSi, a material whose antisymmetric spin-orbit coupling is among the strongest known relative to its critical temperature. By measuring the magnetic penetration depth down to 0.02 Tc, the authors find that the data flatten below about 0.2 Tc and that a dirty local s-wave model fits the low-temperature tail with a zero-temperature gap Δ0 = 1.73 kBTc, close to the BCS value of 1.76. They conclude that the spin-singlet component of the mixed pairing state is highly dominant, that a strong antisymmetric spin-orbit coupling alone does not generate nodes or unconventional behavior, and that LaPtSi is not a promising host for time-reversal-invariant nodal topological superconductivity.

What carries the argument

The central object is the magnetic penetration depth $\Delta\lambda(T)$ measured with a 13.5 MHz tunnel diode oscillator down to about 50 mK. The argument is carried by comparing two functional fits to the low-temperature data: the clean local BCS model, $\Delta\lambda \propto \sqrt{\pi\Delta_0/2k_B T}\,\exp(-\Delta_0/k_B T)$, and the dirty local s-wave model, $\Delta\lambda \propto \exp(-\Delta_0/k_B T)$. The dirty model is applicable because previous work reports a mean free path $l = 43$ Å and a coherence length $\xi_{GL}(0) = 338$ Å, placing the material deep in the dirty limit. The dirty fit's success, with $\Delta_0 = 1.73\,k_B T_c$, is what converts a flat low-temperature tail into the claim of a fully gapped spin-singlet state.

What would settle it

Measure the penetration depth, specific heat, or thermal conductivity of a cleaner LaPtSi single crystal below 0.02 Tc: a power-law tail, such as $\Delta\lambda \propto T^n$ with $n < 3$, or a finite residual linear term in the specific heat would show that the supposed s-wave gap actually has nodes or that the dirty s-wave fit is masking another gap structure.

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Extended reading notes

Core claim

The central claim is that LaPtSi is a conventional, fully gapped s-wave superconductor in the dirty limit. The evidence is the exponential low-temperature penetration depth that flattens below 0.2 Tc, fitted by the dirty local s-wave expression $\Delta\lambda(T) \propto \exp(-\Delta_0/k_B T)$ up to 0.5 Tc with $\Delta_0 = 1.73\,k_B T_c$, nearly identical to the BCS ratio. Because the gap shows no zeros, the authors argue that the spin-singlet component of the parity-mixed pairing state dominates. They then generalize: among noncentrosymmetric superconductors, unconventional gap structures appear only in materials with magnetic order or proximity to a magnetic instability, not simply in those with very large $E_{\mathrm{SO}}/k_B T_c$. Consequently the fully gapped state excludes LaPtSi as a candidate for time-reversal-invariant nodal topological superconductivity, although field-induced topological phases remain possible.

Load-bearing premise

The argument depends on the low-temperature flattening being intrinsic bulk behavior rather than a surface artifact, and on the previously reported dirty-limit parameters applying to this particular sample.

Editorial extensions

If this is right

  • If the claim is correct, LaPtSi should show no residual low-temperature quasiparticle excitations: thermal conductivity, specific heat, and penetration depth should all continue to follow activated exponential forms below 0.2 Tc.
  • The compound can be removed from the short list of candidates for time-reversal-invariant nodal topological superconductivity among noncentrosymmetric materials.
  • The comparative pattern implies that searches for unconventional gap structures in noncentrosymmetric superconductors should weight magnetic proximity more heavily than the ratio $E_{\mathrm{SO}}/k_B T_c$.
  • The earlier specific-heat data that suggested BCS-like behavior down to 0.67 Tc are confirmed and extended into the true low-temperature regime.
  • A fully gapped state leaves open the field-induced topological route discussed in the paper, which does not require the spin-triplet component to be large.

Reading between the lines

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

  • A sharper test of the s-wave assignment would be thermal-conductivity or specific-heat measurements below 0.1 Tc on a cleaner sample; a residual linear term or power-law tail would indicate that surface irregularities are masking nodes.
  • The paper's comparative pattern suggests a testable prediction: noncentrosymmetric superconductors without a magnetic instability should remain fully gapped, so measuring gap structures in the remaining uncharacterized strong-ASOC materials would check this directly.
  • If the dirty s-wave picture holds, the most interesting remaining topological route for LaPtSi is the field-induced phase; angle-resolved or field-dependent penetration-depth measurements could look for that transition.
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Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

3 major / 4 minor

Summary. The manuscript reports magnetic penetration depth measurements on polycrystalline noncentrosymmetric LaPtSi down to 0.02 Tc. The authors observe that the low-temperature penetration depth flattens below about 0.2 Tc, fit the data to clean and dirty local s-wave exponential formulas, and conclude that the dirty s-wave model describes the data better, yielding a zero-temperature gap Δ0 = 1.73 kBTc. They interpret this as evidence that the spin-singlet component of the mixed pairing state is highly dominant and that LaPtSi is not a candidate for time-reversal invariant nodal topological superconductivity. A survey of noncentrosymmetric superconductors is used to argue that unconventional behavior requires proximity to magnetic instability rather than strong antisymmetric spin-orbit coupling alone.

Significance. If the central claim is correct, the paper provides useful evidence that strong antisymmetric spin-orbit coupling does not by itself drive unconventional pairing, and it strengthens the empirical pattern that magnetic correlations are the common ingredient in noncentrosymmetric superconductors with nodal gaps. The measurement itself is significant because the penetration depth is taken to an unusually low reduced temperature, and the saturation of Δλ(T) below 0.2 Tc is a genuine qualitative indicator of a nodeless gap. The fitted Δ0 close to the BCS value is also suggestive. However, the key inference depends on model-comparison and parameter-estimation steps that are not quantitatively documented, so the headline conclusion outruns the presented analysis.

major comments (3)
  1. [Section 3, Eq. (2)] The identification of dirty s-wave pairing rests on a visual comparison of Eq. (1) and Eq. (2), with no fit statistics, residuals, or parameter uncertainties. The reported Δ0 = 1.73 kBTc is given without an error bar, so the reader cannot assess whether the clean model is statistically excluded or whether a single exponential with a different prefactor would also describe the data. Please report χ² values or an equivalent goodness-of-fit criterion, uncertainties on Δ0, and residual plots, and preferably fit the full local BCS and dirty-limit expressions rather than only the low-temperature asymptotes up to 0.5 Tc.
  2. [Section 3, Fig. 1] The flattening below 0.2 Tc is strong qualitative evidence for a nodeless gap, but it does not uniquely select isotropic s-wave pairing: a fully gapped two-gap state, a small second gap, or nodes partly filled by impurity scattering can also produce a saturating curve over the measured range. Since the paper's central claim is that the spin-singlet component is 'highly dominant,' the authors should fit at least one nodal model and one two-gap model to the same data and report which model is preferred. A nodeless gap alone does not constrain the singlet/triplet ratio, because a fully gapped mixed-parity state can still contain a substantial triplet admixture.
  3. [Section 3, text following Eq. (2)] The dirty-limit justification uses l = 43 Å and ξ(0) = 338 Å taken from ref [22], a different sample, rather than from measurements on the polycrystalline sample used here. The exponential dirty-limit form in Eq. (2) and the extracted Δ0 depend on this assumption. Please either characterize the mean free path of the measured sample (e.g., from resistivity or upper critical field) or demonstrate that the fitted Δ0 and the s-wave versus nodal distinction are robust over a plausible range of l/ξ0. Without this, the dirty-limit assignment and the s-wave conclusion remain conditional.
minor comments (4)
  1. [Sample preparation, Section 2] The verb 'cutted' should be 'cut', and 'reaffirming' in the results section is a typographical error.
  2. [Eq. (1)] Equation (1) is ambiguous: the square-root sign should be shown with explicit parentheses, e.g., (πΔ0/(2kBT))^{1/2}, to distinguish the quoted prefactor from √(πΔ0)/(2kBT).
  3. [Fig. 1 caption] The statement that the error bars are the size of the dots needs a numerical indication of the measurement uncertainty; as printed, no error bars are visible in the figure.
  4. [Table I] The selection criterion for Table I is stated as ESO/kBTc > 500 or a nodal gap, but Y2C3 is included despite a reported ratio below 10; the criterion should be stated more precisely so the table entries are self-consistent.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the central dirty s-wave assignment is an empirical fit to new penetration-depth data, checked against an external BCS gap value and external dirty-limit parameters.

full rationale

The paper's central claim is that LaPtSi shows dirty s-wave behavior, inferred by fitting the measured low-temperature penetration depth to Eqs. (1) and (2) and obtaining a gap Delta_0 = 1.73 k_B T_c, close to the BCS value of 1.76 k_B T_c. This is standard parameter estimation from the same data, not a prediction forced by construction: the data could in principle have preferred a different functional form or a different gap ratio, and the BCS comparison is against an external constant. The use of the dirty-limit model in Eq. (2) is justified by independently reported values of the coherence length and mean free path from ref. [22], not by the present fit. The conclusion about spin-singlet dominance and the downplaying of topological candidacy are interpretive consequences of a fully gapped, isotropic gap, not assumptions built into the fit. The paper includes self-citations, but none are load-bearing for the central inference: the penetration-depth data, the fit forms, and the dirty-limit parameters come from this work and from independent prior measurements. Concerns that competing nodal or two-gap models were not quantitatively tested, or that the dirty-limit parameters may not apply to this exact polycrystalline sample, are correctness and robustness issues, not circularity. No equation is defined in terms of the conclusion, and no fitted parameter is relabeled as a prediction. The derivation chain is therefore self-contained with respect to circularity.

Assumptions & free parameters 1 free parameters · 4 assumptions · 0 invented entities

The central claim depends on fitting a single free parameter, the zero-temperature gap Δ0, to the low-temperature penetration depth. The dirty-limit model is taken from prior transport parameters (l=43 Å, ξ=338 Å) rather than measured here. The paper also asserts, without quantitative support, that a near-3K irregularity is a surface artifact. No invented physical entities are introduced.

free parameters (1)
  • Δ0 (zero-temperature superconducting energy gap) = 1.73 kBTc
    Fitted from the exponential decay of Δλ(T) in the dirty local s-wave model (Eq. 2); compared to the BCS value 1.76kBTc to support conventional pairing.
assumptions (4)
  • domain assumption Dirty local limit applies: mean free path l=43 Å << coherence length ξ(0)=338 Å
    Inherited from ref [22] for LaPtSi; used to select the dirty s-wave model (Eq. 2) over the clean model (Eq. 1).
  • standard math Low-temperature penetration depth formulas (Eqs. 1 and 2) are valid approximations for s-wave superconductors in the clean and dirty local limits
    Standard BCS/Tinkham results taken as given; the paper does not derive them.
  • domain assumption Calibration constant G, estimated from a sample of known behavior with the same dimensions, is accurate
    Needed to convert frequency shifts into absolute penetration depth changes; described qualitatively in the experimental section.
  • ad hoc to paper The irregular penetration depth behavior around 3 K is caused by surface irregularities and does not affect the intrinsic low-temperature signal
    Invoked in the text to explain an anomaly without independent modeling or verification.

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Cite this review

Pith. "Pith review of Strong antisymmetric spin-orbit coupling and superconducting properties: The case of noncentrosymmetric LaPtSi." pith.science (2026). https://pith.science/paper/U4ZBTXHB

@misc{pith2026190808828,
  author       = {Pith},
  title        = {Pith review of: Strong antisymmetric spin-orbit coupling and superconducting properties: The case of noncentrosymmetric LaPtSi},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/U4ZBTXHB}},
  note         = {Machine review of arXiv:1908.08828}
}
abstract

In this work we aim to analyze the effect of a strong antisymmetric spin-orbit coupling (ASOC) on superconductivity of noncentrosymmetric LaPtSi. We study the energy gap structure of polycrystalline LaPtSi by using magnetic penetration depth measurements down to 0.02$T_c$. We observed a dirty s-wave behavior, which provides compelling evidence that the spin-singlet component of the mixed pairing state is highly dominant. This is consistent with previous results in the sense that the mere presence of a strong ASOC does not lead to unconventional behaviors. Our result also downplays LaPtSi as a good candidate for realizing time-reversal invariant topological superconductivity.

Figures

Figures reproduced from arXiv: 1908.08828 by the authors.

Figure 1
Figure 1. FIG. 1: Magnetic penetration depth of LaPtSi in the low-temperature regime fitted to clean and [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗

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Works this paper leans on

44 extracted references · 44 canonical work pages

  1. [22]

    Ramakrishnan S, Ghosh K, Chinchure A D, Marathe V R and Chandra G 1995 Phys. Rev. B 52 6784–6795

    work page 1995

  2. [1]

    Frigeri P A, Agterberg D F, Koga A and Sigrist M 2004 Phys. Rev. Lett. 92 097001

    work page 2004

  3. [2]

    Bonalde I, Br¨ amer-Escamilla W and Bauer E 2005 Phys. Rev. Lett. 94 207002

    work page 2005

  4. [3]

    Hayashi N, Wakabayashi K, Frigeri P A and Sigrist M 2006 Phys. Rev. B 73 024504

    work page 2006

  5. [4]

    Yuan H Q, Vandervelde D, Salamon M B, Badica P and Togano K 2006 AIP Conf. Proc. 850 633–634

    work page 2006

  6. [5]

    Ribeiro R L, Bonalde I, Haga Y, Settai R and ¯Onuki Y 2009 J. Phys. Soc. Jpn 78 115002

    work page 2009

  7. [6]

    Fujimoto S 2006 J. Phys. Soc. Jpn. 75 083704

    work page 2006

  8. [7]

    Smidman M, Hillier A D, Adroja D T, Lees M R, Anand V K, Singh R P, Smith R I, Paul D M and Balakrishnan G 2014 Phys. Rev. B 89 094509

    work page 2014

Show all 44 references
  1. [8]

    Phys.: Condens

    Ribeiro R, Caraballo R, Rogl P, Bauer E and Bonalde I 2014 J. Phys.: Condens. Matter 26 235701

    2014

  2. [9]

    Pang G M, Smidman M, Zhao L X, Wang Y F, Weng Z, Che L Q, Chen Y, Lu X, Chen G F and Yuan H Q 2016 Phys. Rev. B 93 060506

    2016

  3. [10]

    Sereni J G, Nieva G L, Huber J G and DeLong L E 1994 Physica C 230 159–162

    1994

  4. [11]

    Singh R P, Hillier A D, Chowdhury D, Barker J A T, Paul D M, Lees M R and Balakrishnan G 2014 Phys. Rev. B 90 104504

    2014

  5. [12]

    Pang G M, Smidman M, Jiang W B, Shi Y G, Bao J K, Tang Z T, Weng Z F, Wang Y F, 7 Jiao L, Zhang J L, Luo J L, Cao G H and Yuan H Q 2016 J. Magn. Magn. Mater 400 84–87

    2016

  6. [13]

    Bauer E and Sigrist M (eds) 2012 Non-centrosymmetric Superconductors: Introduction and Overview (Lecture Notes in Physics vol 847) (Berlin-Heidelberg: Springer-Verlag)

    2012

  7. [14]

    Landaeta J F, Subero D, Machado P, Honda F and Bonalde I 2017 Phys. Rev. B 96 174515

    2017

  8. [15]

    Landaeta J F, Subero D, Catal´ a D, Taylor S V, Kimura N, Settai R, Onuki Y, Sigrist M and Bonalde I 2017 ( Preprint arXiv:1702.06812)

    2017 arXiv

  9. [16]

    Sato M and Fujimoto S 2009 Phys. Rev. B 79 094504

    2009

  10. [17]

    Schnyder A P and Ryu S 2011 Phys. Rev. B 84 060504

    2011

  11. [18]

    Schnyder A P, Brydon P M R and Timm C 2012 Phys. Rev. B 85 024522

    2012

  12. [19]

    Phys.: Condens

    Schnyder A P and Brydon P M R 2015 J. Phys.: Condens. Matter 27 243201

    2015

  13. [20]

    Ghosh P, Sau J D, Tewari S and Sarma S D 2010 Phys. Rev. B 82 184525

    2010

  14. [21]

    Kneidinger F, Michor H, Sidorenko A, Bauer E, Zeiringer I, Rogl P, Blaas-Schenner C, Reith D and Podloucky R 2013 Phys. Rev. B 88 104508

    2013

  15. [23]

    Tinkham M 1996 Introduction to Superconductivity International Series in Pure and Applied Physics (Berlin Heidelberg: McGraw-Hill)

    1996

  16. [24]

    ¯Onuki Y and Settai R 2012Non-centrosymmetric Superconductors: Introduction and Overview (Lecture Notes in Physics vol 847) ed Bauer E and Sigrist M (Berlin Heidelberg: Springer- Verlag) chap 3, pp pp. 81–125

  17. [25]

    Samokhin K V, Zijlstra E S and Bose S K 2004 Phys. Rev. B 69 094514

    2004

  18. [26]

    Bauer E, Khan R T, Michor H, Royanian E, Grytsiv A, Melnychenko-Koblyuk N, Rogl P, Reith D, Podloucky R, Scheidt E W, Wolf W and Marsman M 2009 Phys. Rev. B 80 064504

    2009

  19. [27]

    Ali M N, Gibson Q D, Klimczuk T, Cava R J 2014 Phys. Rev. B 89 020505

    2014

  20. [28]

    Bian G, Chang T R, Sankar R, Xu S Y, Zheng H, Neupert T, Chiu C K, Huang S M, Chang G, Belopolski I, Sanchez D S, Neupane M, Alidoust N, Liu C, Wang B, Lee C C, Jeng H T, Zhang C, Yuan Z, Jia S, Bansil A, Chou F, Lin H and Hasan M Z 2016 Nat. Commun. 7 10556

    2016

  21. [29]

    Winiarski M and Samsel-Czekala M 2015 Intermetallics 56 44–47

    2015

  22. [30]

    Lee K W and Pickett W E 2005 Phys. Rev. B 72 174505

    2005

  23. [31]

    Takeya H, Hirata K, Yamaura K, Togano K, El Massalami M, Rapp R, Chaves F A and 8 Ouladdiaf B 2005 Phys. Rev. B 72 104506

    2005

  24. [32]

    Eguchi G, Peets D C, Kriener M, Yonezawa S, Bao G, Harada S, Inada Y, Zheng G Q and Maeno Y 2013 Phys. Rev. B 87 161203

    2013

  25. [33]

    Alloys Compd

    Uzunok H, Ipsara E, T¨ ut¨ uncu H M, Srivastava G P and Ba¸ soglu A 2016J. Alloys Compd. 681 205–211

  26. [34]

    Sahakyan M and Tran V H 2017 Philos. Mag. 1478–6643

    2017

  27. [35]

    Jiang H, Cao G and Cao C 2015 Sci. Rep. 5 16054

    2015

  28. [36]

    Terashima T, Kimata M, Uji S, Sugawara T, Kimura N, Aoki H and Harima H 2008 Phys. Rev. B 78 205107

    2008

  29. [37]

    Hirose Y, Kishino T, Sakaguchi J, Miura Y, Honda F, Takeuchi T, Etsuji Y, Haga Y, Harima H, Settai R and Onuki Y 2012 J. Phys. Soc. Jpn. 81 113703

    2012

  30. [38]

    Lee W H, Zeng H K, Yao Y D and Chen Y Y 1996 Physica C 266 138–142

    1996

  31. [39]

    Bonalde I, Ribeiro R L, Syu K J, Sung H H and Lee W H 2011 New J. Phys. 13 123022

    2011

  32. [40]

    Mukuda H, Fujii T, Ohara T, Harada A, Yashima M, Kitaoka Y, Okuda Y, Settai R and nuki Y 2008 Phys. Rev. Lett. 100 107003

    2008

  33. [41]

    Yusuke N, Tatsuya S and Tamio O 2007 J. Phys. Soc. Jpn. 76 064714

    2007

  34. [42]

    Akutagawa S and Akimitsu J 2006 Sci. Technol. Adv. Mate 7 2–5

    2006

  35. [43]

    Chen J, Salamon M B, Akutagawa S, Akimitsu J, Singleton J, Zhang J L, Jiao L and Yuan H Q 2011 Phys. Rev. B 83 144529

    2011

  36. [44]

    Yanase Y and Sigrist M 2007 J. Phys. Soc. Jpn. 76 043712 9

    2007

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