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arxiv: 1907.01776 · v1 · pith:NELOSYUUnew · submitted 2019-07-03 · ❄️ cond-mat.supr-con

The Unusual Suppression of Superconducting Transition Temperature in Double-Doping 2H-NbSe₂

Dong Yan , Yishi Lin , Guohua Wang , Zhen Zhu , Shu Wang , Lei Shi , Yuan He , Man-Rong Li
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Hao Zheng Jie Ma Jinfeng Jia Yihua Wang Huixia Luo
This is my paper

Pith reviewed 2026-05-25 09:53 UTC · model grok-4.3

classification ❄️ cond-mat.supr-con
keywords superconductivitytransition metal dichalcogenidesNbSe2doping effectscharge density wavephase diagram
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The pith

Double doping of 2H-NbSe2 with Cu and S lowers Tc to a stable 2 K plateau at high doping levels.

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

The paper examines how simultaneous Cu intercalation and S substitution affect superconductivity in 2H-NbSe2, a material that normally shows a superconducting transition at 7.3 K alongside a charge-density-wave transition at 33 K. Systematic measurements show that Tc falls steadily as the amounts of Cu and S increase, but then levels off near 2 K once doping reaches higher values. This plateau contrasts with the faster Tc suppression seen when Nb and Se are substituted together in a related compound. The authors map the resulting superconducting phase diagram against single-ion doping cases to probe links between Fermi-surface nesting and the superconducting state.

Core claim

In CuxNbSe2-ySy, Tc decreases with rising Cu and S content but remains constant near 2 K once x and y become large; this saturation is absent in the comparison system CuxNb1-xSe2-ySy, where Tc drops more rapidly, and the authors present the contrasting superconducting phase diagrams for the two double-doping routes.

What carries the argument

The combined Cu intercalation plus S-for-Se substitution that produces CuxNbSe2-ySy and its measured Tc versus doping behavior.

If this is right

  • Tc reaches a doping-independent value near 2 K once both intercalant and substituent concentrations are high.
  • The double-doping route produces a superconducting phase diagram distinct from those obtained by single-ion substitution.
  • Simultaneous Nb-site and Se-site substitution suppresses Tc substantially faster than the Cu-intercalation plus S-substitution route.
  • The plateau occurs in a regime where the material remains a layered TMD yet exhibits an uncommonly flat Tc(x,y) dependence.

Where Pith is reading between the lines

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

  • The stabilized 2 K state may reflect a doping-driven alteration of nesting conditions that leaves a residual pairing channel intact.
  • Comparison of the two double-doping schemes suggests that the location of the dopant (intercalant versus substitutional) controls how quickly the Fermi surface is detuned from the superconducting instability.
  • If the plateau survives in cleaner samples, it could mark a new low-temperature regime whose microscopic order parameter differs from the pristine 7.3 K superconductor.

Load-bearing premise

The observed Tc values and their plateau arise from intrinsic electronic or Fermi-surface changes rather than from sample inhomogeneity or disorder introduced by the doping process.

What would settle it

A measurement showing that Tc continues to fall below 2 K or exhibits a sharp drop at still higher Cu and S concentrations, or that structural phase changes coincide exactly with the reported plateau.

Figures

Figures reproduced from arXiv: 1907.01776 by Dong Yan, Guohua Wang, Hao Zheng, Huixia Luo, Jie Ma, Jinfeng Jia, Lei Shi, Man-Rong Li, Shu Wang, Yihua Wang, Yishi Lin, Yuan He, Zhen Zhu.

Figure 1
Figure 1. Figure 1: Structural and chemical characterization of Cu [PITH_FULL_IMAGE:figures/full_fig_p015_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Transport characterization of the normal states and superconducting [PITH_FULL_IMAGE:figures/full_fig_p015_2.png] view at source ↗
Figure 4
Figure 4. Figure 4: Characterization of the critical fields of Cu [PITH_FULL_IMAGE:figures/full_fig_p015_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: The superconducting phase diagram for 2H-CuxNbSe2-ySy and 2H-CuxNb1-xSe2-ySy compared to those of 2H-CuxNbSe2, 2H-NbSe2-xSx, and 2H-FexNbSe2(Refs.16, 24, 28) [PITH_FULL_IMAGE:figures/full_fig_p015_6.png] view at source ↗
Figure 1
Figure 1. Figure 1 [PITH_FULL_IMAGE:figures/full_fig_p016_1.png] view at source ↗
Figure 3
Figure 3. Figure 3 [PITH_FULL_IMAGE:figures/full_fig_p018_3.png] view at source ↗
Figure 4
Figure 4. Figure 4 [PITH_FULL_IMAGE:figures/full_fig_p019_4.png] view at source ↗
Figure 6
Figure 6. Figure 6 [PITH_FULL_IMAGE:figures/full_fig_p020_6.png] view at source ↗
read the original abstract

2H-NbSe2 is one of the most widely researched transition metal dichalcogenide (TMD) superconductors, which undergoes charge-density wave (CDW) transition at TCDW about 33 K and superconducting transition at Tc of 7.3 K. To explore the relation between its superconductivity and Fermi surface nesting, we combined S substitution with Cu intercalation in 2H-NbSe2 to make CuxNbSe2-ySy. Upon systematic substitution of S and intercalation of Cu ions into 2H-NbSe2, we found that when the Cu and S contents increases, the Tc decreases in CuxNbSe2-ySy. While at higher x and y values, Tc keeps a constant value near 2 K, which is not commonly observed for a layered TMD. For comparison, we found the simultaneous substitution of Nb by Cu and Se by S in CuxNb1-xSe2-ySy lowered the Tc substantially faster. We construct a superconducting phase diagrams for our double-doping compounds in contrast with the related single-ions doping systems.

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 experimental results on double-doped 2H-NbSe2 via Cu intercalation (x) and S substitution (y) in CuxNbSe2-ySy. Tc decreases with rising x and y but plateaus near 2 K at higher doping levels; this behavior is contrasted with faster Tc suppression in CuxNb1-xSe2-ySy and with single-ion doping systems, and superconducting phase diagrams are constructed for the double-doped compounds.

Significance. If the reported Tc plateau is intrinsic, the result would be notable for layered TMD superconductors because a doping-independent low-Tc regime is uncommon and could illuminate the interplay between CDW order, Fermi-surface nesting, and superconductivity. The phase-diagram comparison with single-doping cases provides a falsifiable, standard framework for assessing the double-doping effect.

major comments (2)
  1. [Results / phase-diagram section] Results on resistivity and Tc extraction (likely the section presenting the phase diagram and Tc vs. x,y data): the central claim of an unusual plateau at ~2 K requires explicit reporting of transition widths, multiple-sample statistics, and error bars; without these, it remains unclear whether the constant value reflects intrinsic electronic changes or extrinsic factors such as inhomogeneity.
  2. [Experimental methods] Experimental / characterization section: no mention of EDX homogeneity maps, XRD peak widths, or specific-heat confirmation for the high-x,y compositions where the plateau occurs; such data are load-bearing for ruling out the weakest assumption (extrinsic effects) and for establishing that the plateau is not an artifact of sample selection or structural phase changes.
minor comments (2)
  1. Notation inconsistency: the title uses 2H-NbSe₂ while the abstract and text employ CuxNbSe2-ySy; ensure uniform chemical formula and subscript formatting throughout.
  2. [Abstract] The abstract states 'Tc keeps a constant value near 2 K, which is not commonly observed'; a brief literature citation or quantitative comparison to other TMD plateaus would strengthen this phrasing.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive comments on our manuscript. We address each major point below and indicate where revisions will be made to strengthen the presentation of the Tc plateau.

read point-by-point responses

  1. Referee: [Results / phase-diagram section] Results on resistivity and Tc extraction (likely the section presenting the phase diagram and Tc vs. x,y data): the central claim of an unusual plateau at ~2 K requires explicit reporting of transition widths, multiple-sample statistics, and error bars; without these, it remains unclear whether the constant value reflects intrinsic electronic changes or extrinsic factors such as inhomogeneity.

    Authors: We agree that these details are necessary to support the claim of an intrinsic plateau. In the revised manuscript we will add error bars to the Tc values shown in the phase diagrams, report the transition widths (defined as the temperature span between 10% and 90% of the normal-state resistivity) for representative high-x,y samples, and state the number of independently prepared samples measured for each composition to demonstrate reproducibility. These additions will help address concerns about possible inhomogeneity. revision: yes

  2. Referee: [Experimental methods] Experimental / characterization section: no mention of EDX homogeneity maps, XRD peak widths, or specific-heat confirmation for the high-x,y compositions where the plateau occurs; such data are load-bearing for ruling out the weakest assumption (extrinsic effects) and for establishing that the plateau is not an artifact of sample selection or structural phase changes.

    Authors: We will add EDX composition maps and quantitative XRD peak-width analysis for the high-x and high-y samples in a revised experimental section to document homogeneity and the absence of structural phase changes. Specific-heat data were not collected on these compositions; our study relied on transport measurements and comparison with single-doping cases. The observed plateau is reproducible across multiple transport runs, but we acknowledge that calorimetric confirmation would further strengthen the intrinsic interpretation. revision: partial

standing simulated objections not resolved
  • Specific-heat confirmation for the high-x,y compositions

Circularity Check

0 steps flagged

No significant circularity; experimental measurements only

full rationale

The manuscript reports synthesis of CuxNbSe2-ySy, resistivity and magnetization measurements of Tc, and construction of phase diagrams contrasting double-doping versus single-ion doping. No equations, fitted parameters, or theoretical derivations are presented that reduce any claimed result to a quantity defined by the authors' own inputs. The central observation (Tc decrease followed by plateau near 2 K) is a direct experimental finding, not a prediction derived from a model or self-citation chain. Self-citations, if present, are not load-bearing for the reported data.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

This is an experimental materials paper. No free parameters, mathematical axioms, or new postulated entities are introduced; the central claim rests on standard assumptions of uniform doping and accurate composition measurement.

pith-pipeline@v0.9.0 · 5771 in / 1135 out tokens · 24825 ms · 2026-05-25T09:53:45.317349+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

36 extracted references · 36 canonical work pages

  1. [1]

    Lee H N S, McKinzie H, Tannhauser, D S , and Wold A 1969 The low-temperature transport

    work page 1969

  2. [2]

    properties of NbSe2. J. Appl. Phys. 40 602-4. Yang J J , Choi Y J, Oh Y S, Hogan A, Horibe Y, Kim K, Min B I and Cheong S W 2012

    work page 2012

  3. [3]

    Charge-Orbital Density Wave and Superconductivity in the Strong S pin-Orbit Coupled IrTe2:Pd. Phys. Rev. Lett. 108 116402. Rossnagel K 2011 On the origin of charge -density waves in select layered transition -metal

    work page 2011

  4. [4]

    dichalcogenides. J. Phys.: Condens. Matter. 23 213001. Gamble F R, Osiecki J H, Cais M and Pisharody R 1971 I ntercalation complexes of lewis

    work page 1971

  5. [5]

    Chang G, Chang T, Wu Y, Bian G, Huang S, Lee C, M ou D, Huang L, Song Y, Wang B, Wang G, Yeh Y, Yao N, Rault J E, Fevre P L, Bertran F, Jeng H, Kondo T, Kaminski A, Lin H, Liu Z, Song F, Shin S and Hasan M Z 2016 Fermi arc electronic structure and Chern numbers in the type-II Weyl semimetal candidate MoxW1-xTe2. Phys. Rev. B 94 085127. Belopolski I, Sanch...

    work page 2016

  6. [6]

    Alidoust N, Bian G, Neupane M, Huang S, Lee C, Song Y, Bu H, Wang G, Li S, Eda G, Jeng H, Kondo T, Lin H, Liu Z, Song F, Shin S and Hasan M Z 2016 Discovery of a new type of topological Weyl fermion semimetal state in MoxW1-xTe2. Nat. Commun. 7 13643. Zheng H, Xu S, Bian G, Guo C, Chang G, Sanchez D S, Belopolski I, Lee C, Huang S,

    work page 2016

  7. [7]

    ACS Nano 10 1378-85

    Zhang X, Sankar R, Alidoust N, Chang T, Wu F , Neupert T, Chou F, Jeng H, Yao N, Bansil A, Jia S, Lin H and Hasan M Z 2016 Atomic -Scale Visualization of Quantum Interference on a Weyl Semimetal Surface by Scanning Tunneling Microscopy. ACS Nano 10 1378-85. Fei F, Bo X, Wang R, Wu B, Jiang J, Fu D , Gao M, Zheng H, Chen Y, Wang X, Bu

    work page 2016

  8. [8]

    H, Song F, Wan X, Wang B and Wang G 2017 Nontrivial Berry phase and type -II Dirac transport in the layered material PdTe2. Phys. Rev. B 96 041201(R). Revolinsky E, Lautenschlager E P and Armitage C H 1963 Layer str ucture superconductor

    work page 2017

  9. [9]

    Solid State Common. 1 59-61. Smaalen S V 2005 The Peierls transition in low -dimensional electronic crystals. Acta. Cryst

    work page 2005

  10. [10]

    Wang H T, Li L J, Ye D S, Cheng X H and Xu Z A 2007 Effect of Te doping on

    A61 51-61. Wang H T, Li L J, Ye D S, Cheng X H and Xu Z A 2007 Effect of Te doping on

    work page 2007

  11. [11]

    superconductivity and charge-density wave in dichalcogenides 2H-NbSe2-xTex (x = 0, 0.1, 0.2). Chin. Phys. Soc. 16 2471-4. Yokoya T, Kiss T, Chainani A, Shin S, Nohara M and Takagi H 2001 Fermi surface

    work page 2001

  12. [12]

    Science 294 2518-20

    sheet-dependent superconductivity in 2H-NbSe2. Science 294 2518-20. Gabovich A M, Voitenko A I and Ausloos M 2002 Charge - and spin -density waves in

    work page 2002

  13. [13]

    Phys.Rep

    existing superconductors: competition between Cooper pairing and Peierls or excitonic instabilities. Phys.Rep. 367 583-709. Tsuei C C and Kirtley J R 2002 d-Wave pairing symmetry in cuprate

    work page 2002

  14. [14]

    Nature 423 65-7

    Campuzano J C, Sasaki S and Kadowaki K 2003 The origin of mu ltiple superconducting gaps in MgB2. Nature 423 65-7. Örda T and Kristoffe N 2002 Modeling MgB 2 two-gap superconductivity. Physica C:

    work page 2003

  15. [15]

    Fang L, Zou P Y, Wang Y, Tang L, Xu Z, Chen D H Shan C L and Wen H H 2005

    Superconductivity 370 17-20. Fang L, Zou P Y, Wang Y, Tang L, Xu Z, Chen D H Shan C L and Wen H H 2005

    work page 2005

  16. [16]

    W, Williams A J, West D V and Cava R J 2008 Tuning the Charge Density Wave and Superconductivity in CuxTaS2. Phys. Rev. B 78 104520. Morosan E, Zandbergen H W, Dennis B S, Bos J W G, Onose Y, Klimczuk T, Ramirez A P,

    work page 2008

  17. [17]

    Ong N P and Cava R J 2006 Superconductivity in CuxTiSe2. Nat. Phys. 2 544-50. Luo H X, Strychalska -Nowak J, Li J, Tao J, Klimczuk T and Cava R J 2017 S-Shaped

    work page 2006

  18. [18]

    J 2015 Polytypism, polymorphism, and superconductivity in TaSe2-xTex. Proc. Natl. Acad. Sci. 112 E1174-80. Sugawara K, Yokota K, Takei N, Tanokura Y and Sekine T 1994 Three-dimensional

    work page 2015

  19. [19]

    collective flux pinning in the layered superconductor 2H -NbSe2-xSx. J. Low Temp. Phys. 95 645-62. Kusmartseva F, Sipos , erger H, Forró L and Tutiš E 2009 Pressure Induced

    work page 2009

  20. [20]

    Geck J, MacDougall G J, Chiang T C, Cooper S L, Fradkin E and Abbamonte P 2014 Emergence of charge density wave domain walls above the superconducting dome in 1T-TiSe2. Nat. Phys. 10 421-5. Sipos B, Kusmartseva A F, Akrap A, Berger H, Forró L and Tutiš E 2008 From Mott state to

    work page 2014

  21. [21]

    superconductivity in 1T-TaS2. Nat. Mater. 7 960-5. Singh Y, Nirmala R, Ramakrishnan S and Malik S K 2005 Competition between

    work page 2005

  22. [22]

    superconductivity and charge -density-wave ordering in the Lu 5Ir4(Si1−xGex)10 alloy system. Phys. Rev. B 72 045106-13. Ye J T, Zhang Y J, Akashi R, Bahramy M S, Arita R and Iwasa Y 2012 Superconducting

    work page 2012

  23. [23]

    Science 338 1193-6

    Dome in a Gate-Tuned Band Insulator. Science 338 1193-6. Hauser J J, Robbins M and DiSalvo F J 1973 Effect of 3d impurities on the superconducting

    work page 1973

  24. [24]

    transition temperature of the layered compound NbSe2 .Phys. Rev. B 8 1038-42. Voorhoeve-Van Den Berg J M 1972 On the ternary phases Al xNbSe2 and Cu xNbSe2. J

    work page 1972

  25. [25]

    Less-Common. Metals. 26 399-402. Anderson P W, 1959, The theroy of dirty of superconductors . J. Phys. Ch em. Soli ds, 11,

    work page 1959

  26. [26]

    Sugawara K, Yokota K, Tanokura Y, Sekine T, 1993 Anisotropy of flux flow in layered

    26-30. Sugawara K, Yokota K, Tanokura Y, Sekine T, 1993 Anisotropy of flux flow in layered

    work page 1993

  27. [27]

    Sugawara K, Yokota K, Takei N, Tanokura Y, Sekine T, 1994 Dimension of the collective

    work page 1994

  28. [28]

    pinning in the layered superconductor 2H-NbSe2-xSx, Physica B 194-196 1891-1892 Naito M, Tanaka S, 1982 Electrical Transport Properties in 2 H-NbS2, -NbSe2, -TaS2 and

    work page 1982

  29. [29]

    -TaSe2. J. Phys. Soc. Jpn. 51, 219-227. Guillamo I , Suderow H, Vieira S, Cario L, Diener P, Rodiere P, 2008 Superconducting

    work page 2008

  30. [30]

    Density of States and Vortex Cores of 2H-NbS2. Phys. Rev. Lett. 101, 166407. Kačmarčík J, Pribulová Z, Marcenat C, Kleinc T, Rodiè re P, Cario L, Samuely P, 2010

    work page 2010

  31. [31]

    Studies on two-gap superconductivity in 2H-NbS2. Phys. C 470 719-720. Rodrí guez-Carvajal J 2001 Recent developments of the program FULLPROF. Comm

    work page 2001

  32. [32]

    26 12-19

    Powder Diffr. 26 12-19. McMillan W L 1968 Transition temperature of strong -coupled superconductors. Phys. Rev

    work page 1968

  33. [33]

    Wilson J A, Barker A S, Salvo Di F J and Ditz enberger J A 1978 Infrared properties of the

    work page 1978

  34. [34]

    semimetal TiSe2. Phys. Rev. B 18 2866-75. Kohn W 1967 Excitonic Phases. Phys. Rev. Lett. 19 439-42

    work page 1967

  35. [35]

    Werthamer N R, Helfand E and Hohenberg P C 1967 Temperature and Purity Dependence of

    work page 1967

  36. [36]

    the Superconducting Critical Field Hc2. IV. Strong-Coupling Effects. Phys. Rev. 147 415-6. Kresin V Z and Wolf S A 1990 Fundamentals of superconductivity, Plenum Press, New York

    work page 1990