Pith. sign in

REVIEW 4 major objections 6 minor 41 references

Changing the stacking sequence of NbSe2 layers alone reshapes its charge-density-wave order and superconductivity.

Reviewed by Pith at T0; open to challenge. T0 means a machine referee read the full paper against a public rubric. the ladder, T0–T4 →

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗

T0 review · deepseek-v4-flash

2026-08-01 10:06 UTC pith:DINNPKSL

load-bearing objection A solid STM paper reporting a genuinely new coexisting 1Q_C/3Q_I CDW state in 4Ha-NbSe2 with boundary vortices; the main weakness is an unquantified strain detection limit, but the core observation holds. the 4 major comments →

arxiv 2607.20335 v1 pith:DINNPKSL submitted 2026-07-22 cond-mat.supr-con

Stacking-tuned superconductivity and competing charge-density-wave states in NbSe₂

Sandra Sajan , Xinze Yang , Haojie Guo , Tarushi Agarwal , Samuel Ma\~nas-Valero , Carla Boix-Constant , Eugenio Coronado , Fernando de Juan
show 4 more authors
Eduardo H. da Silva Neto Ravi P. Singh Maria N. Gastiasoro Miguel M. Ugeda
This is my paper
classification cond-mat.supr-con
keywords NbSe2polytypismcharge density wavesuperconductivityscanning tunneling microscopystacking engineeringphase slipsdiscommensuration vortices
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

Using high-resolution scanning tunneling microscopy and spectroscopy, the paper claims that the 4Ha polytype of NbSe2 — which keeps the same atomic layers and only rearranges their order along the c axis — hosts two competing charge-density-wave states: a unidirectional commensurate 1Q_C stripe phase and a triangular incommensurate 3Q_I phase. These phases coexist on atomically flat terraces, and their boundaries are decorated by vortices in the CDW phase gradient that act as 2π phase slips, absorbing the momentum mismatch δ = Q_I − Q_C. The paper further claims that superconductivity is stacking-sensitive: both polytypes show multiband pairing, but the 4Ha stack suppresses the smaller superconducting gap and concentrates tunneling weight in the large-gap band. If these claims hold, layer stacking is an intrinsic, strain-free knob for engineering collective electronic order in layered metals.

Core claim

The paper's central claim is that stacking sequence alone can qualitatively transform electronic order in NbSe2. In the 4Ha polytype, scanning tunneling images reveal coexistence of a unidirectional commensurate 1Q_C charge-density wave (ordering vector 2/7 G along one direction) and the triangular incommensurate 3Q_I order familiar from 2H-NbSe2 (wave vectors Q_I = Q_C + δ along three symmetry directions). Phase-resolved analysis of the CDW phase gradient shows vortices pinned to the 1Q_C–3Q_I boundaries; each vortex is a local 2π phase slip where a wavefront is lost, providing the mechanism by which the momentum mismatch δ is accommodated. In the superconducting channel, tunneling spectra

What carries the argument

The key machinery is the contrast between 4Ha (ABA'B', noncentrosymmetric P-6m2) and 2H (AB, centrosymmetric P63/mmc) stacking sequences, combined with three measurement and theoretical tools. First, a phase-resolved local wave-vector measurement algorithm extracts the local CDW wave vector and its gradient directly from STM topographs, avoiding global Fourier transforms that are ill-defined when vortices are present. Second, a Ginzburg-Landau free energy for the multicomponent CDW order parameter φ_n includes a period-seven commensurability energy (coefficient E) that drives a first-order transition between the triangular incommensurate 3Q_I state and the unidirectional commensurate 1Q_C st

Load-bearing premise

The conclusion that the 1Q_C order is intrinsic to 4Ha stacking rather than induced by local strain rests on the sensitivity of the Bragg-vector strain map, whose noise floor is not quantified; in 2H-NbSe2, sub-percent strain is sufficient to stabilize stripe order.

What would settle it

Conduct ultra-high-sensitivity strain mapping on a 4Ha-NbSe2 surface using, for instance, sub-pixel lattice tracking or high-resolution Fourier analysis to see whether the 1Q_C domains are associated with any local Bragg-vector shift below the 2.5% color scale used in the paper. If a strain signature tracking the stripe pattern appears, the 'stacking alone' conclusion fails; if regions remain strain-free at a much lower noise floor, the intrinsic scenario is supported.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Polytypism is established as an intrinsic, strain-free control knob: choosing the 4Ha stack produces a stripe-vs-triangular CDW coexistence that in 2H requires strain to imitate.
  • The phase-slip vortex mechanism gives a generic prescription for how commensurate and incommensurate CDW domains can meet, and predicts similar vortices should appear at other interfaces with mismatched CDW wave vectors.
  • The superconducting gap structure of NbSe2 is not fixed by chemistry; the smaller gap can be selectively suppressed by stacking, implying that interlayer ordering tunes which Fermi-surface sheets participate in pairing.
  • The phase-gradient mapping technique makes discommensuration vortices directly visible in real space, offering a new probe for CDW domain physics.
  • The near-degeneracy of the 1Q_C and 3Q_I states in the 4Ha Ginzburg-Landau phase diagram suggests that modest external perturbations (electric field, pressure, or small strain) could switch between stripe and triangular order.

Where Pith is reading between the lines

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

  • Editorial inference: The same discommensuration-vortex picture could apply to other TMD polytypes (e.g., 4Hb-TaS2 or mixed-stack heterostructures) where interlayer translations create comparable momentum mismatches between CDW components, extending the mechanism beyond NbSe2.
  • Editorial inference: Because these vortices are topological defects in the CDW order parameter, one might ask whether they survive into the superconducting state and act as pinning centers for magnetic vortices, potentially linking CDW and superconducting vortex physics.
  • Editorial inference: The claim of stacking-only control could be tested systematically with a higher-sensitivity strain probe; if the 1Q_C regions show Bragg-vector deviations below the paper's reported 2.5% color scale, the intrinsic interpretation would need revision, while a noise-level strain map would strengthen it.
  • Editorial inference: A natural follow-up is to compare the CDW phase diagrams of 4Ha and 2H under controlled uniaxial strain; if the Ginzburg-Landau picture is right, the 4Ha 1Q_C–3Q_I boundary should be far more strain-sensitive than the 2H one because it sits near a phase transition.

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

4 major / 6 minor

Summary. This manuscript reports a comparative STM/STS study of 4Ha- and 2H-NbSe2. The central empirical claim is that, with identical in-plane atomic structure, the two polytypes host qualitatively different collective orders: 4Ha exhibits coexisting unidirectional commensurate 1Q^C and triangular incommensurate 3Q^I CDW domains on atomically flat terraces, with phase-gradient vortices at their boundaries that accommodate the incommensurability momentum δ; 2H shows only 3Q^I (with 1Q stripe under strain). STS further indicates multiband superconductivity in both, with a weaker secondary gap in 4Ha. A Ginzburg-Landau free energy with commensurability terms is used to argue that the 3Q^I–1Q^C transition is first-order near the observed coexistence. The paper concludes that stacking sequence alone can tune CDW and superconducting order.

Significance. If the strain-exclusion argument can be made quantitative, this would establish polytypism as an intrinsic knob for collective order in van der Waals materials, with a new nanoscale coexistence mechanism. The direct real-space visualization of coexisting CDW states and vortex-like phase slips is a clear advance, and the local wave-vector algorithm is a useful alternative to Lawler-Fujita for systems with vortices. However, the GL part is a rationalization with ad hoc coefficients, and the strain-free claim currently lacks a detection limit, so the broad significance is conditional on closing these gaps.

major comments (4)
  1. [§3, Fig. 3(c,d)] The central claim that stacking alone, rather than strain, stabilizes the 1Q^C phase is not yet supported by a quantified detection limit. The reported 4Ha Bragg-vector fluctuations, ΔG_std=(0.02,0.06) nm^-1, translate to ~0.1–0.35% rms strain for |G|≈18 nm^-1. Refs. 30 and 31 demonstrate that sub-percent strain in 2H-NbSe2 is sufficient to induce unidirectional stripe order. No control measurement (synthetic images with known strain, or an unstrained calibration surface) or noise floor for the local wave-vector algorithm is provided; moreover, no correlation coefficient between ΔG and the 1Q^C/3Q^I domain pattern is computed. The absence of a detected ΔG signal is therefore ambiguous. This is the load-bearing step for the 'stacking alone' conclusion and must be addressed.
  2. [End Matter, Eq. (1) and Fig. 3(e)] The GL phase diagram is constructed with parameters A=-100, A_δ=1/|G_n|^2, C=210, D=100, E=-5.5, F=10 that are chosen without microscopic derivation or error estimate. The first-order 3Q^I–1Q^C transition is placed close to the experimentally observed coexistence by this choice, so the theory rationalizes rather than predicts. The statement that the model 'explains the origin' of the coexistence is therefore overstated. The authors should either derive or constrain the coefficients (e.g., from DFT/electron-phonon calculations or experimental δ), or explicitly label the diagram as a schematic and test how robust the coexistence region is to parameter variations.
  3. [Supplementary Note 2 and main text] The superconductivity comparison rests on fits of a many-parameter two-band McMillan model. For 4Ha the small gap is ⟨Δ2⟩=0.269±0.130 meV, with a relative error around 50%, and the normalized weight w≈0.98 means the secondary component contributes only ~2% of the tunneling conductance; the 'shoulder' is therefore weakly constrained. For 2H, values Δ1=1.08 meV and Δ2=0.72 meV are quoted with no error bars, no number of spectra, and no measure of fit quality. To support the claim that stacking selectively suppresses the secondary gap, the authors should present statistics over multiple spectra/locations and fits for both polytypes under identical conditions, including confidence intervals and a discussion of parameter correlations.
  4. [§3, Fig. 3(h) and Supplementary Note 4] The identification of topological vortices in ∇φ at 1Q^C–3Q^I boundaries is the proposed accommodation mechanism, but it is based on only four vortices and on a single implementation of the local wave-vector algorithm. The note that the Bragg-vector map is vortex-free is reassuring, but the authors do not show a validation of the algorithm on synthetic images with known phase slips or on a disordered/noise image. Because the phase-gradient method is central to the vortex claim, a synthetic test demonstrating that ±2π vortices are recovered with correct chirality (and not produced by boundaries or noise) is needed.
minor comments (6)
  1. [Fig. 3(e)] The axes of the GL phase diagram are not labeled in the manuscript figure. Please add axis labels and a legend for the 1Q^I, 1Q^C, and 3Q^I regions.
  2. [End Matter, local wave-vector algorithm] The text refers to '2H-NbS2' when describing strain mapping; this should presumably be '2H-NbSe2'.
  3. [Eq. (2)] The notation '∇φr0' is unclear; it should be written as '∇φ(r0)'.
  4. [Fig. 1 caption] There is a typo: 'N bSe2' should be 'NbSe2'.
  5. [Main text, superconducting comparison] The T_c values (6.2 K for 4Ha, 7.2 K for 2H) are only given in the Supplementary Information. Citing them in the main text would help contextualize the gap comparison.
  6. [Data availability] No data availability statement is provided. For STM datasets supporting this study, access to raw data or analysis code would strengthen reproducibility.

Circularity Check

0 steps flagged

No significant circularity: the empirical CDW coexistence, phase-gradient vortices, and superconducting-gap comparison are extracted directly from STM/STS data; the GL model is illustrative and not used as a derivation of those observations.

full rationale

The central empirical findings — coexistence of 1Q^C and 3Q^I CDW in 4Ha-NbSe2, the Q^I = Q^C + δ relation, the vortices at phase boundaries, and the multiband superconducting spectra — are presented as direct STM/STS observations, not as outputs of a fitted model. The superconducting gap values are obtained by fitting spectra with a two-band McMillan model, but they are reported as measurements, not used as inputs to derive the stacking conclusion. The Ginzburg-Landau free energy (Eq. 1) is a standard Landau model adapted from prior work, and the phase diagram in Fig. 3(e) is obtained by minimizing trial states with stated parameters. While the chosen parameters place 4Ha near the 1Q–3Q coexistence boundary, the paper does not state that these parameters were fitted to the measured coexistence or to the measured δ; the coexistence and vortices are observed independently and the GL analysis serves as a rationalization rather than a predictive derivation. The local wave-vector algorithm is self-described as developed by the present authors, but it is a measurement procedure with a stated principle, not a self-citation carrying an unverified scientific claim. The absence of a quantified strain-detection limit is a legitimate concern for the 'stacking alone' interpretation, but it is a missing-support/correctness-risk issue, not circularity: the null strain signal is an empirical observation, not an assumption reused as a conclusion. No load-bearing result reduces by construction to its own input.

Axiom & Free-Parameter Ledger

2 free parameters · 3 axioms · 0 invented entities

The empirical core—STM images, FFT, and phase-gradient maps—does not depend on fitted parameters. The theoretical explanation and the quantitative comparison of superconducting gaps do: the GL coefficients are chosen to place the system near a 1Q_C/3Q_I transition, and the McMillan parameters are fits to tunneling spectra.

free parameters (2)
  • Ginzburg-Landau coefficients (A, A_delta, C, D, E, F) = A=-100, A_delta=1/|G_n|^2, C=210, D=100, E=-5.5, F=10
    Chosen by hand at the end of the GL section to locate a 1Q_C/3Q_I first-order boundary near the measured incommensurability; no independent derivation.
  • McMillan two-band parameters (Delta_1, Delta_2, Gamma_1, Gamma_2, Gamma_12, Gamma_21, w, A_1, A_2) = 4Ha: Delta1=0.987 meV, Delta2=0.269 meV, w=0.98; 2H: Delta1=1.08 meV, Delta2=0.72 meV, w=0.68
    Nonlinear least-squares fits to dI/dV spectra; 2H values given without error bars. The claim of weaker secondary gap depends on these fits.
axioms (3)
  • domain assumption Ginzburg-Landau free energy in Eq. (1), including period-seven commensurability term E Re[phi_n^7] and eighth-order term F|phi|^8
    Phenomenological model adapted from refs. [32-34]; the period-7 term is introduced specifically to stabilize the observed 2/7 G commensurate state; not derived from microscopic theory.
  • domain assumption Phase-gradient approximation of Eq. (2): e^{i[k·r+phi(r)]} ≈ e^{i[(k+∇phi_r0)·r+...]}
    The identification of vortices in ∇phi(r) with 2π phase slips relies on slowly varying phase; at the vortex cores the gradient is singular, so only circulation is used. Still, if this approximation is invalid across the boundary, vortex interpretation is affected.
  • domain assumption Imaged surface reconstructs the bulk 4Ha stacking
    STM probes a surface layer; the paper infers stacking from bulk XRD/exfoliation rather than from direct cross-section or atomically resolved stacking registry. If surfaces had mixed stacking, the 1Q_C regions might stem from local stacking faults.

pith-pipeline@v1.3.0-alltime-deepseek · 14258 in / 13017 out tokens · 105346 ms · 2026-08-01T10:06:32.988619+00:00 · methodology

0 comments
read the original abstract

Layer stacking provides a powerful yet underexplored route for reshaping collective quantum order in van der Waals materials. Here we use high-resolution scanning tunneling microscopy and spectroscopy to show that the stacking sequence alone can qualitatively transform the charge density and superconducting orders in NbSe$_2$, while preserving the same in-plane atomic structure. Comparing the 4Ha and 2H polytypes, we find that, unlike the ubiquitous triangular incommensurate $3Q^\mathrm{I}$ order of 2H-NbSe$_2$, 4Ha-NbSe$_2$ hosts two competing CDW states with no measurable correlation with local strain: a unidirectional commensurate $1Q^\mathrm{C}$ phase and a triangular incommensurate $3Q^\mathrm{I}$ phase, with $Q^\mathrm{I}=Q^\mathrm{C}+\delta$. We introduce a phase-resolved analysis that directly maps the gradient of the CDW phases and reveals vortices bound to the $1Q^\mathrm{C}$ - $3Q^\mathrm{I}$ phase boundaries. These vortices accommodate the momentum mismatch $\delta$ through abrupt $2\pi$ phase slips, providing a mechanism by which distinct charge orders coexist. Superconductivity is also reshaped by stacking, while both polytypes exhibit multiband pairing.

Figures

Figures reproduced from arXiv: 2607.20335 by Carla Boix-Constant, Eduardo H. da Silva Neto, Eugenio Coronado, Fernando de Juan, Haojie Guo, Maria N. Gastiasoro, Miguel M. Ugeda, Ravi P. Singh, Samuel Ma\~nas-Valero, Sandra Sajan, Tarushi Agarwal, Xinze Yang.

Figure 1
Figure 1. Figure 1: (a,b) Unit cell of 4Ha-NbSe2 and 2H-NbSe2 respec￾tively, (c) Representative dI/dV and corresponding deriva￾tives (d 2 I/dV 2 ) of the 4Ha and 2H polytypes (Vac = 20 µV, T = 0.34 K). tices pinned to the boundaries between these two phases. These vortices act as localized 2π phase slips that ab￾sorb the momentum mismatch δ, allowing the commen￾surate and incommensurate charge orders to coexist at the nanosca… view at source ↗
Figure 2
Figure 2. Figure 2: (a) Large-scale STM topograph of 4Ha-NbSe [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Topography of a region showing the coexistence of 1 [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: (a) Charge density at the phase boundary (region [PITH_FULL_IMAGE:figures/full_fig_p005_4.png] view at source ↗

discussion (0)

Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.

Reference graph

Works this paper leans on

41 extracted references

  1. [1]

    J. A. Wilson, F. J. Di Salvo, and S. Mahajan, Charge- density waves and superlattices in the metallic layered transition metal dichalcogenides, Advances in Physics 24, 117 (1975)

    1975

  2. [2]

    X. Xi, Z. Wang, W. Zhao, J.-H. Park, K. T. Law, 6 H. Berger, L. Forr´ o, J. Shan, and K. F. Mak, Ising pairing in superconducting NbSe 2 atomic layers, Nature Physics 12, 139 (2016)

    2016

  3. [3]

    C. Heil, S. Ponc´ e, H. Lambert, M. Schlipf, E. R. Margine, and F. Giustino, Origin of superconductivity and latent charge density wave in NbS 2, Physical Review Letters 119, 087003 (2017)

    2017

  4. [4]

    Yokoya, T

    T. Yokoya, T. Kiss, A. Chainani, S. Shin, M. Nohara, and H. Takagi, Fermi surface sheet-dependent supercon- ductivity in 2H-NbSe 2, Science294, 2518 (2001)

    2001

  5. [5]

    Ribaket al., Chiral superconductivity in the alter- nate stacking compound 4H b-TaS2, Science Advances6, eaax9480 (2020)

    A. Ribaket al., Chiral superconductivity in the alter- nate stacking compound 4H b-TaS2, Science Advances6, eaax9480 (2020)

    2020

  6. [6]

    W. Wang, C. Si, W. Lei, F. Xiao, Y. Liu, C. Autieri, and X. Ming, Stacking order and coulomb correlation effect in the layered charge density wave phase of 1T-NbS 2, Physical Review B105, 035119 (2022)

    2022

  7. [7]

    C. J. Butler, M. Yoshida, T. Hanaguri, and Y. Iwasa, Mottness versus unit-cell doubling as the driver of the insulating state in 1T-TaS2, Nature Communications11, 2477 (2020)

    2020

  8. [8]

    J. J. Gao, J. G. Si, X. Luo, J. Yan, Z. Z. Jiang, W. Wang, Y. Y. Han, P. Tong, W. H. Song, X. B. Zhu, Q. J. Li, W. J. Lu, and Y. P. Sun, Origin of the large magnetoresis- tance in the candidate chiral superconductor 4H b-TaS2, Physical Review B102, 075138 (2020)

    2020

  9. [9]

    K. T. Law and P. A. Lee, 1T-TaS 2 as a quantum spin liquid, Proceedings of the National Academy of Sciences 114, 6996 (2017)

    2017

  10. [10]

    Wickramaratne, S

    D. Wickramaratne, S. Khmelevskyi, D. F. Agterberg, and I. I. Mazin, Ising superconductivity and magnetism in NbSe2, Phys. Rev. X10, 041003 (2020)

    2020

  11. [11]

    Hamill, B

    A. Hamill, B. Heischmidt, E. Sohn, and et al., Two-fold symmetric superconductivity in few-layer NbSe2, Nature Physics17, 949 (2021)

    2021

  12. [12]

    Ma˜ nas-Valero, B

    S. Ma˜ nas-Valero, B. M. Huddart, T. Lancaster,et al., Quantum phases and spin liquid properties of 1T-TaS 2, npj Quantum Materials6, 69 (2021)

    2021

  13. [13]

    Y. D. Wang, W. L. Yao, Z. M. Xin,et al., Band insulator to mott insulator transition in 1T-TaS 2, Nature Commu- nications11, 4215 (2020)

    2020

  14. [14]

    Sipos, A

    B. Sipos, A. Kusmartseva, A. Akrap,et al., From mott state to superconductivity in 1T-TaS 2, Nature Materials 7, 960 (2008)

    2008

  15. [15]

    Y. He, D. Yan, L. Shi, S. Wang, Z. Xie, and H. Luo, Re- view of nanoscale layered transition metal chalcogenide superconductors, Applied Materials Letters 10.5185/am- lett.2019.2175 (2018)

    arXiv 2019

  16. [16]

    L. Ma, C. Ye, Y. Yu,et al., A metallic mosaic phase and the origin of mott-insulating state in 1T-TaS 2, Nature Communications7, 10956 (2016)

    2016

  17. [17]

    Martino, A

    E. Martino, A. Arakcheeva, H. Berger,et al., Towards atomically-thin regime in bulk 4H-NbSe 2 with inter- layer disorder, npj 2D Materials and Applications10, 23 (2026)

    2026

  18. [18]

    Kadijk and F

    F. Kadijk and F. Jellinek, On the polymorphism of nio- bium diselenide, Journal of the Less Common Metals23, 437 (1971)

    1971

  19. [19]

    M. Zhou, Y. Gu, S. Ni, B. Ruan, Q. Liu, Q. Yang, L. Chen, J. Yi, Y. Shi, G. Chen, and Z. Ren, Struc- tures, charge density wave, and superconductivity of non- centrosymmetric 4Ha−NbSe 2, Physical Review B108, 224518 (2023)

    2023

  20. [20]

    Naik and S

    I. Naik and S. Sethy, Strong electron–phonon interac- tion establishes correlation between superconducting and charge density wave states in NbSe 2, Current Science 114, 888 (2018)

    2018

  21. [21]

    Naik and A

    I. Naik and A. K. Rastogi, Charge density wave and su- perconductivity in 2H- and 4H-NbSe 2: A revisit, Pra- mana – Journal of Physics76, 957 (2011)

    2011

  22. [22]

    K. Y. Shin, V. Brouet, N. Ru, Z. X. Shen, and I. R. Fisher, Electronic structure and charge-density wave for- mation in LaTe 1.95 and CeTe 2, Physical Review B72, 085132 (2005)

    2005

  23. [23]

    Kikuchi and S

    A. Kikuchi and S. Tsuneyuki, Electronic structure and charge density wave state in polytypes of NbSe2, Surface Science409, 458 (1998)

    1998

  24. [24]

    Patra, T

    C. Patra, T. Agarwal, R. Verma, P. Manna, S. Srivas- tava, R. S. Singh, M. S. Scheurer, B. Singh, and R. P. Singh, Ising Superconductivity in bulk layered noncen- trosymmetric 4H-NbSe 2, Phys. Rev. Lett.135, 216002 (2025)

    2025

  25. [25]

    Volavkaet al., Ising superconductivity in noncen- trosymmetric bulk 4H-NbSe 2, Physical Review Letters 136, 016002 (2026)

    D. Volavkaet al., Ising superconductivity in noncen- trosymmetric bulk 4H-NbSe 2, Physical Review Letters 136, 016002 (2026)

    2026

  26. [26]

    Niet al., Twofold symmetric superconductivity in the bulk ising superconductor 4Ha−NbSe 2, Phys

    S. Niet al., Twofold symmetric superconductivity in the bulk ising superconductor 4Ha−NbSe 2, Phys. Rev. B 113, 104515 (2026)

    2026

  27. [27]

    M. Zhou, S. Ni, Y. Shi, L. Chen, J. Yi, Y. Gu, Q. Liu, B. Ruan, Q. Yang, J. Yu, and Z. Ren, Nodeless two-gap superconductivity revealed by low-temperature specific heat and lower critical field in 4Ha-NbSe2, Physical Re- view B111, 024513 (2025)

    2025

  28. [28]

    F. O. von Rohr, J.-C. Orain, R. Khasanov, and et al., Unconventional scaling of the superfluid density with the critical temperature in transition metal dichalcogenides, Sci. Adv.5, eaav8465 (2019)

    2019

  29. [29]

    S. S. Islam, V. Sazgari, C. Witteveen, J. N. Gra- ham, O. Gerguri, P. Kr´ al, M. Bartkowiak, H. Luetkens, R. Khasanov, F. O. von Rohr, and Z. Guguchia, Pressure- induced enhancement of superfluid density in transition metal dichalcogenides with and without charge density wave, Physical Review Research7, 013324 (2025)

    2025

  30. [30]

    Soumyanarayanan, M

    A. Soumyanarayanan, M. M. Yee, Y. He, and et al., Quantum phase transition from triangular to stripe charge order in NbSe2, Proc. Natl. Acad. Sci. U.S.A.110, 1623 (2013)

    2013

  31. [31]

    S. Gao, F. Flicker, R. Sankar, and et al., Atomic-scale strain manipulation of a charge density wave, Proc. Natl. Acad. Sci. U.S.A.115, 6986 (2018)

    2018

  32. [32]

    W. L. McMillan, Landau theory of charge-density waves in transition-metal dichalcogenides, Phys. Rev. B12, 1187 (1975)

    1975

  33. [33]

    Nakanishi and H

    K. Nakanishi and H. Shiba, Domain-like incommen- surate charge-density-wave states and the first-order incommensurate-commensurate transitions in layered tantalum dichalcogenides. ii. 2H-polytype, Journal of the Physical Society of Japan44, 1465 (1978)

    1978

  34. [34]

    Flicker and J

    F. Flicker and J. van Wezel, Charge ordering geometries in uniaxially strained NbSe2, Phys. Rev. B92, 201103(R) (2015)

    2015

  35. [35]

    W. L. McMillan, Theory of discommensurations and the commensurate-incommensurate charge-density-wave phase transition, Phys. Rev. B14, 1496 (1976)

    1976

  36. [36]

    Meerschaut and C

    A. Meerschaut and C. Deudon, Crystal structure stud- ies of the 3R-Nb 1.09S2 and the 2H-NbSe 2 compounds: Correlation between nonstoichiometry and stacking type (= polytypism), Materials Research Bulletin36, 1721 7 (2001)

    2001

  37. [37]

    Horcas, R

    I. Horcas, R. Fern´ andez, J. M. G´ omez-Rodr ´ ıguez, J. Colchero, J. G´ omez-Herrero, and A. M. Baro, Wsxm: A software for scanning probe microscopy and a tool for nanotechnology, Review of Scientific Instruments78, 013705 (2007)

    2007

  38. [38]

    W. L. McMillan, Transition temperature of strong- coupled superconductors, Physical Review167, 331 (1968)

    1968

  39. [39]

    Szab´ o, P

    P. Szab´ o, P. Samuely, J. Kaˇ cmarˇ c ´ ık, T. Klein, J. Marcus, D. Fruchart, S. Miraglia, C. Marcenat, and A. G. M. Jansen, Evidence for two superconducting energy gaps in MgB2 by point-contact spectroscopy, Physical Review Letters87, 137005 (2001)

    2001

  40. [40]

    D. E. Moncton, J. D. Axe, and F. J. DiSalvo, Study of su- perlattice formation in 2H-NbSe 2 and 2H-TaSe2 by neu- tron scattering, Phys. Rev. Lett.34, 734 (1975)

    1975

  41. [41]

    Tinkham,Introduction to Superconductivity, 2nd ed

    M. Tinkham,Introduction to Superconductivity, 2nd ed. (Dover Publications, Mineola, New York, 2004). END MA TTER Crystal Growth and Structural Characterization Single crystals of both 2H-NbSe 2 and 4Ha-NbSe2 were synthesized using the chemical vapor transport (CVT) method with iodine (I 2) as the transport agent. 2H-NbSe2 crystal growth: Polycrystalline 2...

    2004