Change in charge density wave order beyond the Lifshitz transition in 2H-Tatextsubscript{1pmδ}Stextsubscript{2}
Reviewed by Pith2026-06-29 10:09 UTCgrok-4.3pith:NM356XZLopen to challenge →
The pith
Band filling and interlayer spacing control the charge density wave ordering vector in 2H-TaS₂.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
The 3×3 CDW instability is highly sensitive to band filling, and with increased interlayer spacing a competing soft phonon mode emerges near q=1/2 ΓK corresponding to the 2√3 superstructure observed in the electron-doped self-intercalated phase.
What carries the argument
Ab initio phonon spectrum calculations that track how soft modes at specific wavevectors respond to changes in band filling and interlayer spacing.
If this is right
- The 3×3 CDW requires a narrow range of hole doping to remain stable.
- Electron doping combined with expanded interlayer spacing stabilizes a distinct 2√3 CDW phase.
- The incommensurate-to-commensurate lock-in occurs at a lower temperature than the initial CDW onset.
- Self-intercalation offers a practical route to access different CDW orders by altering both doping and structure.
Where Pith is reading between the lines
- The same parameters of band filling and spacing may govern CDW selection in related transition-metal dichalcogenides.
- Independent tuning of interlayer spacing could stabilize the q=1/2 ΓK mode under the experimentally observed doping sign.
- The sign mismatch between calculated and measured doping for the new mode indicates that intercalation introduces effects beyond simple rigid-band filling.
Load-bearing premise
The experimentally observed 2√3 superstructure in the self-intercalated sample arises from the calculated soft phonon mode near q=1/2 ΓK, even though the calculations produce this instability under hole doping while the experiment infers electron doping.
What would settle it
Measuring the CDW wavevector in samples where doping is varied independently of interlayer spacing to test whether the ordering vector follows the doping dependence seen in the phonon calculations.
Figures
read the original abstract
We investigate electronic instabilities in 2H-TaS\textsubscript{2} and a self-intercalated variant, 2H$^\dagger$-Ta\textsubscript{1+$\delta$}S\textsubscript{2}. In conventional samples, which we determine to be slightly hole-doped, spectral gaps and backfolded features are found as fingerprints of the $3\times3$ charge density wave (CDW). Notably, the backfolded features emerge only at a temperatures below $T\approx$~65~K, substantially lower than the established CDW temperature of 78~K, suggesting an incommensurate-commensurate lock-in transition analogous to the phenomenology of the 2H-TaSe\textsubscript{2}. In contrast, the self-intercalated 2H$^\dagger$ sample exhibits substantial electron doping and signatures of a novel \tworootthree CDW. Using \textit{ab initio} calculations of the phonon spectrum, we demonstrate that the \threebythree instability ($\mathbf{q}=\sfrac{2}{3}\mathbf{\Gamma M}$) is highly sensitive to band filling. Furthermore, with increased interlayer spacing, a competing soft phonon mode emerges near $\mathbf{q}=\sfrac{1}{2}\mathbf{\Gamma K}$, corresponding to the superstructure observed in the 2H$^\dagger$ phase, although in our calculations this instability arises under hole doping rather than the electron doping inferred experimentally. These results establish band filling and interlayer spacing as key control parameters for CDW ordering vectors in 2H-TaS\textsubscript{2}, and highlight a route to engineering electronic instabilities in a prototypical layered material.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript presents ARPES data on conventional 2H-TaS₂ (slightly hole-doped) showing 3×3 CDW signatures with backfolded features below ~65 K, interpreted as an incommensurate-commensurate lock-in, and on self-intercalated 2H†-Ta_{1+δ}S₂ (electron-doped) showing a novel 2×√3 CDW. Ab initio phonon calculations demonstrate that the 3×3 instability (q=2/3 ΓM) is sensitive to band filling, while increased interlayer spacing induces a competing soft mode near q=1/2 ΓK that the authors link to the observed 2×√3 superstructure, despite noting that this mode appears under hole doping in calculations rather than the experimental electron doping. The central claim is that band filling and interlayer spacing are key control parameters for CDW ordering vectors in 2H-TaS₂.
Significance. If the correspondence between the calculated soft mode and observed superstructure can be reconciled, the results would identify concrete tuning knobs for CDW vectors in a prototypical TMD, with potential implications for engineering electronic instabilities. The combination of temperature-dependent ARPES and doping/interlayer-dependent phonon calculations is a strength, though the doping-sign discrepancy limits the direct mapping to microscopic mechanism.
major comments (2)
- [Abstract / phonon calculations] Abstract and phonon-calculation section: the soft mode near q=1/2 ΓK is reported to emerge under hole doping in the calculations, yet the 2H† sample is inferred to be electron-doped from ARPES; this sign reversal means the ab initio instability does not reproduce the experimental ordering vector under the stated conditions, leaving the claimed correspondence between the calculated mode and the 2×√3 CDW unsupported and weakening the assertion that interlayer spacing controls the vector in the manner described.
- [Abstract / discussion] The central claim that the results 'establish band filling and interlayer spacing as key control parameters' rests on the q=1/2 ΓK mode matching the observed 2×√3 superstructure; given the doping mismatch, an explicit reconciliation (e.g., via additional calculations at the experimental doping level or discussion of possible intercalation effects on effective filling) is required before the claim can be considered load-bearing.
minor comments (2)
- [Experimental methods / figures] ARPES figures lack explicit error bars on doping estimates and temperature-dependent intensity; adding these would strengthen the lock-in transition interpretation.
- [Results] Notation for the 2×√3 superstructure and its relation to the calculated q vector should be clarified with a reciprocal-space diagram.
Simulated Author's Rebuttal
We thank the referee for their careful reading of the manuscript and for identifying the doping-sign discrepancy between the phonon calculations and the experimental inference for the 2H† phase. We address each major comment below and indicate where revisions will be made.
read point-by-point responses
-
Referee: [Abstract / phonon calculations] Abstract and phonon-calculation section: the soft mode near q=1/2 ΓK is reported to emerge under hole doping in the calculations, yet the 2H† sample is inferred to be electron-doped from ARPES; this sign reversal means the ab initio instability does not reproduce the experimental ordering vector under the stated conditions, leaving the claimed correspondence between the calculated mode and the 2×√3 CDW unsupported and weakening the assertion that interlayer spacing controls the vector in the manner described.
Authors: We acknowledge the doping-sign mismatch. The manuscript already states in the abstract that the q=1/2 ΓK instability appears under hole doping in the calculations. The central observation remains that increasing the interlayer spacing (as occurs with self-intercalation) stabilizes a competing soft mode at this wavevector whose real-space periodicity matches the observed 2×√3 superstructure. We will expand the discussion section to explicitly address possible origins of the sign discrepancy, including non-rigid-band effects from intercalated Ta atoms and the sensitivity of the mode to small changes in filling near the Lifshitz transition. No additional calculations are feasible within the current computational setup, but the qualitative demonstration that interlayer spacing can switch the dominant instability vector is retained. revision: partial
-
Referee: [Abstract / discussion] The central claim that the results 'establish band filling and interlayer spacing as key control parameters' rests on the q=1/2 ΓK mode matching the observed 2×√3 superstructure; given the doping mismatch, an explicit reconciliation (e.g., via additional calculations at the experimental doping level or discussion of possible intercalation effects on effective filling) is required before the claim can be considered load-bearing.
Authors: The claim is supported by two independent results: (i) the 3×3 instability is shown to be highly sensitive to band filling, consistent with the conventional sample, and (ii) the new soft mode at q≈1/2 ΓK emerges specifically when interlayer spacing is increased, independent of the precise doping sign. We will revise the abstract and discussion to qualify the claim by noting the doping-sign limitation and by adding a paragraph discussing how intercalation may alter the effective filling or screening beyond a simple rigid-band picture. This makes the control-parameter statement more precise without overclaiming a direct microscopic mapping. revision: partial
Circularity Check
No circularity: independent experiment and ab initio calculations
full rationale
The paper reports ARPES measurements on doping and CDW signatures in two samples, then performs separate DFT phonon calculations showing sensitivity of instabilities to band filling and interlayer spacing. No equation reduces an observed ordering vector to a fitted parameter from the same dataset, and no load-bearing claim rests on self-citation. The acknowledged doping-sign mismatch between calculation and experiment is a correctness issue, not a circularity reduction. The central claim that band filling and interlayer spacing are control parameters follows directly from the two independent data sources without self-definition or renaming.
Axiom & Free-Parameter Ledger
axioms (1)
- standard math Standard approximations of density functional theory suffice to identify phonon instabilities in 2H-TaS2
Reference graph
Works this paper leans on
-
[1]
& Mahajan, S
Wilson, J., Di Salvo, F. & Mahajan, S. Charge-density waves and superlattices in the metallic layered transition metal dichalcogenides.Advances in Physics24, 117–201 (1975)
1975
-
[2]
Va ˇno, V .et al.Artificial heavy fermions in a van der Waals heterostructure.Nature599, 582–586 (2021)
2021
-
[3]
Laverock, J.et al.k-resolved susceptibility function of 2H- TaSe2 from angle-resolved photoemission.Phys. Rev. B88, 035108 (2013)
2013
-
[4]
Straub, M.et al.Nature of metallic and insulating domains in the CDW system 1T-TaSe2 (2024). 2411.18205
-
[5]
Hall, J.et al.Environmental Control of Charge Density Wave Order in Monolayer 2H-TaS2.ACS Nano13, 10210–10220 (2019)
2019
- [6]
-
[7]
& Tanaka, S
Naito, M. & Tanaka, S. Electrical Transport Properties in 2H- NbS2, -NbSe2, -TaS2 and -TaSe2.J. Phys. Soc. Jpn.51, 219– 227 (1982)
1982
-
[8]
Phys.13, 103020 (2011)
Guillamón, I.et al.Chiral charge order in the superconductor 2H-TaS2.New J. Phys.13, 103020 (2011)
2011
-
[9]
E.et al.Tuning the charge density wave and super- conductivity in CuxTaS2.Phys
Wagner, K. E.et al.Tuning the charge density wave and super- conductivity in CuxTaS2.Phys. Rev. B78, 104520 (2008)
2008
-
[10]
Ni, S.et al.Crystal growth, superconductivity, and charge den- sity wave of pristine and Pd-intercalated2H−TaS2.Phys. Rev. B108, 075103 (2023)
2023
-
[11]
A., Di Salvo, F
Wilson, J. A., Di Salvo, F. J. & Mahajan, S. Charge-density waves in metallic, layered, transition-metal dichalcogenides. Phys. Rev. Lett.32, 882–885 (1974)
1974
-
[12]
& Yoffe, A
Friend, R. & Yoffe, A. Electronic properties of intercalation complexes of the transition metal dichalcogenides.Advances in Physics36, 1–94 (1987)
1987
-
[13]
Zhao, X.et al.Engineering covalently bonded 2D layered ma- terials by self-intercalation.Nature581, 171–177 (2020)
2020
-
[14]
& Zheng, F
Luo, T., Zhang, M., Shi, J. & Zheng, F. Emergent charge density wave featuring quasi-one-dimensional chains in Ta- intercalated bilayer 2H-TaS2 with coexisting superconductivity. Phys. Rev. B107, L161401 (2023)
2023
-
[15]
& Zheng, F
Yan, Y ., Xiong, L. & Zheng, F. Charge orders in fully inter- calated bilayer TaSe2: Dependence on interlayer stacking and intercalation sites.Phys. Rev. B111, 205437 (2025)
2025
-
[16]
E., Axe, J
Moncton, D. E., Axe, J. D. & DiSalvo, F. J. Neutron scattering study of the charge-density wave transitions in2H−TaSe2 and 2H−NbSe 2.Phys. Rev. B16, 801–819 (1977). 8
1977
-
[17]
& Tanaka, S
Sugai, S., Murase, K., Uchida, S. & Tanaka, S. Studies of lattice dynamics in 2H-TaS2 by Raman scattering.Solid State Com- munications40, 399–401 (1981)
1981
-
[18]
Nature Communications14, 7282 (2023)
Shen, X.et al.Precursor region with full phonon softening above the charge-density-wave phase transition in 2H-TaSe2. Nature Communications14, 7282 (2023)
2023
-
[19]
Rossnagel, K., Rotenberg, E., Koh, H., Smith, N. V . & Kipp, L. Fermi surface, charge-density-wave gap, and kinks in 2H−TaSe2.Phys. Rev. B72, 121103 (2005)
2005
-
[20]
V .et al.Pseudogap and Charge Density Waves in Two Dimensions.Phys
Borisenko, S. V .et al.Pseudogap and Charge Density Waves in Two Dimensions.Phys. Rev. Lett.100, 196402 (2008)
2008
-
[21]
W.et al.Folded superstructure and degeneracy-enhanced band gap in the weak-coupling charge density wave system 2 H-TaSe2.PHYSICAL REVIEW B9 (2018)
Li, Y . W.et al.Folded superstructure and degeneracy-enhanced band gap in the weak-coupling charge density wave system 2 H-TaSe2.PHYSICAL REVIEW B9 (2018)
2018
-
[22]
R.et al.Probing enhanced superconductivity in van der Waals polytypes of V xTaS2.Phys
Pudelko, W. R.et al.Probing enhanced superconductivity in van der Waals polytypes of V xTaS2.Phys. Rev. Materials8, 104802 (2024)
2024
-
[23]
Camerano, L.et al.Darkness in interlayer and charge density wave states of2H-TaS 2.Phys. Rev. B111, L121112 (2025)
2025
-
[24]
A., Singh, O., Frindt, R
Scholz, G. A., Singh, O., Frindt, R. F. & Curzon, A. E. Charge density wave commensurability in 2H-TaS 2 and Ag xTaS2. Solid State Communications44, 1455–1459 (1982)
1982
-
[25]
Tymoshenko, Y .et al.Charge-density-wave quantum critical point under pressure in 2H-TaSe2.Commun Phys8, 352 (2025)
2025
-
[26]
A.et al.Zero-bias conductance peak in detached flakes of superconducting 2H-TaS 2 probed by scanning tun- neling spectroscopy.Phys
Galvis, J. A.et al.Zero-bias conductance peak in detached flakes of superconducting 2H-TaS 2 probed by scanning tun- neling spectroscopy.Phys. Rev. B89, 224512 (2014)
2014
-
[27]
& Depmeier, W
Katzke, H., Tolédano, P. & Depmeier, W. Phase transitions between polytypes and intralayer superstructures in transition metal dichalcogenides.Phys. Rev. B69, 134111 (2004)
2004
-
[28]
Johannes, M. D. & Mazin, I. I. Fermi surface nesting and the origin of charge density waves in metals.Phys. Rev. B77, 165135 (2008)
2008
-
[29]
Harper, J. M. E., Geballe, T. H. & DiSalvo, F. J. Thermal prop- erties of layered transition-metal dichalcogenides at charge- density-wave transitions.Phys. Rev. B15, 2943–2951 (1977)
1977
-
[30]
A., Frindt, R
Scholz, G. A., Frindt, R. F. & Curzon, A. E. Electron Diffraction Investigation of the AgTaS 2 System II. Superlat- tices, Structure, and Charge Density Waves in AgTaS2.physica status solidi (a)72, 375–390 (1982)
1982
-
[31]
A., Naito, M., Frindt, R
Nishihara, H., Scholz, G. A., Naito, M., Frindt, R. F. & Tanaka, S. NMR of 181Ta in 2H-TaS 2 and 2H-TaSe2 - observation of locally commensurate CDW.Journal of Magnetism and Mag- netic Materials31–34, 717–718 (1983)
1983
-
[32]
Wang, Y .et al.Real-space detection and manipulation of two- dimensional quantum well states in few-layerMoS2.Phys. Rev. B105, L081404 (2022)
2022
-
[33]
Hillenius, S. J. & Coleman, R. V . Quantum oscillations and the Fermi surface of2H-TaS 2.Phys. Rev. B18, 3790–3798 (1978)
1978
-
[34]
Craven, R. A. & Meyer, S. F. Specific heat and resistivity near the charge-density-wave phase transitions in2H−TaSe 2 and 2H−TaS 2.Phys. Rev. B16, 4583–4593 (1977)
1977
-
[35]
McMillan, W. L. Theory of discommensurations and the commensurate-incommensurate charge-density-wave phase transition.Phys. Rev. B14, 1496–1502 (1976)
1976
-
[36]
Littlewood, P. B. & Rice, T. M. Theory of the Splitting of Dis- commensurations in the Charge-Density-Wave State of 2 H - TaSe 2.Phys. Rev. Lett.48, 27–30 (1982)
1982
-
[37]
Fujisawaet al.Superposition of√13×√13 and 3×3 super- modulations in TaS2 probed by scanning tunneling microscopy
Y . Fujisawaet al.Superposition of√13×√13 and 3×3 super- modulations in TaS2 probed by scanning tunneling microscopy. InJournal of Physics: Conference Series, vol. 969, 012053 (2018)
2018
-
[38]
Geng, Y .et al.Correlated electrons in the flat band in the charge density wave state of4H b −TaSe xS2−x.Phys. Rev. B110, 115107 (2024)
2024
-
[39]
Date, M.et al.Charge transfer empties the flat band in 4H b- TaS2, except at the surface.Communications Physics9, 60 (2026)
2026
-
[40]
Ribak, A.et al.Chiral superconductivity in the alternate stacking compound 4Hb-TaS2.Science Advances6, eaax9480 (2020)
2020
-
[41]
Almoalem, A.et al.Charge transfer and spin-valley locking in 4Hb-TaS2.npj Quantum Mater .9, 1–7 (2024)
2024
-
[42]
D.et al.Folded pseudochiral Fermi surface in 4Hb- TaSe2 from band hybridization with a charge density wave
Watson, M. D.et al.Folded pseudochiral Fermi surface in 4Hb- TaSe2 from band hybridization with a charge density wave. Commun Mater6, 1–7 (2025)
2025
-
[43]
Hughes, H. P. & Scarfe, J. A. Site Specific Photohole Screen- ing in a Charge Density Wave.Phys. Rev. Lett.74, 3069–3072 (1995)
1995
-
[44]
Domaine, G.et al.Tunable Octdong and Spindle-Torus Fermi Surfaces in Kramers Nodal Line Metals.Nature Communica- tions16, 11128 (2025)
2025
-
[45]
Han, Z.et al.Phase and Composition Engineering of Self-Intercalated 2D Metallic Tantalum Sulfide for Second- Harmonic Generation.ACS Nano18, 6256–6265 (2024)
2024
-
[46]
Small18, 2201975 (2022)
Wang, Z.et al.Giant g-factor in Self-Intercalated 2D TaS2. Small18, 2201975 (2022)
2022
-
[47]
Edwards, B.et al.Chemical Trends of the Bulk and Sur- face Termination-Dependent Electronic Structure of Metal- Intercalated Transition Metal Dichalcogenides.Chem. Mater . 36, 7117–7126 (2024)
2024
-
[48]
Phys.: Conf
Ohta, S.et al.Evaluation of the physical properties and the real space observation in 2H-TaS2 synthesized with flux method.J. Phys.: Conf. Ser .1590, 012004 (2020)
2020
-
[49]
& Sakata, H
Mogami, K., Ohta, S. & Sakata, H. Appearance of unidirec- tional superstructure in silver intercalated 2H-NbSe 2.Surface Science707, 121636 (2021)
2021
-
[50]
Curzon, A. E. & Rajora, O. S. An electron diffraction study of the ordering of silver in AgNbSe2 for 0<x>0.33.physica status solidi (a)87, 157–163 (1985)
1985
-
[51]
Rajora, O. S. & Curzon, A. E. Electrical resistance and differ- ential scanning calorimetric studies of silver intercalated 2H- NbSe2.Journal of the Less Common Metals118, 117–122 (1986)
1986
-
[52]
& Prokudina, M
Mushenok, F., Shevchun, A., Shovkun, D. & Prokudina, M. Two-Step Magnetic Ordering in Intercalated Niobium Dichalcogenide MnXNbS2.Magnetism3, 259–266 (2023)
2023
-
[53]
K.et al.Charge Density Waves in Electron- Doped Molybdenum Disulfide.Nano Lett.21, 5516–5521 (2021)
Bin Subhan, M. K.et al.Charge Density Waves in Electron- Doped Molybdenum Disulfide.Nano Lett.21, 5516–5521 (2021)
2021
-
[54]
Rice, T. M. & Scott, G. K. New Mechanism for a Charge- Density-Wave Instability.Phys. Rev. Lett.35, 120–123 (1975)
1975
-
[55]
Joshi, J.et al.Short-range charge density wave order in 2H−TaS2.Phys. Rev. B99, 245144 (2019)
2019
-
[56]
Berges, J., van Loon, E. G. C. P., Schobert, A., Rösner, M. & Wehling, T. O. Ab initio phonon self-energies and fluctua- tion diagnostics of phonon anomalies: Lattice instabilities from Dirac pseudospin physics in transition metal dichalcogenides. Physical Review B101, 155107 (2020)
2020
-
[57]
Giannozzi, P.et al.QUANTUM ESPRESSO: A modular and open-source software project for quantum simulations of ma- terials.Journal of Physics: Condensed Matter21, 395502 (2009)
2009
-
[58]
Giannozzi, P.et al.Advanced capabilities for materials mod- elling with QUANTUM ESPRESSO.Journal of Physics: Con- densed Matter29, 465901 (2017)
2017
-
[59]
J.et al.The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table
van Setten, M. J.et al.The PseudoDojo: Training and grading a 85 element optimized norm-conserving pseudopotential table. 9 Computer Physics Communications226, 39–54 (2018)
2018
-
[60]
P., Burke, K
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple.Physical Review Letters77, 3865– 3868 (1996)
1996
-
[61]
Monkhorst, H. J. & Pack, J. D. Special points for Brillouin-zone integrations.Physical Review B13, 5188–5192 (1976)
1976
-
[62]
& Mauri, F
Calandra, M., Profeta, G. & Mauri, F. Adiabatic and nonadia- batic phonon dispersion in a Wannier function approach.Phys- ical Review B82, 165111 (2010)
2010
-
[63]
& Mauri, F
Calandra, M. & Mauri, F. Charge-density wave and supercon- ducting dome in NbSe 2 from first principles.Physical Review Letters106, 196406 (2011)
2011
-
[64]
R., Verdi, C
Poncé, S., Margine, E. R., Verdi, C. & Giustino, F. EPW: Electron–phonon coupling, transport and superconducting properties using maximally localized Wannier functions.Com- puter Physics Communications209, 116–133 (2016). Data A vailabilityThe data that support the findings of this study are available from the corresponding author upon reasonable request....
2016
discussion (0)
Sign in with ORCID, Apple, or X to comment. Anyone can read and Pith papers without signing in.