{"id":"930c50d3-5820-410e-904a-1a76b39d08df","arxiv_id":"2505.09752","paper_version":2,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Phosphorus substitution suppresses long-range ordering and the commensurate CDW in BaNi2(As1-xPx)2, while the incommensurate CDW remains soft-phonon-driven and its fluctuations persist to low temperature.","lead":"This paper measures how phosphorus doping changes the charge density waves in the superconductor BaNi2(As1-xPx)2 using X-ray scattering. It finds that the incommensurate charge wave keeps its soft-phonon character and slow fluctuations at all doping levels, while the commensurate wave is not soft-phonon driven.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The C-CDW \"not phonon-driven\" claim rests on a limited negative IXS search; a soft mode at a neighboring q, overdamped, or within ~1 K of T_tri could evade it.","rationale":"The reader's weakest assumption matches my own assessment. I considered other possible weak points: the pseudo-Voigt/Lorentzian decomposition used to define long-range order at high phosphorus content, and the assertion of \"complete softening\" at x≈0.1 despite 3 meV resolution. Those are real limitations but less central: the I-CDW soft-phonon part is directly supported by visible softening and prior higher-resolution work, and the absence of a Bragg-like component at x≥0.09 is consistent with the reported absence of an orthorhombic distortion. The C-CDW mechanism claim, in contrast, rests on a negative result, and the paper's own caveats about unreliable low-energy fits make it the most fragile link. The proposed high-resolution IXS check would settle whether a hidden soft mode exists. I do not think this requires changing the ACCEPT verdict: the authors hedge the lock-in interpretation, the negative search is reasonably designed, and the raw data are deposited. If the check later reveals a hidden soft mode, only the C-CDW mechanism narrative would need revision; the I-CDW phase diagram and soft-phonon evolution would stand.","tokens_in":32038,"tokens_out":7204,"duration_ms":72807,"concrete_test":"Perform high-resolution IXS on the same x≈0.037 batch at the C-CDW wave vectors q_C=(0,1/3,-1/3) and (1/3,0,-1/3) in at least two Brillouin zones, using an analyzer configuration with ≤1.5 meV FWHM and a dense q mesh (step ~0.02 r.l.u.) around q_C, at temperatures 0.5, 1, 2, and 5 K above T_tri and just below it. If any q-dependent softening or overdamped excitation appears at q_C before the transition, the \"not phonon-driven\" claim fails; if only the I-CDW dip at q≈0.28 is present and no anomaly at q_C, the central claim stands.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Section III.D and Figs. 7-8 base the central contrast between the I-CDW and C-CDW on the absence of a phonon anomaly at the commensurate wave vector. The evidence is a negative IXS search on x≈0.037: scans along [0 q q] from (4 1 1) and along [0 0 l] through the C-CDW position, with 3 meV energy resolution, just above (102.5 K) and below (90 K) the triclinic transition. Three detection gaps matter. First, a soft mode that is overdamped or broader than the resolution would appear only as a broad quasielastic hump and could be absorbed into the elastic line; the paper itself notes that low-energy fits become unreliable. Second, the C-CDW wave vector has two tetragonal-domain forms, and the measured trajectory may not cover both domains or a slightly shifted q position. Third, the transition is strongly first order, so any precursor softening could be confined to a very narrow temperature window; 102.5 K may be too far above T_tri to catch it. The subsequent lock-in interpretation is plausible but inherits this negative-evidence fragility. This is the load-bearing assumption for the claim that the C-CDW is not driven by a distinct phonon instability.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a combined thermal diffuse scattering (TDS) and inelastic X-ray scattering (IXS) study of BaNi2(As1-xPx)2 for x ≈ 0.036 to 0.12. Using reciprocal-space reconstructions, line-cut fits with Lorentzian and pseudo-Voigt components, and DFPT-based TDS calculations, the authors show that the incommensurate CDW (I-CDW) fluctuations are largely phononic in origin, that their correlation lengths grow strongly on cooling, and that a resolution-limited Bragg-like component signaling long-range I-CDW order appears for x ≲ 0.075, coinciding with the orthorhombic distortion. For x ≳ 0.075 the I-CDW phonon still softens and the correlation lengths reach similar values, but no long-range order forms. IXS scans around the commensurate wavevector reveal no softening at the C-CDW transition, which the authors interpret as evidence that the C-CDW/triclinic transition is not driven by a distinct phonon instability and may result from a lock-in of the 3D I-CDW order.","tokens_in":32291,"tokens_out":9492,"duration_ms":89580,"significance":"If the conclusions hold, the paper provides a coherent picture of the CDW phase diagram: a soft-phonon-driven I-CDW whose long-range order is coupled to the orthorhombic distortion, and a C-CDW lock-in without its own soft mode. The paper is also notable for the transparency of the analysis (explicit fits, DFPT comparisons, archival data deposit) and for extending the soft-phonon scenario to x≈0.1, where no static order is formed. The main caveat is that the central contrast between I-CDW and C-CDW mechanisms rests on a limited negative IXS search.","major_comments":[{"comment":"The claim that the C-CDW transition is not driven by a distinct phonon instability is based on the absence of a detectable softening in IXS scans taken at only two temperatures, 102.5 K and 90 K, with an energy resolution of 3 meV. This negative result does not exclude a soft-phonon mechanism: a mode that is overdamped or broader than the resolution would appear only as a quasielastic hump and could be absorbed into the elastic line; a precursor softening confined to a narrow temperature window near a strongly first-order transition would be missed by a single measurement above T_tri; and the scanned trajectories may not cover all equivalent C-CDW domain orientations. The authors themselves note in Section III.C that low-energy fits of the I-CDW phonon become unreliable when the mode is broad and close to the elastic line, and the Fig. 8 caption acknowledges that the two zero-energy points at 90 K are fitting artifacts of the strong elastic line. The central mechanistic contrast between the I-CDW (soft-phonon driven) and the C-CDW (not phonon-driven) is therefore not established at the level of certainty claimed in the abstract and Section IV. I recommend either rephrasing the conclusion to 'no evidence for a distinct phonon instability was found within the measured temperature and energy range' or adding IXS measurements with a fine temperature sweep around T_tri, higher energy resolution, and coverage of multiple q positions and domains.","section":"III.D, Figs. 7-8"}],"minor_comments":[{"comment":"In the paragraph listing the diffuse scattering features, 'physically signifant' should be 'physically significant'.","section":"III.A"},{"comment":"The sentence 'This indicates that a much larger I-CDW fluctuation regime upon P-substitution.' is grammatically incomplete; it should read 'This indicates a much larger I-CDW fluctuation regime upon P-substitution.' or similar.","section":"IV"},{"comment":"The figure caption does not fully define all symbols used in the legend (T_Tri, T_Orth, T_I-CDW,long, T_Cross, T_Fluct, T_Peak, T_x). Please spell out each symbol in the caption or refer explicitly to the section where each is defined.","section":"Fig. 4 caption"},{"comment":"The 'critical' correlation lengths xi_a,crit and xi_c,crit are extracted from the x=0 data and then applied to all compositions; the text should state more explicitly that these values are empirical thresholds rather than a microscopic criterion, especially since they are not sufficient to produce long-range order in the high-x samples.","section":"III.B"},{"comment":"The label 'Long-range I-CDW fluctuations' for the high-x region is confusing because no long-range order forms there; consider renaming it 'Long-correlation-length I-CDW fluctuations' or adding a clarifying sentence in the main text.","section":"Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript fits the scope of the journal and the data are of high quality. The main risk is that the categorical statement about the C-CDW not being phonon-driven relies on a negative IXS search with limited temperature and q coverage. I would encourage the editor to request either a softening of that claim or additional measurements, rather than rejecting the paper, because the rest of the analysis is solid and the data are openly deposited."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know. First, this is a genuinely useful systematic TDS/IXS study of P-substituted BaNi2As2 that pins down how the I-CDW evolves: soft-phonon driven across the whole doping range, with long-range 3D order only below x≈0.075 and a fluctuating regime above. Second, the companion claim that the C-CDW/triclinic transition is not phonon-driven rests on a negative IXS search that is real but limited, and the authors are appropriately cautious about it.\n\nThe I-CDW part is the strongest. Correlation lengths come from Lorentzian fits, the order parameter from a pseudo-Voigt component, and a critical correlation length criterion cleanly separates long-range order from fluctuation-dominated behavior. The TDS maps compared against DFPT calculations are careful, and the fact that the sharp Bragg-like peaks are not captured by a phonon-only model supports the static-order interpretation. Raw data are deposited. That is reproducible evidence.\n\nThe soft spot is exactly where the stress-test note points. The C-CDW conclusion comes from two temperatures (102.5 K and 90 K) on one sample, with 3 meV resolution, along two directions. A soft mode that is overdamped, broad, slightly off-q, or confined to a very narrow window near the first-order transition could hide under the elastic line. The paper acknowledges that low-energy fits become unreliable. That said, the accompanying TDS maps above the transition show no diffuse scattering at the C-CDW position, which independently supports the absence of a soft-phonon precursor. So the negative result is plausible, but it is not as strong as the I-CDW positive evidence.\n\nI also think the lock-in interpretation is reasonable but not forced; the paper offers it as a plausible mechanism, not a proof. The DFPT calculations are parent-compound only, but that is standard for substitution studies and the authors do not overclaim.\n\nWho is this for? Anyone working on CDWs, nematicity, or phonon instabilities in iron-pnictide-like superconductors. It advances the phase diagram and gives a clear criterion for long-range order that other groups can use. A serious referee should engage with it. I would accept it with minor-to-moderate revision, mostly asking for a more explicit discussion of the negative-search limitations and possibly an error budget for the correlation-length criterion.","headline":"Systematic TDS/IXS study showing the I-CDW remains soft-phonon driven across P substitution, with a plausible but less secure negative claim about the C-CDW.","tokens_in":32933,"tokens_out":3075,"would_cite":true,"duration_ms":30307,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"BaNi2As2's incommensurate CDW stays soft-phonon driven even where doping suppresses long-range order, while the commensurate CDW is a lock-in, not a separate phonon instability.","keywords":["charge density wave","BaNi2As2","soft phonon","inelastic X-ray scattering","thermal diffuse scattering","phosphorus substitution","triclinic transition","correlation length"],"falsifier":"Measure the phonon dispersion around the commensurate wave vector $q_{\\mathrm{C-CDW}}=(1/3,0,-1/3)$ with energy resolution better than 3 meV, on a sample with $x \\approx 0.037$ just above the triclinic transition; if a phonon branch dips toward zero energy at or near $q_{\\mathrm{C-CDW}}$, the claim that the C-CDW is not soft-phonon driven fails. Alternatively, search for a resolution-limited Bragg-like peak at the I-CDW position in $x \\approx 0.1$ samples cooled below 2 K or in larger crystals; finding one would contradict the claim that long-range I-CDW order fails to develop for $x \\gtrsim 0.075$.","tokens_in":31837,"feed_emoji":"🔬","tokens_out":6523,"duration_ms":57955,"temperature":0.7,"pith_summary":"BaNi2As2 hosts two successive charge-density-wave (CDW) orders: an incommensurate one (I-CDW) that forms with a tiny orthorhombic distortion, and a commensurate one (C-CDW) that appears when the lattice snaps to triclinic. This paper tries to establish how those orders relate and how they evolve when arsenic is replaced by phosphorus. It argues that the I-CDW remains soft-phonon driven even at $x \\approx 0.1$, where no structural distortion or long-range order forms; that long-range 3D I-CDW order develops only below $x \\approx 0.075$ and is what the orthorhombic transition really marks; and that the C-CDW/triclinic transition is a lock-in of that I-CDW order rather than a separate phonon instability. If right, the low-energy physics across the whole phase diagram is governed by resilient slow I-CDW fluctuations, which matters for interpreting the enhanced superconductivity in this material.","feed_headline":"A soft phonon drives the CDW even where doping blocks long-range order","feed_subtitle":"In BaNi2(As,P)2 the incommensurate CDW keeps its phonon instability up to x≈0.1; the commensurate CDW is a lock-in.","key_machinery":"The load-bearing object is the decomposition of the scattering at the I-CDW position into a Lorentzian component (fluctuating order, with inverse correlation length $1/\\xi$) and a resolution-limited pseudo-Voigt component (the static ordered fraction). The paper uses the onset of the pseudo-Voigt component, together with the threshold values $\\xi_{a,\\mathrm{crit}} \\approx 250$ Å and $\\xi_{c,\\mathrm{crit}} \\approx 100$ Å, as the criterion that separates long-range ordered I-CDW from slow I-CDW fluctuations. Supporting this, DFT-based lattice-dynamics calculations reproduce most of the thermal diffuse scattering patterns, identifying which features are phononic and which are static order. The inelastic X-ray measurements provide the complementary evidence: the low-lying optical branch softens at the I-CDW wave vector and not at the C-CDW wave vector.","core_discovery":"On the paper's own terms, the discovery is a unifying picture: phosphorus substitution suppresses the temperatures of the structural transitions, but the I-CDW instability itself barely changes. The diffuse scattering at the I-CDW wave vector grows and sharpens on cooling for every substitution level up to $x \\approx 0.12$; a resolution-limited Bragg-like peak, signalling true long-range order, appears only when in-plane and out-of-plane correlation lengths reach about 250 Å and 100 Å. For $x \\lesssim 0.075$ that peak develops and coincides with the orthorhombic distortion; for $x \\gtrsim 0.075$ the correlation lengths saturate near 100 Å along the $c$ axis, no Bragg-like peak forms, and no orthorhombic distortion is seen. Inelastic scattering on $x \\approx 0.1$ shows the same low-lying optical phonon softening at the I-CDW wave vector as in the parent compound, so the I-CDW is still soft-phonon driven. Around the C-CDW wave vector, no phonon anomaly is found just above the triclinic transition, which the paper takes as evidence that the C-CDW forms by lock-in of the 3D I-CDW order rather than by its own phonon instability.","pith_inferences":["The lock-in picture implies a testable prediction: the C-CDW superstructure peaks should inherit the 3D character and correlation-length anisotropy of the I-CDW right at the transition, so measuring their widths and $q$-dependence just below $T_{\\mathrm{tri}}$ would discriminate lock-in from an independent instability.","If slow I-CDW fluctuations persist into the superconducting state, a higher-resolution quasielastic study at the I-CDW position might reveal changes across $T_c$ that the present 3 meV data could not resolve.","The negative search at the C-CDW position could be sharpened by looking for a soft mode away from the exact commensurate point or with better energy resolution; a broad overdamped mode hidden under the elastic line would change the mechanism story."],"forward_implications":["For phosphorus contents up to at least $x \\approx 0.12$, the I-CDW formation is soft-phonon driven: a low-lying optical phonon softens at the I-CDW wave vector even though long-range order and the orthorhombic distortion are absent.","The minute orthorhombic distortion in the $ab$ plane is the thermodynamic signature of long-range 3D I-CDW ordering, and this ordering only occurs for $x \\lesssim 0.075$.","The C-CDW/triclinic transition is not driven by a distinct phonon instability; it is best viewed as a lock-in of the 3D I-CDW order accompanying the triclinic distortion.","At high phosphorus content, slow, resilient I-CDW fluctuations persist to the lowest temperatures and govern the low-energy lattice and electronic dynamics, plausibly connecting to the observed $E_g$ phonon splitting and nematic-liquid behaviour.","No competition between the I-CDW and superconductivity is resolved; the relevant change for superconductivity appears to be the suppression of the C-CDW."],"supporting_citations":[{"why":"Supplies the original inelastic and diffuse X-ray evidence for soft-phonon I-CDW formation in the parent compound and the baseline data for comparison.","marker":"[17]"},{"why":"Documents phonon softening and slowing-down of CDW fluctuations in the parent compound, supporting the slow-fluctuation interpretation.","marker":"[18]"},{"why":"Provides the thermodynamic transition temperatures and the orthorhombic distortion and $c$-axis anomaly against which the scattering-derived transitions are compared.","marker":"[22]"},{"why":"Reports the $E_g$ phonon splitting and nematic-liquid behaviour used to link slow I-CDW fluctuations to nematicity.","marker":"[26]"},{"why":"Supplies the high-pressure phase diagram and the second I-CDW instability used for comparison with the phosphorus-substitution behaviour.","marker":"[20]"},{"why":"Provides elastoresistivity onset temperatures included in the phase diagram.","marker":"[23]"},{"why":"Reports rotational symmetry breaking and orbital-occupancy enhancement invoked in the lock-in discussion.","marker":"[16]"},{"why":"Time-resolved spectroscopy showing that collective CDW excitations vary smoothly across the two CDW phases, supporting the lock-in interpretation.","marker":"[36]"},{"why":"Sr-substituted comparison showing I-CDW suppression, used to contrast the fluctuation regime in the phosphorus-substituted system.","marker":"[37]"}],"fun_headline_variants":["Doping fails to kill CDW phonon, only long-range order","CDW soft phonon intact; P doping only blocks its ordering","Phosphorus dulls CDW order, not its underlying phonon","Incommensurate CDW stays soft; commensurate one is lock-in only"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The claim that the commensurate CDW is not soft-phonon driven rests on not seeing a phonon anomaly in inelastic scans with 3 meV energy resolution; a soft mode broader than the resolution, at a slightly different wave vector, or hidden under the growing elastic signal would have escaped detection.","fun_headline_variants_meta":{"raw":{"variants":["Doping fails to kill CDW phonon, only long-range order","CDW soft phonon intact; P doping only blocks its ordering","Phosphorus dulls CDW order, not its underlying phonon","Incommensurate CDW stays soft; commensurate one is lock-in only"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000961,"raw_usage":{"total_tokens":4175,"prompt_tokens":1108,"completion_tokens":3067,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":724,"completion_tokens_details":{"reasoning_tokens":2987}},"tokens_in":724,"tokens_out":3067,"duration_ms":21647,"temperature":1.0,"reasoning_tokens":2987,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T21:25:27.435645+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the phonon dispersion around the commensurate wave vector $q_{\\mathrm{C-CDW}}=(1/3,0,-1/3)$ with energy resolution better than 3 meV, on a sample with $x \\approx 0.037$ just above the triclinic transition; if a phonon branch dips toward zero energy at or near $q_{\\mathrm{C-CDW}}$, the claim that the C-CDW is not soft-phonon driven fails. Alternatively, search for a resolution-limited Bragg-like peak at the I-CDW position in $x \\approx 0.1$ samples cooled below 2 K or in larger crystals; finding one would contradict the claim that long-range I-CDW order fails to develop for $x \\gtrsim 0.075$.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the original inelastic and diffuse X-ray evidence for soft-phonon I-CDW formation in the parent compound and the baseline data for comparison."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Documents phonon softening and slowing-down of CDW fluctuations in the parent compound, supporting the slow-fluctuation interpretation."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the thermodynamic transition temperatures and the orthorhombic distortion and $c$-axis anomaly against which the scattering-derived transitions are compared."},{"cited_title":"Frachet, P","cited_arxiv_id":null,"evidence_quote":"Reports the $E_g$ phonon splitting and nematic-liquid behaviour used to link slow I-CDW fluctuations to nematicity."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the high-pressure phase diagram and the second I-CDW instability used for comparison with the phosphorus-substitution behaviour."},{"cited_title":"Lacmann, A.-A","cited_arxiv_id":null,"evidence_quote":"Provides elastoresistivity onset temperatures included in the phase diagram."},{"cited_title":"Ronning, N","cited_arxiv_id":null,"evidence_quote":"Reports rotational symmetry breaking and orbital-occupancy enhancement invoked in the lock-in discussion."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Time-resolved spectroscopy showing that collective CDW excitations vary smoothly across the two CDW phases, supporting the lock-in interpretation."},{"cited_title":"1 P-sample","cited_arxiv_id":null,"evidence_quote":"Sr-substituted comparison showing I-CDW suppression, used to contrast the fluctuation regime in the phosphorus-substituted system."}],"review_version":1}