{"id":"ca2f0091-ae19-4a4e-8b5c-876b24c34ade","arxiv_id":"2412.10818","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"LaNiGa2's superconducting transition temperature forms a pressure dome with a 3.2 K maximum at 14.3 GPa, accompanied by a shift in the fitted band diffusivity ratio but no structural transition.","lead":"This paper reports the first high-pressure study of the superconductor LaNiGa2, showing that its transition temperature rises to a maximum of 3.2 K at 14.3 GPa and then falls, forming a dome-shaped phase diagram. The result matters because it links a possible change in electronic structure to the superconducting behavior of a material that breaks time-reversal symmetry, a rare and contested phenomenon.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The two-band model's fixed coupling constants make the inferred D2/D1 increase non-unique; if lambda values vary under pressure, the claimed electronic-structure link is unsupported. The measured dome itself is not endangered.","rationale":"The measured pressure-temperature phase diagram, including the dome with a maximum near 14.3 GPa and the absence of a structural transition up to 26.3 GPa, is supported by transport data on three samples and by powder XRD. This is the strongest empirical contribution of the paper. The weakest link is the two-band model interpretation: by fixing all superconducting coupling constants, the only free parameters are the band diffusivities, so the apparent D2/D1 increase is conditional on that assumption. The authors honestly concede that the pressure evolution of the parameters cannot be uniquely identified. This does not invalidate the dome, but it means the paper's abstract-level suggestion of a pressure-induced electronic-structure change is not independently established. The same concern was identified by the Pith reader as the weakest assumption, so there is no new objection; the existing CONDITIONAL verdict already captures the need to treat the model-dependent interpretation with care.","tokens_in":9244,"tokens_out":5180,"duration_ms":50198,"concrete_test":"Re-fit the Hc2(T) data at 2, 14.3, and 28.8 GPa with lambda11, lambda22, and lambda12 as free parameters, constrained only by the ambient values and by consistency with the measured Tc, and scan the allowed parameter space. If the increase in D2/D1 near 7 GPa is not robust across all fits that still reproduce the measured Hc2(T) curves, the inferred electronic-structure change is an artifact of the fixed-coupling assumption and should be removed from the central narrative.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Load-bearing concern: Section 3 infers a pressure-induced change of electronic structure from the fitted increase of D2/D1 in the two-band Gurevich model, while fixing the superconducting coupling constants at their ambient-pressure values (lambda11=0.156, lambda22=0.161, lambda12=lambda21=0.012). The Hc2(T) data alone cannot separate changes in diffusivities from changes in coupling constants; as the authors state, 'which parameters change under pressure cannot be uniquely identified.' If the coupling constants also evolve under pressure, the sharp rise in D2/D1 near 7 GPa may be an artifact of that constraint rather than a genuine electronic-structure change. Because the XRD results only rule out a structural transition, this fit is the sole evidence connecting the Tc dome to electronic structure. The dome itself remains a valid experimental observation; what is unsupported is the mechanistic claim in the abstract that the D2/D1 increase suggests pressure-induced electronic-structure changes closely linked to the evolution of superconductivity.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports electrical resistivity and powder X-ray diffraction measurements on single-crystal LaNiGa2 under pressures up to ~28 GPa. The authors find that Tc initially increases slightly to 2.2 K at ~4 GPa, then rises more rapidly to a maximum of 3.2 K at ~14.3 GPa, and decreases monotonically thereafter, forming a superconducting dome. The upper critical field μ0Hc2(0) increases monotonically from 0.8 T at 2 GPa to 1.72 T at 28.3 GPa. Powder XRD shows no structural phase transition up to 26.3 GPa, and the unit-cell volume is fitted to a Birch-Murnaghan equation of state with B0 = 141.9 GPa. Fitting Hc2(T) with a two-band Gurevich model, using ambient-pressure coupling constants, yields a decrease of D1 and an increase of D2/D1 above ~7 GPa, which the authors interpret as a possible pressure-induced electronic structure change.","tokens_in":9425,"tokens_out":8810,"duration_ms":76745,"significance":"If the dome is correct, this is a clean example of a pressure-induced Tc dome in a TRS-breaking superconductor with topological band crossings, and the absence of a structural transition makes it particularly interesting. The three-sample reproducibility and the XRD analysis strengthen the experimental claims. The Hc2 analysis is a useful but model-dependent addition; the authors are transparent about its limitations. The paper will likely stimulate further high-pressure studies, such as muSR and NQR under pressure, and is of interest to the condensed-matter superconductivity community.","major_comments":[{"comment":"The use of Daphne 7373 oil as the pressure medium up to 28 GPa needs justification. Daphne 7373 is known to solidify at about 2.2 GPa at room temperature and at lower pressures at cryogenic temperatures, so the measurements above a few GPa are quasi-hydrostatic rather than truly hydrostatic. Non-hydrostatic stress can broaden the superconducting transition and shift Tc, and pressure inhomogeneity typically increases with pressure. Since the central claim of the paper is the shape of the Tc(P) dome, with a maximum near 14.3 GPa and a decrease at higher pressures, the authors should specify the hydrostatic limit of the medium, report the transition widths as a function of pressure, and discuss whether the observed decrease above 14.3 GPa could be influenced by pressure gradients. If possible, they should compare at least one high-pressure point with measurements using a more hydrostatic medium, such as helium or NaCl.","section":"Section 2 and Fig. 4(a)"},{"comment":"The claim that the deduced increase of D2/D1 near 7 GPa suggests pressure-induced electronic structure changes closely linked to superconductivity is not uniquely supported by the Hc2(T) data alone, because the two-band model calculation fixes the coupling constants (λ11=0.156, λ22=0.161, λ12=λ21=0.012) at their ambient-pressure values. As the authors themselves state, 'which parameters change under pressure cannot be uniquely identified.' The Hc2(T) curves cannot separate changes in band diffusivities from changes in the coupling constants, so the apparent jump in D2/D1 may be an artifact of the fixed-λ assumption. Please soften the abstract's final sentence to reflect this non-uniqueness, or add a robustness test, for example by allowing the coupling constants to vary within plausible ranges and checking whether the D2/D1 increase remains a stable feature.","section":"Abstract and Section 3"}],"minor_comments":[{"comment":"The criterion used to define Tc (midpoint, zero resistance, or onset) is not stated; please specify it in the methods section or the figure caption.","section":"Figure 4(a) and text"},{"comment":"The transport pressures are determined by ruby fluorescence at room temperature, while the XRD pressures are determined at the sample temperature (300 K, as stated). The actual pressure in the transport measurements at low temperatures may differ from the room-temperature value; please discuss the estimated correction or explain why any difference is negligible.","section":"Section 2 and Figure 5"},{"comment":"The phrase 'similar superconducting intraband and interband coupling constants' is vague; please state explicitly that the values are taken from Ref. [23] and note any differences, if any.","section":"Section 3"},{"comment":"Reference [41] for the ruby fluorescence method appears to be a conference paper; a standard archival reference, such as Mao et al., J. Appl. Phys. 49, 3276 (1978), would be more appropriate.","section":"Reference [41]"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the journal's scope and the experimental dataset appears to be of good quality. The main concern is the pressure-medium hydrostaticity, which directly affects the reliability of the observed Tc dome; the authors should be given the opportunity to address it either with a discussion of transition widths and pressure gradients or with a control measurement using a more hydrostatic medium. The interpretation of the D2/D1 ratio should also be tempered in the abstract. If these points are resolved, the paper would be a solid contribution."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First pressure study of LaNiGa2, and the headline result is a clear one: Tc rises from 2 K to a 3.2 K maximum around 14.3 GPa, then falls, across three samples, while powder XRD sees no structural transition up to 26.3 GPa and Hc2 keeps climbing. That is worth knowing. The dome is modest but the phase diagram is a new tuning axis for a TRS-breaking superconductor with topological band crossings, and the monotonic Hc2 with a dome-shaped Tc is the kind of decoupling that invites follow-up.\n\nThe paper does the important things correctly. Three samples show the same Tc evolution. The XRD analysis with Le Bail fits and a Birch-Murnaghan equation of state is standard and seems careful. The change in the curvature of Hc2(T) from two-band-like to single-band-like under pressure is an honest observation. The authors also state plainly that, given the number of model parameters, 'which parameters change under pressure cannot be uniquely identified.' That is the right thing to say.\n\nThe soft spot is the interpretation built on the two-band model. The claim that D2/D1 jumps near 7 GPa and therefore the electronic structure changes is load-bearing for the abstract's suggestion of a link to superconductivity. But the fit fixes the coupling constants at ambient-pressure values from the superfluid density work. If those constants also evolve with pressure, the D2/D1 rise could be an artifact of the constraint. Since the authors admit non-uniqueness, the mechanistic conclusion is not supported by the current analysis. The dome itself does not depend on that fit, so it stands. This is a moderate weakness, not a fatal one.\n\nSmaller issues: no error bars on Tc or Hc2, and no raw data provided for independent re-fitting. The broad resistivity hump above 2 GPa is mentioned and left open, which is fine.\n\nWho gets value from this: the superconductivity community, especially people working on weakly correlated TRS-breaking superconductors and pressure tuning of multiband systems. It deserves a serious referee. I would cite the phase diagram in my own work. The paper is honest, the central measurement is independent of the model, and the overreach is confined to a part the authors themselves flag.","headline":"LaNiGa2's pressure dome is a real new result; the band-diffusivity story is a self-admittedly non-unique fit.","tokens_in":10028,"tokens_out":2265,"would_cite":true,"duration_ms":18911,"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":"LaNiGa2's superconducting transition temperature forms a pressure dome peaking at 3.2 K near 14.3 GPa, with no structural transition up to 26.3 GPa.","keywords":["LaNiGa2","pressure-induced superconducting dome","two-band superconductivity","time-reversal symmetry breaking","upper critical field","high-pressure transport","high-pressure X-ray diffraction","electronic structure"],"falsifier":"Measure the upper critical field together with a direct probe of the superconducting gap under pressure, such as penetration depth or specific heat, and check whether a two-band fit with fixed coupling constants still reproduces both; conversely, a sharp pressure-driven change in quantum-oscillation frequencies or Hall coefficient near 7 GPa would confirm the proposed electronic-structure change, and its absence would undermine the claim.","tokens_in":9001,"feed_emoji":"🧲","tokens_out":9641,"duration_ms":74697,"temperature":0.7,"pith_summary":"This paper reports that applying pressure to the superconductor LaNiGa2 first raises its transition temperature from about 2.1 K to a maximum of 3.2 K near 14.3 GPa, then suppresses it, producing a dome-shaped phase diagram. Powder X-ray diffraction shows the crystal structure stays the same up to 26.3 GPa, so the dome is not caused by a structural phase transition. The authors attribute the enhancement to a possible pressure-induced change in the electronic structure, signaled by a sudden increase around 7 GPa in the ratio of the two band diffusivities ($D_2/D_1$) extracted from the upper critical field. Since LaNiGa2 is a time-reversal-symmetry-breaking superconductor with topological band crossings, mapping how its superconductivity responds to pressure constrains what kind of pairing mechanism can explain it.","feed_headline":"Pressure makes LaNiGa2 superconductivity peak at 3.2 K","feed_subtitle":"A dome-shaped Tc rises to 3.2 K at 14.3 GPa while the crystal stays unchanged, pointing to an electronic-structure effect.","key_machinery":"The central object is the pressure-temperature phase diagram of LaNiGa2, constructed from resistivity transitions of three single-crystal samples in a diamond anvil cell. The argumentative load is carried by a two-band model for the upper critical field: with intraband and interband coupling constants fixed at ambient-pressure values ($\\lambda_{11}=0.156$, $\\lambda_{22}=0.161$, $\\lambda_{12}=\\lambda_{21}=0.012$) taken from the superfluid-density analysis, the only free parameters are the band diffusivities $D_1$ and $D_2$. The ratio $D_2/D_1$ serves as the indicator of electronic-structure change: $D_1$ drops sharply near 7 GPa and $D_2/D_1$ rises toward 1, signaling a shift toward single-band behavior, and the same shift accounts in the model for the continuing increase of $\\mu_0H_{c2}(0)$ even after $T_c$ starts to fall.","core_discovery":"Under pressure, LaNiGa2 develops a dome-shaped $T_c(P)$: $T_c$ barely changes to about 2.2 K near 4 GPa, rises faster above roughly 7 GPa to a maximum of 3.2 K at about 14.3 GPa, and then falls to about 2.9 K by 28 GPa. Over the same range the zero-temperature upper critical field $\\mu_0H_{c2}(0)$ increases monotonically from about 0.8 T to 1.72 T, and the $H_{c2}(T)$ curvature evolves from two-band-like to single-band-like. Fitting with a two-band model while keeping the superconducting coupling constants fixed yields a band diffusivity ratio $D_2/D_1$ that jumps from 0.12 at 7 GPa to 0.45 at 28.8 GPa, which the authors read as a possible pressure-induced electronic-structure change closely linked to the $T_c$ enhancement. The paper explicitly leaves open whether the time-reversal-breaking pairing state persists at high pressure.","pith_inferences":["Editorial inference: the reported jump in $D_2/D_1$ near 7 GPa rests on the assumption that the pairing strengths between the bands stay fixed under pressure; if they also evolve, the jump and its link to the $T_c$ dome could be an artifact.","Editorial inference: a direct test of the proposed electronic-structure change would be pressure-dependent quantum-oscillation measurements or a sharp change in the Hall or Seebeck coefficient near 7 GPa, which would reveal a band-structure or carrier-pockets crossover.","Editorial inference: if the pairing state is tied to the topological band crossings, the high-pressure side of the dome is a natural place to look for a change of order parameter, for example with muon-spin rotation or specific-heat measurements under pressure."],"forward_implications":["If the dome is real, LaNiGa2 can be tuned continuously by pressure from a two-band-like superconductor toward a more single-band-like one, with $T_c$ rising then falling across the crossover.","The absence of any structural transition up to 26.3 GPa means that the non-monotonic $T_c$ does not require a lattice-symmetry change, leaving an electronic origin as the natural explanation.","The monotonic increase of $\\mu_0H_{c2}(0)$ while $T_c$ decreases above 14.3 GPa shows that the upper critical field and the transition temperature are not controlled by the same pressure-dependent quantity.","The pressure range above about 7 GPa is the regime where both the rapid $T_c$ increase and the inferred band-diffusivity change occur, making it the target for further probes of the normal and superconducting states.","A comparison with LaNiC2, whose pressure response shows signs of a competing correlated phase, highlights that LaNiGa2 follows a simpler path: a smooth metallic normal state throughout the measured range."],"supporting_citations":[{"why":"supplies the single-crystal growth, the corrected Cmcm space group, and the calculated topological band features that define the material.","marker":"[35]"},{"why":"provides the ambient-pressure superfluid-density analysis from which the fixed coupling constants used in the two-band fit are taken.","marker":"[23]"},{"why":"the two-band model used to fit Hc2(T) and extract D1 and D2.","marker":"[45,46]"},{"why":"the single-band model whose curvature defines the baseline from which multiband behavior is identified.","marker":"[44]"},{"why":"the high-pressure LaNiC2 study that motivates the comparison and whose competing-phase signature is absent here.","marker":"[39]"},{"why":"an example of a superconductor where Hc2 keeps increasing while Tc decreases under stress, used as a comparison for the same qualitative behavior.","marker":"[47]"},{"why":"reports the NMR/NQR evidence for the absence of magnetic fluctuations, supporting an electronic-structure rather than spin-fluctuation origin for the Tc change.","marker":"[52]"},{"why":"the equation of state used to fit the unit-cell volume and obtain the bulk modulus.","marker":"[51]"}],"fun_headline_variants":["LaNiGa2's Tc dome: 3.2 K peak at 14 GPa","Pressure creates dome in LaNiGa2 superconductivity, peak 3.2 K","LaNiGa2 Tc rises to 3.2 K at 14 GPa, then falls","Dome-shaped Tc in LaNiGa2: peak 3.2 K under pressure","Pressure tunes LaNiGa2's Tc into a dome, max 3.2 K"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The argument assumes that the internal pairing strengths between the two bands of electrons stay the same under pressure, so that all change in the measured upper critical field can be blamed on how fast electrons move in the bands; if the pairing strengths change too, the inferred electronic-structure shift near 7 GPa may be an artifact.","fun_headline_variants_meta":{"raw":{"variants":["LaNiGa2's Tc dome: 3.2 K peak at 14 GPa","Pressure creates dome in LaNiGa2 superconductivity, peak 3.2 K","LaNiGa2 Tc rises to 3.2 K at 14 GPa, then falls","Dome-shaped Tc in LaNiGa2: peak 3.2 K under pressure","Pressure tunes LaNiGa2's Tc into a dome, max 3.2 K"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000909,"raw_usage":{"total_tokens":3882,"prompt_tokens":898,"completion_tokens":2984,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":514,"completion_tokens_details":{"reasoning_tokens":2866}},"tokens_in":514,"tokens_out":2984,"duration_ms":18689,"temperature":1.0,"reasoning_tokens":2866,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T15:34:31.569929+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the upper critical field together with a direct probe of the superconducting gap under pressure, such as penetration depth or specific heat, and check whether a two-band fit with fixed coupling constants still reproduces both; conversely, a sharp pressure-driven change in quantum-oscillation frequencies or Hall coefficient near 7 GPa would confirm the proposed electronic-structure change, and its absence would undermine the claim.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"provides the ambient-pressure superfluid-density analysis from which the fixed coupling constants used in the two-band fit are taken."}],"review_version":1}