{"id":"17549347-5e36-4d8c-9b3f-a464379671c7","arxiv_id":"2608.03908","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"In strained La2PrNi2O7/NdAlO3 films, ARPES finds a nodeless superconducting gap that closes at TC, an inferred specific heat jump, and a strain-independent gamma Fermi pocket.","lead":"ARPES measurements of strained La2PrNi2O7/NdAlO3 films show a superconducting gap that opens at TC, closes completely above TC, and has no node on the measured diagonal cut. The same spectra are used to infer an electronic specific heat jump, and the gamma Fermi pocket appears under every strain condition tested.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Single-diagonal-cut DOS cannot support a thermodynamic specific-heat claim; the 'jump' may be a restatement of the gap opening, not a measured thermodynamic anomaly.","rationale":"The reader's weakest assumption — that a single BZ-diagonal momentum cut is treated as the full electronic DOS — is indeed the load-bearing point. The paper's thermodynamic claim depends entirely on that identification, and the manuscript itself admits the extraction formulas are inexact under strong correlation. The reader's CONDITIONAL verdict is therefore appropriate: the ARPES observations of a gap and coherence peaks are credible, but the 'missing thermodynamic evidence' claim requires a full-BZ DOS integration or a direct calorimetric measurement before it can be accepted. No adjustment to the verdict is needed; the current CONDITIONAL status already captures the required conditions.","tokens_in":9598,"tokens_out":4751,"duration_ms":53031,"concrete_test":"Reconstruct DOS(E) from a full-BZ integration of the measured ARPES spectral function (using the 63 eV Fermi-surface maps in Figs. 1c/4a plus the diagonal 7 eV data, with symmetry and matrix-element normalization) and recompute S and γs. If the jump at TC disappears or its amplitude changes by more than the error bars, the single-cut DOS was not representative and the thermodynamic claim fails. As a complementary decisive check, attempt a direct specific-heat measurement on the same NdAlO3-grown films; the absence of an anomaly at TC would falsify the thermodynamic claim.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim ('missing thermodynamic evidence') requires that the momentum-integrated EDC along the BZ diagonal (Fig. 3a) equals the total electronic DOS. This is not established. The measured Fermi surface contains α, β, and γ pockets with different orbital characters, and ARPES matrix elements weight different cuts differently; a single cut cannot represent the global DOS. The entropy formula in Methods (S = -kB ∫ [f ln f + (1-f) ln(1-f)] DOS(E) dE) is therefore fed with a cut-specific quantity. Moreover, the DOS(EF) used for Fig. 3b is integrated only over EF ± 5 meV while the fitted gap is ~16 meV, so the 'drop' at TC mostly reflects spectral-weight depletion within that narrow window — i.e., the gap opening itself. The paper states that these relations 'become inexact with strong electronic correlation,' and both γs^DOS and γs^Δ are normalized to their 80 K values, so no absolute heat-capacity jump is measured. Under these conditions, the extracted 'specific heat jump' is not an independent thermodynamic observable but a model-dependent restatement of the gap closing.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports laser- and synchrotron-based ARPES measurements on compressively strained La2PrNi2O7/NdAlO3 Ruddlesden–Popper nickelate films. The authors observe a ~16 meV superconducting gap with coherence peaks along the Brillouin-zone diagonal, show that the gap closes by ~60–90 K without a pseudogap, and identify α, β, and γ Fermi pockets. They further extract an electronic entropy and specific-heat coefficient from the momentum-integrated ARPES DOS and from the measured gap, reporting a jump at TC, which they interpret as thermodynamic evidence for the superconducting transition. Strain-dependent measurements show the γ pocket in all films, and DFT is used to discuss Fermi-surface evolution. The paper claims nodeless pairing and s-wave (s±) symmetry.","tokens_in":9800,"tokens_out":8745,"duration_ms":91061,"significance":"The raw spectroscopic observations are valuable: a clean gap closing at TC with no pseudogap is exactly what is needed to identify the superconducting order parameter in a nickelate film, and the strain-dependent Fermi-surface survey is systematic. If the specific-heat jump were genuinely thermodynamic, this would be a major advance and the first such evidence in nickelates. However, the thermodynamic claim is not supported by the analysis as presented. The entropy input is either a single-cut DOS or the measured gap itself, so the 'jump' is a transformation of the gap-opening observation; no absolute heat-capacity anomaly is measured. The nodeless claim is also stronger than the single-cut data justify. The paper's significance is therefore contingent on reframing the claims and providing the missing support.","major_comments":[{"comment":"The DOS(E) used in the entropy integral is obtained by integrating ARPES spectra over momentum along a single BZ-diagonal cut (red line in Fig. 3a inset). The measured Fermi surface contains α, β, and γ pockets with different orbital characters, and ARPES matrix elements weight different cuts and photon energies differently. No evidence is provided that this one-dimensional cut is proportional to the total DOS required by S = −kB∫[f ln f + (1−f) ln(1−f)] DOS(E)dE. Consequently γs^DOS and its 'jump' at TC are cut-specific spectral quantities, not a thermodynamic specific-heat jump. This directly undermines the abstract's 'missing thermodynamic evidence' claim.","section":"Fig. 3a–c and Methods"},{"comment":"γs^Δ is computed by inserting the measured Δ(T) into the BCS density of states D_s^0(E,T) and differentiating the resulting entropy. Since Δ(T) is defined to vanish near TC, a peak in γs^Δ at TC is a mathematical consequence of the gap-opening observation, not an independent thermodynamic signature. The curve is normalized to its value at 80 K, so no absolute heat-capacity anomaly is reported. This is a restatement, not 'further demonstrating a thermodynamic phase transition.'","section":"Methods: Extraction from Δ; Fig. 3e"},{"comment":"DOS(EF) integrates the momentum-integrated EDC only over EF ± 5 meV, whereas the measured gap is ~16 meV. The observed 'sudden drop' across TC is therefore dominated by the depletion of spectral weight within the gap window—i.e., the same gap opening already shown in Fig. 2. The derivative peak in Fig. 3c is a reprocessing of that effect, not a new thermodynamic observable.","section":"Fig. 3b"},{"comment":"The superconducting gap is measured along a single BZ-diagonal cut. A finite gap at this location does exclude the canonical d-wave node that lies on that diagonal, but it does not by itself map the gap over the full Fermi surface. The statement that 'a nodeless behavior is unambiguously established' is stronger than the presented data support; additional k_F points or a full gap map are needed.","section":"Fig. 1e–h and Fig. 2"},{"comment":"The text concedes that the relations used for both types of specific-heat analysis 'become inexact with strong electronic correlation.' This concession directly weakens the central claim, because RP nickelates are strongly correlated. The manuscript does not quantify the error or show why a qualitative jump survives. As written, the thermodynamic conclusion is not established.","section":"§4, thermodynamic-evidence paragraph"}],"minor_comments":[{"comment":"Since γs^DOS and γs^Δ are normalized to their 80 K values, the y-axes are dimensionless; please state this explicitly and consider showing the unnormalized relative change so the reader can judge the magnitude of the reported anomaly.","section":"Fig. 3c,e"},{"comment":"The dashed line is described as 'BCS-like'; please specify the gap equation, Δ0, and TC used for the curve rather than leaving it as a generic dashed guide.","section":"Fig. 2c"},{"comment":"The calculations are performed in a single-layer limit, while the measured films are 3 UC thick. Please justify this approximation or discuss possible finite-thickness effects on the γ-band dispersion and Fermi-surface comparison.","section":"Methods/DFT"},{"comment":"In the equation for S^Δ, clarify whether DOS is the normal-state or superconducting DOS and state the integration limits; the current typesetting is confusing. Several references are also preprints (e.g., refs. 24, 28, 29, 33, 38, 40) and should be updated if published versions exist.","section":"Methods entropy equation"}],"recommendation":"reject","confidential_remarks":"The paper's strongest and headline claim—thermodynamic evidence for the superconducting phase transition—is not supported by the presented analysis. The single-cut DOS and the Δ-derived entropy make the 'specific heat jump' a restatement of the gap opening rather than an independent thermodynamic observable. This is a load-bearing error that cannot be fixed within the manuscript's current scope. The raw gap and Fermi-surface data are valuable; a future submission focused on the gap symmetry and strain-dependent topology, without the thermodynamic overclaim, could be reconsidered."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: the raw ARPES observations are solid and the new heterostructure is genuinely interesting, but the central claim of \"thermodynamic evidence\" does not survive scrutiny. The specific-heat jump is reconstructed from the same ARPES spectra and from the measured gap itself, not measured thermodynamically.\n\nWhat's actually new: the La2PrNi2O7/NdAlO3 system, the absence of a pseudogap, a ~16 meV gap that opens at TC and closes by 70–90 K, and a strain series showing the γ pocket in all superconducting and non-superconducting films. These are valuable results. The data presentation is careful, the fits are shown, and the DFT trend with hole doping captures the γ-band dispersion qualitatively. Credit where it's due: the gap closing at TC without a pseudogap is a clean observation for this material.\n\nThe soft spot is the thermodynamic claim. The DOS used for the entropy/specific-heat extraction comes from integrating the spectral weight along a single BZ diagonal cut (Fig. 3a), not the full Brillouin zone. With α, β, and γ pockets of different orbital character and ARPES matrix-element weighting, that cut is not the global DOS. Worse, the DOS(EF) window is EF ± 5 meV while the gap is ~16 meV, so the \"drop\" across TC mostly reflects the gap opening itself. The alternative estimate uses the measured Δ(T) to construct a BCS DOS—making the jump at TC a mathematical transformation of the gap, not independent confirmation. The authors honestly note the relations become inexact under strong correlation, but that caveat undercuts the headline. The nodeless conclusion also rests on a single cut; it supports nodelessness along the diagonal but doesn't rule out accidental nodes elsewhere.\n\nWho is this for: the nickelate community and ARPES practitioners. It deserves a serious referee because the gap and strain results are worth publishing and discussing. But the thermodynamic wording should be scaled back to \"ARPES-derived estimate consistent with a second-order transition,\" not \"missing thermodynamic evidence.\" The authors should either obtain a real specific-heat measurement or clearly label the extracted quantity as model-dependent.\n\nRecommendation: send to peer review, but with a request for major revision—reframe the thermodynamic claim and either provide a full-BZ DOS or drop the thermodynamic language.","headline":"Credible ARPES gap and strain data, but the 'thermodynamic evidence' claim is an overreach: the specific-heat jump is reconstructed from the same spectra and the measured gap itself, not measured thermodynamically.","tokens_in":10404,"tokens_out":2024,"would_cite":true,"duration_ms":21358,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"ARPES on strained La2PrNi2O7/NdAlO3 films reveals a nodeless superconducting gap that opens at TC and an electronic specific-heat jump, providing thermodynamic evidence for the nickelate superconducting transition.","keywords":["Ruddlesden-Popper nickelates","unconventional superconductivity","angle-resolved photoemission spectroscopy","superconducting gap","nodeless pairing","specific heat","Fermi surface topology","La2PrNi2O7"],"falsifier":"Measure the actual bulk specific heat of the same La2PrNi2O7/NdAlO3 films around 60 K, or repeat the density-of-states reconstruction using ARPES spectra integrated over the whole Brillouin zone; if no specific-heat jump survives in either case, the paper's thermodynamic claim is falsified.","tokens_in":9443,"feed_emoji":"🧲","tokens_out":7946,"duration_ms":69567,"temperature":0.7,"pith_summary":"This paper reports angle-resolved photoemission measurements on compressively strained La2PrNi2O7/NdAlO3 films, a Ruddlesden-Popper nickelate superconductor with zero resistance near 33 K and onset near 60 K. The authors find a superconducting gap of about 16 meV that opens at the transport onset, with sharp coherence peaks and no pseudogap above TC. By integrating the measured spectra over momentum, they reconstruct the electron density of states and, following a method used in cuprates, extract the electronic entropy and specific heat; they find a jump at TC, which they present as the missing thermodynamic evidence for the superconducting phase transition in nickelates. They also show the gap is nodeless, favoring s-wave or s± pairing over d-wave, and that the γ Fermi pocket appears in all films regardless of strain, so its mere presence does not control superconductivity.","feed_headline":"Nickelate film shows thermodynamic jump at TC in ARPES data","feed_subtitle":"Gap opens at TC with coherence peaks and no pseudogap, strengthening the case for s-wave pairing in RP nickelates.","key_machinery":"The central objects are the ARPES-measured superconducting gap Δ(T), quantified by coherence peaks in symmetrized energy distribution curves, and the momentum-integrated electron density of states DOS(E). The paper uses the BCS superconducting density of states, convolved with a Gaussian resolution function, together with the entropy integral S = -kB∫[f ln f + (1-f) ln(1-f)] DOS(E) dE and γs = dS/dT, following the cuprate ARPES-to-specific-heat practice. The nodeless character of the gap along the Brillouin-zone diagonal carries the pairing-symmetry conclusion, while the presence and size of the γ pocket across different substrates carries the Fermi-surface-topology conclusion.","core_discovery":"On a compressively strained La2PrNi2O7/NdAlO3 film, laser ARPES along the Brillouin-zone diagonal reveals a superconducting gap of about 16 meV at 10 K, with prominent coherence peaks and Bogoliubov back-bending. The gap closes at the transport-defined TC, and no pseudogap appears above TC, so the measured gap is taken to be the superconducting order parameter itself. Integrating the same spectra over momentum yields a drop in the density of states at the Fermi level across TC and a corresponding jump in the electronic specific-heat coefficient; a second estimate built from the measured gap via the BCS density of states also shows a jump. The paper concludes that these results provide the mi","pith_inferences":["A natural next test is direct calorimetry on the same heterostructures; the paper's method could be validated or falsified by a bulk specific-heat jump of comparable shape and size.","If the nodeless, pseudogap-free gap is confirmed by other techniques, it sharpens the theoretical constraint: any acceptable pairing theory for RP nickelates must produce a fully gapped order parameter on the relevant Fermi sheets.","The ARPES-derived specific-heat procedure could be exported to other thin-film superconductors where bulk calorimetry is impractical, provided the momentum integration covers the full Brillouin zone rather than a single cut.","Strain studies that vary compressive strain continuously could test whether the bosonic mode implicated by the observed electron-boson coupling is the quantity that tracks TC."],"forward_implications":["If the ARPES-derived specific-heat jump is genuine, nickelate films now have the same triad of evidence as conventional superconductors: zero resistance, diamagnetism, and a thermodynamic jump at TC.","A nodeless gap that closes exactly at TC rules out a pure d-wave order parameter on the dx2-y2 bands, supporting s-wave or s± pairing in RP nickelates.","The coexistence of the γ (dz2) pocket in superconducting and non-superconducting films means the emergence of superconductivity is not controlled simply by the presence of that pocket.","Hole doping in the films places the Fermi level where the γ band is steep; strain mainly reshapes the β pocket, so strain-induced superconductivity is more likely tied to other effects such as octahedral tilts or bosonic-mode coupling."],"supporting_citations":[{"why":"Provides the textbook definition that a specific-heat jump marks the thermodynamic superconducting transition.","marker":"[1]"},{"why":"Supplies the cuprate ARPES method for extracting electronic entropy and specific heat from momentum-integrated spectral weight.","marker":"[2]"},{"why":"Prior RP nickelate films where gap and pseudogap were both seen; also the source of the UHV sample-transfer technique used here.","marker":"[23]"},{"why":"Reports growth, strain, and transport of the La2PrNi2O7/NdAlO3 heterostructures that are the subject of this paper.","marker":"[24]"},{"why":"Provides the α/β/γ Fermi-pocket notation and the bulk La3Ni2O7 comparison showing a flat γ band-top below the Fermi level.","marker":"[25]"},{"why":"Supplies the spectral-function and condensation-energy formalism used to connect measured spectra to electronic entropy.","marker":"[30]"},{"why":"Provides the phenomenological model used to fit symmetrized EDCs and extract the superconducting gap magnitude.","marker":"[41]"},{"why":"Gives the BCS superconducting density of states used to compute entropy and specific heat from the measured gap.","marker":"[50]"}],"fun_headline_variants":["No pseudogap allows direct measure of nickelate superconducting gap","Specific heat jump confirms thermodynamic transition in nickelate films","ARPES reveals nodeless superconducting gap in nickelate film","Thermodynamic jump observed in nickelate superconductor by ARPES","Nickelate superconductors get first thermodynamic proof via specific heat jump"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The load-bearing premise is that the momentum-integrated spectral weight measured along one diagonal cut of the Brillouin zone faithfully represents the full electronic density of states; if that cut is not representative, the extracted specific-heat jump is just the gap opening restated, not a thermodynamic measurement.","fun_headline_variants_meta":{"raw":{"variants":["No pseudogap allows direct measure of nickelate superconducting gap","Specific heat jump confirms thermodynamic transition in nickelate films","ARPES reveals nodeless superconducting gap in nickelate film","Thermodynamic jump observed in nickelate superconductor by ARPES","Nickelate superconductors get first thermodynamic proof via specific heat jump"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000523,"raw_usage":{"total_tokens":2406,"prompt_tokens":823,"completion_tokens":1583,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":567,"completion_tokens_details":{"reasoning_tokens":1495}},"tokens_in":567,"tokens_out":1583,"duration_ms":10568,"temperature":1.0,"reasoning_tokens":1495,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T05:55:53.094154+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the actual bulk specific heat of the same La2PrNi2O7/NdAlO3 films around 60 K, or repeat the density-of-states reconstruction using ARPES spectra integrated over the whole Brillouin zone; if no specific-heat jump survives in either case, the paper's thermodynamic claim is falsified.","supporting_citations":[{"cited_title":"Introduction to Superconductivity (Dover, 2004)","cited_arxiv_id":null,"evidence_quote":"Provides the textbook definition that a specific-heat jump marks the thermodynamic superconducting transition."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the cuprate ARPES method for extracting electronic entropy and specific heat from momentum-integrated spectral weight."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Prior RP nickelate films where gap and pseudogap were both seen; also the source of the UHV sample-transfer technique used here."},{"cited_title":"Electron-like high-temperature superconductivity induced by compressive strain in La2PrNi2O7 thin films","cited_arxiv_id":"2608.01295","evidence_quote":"Reports growth, strain, and transport of the La2PrNi2O7/NdAlO3 heterostructures that are the subject of this paper."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the α/β/γ Fermi-pocket notation and the bulk La3Ni2O7 comparison showing a flat γ band-top below the Fermi level."},{"cited_title":"R., Randeria, M., Jankó, B","cited_arxiv_id":null,"evidence_quote":"Supplies the spectral-function and condensation-energy formalism used to connect measured spectra to electronic entropy."},{"cited_title":"R., Randeria, M., Ding, H","cited_arxiv_id":null,"evidence_quote":"Provides the phenomenological model used to fit symmetrized EDCs and extract the superconducting gap magnitude."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the BCS superconducting density of states used to compute entropy and specific heat from the measured gap."}],"review_version":1}