{"id":"7ce0a497-8dc2-4136-9155-7da1257042fe","arxiv_id":"2412.09375","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Magnetoresistance of pressurized La3Ni2O7 follows a quasi-quadratic field dependence and extended Kohler scaling, leading the authors to conclude the normal state is a multiband metal.","lead":"This paper measures how the electrical resistance of the nickelate superconductor La3Ni2O7 responds to magnetic fields under pressures up to 35 GPa. It finds a simple magnetoresistance behavior that the authors read as evidence for a normal state made of several metallic bands, unlike cuprates.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The extended-Kohler collapse does not by itself establish multiband metallicity: nT is a free temperature-dependent rescaling that could also absorb single-band scattering-anisotropy or fluctuation effects, so the central claim rests on an untested diagnostic assumption.","rationale":"The reader's weakest_assumption is essentially the same as mine: the extended-Kohler scaling is interpreted as evidence of multiband transport, but that interpretation is not unique. I agree with the conditional verdict. I want to stress that the issue is not disagreement with a consensus but the internal logic of the inference: nT is defined by Eq. (4) from a multiband model, yet in practice it is treated as a free function of T that is adjusted to force collapse. A universal scaling with one free parameter per temperature has weak falsifiability. The paper does present genuine new transport data under pressure, a quasi-quadratic field dependence, and a systematic comparison with pnictides and cuprates; those are valuable. But the central claim would be much stronger if nT(T) were cross-validated by Hall measurements or by a two-band Boltzmann calculation with band-structure inputs. Because the abstract says 'suggest' and 'roughly understood,' the manuscript does not overclaim enough to warrant rejection; conditional acceptance with the additional checks is the right disposition.","tokens_in":16198,"tokens_out":5003,"duration_ms":66131,"concrete_test":"Take the same raw MR isotherms and perform an identical collapse using a single-band model with temperature-dependent anisotropic scattering, e.g. tau^(-1)(k,T) = tau0^(-1)[1 + delta(T) cos(2phi)], fitting delta(T) and tau0(T). If the collapse quality and smoothness of delta(T) match Figs. 3(g)-(k), extended-Kohler scaling is not evidence for multiband transport. Better: on the same crystal, measure R_H(T) and rho(T) at fixed pressure, extract n_h*mu_h and n_e*mu_e from a two-band fit, compute nT from Eq. (5), and require quantitative agreement with the scaling-derived nT. A mismatch beyond error bars would force the central claim to be weakened to 'consistent with, but not established by, multiband metallicity.'","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing step is the inference from Eq. (3) (Section III) that successful extended-Kohler scaling implies multiband transport. For that inference to hold, the fitted thermal factor nT(T) must be a physical multiband carrier/mobility combination, not merely an empirical rescaling that absorbs any temperature-dependent violation of Kohler's rule. In the weak-field semiclassical picture, MR ~ (omega_c tau)^2 times a Fermi-surface/anisotropy factor; a single band with a momentum-dependent scattering rate whose anisotropy changes with T, or with spin/charge-fluctuation scattering, also violates Kohler's rule while retaining quasi-quadratic MR. Since nT(T) is one free parameter per isotherm, collapsing the curves in Figs. 3(g)-(k) is expected; no independent constraint (Hall coefficient, two-band Boltzmann fit, or band-structure-derived nT) is provided, and no error bars accompany nT. Eq. (5) is also presented without stating how signs or absolute values are handled inside the fractional powers, so the 'thermal factor' is not a robustly defined observable. The data are new and the wording of the claim is appropriately modest, but the multiband metal conclusion is underdetermined by the scaling analysis alone.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports systematic high-field magnetoresistance (MR) measurements on La3Ni2O7 single crystals under pressures from 4.5 to 34.9 GPa, all performed on the same crystal during a single pressure increase. The authors find that the MR is quasi-quadratic in field (exponent n between 1.75 and 2.1) across the entire pressure-temperature range, that MR increases monotonically with pressure, and that the data violate Kohler's rule but can be collapsed with an extended Kohler's rule using a thermal factor nT (Eq. 3). The extracted nT varies smoothly and approximately linearly with temperature. On this basis, the authors conclude that the normal state of La3Ni2O7 is a multiband metal whose in-plane transport is semiclassical, in contrast to the anomalous MR behavior in cuprates and pnictides.","tokens_in":16470,"tokens_out":5273,"duration_ms":55562,"significance":"If the multiband conclusion is accepted, this is a valuable normal-state characterization of a high-Tc nickelate: the dataset is systematic, the same-crystal pressure study removes some sample-dependent uncertainties, and the comparison with BaFe2(As1-xPx)2 and La2-xSrxCuO4 helps place nickelate transport in context. The presentation of raw MR curves, fits, and extended Kohler plots is a clear strength. However, the central inference from extended Kohler scaling to multiband metallicity is underdetermined: the thermal factor nT is a free fitted rescaling, and the manuscript does not provide an independent test such as Hall-effect measurements, a two-band Boltzmann analysis, or a band-structure-derived estimate of nT. The claim is therefore plausible and potentially important, but it is not yet established by the scaling analysis alone.","major_comments":[{"comment":"The central conclusion rests on the extended Kohler scaling in Eq. (3), but nT is a free parameter chosen independently for each temperature and pressure to collapse the curves. For a pure power law MR = a(T)(μ0H)^n, the collapse is automatic: one can always define nT(T) ∝ a(T)^(-1/n), so the successful collapse in Figs. 3(g)-(k) is not an independent test of the multiband model. Any mechanism that produces a temperature-dependent amplitude in MR while preserving quasi-quadratic field dependence - including a single band with strongly temperature-dependent scattering anisotropy, or spin/charge-fluctuation scattering - can be absorbed into the fitted nT. This is not a remote alternative here: the paper's own introduction cites reports of SDW, CDW, and antiferromagnetic fluctuations in La3Ni2O7. To make the multiband claim load-bearing, the fitted nT(T) should be compared with an independent estimate from Hall measurements, a two-band Boltzmann fit, or band-structure calculations.","section":"Section III, Eqs. (3)-(5)"},{"comment":"The thermal factor nT is not a robustly defined observable as written. In Eq. (5), the expressions nhμh - neμe and nhμh^3 - neμe^3 appear inside fractional powers, but nothing in the text states how signs or absolute values are handled. Since a two-band system with electron and hole carriers can have either difference change sign with temperature or pressure, the literal formula can become undefined or complex while the fitted nT remains positive. The authors should state the domain of validity of Eq. (5) and how the numerical values of nT are extracted from it.","section":"Section III, Eq. (5)"},{"comment":"The nT(T) values in Fig. 3(i) are shown without error bars and without a description of the fitting procedure: the manuscript does not state which field range is used in the collapse, how collapse quality is quantified, or whether nT is determined by a least-squares minimization over the full MR curve. Since the paper later contrasts the claimed smooth linear temperature dependence of nT with the anomalous behavior in pnictides, the absence of uncertainties makes it difficult to evaluate whether the linearity, and the contrast itself, is actually supported by the data.","section":"Section III, Fig. 3(i)"}],"minor_comments":[{"comment":"The sentence 'These results suggest that the normal state of La3Ni2O7 to be a multiband metallic nature' is grammatically incomplete; it should read 'suggests that the normal state of La3Ni2O7 has a multiband metallic nature.'","section":"Abstract"},{"comment":"The name 'Kohler's rule' is misspelled as 'Kohl's rule' in the Introduction and in the caption of Fig. 3; the spelling should be made consistent.","section":"Section I and Fig. 3 caption"},{"comment":"The caption lists 'Extended Kohler plots' for panels (g)-(k) and then lists '(i) The temperature-dependent thermal factors nT'; the panel labeling should be clarified so that the extended Kohler plots and the nT panel are unambiguously identified.","section":"Fig. 3 caption"},{"comment":"The manuscript reports n between 1.75 and 2.1 but does not specify the field window over which the fit is performed or provide error bars for n; stating these details would make the 'quasi-quadratic' characterization more solid.","section":"Section III, Eq. (2)"},{"comment":"The sliding-window fitting procedure for α is only briefly described; the text should specify how R0 and A are treated when the window moves and whether α values at adjacent pressures are statistically distinguishable.","section":"Section III, Eq. (1)"}],"recommendation":"major_revision","confidential_remarks":"The dataset itself is valuable and likely of interest to the community. The main issue is inferential: the extended Kohler scaling is presented as evidence for multiband transport, but with a free per-isotherm rescaling it cannot distinguish between multiband transport and other sources of Kohler-rule violation. If the authors can add an independent multiband diagnostic (e.g., Hall coefficient or a two-band fit with band-structure inputs), the claim would be substantially strengthened; otherwise, the abstract and summary should be reworded to say that the data are consistent with, but do not uniquely establish, a multiband normal state."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Bottom line: this paper gives us a clean, systematic magnetoresistance dataset for La3Ni2O7 across pressures and fields up to 33 T, and the normal state does look like a fairly conventional multiband metal in the ab plane. The claim is modestly worded and probably correct, but the extended Kohler analysis alone does not prove multiband transport. That should be the referee's main ask, not grounds for rejection.\n\nWhat's actually new and good: the pressure-field-temperature MR dataset itself. Same crystal, same pressure run, fields up to 33 T, pressures from 4.5 to 34.9 GPa. The quasi-quadratic field dependence (n between 1.75 and 2.1) is consistent across all conditions, the MR increases monotonically with pressure, and the extended Kohler collapse works cleanly at each pressure. The extracted nT(T) is smooth and linear, with no kinks or anomalies—a useful contrast to pnictides and cuprates. That is real experimental content, not a repackaging of prior work.\n\nThe soft spot is the inference step. nT is a free parameter chosen to make each isotherm collapse, so the successful scaling is expected rather than surprising. The later two-band expression for nT in Eq. (5) is a restatement of the fitting assumption, not a prediction. There are no error bars on nT, and the sign handling inside the fractional powers in Eqs. (4) and (5) is left unexplained. More importantly, a single band with temperature-dependent scattering anisotropy, or with spin/charge fluctuations, could also violate Kohler's rule and produce a fitted nT(T). So the paper's central phrase—\"suggest a multiband metallic nature\"—is doing the right amount of work. It is a suggestion, not a demonstration.\n\nThat said, the conclusion is not wild. Prior NMR and ARPES work already pointed to multiple bands, and the paper cites them. The authors are not claiming a clean proof; the abstract and summary both say \"suggest\" and \"roughly understood.\" I would not call this circular in a damaging sense. It is a phenomenological scaling analysis, and the paper mostly presents it as such. The main missing pieces are an independent estimate of nT from a band-structure or two-band Boltzmann fit, Hall data to constrain carrier densities, and explicit error bars on the scaling parameters.\n\nWho is this for? Anyone working on nickelate superconductors who needs a careful map of normal-state transport under pressure. It is a useful reference dataset, and it deserves a serious referee. My recommendation: send it to review, with the expectation that the authors tighten the interpretation, add uncertainties, and ideally test the multiband assumption against single-band alternatives.","headline":"A useful new high-pressure MR dataset with a modest, probably right multiband claim, but the extended Kohler scaling is a phenomenological restatement, not an independent test.","tokens_in":17016,"tokens_out":1600,"would_cite":true,"duration_ms":20424,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.25.F-","74.70.-b","72.15.Gd"],"model":"deepseek-v4-flash","headline":"This paper argues that the normal state of the nickelate superconductor La3Ni2O7 under pressure is a conventional multiband metal, with its magnetoresistance collapsing onto a single curve via an extended Kohler's rule.","keywords":["magnetoresistance","multiband metal","extended Kohler's rule","nickelate superconductor","La3Ni2O7","high pressure","normal state","transport properties"],"falsifier":"A direct measurement of the Hall coefficient under the same pressures would settle the claim: if the carrier densities and mobilities extracted from Hall data do not reproduce the nT(T) obtained from MR scaling via nT = e(nh μh − ne μe)^{3/2}/(nh $μh^{3}$ − ne $μe^{3}$)^{1/2}, the multiband interpretation would be contradicted. Alternatively, observation of a magnetic or charge-density-wave order whose onset temperature tracks the nT(T) would implicate fluctuations rather than multiband transport.","tokens_in":15985,"feed_emoji":"🧲","tokens_out":5651,"duration_ms":47698,"temperature":0.7,"pith_summary":"The paper seeks to establish that the high-pressure normal state of the bilayer nickelate superconductor La3Ni2O7 is a conventional multiband metal, not an exotic strange metal. It does so by measuring magnetoresistance (MR) at pressures from 4.5 to 34.9 GPa in magnetic fields up to 33 T. Across all pressures and temperatures the MR shows a quasi-quadratic field dependence, and although it violates the standard Kohler's rule, it scales perfectly onto a single curve per pressure when an extended Kohler's rule with a temperature-dependent thermal factor nT is used. The extracted nT varies smoothly and linearly with temperature, with no anomalies, in sharp contrast to cuprates and pnictides. If correct, the normal-state transport above Tc requires no exotic scattering mechanism, and the high-Tc superconductivity emerges from a relatively ordinary metallic state.","feed_headline":"Magnetoresistance reveals nickelate normal state as multiband metal","feed_subtitle":"Quasi-quadratic MR collapses onto one extended-Kohler curve at every pressure, with no anomalies.","key_machinery":"The load-bearing object is the extended Kohler's rule with the thermal factor nT. In a multiband metal, the magnetoresistance scales as MR = f(μ0H/(nT R(0))), where nT accounts for the temperature variation of carrier densities and mobilities summed over bands. For the two observed Fermi sheets (electron-like α and hole-like β), nT is explicitly nT = e(nh μh − ne μe)^{3/2}/(nh $μh^{3}$ − ne $μe^{3}$)^{1/2}. The successful scaling of all MR data at each pressure onto a single curve, together with the quasi-quadratic field exponent n ≈ 2, carries the argument: it shows the violation of Kohler's rule is merely the thermal redistribution of carriers among bands and not a sign of non-Fermi-liquid physics.","core_discovery":"The central discovery is that the normal state of La3Ni2O7 is a multiband metal describable by the semiclassical Boltzmann picture. The authors measured MR on a single crystal under pressures from 4.5 GPa to 34.9 GPa in fields up to 33 T, finding MR(μ0H) ≈ a(μ0H)^n with n ≈ 1.75–2.1 at all temperatures and pressures. The standard Kohler's rule MR = f(μ0H/R(0)) fails because the carrier density changes with temperature, but the extended Kohler's rule MR = f(μ0H/(nT R(0))) collapses all data at each pressure onto one curve. The thermal factor nT, which for two bands is nT = e(nh μh − ne μe)^{3/2}/(nh $μh^{3}$ − ne $μe^{3}$)^{1/2}, grows linearly with temperature and shows no kinks or saturation. The authors conclude that the transport behavior of the normal states in nickelate superconductors can be roughly understood by a multiband metal model, distinguishing La3Ni2O7 from cuprates and pnictides.","pith_inferences":["If the normal state is a conventional multiband metal, the high-Tc pairing mechanism in La3Ni2O7 likely relies on interlayer spin correlations rather than on an exotic strange-metal normal state; the ab-plane transport is then 'normal' while superconductivity is driven by interlayer effects.","A direct two-band fit to Hall effect and MR data could extract quantitative carrier densities and mobilities (nh, ne, μh, μe) and test Eq. (5) without free parameters, providing a sharper falsification of the multiband claim.","The same extended-Kohler analysis could be applied to other nickelate families (e.g., trilayer La4Ni3O10 and La2PrNi2O7) to see whether their normal states are also multiband metals, or whether the bilayer structure is special.","C-axis magnetoresistance measurements would probe interlayer carrier dynamics, which the paper notes are essential for testing the role of interlayer effects in the superconductivity."],"forward_implications":["The normal state of La3Ni2O7 from 4.5 to 34.9 GPa is a semiclassical multiband metal, so the widely reported 'strange metal' behavior in this compound does not require non-Fermi-liquid physics.","The extended Kohler's rule provides a practical tool to extract the thermal factor nT(T) for nickelate superconductors, allowing comparison of band parameters across the phase diagram.","The quasi-quadratic MR and the absence of anomalies in nT(T) distinguish nickelates from cuprates and pnictides, whose nT(T) shows kinks or saturation near quantum critical points.","The smooth, linear nT(T) even in the 'under' region indicates that any hidden order that couples to transport preserves the simple multiband scaling."],"supporting_citations":[{"why":"Reports the discovery of superconductivity near 80 K in La3Ni2O7 under high pressure, defining the material system under study.","marker":"[1]"},{"why":"Provides the bilayer two-orbital model with electron-like α and hole-like β Fermi sheets that justify the two-band expression for nT.","marker":"[4]"},{"why":"Supplies the pressure-driven phase diagram and structural transition boundaries used to label the under, optimal, and over regions.","marker":"[13]"},{"why":"Gives the semiclassical Boltzmann transport picture predicting quadratic magnetoresistance and Kohler scaling.","marker":"[39]"},{"why":"Establishes the standard Kohler's rule framework in BaFe2As2, providing the baseline for judging the nickelate's deviation.","marker":"[40]"},{"why":"Documents the violation of Kohler's rule in cuprates, the anomalous behavior the paper contrasts with the nickelate's clean scaling.","marker":"[42]"},{"why":"Introduces the extended Kohler's rule with the thermal factor nT that the paper adopts for scaling all magnetoresistance data.","marker":"[44]"}],"fun_headline_variants":["Extended Kohler's rule unifies nickelate magnetoresistance data","Multiband metal behavior underlies nickelate normal state","Quasi-quadratic MR collapses onto one extended-Kohler curve for La3Ni2O7","Pressure tunes nickelate into a multiband metal as seen in magnetoresistance","Nickelate normal state is a multiband metal, magnetoresistance shows"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The interpretation that the observed extended-Kohler scaling and the smooth, linear nT(T) uniquely imply multiband transport assumes that no other temperature-dependent mechanism—such as a single band with strongly temperature-dependent scattering anisotropy, or magnetic or density-wave fluctuations—produces the same scaling.","fun_headline_variants_meta":{"raw":{"variants":["Extended Kohler's rule unifies nickelate magnetoresistance data","Multiband metal behavior underlies nickelate normal state","Quasi-quadratic MR collapses onto one extended-Kohler curve for La3Ni2O7","Pressure tunes nickelate into a multiband metal as seen in magnetoresistance","Nickelate normal state is a multiband metal, magnetoresistance shows"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000596,"raw_usage":{"total_tokens":2788,"prompt_tokens":943,"completion_tokens":1845,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":559,"completion_tokens_details":{"reasoning_tokens":1742}},"tokens_in":559,"tokens_out":1845,"duration_ms":12133,"temperature":1.0,"reasoning_tokens":1742,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-11T17:05:17.889452+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A direct measurement of the Hall coefficient under the same pressures would settle the claim: if the carrier densities and mobilities extracted from Hall data do not reproduce the nT(T) obtained from MR scaling via nT = e(nh μh − ne μe)^{3/2}/(nh $μh^{3}$ − ne $μe^{3}$)^{1/2}, the multiband interpretation would be contradicted. Alternatively, observation of a magnetic or charge-density-wave order whose onset temperature tracks the nT(T) would implicate fluctuations rather than multiband transport.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the discovery of superconductivity near 80 K in La3Ni2O7 under high pressure, defining the material system under study."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the bilayer two-orbital model with electron-like α and hole-like β Fermi sheets that justify the two-band expression for nT."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the semiclassical Boltzmann transport picture predicting quadratic magnetoresistance and Kohler scaling."},{"cited_title":"Kasahara, T","cited_arxiv_id":null,"evidence_quote":"Establishes the standard Kohler's rule framework in BaFe2As2, providing the baseline for judging the nickelate's deviation."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Documents the violation of Kohler's rule in cuprates, the anomalous behavior the paper contrasts with the nickelate's clean scaling."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces the extended Kohler's rule with the thermal factor nT that the paper adopts for scaling all magnetoresistance data."}],"review_version":1}