{"id":"b65c1d4a-1c32-4206-ab83-c26bd8b5173b","arxiv_id":"2501.07822","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Photoemission and LDA+DMFT calculations find a Tomonaga-Luttinger to 3D crossover near 150 K in K2Ru8O16, linked to temperature-dependent Fermi-surface warping.","lead":"Experiments and calculations show that the ruthenium oxide K2Ru8O16 switches from one-dimensional to three-dimensional electronic behavior when cooled below about 150 K. The switch appears driven by the Fermi surface becoming more warped at low temperature, so interchain hopping turns coherent.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed quantitative match at T* ~ 150 K rests on a free-electron parabolic-band momentum-broadening estimate; using the measured mass enhancement m*/m_e ~ 1.5 shifts T* to ~100 K, so the 'origin' agreement is not yet established.","rationale":"The reader's CONDITIONAL verdict correctly identifies the quantitative crossover estimate as the weakest link. I focus more sharply on the parabolic-band, free-electron-mass thermal broadening in Fig. 4(b), which converts the DMFT warping trend into a specific T* ≈ 150 K. This step is the one that produces the 'similar crossover temperature' used to claim that warping is the origin of the dimensional crossover. The paper itself notes that including m* would reduce T*, but dismisses it as slight; a factor 1.5 in mass changes T* by roughly a factor 1.5, moving it from ~150 K to ~100 K. That is a significant discrepancy relative to the claimed precision of the match. The experimental observation of a TLL-to-3D crossover near 150 K is plausible and reasonably supported by the scaling collapse and control analyses, so I do not see grounds to reject the paper. But the theoretical origin claim is not quantitatively secured, and the acknowledged single-site DMFT limitation further weakens it. The CONDITIONAL verdict remains appropriate; no verdict change is needed.","tokens_in":22656,"tokens_out":5933,"duration_ms":60900,"concrete_test":"Recompute Fig. 4(b) with the thermal broadening obtained from the actual LDA+DMFT quasi-particle dispersion: Δk(T) = k_B T / (ℏ v_F(k_F)) evaluated along the Γ-Z direction at the Fermi wave vector, using v_F from the renormalized band (or equivalently the DMFT mass enhancement). Check where this line crosses the computed Δk_z(T). If the crossing temperature moves outside roughly 100-200 K, the claimed quantitative match at ~150 K is not established, and the origin claim should be weakened accordingly. A simpler variant: repeat the crossing analysis with m* = 1.5 m_e (and 1.7 m_e) and report the resulting T*.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Fig. 4(b) the authors derive the crossover temperature by comparing LDA+DMFT Fermi-surface warping Δk_z(T) to the thermal momentum broadening Δk = k_B T/(ℏ² k_F/m_e), assuming a single parabolic band and the free-electron mass. The grey line's crossing with the warping data marks T* ≈ 150 K, and the paper calls this a 'spectacular observation' supporting the warping origin. This is the load-bearing quantitative link of the central claim. However, the paper's own DMFT gives m*/m_b ≈ 1.5 and specific heat gives 1.7; replacing m_e by m* = 1.5 m_e increases the slope of the broadening line by 1.5 and lowers the crossing to roughly 100 K, not 'slightly' as claimed in Section III. For a quasi-1D band the correct thermal broadening is set by the actual Fermi velocity along the chain, not by an isotropic free-electron parabola, so the m_e choice has no first-principles justification. Thus the agreement at 150 K is not robust evidence for the mechanism; the conclusion that warping dominates below T* remains quantitatively unverified, particularly given the paper's own caveat that single-site LDA+DMFT is insufficient for 1D systems.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a combined photoemission and LDA+DMFT study of the quasi-one-dimensional hollandite K2Ru8O16, arguing that the system exhibits a Tomonaga-Luttinger liquid (TLL) behavior above approximately 150 K and undergoes a dimensional crossover to a three-dimensional non-Fermi-liquid-like metallic state below that temperature. The experimental evidence includes a scaling collapse of near-EF photoemission spectra with TLL exponent alpha = 0.45 for 300-150 K, the failure of that collapse below 150 K, and the appearance of a Fermi cutoff with monotonically decreasing intensity at EF at low temperature. The theoretical part computes the Fermi-surface warping from LDA+DMFT as a function of temperature and compares it with a simple thermal momentum-broadening estimate, obtaining a crossover temperature near 150 K. The paper concludes that temperature-dependent FS warping, enhanced by correlation, is the origin of the dimensional crossover.","tokens_in":22901,"tokens_out":3566,"duration_ms":38141,"significance":"If the central claim is valid, the paper provides a rare direct spectroscopic observation of a TLL-to-higher-dimensional crossover in a bulk quasi-1D oxide and proposes a concrete microscopic mechanism based on temperature-dependent Fermi-surface warping. The manuscript is commendable for combining high-resolution temperature-dependent photoemission with self-consistent LDA+DMFT calculations, and for explicitly testing alternative explanations such as chemical-potential shifts and Altshuler-Aronov disorder effects. The experimental scaling collapse and its breakdown below 150 K are consistent with earlier transport data, giving internal coherence to the interpretation. However, the quantitative link between the calculated warping and the experimentally determined crossover temperature rests on a simplified free-electron estimate, so the 'origin' claim is not yet established at the same level as the existence of the crossover.","major_comments":[{"comment":"The crossover temperature T* is obtained by comparing the LDA+DMFT warping Δk_z(T) with the thermal momentum broadening Δk = k_B T / (ℏ² k_F / m_e), where m_e is the bare electron mass. This choice of mass is not justified for a quasi-1D band; the relevant scale is the Fermi velocity along the chain. More importantly, the paper's own LDA+DMFT calculation yields m*/m_b ≈ 1.5 and specific heat data give a mass enhancement of 1.7. Replacing m_e by m* = 1.5 m_e in the same formula shifts the crossing from ~150 K to ~100 K, which is not 'slightly reduce T*' as the text claims. The quantitative agreement at 150 K is therefore not robust evidence for the warping mechanism; the claim that warping dominates below T* would need to be reexamined with a proper quasi-1D Fermi velocity or a band-structure-based estimate of the thermal broadening.","section":"§III, Fig. 4(b)"},{"comment":"The assignment of the low-temperature state as 'non-Fermi liquid like behaviour' rests on the appearance of a Fermi cutoff and monotonically decreasing spectral intensity at EF. No quantitative line-shape fit to any non-Fermi-liquid model is provided; the paper only states that no value of the TLL exponent alpha can describe the data. This leaves open alternative interpretations, such as a pseudogap-like suppression of spectral weight or a dimensional crossover into a more conventional three-dimensional metal with reduced density of states near EF. Because the non-Fermi-liquid claim is stated in the abstract and conclusion, it should be either supported by a quantitative fit or explicitly softened to 'Fermi-cutoff behavior with suppressed EF weight'.","section":"§III, Fig. 3(c) and Conclusion"},{"comment":"The temperature dependence of the Fermi-surface warping Δk_z(T) is computed with single-site LDA+DMFT, an approximation that the authors themselves describe as 'insufficient to fully capture the subtleties of one-dimensional systems.' The slope of Δk_z(T) is a load-bearing input for the T* estimate, yet the manuscript does not show how this slope varies with the choice of U and J (the spectral function is shown to be robust, but not the FS-warping slope) or with alternative methods such as cluster DMFT. A sensitivity analysis of Δk_z(T) would help establish whether the near-agreement with the experimental T* is accidental or structurally meaningful.","section":"Appendix D and Fig. 4(a)"}],"minor_comments":[{"comment":"The text refers to the Ru 3d5/2 core-level spectra as being shown in Fig. 2(d), but Fig. 2(d) displays LDA+DMFT spectral functions; the core-level spectra appear in a separate panel. The figure/table cross-references should be corrected.","section":"§II, Fig. 2"},{"comment":"The sentence 'the larger FS warping was observed in the full Brillouin zone (Fig. 1(a))' appears to point to the wrong panel; the Fermi surface is shown in Fig. 1(e) or 1(c), not the band structure in Fig. 1(a).","section":"§III, Fig. 4(a)"},{"comment":"The description of the simulated spectra and the comparison with experiment in Fig. 6(b) is somewhat hard to follow; explicitly stating which lines correspond to which temperature and which are the shifted spectra would improve clarity.","section":"Appendix B, Fig. 6"},{"comment":"The phrase 'monotonously decreasing' should be 'monotonically decreasing' in several places for grammatical correctness.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The paper is a solid experimental and computational study of a known quasi-1D ruthenate, and the observation of a TLL scaling collapse and its breakdown is a valuable contribution. The main weakness is the quantitative 'origin' argument in Fig. 4(b), which rests on an unsubstantiated free-electron mass choice; the authors' own mass enhancement shifts the estimated T* to ~100 K. This is fixable by a more careful estimate or by softening the claim. The fit to the journal's scope in condensed matter/electronic structure is good. I would not reject, but the load-bearing quantitative comparison needs revision."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Here's my take on Ali et al. The experimental core is solid and worth referee time: temperature-dependent PES on K2Ru8O16 showing a clean TLL scaling collapse with alpha = 0.45 from 300 K down to 150 K, and a clear breakdown below, with careful checks against chemical-potential shift and Altshuler-Aronov disorder physics. The LDA+DMFT spectral functions also do real work, reproducing the lower Hubbard band and a mass enhancement ~1.5 that matches specific heat. The authors are admirably candid about single-site DMFT's limits in 1D.\n\nThe soft spot is exactly where the stress-test note lands. The whole quantitative origin story—that FS warping overtakes thermal momentum broadening at T* ~ 150 K—is built on converting k_B T to a momentum spread using a single parabolic band and the free-electron mass. Their own DMFT says m*/m_b ~ 1.5. Put that in, and the crossing drops to ~100 K, not 'slightly' reduced as the paper claims. And for a quasi-1D band, the relevant thermal smearing is set by the chain's Fermi velocity, not an isotropic free-electron parabola. So the claimed quantitative match at 150 K is not evidence for the warping mechanism; it's an artifact of the m_e choice. The qualitative trend—warping grows as T falls—is fine, and the experimental crossover itself is independent. But the 'spectacular observation' of matched temperatures is not established.\n\nMinor quibbles: the low-T non-Fermi liquid label rests on a Fermi cutoff plus decreasing EF intensity, without a quantitative line-shape fit; that's a reasonable suggestion, not a proof. And the DMFT uses U = 5 eV, J = 0.5 eV while cRPA gives 3.3 eV; the paper does show insensitivity to U and J in Appendix A, so this is minor.\n\nWho's it for: people working on quasi-1D correlated oxides. I'd bring it to our reading group; the TLL scaling data is a nice data point, and the warping analysis is a good cautionary tale about back-of-the-envelope estimates. I'd send it to review; the experimental part is solid and the theoretical part is worth publishing after the quantitative claim is fixed or properly hedged.","headline":"Solid experimental evidence for a TLL-to-3D crossover in K2Ru8O16, but the quantitative warping argument for T* ~ 150 K is a free-electron estimate that shifts to ~100 K with the paper's own mass enhancement.","tokens_in":23514,"tokens_out":3730,"would_cite":true,"duration_ms":34484,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["71.27.+a","71.18.+y","79.60.-i","71.10.Pm"],"model":"deepseek-v4-flash","headline":"K2Ru8O16 undergoes a 1D-to-3D electronic crossover at about 150 K, driven by Fermi-surface warping that overtakes thermal broadening as temperature falls.","keywords":["dimensional crossover","Tomonaga-Luttinger liquid","non-Fermi liquid","K2Ru8O16","hollandite","Fermi-surface warping","LDA+DMFT","photoemission spectroscopy"],"falsifier":"Angle-resolved photoemission on single crystals at several temperatures would settle it: if the measured Fermi-surface warping does not grow as temperature is lowered, or if the temperature at which the spectra stop scaling with alpha = 0.45 shifts while the calculated warping curve stays fixed, the proposed mechanism would be falsified.","tokens_in":22406,"feed_emoji":"🔬","tokens_out":7212,"duration_ms":66517,"temperature":0.7,"pith_summary":"The paper argues that the quasi-one-dimensional hollandite K2Ru8O16 undergoes a dimensional crossover at about 150 K, from a Tomonaga-Luttinger liquid (a state of interacting electrons in one dimension) to a three-dimensional non-Fermi-liquid metal, and that this crossover is driven by Fermi-surface warping. High-resolution photoemission spectra collapse onto a single Tomonaga-Luttinger scaling curve with exponent alpha = 0.45 from 300 K down to 150 K, then deviate at lower temperatures where a clear Fermi cutoff appears. Dynamical mean-field calculations based on a local-density-approximation starting point show the Fermi surface becoming progressively more warped as temperature falls. A simple parabolic-band estimate indicates that below roughly 150 K this warping exceeds the momentum broadening caused by thermal energy, so interchain hopping becomes coherent and the one-dimensional behavior is lost. If this picture is correct, it explains why the crossover temperature appears in transport, spectroscopy, and theory at the same value.","feed_headline":"Fermi-surface warping drives 1D-to-3D crossover near 150 K","feed_subtitle":"A Tomonaga-Luttinger liquid gives way to a non-Fermi-liquid metal as warping beats thermal broadening.","key_machinery":"The argument rests on two pieces of machinery. First, the experimental fingerprint: the Tomonaga-Luttinger liquid spectral intensity I(epsilon) proportional to T^$\\alpha$ times an absolute value squared of a Gamma function, whose temperature-collapse with exponent $\\alpha$ identifies one-dimensional behavior; here the collapse holds for $\\alpha$ = 0.45 down to 150 K and fails below. Second, the theoretical engine: the momentum-resolved spectral function A(k, omega) from LDA+DMFT, from which the Fermi-surface warping $\\Delta$ k_z is read off as a function of temperature. The crossover criterion compares this warping to the thermal momentum broadening $\\Delta$ k = k_B T / ($hbar^{2}$ k_F / m_e) of a single parabolic band crossing the Fermi level; T* is where the two curves intersect.","core_discovery":"On the paper's own terms, the central discovery is a mechanism, not just a crossover observation: the 150 K crossover in K2Ru8O16 is set by the competition between temperature-dependent Fermi-surface warping and thermal energy. The warping, which expresses the transverse (interchain) hopping t_perp, grows almost linearly as temperature is lowered in the LDA+DMFT spectral function, while the thermal momentum broadening of a parabolic band shrinks linearly with temperature. The two curves cross near 150 K, matching the temperature at which the photoemission spectra stop following Tomonaga-Luttinger scaling and instead develop a Fermi cutoff with monotonically decreasing intensity at the Fermi level. The paper also shows that alternative explanations, such as a temperature-dependent chemical potential shift or disorder-induced Altshuler-Aronov behavior, cannot reproduce the observed spectral evolution.","pith_inferences":["A direct extrapolation of the same mechanism predicts that applying pressure along the transverse direction, which increases interchain hopping, should raise the crossover temperature T*; the paper's slope of warping versus temperature could be used to estimate the shift.","The comparison uses the free-electron mass in the thermal-broadening estimate; using the experimentally inferred enhanced mass would reduce the slope of the thermal line and move the calculated T* downward, so the precise agreement at 150 K may be somewhat fortuitous.","Because the paper itself notes single-site DMFT is insufficient for one-dimensional systems, non-local correlation effects (e.g., cluster DMFT or coupled-chain calculations) could either sharpen or shift the crossover; testing this would clarify whether the warping trend is an artifact.","The observed failure of the Tomonaga-Luttinger collapse below 150 K could also be tested by directly measuring the momentum dependence with angle-resolved photoemission on single crystals, which would provide a point-by-point confirmation of the warping increase."],"forward_implications":["The measured ~150 K crossover in transport and photoemission is reproduced without invoking structural, magnetic, or charge-order transitions, so the phenomenon is electronic in origin.","The Tomonaga-Luttinger exponent alpha = 0.45 obtained from scaling gives a quantitative measure of the Luttinger parameter K_rho in the high-temperature regime.","Below 150 K the appearance of a Fermi cutoff together with monotonically decreasing spectral weight at the Fermi level means the low-temperature state is a non-Fermi liquid, not a conventional Fermi liquid.","The strong temperature dependence of Fermi-surface warping implies that effective dimensionality in quasi-1D systems is temperature-tunable, which should affect resistivity anisotropy and magnetotransport."],"supporting_citations":[{"why":"Measured transport showing anisotropic metallic behavior and the ~150 K crossover that the paper's photoemission and calculation reproduce.","marker":"[29]"},{"why":"Earlier LDA band structure identifying the single band crossing the Fermi level and the quasi-1D Fermi surface.","marker":"[30]"},{"why":"Reports the specific-heat Sommerfeld coefficient and mass enhancement used to calibrate correlation strength.","marker":"[31]"},{"why":"Provides the theoretical framework in which the crossover temperature is set by the interchain hopping relative to thermal energy.","marker":"[13]"},{"why":"Establishes the Luttinger-to-Fermi-liquid crossover scenario in coupled-chain systems.","marker":"[14]"},{"why":"Supplies the Tomonaga-Luttinger spectral lineshape and its scaling form used to fit the photoemission data.","marker":"[67]"},{"why":"Demonstrates the universal scaling-collapse procedure used to extract the anomalous exponent alpha.","marker":"[69]"},{"why":"Provides the dynamical mean-field code and implementation used for the temperature-dependent spectral functions and Fermi surface.","marker":"[37]"}],"fun_headline_variants":["Warping beats thermal blur to flip 1D metal to 3D at 150 K","Fermi-surface warping outruns thermal broadening at 150 K crossover","1D Luttinger liquid yields to 3D metal as warping wins near 150 K","Why K2Ru8O16 turns 3D at 150 K: warping overtakes thermal energy","Interchain hopping warps Fermi surface, driving 150 K crossover"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The quantitative match between the calculated and measured crossover temperatures rests on the assumption that single-site LDA+DMFT, with Coulomb parameters U = 5.0 eV and J = 0.5 eV chosen by analogy with other 4d systems, gives a reliable temperature trend for the Fermi-surface warping in this quasi-one-dimensional material, and that the free-electron parabolic-band estimate of thermal momentum broadening is a fair comparison.","fun_headline_variants_meta":{"raw":{"variants":["Warping beats thermal blur to flip 1D metal to 3D at 150 K","Fermi-surface warping outruns thermal broadening at 150 K crossover","1D Luttinger liquid yields to 3D metal as warping wins near 150 K","Why K2Ru8O16 turns 3D at 150 K: warping overtakes thermal energy","Interchain hopping warps Fermi surface, driving 150 K crossover"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001287,"raw_usage":{"total_tokens":5251,"prompt_tokens":935,"completion_tokens":4316,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":551,"completion_tokens_details":{"reasoning_tokens":4199}},"tokens_in":551,"tokens_out":4316,"duration_ms":27977,"temperature":1.0,"reasoning_tokens":4199,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T20:35:33.520566+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Angle-resolved photoemission on single crystals at several temperatures would settle it: if the measured Fermi-surface warping does not grow as temperature is lowered, or if the temperature at which the spectra stop scaling with alpha = 0.45 shifts while the calculated warping curve stays fixed, the proposed mechanism would be falsified.","supporting_citations":[{"cited_title":"Kobayashi, Transport properties of quasi-one- dimensional KRu 4O8, Phys","cited_arxiv_id":null,"evidence_quote":"Measured transport showing anisotropic metallic behavior and the ~150 K crossover that the paper's photoemission and calculation reproduce."},{"cited_title":"Toriyama, M","cited_arxiv_id":null,"evidence_quote":"Earlier LDA band structure identifying the single band crossing the Fermi level and the quasi-1D Fermi surface."},{"cited_title":"Foo, W.-L","cited_arxiv_id":null,"evidence_quote":"Reports the specific-heat Sommerfeld coefficient and mass enhancement used to calibrate correlation strength."},{"cited_title":"Biermann, A","cited_arxiv_id":null,"evidence_quote":"Establishes the Luttinger-to-Fermi-liquid crossover scenario in coupled-chain systems."},{"cited_title":"Ohtsubo, J.-i","cited_arxiv_id":null,"evidence_quote":"Supplies the Tomonaga-Luttinger spectral lineshape and its scaling form used to fit the photoemission data."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates the universal scaling-collapse procedure used to extract the anomalous exponent alpha."}],"review_version":1}