{"id":"3051d1fd-8cf4-49bf-a6b5-e798758910e5","arxiv_id":"2607.03287","paper_version":1,"verdict":"ACCEPT","confidence":"HIGH","novelty_score":6.0,"correctness_risk":"low","formal_verification":"none","parameter_count":2,"one_line_summary":"High-pressure SXRD on KMn6Bi5 shows anisotropic lattice compression plus anomalous Mn-nanotube hardening (5–11 GPa) and nanotube reorientation near 11 GPa that correlate with its magnetic–superconducting phase diagram.","lead":"High-pressure single-crystal X-ray diffraction maps how the Mn and Bi nanotubes in KMn6Bi5 compress and reorient up to 12.5 GPa, revealing anomalous Mn-tube hardening between 5–11 GPa and an isostructural reconfiguration near 11 GPa. These local changes track the known collapse of antiferromagnetism and the onset of superconductivity, giving a structural handle on electronic order in this quasi-1D metal.","discovery_kind":"extension","skeptic_critique":{"model":"grok-4.5","headline":"No significant objection identified","rationale":"The Reader correctly identifies that the interpretive link to magnetism is correlative and rests on a prior phase diagram, yet rightly treats this as a normal limitation of a pure structural study rather than a reason to reject. The tabulated lattice parameters, atomic positions and derived distances supply independent, falsifiable crystallographic evidence for the anomalous Mn-nanotube hardening and the isostructural reconfiguration near 11 GPa. Because those observations constitute the paper’s strongest claim and survive scrutiny, no adjustment to the ACCEPT verdict is warranted.","tokens_in":13951,"tokens_out":407,"duration_ms":3766,"concrete_test":"Independently recompute the nanotube radii r_Mn and orientation angles Δ\theta_Mn from the fractional coordinates listed in Table 1 at 5 GPa, 10.85 GPa and 11.72 GPa; if the plateau (r_Mn ≈ 2.30 Å) and the ~26° jump are recovered within the reported uncertainties, the key structural observations are confirmed.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper’s central claim is a set of high-pressure SXRD observations (anisotropic lattice compression, plateau in r_Mn between ~5–11 GPa, ~26° nanotube reorientation and radial collapse near 11 GPa without space-group change). These quantities are extracted directly from the refinements in Tables 1–2 and Figs. 2–4 and are therefore self-contained. The subsequent correlation of those structural features with the published TN(P) and SC dome is explicitly presented as interpretive (Discussion) and is not required for the crystallographic results to stand. High R1 values at the highest pressures and the absence of simultaneous magnetic data under the same conditions are real limitations, but they do not undermine the structural measurements themselves. No internal inconsistency or load-bearing technical flaw that would overturn the strongest claim was found.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.5","summary":"This manuscript reports high-pressure single-crystal X-ray diffraction on the quasi-one-dimensional antiferromagnetic metal KMn6Bi5 up to 12.5 GPa. The structure remains C2/m with no symmetry-breaking transition. Lattice parameters show strong anisotropy (a/a0 ≈ 0.91, b/b0 ≈ 0.94 at 12.5 GPa) and a clear anomaly near 11 GPa (abrupt contraction of a and b, jump in β). Derived nanotube descriptors reveal an anomalous plateau in the Mn-tube radius rMn ≈ 2.30 Å between ~5 and 11 GPa, followed by a ~26° reorientation of both Mn and Bi nanotubes and radial collapse above 11 GPa. Averaged Mn–Mn and Bi–Bi distances exhibit corresponding anisotropic compressibilities. These local coordination changes are correlated with the previously published TN(P) phase diagram and with chemical-pressure trends across the AMn6Bi5 family.","tokens_in":14125,"tokens_out":1118,"duration_ms":8514,"significance":"If the crystallographic results hold, the work supplies the first atomic-scale structural map of the pressure evolution of the [Mn6Bi5] nanotubes that host the magnetic and superconducting orders in this family. The observation of an isostructural nanotube reorientation and the hidden hardening of the inner Mn tube between 5 and 11 GPa are concrete, falsifiable findings that link local Mn coordination to the non-monotonic TN(P) and the subsequent superconducting dome. The tabulated lattice parameters, fractional coordinates, and derived distances (Tables 1–2) constitute a reusable structural dataset for the community. The comparison with chemical-pressure effects in the Na/Rb/Cs analogues further generalizes the result within the AMn6Bi5 series.","major_comments":[{"comment":"Table 1: R1 rises to 17.9 % at 11.72 GPa (and remains 11.9 % at 12.53 GPa), while several Ueq values become large or anomalous (e.g., K Ueq = 0.31(4) Å^{2} at 6.77 GPa). The central claim of a nanotube reorientation and radial collapse rests on the refined coordinates precisely in this pressure window. The manuscript should quantify the impact of the elevated residuals on the uncertainties of rMn, Δ\theta Mn/Δ\theta Bi and the Mn–Mn distances (Table 2), and demonstrate that the ~26° jump and the post-11 GPa contraction remain statistically significant under conservative error propagation or alternative refinement protocols.","section":null},{"comment":"Discussion (paragraphs linking bond hardening to magnetoelastic suppression and 3d hybridization): the causal connection between the observed Mn-tube plateau / reorientation and the collapse of TN / emergence of superconductivity is presented as interpretive correlation with a previously published P–T diagram. No simultaneous magnetic or electronic data under the same pressure conditions are reported. While the structural observations themselves stand independently, the manuscript should more clearly separate the crystallographic facts from the exchange-interaction scenario, and note that direct verification of the proposed 3d-hybridization change would require complementary high-pressure spectroscopy or calculations on the refined structures.","section":null}],"minor_comments":[{"comment":"Abstract and main text: the relative compressibilities are written inconsistently as a/a0=0.91 versus a/a0 ≈ 0.91; standardize the notation.","section":null},{"comment":"Figure 1(b) caption cites Ref. [18] for the phase diagram, but the text and reference list attribute the diagram to Ref. [13]; correct the citation.","section":null},{"comment":"Table 1, Bi4 z-coordinate at 12.53 GPa is listed as 0.244(7), which appears to be a typographical error (likely 0.0244 or similar); verify against the refinement output.","section":null},{"comment":"Experimental section: the pressure-transmitting medium (4:1 methanol–ethanol) is stated to ensure quasi-hydrostatic conditions, but no explicit check of hydrostaticity (e.g., ruby linewidth) above ~10 GPa is given; a brief statement would strengthen confidence in the 11 GPa anomaly.","section":null},{"comment":"Supplemental Material is cited for the full set of individual bond lengths; ensure it is deposited and that the averaged distances used in Figs. 3–4 are unambiguously defined.","section":null}],"recommendation":"minor_revision","confidential_remarks":"The crystallographic core is solid and the data tables are valuable. The elevated R1 values near the key pressure of 11 GPa are the only load-bearing technical concern; once the authors address the error bars on the nanotube descriptors, the paper is suitable for publication. The interpretive link to magnetism is standard for this community and does not require simultaneous measurements to justify the structural report."},"author_rebuttal":null,"desk_editor":{"model":"grok-4.5","letter":"The new result here is the first high-pressure single-crystal refinement that tracks the Mn and Bi nanotube radii, their orientation angles, and the anisotropic Mn–Mn distances up to 12.5 GPa. Between 5 and 11 GPa the inner Mn tube hardens (r_Mn stuck near 2.30 Å) while the outer Bi tube keeps shrinking; near 11 GPa both tubes reorient by ~26° and then collapse radially, all without leaving C2/m. Those numbers are in Tables 1–2 and Figs. 3–4 and were not available before.\n\nThe crystallography itself is clean enough. Lattice parameters, fractional coordinates and Ueqs are tabulated with esds, the space group holds, and the Birch–Murnaghan fit is routine. The axial anisotropy (a soft, b stiff) matches the Q1D architecture, and the comparison to chemical-pressure variants (Na vs Rb/Cs) is useful. R1 climbs to 17.9 % at 11.72 GPa and a few Ueqs get large, but that is expected near the edge of the DAC data and does not erase the plateau or the reorientation.\n\nThe soft spot is the causal story. The Discussion maps the bond hardening onto the drop in TN and the later collapse onto the SC dome by correlating with the group’s earlier P–T diagram; there are no simultaneous magnetic or electronic measurements under the same conditions. That is a normal limitation of a pure structural paper, not a circularity, but it means the “microscopic origin” claim is interpretive rather than demonstrated. Averaged distances are also used, which is fine given the site multiplicity but should be kept in mind.\n\nAnyone working on Mn-based Q1D magnets or pressure-tuned QCPs will want these numbers. The data are reproducible from the tables, the citations are appropriate, and the paper is short and focused. I would send it to referees; a materials journal should take it after the usual polishing of the high-P R-factors and a clearer separation of observation from interpretation.","headline":"Solid high-pressure SXRD that finally gives the atomic-scale nanotube metrics for KMn6Bi5; the magnetism link is correlative but the crystallography stands on its own.","tokens_in":14784,"tokens_out":529,"would_cite":true,"duration_ms":5500,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.5","headline":"High-pressure X-ray diffraction shows Mn nanotubes in KMn6Bi5 harden anomalously then reorient near 11 GPa, tracking the collapse of antiferromagnetism and rise of superconductivity.","keywords":["high-pressure X-ray diffraction","quasi-one-dimensional antiferromagnet","KMn6Bi5","Mn nanotubes","quantum critical point","pressure-induced superconductivity","magnetoelastic coupling"],"falsifier":"A high-pressure neutron or resonant X-ray experiment that maps the actual Mn magnetic moments and exchange couplings through the 5–11 GPa hardening window and the 11 GPa reorientation; if the moments or couplings remain continuous while the structure jumps, or jump while the structure stays smooth, the claimed structural origin of the phase diagram would be ruled out.","tokens_in":14843,"feed_emoji":"🔬","tokens_out":733,"duration_ms":5633,"temperature":0.7,"pith_summary":"KMn6Bi5 is a quasi-one-dimensional antiferromagnetic metal whose magnetic order is suppressed by pressure, giving way to superconductivity near a quantum critical point. Earlier work mapped the pressure–temperature phase diagram but left the atomic-scale structural drivers unclear. This paper reports single-crystal X-ray diffraction up to 12.5 GPa and shows that the lattice compresses anisotropically, with a distinct anomaly near 11 GPa that does not change the crystal symmetry. The inner Mn nanotubes harden (their radius stays nearly constant) between 5 and 11 GPa while the outer Bi tubes continue to shrink; above 11 GPa both tubes contract and rotate by about 26 degrees. These local coordination changes line up with the non-monotonic drop of the Néel temperature and the subsequent appearance of superconductivity, and they also explain why chemical substitution of the alkali ion produces similar or different phase diagrams. The result supplies a concrete microscopic picture of how pressure tunes exchange paths in a low-dimensional magnet.","feed_headline":"Mn nanotubes harden then flip under pressure in KMn6Bi5","feed_subtitle":"Local reorientation near 11 GPa tracks the fall of antiferromagnetism and rise of superconductivity","key_machinery":"The concentric Mn and Bi nanotube radii (rMn, rBi) and their orientation angles (ΔθMn, ΔθBi), together with the four distinct intra-tube Mn–Mn distances; tracking these descriptors under pressure isolates the anisotropic bond hardening and the later isostructural reconfiguration that modify Mn–Mn and Mn–Bi–Mn exchange paths.","core_discovery":"High-pressure single-crystal X-ray diffraction on KMn6Bi5 reveals an anomalous hardening of the Mn nanotube radius (nearly constant at ~2.30 Å) between 5 and 11 GPa, followed by a simultaneous radial collapse and ~26° reorientation of both Mn and Bi nanotubes near 11 GPa without space-group change; these local structural rearrangements furnish the microscopic origin of the non-monotonic TN(P) and the emergence of superconductivity.","pith_inferences":[],"forward_implications":[],"fun_headline_variants":["Mn nanotubes harden then reorient near 11 GPa in KMn6Bi5","Anomalous Mn tube stiffening then flip under pressure in KMn6Bi5","KMn6Bi5 Mn nanotubes lock radius then collapse and rotate at 11 GPa","Pressure freezes then reorients Mn/Bi nanotubes in KMn6Bi5","Mn nanotube hardening anomaly precedes 11 GPa flip in KMn6Bi5"],"cache_read_input_tokens":128,"weakest_assumption_plain":"The paper assumes that the measured changes in averaged Mn–Mn and Mn–Bi distances are the dominant drivers of the exchange interactions that control TN and superconductivity, even though no simultaneous magnetic or electronic data were collected under the same pressure conditions.","fun_headline_variants_meta":{"raw":{"variants":["Mn nanotubes harden then reorient near 11 GPa in KMn6Bi5","Anomalous Mn tube stiffening then flip under pressure in KMn6Bi5","KMn6Bi5 Mn nanotubes lock radius then collapse and rotate at 11 GPa","Pressure freezes then reorients Mn/Bi nanotubes in KMn6Bi5","Mn nanotube hardening anomaly precedes 11 GPa flip in KMn6Bi5"]},"model":"grok-4.5","effort":"low","cost_usd":0.009352,"raw_usage":{"total_tokens":2140,"prompt_tokens":776,"num_sources_used":0,"completion_tokens":113,"cost_in_usd_ticks":93520000,"prompt_tokens_details":{"text_tokens":776,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1251,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":776,"tokens_out":113,"duration_ms":8464,"temperature":1.0,"reasoning_tokens":1251,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-12T03:30:28.580486+00:00","model_set":{"reader":"grok-4.5"},"falsifier":"A high-pressure neutron or resonant X-ray experiment that maps the actual Mn magnetic moments and exchange couplings through the 5–11 GPa hardening window and the 11 GPa reorientation; if the moments or couplings remain continuous while the structure jumps, or jump while the structure stays smooth, the claimed structural origin of the phase diagram would be ruled out.","supporting_citations":[],"review_version":1}