{"id":"a6157b04-8a37-4c77-89cc-48a34c8d6c69","arxiv_id":"2608.11428","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"Quantum anharmonic corrections lower the predicted superconducting transition of YH10 to 260-270 K, and new measurements show clean superconductivity in YH6 and YH9 but no high-temperature superconductivity in Pd- or Al-doped yttrium hydrides.","lead":"This paper combines new high-pressure experiments and first-principles calculations on yttrium superhydrides, reporting sharp superconducting transitions in YH6 and YH9, the first radio-frequency screening signal for YH6, and a revised theoretical estimate that YH10 would superconduct near 260-270 K, not at room temperature.","discovery_kind":"first_principles","skeptic_critique":{"model":"deepseek-v4-flash","headline":"SSCHA pipeline underpredicts YH6 by 26 K without explanation; the YH10 260–270 K range may inherit the same systematic bias, so the room-temperature exclusion is not yet established.","rationale":"The reader's weakest_assumption correctly identifies the core vulnerability: the SSCHA method underpredicts YH6 by roughly 26 K, and the YH10 prediction inherits this systematic uncertainty. My stress-test confirms that this is the single most load-bearing concern because the headline claim is a negative statement about an unsynthesized phase, and all independent checks are either too low (SCDFT) or explicitly heuristic ((Y,Ce)H10). The paper does present real independent support: new RF transmission data, pulsed-field Bc2 measurements, and a multi-method theoretical framework (SSCHA + FBW-ME + SCDFT) that qualitatively agree in lowering YH10 Tc from the original 310–326 K predictions. However, the quantitative boundary of 'room temperature' depends on the exact range 260–270 K, and a systematic offset of the magnitude seen in YH6 is large enough to change the conclusion. The reader's CONDITIONAL verdict is appropriate: the paper should be accepted only if the authors either explain the YH6 discrepancy or explicitly propagate it as an uncertainty in the YH10 claim. I do not see grounds for rejection, since the anharmonic correction in YH9 is well reproduced and the overall trend (SSCHA reduces Tc relative to harmonic predictions) is consistent with established results in LaH10 and H3S. The most direct check is a calibration exercise on YH6 with the YH10-specific computational parameters, followed by an uncertainty statement applied to YH10.","tokens_in":29502,"tokens_out":5301,"duration_ms":51922,"concrete_test":"Recompute the SSCHA-based Tc for YH6 at 200 GPa using the exact same methodology as the YH10 calculation, including the same MTP training procedure, supercell size (4×4×4), final population size (10,000–15,000 configurations), convergence thresholds, and μ* = 0.11. If this reproduces the 198 K value, then quantify the systematic offset against the experimental 224–226 K and apply the same offset to the YH10 SSCHA result of 260 K. If the corrected YH10 Tc is at or above 300 K, or even above the harmonic FBW value of 283 K, the paper must report this systematic uncertainty and soften the room-temperature exclusion; if the corrected value remains below 300 K, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that cubic YH10 has Tc ≈ 260–270 K at 250 GPa, and hence that room-temperature superconductivity is disfavored in binary yttrium superhydrides, rests primarily on the SSCHA anharmonic renormalization. Table 2 shows that the same pipeline gives Tc(SSCHA) = 198 K for Im-3m-YH6 at 200 GPa, while the experimental value is 224–226 K. The paper calls the overall agreement \"excellent\" without explaining or quantifying this 26 K shortfall. For YH9 the SSCHA value (238 K) matches experiment, but YH6 is the closest available analogue to YH10 in the sense that both are cubic hydrogen-rich clathrates with moderate harmonic stability, and there anharmonic corrections degrade agreement rather than improve it. Since YH10 has never been synthesized, there is no direct experimental anchor for the 250 GPa prediction, and the other two numbers cited as support do not independently validate the SSCHA shift: SCDFT gives 221 K but is itself 40–50 K low for YH6 and YH9, and the (Y,Ce)H10 heuristic gives 242–283 K while being explicitly based on strong, unverified assumptions about linear Ce pair-breaking. If the same 26 K underestimate seen in YH6 applies to YH10, the SSCHA result of 260 K would correspond to an actual Tc near 286 K, close to room temperature and outside the stated 260–270 K range. The paper provides no uncertainty estimate, no convergence of the anharmonic correction with respect to supercell size or MTP training set beyond a single converged value, and no calibration check on a system where the SSCHA correction is known to be accurate for a cubic clathrate. Therefore the negative claim, as stated, is more fragile than the multiple-method presentation suggests.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper reinvestigates the yttrium-hydrogen system by combining new high-pressure transport and radio-frequency experiments on YH6 and YH9 with first-principles calculations for YH6, YH9, and YH10. The authors report a sharp 218 K superconducting transition in YH6 at 195 GPa, pulsed-field upper-critical-field data up to 60 T with a slope dBc2/dT = -0.52 T/K, contactless RF susceptibility evidence for YH6, and experiments showing that Pd and Al doping lead to an absence of high-temperature superconductivity above 78-120 K. On the theory side, using SSCHA anharmonic phonons, full-bandwidth Migdal-Eliashberg theory, and SCDFT, the paper predicts that cubic YH10 at 250 GPa has Tc ≈ 260-270 K, well below the earlier ~310-326 K harmonic predictions. The central claim is that room-temperature superconductivity is strongly disfavored in known binary yttrium superhydrides.","tokens_in":29805,"tokens_out":4733,"duration_ms":44285,"significance":"If the YH10 prediction is quantitatively reliable, this is an important revision of a widely cited result and would redirect experimental effort in high-pressure hydride superconductivity. The experimental contributions are notable: the RF transmission study of YH6 is the first contactless magnetic-screening measurement on an yttrium superhydride, and the pulsed-field Bc2 data extend the phase diagram to 60 T with a clean linear slope. The theoretical calculations use state-of-the-art methods (SSCHA, IsoME, SCDFT with the SPG2020 functional) and the authors are transparent in Section V that the (Y,Ce)H10-based estimate rests on strong assumptions. The main weakness is that the headline YH10 prediction lacks a systematic uncertainty estimate and the SSCHA pipeline shows a 26 K underprediction for YH6 that is not explained, so the room-temperature exclusion is not yet quantitatively secured.","major_comments":[{"comment":"The SSCHA result for YH6 at 200 GPa is 198 K, while the experimental value is 224-226 K, a shortfall of roughly 26 K. The text describes the agreement as \"excellent\" without quantifying or explaining this discrepancy. Since YH6 is the closest cubic analogue to YH10, and YH10 has no experimental anchor, the predicted 260-270 K range for YH10 may inherit a similar systematic offset. If a comparable 26 K underestimate applies, the true Tc of YH10 could be near 286 K, which is not below room temperature. Please provide an uncertainty estimate for the SSCHA Tc values, discuss the source of the YH6 shortfall, and, if possible, calibrate the anharmonic correction against YH6 or another well-characterized superhydride.","section":"§IV, Table 2"},{"comment":"The conclusion that palladium and aluminum \"strongly suppress\" high-temperature superconductivity is not fully established because no in-situ X-ray diffraction phase confirmation is presented for the doped samples in DACs Y5 and Y7. The presence of a high-Tc phase (YH6, YH9, or YH10) after laser heating is inferred indirectly from the high Debye temperatures obtained from Bloch-Grüneisen fits, but this is not conclusive. The reported absence of transitions above 120 K or 78 K would be evidence of suppression only if the intended superhydride phase had actually formed. Please either provide phase identification for these samples or soften the claim to state that no high-temperature superconductivity was observed in the Pd- and Al-containing samples.","section":"§III, DACs Y5 and Y7"},{"comment":"The pulsed-field Bc2(T) diagram is attributed to YH6 on the basis of a sharp transport transition at 218 K, yet the authors explicitly state that X-ray diffraction was not performed on this sample. Given that DAC Y2 contained a two-phase mixture of YH6 and YH9, and that the synthesis route is identical, the phase purity of DAC Y1 is an assumption. The lack of in-situ XRD should be acknowledged as a limitation of the phase identification, and the Bc2 slope should be interpreted as that of a sample containing a dominant superconducting phase with Tc = 218 K at 195 GPa, not necessarily a phase-pure YH6 sample.","section":"§I, DAC Y1 and Figure 1"},{"comment":"The consistency check for YH10 using (Y,Ce)H10 data depends on two strong assumptions: a linear Ce pair-breaking rate with concentration, and a dTc/dP extrapolation from 150 to 250 GPa. The authors correctly label this as an estimate, but the subsequent sentence \"This gives a maximum Tc(YH10) of 262 K at 250 GPa\" could be read as an independent cross-check of the SSCHA result, whereas both numbers ultimately derive from the same uncertain assumptions. Please clarify explicitly how much constraining power this heuristic has relative to the first-principles calculation, and consider giving a range that reflects the uncertainty in the Ce suppression rate.","section":"§V"}],"minor_comments":[{"comment":"In the paragraph following Table 2, the text says the superconducting properties are \"summarized in Table 1,\" but the quantities are actually listed in Table 2; please correct the cross-reference.","section":"§IV"},{"comment":"The abstract gives YH6 Tc = 218-221 K, while Table 1 and the text list 224-226 K as the maximum experimental value. Please reconcile these numbers or clarify that the abstract refers to the samples in this work.","section":"Abstract and Table 1"},{"comment":"The sentence \"The radio-frequency experiment was subsequently repeated without XRD analysis, in a DAC Y4 at 140-148 GPa with the same result, but a lower Tc of 211 K\" is internally vague: \"the same result\" and \"a lower Tc\" seem contradictory. Please rephrase to specify which features of the signal were reproduced.","section":"§II"},{"comment":"The reference list contains several entries with publication years 2026 and includes a number of self-citations. While this may be appropriate for an active field, please verify that all cited works are publicly available or in press, and that the in-text citations use the correct reference numbers.","section":"References"}],"recommendation":"major_revision","confidential_remarks":"The central claim of the paper is significant and likely correct in direction, but the quantitative exclusion of room-temperature superconductivity in YH10 depends on the anharmonic correction, which is not yet demonstrated to be reliable within the paper's own validation set. The experimental part is generally solid, but the Pd/Al suppression claim and the phase identification of the pulsed-field sample need either additional evidence or more cautious wording. I would advise the editor to send the paper back for a revision that addresses the uncertainty budget of the SSCHA calculations and the phase-evidence issue. The heavy reliance on self-citations, including several dated 2026, is worth checking but does not affect the technical content."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear X,\n\nYou should know this paper before the next round of the yttrium-hydride debate. It gives the first RF-susceptibility and 60 T pulsed-field data on YH6, and it makes a serious theoretical case that YH10's Tc is 260–270 K, not the widely cited 310–326 K. If those numbers hold, binary yttrium superhydrides fall out of the room-temperature race.\n\nThe experimental parts are mostly solid. The RF screening signal in DAC Y3 is tied to XRD-identified YH6, and the pulsed-field Bc2 slope of –0.52 T/K is a clean first result. The Pd and Al null experiments are weaker as suppression evidence, because there is no XRD showing that a high-Tc hydride phase actually formed in the Y5 and Y7 DACs; absence of a transition above 78–120 K may just mean no superhydride was synthesized. Calling that 'strong suppression' goes a bit beyond the data.\n\nThe theory is the load-bearing piece and the soft spot. The SSCHA plus full-bandwidth Eliashberg pipeline reproduces YH9 almost exactly, which is encouraging. But the same pipeline gives 198 K for YH6 against the experimental 224–226 K, a 26 K shortfall that the paper describes as 'excellent agreement' without explaining or quantifying the offset. YH6 is the closest cubic-clathrate analogue to YH10, so a careful reader cannot be sure the 260 K YH10 number does not inherit a similar bias. If the offset were +26 K, the real value would be near 286 K—still below 300 K, but 'strongly disfavors room-temperature superconductivity' softens to 'probably just misses.' The SCDFT value of 221 K and the (Y,Ce)H10 heuristic of 242–283 K are not independent enough to pin down the precision claim. The authors themselves flag that the heuristic rests on strong assumptions; that is honest, but it does not close the gap.\n\nI do not think the stress-test concern kills the paper. The central qualitative claim—that room-temperature superconductivity in cubic YH10 is much less plausible than previously advertised—survives. What does not survive is the stated 260–270 K precision. The authors need either a calibration test on YH6, or an explicit systematic-error estimate based on the YH6 shortfall, before that range is taken as settled.\n\nThis deserves a serious referee. Send it to review, and ask for uncertainty quantification on the theory plus explicit caveats or phase confirmation on the doping and pulsed-field assignments. For a reading group, the YH6 calibration problem is exactly the kind of thing worth arguing over.","headline":"A genuinely useful update with first RF and pulsed-field YH6 data and a serious anharmonic recalculation of YH10, but the 260–270 K headline needs an explicit calibration error bar before it should be treated as settled.","tokens_in":30472,"tokens_out":2417,"would_cite":true,"duration_ms":25409,"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":"YH10's predicted transition falls to 260-270 K, below room temperature","keywords":["yttrium superhydrides","high-pressure superconductivity","anharmonic phonons","Migdal-Eliashberg theory","upper critical field","radio-frequency susceptibility","room-temperature superconductivity","YH10"],"falsifier":"Synthesize phase-pure cubic YH10 near 250 GPa and measure its superconducting transition by resistance and contactless radio-frequency susceptibility; a transition above about 300 K or below about 250 K would contradict the 260–270 K claim. A less expensive check is to run the same SSCHA-plus-full-bandwidth pipeline on LaH10 and compare its predicted $T_c$ with the measured 250 K, which would expose any systematic offset in the method.","tokens_in":1818,"feed_emoji":"🔬","tokens_out":2448,"duration_ms":107229,"temperature":0.7,"pith_summary":"The paper re-examines yttrium polyhydrides, the hydrogen-rich compounds that have been the leading candidates for high-pressure superconductivity after lanthanum hydrides, and makes both experimental and theoretical claims. Experimentally it reports sharp superconducting transitions in YH6 and YH9 near 218–226 K and 235–243 K, the first contactless radio-frequency detection of YH6, and a pulsed-field phase diagram for YH6 with a linear upper-critical-field slope of $dB_{c2}/dT = -0.52$ T/K. Theoretically it argues that quantum anharmonic lattice vibrations, treated with the stochastic self-consistent harmonic approximation, harden the soft hydrogen modes and lower the predicted $T_c$ of cubic YH10 from the widely cited 310–326 K to about 260–270 K at 250 GPa. If correct, this removes room-temperature superconductivity from the known binary yttrium superhydrides and shifts the search for higher transition temperatures to ternary or other systems.","feed_headline":"YH10's predicted transition falls to 260-270 K, below room temperature","feed_subtitle":"Anharmonic effects downgrade YH10, while YH6 and YH9 show sharp transitions near 220-240 K.","key_machinery":"The load-bearing object is the anharmonically renormalized phonon spectrum obtained from the stochastic self-consistent harmonic approximation (SSCHA), a variational method that includes quantum and thermal nuclear fluctuations beyond the harmonic approximation. These renormalized phonons are fed into isotropic Migdal-Eliashberg equations solved over the full electronic bandwidth, together with a density-of-states rescaling and a self-consistently updated chemical potential. The mechanism that carries the argument is the suppression of soft hydrogen modes: anharmonicity converts the broad manifold of low-frequency modes between 50 and 100 meV into a gap, which reduces $\\lambda$ and raises $\\omega_{\\log}$, so that the predicted $T_c$ of YH10 falls from 283 K to 260 K. The paper also uses the stability parameter $\\xi$, kept below 0.5 in the anharmonic calculations, to argue that the harmonic regime that would produce near-room-temperature estimates is unstable.","core_discovery":"The central claim is that cubic YH10, long predicted to superconduct at or above room temperature, would instead have a critical temperature of roughly 260–270 K at 250 GPa. The argument runs through anharmonic phonon renormalization: the stochastic self-consistent harmonic approximation stabilizes the soft hydrogen vibrations, opens a phonon gap near 50–100 meV, and reduces the electron-phonon coupling from about 3.3 to 2.17, lowering $T_c$ from 283 K (harmonic) to 260 K. The same framework reproduces the measured $T_c$ of YH9 to within about 3%, while underpredicting YH6 by about 26 K; a separate estimate based on cerium substitution in (Y,Ce)H10 gives 262 K as a consistency check. Experimentally, the paper contributes new transport and contactless radio-frequency data on YH6 and YH9, including narrow transitions approaching the thermal-fluctuation limit, a linear $dB_{c2}/dT = -0.52$ T/K slope, dirty-limit upper-critical-field behavior, and strong suppression of high-temperature superconductivity when palladium or aluminum is incorporated.","pith_inferences":["Because the same SSCHA pipeline underpredicts YH6 by about 26 K, a cautious reading is that the true YH10 $T_c$ could be tens of kelvin above 260–270 K; whether it crosses 300 K is not settled by this calculation alone.","If the 260–270 K ceiling holds, the yttrium-hydrogen system peaks near YH9 at 243 K, making YH9 the practically most valuable phase for further study.","The (Y,Ce)H10 consistency check implies an approximate rule of 1.25–2.5 K suppression per atomic percent of cerium; synthesizing (Y,Ce)H10 with low cerium fractions and measuring $T_c$ would test that rule directly.","Applying the same anharmonic-plus-full-bandwidth method to LaH10, whose measured $T_c$ is 250 K, would calibrate the systematic offset and either strengthen or weaken the revised YH10 estimate."],"forward_implications":["If fcc YH10 is ever synthesized, its measured $T_c$ should land near 260–270 K at 250 GPa, not at the older 310–326 K estimates.","Room-temperature superconductivity is not to be found among binary yttrium polyhydrides, so the experimental search should concentrate on ternary, quaternary, or other non-binary hydrides.","The 2–5 K transition widths seen in YH6 and YH9 approach the thermal-fluctuation limit, so high-quality hydride samples can serve as near-intrinsic probes of superconducting fluctuations.","The linear $B_{c2}(T)$ slope and dirty-limit consistency for YH6 provide a benchmark for future upper-critical-field models of superhydrides.","Quantum anharmonicity should be included as a standard ingredient in first-principles $T_c$ predictions for hydrogen-rich superconductors, since omitting it overestimates $T_c$."],"supporting_citations":[{"why":"Supplies the original ~310–326 K YH10 prediction that this paper revises.","marker":"1"},{"why":"Gives the prior sodalite-clathrate YH10 calculation whose $T_c$ is corrected downward.","marker":"2"},{"why":"Reports the experimental 243 K maximum $T_c$ of YH9 used as the main comparison target.","marker":"3"},{"why":"Establishes the 250 K $T_c$ of LaH10, the benchmark against which the revised YH10 value is compared.","marker":"12"},{"why":"Provides the full-bandwidth Migdal-Eliashberg formulation used for the new $T_c$ values.","marker":"59"},{"why":"Describes the stochastic self-consistent harmonic approximation method that supplies the anharmonic phonons.","marker":"63"},{"why":"Demonstrates quantum anharmonic effects in LaH10, the precedent for expecting them in YH10.","marker":"66"},{"why":"Reports (Y,Ce)H10 with $T_c$ around 201 K, the experimental input for the 262 K consistency estimate.","marker":"76"}],"fun_headline_variants":["Anharmonicity kills room-temp superconductivity in YH10","YH10 superconducting Tc revised down to 260 K","YH6 and YH9 shine as YH10 fails to hit 300 K","Experiments and theory: YH10 not a room-temperature superconductor","YH10's Tc drops below 300 K, while YH6 and YH9 stay sharp"],"cache_read_input_tokens":32384,"weakest_assumption_plain":"The calculation assumes that the anharmonic (SSCHA) framework, which predicts YH6 about 26 K below its measured transition, is reliable for YH10 without a stated uncertainty, so the 260–270 K range could inherit a systematic offset of roughly that size.","fun_headline_variants_meta":{"raw":{"variants":["Anharmonicity kills room-temp superconductivity in YH10","YH10 superconducting Tc revised down to 260 K","YH6 and YH9 shine as YH10 fails to hit 300 K","Experiments and theory: YH10 not a room-temperature superconductor","YH10's Tc drops below 300 K, while YH6 and YH9 stay sharp"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001732,"raw_usage":{"total_tokens":6944,"prompt_tokens":1140,"completion_tokens":5804,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":756,"completion_tokens_details":{"reasoning_tokens":5706}},"tokens_in":756,"tokens_out":5804,"duration_ms":32863,"temperature":1.0,"reasoning_tokens":5706,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T14:12:19.683990+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Synthesize phase-pure cubic YH10 near 250 GPa and measure its superconducting transition by resistance and contactless radio-frequency susceptibility; a transition above about 300 K or below about 250 K would contradict the 260–270 K claim. A less expensive check is to run the same SSCHA-plus-full-bandwidth pipeline on LaH10 and compare its predicted $T_c$ with the measured 250 K, which would expose any systematic offset in the method.","supporting_citations":[{"cited_title":"Analysis of the spatial distribution of hydride phases in the sample was performed using the Dioptas 0.7 program 7","cited_arxiv_id":null,"evidence_quote":"Reports the experimental 243 K maximum $T_c$ of YH9 used as the main comparison target."}],"review_version":1}