{"id":"4808d282-87ef-4893-8398-96a3b8e48df5","arxiv_id":"2606.16994","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"On NbP(001), hydrogen adsorption energy barely changes with spin-orbit coupling, but Fermi-arc surface states persist after adsorption and produce a small current-induced spin polarization on the hydrogen itself.","lead":"This paper models hydrogen sitting on the surface of the topological semimetal NbP and asks whether the material's special surface electronic states affect how hydrogen binds and whether the adsorbed hydrogen feels a spin response when current flows. The answer: binding energy stays almost the same, but the surface states do transfer a spin-polarizing response to the hydrogen atom.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The quantitative H-projected spin moment (7e-6 muB) is not a parameter-free prediction: Eq. (8) uses a Kubo-Boltzmann response linear in an unspecified relaxation time tau, so the headline number cannot be assessed from the main text.","rationale":"The reader's weakest assumption is exactly the unspecified relaxation time tau in the projected Kubo-Boltzmann response (Sec. II F, used in Sec. III D). This is the most load-bearing weak point because it directly controls the only quantitative number in the central assertion (7e-6 muB). Other aspects of the paper—e.g., the small SOC-induced change in DeltaG_H*, the persistence of Fermi-arc spectral features, and the momentum-selective pCOHP—are qualitative and supported by the calculations described. The tau dependence does not undermine the qualitative conclusion that topological surface states can be nearly invisible in adsorption thermodynamics while governing a Fermi-level spin response; it only means the reported magnitude is not a parameter-free prediction until the SI is available. The appropriate disposition is to keep the reader's CONDITIONAL verdict, so the recommendation is unchanged.","tokens_in":10646,"tokens_out":5589,"duration_ms":63252,"concrete_test":"Obtain the SI's relaxation-time tests and extract the tau value used to produce m_H ~ 7e-6 muB. Recompute Eq. (8) with tau replaced by (i) the value inferred from NbP's measured ultrahigh mobility via the Drude relation and (ii) bracketing values 0.1 ps and 10 ps. If the resulting H-projected moment spans more than one order of magnitude, the quantitative central claim should be downgraded to a qualitative existence statement unless a first-principles tau is provided.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative claim in Sec. III D is that the H-projected current-induced magnetic moment reaches ~7e-6 muB at 10^5 V/m (Eq. 8). The response tensor chi^H is introduced in Sec. II F as a Kubo-Boltzmann expression whose 'relaxation-time model' is deferred to the SI. In any such model the response is proportional to tau; the main text neither states tau nor a range, and the SI is not included in the reviewed material. Therefore the quoted magnitude is not reproducible or falsifiable from the paper alone. The existence and anisotropy of the response are unaffected by the value of tau, but the specific number 7e-6 muB is exactly the kind of quantitative prediction that needs a parameter-free basis or an explicit sensitivity statement. This is a missing-support issue rather than an inconsistency; it weakens the headline as stated but does not invalidate the qualitative decoupling claim.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper uses DFT and Wannier-based analyses to study hydrogen chemisorption on NbP(001), comparing non-SOC and SOC regimes. It reports adsorption free energies of -0.62 eV (non-SOC) and -0.60 eV (SOC), concluding that SOC leaves the thermodynamic descriptor essentially unchanged. Projected spectral functions and pCOHP analysis are used to argue that H(1s) hybridizes preferentially with the Weyl Fermi arcs at the Fermi level, while the main bonding stabilization occurs in occupied H-Nb states below E_F. Finally, a Kubo-Boltzmann response calculation is used to estimate an H-projected current-induced spin polarization of about 7e-6 mu_B at 10^5 V/m, which the authors interpret as evidence that topological surface states can act as spin-active interfacial channels even when they do not control adsorption thermodynamics.","tokens_in":10795,"tokens_out":4171,"duration_ms":48302,"significance":"If the qualitative claims hold, the paper makes a useful conceptual contribution by separating the thermodynamic role of topological surface states from their Fermi-level spin-active role. The SOC on/off comparison is well designed, and the internal consistency of the main qualitative results (arc persistence, H weight on arcs, bonding below E_F) is credible. The quantitative current-induced moment, however, is not parameter-free: the response is linear in an unspecified relaxation time, so the specific magnitude is not a robust prediction. The paper also depends heavily on an unavailable Supplemental Information for validation, derivations, and sensitivity tests. These issues limit the significance of the quantitative headline but not the qualitative decoupling claim.","major_comments":[{"comment":"The H-projected current-induced moment (about 7e-6 mu_B) is computed from a Kubo-Boltzmann expression that is linear in a phenomenological relaxation time tau. The main text never states tau, its range, or how it was chosen; the derivation and 'relaxation-time tests' are relegated to the SI, which is not part of the reviewed material. Since Eq. (8) inherits this proportionality, the specific magnitude is not a parameter-free prediction and cannot be reproduced or falsified from the paper alone. The existence and anisotropy of the response may be robust, but Sec. III D should either state tau with justification, provide a sensitivity scan in the main text, or explicitly label the number as illustrative.","section":"Sec. II F / Eq. (6)-(8) and Sec. III D"},{"comment":"The claim that SOC leaves adsorption thermodynamics essentially unchanged rests on a 0.01 eV difference in adsorption energy and 0.02 eV in free energy. No convergence checks or error estimates are reported in the main text; ZPE/entropy corrections are deferred to Sec. S2. A 10-20 meV difference is within typical DFT noise for slab calculations (k-point density, smearing, slab thickness, cutoff), so the 'essentially unchanged' conclusion needs a demonstration that the difference is below numerical precision.","section":"Sec. III A"},{"comment":"Several load-bearing results are accessible only through the SI: Wannier validation, ZPE/entropy corrections, relaxation-time tests, the projected moment tensor, non-SOC spectral functions, and additional pCOHP data. As submitted, the main text makes assertions (e.g., the Fermi-arc-selective H coupling, the anisotropy of the response) that cannot be checked without those materials. The SI should be included with the manuscript, or the main text should summarize the validation and sensitivity data needed to support the central claims.","section":"Supplemental Information (general)"}],"minor_comments":[{"comment":"The comparison of H-projected, H-covered surface-Nb, and pristine surface-Nb moments (7e-6, 3e-5, and 9e-5 mu_B) would be clearer if the tensor component and field direction were specified; as written, 'the moment' could mean different components of an anisotropic tensor.","section":"Sec. III D"},{"comment":"Typo: 'preferrentially' should be 'preferentially'.","section":"Conclusions"},{"comment":"Minor formatting: 'dcharacter' and 'd band' should be 'd-character' and 'd-band'.","section":"Introduction"},{"comment":"References [24] and [30] have malformed DOI/URL formatting (the DOI appears embedded in a URL rather than as a standard reference).","section":"References"},{"comment":"The caption mentions 'blue contours mark additional surface-state features' and 'gray contours indicate bulk-projected spectral weight' without defining how surface vs bulk classification was performed; please clarify in the main text or caption.","section":"Fig. 3 caption"}],"recommendation":"major_revision","confidential_remarks":"The stress-test concern about the unspecified relaxation time is valid and is the main reason for major revision. If the SI is supplied, the tau issue may be resolved, but the main text should still state tau or present a sensitivity analysis for the headline moment. The thermodynamic insensitivity claim also needs numerical-error support."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Good paper to know about. The real point is the decoupling: on NbP(001), turning on spin-orbit coupling changes the hydrogen adsorption free energy by only 0.02 eV, while the Fermi-arc states are the dominant H(1s) hybridization channel at E_F and produce a finite adsorbate-local current-induced spin polarization. That combination — near-zero thermodynamic effect, large electronic effect at the Fermi level — is what makes the paper worth reading, and it is genuinely new for the TaAs family.\n\nWhat the paper does well: the SOC on/off comparison is clean because the geometry, termination, and adsorption site are held fixed, so the only moving part is the electronic topology. The Wannier-based projections, momentum-resolved pCOHP, and surface spectral functions are appropriate tools, and the qualitative picture is internally consistent: H–Nb bonding accumulates below E_F, while the Fermi arcs provide a spin-textured channel at E_F. There is no fitting to experimental data, and the cited prior work supports the Fermi-arc assignment. The discussion of the weaker W1 arcs is honest and doesn't overclaim.\n\nThe soft spot is the headline spin moment. The response is a Kubo–Boltzmann expression that is linear in the relaxation time tau, and the main text never states tau or its range — that is deferred to a Supplemental Information we don't have. So the number 7e-6 muB at 10^5 V/m is not reproducible or falsifiable from the paper alone. This is a missing-support issue, not an inconsistency: the existence and anisotropy of the H-projected response do not depend on tau. But a quantitative prediction of this kind needs either a parameter-free basis or an explicit sensitivity statement. The authors should report tau, its range, and the resulting variation in the moment, and the SI should be available.\n\nMinor: the non-SOC comparison figures are mostly in the SI, and a reader of the main text can't fully check the SOC on/off claim without them. Also, the paper ships no input files or code, which is normal for DFT but worth asking about.\n\nThe paper deserves a serious referee. The central decoupling claim is well supported, and the tau issue is fixable in revision. I'd send it out, and I'd expect a revise-and-resubmit rather than a rejection. Anyone working on topological catalysis or spin-orbit effects in chemisorption should read it.","headline":"Decoupling of adsorption thermodynamics from Fermi-arc electronics on NbP is solidly shown; the quantitative spin moment needs the relaxation-time value and sensitivity before the headline number can be trusted.","tokens_in":11345,"tokens_out":2635,"would_cite":true,"duration_ms":26254,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["73.20.At","71.70.Ej"],"model":"deepseek-v4-flash","headline":"The paper argues that on NbP(001) hydrogen chemisorption leaves Weyl Fermi arcs intact, barely changes adsorption free energy under spin–orbit coupling, yet transfers spin texture to the adsorbate through the arc channel, yielding a measura","keywords":["Weyl semimetal","Fermi arcs","hydrogen chemisorption","spin–orbit coupling","current-induced spin polarization","Edelstein effect","NbP(001)","adsorption free energy"],"falsifier":"A spin-resolved photoemission or transport measurement on hydrogen-covered NbP(001) showing that Fermi-arc contours disappear upon adsorption, or a calculation using an independently measured relaxation time that yields an H-projected moment below 10⁻⁷ μB, would contradict the central claim. More directly, if the H-projected spectral function at E_F shows zero weight along the pristine arc contours, the proposed arc–H coupling channel is absent.","tokens_in":10451,"feed_emoji":"🧲","tokens_out":3507,"duration_ms":37451,"temperature":0.7,"pith_summary":"This paper asks whether the exotic surface states of a Weyl semimetal — the Fermi arcs — actually matter for surface chemistry when hydrogen adsorbs. By comparing identical density-functional calculations with and without spin–orbit coupling on the same NbP(001) surface, it shows that the thermodynamic adsorption descriptor changes only weakly (ΔG_H* ≈ −0.62 to −0.60 eV). Yet the Fermi arcs survive hydrogen coverage and are the dominant Fermi-level hybridization channel for the H 1s orbital. That hybridization transfers spin-textured character to the adsorbate, yielding a finite hydrogen-localized current-induced spin polarization (about 7×10⁻⁶ μB at 10⁵ V/m). The broader point is that topological surface states can be thermodynamically unimportant while being electronically and spintronically decisive.","feed_headline":"Hydrogen gains spin from Weyl Fermi arcs on NbP","feed_subtitle":"Spin-orbit coupling barely shifts adsorption energy, yet the arc channel puts spin texture on adsorbed H.","key_machinery":"The paper's central machinery is the spin–orbit-coupling on/off comparison on one fixed NbP(001) slab, keeping crystal structure, termination, and adsorption site identical while switching between a nodal-line surface-state regime and a Weyl Fermi-arc regime. Within this comparison, three projected observables carry the argument: (1) Wannier-projected surface spectral functions that locate H-derived weight in momentum space; (2) projected crystal-orbital Hamilton population (pCOHP) that separates Fermi-level bonding from integrated bonding; and (3) the adsorbate-projected Kubo–Boltzmann spin response that converts Fermi-arc spin texture into a local current-induced moment on H. The Fermi arc","core_discovery":"The central claim is that chemisorbed hydrogen on NbP(001) does not destroy the Weyl Fermi arcs and couples preferentially to them at the Fermi energy. Using Wannier-based surface spectral functions and projected crystal-orbital Hamilton population analysis, the paper finds the arc contours persist after H adsorption, with H(1s) spectral weight appearing exactly on arc regions. Spin–orbit coupling leaves the adsorption free energy essentially unchanged, because the integrated bond strength is built from occupied H–Nb states well below the Fermi level; the arcs contribute little to the total bond energy. But at the Fermi energy, the arcs provide the main spin-textured bonding channel, and a K","pith_inferences":["If the relaxation-time scaling were fixed by independent experiment, the adsorbate-local Edelstein response could serve as a direct probe of Fermi-arc survival: a sudden drop in H-projected spin accumulation would signal arc disruption by other adsorbates or disorder.","The thermodynamic/spin decoupling found here implies that conventional catalytic descriptors such as ΔG_H* miss spin-active functionality; a two-parameter design space — binding energy plus Fermi-level spin coupling — could guide the search for spintronic electrocatalysts.","A testable extension is that, across the TaAs family or at lower H coverage, the H-projected moment should scale with the Fermi-arc spectral weight at E_F, a prediction checkable by spin-resolved photoemission and transport.","Computing the response at multiple well-defined relaxation times, or extracting τ from measured mobilities, would convert the order-of-magnitude moment into a quantitative, parameter-free prediction."],"forward_implications":["Hydrogen adsorption does not kill Fermi arcs, so Weyl-semimetal surfaces can host chemisorbed species without losing their topological surface electronic structure.","On such surfaces, adsorption thermodynamics can be controlled by ordinary bulk and trivial surface states even when topological states dominate Fermi-level hybridization.","The H-projected current-induced spin polarization constitutes a chemically resolved, adsorbate-local spin response, suggesting a route to electrically controlled spin at catalytic interfaces.","The anisotropy and magnitude of the spin response could be engineered by selecting adsorption sites with stronger H–arc overlap."],"fun_headline_variants":["Hydrogen borrows spin from Weyl Fermi arcs on NbP","Fermi arcs give adsorbed hydrogen a spin texture","Spin-polarized hydrogen from NbP's Weyl surface states","Hydrogen's new spin trick: Weyl arcs on NbP surface","Adsorbed H gets spin from NbP Fermi arcs under current"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The headline value of the current-induced spin polarization scales linearly with a phenomenological relaxation time τ whose value is not stated in the main text, so if τ is chosen ad hoc, the number 7×10⁻⁶ μB is not a parameter-free prediction, though the existence and anisotropy of the response would still hold.","fun_headline_variants_meta":{"raw":{"variants":["Hydrogen borrows spin from Weyl Fermi arcs on NbP","Fermi arcs give adsorbed hydrogen a spin texture","Spin-polarized hydrogen from NbP's Weyl surface states","Hydrogen's new spin trick: Weyl arcs on NbP surface","Adsorbed H gets spin from NbP Fermi arcs under current"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000243,"raw_usage":{"total_tokens":1339,"prompt_tokens":688,"completion_tokens":651,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":432,"completion_tokens_details":{"reasoning_tokens":563}},"tokens_in":432,"tokens_out":651,"duration_ms":7542,"temperature":1.0,"reasoning_tokens":563,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-02T11:04:48.184822+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"A spin-resolved photoemission or transport measurement on hydrogen-covered NbP(001) showing that Fermi-arc contours disappear upon adsorption, or a calculation using an independently measured relaxation time that yields an H-projected moment below 10⁻⁷ μB, would contradict the central claim. More directly, if the H-projected spectral function at E_F shows zero weight along the pristine arc contours, the proposed arc–H coupling channel is absent.","supporting_citations":[],"review_version":1}