{"id":"d8d48f73-276c-4b6f-b45d-9eec1a34fd14","arxiv_id":"2607.01947","paper_version":1,"verdict":"UNVERDICTED","confidence":"LOW","novelty_score":5.0,"correctness_risk":"unknown","formal_verification":"none","parameter_count":0,"one_line_summary":"Spin-ARPES on PtBi2 shows spin-polarized singly degenerate Fermi-arc surface states with termination-dependent dispersion, supporting its candidacy for topological superconductivity.","lead":"The paper reports spin- and angle-resolved photoemission spectroscopy measurements showing that Fermi-arc surface states in PtBi2 are singly degenerate and spin-polarized. This experimental confirmation of nontrivial topology is a necessary step toward realizing topological superconductivity in the material.","discovery_kind":"new_application","skeptic_critique":{"model":"grok-4.3","headline":"Interpretation of singly degenerate spin-polarized bands as topological Fermi arcs rests on agreement with DFT rather than direct experimental proof of bulk-boundary correspondence","rationale":"The reader's weakest assumption correctly isolates the interpretive step from raw SARPES intensities to topological classification. Because the review was abstract-only, the full-text concern remains the same: the topology-establishing step is the least secured link and is not altered by the additional termination-dependence data mentioned in the abstract.","tokens_in":1623,"tokens_out":316,"duration_ms":28076,"concrete_test":"Re-analyze the SARPES data with explicit kz-dependent photon-energy scans across multiple terminations; if the candidate arc bands show measurable kz dispersion (>20 meV over 10-20 eV photon range) or fail to match the calculated surface-projected spectral weight, the topological assignment is weakened.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim equates observation of singly degenerate, spin-polarized surface bands (via SARPES) with establishment of nontrivial topology. This requires that no trivial surface states can produce the same signatures and that the observed termination-dependent dispersions uniquely match the calculated topological arcs. The paper notes agreement with first-principles calculations and termination dependence, but the data alone do not exclude matrix-element effects, residual bulk contributions, or trivial Rashba-like states whose spin texture could appear singly degenerate within experimental resolution. No independent check (e.g., kz dispersion or explicit surface spectral function comparison) is described that would falsify a trivial assignment.","agreement_with_reader":"agree"},"referee_report":{"model":"grok-4.3","summary":"The manuscript reports spin- and angle-resolved photoemission spectroscopy (SARPES) measurements on layered PtBi₂, claiming that the Fermi-arc surface states are singly degenerate and spin-polarized. This is presented as establishing their nontrivial topology and as a necessary condition for topological superconductivity. The work additionally reports a strong surface-termination dependence of the arc dispersion (nearly flat or linear), in agreement with first-principles calculations.","tokens_in":1735,"tokens_out":447,"duration_ms":19742,"significance":"If the assignment of the observed states as topological Fermi arcs is robust, the result would supply direct experimental support for the topological character of surface states in a candidate topological superconductor and would highlight termination dependence as a control parameter. The spin-polarization data and termination-dependent bandwidth measurements constitute concrete experimental inputs that could be used to test models of topological superconductivity.","major_comments":[{"comment":"Abstract: The central claim equates observation of singly degenerate, spin-polarized surface bands with establishment of nontrivial topology. This interpretation rests on agreement with DFT calculations and termination dependence rather than an independent experimental verification of bulk-boundary correspondence (e.g., explicit kz dispersion or surface spectral-function comparison that would falsify a trivial Rashba-like assignment). No quantitative details on energy/momentum resolution, background subtraction, or spin-resolution calibration are supplied to support the single-degeneracy assertion.","section":"Abstract"},{"comment":"Results (SARPES data presentation): The manuscript does not describe a concrete test that would exclude matrix-element effects or residual bulk contributions capable of producing apparently singly degenerate spin textures within experimental resolution. Because this step is load-bearing for the topology assignment, the lack of such a falsification criterion weakens the link between the measured spin polarization and the claimed nontrivial topology.","section":"Results"}],"minor_comments":[{"comment":"The abstract would benefit from a brief quantitative statement of data quality (e.g., energy resolution, spin asymmetry magnitude) to allow readers to assess the single-degeneracy claim.","section":"Abstract"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":{"model":"grok-4.3","summary":"We thank the referee for their detailed and constructive comments on our manuscript. We address each major comment below and indicate the revisions made to the manuscript.","responses":[{"response":"The nontrivial topology is inferred from the experimental observation of singly degenerate, spin-polarized Fermi-arc states whose dispersion depends on surface termination in a manner that agrees with our DFT calculations, consistent with the bulk-boundary correspondence. We acknowledge the value of providing quantitative experimental details and will add information on energy/momentum resolution, background subtraction, and spin-resolution calibration to the revised manuscript. Explicit kz dispersion measurements are not straightforward in this system due to its layered structure and limited kz resolution in ARPES, but the termination dependence provides an experimental distinction from bulk or trivial Rashba states.","revision_made":"partial","referee_comment":"[Abstract] Abstract: The central claim equates observation of singly degenerate, spin-polarized surface bands with establishment of nontrivial topology. This interpretation rests on agreement with DFT calculations and termination dependence rather than an independent experimental verification of bulk-boundary correspondence (e.g., explicit kz dispersion or surface spectral-function comparison that would falsify a trivial Rashba-like assignment). No quantitative details on energy/momentum resolution, background subtraction, or spin-resolution calibration are supplied to support the single-degeneracy assertion."},{"response":"In the revised manuscript, we will expand the Results section to include a discussion of matrix-element effects and potential bulk contributions. We will explain that the pronounced surface-termination dependence of the arc dispersion, which matches calculations only for surface states, serves as evidence against dominant bulk contributions. Furthermore, the consistency of the spin polarization across different measurement geometries helps mitigate concerns about matrix elements.","revision_made":"yes","referee_comment":"[Results] Results (SARPES data presentation): The manuscript does not describe a concrete test that would exclude matrix-element effects or residual bulk contributions capable of producing apparently singly degenerate spin textures within experimental resolution. Because this step is load-bearing for the topology assignment, the lack of such a falsification criterion weakens the link between the measured spin polarization and the claimed nontrivial topology."}],"tokens_in":1268,"tokens_out":456,"duration_ms":31095,"standing_objections":[]},"desk_editor":{"model":"grok-4.3","letter":"The main takeaway from this paper is new spin-ARPES measurements on PtBi2 that report spin-polarized, singly degenerate Fermi arcs whose bandwidth changes markedly with surface termination and lines up with the DFT bands.\n\nWhat is actually new is the concrete spin texture data combined with the termination-dependent dispersion for this specific material. The experiment adds a useful experimental data point on the surface states that prior work on PtBi2 had not fully mapped in spin resolution.\n\nThe paper does a straightforward job of showing the SARPES spectra and the comparison to calculations. The termination dependence is a clear experimental observation that helps support the surface assignment.\n\nThe soft spot is exactly the one flagged in the stress-test note. The claim that these bands establish nontrivial topology comes from their match to the calculated arcs rather than from a direct experimental test of bulk-boundary correspondence. The data do not appear to include kz dispersion checks or other independent ways to exclude trivial Rashba-like states or matrix-element effects that could produce similar spin-polarized features within resolution. The abstract also gives no numbers on background subtraction, spin calibration, or how single degeneracy was verified, so the strength of the support is hard to judge from the summary alone.\n\nThis is for people working on ARPES of topological candidates or on PtBi2 as a platform for topological superconductivity. A reader who needs the spin and termination data will find it relevant. The work is coherent enough on its own terms to go to peer review so the community can examine the figures and methods in detail.\n\nRecommendation: send it to referees.","headline":"Spin-ARPES data on PtBi2 shows polarized singly degenerate surface bands with termination dependence, but topology assignment rests on DFT match.","tokens_in":2285,"tokens_out":390,"would_cite":false,"duration_ms":28524,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"grok-4.3","headline":"The Fermi arcs in PtBi₂ are singly degenerate and spin-polarized, establishing their nontrivial topology.","keywords":["PtBi2","Fermi arcs","topological surface states","spin polarization","topological superconductivity","ARPES","surface termination"],"falsifier":"Observation of spin-degenerate or doubly degenerate bands at the reported Fermi-arc locations would contradict the topological assignment.","tokens_in":2531,"feed_emoji":"🔬","tokens_out":548,"duration_ms":22648,"temperature":0.7,"pith_summary":"The paper applies spin- and angle-resolved photoemission spectroscopy to the surface states of PtBi₂. It finds that the Fermi arcs appear singly degenerate and carry clear spin polarization. These properties together establish that the arcs possess nontrivial topology. The same measurements also show that the arc dispersion changes with surface termination to produce either nearly flat or linear bands. Such spin texture and termination control supply necessary ingredients for topological superconductivity to appear in this material.","feed_headline":"Fermi arcs in PtBi₂ shown singly degenerate and spin-polarized","feed_subtitle":"This establishes their nontrivial topology, a necessary condition for topological superconductivity.","key_machinery":"Spin- and angle-resolved photoemission spectroscopy that measures single degeneracy and spin polarization of the Fermi-arc surface states.","core_discovery":"Using spin- and angle-resolved photoemission spectroscopy, we demonstrate that the Fermi arcs in PtBi₂ are singly degenerate and spin-polarized, which establishes their nontrivial topology and constitutes a necessary condition for topological superconductivity. We further uncover a pronounced surface-termination dependence of the Fermi-arc dispersion, yielding either nearly flat or approximately linear bands in agreement with first-principles calculations.","pith_inferences":["Surface termination engineering could be used to adjust the conditions under which topological superconductivity appears.","Similar spin-resolved measurements on related layered compounds might identify additional candidates with comparable arc properties.","If topological superconductivity is realized, the spin-polarized arcs would be the likely location for protected boundary modes."],"forward_implications":["Single degeneracy combined with spin polarization confirms the nontrivial topology of the arcs.","This topology supplies a necessary condition for topological superconductivity to emerge in PtBi₂.","Surface termination tunes the Fermi-arc bandwidth between nearly flat and approximately linear dispersions.","The observed spin texture and bandwidth control together identify key ingredients for topological superconductivity."],"fun_headline_variants":["PtBi₂ Fermi arcs spin-polarized and singly degenerate","ARPES shows spin-polarized arcs in PtBi₂","Termination tunes PtBi₂ Fermi arc dispersion","Spin polarization confirms topology in PtBi₂","Singly degenerate arcs mapped in PtBi₂ by ARPES"],"cache_read_input_tokens":64,"weakest_assumption_plain":"That the measured singly degenerate and spin-polarized bands are the topological Fermi-arc surface states and not trivial states or measurement artifacts.","fun_headline_variants_meta":{"raw":{"variants":["PtBi₂ Fermi arcs spin-polarized and singly degenerate","ARPES shows spin-polarized arcs in PtBi₂","Termination tunes PtBi₂ Fermi arc dispersion","Spin polarization confirms topology in PtBi₂","Singly degenerate arcs mapped in PtBi₂ by ARPES"]},"model":"grok-4.3","cost_usd":0.003292,"raw_usage":{"total_tokens":1696,"prompt_tokens":543,"num_sources_used":0,"completion_tokens":74,"cost_in_usd_ticks":32924500,"prompt_tokens_details":{"text_tokens":543,"audio_tokens":0,"image_tokens":0,"cached_tokens":256},"completion_tokens_details":{"audio_tokens":0,"reasoning_tokens":1079,"accepted_prediction_tokens":0,"rejected_prediction_tokens":0}},"tokens_in":543,"tokens_out":74,"duration_ms":9030,"temperature":1.0,"reasoning_tokens":1079,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-07-03T04:05:49.194913+00:00","model_set":{"reader":"grok-4.3"},"falsifier":"Observation of spin-degenerate or doubly degenerate bands at the reported Fermi-arc locations would contradict the topological assignment.","supporting_citations":[],"review_version":1}