{"id":"5828aff7-4730-4508-bbee-64e18f889a50","arxiv_id":"2411.18227","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"High-resolution STM data on CrBr3/NbSe2 show the in-gap edge states behave like conventional Yu-Shiba-Rusinov impurity states, not Majorana edge modes.","lead":"This study re-examines a layered material previously claimed to host exotic Majorana quasiparticles, using a lower-temperature and higher-resolution scanning tunneling microscope. The authors conclude that the observed edge signals are conventional Yu-Shiba-Rusinov impurity states, not topologically protected Majorana modes.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The YSR claim rests on the unverified assumption that tip approach tunes J; without a quantitative estimate or independent spin probe, 'conclusive' is premature.","rationale":"The paper's central claim—that the CrBr3/NbSe2 edge states are conventional YSR states rather than Majorana modes—rests on two pillars: (i) the discrete spatial distribution correlated with lattice reconstruction, and (ii) the GN-tunable spectral evolution that resembles the YSR quantum phase transition. Pillar (ii) is the more distinctive evidence, but it depends entirely on the assumption that moving the tip closer monotonically increases the exchange coupling J. The authors cite prior work for this effect, but do not demonstrate it in their own system, do not measure J or the spin, and do not rule out alternative tip-induced mechanisms such as electrostatic gating of a non-magnetic localized state. The 3 mV bias makes a large electrostatic force unlikely, yet no order-of-magnitude estimate is given. While the spectral-weight reversal across the merging point is a convincing YSR hallmark, it is not exclusive to YSR. The unclassified 13% of edge spectra and the lack of raw data/code further temper the 'conclusive' language. These limitations do not invalidate the observation, but they justify the CONDITIONAL verdict: the YSR interpretation is plausible and the paper is a valuable contribution, but the evidence is not yet conclusive. The proposed computational check would directly test the load-bearing J-tuning assumption.","tokens_in":12300,"tokens_out":11757,"duration_ms":127302,"concrete_test":"Perform a quantitative estimate (DFT or model Hamiltonian) of the tip-induced change in exchange coupling ΔJ between a Cr edge spin and NbSe2 under the experimental parameters (V_b = 3 mV, I_t = 100–3100 pA, tip-sample distance change ~ 0.5–1 Å). If ΔJ is orders of magnitude smaller than the YSR gap-closing scale Δ/(Sπρ_s) ≈ 1 meV, the J-tuning assumption is implausible and the spectral evolution must be attributed to other tip-induced mechanisms; a comparable ΔJ would make the J-tuning scenario credible.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central argument in 'Tunneling transmissivity-dependent dI/dV spectrum measurements' is that increasing GN (tip closer) tunes the exchange coupling J between a CrBr3 edge spin and the NbSe2 superconductor, driving YSR states across a quantum phase transition. The paper states: 'During this process, the electrostatic force from the approaching tip will affect the coupling between the edge adatoms and the superconductor, leading to variable J values.' However, J is not measured or independently constrained; the localized spins at the edges are inferred solely from lattice reconstruction. The observed 'approach-merge-split-again' evolution and the electron-hole spectral-weight reversal are consistent with YSR, but the same qualitative behavior could arise from a non-magnetic resonant level crossing the Fermi energy if the tip electrostatically gates the local state. Moreover, the experimental bias is only 3 mV, so the tip-induced electrostatic force is tiny; whether it can shift J by the ~meV scale needed to close the YSR gap is not quantified. Therefore, the evidence supports but does not prove the YSR interpretation, and the claim of 'conclusive experimental evidence for the topologically trivial origin' overstates the result.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports a reinvestigation of the CrBr3/NbSe2 heterostructure using ultralow-temperature STM/STS at 40 mK with improved energy and spatial resolution. The authors find that monolayer CrBr3 acts as an insulating barrier, so that the superconducting gap and vortex states measured on the CrBr3 film are nearly identical to those on bare NbSe2. At the edges of CrBr3 islands, they observe two types of in-gap states: zero-energy conductance peaks (ZECPs) and particle-hole symmetric pairs of in-gap conductance peaks. These states are spatially discrete and correlate with lattice reconstruction at the edge. Tunneling transmissivity-dependent measurements show that the ZECP splits with increasing GN, while the pair of in-gap peaks first approach each other, merge into a ZECP, and then split again, with the process being reversible. The authors interpret these behaviors as conventional Yu-Shiba-Rusinov (YSR) states undergoing a quantum phase transition, and argue that their results constitute conclusive evidence for the topologically trivial origin of the edge states, contradicting earlier claims of Majorana edge modes in this heterostructure.","tokens_in":12557,"tokens_out":4158,"duration_ms":39614,"significance":"If the YSR interpretation of the edge states holds, the paper makes an important contribution by resolving a high-profile controversy: it provides a concrete, reproducible counterexample to the claim of topological Majorana edge modes in CrBr3/NbSe2. The study benefits from the higher resolution of the measurements, a direct comparison with bare NbSe2, and the observation of reversible, GN-dependent spectral evolution that is difficult to reconcile with protected Majorana modes. The spatial correlation of the edge states with lattice reconstruction is a useful structural insight. However, the paper's central evidence is qualitative: the YSR assignment is not supported by a quantitative fit of the data to the YSR formula, no spin-sensitive measurement is presented, and the key assumption that tip approach tunes the exchange coupling J is not independently verified. Nevertheless, the work is significant as a systematic experimental study that raises strong caveats against the earlier Majorana interpretation.","major_comments":[{"comment":"The central interpretation rests on the assumption that increasing GN by reducing tip-sample distance monotonically tunes the exchange coupling J between edge spins and NbSe2. The paper states that the electrostatic force from the approaching tip will affect the coupling, but no quantitative estimate or direct measurement of J is provided. Without establishing this monotonic relationship, the observed 'approach-merge-split-again' evolution is not uniquely tied to the YSR energy-versus-J curve. A non-magnetic resonant level whose energy is shifted by tip-induced electrostatic gating could, in principle, produce similar qualitative behavior as it crosses the Fermi energy. Please provide a quantitative model of the tip-induced coupling change, a control experiment on a non-magnetic impurity or defect, or an explicit argument ruling out electrostatic gating as the origin of the spectral evolution. This is a load-bearing point for the main conclusion.","section":"Tunneling transmissivity-dependent dI/dV spectrum measurements (Fig. 4)"},{"comment":"The manuscript twice states that the results provide 'conclusive experimental evidence for the topologically trivial origin' of the edge states. This is an overstatement given that the identification is qualitative: no quantitative fit to the YSR formula ε = Δ(1−a²)/(1+a²) is performed, no spin-resolved STS data are presented, and about 13% of the edge spectra are left unclassified (Supplementary Fig. 6). The data are consistent with a YSR interpretation, but they do not conclusively exclude all alternatives, such as non-magnetic in-gap states or tip-induced artifacts. Please soften the claim to 'strong evidence' or 'consistent with', unless a quantitative analysis that tests the YSR model against the measured spectra is added.","section":"Introduction and Discussion"},{"comment":"The paper infers the existence of localized magnetic moments at the reconstructed CrBr3 edges solely from the observation of in-gap states and the structural reconstruction. The YSR interpretation requires a local spin, yet the magnetic character of these edge sites is not directly demonstrated. A magnetic-field-dependent study would provide a concrete test: YSR states are expected to split linearly with applied magnetic field, whereas non-magnetic bound states would behave differently. Including such data, or at least explicitly discussing the absence of a spin-sensitive probe, would substantially strengthen the central claim.","section":"Discussion (edge states and lattice reconstruction)"}],"minor_comments":[{"comment":"The statement about 'higher spatial resolution (~4.25 pixel/nm)' is misleading because pixel density is a data acquisition grid density, not a physical measure of spatial resolution. Please rephrase to describe the actual sampling density or the physical resolution determined by the tip condition.","section":"Discussion"},{"comment":"The YSR formula is garbled in the text: '𝜀 = Δଵି௔మ / ଵା௔మ' should be typeset as ε = Δ(1−a²)/(1+a²). Please ensure proper mathematical typesetting in the final version.","section":"Introduction"},{"comment":"The sketched phase diagram in Fig. 4h would be more convincing if the experimentally extracted peak positions from Figs. 4a-g were overlaid on the theoretical YSR energy curve. A quantitative comparison of the measured peak energies as a function of GN with the YSR formula would provide stronger support for the interpretation.","section":"Fig. 4"},{"comment":"The paper states that CrBr3 acts as a vacuum barrier with little influence on NbSe2, but also reports a ~30 meV energy shift and weak charge transfer. These statements appear somewhat contradictory and should be reconciled, for example by clarifying that the barrier behavior holds for the low-energy electronic structure while a weak interfacial charge transfer is still present.","section":"Structural and electronic properties of CrBr3/NbSe2 heterostructure"}],"recommendation":"major_revision","confidential_remarks":"The paper addresses a controversial claim in the field and provides a plausible counter-explanation based on YSR states. The main concerns are the unverified assumption about tip-induced tuning of J and the overstatement of 'conclusive' evidence. If the authors can supply a quantitative estimate of the tip effect, a control experiment, or at least a clear argument ruling out electrostatic gating, and temper the conclusiveness of the claims, the paper could become a valuable contribution. The self-citation in refs. 19 and 20 is not load-bearing and is acceptable for the stated purpose of characterizing the effective electron temperature."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Quick take: this is the strongest experimental counter so far to the Kezilebieke Majorana-edge-mode interpretation of CrBr3/NbSe2. The authors resolve lattice reconstruction at the CrBr3 edges, find discrete in-gap states tied to that reconstruction, and show a tunneling-transmissivity evolution that tracks the YSR quantum phase transition. The YSR reading is plausible and probably right; the 'conclusive experimental evidence' phrasing is not.\n\nWhat's new: the pair of particle-hole symmetric in-gap states that ref 41 didn't see; the close correspondence between edge-state positions and the reconstructed edge lattice; and the full approach-merge-split-again sequence with particle-hole weight reversal as the tip approaches. That sequence is a specific, well-documented YSR fingerprint, genuinely hard to square with a protected Majorana mode, which should stay pinned at zero energy. The control data on bare NbSe2 and the vortex comparison are clean and support the claim that the CrBr3 film is a weak perturbing barrier rather than a strongly coupled magnetic layer.\n\nSoft spots, in order. First, the tuning parameter is asserted, not measured: the paper says the tip's electrostatic force changes J, but J is never extracted, and no quantitative fit to the YSR formula is attempted. The paper concedes this in the Discussion ('determination of Simp and J is complicated and beyond the scope'), which is honest, but it means the central inference is pattern-matching, not a parameter-free prediction. The non-magnetic-resonant-level alternative floated in the stress test doesn't survive contact with the data — it wouldn't give the approach-merge-resplit with weight reversal — but stating how large a J shift the tip plausibly induces would tighten the argument. Second, ~13% of edge spectra are set aside as unclassifiable; tolerable, but it should be disclosed where the analysis happens, not just in the supplement. Third, raw data and code are 'available upon request,' weaker than it should be for a claim this consequential. Minor: they don't see the Moiré-modulated in-gap DOS from refs 41/47 and don't dwell on why.\n\nVerdict: the central argument — topologically trivial YSR-like states, not Majorana edge modes — largely holds; only 'conclusive' is out of bounds. The citation pattern is solid; the self-citations are not load-bearing.\n\nFor whom: experimentalists on van der Waals magnet-superconductor interfaces, and anyone who has to weigh the Kezilebieke claim. Worth refereeing — a serious editor should send it out, with referees pressed on the J-tuning assumption and the excluded spectra.","headline":"A credible, data-rich case that CrBr3/NbSe2 edge states are YSR rather than Majorana, weakened only by the 'conclusive' claim and an assumed—not measured—J tuning mechanism.","tokens_in":13071,"tokens_out":6707,"would_cite":true,"duration_ms":52770,"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":"The edge states in CrBr3/NbSe2 that were called Majorana modes are conventional Yu-Shiba-Rusinov bound states.","keywords":["Yu-Shiba-Rusinov states","Majorana edge modes","CrBr3/NbSe2 heterostructure","scanning tunneling microscopy/spectroscopy","quantum phase transition","in-gap bound states","van der Waals heterostructure","topological superconductivity"],"falsifier":"Measure the local magnetic moment of the reconstructed edge sites with spin-polarized scanning tunneling microscopy: if the bright edge sites show no localized spin, or if a zero-energy peak stays pinned at zero energy over the same range of tip approach instead of splitting, the YSR interpretation would lose its support.","tokens_in":12130,"feed_emoji":"🔬","tokens_out":8099,"duration_ms":69821,"temperature":0.7,"pith_summary":"This paper re-examines the CrBr3/NbSe2 heterostructure with an ultralow-temperature scanning tunneling microscope and argues that the zero-energy conductance peaks previously seen at the edges of CrBr3 islands are not Majorana edge modes. The authors find the CrBr3 monolayer is insulating and behaves as a vacuum barrier, so the superconductivity underneath is essentially unchanged. At reconstructed edge segments they resolve two kinds of in-gap states, a zero-energy peak and a pair of particle-hole symmetric bound states, whose spatial positions track the edge lattice reconstruction. As the tip is moved closer, increasing tunneling transmissivity, the zero-energy peak splits and the pair first merges then splits again; the paper reads this as the energy-versus-exchange-coupling curve of Yu-Shiba-Rusinov states crossing a quantum phase transition. If correct, this removes CrBr3/NbSe2 as a candidate Majorana platform and gives a concrete experimental way to tell trivial in-gap peaks from protected topological ones.","feed_headline":"CrBr3/NbSe2 edge peaks are Yu-Shiba-Rusinov states, not Majorana modes","feed_subtitle":"Tunneling spectra trace bound states through a quantum phase transition, telling trivial peaks from topological ones.","key_machinery":"The carrying object is the Yu-Shiba-Rusinov (YSR) energy formula $\\varepsilon = \\Delta\\,(1-a^2)/(1+a^2)$, where $a = J S_{\\mathrm{imp}} \\pi \\rho_s$, which relates the in-gap bound-state energy to the exchange coupling $J$ between a localized magnetic moment and the superconductor. The paper uses the STM tip's approach as a knob: lowering the tip increases tunneling transmissivity $G_N$ and, through tip-sample forces, is assumed to increase $J$ monotonically, so the measured evolution of peak positions traces the YSR curve across the quantum phase transition at $J_{\\mathrm{crit}}$. The lattice reconstruction at CrBr3 edges supplies the localized spins, and the formula's prediction of merging at zero energy and re-splitting with reversed weights is the signature that distinguishes YSR states from Majorana modes.","core_discovery":"The paper's central claim is that the discrete in-gap edge states of CrBr3/NbSe2 are topologically trivial Yu-Shiba-Rusinov (YSR) states, not chiral Majorana edge modes. Using the YSR relation $\\varepsilon = \\Delta (1-a^2)/(1+a^2)$ with $a = J S_{\\mathrm{imp}} \\pi \\rho_s$, the authors argue that increasing the exchange coupling $J$ between a localized edge spin and the NbSe2 superconductor moves the bound states toward zero energy, produces a zero-energy peak at the quantum phase transition $J = J_{\\mathrm{crit}}$, and then splits them again with reversed electron-hole weight. They reproduce this entire sequence by increasing the tunneling transmissivity with the STM tip, which they take to tune $J$. The same spectral evolution is seen on CrBr3 clusters, and the edge states appear only where the CrBr3 lattice reconstructs, which the paper identifies as the source of localized spins. The authors conclude that the previously reported zero-energy peaks are YSR states sitting coincidentally at the quantum phase transition.","pith_inferences":["We infer that the same tip-tuning protocol could be applied to other magnet/superconductor interfaces that show discrete zero-energy peaks, providing a quick spectroscopic screen for trivial versus topological origin.","If the YSR assignment is right, spin-polarized tunneling spectroscopy across the transition should reveal the predicted reversal of electron- and hole-like spectral weight at a given edge site, a prediction the paper does not test.","The mechanism implies that local exchange couplings at reconstructed edges could be deliberately varied by tip-induced strain or voltage, mapping YSR phase diagrams of individual edge spins."],"forward_implications":["The discrete zero-energy peaks at CrBr3/NbSe2 edges should be regarded as YSR states at the quantum phase transition, so they do not provide evidence for topological Majorana edge modes.","CrBr3/NbSe2 in its present form does not realize the proposed chiral topological superconductor; the insulating CrBr3 layer and weak magnetic proximity suppress Shiba bands.","Transmissivity-dependent STS becomes a usable test: a genuine Majorana zero mode should stay at zero energy when tip-sample coupling changes, while YSR peaks split or merge according to the YSR curve.","Edge lattice reconstruction is the microscopic origin of the localized spins, so engineering the reconstruction would control where and at what energy in-gap states appear."],"supporting_citations":[{"why":"Reports the CrBr3/NbSe2 zero-energy edge peaks as Majorana edge modes; this is the claim the paper reinterprets as YSR states.","marker":"41"},{"why":"Supplies the YSR energy formula and the energy-versus-exchange-coupling description that organizes the spectral evolution.","marker":"15"},{"why":"Provides the theoretical picture of YSR states and the quantum phase transition between unscreened and Kondo-screened ground states.","marker":"14"},{"why":"Demonstrates YSR-type in-gap states and Kondo screening competition for magnetic molecules on Pb(111), a reference experimental behavior.","marker":"59"},{"why":"Shows how tuning the coupling of an individual magnetic impurity to a superconductor drives the YSR quantum phase transition, the method the paper adapts.","marker":"60"},{"why":"Establishes the role of impurity-substrate hybridization in YSR quantum phase transitions, supporting the tip-induced coupling picture.","marker":"61"},{"why":"Tracks a spin-polarized Yu-Shiba-Rusinov bound state across a quantum phase transition, matching the spectral evolution the paper reports.","marker":"62"},{"why":"Defines scanning tunneling microscope criteria for detecting and distinguishing Majorana zero modes, against which the splitting behavior is judged.","marker":"9"},{"why":"Characterizes electronic and magnetic properties of epitaxial CrBr3 monolayers on a superconducting substrate, supporting the insulating-barrier and weak-coupling picture.","marker":"45"}],"fun_headline_variants":["CrBr3/NbSe2 edge states are Yu-Shiba-Rusinov, not Majorana","YSR states, not Majorana modes, explain CrBr3/NbSe2 edge peaks","CrBr3/NbSe2 edge peaks are Yu-Shiba-Rusinov, not topological","Edge states in CrBr3/NbSe2 are YSR, not Majorana"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that bringing the STM tip closer increases the exchange coupling between a localized edge spin and the superconductor in a smooth, monotonic way, so the measured spectral changes trace the Yu-Shiba-Rusinov energy curve rather than some other tip-induced effect.","fun_headline_variants_meta":{"raw":{"variants":["CrBr3/NbSe2 edge states are Yu-Shiba-Rusinov, not Majorana","YSR states, not Majorana modes, explain CrBr3/NbSe2 edge peaks","CrBr3/NbSe2 edge peaks are Yu-Shiba-Rusinov, not topological","Edge states in CrBr3/NbSe2 are YSR, not Majorana"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000853,"raw_usage":{"total_tokens":3753,"prompt_tokens":1039,"completion_tokens":2714,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":655,"completion_tokens_details":{"reasoning_tokens":2614}},"tokens_in":655,"tokens_out":2714,"duration_ms":17041,"temperature":1.0,"reasoning_tokens":2614,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T11:23:43.004455+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the local magnetic moment of the reconstructed edge sites with spin-polarized scanning tunneling microscopy: if the bright edge sites show no localized spin, or if a zero-energy peak stays pinned at zero energy over the same range of tip approach instead of splitting, the YSR interpretation would lose its support.","supporting_citations":[{"cited_title":"Topological superconductivity in a van der Waals heterostructure","cited_arxiv_id":null,"evidence_quote":"Reports the CrBr3/NbSe2 zero-energy edge peaks as Majorana edge modes; this is the claim the paper reinterprets as YSR states."},{"cited_title":"& Franke K.J","cited_arxiv_id":null,"evidence_quote":"Supplies the YSR energy formula and the energy-versus-exchange-coupling description that organizes the spectral evolution."},{"cited_title":"& Zhu J.-X","cited_arxiv_id":null,"evidence_quote":"Provides the theoretical picture of YSR states and the quantum phase transition between unscreened and Kondo-screened ground states."},{"cited_title":"& Pascual J.I","cited_arxiv_id":null,"evidence_quote":"Demonstrates YSR-type in-gap states and Kondo screening competition for magnetic molecules on Pb(111), a reference experimental behavior."},{"cited_title":"Tuning the coupling of an individual magnetic impurity to a superconductor: quantum phase transition and transport","cited_arxiv_id":null,"evidence_quote":"Shows how tuning the coupling of an individual magnetic impurity to a superconductor drives the YSR quantum phase transition, the method the paper adapts."},{"cited_title":"Quantum phase transitions and the role of impurity-substrate hybridization in Yu-Shiba-Rusinov states","cited_arxiv_id":null,"evidence_quote":"Establishes the role of impurity-substrate hybridization in YSR quantum phase transitions, supporting the tip-induced coupling picture."},{"cited_title":"Tracking a spin-polarized superconducting bound state across a quantum phase transition","cited_arxiv_id":null,"evidence_quote":"Tracks a spin-polarized Yu-Shiba-Rusinov bound state across a quantum phase transition, matching the spectral evolution the paper reports."},{"cited_title":"& Yazdani A","cited_arxiv_id":null,"evidence_quote":"Defines scanning tunneling microscope criteria for detecting and distinguishing Majorana zero modes, against which the splitting behavior is judged."},{"cited_title":"Electronic and magnetic characterization of epitaxial CrBr3 monolayers on a superconducting substrate","cited_arxiv_id":null,"evidence_quote":"Characterizes electronic and magnetic properties of epitaxial CrBr3 monolayers on a superconducting substrate, supporting the insulating-barrier and weak-coupling picture."}],"review_version":1}