{"id":"4f29618f-e2e7-4d9d-aec4-4262398fbdaf","arxiv_id":"2607.26487","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Same-spin Andreev reflections occur at quantum Hall–superconductor interfaces, and particle loss enables them in the spin-polarized ν=1 regime.","lead":"Electrons hitting a superconductor from a quantum Hall edge can come back as holes in the same spin channel, not only in the opposite one. The authors show this requires particle loss at the interface, which also lets Andreev reflection happen in a fully spin-polarized ν=1 edge.","discovery_kind":"first_principles","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The ν=1 'loss-enabled' claim is not isolated from local ν=2 doping: the authors' rebuttal invokes the 2×2 symmetry lemma, which no longer applies if doping creates a second spin channel, so the h↑ signal may be ordinary ν=2 spin-flip Andreev reflection without loss.","rationale":"The reader's weakest assumption was the ideality of the spin polarizers. That is a real concern, but the more load-bearing issue is the local-ν=2 confound for the flagship loss-enabled ν=1 claim. The reader's rationale does mention 'the assumption that local doping does not secretly make the region ν=2,' but it does not expose why the authors' rebuttal fails: the 2×2 symmetry lemma cannot be applied once a local spin-down channel exists. The reader's stated conditions—error bars, proof of the lemma, data availability—do not include a direct experimental test for local ν=2. Therefore I would keep the CONDITIONAL verdict but add a new essential condition: experimentally exclude local ν=2 as the source of the h↑ signal. This is not a rejection of the theoretical mechanism; the Kwant simulation with explicit loss is independent evidence that the mechanism can work. It is a critique of the experimental discrimination between loss-enabled ν=1 physics and trivial local-ν=2 physics. The concern is internal-consistency-based: the manuscript's own doping admission weakens the central claim, and the symmetry argument used to rescue it is misapplied.","tokens_in":19668,"tokens_out":11443,"duration_ms":104216,"concrete_test":"Perform a local-filling calibration of the ν=1 region by using contact E as a grounded drain (setup f of the Supplementary) while sweeping V_G across the ν=1–ν=2 transition, and record the spin-down downstream signal at zero bias and at the magnon-gap bias. If a spin-down current is present throughout the nominal ν=1 plateau and its onset tracks the appearance of h↑, the observation is explained by local ν=2 and does not isolate loss. Complement this with a Kwant simulation that adds a local ν=2 puddle (no loss) to the ν=1 geometry: if the simulated P_eh histograms match the experimental ν=1 data, then the loss-enabled interpretation is underdetermined by the experiment.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The most striking claim—that particle loss enables same-spin Andreev reflection at ν=1—depends on excluding the possibility that the nominal ν=1 region actually contains a local ν=2 puddle near the superconducting contact. The authors themselves acknowledge this: 'local doping likely exists near the superconducting contact' and the magnon-gap feature 'indicates the presence of a local filling factor ν=2 near the contact.' They then argue that even with doping, loss is still necessary because 'in the absence of loss, Andreev reflections producing h↑ in the downstream channel are suppressed for ν=1 because of the same symmetry arguments, even in the presence of doping [29].' This is an internal inconsistency: the cited 2×2 S-matrix lemma applies only when the full scattering problem has a single electron and a single hole channel. If the doping creates a local spin-down electron state, the relevant BdG S-matrix is at least 4×4 (two spins × electron/hole), and the lemma no longer forces the e↑→h↑ amplitude to vanish. In fact, the authors' own ν=2 data show that h↑ appears without invoking loss as a necessary ingredient. Thus the observed similarity between the ν=1 and ν=2 histograms could be entirely explained by a local ν=2 region, and the experiment does not isolate loss as the enabler. The tight-binding simulation provides theoretical support for the loss mechanism in an idealized geometry, but it does not control the experimental doping confound.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports spin-resolved transport measurements of chiral Andreev edge states (CAES) at a quantum Hall–superconductor interface in graphene. The device uses ν=1 regions as spin polarizers, injects spin-up electrons into a central region tuned to ν=2 or ν=1, and measures downstream resistances in the same and opposite spin channels. The main experimental claims are: (i) spin-flip processes accompany Andreev reflection, so that an incoming spin-up electron can emerge as a hole in the same spin-up channel; (ii) the distribution of the electron–hole imbalance P_eh is exponential, with the electron-side and hole-side decay rates differing by a factor of about two; (iii) at ν=1, where ordinary Andreev reflection is expected to be suppressed, holes in the spin-up channel nevertheless appear, and the authors attribute this to particle loss into the superconductor, invoking non-Hermiticity as the enabling mechanism. The paper includes random-matrix theory for the exponential distribution, Landauer–Büttiker modeling of the measurement schemes, and tight-binding simulations with a loss reservoir.","tokens_in":19968,"tokens_out":8226,"duration_ms":89971,"significance":"If the central claims hold, this is a significant advance. It would provide the first spin-resolved observation of same-spin Andreev reflection at a QH–SC interface, quantify spin-flip scattering through the ratio of electron and hole decay rates, and demonstrate that particle loss can lift the unitary suppression of Andreev reflection in a fully spin-polarized ν=1 edge. The claim has direct implications for proposals to realize chiral Majorana modes in QH–SC hybrids and for the role of non-Hermitian physics in topological superconductors. The paper has notable strengths: the data are openly available, the tight-binding calculations use a reproducible Kwant implementation, and the authors cross-check their measurement interpretation with several Landauer–Büttiker setups and a supplementary spin-filter test on a second device. These elements make the paper unusually transparent. However, the most striking claim—that loss, rather than local doping, enables the ν=1 signal—is not yet established by the evidence presented.","major_comments":[{"comment":"The ν=1 loss-enabled claim is undermined by the doping confound acknowledged in this paragraph. The authors observe a magnon gap indicating a local ν=2 region near the contact, and the ν=1 and ν=2 P_eh histograms in Fig. 4b are nearly identical. The response that even with doping h↑ is suppressed without loss cites Ref. [29], a 2×2 S-matrix lemma. That lemma applies only when the full scattering problem has a single electron and a single hole channel. A local ν=2 puddle adds a spin-down electron channel, making the BdG S-matrix at least 4×4 (two spins × electron/hole); the lemma then imposes no prohibition on e↑→h↑. The authors' own ν=2 data demonstrate h↑ without invoking loss. Thus the experiment does not isolate loss as the enabler; the data are equally explained by ordinary ν=2 Andreev reflection in a doped region. The tight-binding simulation in Fig. 4c,d includes loss by constructi","section":"Results, paragraph beginning 'Finally, we note that local doping likely exists...'"},{"comment":"The spin-resolved measurement assumes the ν=1 polarizers are ideal, transmitting only spin-up and fully blocking spin-down. Under this assumption, negative R_d↑ is evidence of same-spin holes. If a polarizer leaks or spin-mixes, an ordinary opposite-spin hole h↓ can contribute to R_d↑ and mimic same-spin Andreev reflection. The supplementary two-device test (Fig. S2) is a useful cross-check, but it is performed on a different device and provides no quantitative leakage bound. Because the central spin-flip claim rests on the sign structure of R_d↑/R_d↓, the authors should report an upper bound on polarizer leakage or an in-situ check that the spin-up and spin-down channels are cleanly separated in the main device.","section":"Results, 'The left and right regions...' and Fig. 1; Supp. S2"},{"comment":"The exponential form and the field-independent ratio α_h/α_e ≈ 0.5 are central quantitative results. The fits to the log-linear histograms are shown without error bars, confidence intervals, or goodness-of-fit statistics, and α_e and α_h are free parameters of the RMT model rather than predictions. Reporting fit uncertainties (e.g., bootstrap or χ²) would substantiate both the exponential claim and the statement that α_h/α_e is 'nearly constant' in magnetic field. Without them, the distinction between an exponential and a slightly curved distribution, and between a constant ratio and a weakly varying one, cannot be assessed.","section":"Results, 'We can now quantify the strength...' and Fig. 3a inset"}],"minor_comments":[{"comment":"Ref. [29] is an inline lemma in the reference list rather than a conventional citation. It should be moved to the main text or an appendix with a proof, and its domain of validity (number of electron/hole channels) should be stated explicitly.","section":"References / Ref. [29]"},{"comment":"There are several typos: 'corrspond' in the RMT section, 'matirx' in Supplementary S0.7, 'acompanied' in the caption of Fig. 2e, and 'an and' in the introduction. A careful proofread is needed.","section":"Throughout"},{"comment":"The conversion from R_d to P_eh is given for the unpolarized case; the spin-resolved extension is relegated to the supplementary. A one-line statement of the spin-resolved formula in the main text would improve readability.","section":"Eq. (1)"},{"comment":"The magnon emission gap is indicated by a white dashed line but is not quantitatively discussed. Please specify the threshold current and how the gap position is extracted.","section":"Fig. 4a"},{"comment":"The inset reports α_h/α_e versus magnetic field without error bars. Adding error bars or confidence intervals would make the claimed field independence testable.","section":"Inset, Fig. 3a"}],"recommendation":"major_revision","confidential_remarks":"The paper is well written and the spin-filtered data set is valuable, with reproducible open data and simulations. The main risk is the headline ν=1 'loss-enabled' claim: the cited 2×2 symmetry lemma does not apply in the presence of the local ν=2 doping that the authors themselves acknowledge. If the authors cannot provide a lossless control with an explicit local ν=2 region or otherwise rule out the doping explanation, they should soften the claim to an observation consistent with loss-enabled Andreev reflection rather than a demonstration that loss is necessary. The other results—spin-flip Andreev reflection at ν=2 and the exponential P_eh statistics—are likely publishable after the fit statistics are improved."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Two things to know before you read it. The spin-filtered scheme is genuinely well-designed: ν=1 polarizers on both sides of the superconductor, spin-resolved downstream resistances, six bias/detection configurations cross-checked against a Landauer-Büttiker model, plus a two-device filter test in the supplement. The headline claim — that particle loss enables Andreev reflection at ν=1 — is plausible but not experimentally isolated. The paper itself admits local ν=2 doping near the contact, and the rebuttal rests on a 2×2 symmetry lemma that appears only in the reference list, without proof.\n\nWhat is new and solid: at ν=2, the bipolar P_eh histograms in both spin channels are convincing evidence for spin-flip Andreev processes, including electrons returning as holes in their own spin channel. The exponential tails persist across several field ranges; the 2D histogram showing near-zero correlation between spin channels is a clean confirmation of strong loss. The tight-binding simulations with controlled loss reproduce the qualitative features of the experimental histograms, and the code and data are cited.\n\nSoft spots, in order. The exponential fits carry no error bars or goodness-of-fit statistics, so the α_h/α_e ≈ 0.5 claim is under-quantified. The RMT account fits the decay rates to the data; the exponential form is the prediction, and that is fine, but the rates themselves are not. The bigger issue is the ν=1 argument. The 2×2 lemma [29] is doing all the work, both for the no-loss suppression and for the claim that suppression survives doping. The stress-test objection lands: if the puddle's spin-down edge reaches the contact, the asymptotic S-matrix is not 2×2, the lemma no longer forces e↑→h↑ to vanish, and the downstream hole can be ordinary ν=2 same-spin reflection without any loss. Closed-channel intuition would rescue the authors only if the puddle does not open a channel to the superconductor — but the magnon-gap feature they report suggests it does. This is underdetermination, not refutation: the data are consistent with loss-enabled AR, but the experiment cannot discriminate against a local ν=2 region, and the near-identical ν=1 and ν=2 histograms fit both stories.\n\nWho this is for: anyone working on QH–SC hybrids or the chiral Majorana search; the ν=2 spin-resolved data alone is a real contribution.\n\nRecommendation: send it to referees. Insist on a proof or proper citation for the lemma, fit statistics, concrete data links (the availability statement is too vague to act on), and an experimental or analytical strategy that separates loss from local ν=2. With those, the paper would be very strong.","headline":"A careful spin-resolved study with a strong ν=2 result; the ν=1 loss-enabled claim is plausible but underdetermined — the unproven 2×2 symmetry lemma and the admitted local ν=2 doping both need referee attention.","tokens_in":20562,"tokens_out":18874,"would_cite":true,"duration_ms":177808,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["73.43.-f","74.45.+c"],"model":"deepseek-v4-flash","headline":"A quantum Hall edge coupled to a superconductor can reflect electrons back as holes in the same spin channel, and the process survives in the fully spin-polarized ν=1 regime only because particle loss violates the unitarity that would other","keywords":["Andreev reflection","quantum Hall","spin flip","chiral Andreev edge states","particle loss","non-Hermiticity","random matrix theory","spin polarization"],"falsifier":"Measure the spin-resolved downstream resistance at ν=1 in a device whose polarizer has been independently characterized to have, say, >10^3 extinction ratio, while the superconductor contact is made nearly lossless (for example, by minimizing vortices or using a short, high-quality interface). If negative R_d↑ persists in this low-loss limit, the loss-enabling claim is weakened; if it vanishes, the claim is confirmed. Alternatively, directly detect a hole in the spin-up channel using a spin-sensitive detector such as a quantum point contact tuned across the ν=1→ν=2 transition.","tokens_in":19517,"feed_emoji":"⚛️","tokens_out":3860,"duration_ms":53969,"temperature":0.7,"pith_summary":"This paper presents transport evidence that Andreev reflection at a quantum Hall–superconductor interface can flip spin, sending electrons back as holes in the same spin channel. In the fully spin-polarized ν=1 case, theory says this should be impossible: a unitary, particle-hole symmetric scattering matrix with no topology must be diagonal. The authors observe it anyway and argue that particle loss into the superconductor (quasiparticles absorbed by vortices or leaked into normal contacts) breaks the unitarity constraint. They support this with exponential statistics of reflection probabilities, a random-matrix model with loss channels, and tight-binding simulations. If right, the result means non-Hermiticity—not just spin-orbit coupling—must be considered in any hybrid quantum Hall–superconductor device, including proposals for chiral Majorana modes.","feed_headline":"Loss enables same-spin Andreev reflection at ν=1","feed_subtitle":"Holes appear in the same spin channel as the incoming electrons, a process unitarity alone forbids.","key_machinery":"The chiral Andreev edge state (CAES), the hybrid electron-hole mode formed at the quantum Hall–superconductor interface, is measured through spin-resolved downstream resistances R_d↑ and R_d↓ and converted to the probability difference P_eh = P_e − P_h. The theoretical engine is random matrix theory: strong loss is modeled by adding many weakly coupled effective channels, making the S-matrix large, so individual matrix elements become Gaussian-distributed and the observed exponential histograms follow. The load-bearing no-go result is that a lossless ν=1 S-matrix that is unitary, particle-hole symmetric, and has determinant 1 must be diagonal in the particle-hole basis, so same-spin Andreev","core_discovery":"The central claim is that Andreev reflections at a quantum Hall–superconductor interface can flip electron spin, producing a hole in the same spin channel, and that at ν=1 this is enabled by particle loss. In the lossless limit, the ν=1 scattering matrix is 2×2, particle-hole symmetric, unitary, and non-topological, forcing the electron-to-hole conversion amplitude to zero; adding loss (modeled as many extra effective channels) relaxes the constraint, and the authors observe spin-up holes in the outgoing spin-up channel. Evidence includes the sign structure of the spin-resolved downstream resistance R_d↑/R_d↓ and the P_eh histograms, which show bipolar distributions in both spin channels and","pith_inferences":["A clean, low-loss device at ν=1 should show far fewer same-spin holes; this is a testable difference from a genuinely topological e↑/h↑ mode and could be probed by engineering the vortex density or contact transparency.","The same 'loss breaks the no-go' logic may apply to other forbidden processes in spin-polarized edge states, such as crossed Andreev reflection or spin conversion in fractional quantum Hall edges, suggesting a general design principle for non-Hermitian topological hybrids.","If loss is the enabler, then the magnetic-field independence of α_h/α_e is surprising and worth checking at higher fields where vortex effects and loss rates change substantially.","The exponential, single-parameter distribution of reflection probabilities could be used as a fast experimental fingerprint to distinguish loss-enabled processes from coherent topological ones in other superconducting junctions."],"forward_implications":["Proposals for chiral Majorana modes in quantum Hall–superconductor hybrids must explicitly account for loss; a same-spin hole signal alone is not evidence of a topological e↑/h↑ mode.","The exponential P_eh distributions and the near-constant ratio α_h/α_e ≈ 0.5 across magnetic field point to spin-orbit coupling inside the superconductor as the spin-flip source, not the interface.","Strong loss decorrelates the two spin channels, so the independence of R_d↑ and R_d↓ can serve as a diagnostic of loss in future devices.","The ν=1 and ν=2 results look nearly identical because loss channels dominate over the single extra edge channel, meaning loss sets the effective transport scales in these junctions."],"fun_headline_variants":["Loss unlocks same-spin Andreev reflection at ν=1","Spin-flip Andreev at quantum Hall interface requires loss","How particle loss enables same-spin Andreev at ν=1","Loss is the enabler for spin-preserving Andreev reflection"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The experiment assumes the ν_L = ν_R = 1 spin polarizers are ideal—they transmit only spin-up electrons and fully block spin-down with no leakage or spin-mixing—so if they leak, the observed same-spin holes could be ordinary opposite-spin Andreev reflections sneaking through the filter.","fun_headline_variants_meta":{"raw":{"variants":["Loss unlocks same-spin Andreev reflection at ν=1","Spin-flip Andreev at quantum Hall interface requires loss","How particle loss enables same-spin Andreev at ν=1","Loss is the enabler for spin-preserving Andreev reflection"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000487,"raw_usage":{"total_tokens":2228,"prompt_tokens":727,"completion_tokens":1501,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":471,"completion_tokens_details":{"reasoning_tokens":1426}},"tokens_in":471,"tokens_out":1501,"duration_ms":11631,"temperature":1.0,"reasoning_tokens":1426,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T14:43:50.630450+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the spin-resolved downstream resistance at ν=1 in a device whose polarizer has been independently characterized to have, say, >10^3 extinction ratio, while the superconductor contact is made nearly lossless (for example, by minimizing vortices or using a short, high-quality interface). If negative R_d↑ persists in this low-loss limit, the loss-enabling claim is weakened; if it vanishes, the claim is confirmed. Alternatively, directly detect a hole in the spin-up channel using a spin-sensitive detector such as a quantum point contact tuned across the ν=1→ν=2 transition.","supporting_citations":[],"review_version":1}