{"id":"a162357b-1ecb-4525-8772-ba9e5a18c36e","arxiv_id":"2507.20616","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Al/Ni multilayer Josephson junctions show SQUID-like current interference patterns, interpreted as possible chiral edge modes with a doubled magnetic-flux period.","lead":"Josephson junctions made with stacked aluminum and nickel nanolayers show critical-current oscillations that resemble edge-state interference from topological materials, even though these are ordinary metals. The findings suggest that stacking magnetic and nonmagnetic layers might create protected edge channels without intrinsic topological band structure.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The chiral period-doubling claim rests entirely on μ≈5 taken from a different (Al/Ni)70 sample; with μ=1 the Fig. 1c period gives ≈0.8Φ0, not 2Φ0.","rationale":"The reader's weakest_assumption identifies exactly the concern I find most load-bearing: the chiral period-doubling signature is not measured directly but is obtained by multiplying a measured field period by a sensing area whose value depends on a permeability taken from a different sample and selected (between μ=1 and μ=5) to give the best fit. With μ=1, the same Fig. 1c data yield a period close to Φ0, which is the standard period for non-chiral edge or uniformly distributed supercurrents. The other observed features — upward background, asymmetric Js(y), sample-to-sample variation — are consistent with asymmetric edge currents of either chirality, as the paper's own Appendix C shows. I therefore agree with the reader that the chirality claim needs additional evidence, and I would keep the CONDITIONAL verdict. My concern does not move the verdict; it sharpens the condition by specifying a measurable quantity (direct μ of the 10-bilayer stack) that would settle whether the 2Φ0 interpretation survives. The paper itself concedes that 'the definitive topological interpretation requires further validation,' which is properly reflected in a conditional rather than an acceptance verdict.","tokens_in":24018,"tokens_out":4990,"duration_ms":56599,"concrete_test":"Deposit a large-area (≥mm^2) Nb/[Al(3.1)/Ni(1.2-1.3)]10/Al multilayer in the same sputtering run as device fabrication; measure M(H) at 4.2 K with SQUID magnetometry, extract low-field susceptibility χ and μ=1+4πχ; insert this μ into Eq. (1) with the actual electrode thicknesses and λNb=82 nm to recompute t and ΔΦ=ΔH·t·w for Fig. 1c. If ΔΦ is within ~15% of Φ0 rather than 2Φ0, the chiral period-doubling claim fails. As a cross-check, fit the full measured Ic(H) curve of Fig. 1c with Js(y) profiles constrained to produce period Φ0 (μ=1) versus 2Φ0 (μ=5) and compare goodness-of-fit with μ as a free parameter; report which period the data actually select without an a priori μ choice.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central quantitative evidence for chirality is the claim that the Fig. 1c oscillation period is 2Φ0. This is not a direct measurement: the field period ΔH≈7.8 Oe is multiplied by a sensing area s=t·w whose effective magnetic thickness t=560 nm comes from Eq. (1) with μ≈5, a permeability measured on a different, much larger (Al/Ni)70 sample. Appendix A explicitly states that for each device the authors use μ=1 and μ=5 and select the one giving the best fit. If the actual permeability of the 10-bilayer stack is closer to μ=1, the same Eq. (1) gives t≈220 nm (as used in Appendix D), and the Fig. 1c period becomes ΔΦ≈1.7×10^-7 G·cm^2≈0.8Φ0 — i.e., the standard Φ0 period expected for non-chiral edge or supercurrent transport. The upward-displaced SQUID-like envelope and reconstructed asymmetric Js(y) profiles do not rescue chirality, since Appendix C shows those features arise from any asymmetric edge-dominated current distribution, chiral or not. Thus the only feature that distinguishes chiral from non-chiral edge modes is a period that depends on an externally adopted permeability. This is the load-bearing weak point: if μ is near 1 in the measured devices, the headline 'possible chiral hinge modes' loses its quantitative support, although the SQUID-like edge-state observation remains intact.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports magnetic-field-dependent critical current measurements on Nb-based Josephson junctions whose weak links contain stacked (Al/Ni)n multilayers with n up to 10. For the S(NF)10NI(NF)10NS geometry the authors observe SQUID-like Ic(H) oscillations with an upward-shifted background instead of the conventional Fraunhofer pattern, and they reconstruct edge-localized supercurrent density profiles Js(y) from the interference data. They interpret the roughly 2Φ0 oscillation period, together with the edge-localized profiles, as evidence for chiral Andreev edge or hinge modes in a system of ordinary Al and Ni films without intrinsic topological band structure, and they support this interpretation with an analogy to topological photonic alloys. Measurements on devices with an embedded S'IS' trilayer are presented as a control showing conversion of edge-dominated flow into a more uniform Fraunhofer-like supercurrent distribution. The paper explicitly acknowledges that the chirality interpretation is tentative and that independent magnetic characterization of the multilayers remains necessary.","tokens_in":24385,"tokens_out":4953,"duration_ms":59841,"significance":"If the chiral hinge-mode interpretation were established, the work would be significant: it would demonstrate a synthetic, materials-based route to topological edge transport in stacks of ordinary metals, with potential implications for dissipationless interconnects and topological metamaterials. The paper has real strengths: it uses a phase-sensitive Josephson interferometry method suited to probing current distributions, it studies three complementary junction geometries, it reports reproducibility across six nominally identical devices (Fig. A7), and it includes TEM imaging and a detailed Fourier-reconstruction framework in Appendix C. The observed SQUID-like, edge-dominated interference patterns themselves appear to be a robust experimental finding that extends the authors' earlier work. However, the added claim of chirality rests on a single quantitative signature, the 2Φ0 period, whose calibration currently depends on a permeability value taken from a different sample and selected post hoc. As presented, the evidence supports edge-localized supercurrent but does not independently establish chiral directionality.","major_comments":[{"comment":"The central quantitative evidence for chirality, the claimed 2Φ0 period of the Fig. 1c oscillations, is not parameter-free. The field period ΔH ≈ 7.8 Oe is converted to ΔΦ ≈ 4.4 × 10^-7 G·cm^2 using the effective magnetic thickness t = 560 nm from Eq. (1) with μ ≈ 5, a permeability obtained from a different, much larger (Al/Ni)70 sample. Appendix A states that for each sample the authors use μ = 1 and μ = 5 and select the value giving the best fit. With μ = 1 the same Eq. (1) gives t ≈ 220 nm (as used in Appendix D) and ΔΦ ≈ 1.7 × 10^-7 G·cm^2 ≈ 0.8Φ0, i.e., the ordinary Φ0 period expected for non-chiral edge or bulk transport. The period-doubling claim therefore rests on an externally adopted and sample-selected permeability rather than on a direct measurement. An independent determination of μ, or of the effective sensing area, for the actual 10-bilayer devices is required before the chiral interpretation can be sustained.","section":"III.B and Appendix A"},{"comment":"The argument in Appendix D.3 is circular. From ΔH = 13.0 Oe and w = 5 μm the authors obtain t = 320 nm using the standard Φ0/s relation, whereas Eq. (1) gives t = 220 nm for μ = 1 and t = 565 nm for μ ≈ 5. They then write that 'if we follow the assumption of chirality of the edge currents, then the relation for the period ΔH from Φ0/s transforms to 2Φ0/s,' which doubles the inferred thickness to 640 nm and brings it into agreement with μ ≈ 5. The chirality hypothesis is thus used to select μ, and the selected μ is then quoted as supporting chirality. This does not provide independent confirmation and should be removed or reframed as a consistency check only.","section":"Appendix D.3"},{"comment":"The reconstructed supercurrent density profiles are obtained by least-squares fitting an assumed functional form to the same Ic(H) data that they are then used to explain. As Appendix C itself demonstrates in Figs. A2 and A3, an asymmetric edge-dominated current distribution is sufficient to produce an upward-shifted SQUID-like pattern, regardless of whether the edge channels are chiral or not. The Js(y) profiles therefore corroborate edge localization but cannot by themselves distinguish chiral from helical or non-chiral edge currents; the only distinguishing feature discussed in the paper is the oscillation period, whose calibration is the issue raised above.","section":"Appendix C and Figs. 1d, 2d, 3d"},{"comment":"The proposal that local time-reversal-symmetry breaking by superparamagnetic Ni layers can produce topologically protected chiral Andreev hinge modes is based on an analogy to photonic alloys (Ref. [32]); no electronic tight-binding, scattering, or Andreev-spectrum calculation for the Al/Ni multilayer is provided. Given that the experimental period evidence is inconclusive, the manuscript should either present a concrete model demonstrating a topological invariant or chiral Andreev bound states in this parameter regime, or soften the central claim to edge-localized supercurrent with unresolved directionality.","section":"IV and Ref. [32]"}],"minor_comments":[{"comment":"For reproducibility, please provide the explicit layer-thickness sums used in Eq. (1) for each of the three device types; the values t = 560 nm and the sensing areas are quoted without a clear breakdown of dB for the full multilayer stacks.","section":"Section II / Eq. (1)"},{"comment":"The statement that the period is 'approximately twice' Φ0 would benefit from an uncertainty estimate for ΔH and for the resulting ΔΦ, since the period is the main quantitative basis for the chirality claim.","section":"Section III.B"},{"comment":"There are several typographical errors: 'transfer o Cooper pairs' in Section IV, 'illustrating ... illustrating' in the Fig. 2b caption, and 'oscilation' and 'smaal' in Appendix D and the Fig. A7 caption.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The edge-localized SQUID-like behavior appears to be a solid experimental result, and the three-device comparison is a nice design. However, the specifically chiral interpretation is not yet supported because the period-doubling signature depends on a permeability value selected post hoc from a different sample, and Appendix D.3 contains a circular consistency argument. I would be willing to reconsider a revised version that includes independent permeability/magnetometry data on the actual (Al/Ni)10 devices or another unambiguous chiral signature, together with a more restrained interpretation."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this one for the inner S'IS' diagnostic, not for the chirality claim. The data show edge-localized supercurrent in Al/Ni multilayers, and the period-doubling interpretation is the interesting idea, but the 2Φ0 signature rests on adopting μ≈5 from a different 70-bilayer sample. With μ=1 the same Fig. 1c period is about 0.8Φ0, which is the ordinary non-chiral period. That is a load-bearing soft spot.\n\nWhat is genuinely new: the S(NF)10NS'IS'(NF)10NS and S(NF)10NS'IS devices. When the edge current from the outer (NF)10N stacks enters an inner S'IS' junction, the Ic(H) becomes Fraunhofer-like with Φ0 period. That is a clever, semi-quantitative test that the edge current spreads into the inner superconducting film, and it is consistent with chiral (or at least non-helical) modes. The reconstruction of Js(y) from Ic(H) also gives plausible asymmetric edge profiles, though it is a fit.\n\nWhere it gets shaky: the chirality-specific feature. The paper's own Appendix C shows that any asymmetric edge-dominated current distribution produces the upward-shifted SQUID-like pattern; the only feature that distinguishes chiral from non-chiral is the 2Φ0 period. That period is computed with an effective magnetic thickness t=560 nm using μ≈5, measured on a large-area (Al/Ni)70 film. For the actual 10-bilayer devices the permeability is not measured; Appendix A says the authors try μ=1 and μ=5 and keep whichever fits better. That is fitting, not predicting. The Js(y) profiles are also obtained by least-squares fitting an assumed form to the same Ic(H) they are supposed to explain. The paper is honest about these choices, but they mean the chiral conclusion is not forced by the data. The edge-localized current observation remains solid; the 'possible chiral hinge modes' part remains possible.\n\nWho should read it: people working on Josephson interferometry of hybrid multilayer barriers, and anyone interested in whether 'topological-like' edge states can emerge from non-topological metals. It deserves a serious referee — the experimental observation is concrete and the inner-junction test is worth taking seriously, even if the chirality claim needs a direct probe (e.g., measuring permeability on the actual devices, or a non-interference experiment) before it is convincing.","headline":"Solid edge-current evidence, but the chiral 2Φ0 claim leans on a permeability choice rather than a direct measurement.","tokens_in":24879,"tokens_out":2823,"would_cite":false,"duration_ms":31449,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.50.+r","74.78.Fk","73.20.At","75.70.Cn"],"model":"deepseek-v4-flash","headline":"A stack of ten ordinary aluminium/nickel bilayers produces Josephson interference patterns the authors interpret as chiral edge currents.","keywords":["Josephson interferometry","chiral edge states","Andreev reflection","Al/Ni multilayers","SQUID-like oscillations","higher-order topological insulator","supercurrent density","period doubling"],"falsifier":"Measure the magnetic permeability or susceptibility of the actual 10-bilayer junction, or of a sample with identical layer thicknesses and area, rather than importing $\\mu \\approx 5$ from the 70-bilayer film, and recompute the flux period from the measured effective thickness; a value near $\\Phi_0$ instead of $2\\Phi_0$ would remove the period-doubling evidence while leaving the SQUID-like pattern intact. A second decisive check is a local probe of the current or magnetic field at the junction edges, or controlled damage of one edge, which should suppress the chiral contribution if the current truly flows there.","tokens_in":23833,"feed_emoji":"🧲","tokens_out":10997,"duration_ms":120570,"temperature":0.7,"pith_summary":"What the authors try to establish is that a Josephson junction whose weak link is a stack of ten alternating nanometre layers of aluminium and nickel carries its supercurrent almost entirely along the sample edges, and that those edge currents are chiral. The evidence is a set of interference patterns: instead of the usual Fraunhofer lobes, the maximum supercurrent $I_c$ oscillates periodically like a SQUID (a superconducting quantum interference device) with an upward shift and a period close to twice the superconducting flux quantum $2\\Phi_0$. The authors attribute the doubled period to electron and hole branches flowing on opposite edges and coupled by crossed Andreev reflection, the signature of chiral Andreev edge or hinge states. If this is right, such states appear in ordinary metals with no strong spin-orbit coupling and no intrinsic topological band structure, implying that stacking nonmagnetic and ferromagnetic layers is itself a route to topologically protected edge transport.","feed_headline":"Plain Al/Ni stacks show one-way edge currents in Josephson test","feed_subtitle":"Doubled flux period and edge-localized current suggest chiral modes in ordinary metals.","key_machinery":"The load-bearing tool is the Josephson interferogram itself. Since the measured $I_c(H)$ is the Fourier transform of the supercurrent-density profile $J_s(y)$, the shape of the interference pattern tells where current flows: uniform current gives Fraunhofer lobes, edge-localized current gives SQUID-like oscillations, and asymmetric edge current shifts the pattern upward. To convert field period into flux period, the authors use the effective magnetic thickness $t = \\mu d_B + \\lambda_{\\mathrm{Nb}}[\\tanh(d_{S1}/2\\lambda_{\\mathrm{Nb}}) + \\tanh(d_{S2}/2\\lambda_{\\mathrm{Nb}})]$ with $\\lambda_{\\mathrm{Nb}} = 82$ nm. The decisive theoretical input is the predicted contrast between helical and chiral edge states: helical modes give period $\\Phi_0$, whereas chiral modes, whose electron and hole amplitudes live on opposite edges and are connected by crossed Andreev reflection, give period $2\\Phi_0$ together with a positive background. This period-doubling rule is the criterion that carries the chirality claim.","core_discovery":"On the paper's own terms, the central claim is that the supercurrent through a Josephson junction whose weak link is a stack of ten alternating nanometre-thick Al and Ni layers is carried by one-dimensional modes localised at the lateral boundaries of the stack, and that these modes are chiral. The evidence is a set of interference patterns in the maximum supercurrent versus in-plane magnetic field: instead of the Fraunhofer lobes expected for uniform current, the authors observe SQUID-like oscillations with an upwardly displaced background, a slowly decaying envelope, and a field period $\\Delta H \\approx 7.8$ Oe. Using an effective magnetic thickness $t = 560$ nm derived from a measured permeability $\\mu \\approx 5$, this period corresponds to $\\Delta\\Phi \\approx 4.4 \\times 10^{-7}$ G cm$^2$, approximately twice the superconducting flux quantum $\\Phi_0 = hc/2e$. The authors interpret the doubled period as the signature of chiral Andreev edge states, in which an electron on one edge is converted by crossed Andreev reflection into a hole on the opposite edge, so that the interference period is set by $hc/e$ rather than $hc/2e$. Reconstructed supercurrent-density profiles place the current at the edges, and an inner conventional $S'IS'$ junction placed between two multilayers shows a Fraunhofer pattern, which the authors read as the edge current spreading uniformly when it enters a normal superconducting tunnel junction.","pith_inferences":["Replacing Ni with a nonmagnetic metal such as Cu in the same geometry would provide a clean control: if the SQUID-like pattern persists, edge localization does not require ferromagnetic time-reversal breaking; if it vanishes, the Ni magnetization is the active ingredient.","Edge-damage experiments, such as cutting or notching one side of the junction, should suppress one of the two edge channels; a chiral mode would respond differently from a symmetric SQUID formed by two equal edge paths, allowing the two interpretations to be separated.","The photonic-alloy analogy suggests a broader design rule: periodic stacks of magnetically ordered and nonmagnetic layers with local time-reversal breaking may show hinge-like modes at larger bilayer counts, which could be tested in other N/F material pairs without requiring topological band structure."],"forward_implications":["A tunable tabletop source of chiral edge states would emerge: stacking chosen nonmagnetic/ferromagnetic pairs could replace topological single crystals as the platform for studying protected edge transport.","Edge-localized supercurrent means the junctions' magnetic response is concentrated at the boundary, so the interference pattern acts as a built-in probe of edge integrity and local symmetry breaking.","The reversion to a Fraunhofer pattern in the inner $S'IS'$ junction implies that chiral edge current can be coherently converted into ordinary bulk supercurrent, which may matter for wiring edge channels into conventional superconducting circuits.","The onset of SQUID-like behaviour with increasing bilayer number $n$ suggests a collective threshold: enough N/F periods are required to suppress bulk transport and leave edge modes dominant, so varying $n$ is a control knob."],"supporting_citations":[{"why":"It supplies the theoretical prediction that chiral Andreev edge states in a Josephson junction give period-doubled, upward-shifted SQUID-like oscillations.","marker":"[6]"},{"why":"Earlier work by the authors on the same Al/Ni multilayer system established the superparamagnetic barrier, supplied the permeability $\\mu \\approx 5$ used in the flux calibration, and first reported SQUID-like $I_c(H)$ patterns.","marker":"[21]"},{"why":"The Dynes-Fulton relation connects the measured $I_c(H)$ to the supercurrent-density profile $J_s(y)$, and it is the method used here to reconstruct edge-localized current distributions.","marker":"[27]"},{"why":"It provides the comparison set of chiral and helical Josephson interference signatures from topological materials that the experimental patterns are matched against.","marker":"[5]"},{"why":"The topological photonic alloy concept shows that local time-reversal-symmetry breaking with substitutional disorder can produce topologically nontrivial edge states, and it is used as the mechanism for the multilayers' chiral modes.","marker":"[32]"},{"why":"These supply the formula for the effective magnetic thickness $t$ that converts the measured field period into the flux period used for the $2\\Phi_0$ interpretation.","marker":"[28,29]"},{"why":"It supports the dephasing argument for why bulk trajectories decay and near-surface or hinge trajectories dominate in a strongly inhomogeneous weak link.","marker":"[33]"}],"fun_headline_variants":["Al/Ni stacks reveal chiral edge currents in Josephson test","Doubled flux period hints at chiral edge states in metals","Edge-localized supercurrent in Al/Ni multilayers suggests chiral modes","No topology needed: Al/Ni stacks show one-way edge modes","Al/Ni Josephson test finds possible chiral hinge modes"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the effective magnetic thickness of the 10-bilayer junction is $t = 560$ nm, computed with a permeability $\\mu \\approx 5$ measured on a much larger 70-bilayer sample; if the real permeability or sensing area differs, the observed period is no longer twice the flux quantum and the chirality signature vanishes.","fun_headline_variants_meta":{"raw":{"variants":["Al/Ni stacks reveal chiral edge currents in Josephson test","Doubled flux period hints at chiral edge states in metals","Edge-localized supercurrent in Al/Ni multilayers suggests chiral modes","No topology needed: Al/Ni stacks show one-way edge modes","Al/Ni Josephson test finds possible chiral hinge modes"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000181,"raw_usage":{"total_tokens":1359,"prompt_tokens":1047,"completion_tokens":312,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":663,"completion_tokens_details":{"reasoning_tokens":225}},"tokens_in":663,"tokens_out":312,"duration_ms":4101,"temperature":1.0,"reasoning_tokens":225,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T13:25:42.240279+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the magnetic permeability or susceptibility of the actual 10-bilayer junction, or of a sample with identical layer thicknesses and area, rather than importing $\\mu \\approx 5$ from the 70-bilayer film, and recompute the flux period from the measured effective thickness; a value near $\\Phi_0$ instead of $2\\Phi_0$ would remove the period-doubling evidence while leaving the SQUID-like pattern intact. A second decisive check is a local probe of the current or magnetic field at the junction edges, or controlled damage of one edge, which should suppress the chiral contribution if the current truly flows there.","supporting_citations":[{"cited_title":"Mason, Superconductivity on the edge, Science 352, 891 (2016)","cited_arxiv_id":null,"evidence_quote":"It supplies the theoretical prediction that chiral Andreev edge states in a Josephson junction give period-doubled, upward-shifted SQUID-like oscillations."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Earlier work by the authors on the same Al/Ni multilayer system established the superparamagnetic barrier, supplied the permeability $\\mu \\approx 5$ used in the flux calibration, and first reported SQUID-like $I_c(H)$ patterns."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"The Dynes-Fulton relation connects the measured $I_c(H)$ to the supercurrent-density profile $J_s(y)$, and it is the method used here to reconstruct edge-localized current distributions."},{"cited_title":"Qi, C.-Z","cited_arxiv_id":null,"evidence_quote":"It provides the comparison set of chiral and helical Josephson interference signatures from topological materials that the experimental patterns are matched against."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It supports the dephasing argument for why bulk trajectories decay and near-surface or hinge trajectories dominate in a strongly inhomogeneous weak link."}],"review_version":1}