{"id":"aca1c7d7-f9cc-4363-b731-641b0955eabd","arxiv_id":"2505.21861","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"In MBE-grown Cd3As2 asymmetric SQUIDs, the zero-field superconducting diode effect persists with roughly constant strength and polarity for out-of-plane fields up to ±10 mT.","lead":"Researchers measured a superconducting diode effect in an asymmetric SQUID made from an MBE-grown Cd3As2 thin film and found the direction-dependent switching current difference stays about the same for magnetic fields between -10 and +10 mT. The result matters because most superconducting diodes flip their polarity when the magnetic field reverses, while this one does not.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The field-independence of I_c- - I_c+ may be a threshold artifact: all switching currents are read at a fixed 20 µV criterion, and no test shows the plateau survives alternative definitions.","rationale":"The reader's weakest-assumption analysis identifies the 20 µV threshold as the key uncontrolled element, and my independent reading converges on the same point. The paper's central empirical assertion is that ΔI_c = I_c- - I_c+ is constant over -10 to 10 mT. But ΔI_c is not a directly measured quantity; it is constructed from two threshold-crossing currents. The fixed-voltage definition is reasonable when the switching transition is a sharp voltage step, but the IV traces shown in the paper have finite slope in the switching region, and the slope can vary with current direction and magnetic field. Without a threshold-dependence check, the plateau could reflect the crossing of two field-dependent transition branches rather than a field-independent diode property. The observation that the plateau begins to break down just outside the claimed range, at 15 mT, reinforces the need to show that the plateau is not an artifact of threshold choice. I do not think this concern requires rejection: the data may well be correct, and the authors explicitly speculate about the mechanism. But the central claim is conditional on a threshold-independent analysis, which is exactly the condition the reader already imposed. Therefore the verdict remains unchanged: CONDITIONAL.","tokens_in":10139,"tokens_out":3499,"duration_ms":41160,"concrete_test":"Re-extract I_c+ and I_c- from the raw IV traces using at least three independent definitions: (1) linear extrapolation of the normal-state branch to V = 0; (2) the peak of dV/dI; and (3) both a lower and a higher voltage threshold, e.g., 5 µV and 50 µV. Require that ΔI_c(B) be flat within scatter for all definitions in the range -10 to 10 mT; if the plateau appears only at the 20 µV threshold, the central claim is an artifact. Also report repeated field sweeps and per-point error bars for the device.","verdict_should_be":"UNCHANGED","load_bearing_attack":"In Section III, I_c+ and I_c- are defined as the currents at which |V_dc| = 20 µV. For a finite-width resistive transition, the current at a fixed voltage depends on the transition slope and on the normal-state resistance. The paper shows only that the two IV branches overlap in the superconducting and linear regimes; it does not establish that the switching branch has the same shape for both current polarities and at every magnetic field. In fact, Fig. 4d shows ΔI_c decreasing from ~1.5 µA to 0.9 µA between 10 mT and 15 mT, exactly where the transition may broaden as the critical current is suppressed. If the positive and negative transitions broaden differently with field, a fixed threshold will produce a spuriously flat (or sloping) ΔI_c(B). Since the central claim is a plateau in ΔI_c(B), threshold dependence must be ruled out before the claim can be accepted.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports measurements of the superconducting diode effect (SDE) in an asymmetric SQUID fabricated from an MBE-grown Cd3As2 thin film with Al contacts. At zero magnetic field, the switching currents for positive and negative current sweeps differ (I_c+ ≈ 43.3 μA, I_c- ≈ 44.7 μA at T = 0.3 K), reproducing earlier work on exfoliated Cd3As2. The central new claim is that the difference ΔI_c = I_c- − I_c+ remains approximately constant (~1.5 μA) for out-of-plane magnetic fields between −10 mT and +10 mT, i.e., the SDE is symmetric in field and resilient to field strength, before decreasing as the critical field is approached. The authors present a Ginzburg-Landau two-band model for the zero-field SDE and speculate that helimagnetic order in Cd3As2 could explain the field-resilient behavior, while explicitly stating that the exact origin is not known.","tokens_in":10328,"tokens_out":6614,"duration_ms":62020,"significance":"If the field-independence claim holds, the result is of practical interest because superconducting diodes that are insensitive to the polarity and magnitude of stray magnetic fields would be more robust for circuit applications. The paper has clear strengths: the current-voltage measurements are standard, the zero-field SDE is consistent with prior work, the MBE film quality is benchmarked against an exfoliated device, and the authors are transparent that the field-resilience mechanism is a speculation. The zero-field SDE in MBE-grown Cd3As2 SQUIDs is a useful data point. However, the central field-independence claim currently rests on a single device, a fixed voltage threshold, and no quantified uncertainty, so the significance is contingent on additional evidence.","major_comments":[{"comment":"The central claim that ΔI_c is independent of B between −10 and 10 mT is based on switching currents defined by a fixed 20 μV voltage threshold. If the width or shape of the resistive transition changes with magnetic field, or differs between the two sweep directions, the current read at a fixed voltage can shift even when the true switching current is constant, or vice versa. The manuscript provides no test of this possibility, such as extracting switching currents with multiple threshold voltages, fitting the switching branch, or showing full IV traces at intermediate fields. This must be addressed before the field-independence claim can be accepted.","section":"Section III, Fig. 4d"},{"comment":"The robust field-dependence claim is made with data from a single SQUID. The text states that two SQUIDs showed zero-field SDE but that results are presented from one device. In addition, no error bars or scatter estimates are shown for I_c±(B) or ΔI_c(B), and the repeated B = 0 measurements mentioned in the text are not displayed. Without a second device or quantified reproducibility, the word \"robust\" is not established.","section":"Section II, Fig. 4c,d"},{"comment":"The paper motivates the SDE through the diode efficiency η = (I_c+ − I_c−)/(I_c+ + I_c−), but the central figure plots only ΔI_c. Since both I_c+ and I_c− decrease with increasing |B| (Fig. 4c), a constant ΔI_c implies a B-dependent η. The authors should either plot η(B) to demonstrate symmetric-in-field diode efficiency, or explicitly and consistently limit the claim to the current difference.","section":"Introduction and Section III, Fig. 4c,d"}],"minor_comments":[{"comment":"The figure captions contain the typo \"depedence\" instead of \"dependence.\"","section":"Figure captions, Figs. 3 and 4"},{"comment":"The SQUID \"dimension\" of ~1.3 × 1.0 μm² is ambiguous; specify whether this is the loop area or the overall footprint.","section":"Section II, Fig. 1b"},{"comment":"The sentence \"the difference in critical currents is about as same as that at B = 0 mT\" should be rephrased, for example as \"approximately equal to that at B = 0 mT.\"","section":"Section III, Fig. 4a"},{"comment":"The resistance overshoot discussion is qualitative and not used in the central SDE claim; it could be shortened or moved to supplementary material.","section":"Section III, Fig. 1d"},{"comment":"The notation in the Ginzburg-Landau free energy is partially garbled; for instance, $F_i = \\Gamma \\Delta_i^2$ appears twice with the same symbol, and the definitions leading to Eq. (3) should be made unambiguous.","section":"Section IV, Eq. (1)-(3)"},{"comment":"The repeated B = 0 measurements are mentioned in the text but not shown; including them in Fig. 4c or as error bars in Fig. 4d would strengthen the reproducibility claim.","section":"Section III, Fig. 4c,d"}],"recommendation":"major_revision","confidential_remarks":"The paper's central claim—field-independent ΔI_c in an asymmetric Cd3As2 SQUID—is interesting but currently supported by only one device and a single voltage-threshold definition. The threshold-artifact concern is substantive and should be the focus of the revision. If the authors can demonstrate that the plateau survives multiple threshold definitions and provide data from a second device with quantified scatter, the paper would be suitable for publication. The theoretical speculation about helimagnetism is clearly labeled and does not, by itself, affect the experimental claim."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The genuinely new thing here is the combination: zero-field SDE plus a field-symmetric switching-current difference in MBE-grown Cd3As2 SQUIDs. That matters because it moves the effect from exfoliated flakes to a semiconductor-compatible platform, which is the right direction for applications. The zero-field part is consistent with the group's earlier work, and the symmetric-in-field part extends the multiferroic-JJ result to a different material and geometry. That is a legitimate incremental contribution.\n\nWhat the paper does well: the IV measurements are standard and believable, the zero-field SDE is reproduced, the reproducibility check at B = 0 before and after the field sweep is good practice, and the authors are explicit that the helimagnetic explanation is speculation. They don't oversell the mechanism. The device-quality comparison with exfoliated Cd3As2 is also useful.\n\nThe soft spots are real but not fatal. The field-independence claim rests on one SQUID, with no error bars on the field-dependent data and no repeated field sweeps. The 20 µV threshold is fixed, and the stress-test concern about threshold artifacts is legitimate: if the switching transitions broaden differently with field, a fixed voltage cut could produce a spuriously flat ΔI_c(B). But the specific example in the note—the drop to 0.9 µA at −15 mT—lies outside the claimed ±10 mT plateau, so it doesn't by itself break the central claim. The real issue is internal to the plateau: we don't see the transition shapes at each field, and one device gives no handle on device-to-device variability. The Ginzburg-Landau model in Eq. (3) is borrowed, not fitted, and the authors admit it doesn't address field resilience. Citation practice looks clean; Ref. [18] and Ref. [10] are the obvious prior results and are cited as such.\n\nOverall, this is a plausible, honest experimental report with a central claim that is not yet nailed down. It deserves a serious referee, not a desk reject. The referee should ask for threshold-dependence analysis, repeated devices, and error bars. I'd send it to review.","headline":"Incremental but useful: MBE-grown Cd3As2 SQUIDs show a field-symmetric switching-current difference that is plausible but rests on one device and a fixed voltage threshold; worth refereeing with requested robustness checks.","tokens_in":10916,"tokens_out":2245,"would_cite":true,"duration_ms":22825,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["74.50.+r"],"model":"deepseek-v4-flash","headline":"Asymmetric Dirac-semimetal SQUIDs show a superconducting diode whose switching-current difference stays nearly constant from -10 to +10 mT.","keywords":["superconducting diode effect","zero-field diode effect","asymmetric SQUID","Dirac semimetal","Cd3As2","molecular beam epitaxy","helical spin texture","magnetic-field-independent diode"],"falsifier":"Repeat the field sweep while extracting switching currents from several voltage thresholds (for example 5, 20 and 50 µV) or from the peak of $\\mathrm{d}V/\\mathrm{d}I$; if the $I_c^- - I_c^+$ plateau changes with threshold or acquires a slope versus field, the field-independence claim fails.","tokens_in":9950,"feed_emoji":"🧲","tokens_out":8823,"duration_ms":80146,"temperature":0.7,"pith_summary":"The paper reports a superconducting diode effect in asymmetric SQUIDs patterned on MBE-grown Cd3As2 thin films, and claims that the diode's size is independent of the strength and polarity of an out-of-plane magnetic field from -10 to +10 mT. At zero field the positive and negative switching currents differ by about 1.5 µA, and this difference stays nearly constant across the field range rather than changing sign as in conventional field-tuned diodes. If correct, this means a single compact diode could rectify signals even when stray magnetic fields in a circuit reverse direction, removing a practical obstacle to superconducting electronics. The authors tie the zero-field effect to surface-bulk coupling in the Dirac semimetal acting through the SQUID's arm asymmetry, and speculate that a helical magnetic texture may explain the field robustness.","feed_headline":"Asymmetric SQUID diode holds steady in magnetic fields up to 10 mT","feed_subtitle":"Difference in switching currents stays near 1.5 µA as the out-of-plane field sweeps from -10 to +10 mT.","key_machinery":"Two ingredients carry the argument. The first is the asymmetric SQUID geometry: two aluminum/Cd3As2/aluminum Josephson junctions of different widths (about 230 nm and 500 nm) on the same epitaxial film, connected in a loop. The second is a two-band Ginzburg-Landau free energy in which each junction has two superconducting order parameters; a change of variables produces a current-phase relationship $I_s(\\theta,\\psi)$ whose equilibrium phase $\\psi$ breaks time-reversal symmetry. In the SQUID, fluxoid quantization relates the two arm phases, and the antiferromagnetic-like ground state $\\psi_a = -\\psi_b$ suppresses the zero-field diode when the arms are symmetric. The paper uses this model to explain the zero-field SDE in the asymmetric device, while explicitly leaving the magnetic-field resilience unexplained beyond a speculation about helimagnetic order and helical spin texture.","core_discovery":"The central claim is that an asymmetric SQUID made from an MBE-grown Cd3As2 thin film acts as a superconducting diode at zero magnetic field, with positive and negative switching currents differing by roughly 1.5 µA, and that this difference $I_c^- - I_c^+$ remains nearly constant for out-of-plane magnetic fields between -10 and +10 mT. At -15 mT the difference is still 0.9 µA, and it falls to zero only where the field destroys the supercurrent. The authors describe this as a robust, symmetric-in-field diode effect, distinct from field-induced diode effects whose efficiency changes sign when the field reverses.","pith_inferences":["A direct check of the threshold concern would be to repeat the field dependence with several voltage thresholds; if the plateau is threshold-dependent, the claimed field-independence is a measurement artifact.","Comparing symmetric and asymmetric SQUID arms on the same MBE film at finite field would isolate whether the flat $I_c^- - I_c^+$ response comes from the arm asymmetry or from the Cd3As2 itself.","The proposed helical-spin explanation could be tested by local magnetometry or by replacing Cd3As2 with a non-magnetic Dirac semimetal; if the symmetric-in-field diode persists without any magnetic order, the helimagnetic speculation would be unnecessary."],"forward_implications":["Stray-field-tolerant rectification becomes feasible: a diode with this property would keep its rectification direction and strength while random circuit fields around ±10 mT fluctuate in sign.","MBE growth plus direct aluminum deposition means the device is compatible with semiconductor-style fabrication, unlike the exfoliated multiferroic junctions that previously showed symmetric-in-field diode effects.","Because zero-field SDE appears in both MBE-grown and exfoliated Cd3As2 devices, the effect is intrinsic to this material rather than a growth artifact.","The diode vanishes well below the superconducting transition temperature, so its operation window is restricted to low temperatures, at least in this device."],"supporting_citations":[{"why":"shows zero-field SDE in an exfoliated Cd3As2 asymmetric SQUID and supplies the surface-bulk coupling mechanism the present paper extends to MBE-grown films.","marker":"[18]"},{"why":"gives the two-band Ginzburg-Landau model and current-phase relation used to explain why symmetric arms suppress the zero-field diode while asymmetric arms allow it.","marker":"[33]"},{"why":"demonstrates a symmetric-in-field supercurrent diode in multiferroic junctions, the behavior this paper aims to reproduce in a semiconductor-compatible device.","marker":"[10]"},{"why":"describes the MBE growth of Cd3As2 heterostructures that yields the high-quality films used here.","marker":"[16]"},{"why":"predicts helical spin order in Dirac/Weyl semimetals, the speculative origin proposed for the field-resilient SDE.","marker":"[24]"},{"why":"shows pi and 4pi Josephson effects in Cd3As2 and underlies the statement that a TRS-breaking equilibrium phase alone does not produce a zero-field SDE.","marker":"[32]"}],"fun_headline_variants":["Field-immune superconducting diode in asymmetric SQUID","Superconducting diode symmetric under field reversal up to 10 mT","SQUID diode effect constant for fields up to 10 mT","Dirac semimetal SQUID shows field-symmetric diode effect"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The claim presupposes that the 20-microvolt voltage threshold used to mark each switching current captures the true transition equally for both current directions at every field; if the transitions are rounded, the flat 1.5-microamp difference could be a measurement artifact.","fun_headline_variants_meta":{"raw":{"variants":["Field-immune superconducting diode in asymmetric SQUID","Superconducting diode symmetric under field reversal up to 10 mT","SQUID diode effect constant for fields up to 10 mT","Dirac semimetal SQUID shows field-symmetric diode effect"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000964,"raw_usage":{"total_tokens":4058,"prompt_tokens":851,"completion_tokens":3207,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":467,"completion_tokens_details":{"reasoning_tokens":3146}},"tokens_in":467,"tokens_out":3207,"duration_ms":22326,"temperature":1.0,"reasoning_tokens":3146,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T13:21:05.720529+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Repeat the field sweep while extracting switching currents from several voltage thresholds (for example 5, 20 and 50 µV) or from the peak of $\\mathrm{d}V/\\mathrm{d}I$; if the $I_c^- - I_c^+$ plateau changes with threshold or acquires a slope versus field, the field-independence claim fails.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"shows zero-field SDE in an exfoliated Cd3As2 asymmetric SQUID and supplies the surface-bulk coupling mechanism the present paper extends to MBE-grown films."},{"cited_title":"Cuozzo, W","cited_arxiv_id":null,"evidence_quote":"gives the two-band Ginzburg-Landau model and current-phase relation used to explain why symmetric arms suppress the zero-field diode while asymmetric arms allow it."},{"cited_title":"Cuozzo, Anand Johnson Bokka, Gang Qiu, Christopher Eckberg, Yanfeng Lyu, Shuyuan Huyan, Ching-Wu Chu, Kenji Watanabe, Takashi Taniguchi, Kang L","cited_arxiv_id":null,"evidence_quote":"demonstrates a symmetric-in-field supercurrent diode in multiferroic junctions, the behavior this paper aims to reproduce in a semiconductor-compatible device."},{"cited_title":"Rice, C.H","cited_arxiv_id":null,"evidence_quote":"describes the MBE growth of Cd3As2 heterostructures that yields the high-quality films used here."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"predicts helical spin order in Dirac/Weyl semimetals, the speculative origin proposed for the field-resilient SDE."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"shows pi and 4pi Josephson effects in Cd3As2 and underlies the statement that a TRS-breaking equilibrium phase alone does not produce a zero-field SDE."}],"review_version":1}