{"id":"eacfd657-5352-4a79-a59b-adaf61bea590","arxiv_id":"1908.07163","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"A ZnCrTe/(Bi,Sb)2Te3/ZnCrTe sandwich heterostructure shows quantized Hall resistance h/e2 and vanishing longitudinal resistance below 0.1 K, demonstrating QAHE driven by magnetic proximity.","lead":"This paper shows a quantum effect called the quantum anomalous Hall effect, where electricity flows without loss along the edge of a material, in a layered sandwich of a topological insulator and a magnetic insulator. The result matters because it demonstrates that magnetic proximity, not magnetic doping, can drive the effect, opening a cleaner way to build topological devices.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Cr diffusion into the 8-nm BST channel is the unresolved pivot: if SM Section S3 does not quantitatively rule out doping-level Cr, the claimed proximity-driven QAHE is not established.","rationale":"The reader's verdict is CONDITIONAL with moderate confidence, and my stress-test does not move that verdict. The main text contains multiple internally consistent pieces of evidence for proximity: tan(theta_H) peaks near y=0.60 at the charge neutrality point, the Cr-composition dependence is non-monotonic with a maximum at x=0.17, and the AHE hysteresis tracks the ZCT magnetization. These observations support the proximity interpretation but do not uniquely establish it. The QAHE plateau itself is phenomenological: chiral edge conduction will appear whether the exchange gap originates from interface proximity or from Cr impurities inside the BST layer. The only argument separating these two mechanisms is the Cr-diffusion analysis deferred to supplementary Section S3, which is quoted as load-bearing in the main text but is not available for verification here. Because the paper itself makes this the decisive premise, the appropriate verdict remains CONDITIONAL pending inspection of S3. If S3 contains quantitative depth profiling showing Cr in the BST below the doping threshold for QAHE, the concern is resolved and the central claim is well supported; if it is qualitative or lacks sensitivity, the claim remains unverified. I found no independent formal inconsistency in the main-text argument, so no stronger objection is warranted.","tokens_in":7431,"tokens_out":5915,"duration_ms":66228,"concrete_test":"Perform an independent high-resolution STEM-EDS or atom-probe composition profile across the ZCT/BST/ZCT interface on the quantized x=0.17, y=0.60 sample, with sub-nanometer point spacing through the 8-nm BST layer and a Cr detection limit below 1 at%. Compare the integrated Cr content in the BST channel with that of a Cr-doped (Bi,Sb)2Te3 reference film known to exhibit QAHE. If the BST-channel Cr concentration is at or above the reference doping level, the proximity claim is falsified; if it is at least an order of magnitude lower, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is that the h/e2 plateau in ZCT(10 nm)/BST(8 nm)/ZCT(10 nm) with x=0.17, y=0.60 arises from magnetic proximity exchange rather than from the known Cr-doped QAHE in the BST layer. The load-bearing premise is therefore that the 8-nm BST channel contains a negligible Cr concentration. The main text offers only the statement that 'Diffusion of Cr into the BST layer is fairly small or at most not large enough to cause the Cr-doping induced QAHE effect as observed in an optimally Cr-doped BST film (see discussions in Section S 3 in SM),' with the supporting analysis entirely in the unprovided supplementary Section S3. The agreement between the anomalous Hall coercivity and the ZCT magnetization (Fig. 1e) is suggestive but cannot by itself separate interface proximity from a magnetically ordered, dilute Cr-doped BST layer: exchange coupling to ZCT could align a small diffused Cr moment, and the difference between TC(M)=60 K and TC*(AHE)=40 K leaves room for a second magnetic constituent. If S3 lacks quantitative depth-resolved Cr profiling through the BST with sensitivity below the QAHE doping threshold, the central mechanism is not established. This is the single condition on which the proximity interpretation stands or falls.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the observation of the quantum anomalous Hall effect (QAHE) in a Zn_{1-x}Cr_xTe/(Bi_{1-y}Sb_y)_2Te_3/Zn_{1-x}Cr_xTe sandwich heterostructure grown by molecular-beam epitaxy. For x = 0.17 and y = 0.60, the Hall resistance Ryx reaches h/e^2 and the longitudinal resistance Rxx becomes small below 0.1 K under B = 2 T, with the anomalous Hall response tracking the magnetization of the ZCT layers. The authors attribute the effect to magnetic proximity coupling rather than to Cr doping of the BST channel, and they support this by the systematic dependence of the anomalous Hall signal on Sb composition y (Fermi-level tuning) and Cr composition x (FMI transition temperature). The decisive separation from the known Cr-doped QAHE mechanism is deferred to supplementary Section S3.","tokens_in":7674,"tokens_out":5604,"duration_ms":59115,"significance":"Proximity-induced QAHE in an all-telluride heterostructure would be an important advance over magnetically doped topological insulators, potentially combining dissipationless chiral edge transport with less disorder and a wider choice of partner materials. The transport data are internally consistent: the observation of Ryx = h/e^2 with small Rxx, the carrier-type reversal across the charge neutral point, and the correlation of the AHE with the FMI magnetization are all suggestive. The paper contains no free parameters or fitted predictions, and the design rationale based on shared telluride chemistry is clearly stated. However, the central exclusion of Cr-diffusion-induced QAHE rests entirely on unprovided supplementary material, and the comparison of magnetic transition temperatures is less convincing than claimed. These issues must be resolved before the proximity mechanism can be regarded as established.","major_comments":[{"comment":"The sentence 'Diffusion of Cr into the BST layer is fairly small or at most not large enough to cause the Cr-doping induced QAHE effect as observed in an optimally Cr-doped BST film (see discussions in Section S3 in SM)' is the sole basis for excluding the established Cr-doped QAHE mechanism. Since the BST channel is only 8 nm thick and Cr-doped (Bi,Sb)2Te3 is known to exhibit QAHE at low doping, the proximity interpretation stands or falls on this exclusion. The supporting analysis is entirely in the supplementary material, which was not provided for review; an assertion in the main text is not sufficient. Please include the quantitative Cr depth profile through the BST layer with detection sensitivity below the threshold doping for QAHE, or provide a control sample (for example, BST sandwiched between undoped ZnTe layers) that shows no QAHE. Until this is provided, the central mechanism is not established.","section":"Main text, paragraph following Fig. 1(c); SM Section S3"},{"comment":"The text states that the ferromagnetic transition temperatures evaluated from M and from Ryx are 60 K and 40 K, respectively, and that these are 'close with each other', using this agreement as evidence for proximity coupling. A 20 K difference is not negligible relative to the absolute temperatures, and it is in the direction expected if a dilute Cr-doped BST layer with its own magnetic ordering contributes to the anomalous Hall response. Please state the definitions and fitting procedures for both transition temperatures, report their uncertainties, and explicitly assess whether a two-magnetic-constituent scenario can be excluded. This is particularly important because the AHE and the magnetization need not share the same transition temperature in a proximity-coupled system if the induced gap forms only near the interface.","section":"Fig. 1(e) and the surrounding text"}],"minor_comments":[{"comment":"Please report the numerical residual value of Rxx at the lowest temperature and specify whether the quantized plateau persists at zero magnetic field after saturation of the ZCT magnetization. The text says only that 'Rxx approaches zero', and a QAHE claim normally requires explicit zero-field or remanent-state evidence as well as a quantitative upper bound on the longitudinal resistivity.","section":"Fig. 2(a) and Fig. 2(b)"},{"comment":"The text reads 'with a value of around 104 Ω', but the exponent appears to be missing or garbled; please ensure the correct formatting of the sheet resistance value.","section":"Paragraph after Fig. 1(d)"},{"comment":"The optimum Sb composition y ≈ 0.60 is stated to be slightly shifted from y = 0.85-0.95 in single-layer BST, but the origin of this shift is not discussed. A brief explanation, for example in terms of band bending or interface charge transfer at the ZCT/BST interfaces, would strengthen the Fermi-level-tuning argument.","section":"Discussion of y dependence after Fig. 3"},{"comment":"The caption of Fig. 4(b) should state explicitly that the black symbols denote TC* estimated from Arrott-plot analysis of the anomalous Hall resistance, since that information currently appears only in the main text and in the supplementary section reference.","section":"Fig. 4(b) caption and Section S5"},{"comment":"The phrase 'quantization Hall resistance' in the first paragraph should read 'quantized Hall resistance'. The reviewer recommends a careful proofread for similar typographical and formatting issues.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":"The decisive evidence for the proximity mechanism is in SM Section S3, which was not part of the reviewed package. If that section contains quantitative Cr depth profiling and a control experiment, the paper may be suitable after revision. Please ensure the supplementary file is accessible to reviewers and that the two-magnetic-constituent issue raised in the report is explicitly addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague—this is the first credible claim of a proximity-driven QAHE I've seen, and if it holds up it's a real milestone. The authors sandwich a nonmagnetic (Bi,Sb)2Te3 channel between ferromagnetic (Zn,Cr)Te insulators and see the full QAHE signature: Ryx quantized at h/e2, Rxx collapsing below 0.1 K, and the anomalous Hall response tracking the ZCT magnetization. The all-telluride design is a sensible way to get strong exchange coupling, and the composition dependence (Sb tuning, Cr dependence) gives the transport data internal consistency. I'd credit the experimental work: the transport looks clean, and the comparison of the AHE coercivity with M in the ZCT is a nice touch.\n\nThe soft spot is exactly the one the stress-test flags. The claim is that Cr does not diffuse into the 8-nm BST channel, but the main text only says it is 'fairly small or at most not large enough', with the evidence deferred to Section S3 of the supplementary. For a reader without that supplement, the known Cr-doped QAHE remains a live alternative explanation. There is no nonmagnetic control sample, and the slight mismatch between TC from magnetization (60 K) and from AHE (40 K) leaves room for a second magnetic constituent. That doesn't kill the paper, but it makes the proximity interpretation conditional on evidence we don't see.\n\nIf Section S3 contains quantitative depth-resolved Cr profiling through the BST with sensitivity below the QAHE doping threshold, then the mechanism is likely established and the paper is a genuine first. If it only has qualitative EDS or a hand-waving argument, the central claim is not yet supported. I'd want a referee to check that supplement carefully.\n\nThe citation pattern looks fine; the prior FMI/TI works cited (EuS, YIG, TIG) indeed only showed small anomalous Hall angles, so the novelty claim is not oversold. The authors are also honest about the spatial inhomogeneity and the role of Cr in the FMI.\n\nRecommendation: this deserves serious peer review, not desk rejection. The transport data are strong enough to warrant a careful referee, and the key question is narrowly focused on the supplementary material. If the diffusion evidence holds, accept; if not, require a nonmagnetic control or direct Cr quantification before publication.","headline":"A first proximity-effect QAHE candidate with solid transport data, but the mechanism hinges on supplementary Cr-diffusion evidence the main text doesn't include.","tokens_in":8221,"tokens_out":3213,"would_cite":true,"duration_ms":31125,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["73.43.Cd","75.70.Cn","73.20.At"],"model":"deepseek-v4-flash","headline":"The paper reports the quantum anomalous Hall effect in a ZnCrTe/(Bi,Sb)2Te3/ZnCrTe sandwich, reaching h/e^2 with vanishing longitudinal resistance below 0.1 K through magnetic proximity rather than by doping the topological insulator…","keywords":["quantum anomalous Hall effect","magnetic proximity effect","topological insulator","ferromagnetic insulator","all-telluride heterostructure","ZnCrTe","BiSbTe","chiral edge states"],"falsifier":"Measure the chromium concentration profile across the 8-nm BST layer after growth, using atom-probe tomography or high-resolution energy-dispersive X-ray spectroscopy. If the Cr content in the channel approaches the level known to produce the QAHE in Cr-doped BST, the proximity interpretation is not needed; in that case, a control sample with an inert diffusion barrier at the ZCT/BST interfaces should lose the quantized Hall response, whereas a true proximity effect would not.","tokens_in":7259,"feed_emoji":"🧲","tokens_out":3412,"duration_ms":35500,"temperature":0.7,"pith_summary":"The paper reports the quantum anomalous Hall effect in a sandwich of two ferromagnetic insulator layers, (Zn,Cr)Te, around a non-magnetic topological insulator, (Bi,Sb)2Te3, without magnetically doping the topological insulator itself. For the optimized composition x = 0.17 and y = 0.60, the Hall resistance reaches h/$e^{2}$, about 25.8 kΩ, while the longitudinal resistance approaches zero below 0.1 K. The anomalous Hall response tracks the magnetization of the ferromagnetic layers, and the paper argues that the effect is driven by an exchange gap opened at the topological surface states through magnetic proximity coupling across the all-telluride interfaces. If this is right, it establishes proximity coupling as a workable route to the QAHE, an alternative to the doped systems that have dominated the field.","feed_headline":"All-telluride sandwich reaches quantized Hall resistance","feed_subtitle":"A (Zn,Cr)Te/(Bi,Sb)2Te3 sandwich hits h/e^2 below 0.1 K, opening a doping-free path to chiral-edge devices.","key_machinery":"The central object is the ferromagnetic-insulator/topological-insulator/ferromagnetic-insulator sandwich, specifically Zn1-xCrxTe/(Bi1-ySby)2Te3/Zn1-xCrxTe, where the common tellurium sublattice lets the topological surface states, originating from Te 5p orbitals, extend into the ferromagnet and hybridize with Cr 3d states. That p–d hybridization is the mechanism that opens the exchange gap at the surface states, and the Sb composition y tunes the Fermi level into that gap. The anomalous Hall angle, tanθH = σxy/σxx, is used as the measure of how close the system is to the quantized state, reaching above 2.5 at 0.5 K for the optimal composition.","core_discovery":"The central claim is that the quantum anomalous Hall effect can be driven purely by magnetic proximity coupling in an all-telluride heterostructure. In a ZCT/BST/ZCT sandwich with x = 0.17 and y = 0.60, the Hall resistance Ryx saturates at ±h/e2 and the sheet resistance Rxx falls toward zero below 0.1 K, with the anomalous Hall response faithfully following the magnetization of the (Zn,Cr)Te ferromagnetic insulator layers. The paper attributes the effect to a sizable exchange gap at the topological surface states, formed by strong hybridization between the Te 5p states of the topological insulator and the Cr 3d states of the ferromagnet, with the Fermi level tuned into the gap by the Sb composition y = 0.60. This is presented as distinct from the previously known QAHE in Cr-doped (Bi,Sb)2Te3, where the magnetic order and the channel doping occur in the same material.","pith_inferences":["If true, the proximity route decouples the magnetic order from the transport channel, which may allow higher-quality channels than doped QAHE systems while still achieving quantization.","A direct measurement of the chromium profile across the BST layer would settle whether this is genuinely a proximity effect; the paper defers this evidence to supplementary material, making it the key point to check.","The same all-telluride interface strategy could be tried with other telluride-based ferromagnets or with superconducting tellurides in place of one FMI layer, potentially bringing chiral Majorana modes into reach without magnetic doping."],"forward_implications":["The QAHE can be realized without magnetic doping of the topological insulator, avoiding the disorder introduced by dopant atoms in the channel.","The anomalous Hall response tracks the magnetization of the insulating ferromagnet, meaning the chiral edge current can be controlled by the magnetic state of the adjacent FMI layers rather than by the bulk channel.","A ferromagnetic insulator with a higher Curie temperature, for example donor-doped (Zn,Cr)Te, could raise the temperature at which the QAHE is observable.","The all-telluride design principle should extend to other telluride families, potentially combining topological surface states with ferroelectric or superconducting telluride layers in the same heterostructure.","The observation that the optimum Sb composition is shifted from the single-layer BST value indicates that the interface environment modifies the surface-state dispersion, which must be accounted for in future device design."],"supporting_citations":[{"why":"First demonstration of the QAHE in Cr-doped (Bi,Sb)2Te3; defines the target phenomenon and the doping route this work seeks to replace.","marker":"[4]"},{"why":"Theoretical prediction that a sizable exchange gap in a TI surface leads to the QAHE; supplies the mechanism being tested.","marker":"[3]"},{"why":"Earlier FMI/TI proximity experiment with EuS that showed exchange-driven AHE; the approach this work extends to full quantization.","marker":"[12]"},{"why":"Shows that the Fermi energy of (Bi,Sb)2Te3 can be tuned by Sb composition; basis for choosing y = 0.60.","marker":"[21]"},{"why":"Demonstrates surface-dominated transport in BST such as integer QHE; justifies BST as the channel material.","marker":"[22]"},{"why":"Identifies ZnCrTe as a ferromagnetic insulator with perpendicular magnetization; the FMI layer used here.","marker":"[24]"},{"why":"Reports the QAHE in Cr-doped BST below 0.1 K; the comparison benchmark for the transport signatures in the sandwich.","marker":"[25]"}],"fun_headline_variants":["Magnetic proximity drives QAHE in all-telluride stack","Proximity-induced QAHE in telluride heterostructure","Sandwich all-telluride layers hit quantized Hall resistance","No magnetic doping: proximity effect yields QAHE"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The result stands on the claim that chromium from the (Zn,Cr)Te layers does not diffuse into the (Bi,Sb)2Te3 channel in large enough amounts to dope it; if that premise fails, the observed quantization is the already-known Cr-doped QAHE rather than a proximity effect.","fun_headline_variants_meta":{"raw":{"variants":["Magnetic proximity drives QAHE in all-telluride stack","Proximity-induced QAHE in telluride heterostructure","Sandwich all-telluride layers hit quantized Hall resistance","No magnetic doping: proximity effect yields QAHE"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000868,"raw_usage":{"total_tokens":3781,"prompt_tokens":984,"completion_tokens":2797,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":600,"completion_tokens_details":{"reasoning_tokens":2726}},"tokens_in":600,"tokens_out":2797,"duration_ms":19985,"temperature":1.0,"reasoning_tokens":2726,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:24:29.505337+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the chromium concentration profile across the 8-nm BST layer after growth, using atom-probe tomography or high-resolution energy-dispersive X-ray spectroscopy. If the Cr content in the channel approaches the level known to produce the QAHE in Cr-doped BST, the proximity interpretation is not needed; in that case, a control sample with an inert diffusion barrier at the ZCT/BST interfaces should lose the quantized Hall response, whereas a true proximity effect would not.","supporting_citations":[{"cited_title":"Chang, J","cited_arxiv_id":null,"evidence_quote":"First demonstration of the QAHE in Cr-doped (Bi,Sb)2Te3; defines the target phenomenon and the doping route this work seeks to replace."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Theoretical prediction that a sizable exchange gap in a TI surface leads to the QAHE; supplies the mechanism being tested."},{"cited_title":"Katmis, V","cited_arxiv_id":null,"evidence_quote":"Earlier FMI/TI proximity experiment with EuS that showed exchange-driven AHE; the approach this work extends to full quantization."},{"cited_title":"Zhang, C.-Z","cited_arxiv_id":null,"evidence_quote":"Shows that the Fermi energy of (Bi,Sb)2Te3 can be tuned by Sb composition; basis for choosing y = 0.60."},{"cited_title":"Yoshimi, A","cited_arxiv_id":null,"evidence_quote":"Demonstrates surface-dominated transport in BST such as integer QHE; justifies BST as the channel material."},{"cited_title":"Saito, W","cited_arxiv_id":null,"evidence_quote":"Identifies ZnCrTe as a ferromagnetic insulator with perpendicular magnetization; the FMI layer used here."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports the QAHE in Cr-doped BST below 0.1 K; the comparison benchmark for the transport signatures in the sandwich."}],"review_version":1}