{"id":"57d660f7-062e-460e-b2d8-46f576e4b38d","arxiv_id":"1908.07096","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"InAs/EuS grown coherently; Fermi level sits in InAs conduction band and EuS gap; magnetic moments stay in EuS with a suppressed moment at the interface and no detectable induced InAs moment.","lead":"This paper grows and characterizes a clean, atomically matched interface between the semiconductor InAs and the magnetic insulator EuS, showing that the magnetic order stays mostly in the EuS and barely leaks into InAs. It matters because such interfaces are candidates for quantum and spintronic devices that aim to work without external magnetic fields.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed 2.7-fold interfacial Eu moment suppression rests on a single RXRR fit with EuO-derived scattering factors, no birefringence, and a 1.4 Å interfacial layer comparable to the fitted roughness; an alternative-model refit is needed.","rationale":"The reader's weakest assumption is the same one I would identify: the RXRR-derived magnetic depth profile is the load-bearing part of the magnetic-structure claim. I agree with the CONDITIONAL verdict. The paper's own supplementary text flags the three modeling choices that make the suppression factor provisional: EuO-based scattering factors, neglected birefringence, and a simplified layer stack with a 1.4 Å interfacial layer. The PNR measurement, while a useful independent check of the localization of magnetization, cannot resolve the claimed interfacial suppression, so the suppression rests entirely on one fit. This is not a reason to reject the paper: the epitaxial structure, band alignment, and absence of a detected InAs moment are supported by separate measurements and by DFT, and the authors are transparent about the limitations. But the specific quantitative claim of a 2.7-fold reduced Eu moment should be treated as model-dependent until an alternative-model refit or direct measurement of the interfacial spectral function rules out an artifact. Thus the verdict remains CONDITIONAL, and the reader's verdict is unchanged.","tokens_in":17680,"tokens_out":8237,"duration_ms":91691,"concrete_test":"Reanalyze the published RXRR data of Fig. S7 with an alternative model in which the 1.4 Å interfacial layer is removed and the InAs/EuS interface roughness and/or a graded magnetic profile are free parameters, using the same Dyna software and the same EuO-derived scattering factors. Then run a Markov-chain Monte Carlo or bootstrap to estimate the 95% confidence interval on the interfacial moment-reduction factor. If the model without the 1.4 Å layer fits within the reported statistical uncertainty, or if the confidence interval on the reduction factor includes 1.0, the claimed 2.7-fold suppression is not uniquely established by the current analysis.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The most load-bearing part of the central claim is the depth-resolved magnetic profile, specifically the suppression of the Eu moment in the EuS layer nearest InAs. The only quantitative evidence for that suppression is the RXRR analysis in Supplementary Section 3 and Table S2, which yields a 1.4 Å interfacial EuS layer with a magnetic moment reduced by a factor of 2.7 relative to bulk. This result is not independently confirmed by PNR: the PNR data in Table S1 and Fig. S5 only identify the magnetic thickness with the EuS layer, and the main text states that at the ~2 Å resolution with 3 Å roughness, one cannot conclude whether there is weak magnetization in InAs. The RXRR analysis itself relies on three model choices explicitly acknowledged in the supplement: (1) EuS resonant scattering factors taken from EuO literature via Kramers-Kronig rather than measured on this film; (2) neglect of birefringence; and (3) a deliberately simple layer structure. The fitted interfacial layer is 1.4 Å thick, which is sub-monolayer and comparable to the fitted InAs/EuS roughness of 1.9 Å, so the reduced moment could be absorbing an artifact of the structural model—roughness, intermixing with modified scattering factors, or a changed Eu valence/lineshape at the interface—rather than representing a real 2.7-fold suppression. If the suppression is not real, the broader picture remains partially supported, but the specific interfacial-suppression claim is not established.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports the growth and characterization of epitaxial InAs/EuS heterostructures, combining aberration-corrected STEM, SX-ARPES, PNR, XMCD, RXRR, and DFT calculations. The central claims are that the interface is coherent and dislocation-free, that the Fermi level lies near the InAs conduction band and inside the EuS gap, that the ferromagnetic moment is largely confined to EuS with a suppressed Eu moment in the interfacial EuS layer, and that no induced moment in InAs is detected, while DFT suggests a weak exchange field in the adjacent InAs layers.","tokens_in":18155,"tokens_out":4280,"duration_ms":40882,"significance":"If the results hold, this work provides a carefully characterized semiconductor/ferromagnetic-insulator platform relevant for topological superconductivity and spintronics. The study is valuable for its multi-technique approach and for explicitly reporting detection limits in the magnetic measurements. The atomic-resolution STEM and band-alignment measurements are strong assets, and the transparent discussion of the RXRR model assumptions is commendable; at the same time, the quantitative interfacial moment suppression is the least robust part of the central claim, so the paper merits revision rather than acceptance in its present form.","major_comments":[{"comment":"The claimed 2.7-fold suppression of the interfacial Eu moment is extracted from a single RXRR fit using EuO-derived scattering factors, neglecting birefringence, and assuming a simplified layered model, as acknowledged in the supplement. The fitted interfacial layer thickness is 1.4 Å, while the interface roughness at the InAs/EuS boundary is fitted to 1.9 Å, so the reduced moment could be an artifact of the structural model rather than a physical suppression. Please provide an uncertainty estimate for the suppression factor and a robustness check, for example by refitting with alternative scattering factors (ideally from measured M5-edge XANES/XMCD on this film) and with a graded-interface or intermixed-layer model. Without such an analysis, the quantitative suppression claim in the abstract and conclusions is not established.","section":"Supplementary Section 3, Table S2"},{"comment":"The DFT calculation in Figure 4 reports spin moments of about 0.08 μB on In and 0.04 μB on As, but the abstract and conclusions refer to 'a small exchange field in the InAs layer' without providing a value. Since the exchange field is the physically relevant quantity for proximity effects, the authors should either quantify the exchange splitting (in meV) from their calculation, or rephrase the claim to state that only a weak spin polarization is found. As written, the step from computed local moments to an exchange field is not justified.","section":"Section 3, 'Distribution of magnetic moments', and Conclusions"}],"minor_comments":[{"comment":"The statement 'The order of the plane rotational symmetry (PRS) of EuS on InAs is 2 and its bi-crystal variant is 1 (see ref. 2 for analysis)' cites Ref. 2, which is a nanowire epitaxy paper; this reference does not appear to support the PRS analysis and should be replaced or clarified.","section":"Section 3, 'Epitaxy of EuS on InAs'"},{"comment":"The phrase 'we ak magnetization' contains a typo; it should read 'weak magnetization'.","section":"Conclusions"},{"comment":"The MMS values and the interfacial layer thickness are reported without uncertainties; please add error bars or state explicitly that these are best-fit values without quoted confidence intervals.","section":"Supplementary Table S2"},{"comment":"The main text does not state that the RXRR measurements were performed on a sample with an As capping layer (20 nm As), whereas the PNR sample used AlOx; please state the sample structure explicitly when comparing the magnetic depth profiles, since the capping layer could influence the magnetic structure.","section":"Main text, 'Distribution of magnetic moments'"},{"comment":"The reflectivity curves and asymmetry scans are shown without error bars; if the error bars are smaller than the symbols, please state this explicitly.","section":"Supplementary Figure S7"},{"comment":"The claim that the In XMCD signal is below the detection limit would be strengthened by a quantitative detection-limit estimate (e.g., from the noise level at the In L3 edge) rather than only a qualitative statement.","section":"Main text, XMCD discussion"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is a solid experimental study with strong complementary characterization, but the headline quantitative result—the 2.7-fold interfacial Eu moment suppression—relies on model assumptions that are acknowledged but not tested. I recommend requesting a robustness analysis of the RXRR fits before publication. The DFT exchange-field claim is also somewhat overstated relative to what is actually computed. These are fixable within the manuscript's scope, hence major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The thing to know about this paper is that it is a genuinely useful materials-science report with one number in it that I would not take to the bank. The platform claims — coherent epitaxy, clean band alignment, ferromagnetism confined to EuS — are well supported. The 2.7× suppression of the interfacial Eu moment is the weakest link, and the stress-test note is right to flag it.\n\nWhat's actually new: Goschew et al. already grew EuS on InAs, but that was a growth study. This paper delivers the first atomic-scale interface model (STEM/GPA with image simulation), the first band alignment measurement via SX-ARPES showing the Fermi level near the InAs conduction band and inside the EuS gap, and a depth-resolved magnetic profile combining PNR, XMCD, and RXRR. The DFT estimate of the weak exchange field is a separate independent calculation, so the claim structure is not circular.\n\nWhat's done well: The authors use multiple complementary techniques and are honest about detection limits. PNR and XMCD together establish that the ferromagnetic component is essentially all in EuS and that any induced InAs moment is below detection. They also report clean XANES/XMCD showing Eu2+ without Eu3+ contamination, a useful quality check. The structural characterization is careful, and the interface model is consistent with HAADF simulations.\n\nSoft spots: The interfacial moment suppression factor of 2.7 comes entirely from a single RXRR fit. The supplement acknowledges the scattering factors are taken from EuO via Kramers-Kronig, birefringence is neglected, and the structural model is deliberately simple. The fitted interfacial layer is 1.4 Å thick, comparable to the fitted roughness of 1.9 Å. That is a lot of model dependence for a quantitative claim. The qualitative conclusion that the moment is reduced near the interface is plausible and consistent with interfacial intermixing seen in STEM, but the exact factor is not established. The paper would be improved by a robustness test and by releasing the reflectivity data.\n\nWho this is for: Researchers building semiconductor/ferromagnetic-insulator hybrids for topological or spintronic applications, and MBE growers. This is a solid enabling materials result, not a breakthrough in physics.\n\nRecommendation: It deserves peer review — it's a careful multi-technique study with a plausible and useful message. I would ask the authors to refit the RXRR with alternative layer models and to provide error bars or a sensitivity analysis on the suppression factor before publication. If that came back and the suppression held, I'd be comfortable with the claim as stated.","headline":"A careful, useful materials study whose central claims hold, but whose headline interfacial moment-suppression number is model-dependent and should be treated with caution.","tokens_in":18616,"tokens_out":3090,"would_cite":true,"duration_ms":32296,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper establishes that a fully coherent, dislocation-free InAs/EuS interface can be grown with the Fermi level near the InAs conduction band and inside the EuS gap, and that the ferromagnetic moment is confined to EuS with a…","keywords":["InAs/EuS heterostructure","ferromagnetic insulator","molecular beam epitaxy","band alignment","magnetic proximity effect","polarized neutron reflectivity","resonant X-ray reflectivity","XMCD"],"falsifier":"Refit the resonant X-ray reflectivity data using experimentally measured EuS magneto-optical constants instead of EuO-derived ones and include birefringence; if the interfacial layer no longer shows a moment reduction of about 2.7-fold, the paper's central magnetic-structure claim is falsified. Alternatively, an element-specific depth-resolved measurement of the Eu moment with sub-nanometer resolution that shows a uniform moment up to the InAs interface would refute the suppression.","tokens_in":1714,"feed_emoji":"🧲","tokens_out":2737,"duration_ms":76594,"temperature":0.7,"pith_summary":"This paper shows that a fully coherent, dislocation-free interface can be grown between the semiconductor InAs and the ferromagnetic insulator EuS by molecular beam epitaxy, despite the two crystals having different structures but a small lattice mismatch of about 1%. The band alignment is favorable: the Fermi level sits near the InAs conduction band and inside the EuS bandgap, so the semiconductor remains conducting while the insulator stays insulating. Magnetic depth profiling by polarized neutron and resonant X-ray reflectivity finds that the ferromagnetic moment is confined to the EuS film, with a suppression of the Eu moment in a thin interfacial layer, and no induced magnetic moment in InAs within detection limits. First-principles calculations indicate only a weak exchange field in InAs, far weaker than reported for graphene/EuS or Bi2Se3/EuS. A sympathetic reader would care because this establishes a structurally ideal but magnetically weak-proximity hybrid, which sets expectations for zero-field topological devices based on InAs/Al/EuS: the exchange field would likely need to come from the EuS/Al part, not directly from EuS into InAs.","feed_headline":"Dislocation-free InAs/EuS interface keeps magnetism confined to EuS","feed_subtitle":"Fermi level sits at the InAs conduction band while the EuS interface moment drops ~2.7-fold.","key_machinery":"The argument is carried by the combination of a nearly lattice-matched epitaxial interface (rock-salt EuS on zinc-blende InAs with about 1% mismatch) and three depth-sensitive probes: soft-X-ray ARPES for band alignment, polarized neutron reflectivity and resonant X-ray reflectivity at the Eu M4,5 edges for the magnetic depth profile, plus spin-polarized density-functional theory for the expected proximity polarization. The resonant X-ray reflectivity analysis, which uses magnetic scattering factors for EuS obtained from EuO literature values via a Kramers-Kronig transformation, is what yields the specific interfacial layer with a moment reduced by a factor of 2.7.","core_discovery":"The central claim is that InAs/EuS forms a coherent, cube-on-cube epitaxial interface with no misfit dislocations, with the Fermi level at the interface close to the InAs conduction band and inside the EuS gap, and with a magnetic profile in which the ferromagnetic order is localized in the EuS film and the Eu moment in the monolayer nearest InAs is reduced by a factor of about 2.7 relative to bulk. The paper further claims that no static magnetic proximity effect in the InAs is detectable by XMCD within its sensitivity, while density-functional calculations predict a small induced spin polarization of about 0.08 $\\mu_B$ per interfacial In atom. The authors interpret the interfacial moment suppression as resulting from intermixing at the interface, dilution of the Eu moment density, and enhanced next-nearest-neighbor antiferromagnetic interactions of the kind known in Eu$_x$Sr$_{1-x}$S.","pith_inferences":["If the interfacial Eu moment suppression is real, gating InAs to push the electron wavefunction closer to the interface might recover a detectable proximity effect; this is a testable prediction that goes beyond the paper's measurements.","The paper's use of EuO scattering factors for EuS could be checked by measuring the EuS magneto-optical constants directly; if those constants differ substantially, the claimed 2.7-fold suppression may need revision.","The same growth approach could be tried on InSb or on InAs nanowire facets, where reduced dimensionality might alter the balance of nearest- versus next-nearest-neighbor exchange and change the interfacial suppression.","The absence of an induced moment in InAs mirrors earlier null results in normal-metal/ferromagnetic-insulator hybrids, suggesting that a strong static proximity effect requires a metallic spacer or a semiconductor with different orbital character at the Fermi level."],"forward_implications":["For InAs/Al/EuS topological structures, the Zeeman splitting must be supplied by the EuS/Al exchange coupling, not by direct proximity into InAs, because the induced moment in InAs is below detection and weak in the calculations.","The coherent, dislocation-free interface removes structural disorder as a complication, so any residual proximity effect in InAs is intrinsic and weak.","The band alignment with Fermi level near the InAs conduction band and in the EuS gap means field-effect gating of InAs remains possible without parallel conduction through the EuS.","The suppressed interfacial Eu moment means the magnetic stray-field profile starts slightly below the bulk value, so devices relying on stray fields should account for a weakened interfacial monolayer.","The material combination is a clean testbed for studying antiferromagnetic next-nearest-neighbor interactions at a ferromagnet/semiconductor interface."],"supporting_citations":[{"why":"Prior demonstration that EuS can be grown epitaxially on InAs(100), establishing the growth compatibility this paper builds on.","marker":"17"},{"why":"Reported strong exchange field in graphene/EuS, the baseline for the much weaker proximity effect found here.","marker":"12"},{"why":"Proximity-induced ferromagnetic order in Bi2Se3/EuS, another baseline for comparison.","marker":"13"},{"why":"Showed exchange splitting in EuS/Al superconducting films, motivating the InAs/Al/EuS route.","marker":"16"},{"why":"Demonstrated that next-nearest-neighbor antiferromagnetic interactions dominate in EuxSr1-xS, used to explain the suppressed interfacial moment.","marker":"55"},{"why":"Provided the EuS 4f-to-conduction-band gap of about 1.7 eV used for the band-alignment interpretation.","marker":"49"},{"why":"Supplied the fitting model used to analyze the polarized neutron reflectivity data.","marker":"51"},{"why":"The exchange-correlation functional used in the first-principles calculations.","marker":"66"}],"fun_headline_variants":["Coherent InAs/EuS interface confines magnetism to EuS","Interfacial Eu moment drops 2.7-fold in coherent InAs/EuS","No misfit dislocations: InAs/EuS keeps band alignment","Coherent InAs/EuS: Fermi level at CB, magnetism stays in EuS"],"cache_read_input_tokens":20608,"weakest_assumption_plain":"The extracted magnetic depth profile assumes that the magnetic scattering factors for EuS can be taken from EuO literature values via a Kramers-Kronig transformation, that birefringence can be neglected, and that a simplified layered structure captures the interface; if any of these assumptions fails, the claimed 2.7-fold interfacial moment suppression could be an artifact.","fun_headline_variants_meta":{"raw":{"variants":["Coherent InAs/EuS interface confines magnetism to EuS","Interfacial Eu moment drops 2.7-fold in coherent InAs/EuS","No misfit dislocations: InAs/EuS keeps band alignment","Coherent InAs/EuS: Fermi level at CB, magnetism stays in EuS"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000953,"raw_usage":{"total_tokens":4058,"prompt_tokens":935,"completion_tokens":3123,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":551,"completion_tokens_details":{"reasoning_tokens":3037}},"tokens_in":551,"tokens_out":3123,"duration_ms":21702,"temperature":1.0,"reasoning_tokens":3037,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:25:51.941640+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Refit the resonant X-ray reflectivity data using experimentally measured EuS magneto-optical constants instead of EuO-derived ones and include birefringence; if the interfacial layer no longer shows a moment reduction of about 2.7-fold, the paper's central magnetic-structure claim is falsified. Alternatively, an element-specific depth-resolved measurement of the Eu moment with sub-nanometer resolution that shows a uniform moment up to the InAs interface would refute the suppression.","supporting_citations":[],"review_version":1}