{"id":"465f0656-47a4-4f74-81e3-850dab55788d","arxiv_id":"2607.14031","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Electric-field switching of a ferroelectric antiferromagnet gates spin-to-charge conversion in Bi2Te3, with the signal vanishing when the topological surface states are quenched at 5 nm.","lead":"Researchers grew thin films of the topological insulator Bi2Te3 on the insulating magnetic material BiFeO3 and showed that switching BiFeO3's electric polarization changes a voltage produced by spin-to-charge conversion in Bi2Te3. The effect is strongest for films thicker than 10 nm and disappears at 5 nm, suggesting surface states are responsible.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central surface-state claim is undercut by the manuscript's own contradiction: it attributes the thickness dependence to surface-channel evolution, then says the same dependence suggests bulk conduction. No control distinguishes these.","rationale":"After reading the full text, the central assertion is not the existence of the nonlocal voltage—the electrical data may be real—but its attribution to topological surface states. The most load-bearing link in that argument is the thickness dependence: it is the only evidence connecting VSCC to surface-state physics. The manuscript breaks this link internally. The sentence 'The conventional thickness dependence observed here suggests that spin transport is primarily governed by bulk conduction, as surface-state contributions are expected to be independent of thickness' is a limitation statement that directly contradicts the preceding interpretation of the same data. A reviewer is left with two mutually exclusive causal narratives. The raw observation (an electric-field-modulated nonlocal voltage that decreases with thickness) may still be real, but it cannot support the abstract's conclusion until this contradiction is resolved. The HLN coherency factor is not an independent arbiter because the extraction includes bulk contributions, as the text itself notes. The lack of a control without topological surface states leaves open the possibility that the thickness trend is a generic thin-film effect. This is not an ad hominem; it is an internal inconsistency in the argument. The reader identified the same region of concern (contradiction and controls) in the rationale, though chose the artifact question as the weakest assumption; hence 'partial' agreement. My suggested test—a matched non-topological control on the same BFO—would directly settle whether the thickness dependence is specific to topological surface states. I keep the verdict at CONDITIONAL (unchanged) because the paper can be repaired with additional controls and a clarified interpretation, but not accepted as-is.","tokens_in":12789,"tokens_out":6432,"duration_ms":60842,"concrete_test":"Fabricate identical nonlocal devices on the same BFO using a non-topological control channel (e.g., 5–70 nm sputtered Au or a trivial semiconductor with comparable resistivity and no spin-momentum locking) and measure ΔVSCC vs thickness with the same electric-field protocol. If the control replicates the thickness trend and field modulation, the signal is not specific to topological surface states; if it is flat or zero, the surface-state attribution gains support. Additionally, re-derive the predicted VSCC from the measured HLN α using a quantitative surface-versus-bulk conversion model rather than a visual correlation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's headline conclusion—'spin-momentum-locked surface states dominate interfacial spin transport'—rests on the thickness series in Fig. 4 and the HLN coherency factor. But the Results section contains a direct contradiction. After writing that VSCC 'remains nearly constant ... down to ~20 nm, indicative of being dominated by the surface' and that the coherency factor 'shows excellent agreement with the spin-transport data, indicating that the efficiency of spin–charge conversion is dominated by the topological surface states,' the same paragraph concludes: 'The conventional thickness dependence observed here suggests that spin transport is primarily governed by bulk conduction, as surface-state contributions are expected to be independent of thickness.' If surface states are thickness-independent, the suppression of VSCC below 20 nm cannot be used as evidence of their dominance; it may reflect bulk conduction, increased disorder, or a thickness-dependent conversion efficiency unrelated to topology. The HLN α values are also extracted from total magnetoconductance with an acknowledged bulk contribution, so they are only a proxy, not an independent proof. No non-topological control is reported, and no conversion model turns the raw ΔVSCC into a surface-state-specific spin Hall angle. As written, the paper's own limitation statement prevents the central claim from being established.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports nonlocal spin-transport measurements in sputter-deposited Bi2Te3 films on epitaxial BiFeO3, claiming electric-field control of spin-charge conversion through the ferroelectric antiferromagnet. The authors present structural characterization, temperature-dependent resistivity, Hall and magnetoconductance measurements, and a thickness series of the nonlocal voltage VSCC. They interpret the thickness dependence and the HLN coherency factor as evidence that topological surface states dominate interfacial spin transport, with electric-field-controlled polarization of BiFeO3 modulating the magnon-mediated signal. The paper also compares VSCC with reported Pt and SrIrO3 values and argues for technological relevance of sputtered Bi2Te3.","tokens_in":13072,"tokens_out":3665,"duration_ms":37981,"significance":"If the central claim were established, this work would demonstrate electric-field-controlled spin-charge conversion through an insulating antiferromagnetic magnon medium, using a scalable sputtered topological insulator. The experimental design has notable strengths: a nonlocal geometry without an applied magnetic field, measurement of VSCC in the remanent polarization state, structural characterization of the heterointerface, and current-polarity and second-harmonic checks relevant to thermal artifacts. The reported magnitudes, if normalized properly, could be meaningful for spin-orbitronic applications. However, as written, the central interpretation is undermined by an internal contradiction and by the absence of independent, quantitative support for surface-state dominance. The work is potentially significant but currently falls short of establishing its headline conclusion.","major_comments":[{"comment":"The manuscript contains a direct contradiction that is load-bearing for the central claim. It states that VSCC 'remains nearly constant ... down to ~20 nm, indicative of being dominated by the surface' and that the thickness-dependent coherency factor shows 'excellent agreement with the spin-transport data, indicating that the efficiency of spin–charge conversion is dominated by the topological surface states.' The same paragraph then concludes: 'The conventional thickness dependence observed here suggests that spin transport is primarily governed by bulk conduction, as surface-state contributions are expected to be independent of thickness.' These statements cannot both hold: if surface-state contributions are thickness-independent, the observed suppression below ~15 nm cannot be used as evidence of surface-state dominance. The authors must resolve this inconsistency and provide a model","section":"Results, Fig. 4 paragraph"},{"comment":"The HLN coherency factor is not an independent probe of topological surface-state transport. The manuscript itself acknowledges that 'the measured magnetoconductivity reflects parallel transport through both topological surface states and the conducting bulk, and the extracted HLN prefactor represents an effective contribution from multiple transport channels rather than isolated surface states.' The mapping of α to 1/π or 1/2π assumes the channels are purely 2D topological surface channels, which is not established given the admitted bulk contribution. Therefore, the agreement between ΔVSCC and α in Fig. 4 does not independently confirm that the spin-charge conversion is surface-dominated. A quantitative decomposition of the magnetoconductance into surface and bulk channels is needed.","section":"Results, magnetoconductance analysis (Fig. 2C and Fig. 4)"},{"comment":"The thickness dependence is the central evidence for the topology-related conclusion, yet Fig. 4 shows no error bars, and the text does not report the number of devices or repeated measurements per thickness. Unlike Fig. 3, where a standard deviation is mentioned, the key ΔVSCC versus tBi2Te3 data lack uncertainty estimates. Given that the entire interpretation hinges on the trend in this figure, the authors need to provide replicate counts, error bars, and a statistical assessment of the thickness trend.","section":"Fig. 4 and thickness series"},{"comment":"The claimed 'orders of magnitude larger than Pt' comparison and the inferred spin Hall angle are not substantiated by a quantitative conversion model. The RSCC comparison in Fig. 3D uses literature values from different device geometries and does not normalize for spin injection efficiency, magnon transport efficiency, or interface transparency. Moreover, the Methods derivation (Eqs. 1–9) is explicitly phenomenological and allows the sign reversal to arise from either surface IEE or bulk ISHE, or a crossover between them (Sec. 0.3). Without a quantitative conversion model and without a non-topological control sample measured in the same setup, the conclusion that spin-momentum-locked surface states dominate is not established.","section":"Results, comparison with Pt and SrIrO3; Methods, sign-reversal derivation"}],"minor_comments":[{"comment":"The text refers to 'shown in Fig. 1B' when discussing the ferroelectric polarization and VSCC hysteresis; the correct reference appears to be Fig. 3B. Please check all figure cross-references.","section":"Fig. 3B text"},{"comment":"The sentence 'Though the resistance of the lowest thickness is the largest (Fig. 2A)' should refer to Fig. 2B (resistivity versus temperature), not Fig. 2A (device geometry).","section":"Results, resistivity discussion"},{"comment":"Typo: 'V oltage' should be 'Voltage'. Also, the caption should clarify which axis corresponds to polarization and which to VSCC.","section":"Fig. 3B caption"},{"comment":"The subsection numbering 'Methods 0.2' and internal references such as 'Equation.8' are awkward; please renumber and unify equation references.","section":"Methods, sign-reversal section"},{"comment":"The phrase 'unprecedented direct evidence' is an overstatement. A more measured description, given the acknowledged bulk contribution, would be appropriate.","section":"Introduction/abstract"},{"comment":"Some references are duplicated (e.g., Ref. 13 and 35 are both Kondou et al., Nature Physics 12, 1027 (2016)); consolidate to avoid confusion.","section":"General"}],"recommendation":"major_revision","confidential_remarks":"The paper reports an interesting device concept and a substantial set of measurements, but the central claim—that topological surface states dominate the spin-charge conversion—is not currently supported because of an internal contradiction in the interpretation of the thickness dependence and the lack of an independent, quantitative probe. The issue is fixable in principle by adding control experiments, error bars/replicates, and a decomposition model, so I recommend major revision rather than rejection. The editor may also wish to ask the authors to clarify the relationship between this work and closely related prior reports on SrIrO3/BiFeO3 to ensure the novelty claim is precise."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The paper reports a nonlocal spin-transport measurement of Bi2Te3 on BiFeO3 with electric-field control of the spin-charge conversion voltage, and a thickness series showing that the signal is robust above ~20 nm and vanishes at 5 nm. That thickness series is new relative to the same group's earlier works, and the structural data are thorough. The electric-field hysteresis loop tracking the ferroelectric polarization is a clean experimental demonstration.\n\nThe problem is the central mechanism claim. The Results paragraph on Fig. 4 says the thickness dependence is 'indicative of being dominated by the surface' and that the HLN coherency factor 'shows excellent agreement,' then immediately concludes that 'the conventional thickness dependence observed here suggests that spin transport is primarily governed by bulk conduction, as surface-state contributions are expected to be independent of thickness.' Those two statements cannot both be load-bearing for the same conclusion. The paper needs to resolve what the thickness dependence actually means.\n\nThere are also missing controls. The thickness dependence has no error bars or replicate counts; there is no non-topological reference electrode measured in the same geometry; and the HLN coherency factor is extracted from transport with an admitted bulk contribution, so it is not independent evidence of surface-state dominance. The quantitative comparison with SrIrO3 and the suggested spin Hall angle come from raw voltage magnitude, not a conversion model. The Methods sign-reversal derivation is phenomenological and explicitly allows a bulk ISHE origin, so it does not isolate the surface state.\n\nThe experiment is likely real and the empirical result is worth knowing, but the paper overclaims the surface-state interpretation. It deserves peer review because the question matters and the data are plausible, but it needs major revision: resolve the contradiction, add error bars and a control, and either support or retract the surface-state dominance claim.","headline":"New Bi2Te3/BFO thickness-series data, but the central surface-state claim is undercut by an internal contradiction and missing controls.","tokens_in":13663,"tokens_out":3888,"would_cite":true,"duration_ms":37076,"reading_group":"yes","serious_thinker":"no","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper reports electric-field control of spin-charge conversion in Bi2Te3/BiFeO3 heterostructures, and argues that topological surface states, not the bulk, mediate the interfacial spin transport.","keywords":["spin-charge conversion","topological insulator","ferroelectric antiferromagnet","magnon spin transport","inverse Edelstein effect","electric-field control","nonlocal spin transport","weak antilocalization"],"falsifier":"Measure a control device with the BiFeO3 layer replaced by a nonmagnetic insulator of comparable resistivity, or with a magnetic field applied to suppress magnon transport; if the polarization-following voltage survives or does not scale with the remanent antiferromagnetic state, the spin-mediated interpretation of VSCC fails. Alternatively, calibrate the injected spin current with a ferromagnetic spin detector of known efficiency and compare the extracted spin Hall angle.","tokens_in":12640,"feed_emoji":"⚡","tokens_out":5641,"duration_ms":47649,"temperature":0.7,"pith_summary":"Spin-charge conversion in the topological insulator Bi2Te3 can be switched by an electric field when the Bi2Te3 is placed on an insulating ferroelectric antiferromagnet, BiFeO3. Using a nonlocal geometry with no magnetic field, the authors find a voltage that follows the ferroelectric polarization and reverses with current polarity, a signature they attribute to magnon transport through BiFeO3 and inverse Edelstein detection at a second Bi2Te3 electrode. The decisive observation is thickness dependence: the conversion stays robust above 10 nm of Bi2Te3, then drops sharply and vanishes at 5 nm, in parallel with the loss of weak-antilocalization coherency. The paper argues this is the hybridization-induced transition of ultrathin Bi2Te3 to a trivial insulator, establishing that spin-momentum-locked surface states, not the bulk, dominate interfacial spin transport. A sympathetic reader would care because it demonstrates electric-field control of spin flow through a fully insulating magnetic barrier, a practical route to low-power, nonvolatile spintronic devices.","feed_headline":"Electric field controls spin transport in Bi2Te3 via an antiferromagnet","feed_subtitle":"A nonlocal device ties the spin signal to topological surface states, with conversion vanishing below 10 nm of Bi2Te3.","key_machinery":"The central object is the nonlocal spin-transport device: a current-driven Bi2Te3 wire injects a nonequilibrium spin polarization via the Edelstein effect; the polarization is carried through the insulating, antiferromagnetic BiFeO3 by magnons; a second Bi2Te3 electrode converts the arriving spin accumulation back into a voltage via the inverse Edelstein effect. The identity that carries the argument is the parallel between the thickness dependence of the conversion voltage and the coherency factor extracted from weak-antilocalization fits: both fall together as Bi2Te3 is thinned, tying the conversion efficiency to the coherence of topological surface-state channels (single versus double two","core_discovery":"The central claim is that the spin-charge conversion voltage measured across a Bi2Te3/BiFeO3 bilayer is carried by the topological surface states of Bi2Te3, not by its conducting bulk. The authors show that this voltage tracks the ferroelectric polarization of BiFeO3, reverses sign when the injection current is reversed, and persists only for Bi2Te3 thicknesses above roughly 10 nm. Below that thickness the signal collapses, matching the reduction of the weak-antilocalization coherency factor and consistent with a hybridization gap that turns the ultrathin film into a trivial insulator. They conclude that spin-momentum-locked surface states dominate interfacial spin transport in this decouple","pith_inferences":["If the mechanism is right, the same device architecture should allow electric-field tuning of spin transport by reversing ferroelectric polarization at remanence, enabling nonvolatile memory-like switching without continuous power.","A testable extension is to thin or dope Bi2Te3 to move the Fermi level closer to the Dirac point; the model predicts the inverse Edelstein voltage should grow as the bulk channel is suppressed.","One could probe the magnon channel directly by introducing a nonmagnetic spacer between Bi2Te3 and BiFeO3; if the signal is truly magnon-mediated, even a few nanometers of a nonmagnetic insulator should kill it.","The thickness dependence suggests a route to device integration: choose a thickness just above 10 nm to retain robust surface-state conversion while minimizing bulk conduction."],"forward_implications":["Electric-field control of spin-charge conversion can be achieved in an all-insulating magnetic interface, without any applied magnetic field.","Spin transport through the antiferromagnetic insulator BiFeO3 is mediated by magnons, giving a nonlocal channel that is robust against charge shunting because BiFeO3 is a GΩ resistor.","The thickness threshold near 10 nm provides a design rule: topological-insulator spin devices must keep the active layer thick enough to avoid surface-state hybridization.","Sputter-deposited Bi2Te3 on BiFeO3 can serve as a scalable platform for spin-charge interconversion, with efficiencies comparable to or better than oxide spin-orbit metals.","If the measured voltage magnitude corresponds to the claimed conversion, the effective spin Hall angle of Bi2Te3 is close to theoretical estimates, making it a strong candidate for low-power spin logic."],"fun_headline_variants":["Electric field controls spin transport in Bi2Te3/BiFeO3","Topological surface states dominate spin transport under electric field","Spin-charge conversion vanishes below 10 nm in Bi2Te3 stack","Ferroelectric antiferromagnet gates Bi2Te3 spin transport","Bi2Te3/BiFeO3: electric field tunes spin-charge conversion"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The measured voltage is genuinely generated by spin injection into BiFeO3, magnon transport through it, and inverse Edelstein detection at the second Bi2Te3 electrode, rather than by ferroelectric switching, thermal gradients, or a charge artifact.","fun_headline_variants_meta":{"raw":{"variants":["Electric field controls spin transport in Bi2Te3/BiFeO3","Topological surface states dominate spin transport under electric field","Spin-charge conversion vanishes below 10 nm in Bi2Te3 stack","Ferroelectric antiferromagnet gates Bi2Te3 spin transport","Bi2Te3/BiFeO3: electric field tunes spin-charge conversion"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000665,"raw_usage":{"total_tokens":2911,"prompt_tokens":820,"completion_tokens":2091,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":564,"completion_tokens_details":{"reasoning_tokens":2008}},"tokens_in":564,"tokens_out":2091,"duration_ms":15786,"temperature":1.0,"reasoning_tokens":2008,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-02T02:57:32.536663+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure a control device with the BiFeO3 layer replaced by a nonmagnetic insulator of comparable resistivity, or with a magnetic field applied to suppress magnon transport; if the polarization-following voltage survives or does not scale with the remanent antiferromagnetic state, the spin-mediated interpretation of VSCC fails. Alternatively, calibrate the injected spin current with a ferromagnetic spin detector of known efficiency and compare the extracted spin Hall angle.","supporting_citations":[],"review_version":1}