{"id":"a1ee86cf-eaaa-4c4a-8699-c9726776cb37","arxiv_id":"2411.19062","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"In a TaIrTe4/Py device, the nonlinear planar Hall effect and spin-orbit torque are measured together and show opposite anisotropy along the [100] and [010] crystal directions.","lead":"This paper reports the first simultaneous observation of two charge-to-spin conversion effects, the nonlinear planar Hall effect and spin-orbit torque, in a single device made from the Weyl semimetal TaIrTe4 and a magnetic layer. It finds that the two effects respond differently along the two crystal directions, which could help design spintronic devices using topological materials.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Uncontrolled thermal background in Eq. (3) could mimic the cosφ components; without control samples the NPHE/SOT separation and the central anisotropy claim are not independently secured.","rationale":"The paper's central claim is a simultaneous observation of NPHE and SOT with distinct crystallographic anisotropy. The experimental analysis rests on a harmonic Hall decomposition in which the DL-SOT and NPHE share the same cosφ angular dependence and are separated only by their presumed field dependence. The thermal term R_xy^∇T is explicitly present in Eq. (3) but is never bounded experimentally. While the linear-in-I and linear-in-H scaling in Figure 3 is consistent with the expected NPHE, several thermoelectric effects in the ferromagnet also produce second-harmonic voltages that grow with current and can have weak or linear magnetic-field dependence; without a control that isolates the Py layer's thermal response, the fitted χ_NPHE and H_DL cannot be uniquely attributed. This is the weakest link in the causal chain from data to the anisotropy claim. I do not see an internal inconsistency in the equations; the issue is an external validation gap. The paper does provide useful characterization (Raman, XRD) and a plausible physical interpretation, but the absence of control samples and error bars means the quantitative efficiencies and the anisotropy ratios should be treated as provisional. The reader's CONDITIONAL verdict already captures this. I propose no change, with the recommendation that the controls described in concrete_test be run before the claim of 'first simultaneous observation' is accepted at face value.","tokens_in":11995,"tokens_out":5992,"duration_ms":57483,"concrete_test":"Fabricate a control device identical to the TaIrTe4/Py Hall bar but with TaIrTe4 replaced by a 117 nm Cu film (or a nonmagnetic metal of comparable resistivity), preserving the Py/interface and thermal environment without the Weyl semimetal. Measure the second harmonic Hall signal R_xy^2ω(φ) over the same H (100 Oe–6 T) and I (1.4–2.2 mA) ranges and extract the cosφ coefficient. If the control shows a cosφ component of magnitude comparable to the NPHE part in the real device, or with a field dependence that overlaps the A/(H+H_K)+B H fit, then the assumed negligibility of R_xy^∇T fails and the extracted H_DL and χ_NPHE are ambiguous. If the control yields a negligible cosφ coefficient, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"Equations (1)–(3) separate the second-harmonic Hall signal into a cosφcos2φ term (FL-torque + Oersted) and a cosφ term modeled as R_A H_DL/(H+H_K) + R_xy^∇T + 2χ_NPHE H. The DL-SOT and NPHE terms share the same angular dependence, so the decomposition hinges entirely on their different field scaling: 1/(H+H_K) versus linear-in-H. The thermal term R_xy^∇T is asserted to be negligible/removable but is never independently characterized. The anomalous Nernst effect and spin Seebeck effect in the 7 nm Py layer can produce a cosφ second-harmonic component whose field dependence is often weak or complex; such a component would be absorbed into the fitted H_DL or χ_NPHE parameters. No control experiments (TaIrTe4-only, Py-only, or Cu/Py) are reported. Because the central claim is the simultaneous observation and distinct anisotropy of NPHE and SOT in a single bilayer, an uncorrected thermal background of the same symmetry could distort or even mimic the reported effects. The linear-in-I and linear-in-H scaling shown in Figure 3 is consistent with NPHE, but it is also the scaling expected for some Joule-heating-driven thermoelectric signals, so it does not by itself rule out thermal contamination.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports harmonic Hall measurements on TaIrTe4/Py bilayers and claims the first simultaneous observation of the nonlinear planar Hall effect (NPHE) and spin-orbit torques (SOT) in a TaIrTe4-based heterostructure. The authors develop a field-dependent decomposition based on Eqs. (1)-(3) to separate the second-harmonic Hall signal into field-like SOT, damping-like SOT, and NPHE contributions, and they report distinct anisotropies: stronger NPHE and field-like SOT along the [100] direction, and larger damping-like SOT along the [010] direction. The results are interpreted in terms of Fermi-arc surface states versus bulk spin Hall contributions.","tokens_in":12346,"tokens_out":9439,"duration_ms":81472,"significance":"If the experimental decomposition is reliable, the paper advances the field by showing that linear and nonlinear charge-spin conversion can be characterized simultaneously in a single device, and by using the different field scalings of DL-SOT (1/(H+H_K)) and NPHE (linear in H) to separate them. The reported anisotropy pattern is a concrete, falsifiable observation that can guide theory on surface versus bulk mechanisms. The authors also provide a clear device fabrication and measurement description. However, the quantitative conclusions currently rest on unverified assumptions about the thermal background and on unspecified electrical parameters, so the significance is conditional on additional controls and error analysis.","major_comments":[{"comment":"The separation of R_DL+NPHE into a 1/(H+H_K) component and a linear-in-H NPHE component requires that the thermal term R_xy^∇T be negligible or removable, but this is never demonstrated. The manuscript states the thermal contributions (anomalous Nernst and spin Seebeck effects in the 7-nm Py layer) without quantifying them, and no control experiments (TaIrTe4-only, Py-only, or Cu/Py devices) or frequency-dependent harmonic measurements are reported to bound their magnitude. Because these thermal effects produce second-harmonic signals with the same cosφ symmetry and with weak or non-linear field dependences, they can be absorbed into the fitted H_DL or χ_NPHE parameters. The linear-in-I and linear-in-H scaling shown in Figures 3(c)-(d) is consistent with NPHE but also with Joule-heating-driven thermoelectric signals, so it does not by itself rule out a thermal background. Please provide control experiments or an independent estimate of R_xy^∇T, and preferably measurements at multiple AC frequencies.","section":"Sec. B, Eq. (3)"},{"comment":"The quoted efficiencies θ_FL = 0.57 and θ_DL = 0.93 depend on the current density j in the TaIrTe4 layer, the Oersted field H_Oe, the anisotropy field H_K, and the saturation magnetization M_s of Py. The manuscript does not report the values of H_K, M_s, the resistivities used for the current-sharing calculation among TaIrTe4, Py, and Cu, or the effective cross-sectional area used for j. The conversion from measured second-harmonic voltages to effective fields is therefore not reproducible, and no uncertainty is assigned to the final spin-Hall efficiencies. Please provide these parameters and error bars, and state the formula used to compute the current density in the TaIrTe4 layer.","section":"Sec. D, Eqs. (2)-(3) and Fig. 4(f)"},{"comment":"The central claim of anisotropy (five-fold difference in the nonlinear coefficient χ between [100] and [010], and opposing anisotropies for FL-SOT and DL-SOT) appears to be based on a single device per crystallographic direction, since the Supporting Information is only cited for the [010] data and no sample-to-sample variability is discussed. Without multiple devices or an explicit reproducibility statement, the quantitative ratios and the assignment of the anisotropy to intrinsic crystal properties are not fully established. Please report the number of devices measured, the spread of values, and the statistical significance of the anisotropy.","section":"Sec. E, Fig. 5"}],"minor_comments":[{"comment":"The manuscript contains several typos and notation inconsistencies, including the title 'anisotrop y', the inconsistent use of 'TaIrTe₄' and 'TaIrTe4', and the spacing in 'charge –spin'. Please proofread carefully.","section":"Throughout"},{"comment":"The sentence 'the value of 1/H will be larger than 1/(H_K − H)' appears to have a typo: Eq. (3) contains 1/(H_K + H), so the comparison should be between 1/H and 1/(H_K + H). Please correct this.","section":"Sec. B, after Eq. (3)"},{"comment":"The sign convention for H_FL is not defined; please specify whether H_FL is taken positive along or opposite to the Oersted field direction and how that affects the extracted value of θ_FL.","section":"Eq. (2)"},{"comment":"Please define all quantities in χ = ρ_xy^2ω/(E_x H_y), including whether E_x is the applied electric field along the current direction and H_y is the in-plane magnetic field component; state the assumed angle between current and magnetic field when reporting the value of χ.","section":"Sec. E, definition of χ"},{"comment":"In the formula θ_SH = 2e μ0 M_s t H_FL(DL)/(ℏ j), clarify the units of j (A m^-2) and state whether j is the current density in the TaIrTe4 layer only or averaged over the full heterostructure; this is needed to interpret the reported values.","section":"Sec. D, spin-Hall angle formula"}],"recommendation":"major_revision","confidential_remarks":"The paper is within the scope of a condensed-matter physics or spintronics journal, and the central observation is interesting. However, the separation of NPHE and SOT from a thermal background is not secured without control experiments, and the absence of error analysis and input parameters prevents a reliable quantitative assessment. I recommend that the editor invite a major revision with the request for control devices, multiple measurements, and full parameter disclosure. I found no evidence of scientific misconduct; the manuscript is a conventional experimental report in its current state."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Hi [Colleague],\n\nThis paper is worth a look. The authors report the first simultaneous observation of NPHE and SOT in a TaIrTe4/Py heterostructure, and they show that the nonlinear response and the field-like torque are stronger along [100] while the damping-like torque is stronger along [010]. That opposite anisotropy is the genuinely new piece, and it connects to a sensible picture of Fermi-arc surface states governing NPHE and FL-SOT, with bulk SHE governing DL-SOT.\n\nWhat the paper does well: the harmonic Hall measurements are standard, and the field-dependent crossover—cosφcos2φ at low fields to cosφ at high fields—is presented clearly. The linear scaling of the high-field cosφ component with both I and H is solid evidence for a nonlinear planar Hall effect, and the fact that they extract the NPHE contribution in the same device as the SOT is a useful advance.\n\nThe soft spots are in the quantitative separation. Equation (3) puts the DL-SOT and NPHE terms in the same angular channel, separated only by their field dependence: 1/(H+H_K) vs. linear in H. The thermal term R_xy^∇T is included but never independently characterized. The anomalous Nernst effect and spin Seebeck effect in the 7 nm Py can produce a cosφ second-harmonic signal with a field dependence that is not necessarily constant; if any part of it scales like 1/(H+H_K) or linearly with H, it will leak into the extracted H_DL or χ_NPHE. There are no control samples (TaIrTe4-only, Py-only, Cu/Py) to bound this background. The linear-in-H scaling in Figure 3 is consistent with NPHE, but it is also what you would expect from some Joule-heating-driven thermoelectric signals.\n\nThe efficiencies θ_FL=0.57 and θ_DL=0.93 depend on the current density in the TaIrTe4 layer, which is estimated without stated resistivities and without error bars. The anisotropy ratios are probably more robust than the absolute numbers, but even those rely on the same decomposition.\n\nNone of this is fatal. The qualitative message—simultaneous observation and distinct anisotropies—likely holds. But as written, the quantitative claims are not fully secured.\n\nWho should read this: anyone working on charge-spin conversion in topological semimetals. It should be sent to peer review; a serious referee will ask for control samples, a thermal background analysis, and error bars. That process would strengthen the paper rather than sink it.\n\nMy vote: accept for review, with the expectation of major revision.\n\nBest.","headline":"Simultaneous NPHE and SOT in a single TaIrTe4/Py device with an interesting opposite anisotropy, but the quantitative separation lacks thermal controls and error bars.","tokens_in":12819,"tokens_out":4104,"would_cite":true,"duration_ms":37484,"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":"The paper reports simultaneous observation of the nonlinear planar Hall effect and spin-orbit torque in one TaIrTe4/Py heterostructure, with the two effects peaking along different crystal axes.","keywords":["Weyl semimetal","TaIrTe4","nonlinear planar Hall effect","spin-orbit torque","harmonic Hall measurement","charge-spin conversion","anisotropy","spin-momentum locking"],"falsifier":"Repeat the high-field harmonic Hall measurement on a bare TaIrTe4 flake (without the Py layer) in the same Hall geometry; if the linear-in-$H$ $\\cos\\varphi$ second-harmonic resistance remains, the NPHE attribution is supported, whereas if it disappears, the term assigned to NPHE is actually a magnetization-related artifact of the ferromagnetic layer.","tokens_in":11821,"feed_emoji":"🧲","tokens_out":9437,"duration_ms":72543,"temperature":0.7,"pith_summary":"The paper reports the first simultaneous observation of the nonlinear planar Hall effect (NPHE) and spin-orbit torque (SOT) in a single Weyl semimetal heterostructure, TaIrTe4/Py. It develops a magnetic-field-dependent harmonic Hall measurement that separates the three contributions and finds that the two effects respond to different crystallographic directions: NPHE and field-like SOT are stronger along [100], while damping-like SOT is stronger along [010]. If the separation is sound, this means linear and nonlinear charge-spin conversion can be characterized in one device and that their anisotropies reveal distinct surface and bulk mechanisms. The result matters for spintronics because it suggests crystal-direction engineering of topological materials could control the type and efficiency of charge-spin conversion.","feed_headline":"Nonlinear Hall and spin torque seen in one Weyl semimetal device","feed_subtitle":"The two effects prefer opposite crystal axes, revealing separate surface and bulk mechanisms.","key_machinery":"The method rests on the harmonic Hall decomposition in Eqs. (1)-(3): the second harmonic signal is split into a field-like term $R_{FL+Oe}$ proportional to $\\cos\\varphi\\cos 2\\varphi$ and a damping-like plus nonlinear term $R_{DL+NPHE}$ proportional to $\\cos\\varphi$, with the NPHE component identified by its linear dependence on the in-plane magnetic field $H$. The nonlinear Hall coefficient $\\chi = \\rho_{xy}^{2\\omega}/(E_x H_y)$ quantifies the strength of the nonlinear charge-spin conversion. The separation is made field-dependent: at low fields the signal is dominated by $R_{FL+Oe}$, while at high fields the linear-in-$H$ NPHE term grows and must be removed before the damping-like field $H_{DL}$ is obtained from the remaining $1/(H_K+H)$ dependence.","core_discovery":"The central claim is that in a TaIrTe4/Py bilayer the second harmonic Hall resistance $R_{xy}^{2\\omega}$ contains a detectable nonlinear planar Hall contribution that is linear in magnetic field and follows $\\cos\\varphi$, which must be subtracted before the spin-orbit torque efficiencies are extracted. After this subtraction, the field-like SOT efficiency $\\theta_{\\mathrm{FL}}$ is found to be $0.57$ along [100] and the damping-like efficiency $\\theta_{\\mathrm{DL}}$ to be $0.93$ along [010], while the nonlinear Hall coefficient $\\chi = \\rho_{xy}^{2\\omega}/(E_x H_y)$ takes values of $0.74$ and $0.15$ mΩ·V$^{-1}$·μm$^2$·T$^{-1}$ along [100] and [010], respectively. The authors interpret the stronger NPHE and field-like torque along [100] as a signature of the spin-momentum-locked Fermi arc surface states, and the stronger damping-like torque along [010] as a signature of the bulk spin Hall effect.","pith_inferences":["If the decomposition is robust, the same field-dependent harmonic Hall procedure could be applied to other type-II Weyl semimetals and topological semimetals to map their charge-spin conversion anisotropy without fabricating separate samples for each effect.","The positive correlation between NPHE and field-like SOT along [100] suggests a shared surface origin; a thickness series of TaIrTe4 or a controlled surface-state modification (for example via capping layers) could test whether suppressing the Fermi arc contribution weakens both effects together.","The claim that damping-like SOT is bulk-dominated could be cross-checked by spin-pumping experiments on the same TaIrTe4 crystals, or by comparing the measured $\\theta_{DL}$ anisotropy with ab initio calculations of the bulk spin Hall conductivity."],"forward_implications":["TaIrTe4 can serve as a single material in which both nonlinear charge-spin conversion and spin-orbit torque are measurable, with crystal orientation selecting which effect dominates.","The nonlinear Hall coefficient $\\chi$ is five times larger along [100] than along [010], so current-direction engineering can tune the efficiency of nonlinear charge-spin conversion.","The opposite anisotropies of field-like and damping-like torques point to different mechanisms, surface spin-momentum locking versus bulk spin Hall effect, that can be investigated separately in the same device.","The simultaneous measurement provides a direct way to correlate linear and nonlinear conversion efficiencies without sample-to-sample variations.","The extracted spin Hall angles of 0.57 (field-like) and 0.93 (damping-like) are large enough to matter for SOT applications in topological semimetal devices."],"supporting_citations":[{"why":"Supplies the cosφ angular dependence and the conceptual framework for the nonlinear planar Hall effect used in Eq. (1).","marker":"[10]"},{"why":"Establishes TaIrTe4 as a type-II Weyl semimetal with two pairs of Weyl points, the material platform studied.","marker":"[26]"},{"why":"Provides angle-resolved photoemission evidence that the Fermi arcs extend along k_y with spin polarization along the same direction, used to interpret the [100]-vs-[010] anisotropy.","marker":"[29]"},{"why":"Reports room-temperature nonlinear Hall effect in TaIrTe4, the nonlinear charge-spin conversion that this paper observes simultaneously with SOT.","marker":"[30]"},{"why":"Reports field-free SOT switching of perpendicular magnetization using TaIrTe4, the linear charge-spin conversion measured here in the same material.","marker":"[31]"},{"why":"Establishes the harmonic Hall voltage measurement technique used to extract the spin-orbit torque effective fields.","marker":"[35]"},{"why":"Documents the thermal contributions (R_xy^{∇T}) that must be removed from the harmonic Hall signal, a step on which the decomposition relies.","marker":"[37]"},{"why":"Provides the formula $\\theta_{SH} = 2e\\mu_0 M_s t H_{FL(DL)}/\\hbar J$ used to convert the measured effective fields into spin Hall angles.","marker":"[56]"}],"fun_headline_variants":["Weyl semimetal shows anisotropic charge-spin conversion","Opposite axes for Hall and spin torque in Weyl semimetal","Nonlinear Hall and spin torque anisotropic in TaIrTe4","Two spin effects, one crystal, different axes in Weyl semimetal","Weyl semimetal splits spin effects along distinct axes"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the second harmonic Hall voltage is a clean sum of three known angular- and field-dependent terms, namely field-like torque, damping-like torque, and a nonlinear planar Hall term that is linear in magnetic field, so that any additional contribution sharing the same symmetries would be misassigned and would distort the reported anisotropies.","fun_headline_variants_meta":{"raw":{"variants":["Weyl semimetal shows anisotropic charge-spin conversion","Opposite axes for Hall and spin torque in Weyl semimetal","Nonlinear Hall and spin torque anisotropic in TaIrTe4","Two spin effects, one crystal, different axes in Weyl semimetal","Weyl semimetal splits spin effects along distinct axes"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000797,"raw_usage":{"total_tokens":3536,"prompt_tokens":1003,"completion_tokens":2533,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":619,"completion_tokens_details":{"reasoning_tokens":2456}},"tokens_in":619,"tokens_out":2533,"duration_ms":18011,"temperature":1.0,"reasoning_tokens":2456,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T10:33:57.964842+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Repeat the high-field harmonic Hall measurement on a bare TaIrTe4 flake (without the Py layer) in the same Hall geometry; if the linear-in-$H$ $\\cos\\varphi$ second-harmonic resistance remains, the NPHE attribution is supported, whereas if it disappears, the term assigned to NPHE is actually a magnetization-related artifact of the ferromagnetic layer.","supporting_citations":[],"review_version":1}