{"id":"9badc78b-33fb-4de8-aadc-d352041e6194","arxiv_id":"1908.01396","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"Electrically generated valley-locked spins in monolayer WSe2 are observed as a nonlocal spin signal in graphene, providing the first all-electrical demonstration of out-of-plane spin generation via the valley Hall effect.","lead":"This paper reports electrical generation of out-of-plane polarized spin currents in a monolayer of the semiconductor WSe2, detected in an adjacent graphene channel through a magnetic contact. If correct, it provides an all-electrical spin source for field-free switching of perpendicular magnets in spin-orbit torque memory.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The central claim relies on a small nonlocal signal (~µV) that is presented as an average of three datasets with linear background subtraction in some traces and no error bars; without per-device raw traces and significance tests, the 'observation' is not established.","rationale":"The reader's weakest_assumption focused on the transfer of the Py AHE calibration to the actual detector. While that is a legitimate quantitative concern, the qualitative spin interpretation does not strictly depend on the exact saturation field of the calibration bar: zero signal at Bz=0, saturation at high field, and current-polarity reversal would still support out-of-plane spin accumulation even if the detector magnetization differed somewhat from the standalone Hall bar. In contrast, the statistical solidity of the raw nonlocal data is genuinely load-bearing: if the reported effect is not reproducibly above noise in individual datasets, no amount of calibration or modeling can rescue the central claim. The paper itself signals the issue by averaging three datasets and subtracting backgrounds in some supplementary curves, yet omits error bars and raw data deposition. The verdict remains CONDITIONAL because these issues could be resolved by providing the unprocessed per-device traces and significance analyses; the reader's conditional acceptance already aligns with this position, though the specific weakest assumption differs. I do not see an internal inconsistency that would justify rejection, and the NM control plus current-polarity reversal provide meaningful protection against trivial charge-related artifacts.","tokens_in":11138,"tokens_out":17468,"duration_ms":211432,"concrete_test":"Request the raw per-device Rnl(Bz) traces for all devices shown in Fig. S7, before averaging and before any background subtraction. Reanalyze each trace with a fixed protocol and compute per-point mean and standard error: (i) the Bz=0 baseline must be consistent with zero within noise in every device; (ii) the sign reversal under current reversal must be reproduced in each individual device; (iii) the saturated |Rnl| at |Bz|>0.8 T must exceed the Bz=0 baseline by more than 3σ of the per-device noise. If any device fails these criteria, the averaged curve and background subtraction may be driving the claimed observation.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim is an experimental observation, but the evidence in Fig. 3a is an average of three datasets, and Supplementary Section II states that in two of the six traces (Fig. S7d,f) a linear background was subtracted. The magnitude of the saturated nonlocal resistance is not reported with error bars; the theoretical estimate in Section VII is only a factor-of-3 upper bound, so the measured signal is on the order of ~6 µV for a 2 µA bias. If the individual raw traces do not each show a clear zero baseline at Bz=0, a monotonic mz-like increase, and a reversal with current polarity, then the averaged curve and background subtraction could create the appearance of a saturating signal from noise or drift. The load-bearing assumption is that the reported averaged behavior represents a statistically significant, reproducible effect in the raw data, rather than an artifact of the averaging/subtraction protocol. This is more directly load-bearing than the Py calibration transfer because even a perfect mz calibration does not establish the signal if the underlying data are not significantly above noise.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports an all-electrical nonlocal spin valve measurement in a monolayer WSe2/graphene hybrid device. A DC current through p-doped WSe2 is claimed to generate a transverse spin current with out-of-plane polarization via the spin-locked valley Hall effect; the spins diffuse into a graphene channel and are detected by a permalloy (Py) electrode whose magnetization is tilted out of plane by a perpendicular field. The authors support the claim with a nonmagnetic control, an independent AHE calibration of mz(Bz), a semiclassical sign analysis, and a drift-diffusion model.","tokens_in":11295,"tokens_out":4786,"duration_ms":43893,"significance":"If the observation is robust, this would be the first all-electrical generation and detection of out-of-plane spin polarization via the valley Hall effect in a TMD, with direct relevance for SOT-MRAM and valleytronics. The paper's strengths include the use of a nonmagnetic control, the sign analysis based on Berry curvature and spin-valley locking, and the observation that the nonlocal resistance saturation tracks the independently measured AHE curve. The device geometry and room-temperature operation are also notable. However, the experimental evidence currently rests on a small number of averaged traces without error bars, and the magnitude modelling is a consistency check rather than a parameter-free prediction.","major_comments":[{"comment":"The central claim rests on the nonlocal resistance data in Fig. 3a, which are presented as an average of three datasets with no error bars or per-trace statistics. Supplementary Section II states that in two of the six traces (Fig. S7d,f) a linear background was subtracted. This is a load-bearing issue: if the individual traces do not each show a clear zero baseline at Bz=0, a monotonic mz-like increase, and a reversal with current polarity, the averaging and background subtraction could generate the apparent saturating signal from noise or drift. Please show the raw individual traces, quantify the signal-to-noise and the significance of the effect per trace, and specify the averaging procedure and the background subtraction criteria.","section":"Main text Fig. 3a; Supplementary Section II"},{"comment":"The interpretation of Rnl(Bz) as tracking mz(Bz) relies on transferring the anomalous Hall curve measured on a standalone Py Hall bar to the actual Py probe on graphene. The calibration assumes that the small Py electrode on graphene has the same demagnetization field, anisotropy, and field history as the Hall bar. If the real probe rotates differently, the saturation field and zero-crossing of Rnl would not be expected to match the AHE curve. Please provide evidence that the calibration transfer is valid, for example a local magnetization measurement on a geometrically identical probe, or, failing that, soften the claim that Rnl mirrors the independently measured mz.","section":"Main text Figs. 2-3a"},{"comment":"The sign derivation contains an internal inconsistency in the definition of Vnl. The text defines Vnl = V_NM - V_FM for magnetization along +z, but for magnetization along -z it writes Vnl = V_FM - V_NM > 0, which is the opposite sign convention. Since the sign of the nonlocal voltage is a central claim that distinguishes the spin polarization direction, this inconsistency needs to be resolved and the signs of all four quadrants in Fig. 4 re-derived consistently.","section":"Supplementary Section III"}],"minor_comments":[{"comment":"The heading 'Upper Bond' should be 'Upper Bound'.","section":"Supplementary Section VII heading"},{"comment":"The caption is truncated (it ends with 'lch=1.2um, w1'); please complete the figure caption.","section":"Fig. 4 caption"},{"comment":"The symbols sz and mz are used without formal definition; please define those quantities when they first appear.","section":"Main text and Fig. 4"},{"comment":"The model contains free parameters (alpha, beta, lv, lv', and sigma_xy_VH), so the 'upper bound' estimate is not parameter-free. The factor-of-3 agreement with experiment should be presented as a consistency check, not as a parameter-free prediction.","section":"Supplementary Sections VI-VII"},{"comment":"The control device in Fig. 3b consists of a single trace; please state whether the control experiment was reproduced in multiple devices or provide additional control datasets.","section":"Main text and Supplementary Section II"}],"recommendation":"major_revision","confidential_remarks":"The paper addresses an important question, but the experimental evidence is not yet at the level where the word 'unambiguous' is justified. The main concerns are the averaging without error bars, background subtraction in some supplementary traces, and the calibration-transfer assumption. The sign derivation in Supplementary Section III also needs to be made internally consistent. I recommend major revision to address these load-bearing issues."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"You should read this one if you care about all-electrical spin sources for SOT-MRAM. The claim is that monolayer WSe2, when p-doped and driven by a charge current, generates a transverse spin current with out-of-plane polarization via the spin-locked valley Hall effect, and that this spin current is detected nonlocally by a Py contact whose magnetization is tilted out of plane by an external field. That would be a first: prior work used optical injection or Kerr rotation, not a purely electrical generation/detection chain.\n\nWhat the paper does well: the device geometry is sensible, there is a nonmagnetic control that shows no signal, and the sign of the nonlocal voltage is derived from standard Berry-curvature semiclassics rather than fit after the fact. The strongest piece of evidence is Fig. 3a, where the field dependence of the nonlocal resistance tracks the independently measured anomalous Hall curve of a Py Hall bar, including saturation above about 0.8 T. That agreement is not trivial and it is the right kind of fingerprint.\n\nThe soft spots are real and concentrated in the data presentation. The central observation is a small signal on the order of microvolts, but the main plot is an average of three datasets with no error bars, and the supplement admits that two of six individual traces had a linear background subtracted. That is exactly the kind of processing that can manufacture a saturating curve from drift or noise. The calibration transfer from a standalone Py Hall bar to the actual probe in the device is also a concern, though less damaging than the averaging/subtraction issue, because the saturation field matching gives some indirect support. The theoretical magnitude estimate is only an upper bound and depends on several interface parameters (alpha, beta, the valley diffusion lengths), so it does not independently confirm the effect.\n\nIn short, the central claim is plausible and potentially important, but the paper oversells it with the word \"unambiguous.\" As presented, I would not treat this as a closed result. I would send it to a serious referee, because the question matters and the authors have the right device concept. But the referee should require per-device raw traces with error bars, an explicit justification for every background subtraction, and preferably a direct magnetization measurement on the actual probe contact. If those conditions are met, this could become the first convincing all-electrical demonstration. I would bring it to reading group so people can argue about what counts as sufficient evidence.","headline":"Plausible first all-electrical spin-valley Hall effect in WSe2, but the evidence is thinner than the paper's wording—small signals, averaged without error bars, and linear background subtraction in some traces—so it deserves peer review with a demand for raw data.","tokens_in":11907,"tokens_out":1736,"would_cite":true,"duration_ms":21342,"reading_group":"yes","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 an all-electrical WSe2/graphene device that produces a transverse out-of-plane spin current via the spin-locked valley Hall effect and detects it with a ferromagnetic nonlocal probe.","keywords":["valley Hall effect","spin-valley locking","out-of-plane spin polarization","WSe2","nonlocal spin valve","graphene spin channel","spin current generation","transition metal dichalcogenides"],"falsifier":"Replace the in-plane-anisotropy probe with a perpendicularly magnetized electrode: the out-of-plane spin interpretation predicts a maximum nonlocal signal at zero field that reverses with current polarity, whereas an in-plane probe requires the field to cant the magnetization and so shows signal only for $|B_z|>0$. Observing the zero-field signal with a perpendicular detector would confirm the claim; failing to see it would refute the central interpretation.","tokens_in":10886,"feed_emoji":"🧲","tokens_out":11932,"duration_ms":113509,"temperature":0.7,"pith_summary":"The paper claims that an ordinary charge current through p-doped monolayer WSe2 produces a transverse current of spins polarized out of the plane, through the spin-locked valley Hall effect in the valence band. The spins are injected into an overlapping graphene channel and detected as a nonlocal voltage across a ferromagnetic contact whose magnetization is tilted by an out-of-plane magnetic field. The measured resistance tracks the contact's out-of-plane magnetization component, disappears when the contact is nonmagnetic, and reverses sign when the current direction reverses. If correct, this is the first all-electrical demonstration of out-of-plane spin generation in a two-dimensional transition metal dichalcogenide, and it provides a spin source that could switch perpendicularly magnetized memories without the external-field assistance that conventional spin Hall materials require.","feed_headline":"WSe2 device turns charge current into out-of-plane spin current","feed_subtitle":"The spin source could switch perpendicular magnets without an external field.","key_machinery":"The load-bearing mechanism is spin-valley locking in the WSe2 valence band: time-reversal symmetry enforces $\\Omega(K)=-\\Omega(-K)$ and $s(K)=-s(-K)$, and the ~450 meV spin splitting leaves only one spin sub-band at the Fermi level per valley. The anomalous velocity $\\boldsymbol{v}=(e/\\hbar)\\,\\boldsymbol{E}\\times\\boldsymbol{\\Omega}(\\boldsymbol{k})$ then sends opposite-spin holes to opposite transverse edges, converting a longitudinal charge current into a transverse out-of-plane spin current, the coupled valley and spin Hall effect. The detection harnesses a permalloy electrode with in-plane anisotropy: an external $B_z$ tilts its magnetization out of plane by a controllable fraction $m_z$, independently calibrated by anomalous Hall effect on a co-processed Hall bar, so the nonlocal voltage is a direct map of the out-of-plane spin chemical potential in the graphene channel.","core_discovery":"Under a bias applied to p-doped monolayer WSe2, holes in the valence band are spin-valley locked: the K valley carries one out-of-plane spin and the -K valley the opposite. The finite Berry curvature gives these valleys opposite anomalous velocities, so the electric field separates them transversely; the result is a spin current with polarization $\\pm z$ flowing into the overlaying graphene. The nonlocal ferromagnetic detector measures the spin chemical potential only through its out-of-plane component, which is why the signal grows continuously as the applied field $B_z$ pulls the detector magnetization out of plane and saturates for $|B_z|>0.8$ T. Reversing the charge current reverses the spin polarization, and replacing the ferromagnetic probe with a nonmagnetic electrode removes the signal. A drift-diffusion model with valley chemical potentials and interface valley-memory loss reproduces the sign of the nonlocal voltage and puts the interfacial spin polarization at about 38%.","pith_inferences":["If the claim holds, other monolayer transition metal dichalcogenides with large valence-band spin splitting, such as MoSe2 and WS2, should show the same effect, and the relative nonlocal signal sizes could be compared with their predicted spin splittings.","Integrating the same WSe2 source with a perpendicularly magnetized electrode should enable an attempt at field-free spin-orbit torque switching; a successful switching experiment would be a direct device-level validation of the out-of-plane spin interpretation.","Because conduction-band spin splitting in these materials is small, switching the doping from p-type to n-type should suppress the out-of-plane spin signal, providing a clean test that separates valley Hall spin generation from ordinary spin Hall effects.","The interface valley-memory-loss model predicts that improving the WSe2/graphene interface, for example by a barrier layer or a cleaner transfer, should move the measured nonlocal voltage toward the calculated roughly three-times-larger upper bound, a quantitative target for materials engineering."],"forward_implications":["A monolayer WSe2 device can act as a purely electrical source of out-of-plane spin current, with no optical excitation and no external magnetic field required for generation.","Because reversing the charge current reverses the spin polarization, the same device can serve as a switchable spin source for a perpendicularly magnetized electrode.","The nonlocal-voltage-versus-$B_z$ method, calibrated by anomalous Hall effect on a co-processed Hall bar, can be applied to other two-dimensional materials to test for out-of-plane spin accumulation.","The saturation value of the nonlocal signal, compared with the no-loss upper bound, gives a quantitative estimate of the spin/valley polarization surviving the WSe2/graphene interface, about 38% in these devices.","The sign of the nonlocal voltage is tied to the Berry curvature sign and the valley/spin index, so the measurement is a direct electrical readout of the valley polarization flowing into the channel."],"supporting_citations":[{"why":"Predicts coupled spin and valley physics in monolayer TMDs: opposite spins locked to opposite valleys, with the valley Hall effect producing an out-of-plane spin current.","marker":"[10]"},{"why":"Calculates the ~450 meV valence-band spin splitting in WSe2, the feature that makes the hole transport spin-polarized at the Fermi level.","marker":"[11]"},{"why":"Earlier all-electrical observation of valley-coupled topological currents in MoS2; it supplies the electrical measurement geometry the present experiment adapts.","marker":"[17]"},{"why":"Independent all-electrical demonstration of intrinsic valley Hall transport in MoS2, confirming the Berry-curvature mechanism in a related material.","marker":"[18]"},{"why":"Prior direct detection of valley/spin injection from MoS2 into graphene, but with optical excitation; the present work replaces that with electrical generation.","marker":"[24]"},{"why":"Describes the oxygen-plasma p-doping scheme used to convert the top WSe2 layer to WOx and give sufficient hole carriers in the valence band.","marker":"[26]"},{"why":"Establishes the nonlocal spin-valve detection scheme in graphene that the paper uses to read out the diffused spin chemical potential.","marker":"[27]"},{"why":"The original direct electronic measurement of the spin Hall effect with a nonlocal ferromagnetic probe, the detection principle behind the $B_z$-tilted probe.","marker":"[29]"}],"fun_headline_variants":["Coupled valley and spin Hall effect observed in WSe2","WSe2 generates out-of-plane spin current via valley Hall effect","Valley-spin lock yields out-of-plane spin current in WSe2","WSe2 spin source could switch PMA magnets without external field"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that the magnetic probe in the nonlocal device tilts out of plane under $B_z$ exactly as the separate calibration Hall bar does; if the two rotate differently, the overlay between measured signal and $m_z(B_z)$ loses its meaning.","fun_headline_variants_meta":{"raw":{"variants":["Coupled valley and spin Hall effect observed in WSe2","WSe2 generates out-of-plane spin current via valley Hall effect","Valley-spin lock yields out-of-plane spin current in WSe2","WSe2 spin source could switch PMA magnets without external field"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.001131,"raw_usage":{"total_tokens":4752,"prompt_tokens":1051,"completion_tokens":3701,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":667,"completion_tokens_details":{"reasoning_tokens":3625}},"tokens_in":667,"tokens_out":3701,"duration_ms":23395,"temperature":1.0,"reasoning_tokens":3625,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T15:14:36.378832+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Replace the in-plane-anisotropy probe with a perpendicularly magnetized electrode: the out-of-plane spin interpretation predicts a maximum nonlocal signal at zero field that reverses with current polarity, whereas an in-plane probe requires the field to cant the magnetization and so shows signal only for $|B_z|>0$. Observing the zero-field signal with a perpendicular detector would confirm the claim; failing to see it would refute the central interpretation.","supporting_citations":[],"review_version":1}