{"id":"34d2277b-ed7b-4dd2-8be7-fe1b9bcc1891","arxiv_id":"2505.04244","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"A single GeTe-Ni junction shows spin-valve-like magnetoresistance hysteresis at room temperature for in-plane fields, attributed by the authors to spin-dependent scattering between topological surface states of GeTe and ferromagnetic nickel.","lead":"GeTe-nickel junctions show magnetic-field hysteresis in electrical resistance, with resistance peaks that mirror when the field sweep direction reverses, even at room temperature. The authors attribute this spin-valve-like behavior to scattering between nickel's magnetization and the spin-polarized surface states of the topological semimetal, which could matter for ambient-temperature spintronics.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The spin-valve interpretation requires the GeTe surface-state spin texture to act as a second switchable magnetic layer; no measurement or established mechanism supports this, and the GeTe-Au control cannot exclude Ni-only magnetoresistance.","rationale":"The observed transport data are plausible, and the device-to-device consistency, the Cd3As2 comparison, and the flat Au reference are useful independent checks. The stress test, however, identifies a deeper problem than missing controls. The paper needs a second switchable magnetic layer to explain a spin valve, and it assigns this role to surface-state spin textures without supplying either a measurement or a theoretical mechanism for their field-induced reorientation. In a time-reversal-invariant nonmagnetic semimetal, the equilibrium spin texture of Rashba-split or Fermi-arc surface states has zero net spin density; spin-momentum locking ties spin to k, so an external magnetic field cannot act as a torque that reorients the texture like a ferromagnet. The diamagnetic bulk argument in Section IV rules out bulk ordering but does not close this conceptual gap. The GeTe-Au control is insufficient because it contains no nickel: it can only show that Ni is necessary, not that topological surface states are the relevant Ni-dependent scattering partner. The PbTe-Ni control proposed above would directly test whether topological surface states are required. Until such a control is done, the central mechanism claim remains conditional. No change to the reader's CONDITIONAL verdict is needed.","tokens_in":11306,"tokens_out":6607,"duration_ms":69705,"concrete_test":"Prepare the same three-point junction geometry with a nontopological, nonmagnetic, strongly spin-orbit-coupled semiconductor of similar carrier density, for example PbTe, replacing GeTe, using the same Ni leads and the same measurement protocol. Measure dV/dI(H) at 300 K for in-plane magnetic fields. If PbTe-Ni reproduces the mirrored hysteresis, the topological surface-state texture is not required for the effect; if the response is flat, the surface-state interpretation is supported.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central mechanism claim is not merely under-controlled; it presupposes a property that is probably absent. A spin valve requires two magnetic layers whose relative orientation can be switched. The paper proposes that the spin-momentum-locked surface-state texture of alpha-GeTe (and similarly Cd3As2 Fermi arcs) is the second layer, stating in Section IV that both spin-ordered layers can be reoriented by fields around ±0.5 kOe. But these are spin-momentum-locked states in a time-reversal-invariant, nominally nonmagnetic material. Such textures carry no net equilibrium magnetization that an external field can reverse hysteretically; the spin direction is locked to crystal momentum, not to the field. No magnetization, spin-resolved transport, or Hanle or spin-torque measurement is presented to show a switchable surface-state magnetization. The flat GeTe-Au reference in Fig. 3(b) removes Ni and therefore cannot exclude Ni-only mechanisms such as interface magnetoresistance, stray-field effects, or anisotropic magnetoresistance of the Ni film. The Cd3As2-Ni comparison shows universality across topological semimetals, but it does not isolate topological surface states from generic semimetal/Ni interface effects. Thus the load-bearing assumption, a switchable surface-state magnetic layer, is unverified and is in tension with the nonmagnetic, spin-momentum-locked nature of the surface states.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports differential resistance dV/dI(H) measurements of single GeTe-Ni and Cd3As2-Ni junctions at room temperature and 4.2 K. For magnetic fields parallel to the junction plane, the authors observe hysteretic dV/dI(H) curves with mirrored peaks centered at about ±0.5 kOe at room temperature; for normal fields, similar features appear only at low temperatures. A reference GeTe-Au junction shows flat dV/dI(H). On this basis, the authors attribute the effect to spin-valve-like spin-dependent scattering between the spin textures of topological surface states in the semimetal and the ferromagnetic nickel electrode, and claim that this enables room-temperature spin-to-charge conversion in α-GeTe.","tokens_in":11563,"tokens_out":3343,"duration_ms":37864,"significance":"If the proposed mechanism is correct, the observation would be significant: a single ferromagnetic contact on a nonmagnetic topological semimetal could provide a spin-valve response and efficient spin-to-charge conversion at ambient conditions. The paper has clear experimental strengths: it reports measurements on multiple junctions, includes a Cd3As2 comparison and a GeTe-Au reference, verifies sample phase purity by XRD and EDX, checks sweep-rate independence, and shows that the peak positions are insensitive to dc bias current. However, the central mechanistic claim rests on assumptions that are not directly tested, and at least one of these assumptions is in tension with the known physics of spin-momentum-locked surface states in nonmagnetic semimetals. The empirical observation may be valuable, but the paper's interpretation as a surface-state spin valve is not established by the presented data.","major_comments":[{"comment":"The load-bearing assumption is that the spin texture of the nonmagnetic topological semimetal acts as a second switchable magnetic layer whose orientation relative to the Ni electrode changes the junction resistance. However, spin-momentum-locked surface states in a time-reversal-invariant nonmagnetic material carry no net equilibrium magnetization; their spin direction is locked to crystal momentum and cannot be hysteretically reoriented by an external magnetic field as if it were a ferromagnet. No magnetization measurement, spin-resolved transport, Hanle measurement, or spin-torque experiment is presented to demonstrate a switchable surface-state magnetization. The observed hysteresis can therefore not be uniquely attributed to the proposed spin-valve mechanism.","section":"Section IV, paragraphs 1-4"},{"comment":"The GeTe-Au reference junction is flat, but this control removes the nickel electrode entirely and thus cannot exclude mechanisms that require nickel but do not involve topological surface states, such as Ni-driven interface magnetoresistance, stray-field effects, or anisotropic magnetoresistance of the Ni film. To support the claim that the effect is specific to spin-texture scattering, the authors need a control with Ni on a non-topological semimetal or a nonmagnetic metal, or a direct comparison of Ni-only structures.","section":"Section III, Fig. 3(b)"},{"comment":"The argument that the effect cannot be solely ascribed to Ni reorientation relies on the temperature dependence of the normal-field response and on the different reorientation fields in Cd3As2-Ni versus GeTe-Ni. However, the hysteresis loop of the Ni film itself is never measured. If the observed resistance changes simply track the magnetization reversal of the Ni electrode or of a Ni-related interfacial magnetic layer, then the different coercivity-like fields could reflect differences in the local magnetic environment rather than an intrinsic property of the topological surface states. A direct magnetization or anomalous Hall measurement on the same Ni film, or a control junction with Ni on a trivial semimetal, is needed.","section":"Section IV, paragraph 5"},{"comment":"The sign of the in-plane magnetoresistance is positive in one GeTe-Ni junction and negative in the other, attributed to device-to-device variation. In a conventional spin valve, the sign of the resistance change depends on the equilibrium relative orientation of the two magnetic layers. If the surface-state spin texture is the second layer, the sign should be reproducible or its variation should be explained by a concrete mechanism such as different crystallographic orientation or interface quality. Without such an explanation, the sign variability weakens the spin-valve interpretation and suggests that spurious contributions may be present.","section":"Section III, Fig. 2(a) and (c)"}],"minor_comments":[{"comment":"The inset of Fig. 1 mentions '10 µm separated thick Ni ferromagnetic leads,' while the text says '10 µm wide ferromagnetic Ni leads'; please clarify whether 10 µm is the width, the separation, or both.","section":"Section II, Fig. 1 caption and text"},{"comment":"There is a typo: 'CeTe-Ni' should be 'GeTe-Ni'.","section":"Section III, paragraph 2"},{"comment":"The word 'nichel' appears in the description of thermal evaporation; it should be 'nickel'.","section":"Section II, paragraph 3"},{"comment":"The author list in reference 39 contains the garbled string 'J. S/suppress lawińska'; this reference needs to be corrected.","section":"Reference 39"}],"recommendation":"major_revision","confidential_remarks":"The experimental data appear to show a genuine hysteretic magnetoresistance in GeTe-Ni and Cd3As2-Ni junctions, but the paper's central mechanistic conclusion is not supported by the presented controls. The authors may be able to strengthen the manuscript by adding a Ni-only or trivial-semimetal control, measuring the magnetization of the Ni film, and softening the interpretation to distinguish the empirical observation from the surface-state spin-valve mechanism. As it stands, the claim of room-temperature spin-to-charge conversion mediated by topological surface states goes beyond what the data establish."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe thing to know: this paper reports a room-temperature hysteretic dV/dI(H) response in single GeTe-Ni junctions with in-plane field, mirrored peaks, and similar behavior in Cd3As2-Ni. That observation is new and the data look genuine. The interpretation, however, leans heavily on a mechanism that the transport data do not support.\n\nGenuine strengths first. The sample prep is careful: XRD shows single-phase α-GeTe, EDX confirms composition, and the paper includes two GeTe-Ni junctions, a Cd3As2-Ni junction, and a flat GeTe-Au reference. The anisotropy—effect at room temperature only for in-plane field, appearing in normal field only at 4.2 K—is a real constraint. So is the insensitivity to dc bias. These are useful controls for a transport study.\n\nThe soft spot is the spin-valve model. A spin valve needs two magnetic layers whose relative orientation switches. The paper assigns that role to the topological surface-state spin texture. But a spin-momentum-locked state in a nonmagnetic, time-reversal-invariant semimetal carries no net equilibrium magnetization that an external field can reverse hysteretically. The texture twists with crystal momentum, not with the field. No magnetization, Hanle, spin-torque, or spin-resolved measurement is offered to show a switchable surface-state layer. The Au reference removes Ni entirely, so it cannot exclude Ni-only magnetoresistance, stray-field effects, or interface-chemistry magnetism. The Cd3As2 comparison broadens the phenomenology but still involves the same Ni contact. These are not minor caveats; they bear directly on the central claim. The paper also calls the effect \"efficient spin-to-charge conversion\" without measuring any conversion signal.\n\nIs the effect real? Probably there is some reproducible hysteretic magnetoresistance tied to the Ni electrode. Whether topological surface states are involved at all remains an open question. I would publish the observation, but only with the spin-valve mechanism reframed as one possible explanation and with a clear statement of what is missing.\n\nRecommendation: send to peer review. The experiment deserves scrutiny and the authors have done enough careful work to warrant referee time. With the mechanism section rewritten and controls added, this could become a useful report. If no further experiments are possible, the title and abstract need to stop asserting spin-valve scattering from surface states.","headline":"Room-temperature hysteresis in GeTe-Ni junctions is likely real, but the topological surface-state spin-valve mechanism is not established by the present data.","tokens_in":12112,"tokens_out":2795,"would_cite":true,"duration_ms":29520,"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":"A single GeTe–nickel junction shows room-temperature spin-valve hysteresis that the authors trace to spin-dependent scattering between topological surface states and the ferromagnetic nickel electrode.","keywords":["spin-valve effect","topological semimetal","surface states","spin-momentum locking","Rashba splitting","magnetoresistance","spin-to-charge conversion","GeTe-Ni junction"],"falsifier":"Make an identical three-point measurement on a GeTe–Pt junction: platinum has comparable spin-orbit coupling but no topological surface states, so if the same mirrored $dV/dI(H)$ hysteresis appears there, the topological-surface-state explanation fails; alternatively, insert a 1–2 nm insulating barrier between the nickel and GeTe and check whether the spin-valve signal survives decoupling of the direct interface.","tokens_in":11110,"feed_emoji":"🧲","tokens_out":11152,"duration_ms":95457,"temperature":0.7,"pith_summary":"The paper reports that a single junction between the nonmagnetic topological semimetal $\\alpha$-GeTe and a thick nickel film behaves like a spin valve: in an in-plane magnetic field, the differential resistance $dV/dI(H)$ shows mirrored hysteresis with peaks centered at $\\pm 0.5$ kOe even at room temperature. The authors attribute this to spin-dependent scattering between the spin-textured topological surface states of $\\alpha$-GeTe and the ferromagnetic nickel electrode. Supporting observations are the flat magnetoresistance of a GeTe–Au reference junction, a similar spin-valve response in Cd$_3$As$_2$–Ni junctions, and the strong anisotropy between in-plane and out-of-plane fields. If the interpretation is right, a nonmagnetic topological semimetal can give efficient spin-to-charge conversion at ambient conditions using only one ferromagnetic contact.","feed_headline":"A single GeTe–nickel contact acts as a room-temperature spin valve","feed_subtitle":"Mirrored resistance hysteresis at 300 K in a GeTe–nickel junction, suggesting practical spin-to-charge conversion.","key_machinery":"The load-bearing mechanism is the spin-valve effect: resistance depends on the relative alignment of two spin-polarized layers, here the ferromagnetic nickel film and the spin-momentum-locked surface states of the topological semimetal. The second layer is not a conventional magnet but a spin texture with in-plane spin orientation, reoriented by low in-plane fields around $\\pm 0.5$ kOe; out-of-plane reorientation requires larger fields near $\\pm 2$ kOe, matching the observed anisotropy. The mirrored $dV/dI(H)$ peaks for opposite sweep directions are the signature that the two spin systems reverse at different fields, with antiparallel orientation in between.","core_discovery":"In the paper's own terms, the central claim is that the spin-valve hysteresis observed in GeTe–Ni junctions originates from spin-dependent scattering between the spin textures of the topological surface states and the ferromagnetic nickel electrode. The bulk of $\\alpha$-GeTe is diamagnetic and the GeTe–Au reference is flat, so the authors conclude that the nickel electrode is essential but not sufficient: the semimetal's spin-momentum-locked surface states act as a second spin-polarized layer whose orientation relative to nickel can be switched by magnetic field. The same behavior in Cd$_3$As$_2$–Ni junctions indicates that the effect is not specific to GeTe's bulk spin textures, pointing to the surface states as the common element. Room-temperature operation in in-plane fields follows from the giant Rashba splitting and finite Berry curvature of $\\alpha$-GeTe at 300 K.","pith_inferences":["If the paper is right, the surface-state spin texture is effectively acting as a magnetic layer with no net magnetization; a direct test would be to tune the surface-state spin polarization by doping or electrostatic gating and check that the hysteresis amplitude tracks it.","The same mechanism suggests that other nonmagnetic topological materials with strongly spin-polarized surface states could replace GeTe and offer switching fields set by their own spin-texture anisotropy.","A control with a heavy nonmagnetic metal such as Pt (strong spin-orbit coupling but no topological surface states) would isolate the topological contribution; if Pt shows the same hysteresis, the surface-state explanation would need revision.","The paper does not directly measure the relative orientation of the nickel and surface-state spins; a spin-sensitive probe, such as tunneling magnetoresistance through a barrier or magneto-optical imaging of the nickel electrode, could verify the assumed antiparallel configuration."],"forward_implications":["A single ferromagnetic contact suffices: no second ferromagnetic layer or exchange-biased reference layer is needed for a spin-valve-like response.","Room-temperature spin-to-charge conversion becomes possible at ambient conditions in $\\alpha$-GeTe–Ni junctions, with switching fields near $\\pm 0.5$ kOe for in-plane fields.","The effect appears generic to ferromagnet–topological-semimetal junctions, since both GeTe and Cd$_3$As$_2$ show similar hysteresis, so other spin-textured semimetals should behave likewise.","The flat GeTe–Au reference shows that the hysteretic signal is not an intrinsic property of the semimetal or its contacts to normal metals, but requires the ferromagnetic electrode.","The insensitivity of the peaks to dc bias current indicates that the effect is not driven by current-induced torques, supporting an equilibrium spin-texture mechanism."],"supporting_citations":[{"why":"It establishes the giant Rashba-split surface states of $\\alpha$-GeTe(111) and their decoupling from the bulk, which are the presumed spin-textured layer in the junction.","marker":"45"},{"why":"It reports the nontrivial spin textures and type-II Weyl fermions in $\\alpha$-GeTe, used to argue that surface-state, not bulk, spin textures are the common element.","marker":"47"},{"why":"It demonstrates nearly complete spin polarization of Fermi arcs in a nonmagnetic Weyl semimetal, supporting the surface states as a strongly spin-polarized layer.","marker":"6"},{"why":"It describes the in-plane, predominantly antiparallel spin textures of neighboring Fermi arcs, the basis for treating the surface states as a switchable spin layer.","marker":"2"},{"why":"It defines the spin-valve effect as resistance depending on the relative magnetization orientation of two ferromagnetic layers, the framework the paper applies to nickel and the surface states.","marker":"22"},{"why":"It provides earlier experimental evidence of spin-valve behavior in ferromagnet–topological-material contacts, and the junction preparation technique used here.","marker":"31"},{"why":"It similarly demonstrates spin-dependent transport in topological-material junctions with ferromagnetic leads, supporting the feasibility of the observed effect.","marker":"32"},{"why":"It shows the nonlinear Hall effect in $\\alpha$-GeTe at 300 K, evidence of finite Berry curvature at room temperature that the authors link to the room-temperature spin valve.","marker":"48"},{"why":"It gives the carrier concentration of GeTe used to show that the series resistance of the lead and bulk is far below the measured interface resistance.","marker":"53"}],"fun_headline_variants":["GeTe–Ni junction: room-temperature spin valve from surface states","Topological surface states drive room-temperature spin valve in GeTe–Ni","Spin-valve effect at 300 K from topological surface states in GeTe–Ni junction","Single GeTe–Ni junction: room-temperature spin valve via spin textures","Topological surface states enable room-temperature spin valve in GeTe–Ni contact"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the flat GeTe–Au reference junction rules out every nickel-related magnetoresistance mechanism, leaving scattering between the topological surface states and the nickel electrode as the only source, but the Au reference contains no nickel and therefore cannot exclude effects that require nickel but not the surface states, such as nickel-driven interface magnetoresistance or stray-field effects.","fun_headline_variants_meta":{"raw":{"variants":["GeTe–Ni junction: room-temperature spin valve from surface states","Topological surface states drive room-temperature spin valve in GeTe–Ni","Spin-valve effect at 300 K from topological surface states in GeTe–Ni junction","Single GeTe–Ni junction: room-temperature spin valve via spin textures","Topological surface states enable room-temperature spin valve in GeTe–Ni contact"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000868,"raw_usage":{"total_tokens":3734,"prompt_tokens":892,"completion_tokens":2842,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":508,"completion_tokens_details":{"reasoning_tokens":2742}},"tokens_in":508,"tokens_out":2842,"duration_ms":17329,"temperature":1.0,"reasoning_tokens":2742,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T23:33:01.254285+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Make an identical three-point measurement on a GeTe–Pt junction: platinum has comparable spin-orbit coupling but no topological surface states, so if the same mirrored $dV/dI(H)$ hysteresis appears there, the topological-surface-state explanation fails; alternatively, insert a 1–2 nm insulating barrier between the nickel and GeTe and check whether the spin-valve signal survives decoupling of the direct interface.","supporting_citations":[{"cited_title":"Kremer, T","cited_arxiv_id":null,"evidence_quote":"It establishes the giant Rashba-split surface states of $\\alpha$-GeTe(111) and their decoupling from the bulk, which are the presumed spin-textured layer in the junction."},{"cited_title":"Guedes, Marco Caputo, Milan Radovi\\'c, Valentine V","cited_arxiv_id":null,"evidence_quote":"It reports the nontrivial spin textures and type-II Weyl fermions in $\\alpha$-GeTe, used to argue that surface-state, not bulk, spin textures are the common element."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It demonstrates nearly complete spin polarization of Fermi arcs in a nonmagnetic Weyl semimetal, supporting the surface states as a strongly spin-polarized layer."},{"cited_title":"Dieny, V","cited_arxiv_id":null,"evidence_quote":"It defines the spin-valve effect as resistance depending on the relative magnetization orientation of two ferromagnetic layers, the framework the paper applies to nickel and the surface states."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It similarly demonstrates spin-dependent transport in topological-material junctions with ferromagnetic leads, supporting the feasibility of the observed effect."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"It gives the carrier concentration of GeTe used to show that the series resistance of the lead and bulk is far below the measured interface resistance."}],"review_version":1}