{"id":"734676e8-38b1-43da-8bb1-58e28300620d","arxiv_id":"2505.10984","paper_version":1,"verdict":"REJECT","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"high","formal_verification":"none","parameter_count":3,"one_line_summary":"YBCO thin films near Tc show very large angle-dependent magnetoresistance and planar Hall effect, interpreted as evidence for strong spin-orbit coupling and spin-polarized quasiparticles.","lead":"Researchers report exceptionally large anisotropic magnetoresistance and a planar Hall effect near the superconducting transition of YBCO thin films, which they attribute to spin-orbit coupling in a material long thought to lack it. If correct, the result overturns a core assumption about cuprates and opens a route to superconducting spintronics at liquid nitrogen temperature.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The >1000% AMR and sin-cos PHE are measured inside the superconducting transition without modeling the anisotropic critical-field baseline, so the claimed direct evidence for strong spin-orbit coupling in YBCO is not established.","rationale":"The reader's weakest assumption identifies the same decisive gap: the paper never excludes the anisotropic critical-field response of YBCO as the origin of the angular magnetoresistance. This is not a minor correction but the dominant physics at 88 K and 8 T, where the superconducting transition boundary is sharply angle-dependent. The planar Hall signal can be a tensor consequence of an angle-dependent longitudinal resistance, so it does not independently fingerprint spin-orbit coupling. The paper's phenomenological model is explicitly qualitative and its field-dependent fits use three free parameters without predictive constraints. I therefore see no reason to change the reader's REJECT verdict: the transport data may be valuable, but the central claim of strong spin-orbit coupling in YBCO is unsupported as presented.","tokens_in":9879,"tokens_out":11734,"duration_ms":131724,"concrete_test":"Use the same films' measured R(H_z, T=88K) and an independently estimated anisotropy gamma = Hc2_ab/Hc2_c to compute the expected Rxx(theta) from the anisotropic-GL critical-field formula Hc2(theta) = Hc2_c / sqrt(cos^2(theta) + gamma^2 sin^2(theta)); compare with Fig. 3b. If this no-SOC baseline reproduces the sharp in-plane dips and the >1000% amplitude, the central claim is not supported. As an additional control, remeasure Rxy(phi) with current and voltage contacts swapped to rule out contact-misalignment conversion of Rxx into the purported planar Hall effect.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing assumption is that the angular magnetotransport near Tc cannot be explained by the conventional anisotropic upper critical field of a layered superconductor. The measurements are taken at 88 K and 8 T, inside the superconducting transition, where YBCO has Hc2_ab >> Hc2_c. Fig. 3b shows the expected fingerprint: Rxx is high whenever the field has an out-of-plane component and drops sharply when the field is within about 10 degrees of the film plane. The paper does not model or subtract this baseline, nor does it measure the angular Hc2 of the same films. The reported cos^2(phi) longitudinal dependence and sin(phi)cos(phi) transverse dependence are generic forms for an angle-dependent resistivity; a small contact asymmetry in a Hall bar converts a large angle-dependent Rxx directly into a spurious PHE of the observed symmetry. The field-dependence fit Rxy = nQP/(1+exp(H1/(H+H0))) is a generic S-shaped curve with three free parameters and no independent constraint from spin-orbit physics. The manuscript's own language ('We propose', 'a simplistic model', 'Further studies are required') concedes the SOC model is not quantitative. Therefore the central claim of direct experimental evidence for SOC in YBCO rests on excluding a textbook baseline that is never addressed.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports angular-dependent longitudinal and transverse resistances in YBCO thin films measured near the superconducting transition (88 K, 8 T), including an in-plane anisotropic magnetoresistance in excess of 1000%, a planar Hall resistance of order 1 ohm, and nonlinear current-dependent Hall signals. The authors attribute these observations to spin-polarized quasiparticle transport and strong spin-orbit coupling, and they claim direct experimental evidence of SOC in a cuprate superconductor. Additional measurements as functions of temperature, magnetic field, film thickness, and doping are presented to support the proposed picture.","tokens_in":10193,"tokens_out":11036,"duration_ms":121779,"significance":"If the interpretation were correct, the work would be significant for superconducting spintronics and for the current understanding of spin-orbit coupling in cuprates. The experimental data are systematic, the figures are clear, and the paper explicitly connects its observations to recent spin-resolved photoemission results in bismuth-based cuprates. However, the central claim is not established: the measurements are performed inside the superconducting transition, and a conventional baseline, namely the anisotropic upper critical field of a layered superconductor, is neither modeled nor excluded. The transverse signal may also be contaminated by contact misalignment in the presence of a very large angle-dependent longitudinal resistance. The raw observations are potentially interesting, but the claimed SOC evidence is not supported by the analysis as presented.","major_comments":[{"comment":"The sharp drop in Rxx when the field is within about 10 degrees of the film plane is the expected signature of the anisotropic upper critical field of layered YBCO, where Hc2_ab is much larger than Hc2_c. At 88 K and 8 T, for most out-of-plane angles the perpendicular field component exceeds Hc2_c, driving the film into a high-resistance state, while for angles near theta = 90 degrees and 270 degrees the perpendicular component drops below Hc2_c and the film becomes superconducting. The manuscript does not measure Hc2(theta) for these films and does not fit or subtract an anisotropic Ginzburg-Landau or effective-mass model. Therefore the observed angular dependence of Rxx cannot be attributed to spin-orbit coupling without first excluding this textbook mechanism.","section":"Fig. 3b and 'Sample description and planar Hall effect measurements'"},{"comment":"The planar Hall signal of order 1 ohm is measured in a geometry in which the longitudinal resistance varies by more than 1000% with angle. Under these conditions, a small contact offset in the Hall bar can mix a fraction of the large angle-dependent longitudinal resistance into the transverse channel, producing a spurious signal with the observed sin(phi)cos(phi) symmetry. The manuscript does not report antisymmetrization with respect to field reversal or current reversal, nor does it quantify the contact misalignment. The existence of an intrinsic planar Hall effect is therefore not established.","section":"Fig. 1d and 'Sample description and planar Hall effect measurements'"},{"comment":"The field dependence of Rxy is fitted with the three-parameter expression Rxy = nQP/(1 + exp(H1/(H + H0))). This is a generic sigmoid and can describe many smooth saturation curves, including the ordinary field-induced suppression of superconductivity in the transition region. The parameters nQP, H1, and H0 are not independently determined by any spin-orbit or quasiparticle model, so the quality of the fit does not provide evidence for spin-polarized quasiparticles or strong spin-orbit coupling.","section":"Fig. 2d and field-dependence fits"},{"comment":"The sign reversal of the nonlinear Hall signal R_NL_xy is rationalized by invoking doping-dependent helicity from reference [24], but no spin-texture measurement or microscopic calculation for YBCO is provided. This is a post hoc explanation rather than a tested prediction. Moreover, the manuscript itself describes the model as 'a simplistic model' and states that 'further studies are required'. This language is inconsistent with the abstract's claim of 'direct experimental evidence of SOC in YBCO', and it further weakens the central conclusion.","section":"'Signatures of the spin-orbit coupling'"}],"minor_comments":[{"comment":"The figure axis and the text do not make explicit whether the plotted quantity is the raw Rxx or a normalized anisotropic magnetoresistance ratio. If AMR is defined as [R(phi)-R_min]/R_min, the definition should be stated in the caption or text.","section":"Fig. 1d"},{"comment":"The label 'AHE dips' is misleading for a non-magnetic superconductor; the sign-reversing Hall effect observed near Tc is not an anomalous Hall effect in the conventional sense. Consider using a term such as 'Hall-sign-reversal dips'.","section":"Fig. 4a"},{"comment":"A dc current of 5 mA is applied to Hall bars with widths of 20-50 microns and thicknesses down to 15 nm. This corresponds to a large current density, and current-induced heating or phase-slip processes near Tc could affect the measured nonlinear signals. The authors should comment on current-density checks or show that the signals are independent of current.","section":"Methods and device fabrication"},{"comment":"The text repeatedly refers to 'a typical YBCO device' for the central results. The number of measured devices and the device-to-device variation should be reported, especially for the doping and thickness comparisons in Fig. 4.","section":"Throughout"}],"recommendation":"reject","confidential_remarks":"The central difficulty is that the observed angular magnetoresistance near Tc is very plausibly explained by the conventional anisotropic upper critical field of YBCO, and the manuscript never tests this baseline. The planar Hall signal may also be a contact-artifact of the large longitudinal anisotropy. These are not small presentation issues; they undermine the paper's core claim. A future resubmission could be considered if the authors provide angular Hc2 measurements of the same films, a quantitative model of the conventional baseline, and contact-misalignment calibrations, but the manuscript in its present form does not support the claimed direct evidence of spin-orbit coupling in YBCO."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe headline: this paper reports a genuinely new observation—anisotropic magnetoresistance in excess of 1000% and a planar Hall resistance near 1 ohm in YBCO thin films near Tc, with no ferromagnet anywhere in the device. That is not something I have seen before in a centrosymmetric cuprate, so it deserves attention.\n\nWhat the paper does well: the measurements are systematic. They cover temperature, field amplitude, field angle, film thickness, and doping. The PHE tracks the superconducting transition, vanishes in the normal state, and correlates with the dip in the out-of-plane Hall effect across three film thicknesses. The nonlinear transverse and longitudinal signals follow cos and sin angular dependencies. The experimental work looks careful, and the data are presented clearly.\n\nThe soft spot is exactly where the reader put it, and it is a load-bearing one. The central claim—that these effects come from spin-polarized quasiparticles and strong spin-orbit coupling—depends on ruling out the conventional anisotropic upper critical field of layered YBCO. Figure 3b shows the resistance dropping sharply when the field is within about 10 degrees of the film plane, which is precisely what you expect from Hc2_ab >> Hc2_c. The paper never models this baseline, never measures the angular Hc2 of the same films, and never shows that an anisotropic mass or flux-flow model fails to reproduce the data. Without that, the \"AMR\" is just what a layered superconductor does near Tc when you rotate the field from out-of-plane to in-plane.\n\nThe planar Hall effect also has a plausible trivial origin: any large angle-dependent Rxx, combined with a small contact misalignment, produces a sin(phi)cos(phi) transverse signal. No control experiments are shown—no contact swaps, no field-reversal symmetrization, no test on a non-superconducting anisotropic film. The field-dependence fit is a generic three-parameter sigmoid, and the sign change in the nonlinear signal is rationalized post hoc. The paper's own language admits the model is simplistic and qualitative, which is honest, but the abstract claims \"direct experimental evidence of SOC.\" That mismatch is hard to ignore.\n\nTo be fair, the data are probably real, and the PHE near Tc is unusual even if its origin is not spin-orbit. A referee should ask for the Hc2 baseline and the control experiments. That is a fixable omission, not a fatal one in the data themselves.\n\nWho is this for? People working on cuprate spin-orbit physics and superconducting spintronics. If read as \"we have a new anomalous magnetotransport effect near Tc,\" it is useful. If read as \"YBCO has strong SOC,\" it is not established.\n\nRecommendation: send it to peer review. The experimental observation is new and potentially important enough to justify referee time. I would not cite it as evidence of SOC yet, and I would want the baseline addressed. But I would bring it to reading group to discuss what the field should demand before accepting such claims.\n\nBest,\n[You]","headline":"Striking new data on anisotropic magnetotransport near Tc in YBCO, but the SOC interpretation is undercut by an untested anisotropic Hc2 baseline.","tokens_in":10729,"tokens_out":2711,"would_cite":false,"duration_ms":29873,"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":"This paper reports that YBCO thin films show anisotropic magnetoresistance in excess of 1000% and a planar Hall resistance near 1 Ω at 88 K and 8 T, attributing both to spin-polarised quasiparticles and strong spin-orbit coupling.","keywords":["high-temperature superconductors","YBa2Cu3O7-x","spin-orbit coupling","anisotropic magnetoresistance","planar Hall effect","spin-polarized quasiparticles","cuprate superconductors","nonlinear Hall effect"],"falsifier":"Measure, on the same films, the in-plane and out-of-plane upper critical fields (or the resistive transition width as a function of field angle), and compare the angular width of the low-resistance state with the anisotropy of the transition; if the width tracks the anisotropic Hc2 rather than the quasiparticle population, the SOC interpretation fails. Alternatively, rotate the in-plane field with current along two perpendicular crystallographic directions: an SOC origin should rotate the sin/cos patterns with the current axis, while a transition-anisotropy artifact would follow the film plane.","tokens_in":9666,"feed_emoji":"🧲","tokens_out":6707,"duration_ms":62201,"temperature":0.7,"pith_summary":"This paper reports that in thin films of the high-temperature superconductor YBa2Cu3O7−x (YBCO), rotating a magnetic field of 8 T in the plane of the film at 88 K produces an anisotropic magnetoresistance greater than 1000% and a planar Hall resistance close to 1 Ω. The angular symmetries (cos²(φ) and sin(φ)cos(φ)) are the ones seen in ferromagnets, but YBCO is not ferromagnetic and the signals vanish in the normal state. The paper argues that both effects come from quasiparticles that become spin-polarised through Zeeman splitting near the superconducting transition and then scatter anisotropically because of strong spin-orbit coupling. It also reports nonlinear, current-direction-dependent Hall and magnetoresistance signals consistent with spin-polarised transport. If correct, the findings overturn the long-held assumption that spin-orbit coupling is negligible in centrosymmetric cuprates and open a route to superconducting spintronics operating near liquid-nitrogen temperature.","feed_headline":"Magnetoresistance over 1000% traced to spin-orbit in YBCO","feed_subtitle":"A planar Hall signal near 1 ohm appears only at the superconducting transition, pointing to spin-polarised quasiparticles.","key_machinery":"The central mechanism is the spin-polarised quasiparticle. Near Tc, an in-plane magnetic field Zeeman-splits the quasiparticle density of states, populating spin-polarised quasiparticles; strong spin-orbit coupling then produces anisotropic scattering whose angular symmetry is cos²(φ) for the longitudinal resistance and sin(φ)cos(φ) for the planar Hall resistance. A second ingredient is the phenomenological saturation law Rxy = nQP/(1 + exp(H1/(H + H0))), which ties the Hall amplitude to the field-induced quasiparticle density, and the model of a Rashba-type intrinsic field that gives the nonlinear, unidirectional resistance components.","core_discovery":"The paper's central claim is that YBCO, a centrosymmetric cuprate long thought to have negligible spin-orbit coupling, shows transport signatures of strong SOC near its superconducting transition: at 88 K and 8 T, the longitudinal resistance varies with the in-plane field angle as cos²(φ) with an anisotropy exceeding 1000%, while the transverse planar Hall resistance shows sin(φ)cos(φ) behaviour close to 1 Ω. These signals appear only at the onset of superconductivity, peak exactly at the end of the transition, and vanish in the normal state. The paper interprets them as spin-polarised quasiparticle transport: an in-plane field Zeeman-splits the quasiparticle density of states, and strong SOC with spin-momentum locking converts that spin polarisation into anisotropic longitudinal and transverse resistances. It also reports nonlinear, current-direction-dependent Hall and magnetoresistance components with cos(φ) and sin(φ) angular forms, which it models through a Rashba-like intrinsic field. The conclusion is direct experimental evidence of SOC in YBCO and a route towards superconducting spintronics at liquid-nitrogen temperatures.","pith_inferences":["If the SOC interpretation is right, spin-polarised quasiparticles should be detectable by nonlocal spin-transport experiments, such as spin injection through a YBCO channel, which would provide an independent test beyond the resistance measurements.","Because the planar Hall effect is the transverse counterpart of any angle-dependent longitudinal resistance, a clean comparison would be to measure a layered superconductor with similar upper-critical-field anisotropy under the same protocol, since a pure anisotropy artifact would reproduce the effect while an SOC origin would not.","The sign reversal of the nonlinear Hall signal with temperature and doping maps naturally to the helicity of spin-momentum locking, offering a potential transport-based readout of cuprate spin texture across the phase diagram.","Extending the measurements to underdoped films, where the superconducting window broadens, could reveal how the quasiparticle recombination lifetime controls the magnitude and angular width of the effect."],"forward_implications":["Spin-orbit coupling must be added to the physics of cuprate superconductors, at least near the transition, where quasiparticle transport is sensitive to spin texture.","The planar Hall effect and anisotropic magnetoresistance provide a contact-level probe of quasiparticle spin polarisation without requiring a ferromagnet or proximity junction.","The effects can be tuned by oxygen doping, film thickness, temperature, and magnetic field, suggesting that spin-dependent transport in YBCO is controllable.","The observed nonlinear, unidirectional resistance components make YBCO a candidate for studying nonreciprocal transport and possibly nonreciprocal superconducting spintronics.","Because the signals appear near 88 K, the effect operates in a practically accessible temperature window for liquid-nitrogen-cooled devices."],"supporting_citations":[{"why":"Reports hidden spin-momentum locking in a cuprate superconductor, the key precedent that cuprates can host significant SOC.","marker":"[22]"},{"why":"Provides spin-polarisation measurements in bismuth-based cuprates that support the existence of nontrivial spin textures.","marker":"[23]"},{"why":"Shows doping-dependent spin-momentum locking, which the paper uses to explain the sign change of the nonlinear signals.","marker":"[24]"},{"why":"Theoretical predictions of spin-orbit-driven phenomena in cuprate superconductors that the transport results are claimed to confirm.","marker":"[25]"},{"why":"Establishes the Zeeman-splitting mechanism by which an in-plane magnetic field creates spin-polarised quasiparticles in superconductors.","marker":"[14]"},{"why":"Reports spontaneous rotational symmetry breaking in cuprates, the alternative explanation that the paper tests and rules out for the PHE.","marker":"[21]"},{"why":"Introduces bilinear magnetoresistance as a probe of three-dimensional spin texture, the model used for the nonlinear longitudinal response.","marker":"[41]"},{"why":"Demonstrates the nonlinear planar Hall effect in topological systems, the analogue for the nonlinear transverse response reported here.","marker":"[42]"},{"why":"Provides the theory for linear and nonlinear planar Hall effects in topological insulator thin films, used for the qualitative modelling.","marker":"[44]"}],"fun_headline_variants":["YBCO spin-orbit: 1000% AMR and planar Hall at Tc","Cuprates show spin-orbit: giant magnetoresistance without ferromagnet","High-Tc superconductor YBCO exhibits strong spin-orbit at transition","Planar Hall near Tc reveals spin-orbit in YBCO, no ferromagnet"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"Everything hangs on the assumption that the sharp resistance drop for fields nearly in the film plane comes from spin-polarised quasiparticle scattering, rather than from the well-known anisotropy of layered YBCO's superconducting transition in a magnetic field.","fun_headline_variants_meta":{"raw":{"variants":["YBCO spin-orbit: 1000% AMR and planar Hall at Tc","Cuprates show spin-orbit: giant magnetoresistance without ferromagnet","High-Tc superconductor YBCO exhibits strong spin-orbit at transition","Planar Hall near Tc reveals spin-orbit in YBCO, no ferromagnet"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000243,"raw_usage":{"total_tokens":1567,"prompt_tokens":1020,"completion_tokens":547,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":636,"completion_tokens_details":{"reasoning_tokens":457}},"tokens_in":636,"tokens_out":547,"duration_ms":5747,"temperature":1.0,"reasoning_tokens":457,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-15T21:00:31.927207+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure, on the same films, the in-plane and out-of-plane upper critical fields (or the resistive transition width as a function of field angle), and compare the angular width of the low-resistance state with the anisotropy of the transition; if the width tracks the anisotropic Hc2 rather than the quasiparticle population, the SOC interpretation fails. Alternatively, rotate the in-plane field with current along two perpendicular crystallographic directions: an SOC origin should rotate the sin/cos patterns with the current axis, while a transition-anisotropy artifact would follow the film plane.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Reports hidden spin-momentum locking in a cuprate superconductor, the key precedent that cuprates can host significant SOC."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides spin-polarisation measurements in bismuth-based cuprates that support the existence of nontrivial spin textures."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Shows doping-dependent spin-momentum locking, which the paper uses to explain the sign change of the nonlinear signals."},{"cited_title":"M., Allocca, A","cited_arxiv_id":null,"evidence_quote":"Theoretical predictions of spin-orbit-driven phenomena in cuprate superconductors that the transport results are claimed to confirm."},{"cited_title":"S., Silaev, M., Virtanen, P","cited_arxiv_id":null,"evidence_quote":"Establishes the Zeeman-splitting mechanism by which an in-plane magnetic field creates spin-polarised quasiparticles in superconductors."},{"cited_title":"T., He, X","cited_arxiv_id":null,"evidence_quote":"Reports spontaneous rotational symmetry breaking in cuprates, the alternative explanation that the paper tests and rules out for the PHE."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Introduces bilinear magnetoresistance as a probe of three-dimensional spin texture, the model used for the nonlinear longitudinal response."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Demonstrates the nonlinear planar Hall effect in topological systems, the analogue for the nonlinear transverse response reported here."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the theory for linear and nonlinear planar Hall effects in topological insulator thin films, used for the qualitative modelling."}],"review_version":1}