{"id":"ce4432c8-f155-4a08-a298-d6ede3d5d01e","arxiv_id":"2506.06996","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"Spin pumping and the inverse spin Hall effect can electrically read out strongly coupled magnon-photon modes in a superconducting resonator/YIG hybrid at 1.4 K, with the coupling weakened by high microwave power.","lead":"This paper electrically detects strongly coupled microwave photons and magnons at 1.4 kelvin by measuring a spin-pumping voltage in a platinum layer on a yttrium iron garnet film placed on a superconducting resonator. The result matters because electrical readout is a practical route to integrating magnon-photon hybrid systems into quantum circuits.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The electrical-detection claim rests on V_SP being pure ISHE spin pumping, but no rectification/thermoelectric separation is performed even though Ref. [41] is cited; a large background would bias the extracted linewidths and g.","rationale":"The reader's weakest assumption is the most load-bearing one. The sole reason to credit 'electrical detection via ISHE' is the assumption that the measured V(H) is dominated by spin pumping. The paper explicitly cites Ref. [41], the standard method for separating spin pumping from spin rectification, but does not use it; under the manuscript-in-scope rule this is an explicit missing support. The concern is concrete rather than formal because all electrical data are at +20 dBm, a power where the manuscript itself demonstrates resonator nonlinearity and mode bifurcation. A sizable rectification or thermoelectric background would bias the extracted linewidths and coupling strength, directly affecting the g = 105 ± 5 MHz claim and the power-dependence conclusion. The VNA avoided crossing independently supports strong coupling, so the qualitative magnon-photon hybridization does not stand or fall on the electrical measurement; but the paper's headline electrical claim does. The proposed Ref. [41] decomposition plus a thermoelectric control would settle this. Because this was already the basis of the reader's CONDITIONAL verdict, my read does not change the verdict.","tokens_in":9660,"tokens_out":11092,"duration_ms":128916,"concrete_test":"Apply the universal method of Ref. [41] to the field-swept V(H) traces of Fig. 2(b): decompose each trace into V_sym L(H) + V_asym dL/dH and require |V_asym| << |V_sym| near the avoided crossing; also check field-reversal and 180-degree-rotation symmetry of the symmetric component. If the antisymmetric or rotation-odd component is not small, the reported linewidths and electrical g are contaminated by spin rectification. In addition, a control sample with Au replacing Pt would isolate thermoelectric/bolometric backgrounds.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The paper's central new result is the electrical detection of strong magnon-photon coupling through a DC voltage across Pt. The argument requires V(H) to be dominated by ISHE spin pumping, V_SP ∝ |m|^2. Section III states this relation and cites Ref. [41] (the universal separation method), but the experiment never applies it: no field-reversal, in-plane-angle, or control-sample measurement is reported. The risk is concrete because all electrical data are taken at +20 dBm, where the authors' own VNA data show the NbN resonator is nonlinear and bifurcated; in this regime spin-rectification and thermoelectric backgrounds are not negligible. Those backgrounds are not removed by fitting Eq. (2), because that fit uses only peak positions and widths and models near-crossing asymmetry as phase correlation. If a significant background exists, the linewidth broadening in Fig. 2(c) and g = 105 ± 5 MHz are biased, and the agreement with VNA (g = 90 ± 4 MHz) is not exculpatory because the VNA reference is taken in the same nonlinear regime. Internal inconsistencies, e.g., hybridization fields 1.215/1.220 kOe versus 1.275 kOe in Figs. 3-4, further lower confidence in the quantitative parameters. The VNA-only strong-coupling evidence is not at stake; the ISHE-spin-pumping identification is.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports the electrical detection of strongly coupled magnon-photon modes in a YIG/Pt bilayer flip-chipped onto a NbN superconducting coplanar resonator at 1.4 K. A DC voltage across the Pt layer, attributed to the inverse spin-Hall effect (ISHE) from spin pumping, is recorded as a function of magnetic field at fixed microwave frequencies. The data show an avoided crossing of the magnon and resonator modes, a linewidth increase of the magnon mode near the coupling region, and a coupling strength g = 105 ± 5 MHz extracted from fits to the coupled-oscillator dispersion of Ref. [20], in approximate agreement with g = 90 ± 4 MHz obtained from VNA transmission spectra under the same conditions. Power-dependent experiments show that the frequency separation of the hybrid modes shrinks with increasing power, which the authors attribute to the onset of nonlinearity/bifurcation in the superconducting resonator above a threshold power; the appearance of bifurcation in the unloaded and loaded resonator is documented. The central claim is that the spin-pumping voltage provides a faithful electrical readout of the magnon-polariton states and of the power dependence of the coupling.","tokens_in":9946,"tokens_out":13758,"duration_ms":142746,"significance":"The qualitative result — an electrically detected avoided crossing with a correlated linewidth broadening, cross-checked against microwave transmission — is a useful demonstration for hybrid magnon-superconductor circuits operating at cryogenic temperature, where electrical readout is a practical advantage. The paper should be credited for several strengths: the avoided crossing and linewidth enhancement are directly visible in the data rather than being generated by the model; the electrical and VNA channels are measured in a common cryogenic configuration; the fitted parameters (effective magnetization, damping, resonator loss) are consistent between the two channels; and the characterization of the resonator's power-dependent bifurcation is careful and includes the unloaded-resonator control. The power-dependent suppression of the coupling, if confirmed, is an interesting observation for the community.","major_comments":[{"comment":"The identification of the measured DC voltage with ISHE spin pumping is not experimentally established. The analysis assumes V_SP ∝ |m|^2 and the text explicitly cites the universal separation method of Ref. [41], yet no field-reversal, in-plane-angle, or control-sample separation of spin pumping from spin-rectification and thermoelectric contributions is reported. All electrical data were taken at +20 dBm, where the authors' own VNA data (Figs. 3(c)-(d)) place the loaded resonator at or above the onset of bifurcation; in this regime spin-rectification and thermoelectric backgrounds are not negligible, and the approximately Lorentzian shape far from the crossing does not exclude a symmetric rectification component. Because the fits to Eq. (2) use only peak positions and widths, a background would directly bias the linewidth enhancement in Fig. 2(c) and the extracted g = 105 ± 5 MHz; the VNA comparison (g = 90 ± 4 MHz) does not resolve this because it is acquired in the same nonlinear regime. A quantitative bound on the rectification contribution, or the symmetry-based separation of Ref. [41], is needed to support the central electrical-detection claim.","section":"Sec. III, Fig. 2 and Eq. (2), with Ref. [41]"},{"comment":"The hybridization field is quoted as approximately 1.25 kOe in Fig. 2(a), 1.220 kOe at -30 dBm and 1.215 kOe at +20 dBm in Fig. 3(b), and 1.275 kOe in Fig. 4(b), with the text asserting in one place that the hybridization field remains constant across powers. With the fitted 4πM_eff = 2.03 kOe and γ = 2.83 GHz/kOe, these fields correspond to bare Kittel frequencies of approximately 5.73, 5.64, and 5.81 GHz, respectively, which is a larger spread than the stated resonator-frequency uncertainty. Since g is extracted from the mode separation at the hybridization field, a roughly 200 MHz ambiguity in the underlying resonator frequency between the electrical and VNA data sets weakens the quantitative comparison (105 versus 90 MHz). The authors should report the resonator frequency actually used in each run, or provide a field/frequency calibration check, and explain the inconsistency.","section":"Sec. III, Figs. 2-4"},{"comment":"The power dependence of the coupling is inferred from the frequency separation of the upper and lower hybrid branches at the crossing field, but the measurements in that regime are taken where the resonator is explicitly nonlinear: the unloaded resonator already bifurcates above -15 dBm and the loaded resonator above about +15 dBm, with strongly asymmetric lineshapes and abrupt jumps (Fig. 3(d)). Peak positions extracted from such distorted lineshapes are not a reliable proxy for 2g, so the decreasing separation with power does not by itself establish a decrease in the coupling strength. The trend should be validated either by measurements in the linear regime (below the bifurcation threshold of the loaded device) or by fitting the full coupled-oscillator model, including the nonlinear lineshape, to the spectra.","section":"Sec. III, Fig. 4(b) and Fig. 3(d)"}],"minor_comments":[{"comment":"The loaded resonator frequency appears as approximately 5.8 GHz in Sec. II and as 5.9 GHz in the discussion of Fig. 3(d); please reconcile the value used for the loaded device.","section":"Secs. II and III"},{"comment":"The three microwave powers used in Fig. 4(a) are not specified in the text; please give the actual power values.","section":"Sec. III and Fig. 4(a)"},{"comment":"The parenthetical statement that the hybridization field remains constant at 1.275 kOe directly conflicts with the stated shift from 1.220 to 1.215 kOe in the VNA data; please clarify the measurement conditions for each run.","section":"Sec. III, Fig. 4(b)"},{"comment":"Typo: 'in an high-cooperativity system' should read 'in a high-cooperativity system'.","section":"Sec. I"},{"comment":"The sentence 'At the resonance frequency of the SC resonator of ~5.8 GHz, a vanishingly small signal is observed' is ambiguous; it is not clear whether it refers to the spin-pumping signal of the magnon mode at the crossing or to a resonator-frequency band in the voltage map, and it should be clarified.","section":"Sec. III"},{"comment":"The electrical fit to Eq. (2) quotes no uncertainties for 4πM_eff and γ, while the VNA fit quotes 4πM_eff = 2.02 ± 0.10 kOe; a brief description of the fitting procedure, fitting ranges, and uncertainty propagation for the five correlated parameters would strengthen the quantitative comparison between the two channels.","section":"Sec. III, Fig. 2 and Eq. (2)"}],"recommendation":"major_revision","confidential_remarks":"The manuscript is within the journal's scope and the qualitative phenomena appear real; I found no indication of fabrication, and the avoided crossing and linewidth broadening are directly visible in the displayed data. My main editorial concern is that the authors cite Ref. [41], the standard symmetry-based method for separating spin pumping from spin rectification, and even use the proportionality V_SP ∝ |m|^2, yet omit the control experiment whose absence undermines the quantitative electrical claim at the very power where the resonator is nonlinear. This is a fixable omission rather than an intrinsic flaw. I would also urge the editor to ask the authors to supply the resonator frequency and field calibration for each data set, since the hybridization-field inconsistency (1.215-1.275 kOe) is currently unexplained and, if it reflects a frequency drift between runs, it affects the headline comparison of g."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Read this carefully. The central result is solid: they show electrical detection of strongly coupled magnon-photon modes in a NbN superconducting coplanar resonator at 1.4 K via spin pumping ISHE, and the extracted coupling strength agrees with VNA transmission. The avoided crossing and linewidth broadening are visible in the raw data, not manufactured by fitting.\n\nWhat's actually new is the combination: prior work did spin-pumping detection in a copper cavity at moderate temperature (Bai et al.) and strong coupling in superconductor/YIG devices via microwave transmission (Li et al.). This paper brings ISHE electrical readout to the superconducting hybrid platform at cryogenic temperature, and adds a power-dependent tuning mechanism through resonator nonlinearity. The experiment is well executed: flip-chip YIG/Pt on NbN, fitting to the coupled-oscillator model, and VNA cross-check. The explanation for the vanishing resonator mode at high power away from the coupling region is plausible and supported by the unloaded resonator bifurcation data.\n\nSoft spots, in proportion. The biggest is the lack of spin-rectification separation. V_SP is assumed to be pure ISHE spin pumping, with no field-reversal or angle-dependent control, even though the universal separation method (Ref. [41]) is cited. All electrical data are taken at +20 dBm, where the resonator is strongly nonlinear and bifurcated; rectification and thermoelectric backgrounds can be significant there. If such a background exists, the extracted linewidth and coupling strength could be biased, and the agreement with VNA is not exculpatory because the VNA reference is also taken at +20 dBm. That's a real weakness, but it does not invalidate the main demonstration: the avoided crossing and linewidth broadening are robust features. The hybridization field inconsistency (1.215/1.220 vs 1.275 kOe in Figs. 3 and 4) is confusing and should be fixed. The power-dependent data lack error bars, so the claim of decreasing g with power is more qualitative than quantitative.\n\nOverall, the paper is a credible advance for hybrid magnon-photonics. It's worth a serious referee, but needs major revision: add a rectification control (or at minimum a field-polarity swap), re-plot the power dependence with uncertainties, and reconcile the hybridization field values. I'd bring it to a reading group – there's a good discussion about how much clean evidence is needed to claim electrical detection in the nonlinear regime.","headline":"A credible demonstration of electrical detection of strongly coupled magnon-photon modes in a superconducting resonator at 1.4 K, but the missing spin-rectification separation and inconsistent hybridization fields demand revision before the quantitative claims hold.","tokens_in":10510,"tokens_out":2305,"would_cite":true,"duration_ms":23318,"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":"Electrical readout catches magnons and photons coupling at 1.4 K","keywords":["magnon-polaritons","spin pumping","inverse spin Hall effect","superconducting resonator","NbN","strong magnon-photon coupling","YIG/Pt bilayer","microwave power nonlinearity"],"falsifier":"Re-measure the voltage signal with the external magnetic field reversed, or rotate the sample by 180 degrees in the plane, using the universal method of separating spin pumping from spin rectification; if a rectification component of comparable size appears, the electrically extracted linewidths and coupling strength would be distorted. A second check is to measure the coupling strength at low microwave powers where the resonator is linear: if $g$ still decreases with power in that regime, the nonlinear-resonator explanation would be incomplete.","tokens_in":9450,"feed_emoji":"🧲","tokens_out":6206,"duration_ms":59881,"temperature":0.7,"pith_summary":"This paper tries to establish that strong coupling between microwave photons and magnons can be detected electrically, not just by microwave transmission, in a thin-film hybrid at cryogenic temperature. The experiment pairs a bilayer of the magnetic insulator yttrium iron garnet (YIG) with platinum (Pt) and places it onto a superconducting NbN coplanar resonator, reading out the spin-pumping voltage generated by the inverse spin Hall effect at 1.4 K. The voltage spectra show the avoided crossing and linewidth broadening that mark hybridized magnon-photon modes, and the coupling strength extracted electrically ($g = 105 \\pm 5$ MHz) is close to the value from microwave transmission ($g = 90 \\pm 4$ MHz). The paper also reports that the coupling weakens with increasing microwave power because the superconducting resonator becomes nonlinear above a threshold. If the electrical readout is genuine, it offers a route to detecting light-matter coupling in hybrid quantum circuits without bulky cavities.","feed_headline":"Electrical readout catches magnons and photons coupling at 1.4 K","feed_subtitle":"DC voltage across a platinum strip reveals the same avoided-crossing signature as microwave transmission at 1.4 K.","key_machinery":"The load-bearing object is the flip-chip hybrid: a 200 nm YIG film with a 3 nm Pt strip placed on top of a NbN coplanar waveguide resonator, where the resonator mode volume is small and the magnon mode of YIG couples to the microwave magnetic field through the Zeeman interaction. Spin pumping turns the coherent precession into a spin current across the YIG/Pt interface, and the inverse spin Hall effect converts that spin current into a DC voltage measured with a lock-in. The argument is carried by the coupled-oscillator model expressed in Eq. (2), which gives both the resonance field positions (real part) and the coupled-mode linewidths (imaginary part), together with the proportionality $V_{\\mathrm{SP}} \\propto |m|^2$, which ties the measured voltage to the squared magnetization amplitude. This machinery lets the authors extract $g$, $\\alpha$, $\\beta$, and $4\\pi M_{\\mathrm{eff}}$ from electrical data alone and compare them with independent VNA transmission fits.","core_discovery":"On the paper's own terms, the central discovery is that the inverse spin Hall voltage across a platinum stripe can serve as a direct electrical reporter of strongly coupled magnon-photon modes at 1.4 K. As the magnetic field is swept at fixed microwave frequency, the spin-pumping voltage follows a Kittel-like magnon mode that splits into two branches near the resonator frequency, and the magnon linewidth broadens as the modes hybridize. Fitting the field-frequency map to the coupled-oscillator dispersion of Eq. (2) gives an effective magnetization $4\\pi M_{\\mathrm{eff}} = 2.03$ kOe, damping $\\alpha = 9.9 \\pm 3 \\times 10^{-4}$, resonator loss $\\beta = 5.5 \\pm 0.6 \\times 10^{-3}$, and a coupling strength $g = 105 \\pm 5$ MHz, all consistent with the parameters obtained from microwave transmission, where $g = 90 \\pm 4$ MHz. The authors interpret the reduction of the coupling at high microwave power, and the simultaneous disappearance of the bare resonator mode, as the signature of a nonlinear regime of the NbN resonator driven into mode bifurcation, with the hybridized state partially restoring the observable signal.","pith_inferences":["If the electrical readout survives at single-photon power levels, it could serve as an on-chip transducer that connects magnonic and superconducting quantum circuits without a separate microwave link.","The power-dependent decrease of $g$ suggests a possible in-situ tuning knob for magnon-photon coupling, although here it is mediated by added dissipation rather than a clean dispersive shift.","Applying the spin-pumping versus spin-rectification separation at 1.4 K would test whether the voltage lineshape asymmetry near the coupling region is purely a phase-correlation effect or contains a rectification admixture.","Material-level control of NbN grain boundaries, which the paper identifies as weak links, could raise the power threshold for nonlinearity and widen the linear operating range of such hybrids."],"forward_implications":["Strongly coupled magnon-photon modes can be detected electrically in a thin-film, chip-compatible geometry, without a three-dimensional cavity.","The coupling strength read out electrically ($g = 105 \\pm 5$ MHz) agrees with microwave transmission ($g = 90 \\pm 4$ MHz), so spin pumping provides an independent and comparable measure of the avoided-crossing gap.","Magnon linewidth broadening near the coupling region confirms that hybridization increases the effective damping in a way consistent with the coupled-oscillator model.","Microwave power tunes the coupling strength: above a threshold the NbN resonator enters a nonlinear regime, the coupling weakens, and the bare resonator mode is suppressed.","Loading the resonator with the YIG/Pt bilayer shifts the nonlinearity threshold from about $-15$ dBm to above $+15$ dBm, because the added losses broaden the resonator and reduce its intensity."],"supporting_citations":[{"why":"Supplies the coupled-oscillator dispersion relation (Eq. 2) and the $V_{\\mathrm{SP}} \\propto |m|^2$ relation used to fit spin-pumping spectra.","marker":"[20]"},{"why":"Demonstrates strong magnon-photon coupling in on-chip ferromagnet-superconductor devices, the geometry this experiment extends to electrical readout.","marker":"[16]"},{"why":"Provides the planar-geometry strong-coupling result against which the comparatively high extracted $g$ is set.","marker":"[19]"},{"why":"Gives the YIG/Pt damping increase and spin-mixing conductance used to characterize the Pt overlayer.","marker":"[36]"},{"why":"Describes the NbN deposition used to fabricate the superconducting coplanar resonator.","marker":"[37]"},{"why":"Defines the universal method for separating spin pumping from spin rectification, the standard check the electrical signal is implicitly measured against.","marker":"[41]"},{"why":"Explains the mode-bifurcation nonlinearity in NbN resonators that the paper uses to interpret power-dependent suppression of the resonator mode.","marker":"[42]"},{"why":"Attributes cryogenic microwave losses in the GGG substrate to the loaded-resonator quality-factor reduction from 1210 to 105.","marker":"[43]"}],"fun_headline_variants":["Spin Hall voltage sees magnon-photon coupling at 1.4 K","Electrical readout of strongly coupled magnons and photons","Voltage maps magnon-photon hybridization in hybrid resonator","Inverse spin Hall effect detects magnon-photon modes"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The analysis assumes that the DC voltage measured across the platinum strip comes entirely from inverse spin Hall spin pumping of coherent magnetization precession, with no separately measured spin-rectification or thermoelectric background.","fun_headline_variants_meta":{"raw":{"variants":["Spin Hall voltage sees magnon-photon coupling at 1.4 K","Electrical readout of strongly coupled magnons and photons","Voltage maps magnon-photon hybridization in hybrid resonator","Inverse spin Hall effect detects magnon-photon modes"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000199,"raw_usage":{"total_tokens":1357,"prompt_tokens":915,"completion_tokens":442,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":531,"completion_tokens_details":{"reasoning_tokens":372}},"tokens_in":531,"tokens_out":442,"duration_ms":5208,"temperature":1.0,"reasoning_tokens":372,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-07T05:44:09.351226+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-measure the voltage signal with the external magnetic field reversed, or rotate the sample by 180 degrees in the plane, using the universal method of separating spin pumping from spin rectification; if a rectification component of comparable size appears, the electrically extracted linewidths and coupling strength would be distorted. A second check is to measure the coupling strength at low microwave powers where the resonator is linear: if $g$ still decreases with power in that regime, the nonlinear-resonator explanation would be incomplete.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Provides the planar-geometry strong-coupling result against which the comparatively high extracted $g$ is set."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Gives the YIG/Pt damping increase and spin-mixing conductance used to characterize the Pt overlayer."},{"cited_title":"Polakovic, S","cited_arxiv_id":null,"evidence_quote":"Describes the NbN deposition used to fabricate the superconducting coplanar resonator."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Defines the universal method for separating spin pumping from spin rectification, the standard check the electrical signal is implicitly measured against."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Explains the mode-bifurcation nonlinearity in NbN resonators that the paper uses to interpret power-dependent suppression of the resonator mode."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Attributes cryogenic microwave losses in the GGG substrate to the loaded-resonator quality-factor reduction from 1210 to 105."}],"review_version":1}