{"id":"2f59b0b7-66e8-4bba-b7d6-6fa2234d80e8","arxiv_id":"1908.01159","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":5.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"In overdoped Pr1-xLaCexCuO4, the development of Cu-spin correlation decreases with doping and is negligible at x=0.20, where superconductivity is absent.","lead":"Muon spin relaxation measurements on overdoped electron-doped cuprate crystals show that the development of copper-spin correlations weakens as doping increases and nearly vanishes where superconductivity disappears. The result strengthens the case that low-energy spin correlations and superconductivity are linked across the entire doping range of these high-temperature superconductors.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"x=0.17 muSR data stop at 9 K, above its Tc ~ 5 K, so the claim of negligible Cu-spin correlation development there is not empirically supported.","rationale":"I read the paper's central claim as a doping-dependent coexistence between the development of low-energy Cu-spin correlation and superconductivity, with x=0.17 and x=0.20 providing the overdoped end of the trend. The x=0.20 sample is non-superconducting and measured to 0.3 K, so its null result is meaningful. The x=0.17 sample, however, is superconducting with Tc ~ 5 K, but the lowest measured temperature is 9 K, above Tc. The observed lack of lambda/As enhancement down to 9 K does not constrain the superconducting state of x=0.17. Since the reference x=0.14 data at 9 K are within its SC state (Tc ~ 20 K), the comparison is biased in a way that could produce the appearance of a weakened correlation simply because the SC state of x=0.17 was not accessed. This is a concrete experimental gap rather than an interpretive ambiguity and can be settled by extending measurements below Tc. The reader's identified weakest assumption about muon-site assignment and the two-component decomposition is also legitimate, but the temperature coverage issue is more immediate and more load-bearing: even if the decomposition is exactly correct, the x=0.17 conclusion lacks evidence in the relevant temperature range. I therefore maintain the conditional verdict but disagree with the specific weakest assumption identified by the reader.","tokens_in":8253,"tokens_out":6256,"duration_ms":56028,"concrete_test":"Perform ZF-muSR on the same x=0.17 crystal at temperatures below its Tc of ~5 K, e.g., at 2 K and 0.3 K, and fit with Eq. (1). If lambda or As shows a steep increase below Tc, the paper's claim of negligible Cu-spin correlation development in x=0.17 is refuted. If no increase appears down to 0.3 K, the concern is resolved.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim that the development of Cu-spin correlation weakens with increasing x and is negligibly small in the heavily overdoped regime rests on two new samples, x=0.17 and x=0.20. For x=0.20, a non-superconductor, ZF-muSR was measured down to 0.3 K and the null result is meaningful. For x=0.17, however, the lowest measured temperature is 9 K (Section III and Fig. 2(b)), while its Tc is ~5 K as shown in Fig. 1. The superconducting state of x=0.17 was therefore never probed. The comparison with x=0.14 at 9 K is uncontrolled: x=0.14 has Tc ~ 20 K and is deep in its superconducting state at 9 K, where lambda and As are enhanced, whereas x=0.17 at 9 K is above its own transition. The development seen in x=0.14 sets in below ~30 K, but the characteristic temperature for x=0.17 could plausibly be lower, possibly tied to its Tc. Without data below ~5 K, the absence of a steep increase in lambda or As for x=0.17 cannot be taken as evidence that the Cu-spin correlation does not develop. Thus the 'weakens with increasing x' trend is actually supported only by the single non-superconducting x=0.20 sample and by a comparison that does not enter the SC state of x=0.17.","agreement_with_reader":"disagree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This manuscript reports muon spin relaxation (µSR) measurements on the electron-doped cuprate Pr1−xLaxCexCuO4 (PLCCO) at overdoped concentrations x = 0.17 and 0.20, with x = 0.14 results from prior work included for comparison. The authors observe that, unlike the x = 0.14 sample, the x = 0.17 and x = 0.20 samples do not show a low-temperature increase in the stretched-exponential relaxation rate λ or a recovery of the initial asymmetry As. They interpret this as evidence that the development of low-energy Cu-spin correlation weakens with increasing electron doping and is negligibly small in the heavily overdoped non-superconducting x = 0.20 sample. Combining this with earlier work on the undoped and underdoped regimes, they argue that the Cu-spin correlation is intimately related to superconductivity across the entire doping range of electron-doped cuprates, paralleling the behavior in hole-doped cuprates.","tokens_in":8553,"tokens_out":3600,"duration_ms":38187,"significance":"If the conclusions are correct, the paper provides a useful extension of the muon spin relaxation results from the underdoped/slightly overdoped regime into the heavily overdoped regime of an electron-doped cuprate, and it strengthens the case for a universal connection between the development of low-energy Cu-spin correlations and superconductivity in both electron- and hole-doped cuprates. The new x = 0.20 data, which extend to 0.3 K across the composition where superconductivity disappears, are a valuable addition. The comparison between the overdoped electron-doped and hole-doped phase diagrams is physically motivated and timely. The paper does not present new formalism or code, but the experimental data and the qualitative trend are of interest to the cuprate community.","major_comments":[{"comment":"The x = 0.17 ZF-µSR data are measured only down to 9 K, which is above the superconducting transition temperature Tc ≈ 5 K reported in Fig. 1 for this sample. The x = 0.14 comparison, by contrast, is deep in its superconducting state at 9 K (Tc ≈ 20 K), where its λ and As are already enhanced. Therefore, the comparison at 9 K is uncontrolled: the absence of a low-temperature increase in λ and As for x = 0.17 cannot be distinguished from the possibility that such a development would set in below Tc. The central statement that the Cu-spin correlation 'weakens with increasing x' is thus empirically supported only by the x = 0.20 data, and the intermediate-x part of the trend rests on a null result that does not probe the superconducting state of x = 0.17. The authors should either provide ZF-µSR data for x = 0.17 at temperatures below 5 K or substantially soften the doping-dependence claim in the abstract and conclusions.","section":"Section III, Fig. 2(b) and Fig. 3"},{"comment":"The temperature dependences of the fitted parameters As, β, σ, and λ are shown without error bars or confidence intervals. Because the main inference is a null result—the absence of a steep increase in λ and of an enhancement in As at low temperatures—the reader cannot assess whether the small variations seen in Fig. 3 for x = 0.17 and x = 0.20 are statistically meaningful. The authors should report uncertainties on these fit parameters, or at least provide a representative fit with error bars, so that the null claim is quantified rather than visual.","section":"Section III, Fig. 3"},{"comment":"The two-component decomposition of the spectra into a stretched exponential attributed to Cu-spin–related relaxation and a Gaussian component attributed to static Pr3+ moments is justified by a two-muon-stopping-site picture, but this picture relies on an unpublished first-principles calculation (Ref. [29]) and is in tension with earlier one-site dipole-field calculations (Refs. [26,27]). If the muon stopping sites are not as assumed, the physical assignment of λ and As to the Cu-spin correlation is not unique, and the negative result for the heavily overdoped sample would not be specifically diagnostic of the Cu-spin correlation. The authors should make the muon-site calculation available (e.g., as a preprint or supplementary material) or provide an independent validation of the two-component decomposition, such as a consistent analysis with different fitting forms.","section":"Section III, Eq. (1) and muon stopping-site discussion"}],"minor_comments":[{"comment":"The heading 'SUMMAR Y' contains an erroneous space and should be 'SUMMARY'.","section":"Section IV heading"},{"comment":"The title contains an apparent typo, 'ove rdoped', which should be corrected to 'overdoped'.","section":"Title"},{"comment":"In Fig. 2(d), the panel for x = 0.20 at 10 K and 0.3 K is informative, but the label '(Tc < 2 K)' is redundant with the text and should be consistent with Section II, where the x = 0.20 sample is described as showing no observable Meissner diamagnetism.","section":"Figure 2"},{"comment":"Reference [29] is cited as 'unpublished'. Since this calculation is used to justify the two-site decomposition central to the interpretation, the authors should either replace it with a published or preprint version or include the calculation details in an appendix.","section":"References"},{"comment":"The text says the LF-µSR results for x = 0.20 indicate 'fluctuating internal fields at the muon site due to Cu spins'. This is consistent with the authors' earlier work, but the wording 'negligibly small development' should be clarified to mean the absence of growth in the low-energy Cu-spin correlation, not the absence of Cu-spin fluctuations altogether, which the LF data actually confirm.","section":"Section III, LF-µSR paragraph"}],"recommendation":"major_revision","confidential_remarks":"The main substantive gap is the x = 0.17 data, which stop above Tc; this is directly acknowledged in the text ('down to 9 K') and is load-bearing for the claimed doping trend. The error-bar issue in Fig. 3 and the reliance on an unpublished muon-site calculation are also consequential but fixable. If lower-temperature x = 0.17 data cannot be obtained, the authors should scope the conclusions to the x = 0.14 vs x = 0.20 comparison and explicitly state the temperature limitation."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Dear [Colleague],\n\nThe headline: this paper reports genuinely new muSR data on overdoped PLCCO, but its central trend line for x=0.17 is built on a measurement window that never reaches the superconducting state. The x=0.20 null result is the clean part, and it's a useful data point.\n\nWhat's new: ZF- and LF-muSR on single crystals with x=0.17 and 0.20, extending the group's earlier x=0.14 work. The x=0.20 sample is non-superconducting and was measured down to 0.3 K; the absence of any low-temperature growth in the stretched-exponential rate lambda and the initial asymmetry As is a solid negative result. That deserves credit.\n\nThe soft spot: for x=0.17 the lowest temperature in the ZF spectra is 9 K (Fig. 2(b)), while Tc is about 5 K (Fig. 1). You never probe the superconducting state. The development in x=0.14 appears below about 30 K, roughly 1.5 times its Tc. If the same ratio holds at x=0.17, you'd expect the onset below about 7.5 K, inside the unmeasured range. So the comparison at 9 K between x=0.14 (deep in the SC state) and x=0.17 (above its transition) doesn't support the claim that the Cu-spin correlation is negligibly small in x=0.17, nor the monotonic 'weakens with increasing x' statement. The x=0.20 data alone support the narrower and more interesting conclusion: where superconductivity disappears, the low-energy Cu-spin correlation development also disappears.\n\nTwo smaller issues: Fig. 3 shows the fitted parameters without error bars, and the two-component decomposition rests on an unpublished muon-stopping-site calculation [29]. These are fixable and secondary.\n\nFor the electron-doped cuprate community this is a worthwhile incremental paper. The x=0.20 result is citable even if the x=0.17 interpretation is not. I'd send it to peer review, but the referee should require either data below 5 K for x=0.17 or an explicit statement that the x=0.17 behavior is unresolved. As written, the abstract and summary overstate what the data show.","headline":"New muSR data on overdoped PLCCO, but the x=0.17 claim rests on measurements that never enter the superconducting state.","tokens_in":9121,"tokens_out":4691,"would_cite":false,"duration_ms":43433,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["76.75.+i","74.72.-h"],"model":"deepseek-v4-flash","headline":"Using muon spin relaxation, this paper shows that in overdoped electron-doped cuprates the low-energy copper-spin correlation weakens with electron doping and is negligibly small in the heavily overdoped sample where superconductivity…","keywords":["muon spin relaxation","electron-doped cuprates","Pr1-xLaCexCuO4","overdoped regime","Cu-spin correlation","high-Tc superconductivity","antiferromagnetic fluctuations","muon stopping site"],"falsifier":"Measure the same $x = 0.20$ crystal with a probe that sees Cu-spin fluctuations directly, such as inelastic neutron scattering or $^{63}$Cu NMR, looking for low-energy antiferromagnetic fluctuations near $(\\pi, \\pi)$. Clear low-energy Cu-spin fluctuations coexisting with flat muSR parameters would indicate that the muon-site or decomposition assumption, not the spin physics, produced the negative result; their absence would confirm it.","tokens_in":8072,"feed_emoji":"🧲","tokens_out":7828,"duration_ms":69270,"temperature":0.7,"pith_summary":"Muon spin relaxation measurements on single crystals of the electron-doped cuprate Pr$_{1-x}$LaCe$_x$CuO$_4$ at $x = 0.17$ and $0.20$ show that the slow, fluctuating copper-spin correlations seen in less-doped superconducting crystals are progressively suppressed as overdoping increases. In the $x = 0.20$ crystal, which shows no superconductivity down to 2 K, the development of this correlation is negligibly small. The authors argue that this completes a doping-axis picture in which low-energy Cu-spin correlation coexists with superconductivity from the undoped through the overdoped regime, and they draw a parallel with hole-doped cuprates, where spin correlations also disappear at the endpoint of the superconducting dome. If right, the result ties the mechanism of electron-doped superconductivity to Cu-spin fluctuations across the entire phase diagram.","feed_headline":"Spin correlations vanish with superconductivity in overdoped cuprate","feed_subtitle":"Muon-spin data show the copper-spin signal fades with overdoping and is gone by x = 0.20, where Tc disappears.","key_machinery":"The load-bearing object is the two-component function used to fit the zero-field muon spin relaxation spectra, $$A(t) = A_s\\exp[-(\\$\\lambda$ t)^\\$\\beta$] + A_G\\exp[-\\$sigma^{2}$ $t^{2}$] + A_{\\mathrm{base}},$$ where the stretched-exponential term carries the combined nuclear and Cu-spin signal and the Gaussian term isolates the static Pr$^{3+}$ moments. The physics of the paper is carried by the temperature dependence of $\\lambda$, the stretched-exponential rate, and of the long-time asymmetry: a steep low-temperature increase of $\\lambda$ with recovery of the asymmetry toward 1/3 signals the development (slowing down) of Cu-spin fluctuations, while flat behavior indicates negligible correlation. The interpretation relies on the muon stopping-site assignment from a first-principles calculation that places one muon site near the CuO$_2$ plane (sensing Cu spins) and another near the (Pr,La,Ce)-O layer (sensing Pr$^{3+}$ moments), which makes the two-component decomposition physical rather than purely empirical.","core_discovery":"The paper's central claim is that the development of low-energy antiferromagnetic Cu-spin correlation in Pr$_{1-x}$LaCe$_x$CuO$_4$ is doping-dependent in the overdoped regime: it is present where superconductivity appears ($x = 0.14$, $T_c \\simeq 20$ K, and $x = 0.17$, $T_c \\simeq 5$ K), weakens with increasing $x$, and is negligibly small at $x = 0.20$, where the Meissner signal is unobservable. The evidence comes from zero-field and longitudinal-field muon spin relaxation spectra fitted with a two-component function that separates a stretched-exponential contribution (nuclear and Cu-spin fields) from a Gaussian contribution (static Pr$^{3+}$ moments). The absence at $x = 0.17$ and $0.20$ of a low-temperature steep increase in the relaxation rate $\\lambda$ and of a recovery of the asymmetry toward 1/3 is read as the absence of appreciable Cu-spin correlation development. Combined with earlier results in the undoped and underdoped regimes, the authors conclude that low-energy Cu-spin correlation is intimately related to superconductivity in the entire doping range of the electron-doped cuprates.","pith_inferences":["A quantitative test would map the doping interval between $x = 0.17$ and $0.20$: if the spin-correlation development vanishes at the same $x$ as $T_c$, the link is quantitative, not merely qualitative.","If the same muon-site assignment holds in other T'-structure electron-doped cuprates such as Nd$_{2-x}$Ce$_x$CuO$_4$, the same overdoped suppression should be observable there, which would make the effect a generic property of the family rather than specific to PLCCO.","The result sharpens the debate over superconductivity in undoped (Ce-free) T'-cuprates: whatever microscopic doping mechanism applies, the superconducting state would still require the same Cu-spin correlations seen in the doped crystals."],"forward_implications":["The electron-doped cuprate phase diagram gains a magnetic counterpart to the hole-doped one: Cu-spin correlations appear across the superconducting region and die out as superconductivity disappears in the overdoped regime.","At $x = 0.20$ the muSR data imply a nearly paramagnetic Cu-spin state down to 0.3 K, so the loss of superconductivity in heavily overdoped PLCCO is accompanied by the disappearance of fluctuating spin correlations, not by a frozen magnetic state.","A theory of electron-doped high-$T_c$ superconductivity that omits low-energy Cu-spin fluctuations would leave this doping-axis correlation unexplained, since the magnetic signal tracks $T_c$ from the undoped parent to the overdoped endpoint.","The two-site muon interpretation makes a concrete prediction: a direct measure of the Cu-spin contribution (for example NMR or neutron scattering on the same crystals) should show the same doping trend as the muSR parameter $\\lambda$."],"supporting_citations":[{"why":"Supplies the $x=0.14$ comparison data and the two-component fitting function used throughout.","marker":"[20]"},{"why":"Shows by neutron scattering that the characteristic Cu-spin-correlation energy in overdoped PLCCO decreases with $x$ and seems to vanish with superconductivity, motivating the muSR study.","marker":"[18]"},{"why":"Provides the hole-doped parallel: in Zn-substituted LSCO, muSR shows the development of Cu-spin correlation weakens with doping and disappears near where superconductivity ends.","marker":"[3]"},{"why":"Reports muSR evidence of short-range magnetic order coexisting with superconductivity in undoped and underdoped electron-doped cuprates, anchoring the entire-doping argument.","marker":"[16]"},{"why":"Unpublished first-principles calculation cited for two muon stopping sites, one near the CuO$_2$ plane and one near the (Pr,La,Ce)-O layer, making the two-component decomposition physical.","marker":"[29]"},{"why":"Establishes the static Pr$^{3+}$ moment contribution to the muSR spectra, which the Gaussian component must isolate.","marker":"[25]"},{"why":"Gives the improved reduction-annealing recipe used for the heavily overdoped $x=0.20$ crystal, so the non-superconducting state is attributed to doping rather than to sample preparation.","marker":"[12]"}],"fun_headline_variants":["Muon spins reveal copper spin correlation fades with overdoping","Overdoped cuprate: spin correlation vanishes with superconductivity","Copper spin correlation tracks superconductivity in overdoped cuprate","Spin correlation disappears as overdoping kills superconductivity","Spin correlation and Tc vanish together in overdoped cuprate"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The conclusion depends on the stretched-exponential component being a faithful measure of Cu-spin fluctuations, which rests in turn on the muon stopping-site assignment and on the two-component decomposition being unique; the site calculation is cited as unpublished, so the negative result at $x = 0.20$ could in principle reflect a muon-site or fitting artifact rather than the disappearance of Cu-spin correlation.","fun_headline_variants_meta":{"raw":{"variants":["Muon spins reveal copper spin correlation fades with overdoping","Overdoped cuprate: spin correlation vanishes with superconductivity","Copper spin correlation tracks superconductivity in overdoped cuprate","Spin correlation disappears as overdoping kills superconductivity","Spin correlation and Tc vanish together in overdoped cuprate"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000182,"raw_usage":{"total_tokens":1343,"prompt_tokens":1011,"completion_tokens":332,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":627,"completion_tokens_details":{"reasoning_tokens":247}},"tokens_in":627,"tokens_out":332,"duration_ms":3977,"temperature":1.0,"reasoning_tokens":247,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T15:21:20.002471+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the same $x = 0.20$ crystal with a probe that sees Cu-spin fluctuations directly, such as inelastic neutron scattering or $^{63}$Cu NMR, looking for low-energy antiferromagnetic fluctuations near $(\\pi, \\pi)$. Clear low-energy Cu-spin fluctuations coexisting with flat muSR parameters would indicate that the muon-site or decomposition assumption, not the spin physics, produced the negative result; their absence would confirm it.","supporting_citations":[{"cited_title":"It is noted that the change of the spectra above 100 K shown in Fig","cited_arxiv_id":null,"evidence_quote":"Supplies the $x=0.14$ comparison data and the two-component fitting function used throughout."},{"cited_title":"[19] From the former µ SR measurements in the SC polycrystal of PLCCO with x = 0","cited_arxiv_id":null,"evidence_quote":"Shows by neutron scattering that the characteristic Cu-spin-correlation energy in overdoped PLCCO decreases with $x$ and seems to vanish with superconductivity, motivating the muSR study."},{"cited_title":"Adachi, N","cited_arxiv_id":null,"evidence_quote":"Provides the hole-doped parallel: in Zn-substituted LSCO, muSR shows the development of Cu-spin correlation weakens with doping and disappears near where superconductivity ends."},{"cited_title":"Adachi, A","cited_arxiv_id":null,"evidence_quote":"Reports muSR evidence of short-range magnetic order coexisting with superconductivity in undoped and underdoped electron-doped cuprates, anchoring the entire-doping argument."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Unpublished first-principles calculation cited for two muon stopping sites, one near the CuO$_2$ plane and one near the (Pr,La,Ce)-O layer, making the two-component decomposition physical."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes the static Pr$^{3+}$ moment contribution to the muSR spectra, which the Gaussian component must isolate."},{"cited_title":"Adachi, Y","cited_arxiv_id":null,"evidence_quote":"Gives the improved reduction-annealing recipe used for the heavily overdoped $x=0.20$ crystal, so the non-superconducting state is attributed to doping rather than to sample preparation."}],"review_version":1}