Superconductivity of Pure H3S Synthesis from Elemental Sulfur and Hydrogen

Harushige Nakao; Katsuya Shimizu; Mari Einaga; Masafumi Sakata; Masaomi Kitagaki; Naohisa Hirao; Saori Kawaguchi; Yasuo Ohishi

REVIEW 4 major objections 6 minor 12 references

Superconductivity of Pure H3S Synthesis from Elemental Sulfur and Hydrogen

T0 review · 4 major / 6 minor · reviewed 2026-08-14 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read Pure H3S made from elemental sulfur and hydrogen shows a superconducting transition at 200 K, with a 186 K offset—the highest in the S–H system.

desk verdict First transport data on directly synthesized H3S, with the superconducting step landing right on the known Tc(P) curve; the claim is plausible but rests on a single two-probe resistance drop with no zero resistance or magnetic screening. read the letter →

arxiv 1908.02826 v1 pith:LJA6MXZ5 submitted 2019-08-07 cond-mat.supr-con

Harushige Nakao , Mari Einaga , Masafumi Sakata , Masaomi Kitagaki , Katsuya Shimizu , Saori Kawaguchi , Naohisa Hirao , Yasuo Ohishi This is my paper · ORCID

classification cond-mat.supr-con

keywords H3Ssulfurhydridehigh-pressuresuperconductivitydirectsynthesisdiamondanvilcellpowderX-raydiffractionhydrogen-richsuperconductor200Ktransition

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

The paper reports that H3S synthesized directly from elemental sulfur and hydrogen under high pressure becomes superconducting at temperatures close to 200 K. The authors performed the first resistance measurements on this directly synthesized material and observed a sharp resistance drop at Tonset ~ 200 K and Toffset ~ 186 K at 146 GPa. The sample contains no excess sulfur and shows much sharper X-ray diffraction peaks than H3S made from decomposing H2S, consistent with a narrower transition. If the identification holds, hydrogen deficiency and poor crystallinity are not necessary for high-temperature superconductivity in the sulfur-hydrogen system, and the 186 K offset is the highest yet reported for that system. This matters because it separates the intrinsic Tc of H3S from the effects of sample quality.

What carries the argument

The central object is the phase-pure H3S sample with a body-centered-cubic sulfur sublattice (Im3m structure), prepared by laser heating of a sulfur-hydrogen mixture near 150 GPa under hydrogen-excess conditions. The argument rests on three pieces: direct synthesis yields no excess sulfur and much improved crystallinity, as shown by sharp PXRD peaks; the sharp resistance step near 200 K is anchored to superconductivity by its position on the established Tc(P) curve and by the absence of any known low-temperature structural transition; and the narrow transition width of about 14 K is read as a consequence of the sample's crystalline quality. The electrical measurement is AC two-probe resistance, pressure is determined from the diamond Raman edge, and the structural identification uses synchrotron PXRD with wavelength 0.41235 Å.

What would settle it

Cool the same directly synthesized H3S sample at 146 GPa from 200 K to below 186 K while measuring four-probe resistance and magnetic susceptibility; observing zero resistance and a diamagnetic Meissner signal would confirm the step is superconductivity, while their absence—or a low-temperature X-ray diffraction scan showing a structural transition across this range—would falsify the claim.

Watch

Extended reading notes

Core claim

The central claim is that H3S synthesized directly from elemental sulfur and molecular hydrogen, via the reaction 3H2 + 2S -> 2H3S under hydrogen-excess conditions, is superconducting at high pressure. In a diamond anvil cell at 150 GPa, the authors laser-heated a sulfur-hydrogen mixture and observed a resistance drop to about 16 Ω; synchrotron powder X-ray diffraction then identified cubic Im3m H3S with a = 3.1027(5) Å and no residual sulfur. On cooling at 146 GPa, the resistance was metallic until a sharp step at about 200 K, reaching an offset near 186 K. The step is assigned to a superconducting transition because its pressure-temperature point closely matches the known Tc(P) curve of H3S derived from H2S, and because earlier diffraction work found no low-temperature structural phase transition in that region. Zero resistance was not observed because the measurement used a two-probe configuration, with residual resistance attributed to contacts and gold leads; the paper concludes that Toffset ~ 186 K is the highest offset temperature reported in the sulfur-hydrogen system.

Load-bearing premise

The sharp resistance drop at about 200 K is assumed to be an intrinsic superconducting transition of the H3S sample rather than a contact or probe artifact or a structural phase transition; if that assumption fails, the central claim does not follow.

Editorial extensions

If this is right

If the transition is superconducting, the high Tc of the sulfur-hydrogen system does not require the H2S decomposition route; direct synthesis yields a cleaner material with the same high onset.
The highest offset temperature of 186 K in the S-H system implies that better-crystallized samples can complete the resistive transition at higher temperature, suggesting disorder mostly broadens and lowers the transition's end point.
The sharper diffraction peaks and narrower transition indicate that crystalline quality, not just stoichiometry, controls the spread of Tc seen in earlier H2S-derived samples.
The demonstration opens a route for controlled variation of the synthesis—such as adjusting hydrogen excess or substituting deuterium—without sulfur contamination, enabling cleaner tests of superconductivity mechanisms.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

A natural next step is a four-probe or magnetic measurement on the same synthesis route; confirming zero resistance and a Meissner signal would make the direct-synthesis method the standard preparation for studying H3S superconductivity.
The same direct-synthesis approach could be applied to deuterium substitution (D3S) under identical hydrogen-excess conditions to measure the isotope effect in a stoichiometrically clean sample, which the H2S route cannot provide as cleanly.
The sharper transition in this cleaner material suggests that part of the Tc spread in H2S-derived samples comes from disorder; this could be tested by deliberately adding sulfur impurities to directly synthesized H3S and observing whether Toffset degrades.

Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Dear Colleague,

The thing to know: this is the first resistance measurement on H3S made from elemental sulfur and hydrogen, and the sharp step at 200 K and 146 GPa lands right on the known Tc(P) curve. I think the superconducting identification is probably right. The paper is short, honest about its own limits, and the XRD showing clean Im-3m H3S with sharp peaks is solid.

Credit where due: the synthesis method was already published by Guigue and Goncharov, but nobody had managed to get transport data on directly synthesized material. That is a genuine new data point, and the narrower transition width compared to H2S-derived H3S is a reasonable qualitative observation, consistent with better crystallinity.

Soft spots, in proportion. The measurement is AC two-probe with no zero resistance and no magnetic screening. The authors say this outright, so they are not hiding it. Given two-probe geometry, contact resistance is a legitimate worry, especially because they describe the laser-heating resistance drop as likely a partial restoration of contact. The load-bearing question is whether the later sharp step at 200 K is intrinsic to bulk H3S or something in the contact. They argue against a structural transition by citing prior low-T PXRD on compressed H2S and theory, but they did not run low-T XRD on this exact sample. That is a fair caveat, not a fatal one. Also, the "highest Toffset" claim rests entirely on this single curve, with no error bars; it is a little under-supported.

Is the central argument sound? Mostly, yes. The step occurs at the pressure-temperature point where H3S is known to superconduct, the sample is confirmed to be Im-3m H3S, and the metallic behavior above the step is consistent. A contact artifact would not typically produce a sharp step right at the known Tc, but the evidence is one channel only.

Who is this for? People working on high-pressure hydride superconductors. It is a confirmation and refinement, not a paradigm shift. I would send it to a serious referee; the authors have done the community a service by getting transport data on the clean direct-synthesis system, and the soft spots are exactly the kind of thing a referee should probe.

Recommendation: accept for peer review, with the expectation that referees will ask whether the step could be a contact or structural artifact, and will want error bars or a Meissner attempt. The core result is worth publishing even if the "highest Toffset" framing needs tempering.

Referee Report

4 major / 6 minor

Summary. The manuscript reports the first electrical resistance measurements on H3S synthesized directly from elemental sulfur and hydrogen in a diamond anvil cell. The authors load S and H2, compress to 150 GPa, laser-heat to synthesize Im-3m H3S, and confirm the structure by synchrotron powder X-ray diffraction. On cooling at 146 GPa they observe a sharp resistance drop with Tonset ~ 200 K and Toffset ~ 186 K, and they attribute this step to a superconducting transition based on its proximity to the known Tc(P) of H3S and on the absence of known structural transitions in this pressure range. The paper acknowledges that the two-probe method prevents observation of zero resistance and that the laser-heating resistance drop was likely a contact artifact.

Significance. If the identification is correct, the paper provides the first transport evidence for superconductivity in stoichiometric, impurity-free H3S made by direct synthesis, with a sharper transition width and the highest Toffset reported in the S-H system. The synthesis route and structural characterization are well documented, and the comparison to external Tc(P) data is appropriate and avoids circular reasoning. The main limitation is that the central claim rests on a single two-probe resistance trace, with no zero-resistance plateau, no Meissner measurement, no magnetic-field dependence, and no low-temperature structural data on this exact sample. The result is plausible and valuable but the evidence is not yet conclusive.

major comments (4)

[Section 3 (conclusion paragraph)] The conclusion that the sharp resistance step corresponds to a superconducting transition is stronger than the evidence supports. The measurement is AC two-probe, zero resistance was not observed, no Meissner signal was measured, and no magnetic-field dependence is reported. The paper itself attributes the laser-heating resistance drop to a partial restoration of electrical contact between the sample and the Au probe, which shows that contact artifacts are a known issue in this geometry. The 200 K step could in principle also be a contact or probe artifact, or a structural/electronic transition. Please rephrase the conclusion to state that the step is 'consistent with a superconducting transition,' and add a detailed discussion of the possible artifacts and why they are considered unlikely.
[Section 3 (paragraph on absence of phase transition)] The exclusion of a structural phase transition is based on prior low-temperature PXRD on compressed H2S [6] and on theoretical calculations, not on low-temperature X-ray diffraction of the present directly synthesized sample. Because the synthesis route and sample quality differ from those in Ref. [6], the absence of a structural transition in this specific sample is not established. The authors should either provide low-temperature XRD data for a directly synthesized sample or explicitly state that this check was not performed and treat this as a limitation.
[Fig. 3 and accompanying text] The manuscript shows heating and cooling resistance curves but does not state whether the resistance step was reproduced in both directions or whether any hysteresis was observed. A superconducting transition should be reversible with no hysteresis, whereas a first-order structural transition might show hysteresis. Please report the heating and cooling traces quantitatively, including the measurement current/frequency and the noise floor, and indicate whether the step position and width are identical on heating and cooling.
[Section 3 (resistivity estimate)] The resistivity estimate is obtained by subtracting a 'residual resistance' that is not independently measured, and the residual resistance itself may be temperature dependent. The procedure for determining the residual resistance and its uncertainty is not described, and no error bars are given for the resistance or the pressure. The agreement of the estimated resistivity with Drozdov's range does not constitute evidence for superconductivity. Please provide the raw resistance trace, a clear description of how the residual resistance was extracted, and estimates of the experimental uncertainties.

minor comments (6)

[Abstract and Introduction] The word 'superconductive' is used in place of 'superconducting' throughout; please use consistent terminology. Also, 'no hydrogen deficiency is caused' should be rephrased to 'no hydrogen deficiency occurs' or 'no hydrogen deficiency is introduced.'
[Section 2 (experimental methods)] The AC two-probe measurement is not fully described. Please specify the excitation frequency and amplitude and whether a lock-in amplifier was used.
[References] Reference [2] is cited as Schilling et al., Nature 363 (1983); the correct year is 1993. Please correct this citation and check all other references for accuracy and consistency.
[Fig. 3 caption] The figure caption is missing from the text. The caption should identify the red and blue lines as heating and cooling, state the pressure (146 GPa), and give the units of the axes.
[Section 3 (XRD analysis)] The statement that the peak positions 'perfectly fit' Im-3m H3S is subjective. Please provide a quantitative measure of the fit, such as the observed and calculated peak positions or a residual plot.
[Section 3 (Toffset claim)] The claim that Toffset = 186 K is the highest in the S-H system should be supported by listing the Toffset values from the cited previous work (e.g., Refs. [1] and [6]) so the reader can verify the comparison.

Circularity Check

0 steps flagged · score 0.0 of 10

No circularity: the superconducting-transition claim is an experimental measurement benchmarked against independent prior Tc(P) data, not a derivation from fitted inputs.

full rationale

This is an experimental paper reporting electrical resistance measurements of directly synthesized H3S. There is no derivation chain, no fitting of parameters to data, and no quantity that is defined in terms of the claimed result. The central claim is that a sharp resistance step near 200 K at 146 GPa corresponds to a superconducting transition. The paper supports this identification by comparing the observed pressure-temperature point with Tc(P) data from Drozdov et al. [1] and from the authors' own prior work [6], and by citing prior low-temperature PXRD and theoretical calculations to argue against a structural transition. The citation of the authors' own prior work [6] is normal experimental precedent: it supplies independent Tc(P) measurements and structural data obtained on separately prepared samples, not a definition of the present result. The paper also transparently discusses limitations: the measurement is AC two-probe, zero resistance was not observed, no Meissner measurement was made, and the resistance drop during laser heating is attributed partly to contact restoration. These are validity concerns about interpretation, not circularity. No equation reduces to an input, no fitted parameter is renamed a prediction, and no uniqueness claim is imported from a self-citation. Therefore the circularity score is 0.

Assumptions & free parameters 0 free parameters · 4 assumptions · 0 invented entities

No free parameters or invented entities are introduced. The result is an experimental observation whose interpretation rests on calibration standards and on prior structural and thermodynamic results, as listed.

assumptions (4)

domain assumption Diamond Raman pressure calibration is valid at ~150 GPa.
Pressure is determined from the stress-induced Raman peak of diamond [11], a standard method, but the pressure value enters the identification of the P-T point with previously measured Tc.
domain assumption The observed resistance drop is intrinsic superconductivity rather than a contact artifact or structural phase transition.
The paper argues this from the match to known Tc(P) and the absence of phase transitions in prior PXRD [6], but no zero-resistance or Meissner signal is presented for this sample.
domain assumption Hydrogen-excess synthesis conditions yield stoichiometric H3S without hydrogen deficiency.
The paper relies on the conclusions of Guigue et al. [9] and Goncharov et al. [10] that direct synthesis under hydrogen excess avoids hydrogen deficiency; this is assumed rather than directly measured in the present sample.
domain assumption No structural phase transition occurs in the temperature range of the resistance anomaly.
The paper cites prior PXRD measurements [6] and theoretical calculations; no low-temperature XRD on this specific sample is shown.

how reviews work

0 comments

Cite this review

Pith. "Pith review of Superconductivity of Pure H3S Synthesis from Elemental Sulfur and Hydrogen." pith.science (2026). https://pith.science/paper/LJA6MXZ5

@misc{pith2026190802826,
  author       = {Pith},
  title        = {Pith review of: Superconductivity of Pure H3S Synthesis from Elemental Sulfur and Hydrogen},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/LJA6MXZ5}},
  note         = {Machine review of arXiv:1908.02826}
}

read the original abstract

Superconductive H3S synthesized from H2S is very poorly crystallized, and has excess sulfur as impurity (3H2S -> 2H3S + S). The phase transition process undergoes in sulfur excess condition, which might cause hydrogen deficiency. The influence of hydrogen deficiency is not clear. Therefore investigation on the superconductivity in H3S with no hydrogen deficiency is demanded. Two groups performed synthesis of H3S from elemental sulfur and hydrogen (direct synthesis) and their results have shown that no hydrogen deficiency is caused when the direct synthesis is performed under hydrogen excessive condition. However, no measurements of superconductivity has been carried out because of the major technical difficulties in hydrogen experiments in diamond anvil cells (DACs). Here, we report the first electrical resistance measurements in superconductive H3S synthesized from elemental sulfur and hydrogen (3H2 + 2S -> 2H3S). Our powder X-ray diffraction (PXRD) using a synchrotron X-ray revealed that synthesized H3S has much improved crystalline quality and no sulfur as reported in previous works. We observed a superconducting transition with a sharp drop of the resistance at Tonset = 200 K and we obtained the highest Toffset of 186 K in S-H system.

Figures

Figures reproduced from arXiv: 1908.02826 by the authors.

**Figure 1.** A photo image of the sample after loading at 25 GPa (RT). Gold (Au) probes are connected to a rectangle-shaped sulfur and hydrogen is beneath the sulfur. The photo was taken in transmission and reflection illumination [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗

**Figure 2.** Integrated PXRD patterns obtained with subtraction of the background for compressed H2S [6] (top), H3S synthesized from sulfur and H2 (bottom, black solid line) and S+H2 mixture before laser heating (bottom, red solid line). The symbols g and * indicate the reflection of insulation layer of the gasket and unknown. The red and green ticks indicate the peak positions of the H3S with bcc-structure sulfur and and β-Po e… view at source ↗

**Figure 3.** Temperature dependence of the sample resistance after laser heating (146 GPa). Red and blue lines represent the sample resistance in the heating process and cooling process, respectively. 6 [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗

Figures from the paper (1 more)

**Figure 4.** Figure 4: Pressure dependence of Tc obtained in previous works with compressed H2S by Drozdov et al. and our group (open circles from ref [1], black solid circles from ref [6], black solid triangles from other runs by our group). Red colored circle represents the pressure-temper…

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

12 extracted references · 11 canonical work pages

[6]

Einaga, M

M. Einaga, M. Sakata, T. Ishikawa, K. Shimizu, M. I. Eremets, A. P. Drozdov, I. A. Troyan, N. Hirao, and Y. Ohishi, Nat. Phys. 12, 835 (2016)

work page 2016
[1]

A. P. Drozdov, M. I. Eremets, I. A. Troyan, V. Ksenofontov, and S. I. Shylin, Nature 525, 73 (2015)

work page 2015
[2]

Schilling, M

A. Schilling, M. Cantoni, J. D. Guo, and H. R. Ott, Nature 363, 56 (1983)

work page 1983
[3]

N. W. Ashcroft, Phys. Rev. Lett. 92, 187002 (2004)

2004
[4]

Y. Li, J. Hao, H. Liu, Y. Li, and Y. Ma, J. Chem. Phys. 140, 174712 (2014)

work page 2014
[5]

D. Duan, Y. Liu, F. Tian, D. Li, X. Huang, Z. Zhao, H. Yu, B. Liu, W. Tian, and T. Cui, Sci. Rep. 4, 6968 (2015)

work page 2015
[7]

Fujihisa, H

H. Fujihisa, H. Yamawaki, M. Sakashita, A. Nakayama, T. Yamada, and K. Aoki, Phys. Rev. B 69, 214102 (2004)

work page 2004
[8]

A. F. Goncharov, S. S. Lobanov, I. Kruglov, X. M. Zhao, X. J. Chen, A. R. Oganov, Z. Konˆ opkov´ a, and V. B. Prakapenka, Phys. Rev. B93, 174105 (2016)

work page 2016

Show all 12 references

[9]

Guigue, A

B. Guigue, A. Marizy, and P. Loubeyre, Phys. Rev. B 95, 020104(R) (2017)

2017
[10]

A. F. Goncharov, S. S. Lobanov, V. B. Prakapenka, and E. Greenberg, 95, 140101(R) (2017)

2017
[11]

Akahama, H

Y. Akahama, H. Kawamura, J. Appl. Phys. 96, 3748 (2004)

2004
[12]

Kometani, M

S. Kometani, M. I. Eremets, K. Shimizu, M. Kobayashi, and K. Amaya, 66, 2564 (1997). 5 Fig. 1: A photo image of the sample after loading at 25 GPa (RT). Gold (Au) probes are connected to a rectangle-shaped sulfur and hydrogen is beneath the sulfur. The photo was taken in trans...

1997

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

[1] [6]

Einaga, M

M. Einaga, M. Sakata, T. Ishikawa, K. Shimizu, M. I. Eremets, A. P. Drozdov, I. A. Troyan, N. Hirao, and Y. Ohishi, Nat. Phys. 12, 835 (2016)

work page 2016

[2] [1]

A. P. Drozdov, M. I. Eremets, I. A. Troyan, V. Ksenofontov, and S. I. Shylin, Nature 525, 73 (2015)

work page 2015

[3] [2]

Schilling, M

A. Schilling, M. Cantoni, J. D. Guo, and H. R. Ott, Nature 363, 56 (1983)

work page 1983

[4] [3]

N. W. Ashcroft, Phys. Rev. Lett. 92, 187002 (2004)

2004

[5] [4]

Y. Li, J. Hao, H. Liu, Y. Li, and Y. Ma, J. Chem. Phys. 140, 174712 (2014)

work page 2014

[6] [5]

D. Duan, Y. Liu, F. Tian, D. Li, X. Huang, Z. Zhao, H. Yu, B. Liu, W. Tian, and T. Cui, Sci. Rep. 4, 6968 (2015)

work page 2015

[7] [7]

Fujihisa, H

H. Fujihisa, H. Yamawaki, M. Sakashita, A. Nakayama, T. Yamada, and K. Aoki, Phys. Rev. B 69, 214102 (2004)

work page 2004

[8] [8]

A. F. Goncharov, S. S. Lobanov, I. Kruglov, X. M. Zhao, X. J. Chen, A. R. Oganov, Z. Konˆ opkov´ a, and V. B. Prakapenka, Phys. Rev. B93, 174105 (2016)

work page 2016