Comment on: Observation of a first order phase transition to metal hydrogen near 425 GPa

Isaac F. Silvera; Ranga Dias

arxiv: 1907.03198 · v1 · pith:GUED3YCTnew · submitted 2019-07-06 · ❄️ cond-mat.other

Comment on: Observation of a first order phase transition to metal hydrogen near 425 GPa

Isaac F. Silvera , Ranga Dias This is my paper

Pith reviewed 2026-05-25 01:21 UTC · model grok-4.3

classification ❄️ cond-mat.other

keywords metallic hydrogenhigh pressureinsulator-metal transitiondiamond anvil cellhydrogen phase transitioncomment

0 comments

The pith

Loubeyre et al. claim metallic hydrogen at 425 GPa without evidence of the insulator-to-metal transition.

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

This comment asserts that the reported observation of metallic hydrogen near 425 GPa does not meet the standard of proof because it omits data showing the transition from an insulating to a metallic state. The authors review that comparable pressures and effects such as sample darkening and conductivity were already documented in earlier experiments. They conclude that the new work largely repeats prior results without advancing the evidentiary basis for the metallic phase.

Core claim

LOD claim to have produced metallic hydrogen at a pressure of 425 GPa, without the necessary supporting evidence of an insulator to metal transition. Most of the results have been reported earlier. Zha et al. studied hydrogen at low temperature up to 360 GPa in 2012 and reported absorption studies up to 0.1 eV. Eremets et al. studied dense hydrogen up to 480 GPa and reported darkening and semi-metallic behavior around 440 GPa. In 2016 hydrogen was reported opaque at 420 GPa and in 2017 atomic metallic hydrogen was observed at 495 GPa.

What carries the argument

The requirement to observe an insulator-to-metal transition as the essential evidence needed to claim metallic hydrogen.

If this is right

Without evidence of the transition the claim of metallic hydrogen at 425 GPa cannot stand.
Prior work already reached similar or higher pressures with related observations of opacity and conductivity.
Consistent use of transition evidence would require future experiments to meet the same standard applied to earlier studies.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Requiring the transition signature could push experiments to combine optical and electrical measurements in the same run.
This approach might reduce disputes by focusing on a single observable that directly indicates the metallic state.

Load-bearing premise

That an explicit demonstration of the insulator-to-metal transition is required to validate a claim of metallic hydrogen rather than other signs such as opacity or conductivity.

What would settle it

A clear discontinuous change in optical reflectivity or electrical conductivity marking the insulator-to-metal transition in the LOD experiment at 425 GPa would support their claim.

Figures

Figures reproduced from arXiv: 1907.03198 by Isaac F. Silvera, Ranga Dias.

**Figure 1.** Figure 1: a) Images of hydrogen from LOD in reflected light. All three photos show a small dark or black sample near the middle; in particular the middle image is claimed to be MH. We estimate that the linear dimensions of the sample are 5-6 microns. b) Images from Dias and Silvera. The left image is back lit and H2 is transparent; the middle photo shows an opaque sample that is black in reflection; the bright ring … view at source ↗

**Figure 2.** Figure 2: Integrated transmitted intensity over the IR range (1800 cm-1 to 3800 cm-1 ) versus pressure, normalized to a 295 GPa pressure spectrum. The inset shows a photo of the darkening of the sample, around 420 GPa. 300 325 350 375 400 425 0 20 40 60 80 100 IR intensity cm-1 (a.u) Pressure (GPa) Dias & Silvera 2017 300 K (b) 150 GPa 420 GPa 30µm 82 K (a) Culet H2 [PITH_FULL_IMAGE:figures/full_fig_p004_2.png] view at source ↗

**Figure 3.** Figure 3: Some observations of hydrogen at high pressure in conflict with LOD. [PITH_FULL_IMAGE:figures/full_fig_p005_3.png] view at source ↗

**Figure 4.** Figure 4: Raman spectrum of diamond at various pressure [PITH_FULL_IMAGE:figures/full_fig_p006_4.png] view at source ↗

**Figure 5.** Figure 5: Calibrations of the peak frequency of the IR vibron in hydrogen [PITH_FULL_IMAGE:figures/full_fig_p008_5.png] view at source ↗

**Figure 6.** Figure 6: LOD experimental geometry. Their sample can be considered as a pinhole, and the light passing through it will be cast out by diffraction, with intensity as a function of θ described by the Airy disk equation. We examine how much of the diffracted light will be captured by their objective [PITH_FULL_IMAGE:figures/full_fig_p009_6.png] view at source ↗

**Figure 7.** Figure 7: Shown is the fraction of transmitted light [PITH_FULL_IMAGE:figures/full_fig_p010_7.png] view at source ↗

**Figure 8.** Figure 8: Putative theoretical phase diagram of solid hydrogen [PITH_FULL_IMAGE:figures/full_fig_p011_8.png] view at source ↗

read the original abstract

Loubeyre, Occelli, and Dumas (LOD) [1] claim to have produced metallic hydrogen (MH) at a pressure of 425 GPa, without the necessary supporting evidence of an insulator to metal transition. The paper is much ado about nothing. Most of the results have been reported earlier. Zha, Liu, and Hemley [2] studied hydrogen at low temperature up to 360 GPa in 2012; they reported absorption studies up to 0.1eV. Eremets et al [3] studied dense hydrogen up to 480 GPa using standard bevel diamonds. They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa. In 2016 Dias, Noked, and Silvera [4] reported hydrogen was opaque at 420 GPa. In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5].

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This comment correctly notes that LOD's metallic hydrogen claim at 425 GPa shows no clear insulator-metal transition, but it lists prior citations without comparing setups.

read the letter

The key point is that LOD reported metallic hydrogen at 425 GPa without showing the insulator-to-metal transition that would confirm the phase change. The comment assembles earlier work at comparable pressures that stopped short of that claim: Zha et al. on absorption to 0.1 eV at 360 GPa, Eremets et al. on semi-metallic conductivity near 440 GPa up to 480 GPa, and the authors' own earlier reports of opacity at 420 GPa and atomic metallic hydrogen only at 495 GPa. This is useful context for what the subfield has treated as sufficient evidence so far. The paper does nothing new experimentally or theoretically; it is a short comment that relies on existing literature. The soft spot is exactly the one in the stress-test note. The argument treats the prior experiments as setting a clear bar, yet supplies no side-by-side check on pressure scales, temperatures, anvil types, or diagnostics to show the conditions are equivalent. Without that, it is hard to judge whether LOD simply used a different threshold or whether the setups truly match. The citation pattern leans on the authors' own prior papers, which is typical for comments but leaves the load-bearing claim resting on summary rather than direct comparison. This is for people already following the high-pressure hydrogen debate who want a reminder of the evidentiary history. A reader outside that niche gets little. It deserves peer review because comments on high-stakes experimental claims can help clarify standards even when the comment itself is brief and the comparison work is incomplete.

Referee Report

1 major / 0 minor

Summary. This comment paper asserts that Loubeyre, Occelli, and Dumas (LOD) claim to have produced metallic hydrogen at 425 GPa without providing evidence of an insulator-to-metal transition. It states that most results were reported earlier, citing Zha et al. (absorption to 0.1 eV at 360 GPa), Eremets et al. (semi-metallic conductivity near 440 GPa up to 480 GPa), and the authors' prior work (opacity at 420 GPa; atomic MH at 495 GPa), concluding that the LOD claim is 'much ado about nothing.'

Significance. If the critique is substantiated, the comment would highlight evidentiary standards for metallization claims in high-pressure hydrogen experiments, emphasizing the need for explicit transition signatures rather than indirect indicators like opacity or conductivity. This could affect interpretation of diamond-anvil-cell results in condensed-matter physics, but the absence of condition-by-condition comparisons reduces its standalone impact.

major comments (1)

[Abstract paragraph citing prior experiments] The central assertion that LOD lacks transition evidence because prior experiments did not claim metallic hydrogen rests on the unexamined premise that the cited works (Zha et al. [2], Eremets et al. [3], Dias/Silvera [4,5]) used equivalent diagnostics, pressure scales, anvil geometries, and temperature conditions. No parameter-by-parameter comparison is supplied in the text listing these citations, which is load-bearing for the claim that those non-claims establish the required evidentiary bar.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the constructive comment. We address the major point below and agree that additional clarification on experimental conditions would improve the manuscript.

read point-by-point responses

Referee: The central assertion that LOD lacks transition evidence because prior experiments did not claim metallic hydrogen rests on the unexamined premise that the cited works (Zha et al. [2], Eremets et al. [3], Dias/Silvera [4,5]) used equivalent diagnostics, pressure scales, anvil geometries, and temperature conditions. No parameter-by-parameter comparison is supplied in the text listing these citations, which is load-bearing for the claim that those non-claims establish the required evidentiary bar.

Authors: We agree that the manuscript would be strengthened by explicitly addressing potential differences in experimental parameters. The central claim of the comment is factual and does not presuppose identical conditions: the cited works (Zha et al., Eremets et al., and our own prior reports) reached comparable pressures yet did not claim observation of an insulator-metal transition or metallic hydrogen, as stated in their abstracts and conclusions. This absence of claim is itself informative regarding evidentiary standards. Nevertheless, to address the referee's concern we will add a concise paragraph summarizing key differences (e.g., Zha et al. limited absorption to 0.1 eV without conductivity data; Eremets et al. reported only semi-metallic conductivity without claiming full metallization; our 420 GPa opacity measurement was not accompanied by a transition signature). A short table comparing pressure, temperature, diagnostics, and anvil type will also be included. This revision clarifies rather than alters the argument. revision: partial

Circularity Check

0 steps flagged

Minor self-citation for historical context; central critique of LOD's evidence threshold stands independently

full rationale

The comment asserts that LOD produced metallic hydrogen at 425 GPa without insulator-to-metal transition evidence, then lists prior experiments (Zha et al., Eremets et al., and authors' own [4][5]) that reached comparable pressures without claiming metallic hydrogen. The self-citations appear only to document what was reported earlier and do not supply the load-bearing premise that LOD itself failed to demonstrate the transition; that premise is presented as a direct reading of reference [1]. No equations, fitted parameters, uniqueness theorems, or ansatzes are present, so none of the enumerated circularity patterns apply. The self-citation is therefore non-load-bearing and does not reduce the paper's argument to its own inputs.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The comment rests on the domain assumption that established criteria exist for confirming an insulator-to-metal transition in hydrogen and that the cited prior studies meet or define those criteria.

axioms (1)

domain assumption Standard identification of metallic hydrogen requires direct evidence of an insulator-to-metal transition via optical absorption or electrical conductivity measurements.
Invoked when the abstract states that LOD lacks 'the necessary supporting evidence of an insulator to metal transition'.

pith-pipeline@v0.9.0 · 5710 in / 1238 out tokens · 25236 ms · 2026-05-25T01:21:21.978576+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

44 extracted references · 44 canonical work pages · 9 internal anchors

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Eremets et al

studied hydrogen at low temperature up to 360 GPa in 2012; they reported absorption studies up to 0.1eV. Eremets et al

work page 2012
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They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa

studied dense hydrogen up to 480 GPa using standard bevel diamonds. They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa. In 2016 Dias, Noked, and Silvera

work page 2016
[3]

In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5]

reported hydrogen was opaque at 420 GPa. In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5]. LOD did not acknowledge or discuss any earlier work relative to their observations. They report a high-pressure phase diagram that strongly disagrees with the existing literature. They fail to acknowledge th...

work page 2017
[4]

In 2011 Eremets and Troyan studied hydrogen to 300 GPa and claimed metallization [7]

at even lower pressures; eventually it was conceded that there was no metallization in hydrogen or deuterium up to pressures of 216 GPa [10]. In 2011 Eremets and Troyan studied hydrogen to 300 GPa and claimed metallization [7]. Although they discovered two important new phases of molecular hydrogen, there was no evidence of MH [2,11] and eventually they c...

work page 2011
[5]

The inset shows a photo of the darkening of the sample, around 420 GPa

Integrated transmitted intensity over the IR range (1800 cm-1 to 3800 cm-1) versus pressure, normalized to a 295 GPa pressure spectrum. The inset shows a photo of the darkening of the sample, around 420 GPa. 300 325 350 375 400 4250 20 40 60 80 100IR intensity cm-1(a.u) Pressure (GPa) Dias & Silvera 2017 300 K(b)150 GPa420 GPa30µm(a)82 KCuletH2 hydrogen w...

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RESEARCHER IR VIBRON FREQUENCY OF HYDROGEN AT LOW TEMPERATURES (80-100K) VISUAL OBSERVATION CONCLUSION Loubeyre FU BM (2002 and

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4040cm-1 Solid hydrogen was observed to turn completely opaque BMack hydrogen reported Zha FU BM (2012 and

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LOD neglect the effects of diffraction losses through their small sample hole in a metallic gasket

The third possibility is diffraction losses due to sample geometry. LOD neglect the effects of diffraction losses through their small sample hole in a metallic gasket. In general, when the wavelength of light is of the order of the hole size, or larger, the light will be cast out by Fraunhofer diffraction. Since they do not disclose the size of their samp...

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[1] [1]

Eremets et al

studied hydrogen at low temperature up to 360 GPa in 2012; they reported absorption studies up to 0.1eV. Eremets et al

work page 2012

[2] [2]

They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa

studied dense hydrogen up to 480 GPa using standard bevel diamonds. They reported darkening of the sample and electrical conductivity in which they reported semi-metallic behavior around 440 GPa. In 2016 Dias, Noked, and Silvera

work page 2016

[3] [3]

In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5]

reported hydrogen was opaque at 420 GPa. In 2017 Dias and Silvera observed atomic metallic hydrogen at 495 GPa in the temperature range 5.5-83 K [5]. LOD did not acknowledge or discuss any earlier work relative to their observations. They report a high-pressure phase diagram that strongly disagrees with the existing literature. They fail to acknowledge th...

work page 2017

[4] [4]

In 2011 Eremets and Troyan studied hydrogen to 300 GPa and claimed metallization [7]

at even lower pressures; eventually it was conceded that there was no metallization in hydrogen or deuterium up to pressures of 216 GPa [10]. In 2011 Eremets and Troyan studied hydrogen to 300 GPa and claimed metallization [7]. Although they discovered two important new phases of molecular hydrogen, there was no evidence of MH [2,11] and eventually they c...

work page 2011

[5] [5]

The inset shows a photo of the darkening of the sample, around 420 GPa

Integrated transmitted intensity over the IR range (1800 cm-1 to 3800 cm-1) versus pressure, normalized to a 295 GPa pressure spectrum. The inset shows a photo of the darkening of the sample, around 420 GPa. 300 325 350 375 400 4250 20 40 60 80 100IR intensity cm-1(a.u) Pressure (GPa) Dias & Silvera 2017 300 K(b)150 GPa420 GPa30µm(a)82 KCuletH2 hydrogen w...

work page 2017

[6] [6]

RESEARCHER IR VIBRON FREQUENCY OF HYDROGEN AT LOW TEMPERATURES (80-100K) VISUAL OBSERVATION CONCLUSION Loubeyre FU BM (2002 and

All had approximately the same thickness. RESEARCHER IR VIBRON FREQUENCY OF HYDROGEN AT LOW TEMPERATURES (80-100K) VISUAL OBSERVATION CONCLUSION Loubeyre FU BM (2002 and

work page 2002

[7] [7]

4040cm-1 Solid hydrogen was observed to turn completely opaque BMack hydrogen reported Zha FU BM (2012 and

work page 2012

[8] [8]

4002cm-1 Sample still Transparent, no bMack hydrogen reported Dias and Silvera (2016 and

work page 2016

[9] [9]

4005cm-1 Sample still Transparent (Yellowish to Red in color) no bMack hydrogen reported Both reflected and transmitted light Both reflected and transmitted light Eremets et al (2016 and

work page 2016

[10] [10]

LOD neglect the effects of diffraction losses through their small sample hole in a metallic gasket

The third possibility is diffraction losses due to sample geometry. LOD neglect the effects of diffraction losses through their small sample hole in a metallic gasket. In general, when the wavelength of light is of the order of the hole size, or larger, the light will be cast out by Fraunhofer diffraction. Since they do not disclose the size of their samp...

work page arXiv 1993

[11] [11]

Observation of a first order phase transition to metal hydrogen near 425 GPa

P. Loubeyre, F. Occellis, and P. Dumas, Observation of a first order phase transition to metal hydrogen near 425 GPa., ArXiv:1906.05634 (2019)

work page internal anchor Pith review Pith/arXiv arXiv 1906

[12] [12]

C.-S. Zha, Z. Liu, and R. J. Hemley, Synchrotron Infrared Measurements of Dense Hydrogen to 360 GPa, Phys. Rev. Lett. 108, 146402 (2012)

work page 2012

[13] [13]

M. I. Eremets, A. P. Drozdov, P. P. Kong, and H. Wang, Molecular semimetallic hydrogen, arXiv:1708.05217 (2017)

work page internal anchor Pith review Pith/arXiv arXiv 2017

[14] [14]

R. Dias, O. Noked, and I. F. Silvera, New Quantum Phase Transition in Dense Hydrogen: The Phase Diagram to 420 GPa, arXiv:1603.02162v1 (2016)

work page internal anchor Pith review Pith/arXiv arXiv 2016

[15] [15]

Dias and I

R. Dias and I. F. Silvera, Observation of the Wigner-Huntington Transition to Solid Metallic Hydrogen, Science 355, 715 (2017)

work page 2017

[16] [16]

H. K. Mao and R. J. Hemley, Optical Studies of Hydrogen above 200 Gigapascals: Evidence for Metallization by Band Overlap, Science 244, 1462 (1989)

work page 1989

[17] [17]

M. I. Eremets and I. A. Troyan, Conductive Dense Hydrogen, Nature Materials 10, 927 (2011)

work page 2011

[18] [18]

I. F. Silvera, Evidence for Band Overlap Metallization of Hydrogen, Science 247, 863 (1990)

work page 1990

[19] [19]

H. K. Mao, R. J. Hemley, and M. Hanfland, Infrared Reflectance Measurements of the Insulator-Metal Transition in Solid Hydrogen, Phys. Rev. Lett. 65, 484 (1990)

work page 1990

[20] [20]

R. J. Hemley, H.-K. Mao, A. F. Goncharov, M. Hanfland, and V. Struzhkin, Synchrotron Infrared Spectroscopy to 0.15 eV of H2 and D2 at Megabar Pressures, Phys. Rev. Lett. 76, 1667 (1996)

work page 1996

[21] [21]

W. J. Nellis, A. L. Ruoff, and I. F. Silvera, Has Metallic Hydrogen Been Made in a Diamond Anvil Cell?, arXiv:1201.0407v1 (2012)

work page internal anchor Pith review Pith/arXiv arXiv 2012

[22] [22]

M. I. Eremets, I. A. Troyan, P. Lerch, and A. Drozdov, Infrared study of hydrogen up to 310GPa at room temperature, High Pressure Research 33, 377 (2013)

work page 2013

[23] [23]

Comment on: Observation of the Wigner-Huntington transition to metallic hydrogen

P. Loubeyre, F. Occelli, and P. Dumas, Comment on: Observation of the Wigner-Huntington transition to metallic hydrogen., condensed matter arXiv:1702.07192 (2017)

work page internal anchor Pith review Pith/arXiv arXiv 2017

[24] [24]

M. I. Eremets and A. P. Drozdov, Comments on the claimed observation of the Wigner-Huntington Transition to Metallic Hydrogen, Condensed matter arXiv:1702.05125 (2017)

work page internal anchor Pith review Pith/arXiv arXiv 2017

[25] [25]

A. F. Goncharov and V. V. Struzhkin, Comment on Observation of the Wigner-Huntington transition to metallic hydrogen, arXiv:1702.04246 (2017)

work page internal anchor Pith review Pith/arXiv arXiv 2017

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