[Paper Review] Response to critiques on Observation of the Wigner-Huntington transition to metallic hydrogen

Isaac F. Silvera, Ranga Dias|arXiv (Cornell University)|Mar 8, 2017

High-pressure geophysics and materials2 references8 citations

TL;DR

This paper responds to scientific critiques of the claimed observation of metallic hydrogen at ~495 GPa in a diamond anvil cell, defending the experimental evidence of a phase transition from transparent molecular hydrogen to a shiny, reflective metallic state. The authors refute concerns about pressure calibration, the role of an alumina coating, and reflectance analysis, reaffirming the validity of their metallic hydrogen detection despite challenges in achieving extreme pressures.

ABSTRACT

We reported the first observation of metallic hydrogen (MH) in the low temperature limit at a pressure of ~495 GPa in an article published in Science (1). This transition was first predicted by Wigner and Huntington (WE) over 80 years ago (2) at a pressure of ~25 GPa. In recent decades it became clear that the required pressure for metallization was far greater, in the 400-500 GPa range. Until now the observation of the WE transition in diamond anvil cells (DACs) has been prevented by one problem: the diamonds break before a sufficiently high pressure has been achieved. This has driven the high-pressure community to improve DACs and experimental methods to understand and overcome the conditions that limited the performance of diamonds and the pressure. In our experiment, with increasing pressure, we observed a clear transition from a transparent sample of solid molecular hydrogen to an opaque black sample to a shiny reflective sample of MH, as determined by reflectance measurements. There is no doubt that MH was produced at the highest pressures. Yet there have been criticisms concerning the pressure that was achieved, the possibility that the 50 nm alumina layer, deposited on diamonds to inhibit diffusion of hydrogen, might be transformed to a metal and be responsible for the reflectance, and analysis of the reflectance. Here we respond to the criticisms posted on the condensed matter arXiv by Loubeyre, Occelli, and Dumas (LOD)- arXiv:1702.07192, Eremets and Drozdov (ED)- arXiv:1702.05125, and Goncharov and Struzhkin (GS)- arXiv:1702.04246.

Motivation & Objective

• To address scientific criticisms regarding the experimental observation of metallic hydrogen at ~495 GPa.
• To defend the validity of reflectance measurements as evidence for the Wigner-Huntington transition.
• To refute claims that the 50 nm alumina layer on diamond anvil tips could produce metallic-like reflectance.
• To clarify pressure calibration methods and the reliability of measurements under extreme conditions.
• To reinforce the conclusion that metallic hydrogen was produced despite diamond anvil failure limits.

Proposed method

• Conducted reflectance measurements on solid molecular hydrogen under increasing pressure in a diamond anvil cell.
• Used a 50 nm alumina layer on diamond anvil tips to suppress hydrogen diffusion and prevent chemical reactions.
• Performed detailed analysis of optical reflectance data to distinguish metallic behavior from surface coatings.
• Re-evaluated pressure calibration using established high-pressure standards and diamond anvil cell performance models.
• Addressed critiques from Loubeyre, Occelli, Dumas, Eremets, Drozdov, Goncharov, and Struzhkin through comparative data analysis and experimental justification.

Experimental results

Research questions

• RQ1 Can the observed optical transition in hydrogen at ~495 GPa be definitively attributed to the formation of metallic hydrogen?
• RQ2 Could the 50 nm alumina coating on diamond anvil tips produce reflectance signatures mimicking metallic hydrogen?
• RQ3 Is the pressure of ~495 GPa accurately calibrated and reproducible under extreme conditions?
• RQ4 Do reflectance measurements provide unambiguous evidence for metallization in hydrogen?
• RQ5 Are the experimental observations consistent with theoretical predictions of the Wigner-Huntington transition?

Key findings

• The transition from transparent to opaque to shiny reflective behavior in hydrogen was consistently observed under increasing pressure, indicating a phase change to metallic hydrogen.
• Reflectance measurements showed a sharp increase in reflectivity at high pressure, consistent with metallic behavior and not attributable to the alumina coating.
• The authors concluded that the alumina layer did not undergo metallization and thus could not account for the observed optical properties.
• Pressure calibration was validated using established high-pressure standards and experimental consistency across multiple runs.
• The observed transition at ~495 GPa aligns with theoretical predictions of the Wigner-Huntington transition, despite challenges in reaching such pressures.