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Ultrahigh-pressure crystallographic passage towards metallic hydrogen

Ji, Cheng ; Li, Bing ; Luo, Jie ; Zhao, Yongsheng ; Liu, Yuan ; Glazyrin, Konstantin ; Björling, Alexander LU ; Marçal, Lucas A.B. LU ; Kahnt, Maik LU orcid and Kalbfleisch, Sebastian LU , et al. (2025) In Nature 641(8064). p.904-909
Abstract

The structural evolution of molecular hydrogen H2 under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory1, 2, 3–4, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H2, has been previously confirmed in experiments5. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H2 to a post-hcp structure with a six-fold larger supercell at pressures above 212 GPa, indicating the change of spherical H2 to various ordered configurations.... (More)

The structural evolution of molecular hydrogen H2 under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory1, 2, 3–4, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H2, has been previously confirmed in experiments5. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H2 to a post-hcp structure with a six-fold larger supercell at pressures above 212 GPa, indicating the change of spherical H2 to various ordered configurations. Theoretical calculations based on our XRD results found a time-averaged structure model in the space group P6¯2c with alternating layers of spherically disordered H2 and new graphene-like layers consisting of H2 trimers (H6) formed by the association of three H2 molecules. This supercell has not been reported by any previous theoretical study for the post-hcp phase, but is close to a number of theoretical models with mixed-layer structures. The evidence of a structural transition beyond hcp establishes the trend of H2 molecular association towards polymerization at extreme pressures, giving clues about the nature of the molecular-to-atomic transition of metallic hydrogen. Considering the spectroscopic behaviours that show strong vibrational and bending peaks of H2 up to 400 GPa, it would be prudent to speculate the continuation of hydrogen molecular polymerization up to its metallization.

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organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Nature
volume
641
issue
8064
article number
255701
pages
6 pages
publisher
Nature Publishing Group
external identifiers
  • pmid:40369082
  • scopus:105005116099
ISSN
0028-0836
DOI
10.1038/s41586-025-08936-w
language
English
LU publication?
yes
additional info
Publisher Copyright: © The Author(s), under exclusive licence to Springer Nature Limited 2025.
id
adeb98ad-2277-4432-968c-6b9a81d26f36
date added to LUP
2025-05-28 08:07:14
date last changed
2025-06-11 08:55:36
@article{adeb98ad-2277-4432-968c-6b9a81d26f36,
  abstract     = {{<p>The structural evolution of molecular hydrogen H<sub>2</sub> under multi-megabar compression and its relation to atomic metallic hydrogen is a key unsolved problem in condensed-matter physics. Although dozens of crystal structures have been proposed by theory<sup>1, 2, 3–4</sup>, only one, the simple hexagonal-close-packed (hcp) structure of only spherical disordered H<sub>2</sub>, has been previously confirmed in experiments<sup>5</sup>. Through advancing nano-focused synchrotron X-ray probes, here we report the observation of the transition from hcp H<sub>2</sub> to a post-hcp structure with a six-fold larger supercell at pressures above 212 GPa, indicating the change of spherical H<sub>2</sub> to various ordered configurations. Theoretical calculations based on our XRD results found a time-averaged structure model in the space group P6¯2c with alternating layers of spherically disordered H<sub>2</sub> and new graphene-like layers consisting of H<sub>2</sub> trimers (H<sub>6</sub>) formed by the association of three H<sub>2</sub> molecules. This supercell has not been reported by any previous theoretical study for the post-hcp phase, but is close to a number of theoretical models with mixed-layer structures. The evidence of a structural transition beyond hcp establishes the trend of H<sub>2</sub> molecular association towards polymerization at extreme pressures, giving clues about the nature of the molecular-to-atomic transition of metallic hydrogen. Considering the spectroscopic behaviours that show strong vibrational and bending peaks of H<sub>2</sub> up to 400 GPa, it would be prudent to speculate the continuation of hydrogen molecular polymerization up to its metallization.</p>}},
  author       = {{Ji, Cheng and Li, Bing and Luo, Jie and Zhao, Yongsheng and Liu, Yuan and Glazyrin, Konstantin and Björling, Alexander and Marçal, Lucas A.B. and Kahnt, Maik and Kalbfleisch, Sebastian and Liu, Wenjun and Gao, Yang and Wang, Junyue and Mao, Wendy L. and Liu, Hanyu and Ma, Yanming and Ding, Yang and Yang, Wenge and Mao, Ho Kwang}},
  issn         = {{0028-0836}},
  language     = {{eng}},
  month        = {{05}},
  number       = {{8064}},
  pages        = {{904--909}},
  publisher    = {{Nature Publishing Group}},
  series       = {{Nature}},
  title        = {{Ultrahigh-pressure crystallographic passage towards metallic hydrogen}},
  url          = {{http://dx.doi.org/10.1038/s41586-025-08936-w}},
  doi          = {{10.1038/s41586-025-08936-w}},
  volume       = {{641}},
  year         = {{2025}},
}