Ultrahigh-pressure crystallographic passage towards metallic hydrogen

Cheng Ji, Bing Li, Jie Luo, Yongsheng Zhao, Yuan Liu, Konstantin Glazyrin, Alexander Björling, Lucas A. B. Marçal, Maik Kahnt, Sebastian Kalbfleisch, Wenjun Liu, Yang Gao, Junyue Wang, Wendy L. Mao, Hanyu Liu, Yanming Ma, Yang Ding, Wenge Yang and Ho-Kwang Mao ()
Additional contact information
Cheng Ji: Center for High Pressure Science and Technology Advanced Research
Bing Li: Center for High Pressure Science and Technology Advanced Research
Jie Luo: Jilin University
Yongsheng Zhao: Center for High Pressure Science and Technology Advanced Research
Yuan Liu: Jilin University
Konstantin Glazyrin: Deutsches Elektronen-Synchrotron
Alexander Björling: Lund University
Lucas A. B. Marçal: Lund University
Maik Kahnt: Lund University
Sebastian Kalbfleisch: Lund University
Wenjun Liu: Argonne National Laboratory
Yang Gao: Center for High Pressure Science and Technology Advanced Research
Junyue Wang: Center for High Pressure Science and Technology Advanced Research
Wendy L. Mao: Stanford University
Hanyu Liu: Jilin University
Yanming Ma: Jilin University
Yang Ding: Center for High Pressure Science and Technology Advanced Research
Wenge Yang: Center for High Pressure Science and Technology Advanced Research
Ho-Kwang Mao: Center for High Pressure Science and Technology Advanced Research

Nature, 2025, vol. 641, issue 8064, 904-909

Abstract: 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 theory1–4, 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 $$P\bar{6}2c$$ P 6 ¯ 2 c 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.

Date: 2025
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DOI: 10.1038/s41586-025-08936-w

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