Journal Article

PUBDB-2025-01655

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Ultrahigh-pressure crystallographic passage towards metallic hydrogen

Ji, C.Extern* ; Li, B.Extern* ; Luo, J.Extern* ; Zhao, Y.Extern*DESY* ; Liu, Y.Extern* ; Glazyrin, K.XFEL.EU*DESY* ; Björling, A. ; Marçal, L. A. B. ; Kahnt, M.Extern* ; Kalbfleisch, S.Extern* ; Liu, W. ; Gao, Y.Extern* ; Wang, J. ; Mao, W.Extern*XFEL.EU* ; Liu, H. ; Ma, Y.Extern* ; Ding, Y. ; Yang, W. ; Mao, H.-K. (Corresponding author)Extern*

2025
Nature Publ. Group London [u.a.]

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Please use a persistent id in citations: doi:10.1038/s41586-025-08936-w  doi:10.3204/PUBDB-2025-01655

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. Theoretical calculations based on our XRD results found a time-averaged structure model in the space group 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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Contributing Institute(s):

1. DOOR-User (DOOR ; HAS-User)
2. PETRA-D (FS-PETRA-D)

Research Program(s):

1. 632 - Materials – Quantum, Complex and Functional Materials (POF4-632) (POF4-632)
2. 6G3 - PETRA III (DESY) (POF4-6G3) (POF4-6G3)
3. FS-Proposal: I-20190637 (I-20190637) (I-20190637)
4. FS-Proposal: I-20220481 (I-20220481) (I-20220481)
5. FS-Proposal: I-20230465 (I-20230465) (I-20230465)

Experiment(s):

1. PETRA Beamline P02.2 (PETRA III)

Appears in the scientific report 2025

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