TY  - JOUR
AU  - Ji, Cheng
AU  - Li, Bing
AU  - Luo, Jie
AU  - Zhao, Yongsheng
AU  - Liu, Yuan
AU  - Glazyrin, Konstantin
AU  - Björling, Alexander
AU  - Marçal, Lucas A. B.
AU  - Kahnt, Maik
AU  - Kalbfleisch, Sebastian
AU  - Liu, Wenjun
AU  - Gao, Yang
AU  - Wang, Junyue
AU  - Mao, Wendy
AU  - Liu, Hanyu
AU  - Ma, Yanming
AU  - Ding, Yang
AU  - Yang, Wenge
AU  - Mao, Ho-Kwang
TI  - Ultrahigh-pressure crystallographic passage towards metallic hydrogen
JO  - Nature
VL  - 641
IS  - 8064
SN  - 0028-0836
CY  - London [u.a.]
PB  - Nature Publ. Group
M1  - PUBDB-2025-01655
SP  - 904 - 909
PY  - 2025
AB  - 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.
LB  - PUB:(DE-HGF)16
C6  - pmid:40369082
UR  - <Go to ISI:>//WOS:001488377700001
DO  - DOI:10.1038/s41586-025-08936-w
UR  - https://bib-pubdb1.desy.de/record/627880
ER  -