Ultrahigh-pressure crystallographic passage towards metallic hydrogen

• 成果类型: Article
• 署名作者: Ji, Cheng; Li, Bing; Luo, Jie; Zhao, Yongsheng; Liu, Yuan; Glazyrin, Konstantin; Bjorling, Alexander; Marcal, Lucas A. B.; Kahnt, Maik; Kalbfleisch, Sebastian; Liu, Wenjun; Gao, Yang; Wang, Junyue; Mao, Wendy L.; Liu, Hanyu; Ma, Yanming; Ding, Yang; Yang, Wenge; Mao, Ho-Kwang
• 署名单位: Jilin University; Jilin University; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Lund University; Laboratorio Nacional de Luz Sincrotron (LNLS); United States Department of Energy (DOE); Argonne National Laboratory; Stanford University; Stanford University; United States Department of Energy (DOE); SLAC National Accelerator Laboratory; Jilin University
• 刊物名称: Nature
• ISSN/ISSBN: 0028-1887
• DOI: 10.1038/s41586-025-08936-w
• 发表日期: 2025-05-22
• 关键词: x-ray-diffraction; molecular-hydrogen; PHASE-TRANSITION; quantum

摘要

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 P62c\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$P\bar{6}2c$$\end{document} 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.