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Nature. 2019 Sep;573(7775):558-562. doi: 10.1038/s41586-019-1565-9. Epub 2019 Sep 25.

Ultrahigh-pressure isostructural electronic transitions in hydrogen.

Author information

1
Center for High Pressure Science and Technology Advanced Research, Beijing, China.
2
High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL, USA.
3
Center for the Study of Matter at Extreme Conditions and Department of Mechanical and Materials Engineering, Florida International University, Miami, FL, USA.
4
Advanced Photon Source, Argonne National Laboratory, Argonne, IL, USA.
5
High Pressure Collaborative Access Team (HPCAT), X-ray Science Division, Argonne National Laboratory, Lemont, IL, USA.
6
Condensed Matter Theory, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden.
7
DAC Tools LLC, Naperville, IL, USA.
8
Center for Advanced Radiation Sources, University of Chicago, Chicago, IL, USA.
9
Department of Geological Sciences, Stanford University, Stanford, CA, USA.
10
Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
11
Center for High Pressure Science and Technology Advanced Research, Beijing, China. maohk@hpstar.ac.cn.

Abstract

High-pressure transitions are thought to modify hydrogen molecules to a molecular metallic solid and finally to an atomic metal1, which is predicted to have exotic physical properties and the topology of a two-component (electron and proton) superconducting superfluid condensate2,3. Therefore, understanding such transitions remains an important objective in condensed matter physics4,5. However, measurements of the crystal structure of solid hydrogen, which provides crucial information about the metallization of hydrogen under compression, are lacking for most high-pressure phases, owing to the considerable technical challenges involved in X-ray and neutron diffraction measurements under extreme conditions. Here we present a single-crystal X-ray diffraction study of solid hydrogen at pressures of up to 254 gigapascals that reveals the crystallographic nature of the transitions from phase I to phases III and IV. Under compression, hydrogen molecules remain in the hexagonal close-packed (hcp) crystal lattice structure, accompanied by a monotonic increase in anisotropy. In addition, the pressure-dependent decrease of the unit cell volume exhibits a slope change when entering phase IV, suggesting a second-order isostructural phase transition. Our results indicate that the precursor to the exotic two-component atomic hydrogen may consist of electronic transitions caused by a highly distorted hcp Brillouin zone and molecular-symmetry breaking.

PMID:
31554980
DOI:
10.1038/s41586-019-1565-9

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