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There is now a CONTENT FREEZE for Mercury while we switch to a new platform. It began on Friday, March 10 at 6pm and will end on Wednesday, March 15 at noon. No new content can be created during this time, but all material in the system as of the beginning of the freeze will be migrated to the new platform, including users and groups. Functionally the new site is identical to the old one. webteam@gatech.edu
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We report direct evidence of a new phase of molecular hydrogen (H2) observed in a system of H2 adsorbed in a graphitic nano-porous carbon at temperatures (74-92 K) and pressures (>76 bar) well above the critical point of bulk H2. The system is studied with deep inelastic neutron scattering (DINS), where ‘deep’ refers to the high energy of the incident neutrons which penetrate deeply into the system to study its individual atoms within their local environment. Normally scattering becomes fully incoherent, reflecting only correlations of a single particle with itself at a later time, at momentum transfers Q>10-12 Å-1, where 1/Q is smaller than the length scale of the thermal fluctuations of the atoms. But in this new phase, we observe novel spectral features that remain coherent, reflecting inter-atomic correlations, up to the highest momentum transfers measured, 35 Å-1. This corresponds to length scales several times smaller than the H-H bond, indicating that the system has transitioned to a strongly correlated state. Hydrogen adsorption measurements also show evidence of an exothermic phase transition with H2 denser in the novel phase. We present the results of several experiments on this system, then propose a model of H2-H2 nuclear spin correlations mediated through a quantum exchange interaction to explain the measured properties. Future work needed to further probe the system and prove the existence of nuclear spin correlations is discussed.
