Semimetallic molecular hydrogen at pressure above 350 GPa

By M. Eremets, A. Drozdov, P. Kong, Hongbo Wang. Nature Physics, 2017

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According to theoretical predictions, insulating molecular hydrogen dissociates and transforms into an atomic metal at pressures P ≈ 370–500 GPa (refs. 1–3). In another scenario, the metallization first occurs in the 250–500 GPa pressure range in molecular hydrogen through overlapping of electronic bands4–7. The calculations are not accurate enough to predict which option is realized. Here, we show that at a pressure of 350–360 GPa and temperatures <200 K, the hydrogen starts to conduct, and that the temperature dependence of the electrical conductivity is typical of a semimetal. The conductivity, measured up to 440 GPa, increases strongly with pressure. Raman spectra, measured up to 480 GPa, indicate that hydrogen remains a molecular solid at pressures up to 440 GPa, while at higher pressures the Raman signal vanishes, probably indicating further transformation to a good molecular metal or to an atomic state.The predicted metallization of hydrogen has long fascinated high-pressure physicists. Conductivity and spectroscopic measurements now reveal that above pressures of 350 GPa, hydrogen starts to conduct in a manner akin to a semimetal.

Subfields: Atomic and Molecular Physics, and Optics, Geophysics, Physical and Theoretical Chemistry

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