Black metal hydrogen above 360 GPa driven by proton quantum fluctuations

Production of metallic hydrogen is one of the top three open quests of physics. Recent low temperature optical, resistivity, and infrared (IR) transmission experiments show different metallization pressures, varying from 360GPa to 490GPa. In this work, we simulate structural properties, and vibrational Raman, IR and optical spectra with inclusion of proton quantum effects. We confirm the C2/c-24 as the best candidate for phase III at low temperatures from 250GPa to 420GPa. We demonstrate that nuclear quantum effects downshift the vibron frequencies of 1000 cm-1 and are responsible of the strong increase with pressure of the Raman vibron linewidth in the 260-360 GPa range detected in experiments. The C2/c-24 phase becomes metallic at 380GPa due to band overlap, as suggested by transport data. Despite its metallic character, we find a transparent window in the IR up to 450GPa and low reflectivity independent on the energy, both consistent with Ref. 4 and with the observation of a black phase above 320GPa. As the black phase persists even above 450GPa, the shiny phase observed at 490GPa is inconsistent with phase III. By correctly accounting for nuclear quantum effects, we reconcile all contradictions in existing experimental scenarios.