  Solid rigidity and liquid-scale mobility are thought incompatible in
elemental substances. One cannot have an elemental solid that is long-range
positionally ordered wherein the atoms flow like in a liquid simultaneously.
The only exception might be the hypothetical supersolid state of 4He. In this
work, we demonstrate that such exotic state could exist even in the classical
regime. Using ab initio molecular dynamics (AIMD) and ab initio path integral
molecular dynamics (AI-PIMD), a novel state of dense hydrogen which
simultaneously has both long-range spatial ordering and liquid-scale atomic
mobility is discovered at 1~1.5 TPa (1 TPa=10000000 atmospheric pressures). The
features distinct from a normal solid and liquid are carefully characterized,
with the stability and melting behavior are investigated. Extensive AI-PIMD
simulations further revealed that this state might be (meta-)stable even at
ultra-low temperatures, suggesting an emerging candidate for an alternative
type of supersolid state in dense metallic hydrogen.
