On October 5th 2016, Ranga Dias and Isaac F. Silvera of Lyman Laboratory of Physics, Harvard University released the first experimental evidence that solid metallic hydrogen has been synthesized in the laboratory.
It took 495 GPa pressure to create. The sample is being held in the cryostat in liquid nitrogen.
Atomic metallic hydrogen, if metastable at ambient pressure and temperature could be used as the most powerful chemical rocket fuel, as the atoms recombine to form molecular hydrogen. This light-weight high-energy density material would revolutionize rocketry, allowing single-stage rockets to enter orbit and chemically fueled rockets to explore our solar system. To transform solid molecular hydrogen to metallic hydrogen requires extreme high pressures.