Link: https://en.wikipedia.org/wiki/Metallic_hydrogen

Often called the Holy Grail of High-pressure physics, Metallic hydrogen is a phase of hydrogen which behaves like an electrical conductor, predicted in 1935. It has been claimed to be produced a few times in a laboratory, but always under skepticism.

Silvera stated that they did not repeat their experiment, since more tests could damage or destroy their existing sample, but assured the scientific community that more tests are coming.

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In June 2019 a team at the Commissariat à l'énergie atomique et aux énergies alternatives (French Alternative Energies & Atomic Energy Commission) claimed to have created metallic hydrogen at around 425GPa using a toroidal profile diamond anvil cell produced using electron beam machining.