It only took 80 years, but we may have finally got a glimpse of elusive metallic hydrogen. Hydrogen is the most abundant element in the universe, and when put under high pressure – such as at the center of gas giants like Jupiter – it starts behaving like a metal.
Researchers from the University of Edinburgh used diamond anvils to apply a pressure of 3.25 million atmospheres on hydrogen molecules, which they saw enter a new solid state phase. This is called Phase V, which is thought to be the beginnings of metallic hydrogen.
Hydrogen is usually found in molecular form: two hydrogen atoms are bound together and they share their two electrons. In 1935, it was predicted that, under sufficient compression, this molecular bond would break and the atoms would organize themselves into an atomic solid metallic configuration, with electrons loosely bound to the atoms just like copper or iron.
"The past 30 years of the high-pressure research saw numerous claims of the creation of metallic hydrogen in the laboratory, but all these claims were later disproved,” Professor Eugene Gregoryanz, who led the research, said in a statement. “Our study presents the first experimental evidence that hydrogen could behave as predicted, although at much higher pressures than previously thought. The finding will help to advance the fundamental and planetary sciences."
The newly discovered phase is not the pure metallic state predicted by the theory, but more the onset phase, where molecular bonds are being broken but the metallic properties have not arisen in full. The study suggests that an even higher pressure is necessary to obtain the long sought metallic hydrogen state. And the diamond anvils used in this experiment might not be enough to produce the pressure necessary to create metallic hydrogen.
The study, which is published in Nature, is likely to be met with skepticism. High-pressure techniques and small samples can have large errors, so the team’s work will be inspected carefully.
If the results are confirmed, different techniques will have to be used to achieve the metallic hydrogen. The pressure necessary to produce it is probably slightly beyond our current capabilities.
2