Diamonds put the squeeze on hydrogen R. Dias and I.F. Silvera

Metallic hydrogen has been created in the lab for the first time, by squeezing a sample of the element to pressures beyond what exists at the centre of the Earth. The creation of a substance first predicted more than 80 years ago could one day lead to superfast computers or souped-up rocket fuel.

Two researchers at Harvard University achieved the feat using diamonds to squeeze solid hydrogen at low temperatures, until the atoms were so packed that they started to share electrons. The shared cloud of electrons indicated a transition into a metallic state, making the hydrogen shiny and electrically conductive.

“If this experiment is reproducible, it solves experimentally one of the major outstanding problems in all of physics,” says Jeffrey McMahon at Washington State University in Pullman.


“At a fundamental level, we’re considering the simplest atomic system in the periodic table of the elements, so we would like to understand that system and all of its properties,” says Isaac Silvera at Harvard University, who made the breakthrough with his colleague Ranga Dias.

Landmark prediction

In 1935, Eugene Wigner and Hillard Bell Huntington predicted that at a pressure of 25 gigapascals (GPa), solid molecular hydrogen would turn into a metal. Since 25 GPa is a pressure over 200 times that at the bottom of the Mariana trench, their claim was impossible to verify.

As our knowledge of the quantum world and its application to materials improved, that pressure threshold kept going up, staying well out of the range anyone could create in a lab. More recent estimates put the pressure for hydrogen to go metallic at between 400 and 500 GPa.

When Silvera and Dias managed to turn hydrogen metallic, it was at a pressure of 495 GPa, well beyond the 360 GPa of Earth’s core.

They were able to obtain such a high pressure by crushing the solid hydrogen between the flattened tips of two synthetic diamonds. To prevent the diamonds from cracking, the tips were carefully polished to remove surface defects, heated to remove any residual internal stresses, and coated in alumina, an extremely hard compound of aluminium and oxygen that hydrogen can’t seep through.

At relatively low pressures, the compressed solid hydrogen was transparent. As the compression intensified, it began to turn opaque and black.

But at 495 Gpa, the hydrogen was shiny and reflective, indicating its transformation into a metal (although the researchers can’t be sure whether it was solid or liquid).

Hydrogen in transition R. Dias and I.F. Silvera

“It’s not too surprising that it happens – I mean, it’s been predicted by theory for 80 years – but it’s nice that they’re finally seen it and now they can start getting more quantitative data,” says David Ceperley at the University of Illinois at Urbana-Champaign.

The researchers predict that metallic hydrogen might be a room-temperature superconductor and could possibly exist, once created, at normal pressures. This would mean it could be could potentially be used to make superconducting wires that carry electricity vast distances without dissipating any power. The team also speculates that metallic hydrogen is so energy-dense that it could one day be used to create rocket fuel vastly more potent than anything we have at present – revolutionising how we put things in space.

Journal reference: Science, DOI: 10.1126/science.eaal1579