US team claims world first with creation of metallic hydrogen

Scientists at Harvard University have succeeded in making metallic hydrogen, a material which despite being theorised over a century ago has never been created on Earth.

The material could have a range of applications, including as a room-temperature superconductor, and a rocket fuel that could help humans explore the far reaches of space.

Described by lead researcher Prof Isaac Silvera as “the holy grail of high pressure physics”, the breakthrough is detailed in a paper published in the latest issue of Science.

“It’s the first-ever sample of metallic hydrogen on Earth,” said Silvera, “so when you’re looking at it, you’re looking at something that’s never existed before.”

To create the material the team squeezed a tiny hydrogen sample at 495 gigapascal (GPa), which is greater than the pressure at the center of the Earth.

At these extreme pressures solid molecular hydrogen, which consists of molecules on the lattice sites of the solid, breaks down, and the tightly bound molecules dissociate to transform into atomic hydrogen, which is a metal.

While the work creates an important window into understanding the general properties of hydrogen, it also offers tantalising hints at potentially revolutionary new materials.

“One prediction that’s very important is metallic hydrogen is predicted to be meta-stable,” Silvera said. “That means if you take the pressure off, it will stay metallic, similar to the way diamonds form from graphite under intense heat and pressure, but remain diamonds when that pressure and heat are removed.”

Understanding whether the material is stable is important, Silvera said, because predictions suggest metallic hydrogen could act as a superconductor at room temperatures.

“As much as 15 per cent of energy is lost to dissipation during transmission,” he said, “so if you could make wires from this material and use them in the electrical grid, it could change that story.”

According to postdoctoral research fellow Ranga Dias the material could have a range of disruptive applications including in maglev systems for high-speed trains, and ultra efficient electric cars. He added that because superconductors have zero resistance, superconducting coils made from the material could be used to store excess energy.

The material could also play a role in helping humans explore the far reaches of space, as a more powerful rocket propellant. “It takes a tremendous amount of energy to make metallic hydrogen,” Silvera explained. “And if you convert it back to molecular hydrogen, all that energy is released, so that would make it the most powerful rocket propellant known to man, and could revolutionize rocketry.”