In addition to helping scientists answer some fundamental questions about the nature of matter, the material is theorized to have a wide range of applications, including as a room-temperature superconductor.

"This is the Holy Grail of high-pressure physics," Silvera said of the quest to find the material. "It's the first-ever sample of metallic hydrogen on Earth, so when you're looking at it, you're looking at something that's never existed before."

In their experiments, Silvera and Dias squeezed a tiny hydrogen sample at 495 gigapascal (GPa), or more than 71.7 million pounds per square inch, which is greater than the pressure at the center of the Earth. At such extreme pressures, Silvera explained, solid molecular hydrogen, which consists of molecules on the lattice sites of the solid, breaks down, and the tightly bound molecules dissociate to transforms into atomic hydrogen, which is a metal.