To create it, the scientists squeezed a hydrogen sample at which pressure molecular hydrogen transforms into atomic hydrogen – which is a metal.
"Metallic hydrogen is predicted to be meta-stable," researcher Isaac Silvera said. "That means if you take the pressure off, it will stay metallic.”
According to the researchers, understanding whether the material is stable is important because predictions suggest metallic hydrogen could act as a superconductor at room temperatures.
A room temperature superconductor could make magnetic levitation possible, as well as making electric cars more efficient and improving the performance of many electronic devices.
