It has long been predicted that hydrogen would become metallic when subjected to enough pressure, but researchers have been disappointed in the past when using pressures as high as 300 gigapascals at low temperatures. Mikhail Eremets and Ivan Troyan at the Max Planck Institute for Chemistry in Mainz, Germany, have produced opaque, conducting hydrogen by squeezing it with pressures greater than 220 gigapascals at room temperature.

At 260–270 gigapascals, the hydrogen became a reflective metal. The duo coated the diamond anvil cells used to pressurize the sample with thin layers of copper, gold or other materials to prevent hydrogen diffusing in and breaking the diamond. The study opens avenues of research into the structure of different phases of hydrogen.

Nature Mater. 10.1038/nmat3175 (2011)