Harvard researchers have studied and observed solid hydrogen under pressure at low temperatures. With increasing pressure we observe changes in the sample, going from transparent, to black, to a reflective metal, the latter studied at a pressure of 495 GPa. They have measured the reflectance as a function of wavelength in the visible spectrum finding values as high as 0.90 from the metallic hydrogen. They have fit the reflectance using a Drude free electron model to determine the plasma frequency of 30.1 eV at T= 5.5 K, with a corresponding electron carrier density of 6.7x10^23 particles/cm3 , consistent with theoretical estimates. The properties are those of a metal. Solid metallic hydrogen has been produced in the laboratory.

* they have made some metallic hydrogen and have it in a cryostat in liquid nitrogen
* they might leave it under pressure and let it warm to room temperature or they could keep it cold and release the pressure
* they are planning to test for high temperature superconductivity

If it stays a metal at room temperature and after releasing pressure and was also a superconductor then it would be the holy grail of physics.

Controlled nuclear fusion, production of metallic hydrogen, and high temperature superconductivity have been listed as the top three key problems of physics. These problems all involve hydrogen and its isotopes.

UPDATE - Nextbigfuture has written about the work of co-author Isaac Silvera, who had a NASA Advanced innovation project looking at using solid metallic hydrogen for rocket fuel and ways to lower the pressure needed to create metallic hydrogen

Early theoretical predictions of metallic hydrogen being created at a pressure of 25 GPa (100GPa=1megabar) was way off. Modern quantum Monte-Carlo methods, as well as density functional theory (DFT), predict a pressure of ~400 to 500 GPa for the transition. The most likely space group for the atomic lattice is I41/amd. Metallic hydrogen has been predicted to be a high temperature superconductor, first by Ashcroft, with critical temperatures possibly higher than room temperature. Moreover, SMH is predicted to be metastable so that it may exist at room temperature when the pressure is released. If so, and superconducting, it could have an important impact on mankind’s energy problems and would revolutionize rocketry as a powerful rocket propellant

SMH at 495 GPa is about 15-fold denser than zero-pressure hydrogen. In Table I they compare solid atomic hydrogen to other elements in the first column of the periodic table, and see a remarkable contrast in properties.

As of the writing of this article they are maintaining the first sample of the first element in the form of solid metallic hydrogen at liquid nitrogen temperature in a cryostat. This valuable sample may survive warming to room temperature and the DAC could be extracted from the cryostat for greatly enhanced observation and further study. Another possibility is to cool to liquid helium temperatures and slowly release the load to see if SMH is metastable. An important future measurement is to study this metal for high temperature superconductivity.

SOURCE- Arxiv