Solid metallic hydrogen has been produced in the laboratory

Did they test if it's super conducting?

They comment about this at the end of the paper: "As of the writing of this article we 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."

Super cool stuff! There are some greatly quotable sentences in the paper:

> Moreover, SMH (solid metal hydrogen) 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.

> The principal limitation for achieving the required pressures to observe SMH in a DAC (diamond anvil cell) has been failure of the diamonds.

> The sample was cryogenically loaded at 15 K and included a grain of ruby for pressure determination.

> As of the writing of this article we are maintaining the first sample of the first element in the form of solid metallic hydrogen at liquid nitrogen temperature in a cryostat.

If it's stable at room temperature wouldn't it make a really high density fuel too?

Metallic Hydrogen can also be a liquid and even a gas, the metallic part indicates it's an electric conductor, not a solid. The "idea" behind metallic hydrogen is that since hydrogen is above the alkali metals in the periodic tables there should be a phase where it behaves like a metal, the state of the phase is not defined as a solid/gas/liquid in fact in all honesty it would exist as all 3 and more.

The first production of metallic oxygen was a liquid, this is the first solid one, tho at these pressures it's really unlikely that it would effective as fuel store. One of the more interesting parts about metallic hydrogen is the information we learn also applies to hydrides (hydrogen alloys) especially things like Lithium-Hydrogen since basically you can stabilize a large amount of hydrogen atoms (6 or more) around a single atom of Lithium, this might actually be very interesting for a lot of applications including energy storage. Hydrides should be considerably more stable and more importantly at considerably lower pressures which would mean that they can actually be used for various applications since you are not going to find something that only can exist at 400 gPA levels of pressure or higher very useful for high stress applications.