I had heard that the large radiation belts around Jupiter may be formed by liquid metallic hydrogen in (or around) Jupiter's core (which Wikipedia says haven't been observed in labs yet due to the immense pressure required), but I don't understand how the liquid metallic hydrogen can form a planetary magnetic field. The article also says that the hydrogen can act as a conductor, is this somehow related to moving electric fields forming magnetic fields?
As you stated, we have not been able to simulate the pressure and temperatures required to generate those that are believed to exist in Jupiter's interior other than in short-lived shockwave experiments, according to the NASA webpage A Freaky Fluid inside Jupiter?, observing that
Going further, according to the article Jumpin' Jupiter! Metallic Hydrogen (Lawrence Livermore National Laboratory), discuss the shock wave results, finding the level at which hydrogen metallises as being
The findings from the researchers above are summarised in the diagram below
The source is the Jumping Jupiter link above.