Squeezing the most out of it

This lay-term sentence is paraphrasing the most important conjecture of Condensed Matter Physics. It was postulated in 1935 by Hillard Huntington and Eugene Wigner. Some 85 years later though, it is still not fully proven.

Some recent observations published this January in Nature are showing promising results with samples of hydrogen turning shiny, a distinctive metallic property. This is at over 400 gigapascals, an order of magnitude more than was originally predicted.

The covalent bonds in individual Hydrogen molecules vibrate at a frequency dependent on its phase.  Normally, we would assume this “vibron” frequency should increase as pressure gets higher because the equally charged atoms are forced closer together and thus repulse each other more strongly. This is similar to a merry-go-round spinning faster if the two people on it get closer together.

To observe what really happens we use diamond anvils, contraptions capable of recreating pressures comparable to those inside Jupiter. However, as we look through the anvil at increasingly higher pressures, we see at one point the vibron frequency suddenly starts to decrease.

This is highly exciting and could mean a plethora of different things, but it most probably suggests that the bonds between the atoms are weakening. This means the metaphorical merry-go-round is about to melt into a blob of superconducting sci-fi metallic Hydrogen with exciting properties.

Despite the coronavirus outbreak I have been to be able to start helping with research remotely at the University of Edinburgh looking at why does this unexpected turnover happen. Instead of using diamond anvils, however, the research utilises the even more exciting National Supercomputer to model many Hydrogen atoms down to their Quantum, wave-like properties. We are using the power of Density Functional Theory modelling in order to try match what the experiments are seeing.

The aim is to try and predict what happens under pressures the anvils aren’t able to create, helping to uncover what really happens at these extreme conditions only possible inside the largest planets of our solar system (for now).