If you thought the most expensive material on the planet was a diamond, you were likely not considering radioactive elements like plutonium (or drugs like LSD), or very rare like californium. Scientists at Harvard have added a new one to the list of most expensive materials and it may even be at the top of the list - hydrogen metal.
DAC (diamond anvil cells) used for megabar (high pressure) research
Using similar principles to create artificial diamonds (high pressure), they have started to create (very) small quantities of hydrogen metal. Why is this important? It has the potential to revolutionize technology, from super fast computers (low resistance), levitating trains (magnets) and anything involving electricity. Hydrogen in metal form has never been found to exist naturally, so the samples at Harvard are the first of their kind. The next steps are to confirm that the material is stable at room temperature, and figure out ways to make its creation less energy intensive. It would be amazing to see (theoretical) fusion reactors used to create materials like this without using the planets' natural resources.