The nature of dense hydrogen is a central problem in physics and its abundance, for example, in gas giants such as Jupiter and Saturn means that it is critical to our understanding of the universe. In spite of the tremendous progress made over the last 80 years, important gaps in our understanding of the hydrogen phase diagram remain, with arguably the most challenging issue being the solid to liquid melting transition at ultra-high pressures.
This study, involving a group of researchers from the Thomas Young Centre at UCL, as well as from Peking University, Cambridge and York, presents a fundamental advance in the understanding of dense hydrogen which has far reaching implications for a wide range of scientific fields.
The scientists from the four universities looked, in an international effort, at the melting of hydrogen by computer simulation of the coexistence of the solid and liquid phases, for the first time taking the quantum motion of the protons into account explicitly. The findings show a low-temperature metallic atomic liquid phase of hydrogen at pressures 900 GPa and above, down to 50K, the lowest temperature that can be reliably simulated. The existence of this low temperature liquid is associated with a negative slope of the melting line between atomic liquid and solid phases at pressures between 500 and 800 GPa. These results are highly quantum in nature, with classical simulations demonstrating completely different behaviour, with the simulations showing considerably higher melting points. This study confirms the existence of this phase in simulations and shows how the quantum motion of the protons plays a critical role in its stabilisation.
This work has been published in Nature Communications
Journal link:Nature Communications