Disclosing the phase transformations of solid hydrogen under very high pressures up to its metallic state has been for many years a very challenging and fascinating problem. Various claims of the observation of metal hydrogen over the past 30 years have remained controversial.

Here, we will present our recent efforts to reach the metal hydrogen phase. Pressure in excess of 400 GPa could be achieved by using the recently developed Toroidal Diamond Anvil Cell [1]. The structural and electronic properties have been characterized by the non-invasive synchrotron infrared spectroscopy [2]. A first order phase transition to the metallic state is observed.

Comparison with most advanced ab-initio calculations will be discussed. Perspective measurements for disclosing further the properties of metal hydrogen will be presented.

References:

[1] A. Dewaele, P. Loubeyre, F. Occelli, O. Marie and M. Mezouar. Nat. Com. 9, 2913 (2018).

[2] Paul Loubeyre, Florent Occelli and Paul Dumas, Phys. Rev. B 87, 134101 (2013).