Elements at megabar pressures
Dr. Mikhail Eremets (Max-Planck-Institut für Chemie, Mainz)

We will present recent developments in high pressure physics. Pressure is a powerful tool for study of solids by continuous changing of lattice parameters. At high densities interatomic distances significantly decrease and dielectrics eventually turn to metals. Boron for instance, transforms to metal and superconductor at ∼200 GPa (2 Mbars) (Science 2004). Recently pressures above 400 GPa were achieved that will allow compressing solid hydrogen ∼20 fold and making realistic search for metallic hydrogen. This simplest metal is considered the Holy Grail of the modern physics of condensed matter. It should be a superconductor with a high critical temperature Tc ∼200 K. Moreover, this superconductor might exist at ambient pressure. Metallic hydrogen might acquire a new quantum state, namely the metallic superfluid and the su perconducting superfluid. We explored also other approaches to achieve metallic hydrogen at lower pressures by compression of hydrogen dominate materials such as SiH4 (Science 2009), and also melted hydrogen.
Metals under compression supposedly remain in metallic state but at high densities the core electrons come in to play and the electronic structure significantly departs from the simple metal: sodium transforms to transparent dielectric at pressures of ≈200 GPa (Nature 2009).
Nitrogen represents a unique way of transformation – from the molecular triple bonded N≡N solid to a polymeric structure in which each atom is bonded to three nearest neighbours by single covalent bonds (Nature 2001, Nature Mater. 2004). This is a high energy density material, because nitrogen exhibits a uniquely large difference in energy between the 1/3 triple and the single bond.