Metallization of Fluid Hydrogen at 140 GPA (1.4 Mbar)

Abstract

The properties of hydrogen at high pressures and temperatures are important for the interiors of giant planets, such as Jupiter and Saturn, and for Inertial Confinement Fusion. Electrical conductivity measurements indicate that hydrogen becomes a metallic fluid at 140 GPa, ninefold initial liquid-H2 density, and 2600 K. Metallization density is defined to be that at which the electronic bandgap Eg is reduced by pressure to Eg — kBT, at which point Eg is filled in by fluid disorder to produce a metallic density of states with a Fermi surface and the minimum conductivity of a metal. High pressures and temperatures were obtained with a two-stage gun, which accelerates an impactor up to 7 km/s. A strong shock wave is generated on impact with a holder containing liquid hydrogen at 20 K. The impact shock is split into a shock wave reverberating in hydrogen between stiff Al2O3 anvils. This dynamic compression heats hydrogen quasi-isentropically to about twice its melting temperature at 100 Gpa pressures and lasts ~100 ns, sufficiently long to achieve equilibrium and sufficiently short to preclude loss of hydrogen by mass diffusion and chemical reactions.