Minimum metallic conductivity of fluid hydrogen at 140 GPa (1.4 Mbar)

Abstract

Electrical conductivity measurements indicate that fluid hydrogen achieves the minimum conductivity of a metal at 140 GPa, ninefold initial liquid-H 2 density, and 2600 K. Metallization density is defined to be that at which the electronic mobility gap E g is reduced by pressure to E g ϳk B T, at which point E g 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/sec. 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 two stiff Al 2 O 3 anvils. This compression heats hydrogen quasi-isentropically to about twice its melting temperature and lasts ϳ100 ns, sufficiently long to achieve equilibrium and sufficiently short to preclude loss of hydrogen by diffusion and chemical reactions. The measured conductivity increases four orders of magnitude in the range 93 to 140 GPa and is constant at 2000 ͑⍀ cm͒ Ϫ1 from 140 to 180 GPa. This conductivity is that of fluid Cs and Rb undergoing the same transition at 2000 K. This measured value is within a factor of 5 or less of hydrogen conductivities calculated with ͑i͒ minimum conductivity of a metal, ͑ii͒ Ziman model of a liquid metal, and ͑iii͒ tight-binding molecular dynamics. At metallization this fluid is ϳ90 at. % H 2 and 10 at. % H with a Fermi energy of ϳ12 eV. Fluid hydrogen at finite temperature undergoes a Mott transition at D m 1/3 a*ϭ0.30, where D m is the metallization density and a* is the Bohr radius of the molecule. Metallization occurs at a lower pressure in the fluid than predicted for the solid probably because crystalline and orientational phase transitions in the ordered solid do not occur in the fluid and because of many-body and structural effects. Tight-binding molecular dynamics calculations by Lenosky et al. suggest that fluid metallic hydrogen is a novel state of condensed matter. Protons are paired transiently and exchange on a timescale of a few molecular vibrational periods, ϳ10 Ϫ14 sec. Also, the kinetic, vibrational, and rotational energies of the dynamically paired protons are comparable. ͓S0163-1829͑99͒02805-2͔

Transition to a Virtually Incompressible Oxide Phase at a Shock Pressure of 120 GPa (1.2 Mbar):Gd3Ga5O12

“…The prototypical example is observation of minimum metallic conductivity (MMC) of dense fluid hydrogen at 140 GPa, nine-fold compression of liquid density, and 3000 K [1][2][3]. The high pressure and density and relatively low temperature are achieved by multiple-shock compression [2].…”

Modeling asymmetric cavity collapse with plasma equations of state

“…These differences can be understood by examining the differences in the principal Hugnoiots. The multiple-shock compression present within the gas can be thought of in two steps; a single strong shock followed by quasi-isentropic compression from this once-shocked state [47]. As shown in to rise.…”

High-pressure tailored compression: Controlled thermodynamic paths

“…With these tools, they have simulated the physical conditions in the Earth's core and planetary interiors [1,2], probed a wide range of high pressure and temperature material properties [5][6][7][8][9][10], synthesized novel materials [11,12], and solved long standing physics problems such as the metallization of hydrogen [13]. These extreme conditions were achieved through three main techniques: static, shock and quasi-isentropic compressions [13][14][15][16][17][18][19][20][21][22][23][24]. Since the pioneering work by P. W. Bridgman [25], advances in diamond anvil cell technology have pushed the peak pressure by static compression from 200 kbars to more than 4 megabars [21,22].…”

“…Since the pioneering work by P. W. Bridgman [25], advances in diamond anvil cell technology have pushed the peak pressure by static compression from 200 kbars to more than 4 megabars [21,22]. Similarly, shock compression and quasi-isentropic compression techniques [13][14][15][16][17][18][19][20] can load samples to megabar pressures in a fraction of a nanosecond to microseconds.Future advances will likely push the peak pressure higher and extend the pressure loading time. However, these techniques will continue to be limited to a portion of the high pressure phase diagram by their characteristic loading rate and a single thermodynamic path.…”

“…The ability to attain extreme pressure and temperature conditions has given investigators in fields as diverse as biology, condensed matter physics, and earth and planetary sciences the tools to explore material behavior at megabar pressures and at thousands of degrees [1][2][3][4][5][6][7][8][9][10][11][12][13]. With these tools, they have simulated the physical conditions in the Earth's core and planetary interiors [1,2], probed a wide range of high pressure and temperature material properties [5][6][7][8][9][10], synthesized novel materials [11,12], and solved long standing physics problems such as the metallization of hydrogen [13].…”