Bulletin of the American Physical Society
18th Biennial Intl. Conference of the APS Topical Group on Shock Compression of Condensed Matter held in conjunction with the 24th Biennial Intl. Conference of the Intl. Association for the Advancement of High Pressure Science and Technology (AIRAPT)
Volume 58, Number 7
Sunday–Friday, July 7–12, 2013; Seattle, Washington
Session Z2: CM.1 Equation of State: Hydrogen II |
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Chair: Eugene Gregoryanz, The University of Edinburgh Room: Grand Ballroom II |
Friday, July 12, 2013 11:00AM - 11:15AM |
Z2.00001: High Temperature Studies of Hydrogen and Deuterium at Extreme Pressures Ross Howie, Philip Dalladay-Simpson, Christophe Guilliame, Eugene Gregoryanz Melting characteristics is an essential diagnostic in studying the properties of the interactions within a material as well as differences between the solid and liquid states. Hydrogen despite being a simple system displays immense complexity and rich physics when under extreme pressures [1]; therefore it is important to broaden our understanding of quantum systems by studying hydrogen in extended pressure-temperature regimes. Previous experimental data alludes to a maximum in the melting curve [2], which has major implications for the existence of a ground state liquid at higher pressures [3]. Recent experimental advances have allowed us to probe melting in a new region of pressure-temperature space previously inaccessible due to the chemical reactivity of H$_{2}$. Through a series of high temperature Raman spectroscopic experiments we have investigated the melting curve of hydrogen and deuterium in excess of 1000K within the megabar range, conditions previously unattainable. This study not only will show the first experimental melting data on deuterium but also allow for much needed isotopic comparisons in the high temperature regime. \\[4pt] [1] R. T. Howie \textit{et al. Phys. Rev. Lett}., \textbf{108}, 2012.\\[0pt] [2] E. Grgoryanz. \textit{et al. Phys. Rev. Lett}., \textbf{90}, 175701, 2003.\\[0pt] [3] E. Babaev \textit{et al. Nature}, \textbf{431}, 666, 2004. [Preview Abstract] |
Friday, July 12, 2013 11:15AM - 11:30AM |
Z2.00002: Dense Hydrogen in a New Light Russell Hemley TBD [Preview Abstract] |
Friday, July 12, 2013 11:30AM - 12:00PM |
Z2.00003: Cold hydrogen EOS / phase diagram from DAC experiments to 300 GPa Invited Speaker: Mikhail Eremets Two new phases of hydrogen have been discovered at room temperature[1]: phase IV above 220 GPa and phase V above ?280 GPa. In the present work we studied these phases in a wide temperature range with the aid of Raman, infrared absorption, and electrical measurements at pressures up to 340 GPa. Also, we revised the I-III phase boundary and thus have built a new phase diagram of hydrogen. In particular, we established a new triple point at the phase diagram at 208 GPa and T=308 K. Our new data further support the previous work[1] that hydrogen is semiconductor in phase IV and most likely semimetal in phase V. 1. Eremets, M.I. and I.A. Troyan, Conductive dense hydrogen. Nature Materials, 2011. 10: p. 927-931. [Preview Abstract] |
Friday, July 12, 2013 12:00PM - 12:30PM |
Z2.00004: Multi-MBar studies of Oxygen and Hydrogen Invited Speaker: Philip Dalladay-Simpson The study of simple archetypal molecular systems having an electronic structure heavily altered by ultra-high compression holds the promise of major breakthroughs in our understanding of matter. Among these systems, oxygen and deuterium are of particular interest due to their abundance in the Universe. We have used optical and synchrotron x-ray diffraction techniques to probe O$_2$ and H$_2$ (D$_2$) to above 300 GPa. Our study on dense oxygen more than doubles the pressure range at which it had been investigated before; the picture we observe is quite different from what was experimentally reported and predicted by theory. Our experiments on dense hydrogen (deuterium) reveal the appearance of a new semiconducting phase at above 220 GPa which persists up to 320 GPa - the highest pressure reached in our studies. This phase is characterized by emergence of intense, well defined low frequency Raman bands, together with the unprecedented softening of the vibron, $\nu_1$, and appearance of a secondary vibron, $\nu_2$ and slowly closing band-gap. Analysis of the Raman spectra suggests a peculiar graphene-like structure consisting of both atomic and molecular layers. For both systems we will discuss the differences in results and interpretations which currently present in the literature. [Preview Abstract] |
Friday, July 12, 2013 12:30PM - 12:45PM |
Z2.00005: Laser shocks in diamond anvil cells pre-compressed to 6 GPa: Revealing the density and temperature contributions of the transition to conductive fluid hydrogen Paul Loubeyre, Stephanie Brygoo, Ryan Rygg, Marius Millot, Amy Lazicki, Dylan Spaulding, Peter Celliers, Jon Eggert, Tom Boehly, Gilbert Collins, Raymond Jeanloz The quest for metallic hydrogen at high pressures represents a longstanding problem in condensed matter physics. It seems that pressures in excess of 400 GPa are needed to observe the metallic state of crystalline hydrogen. On the other hand, electrically conductive fluid hydrogen has been observed at much lower pressures, first by gas-gun compression and subsequently by laser-shock compression of cryogenic deuterium. But the relation between conductive and metallic states of hydrogen is debated, due to the combined influence of density and temperature. When the density contribution is predominant, a first-order plasma phase transition (PPT) is expected, and can be considered to represent the metallization of dense fluid hydrogen. We revisit this question by presenting Hugoniot measurements on deuterium pre-compressed in diamond anvil cells up to 6 GPa. The temperature and density contributions to electrical conductivity can be disentangled. The prediction of ab-initio calculations are compared to our data set, and a reasonable location for expecting the PPT transition line will be discussed. [Preview Abstract] |
Friday, July 12, 2013 12:45PM - 1:00PM |
Z2.00006: Molecular dynamics for Raman modes of high pressure phases of hydrogen Ioan-Bogdan Magdau, Graeme John Ackland We present ab initio molecular dynamics (MD) calculations of hydrogen at high temperature. We calculated the Raman spectra for phases III and IV and make direct comparison of Raman vibrons with experiment. The MD structures are sensitive to initial conditions and system size, but experimental comparison provides excellent discrimination between structures found, and enables us to explain some of the existing anomalies in the literature. Structures observed for pressure-temperature conditions of phase IV are based on layers of ordered molecules and layers of either static or freely rotating hexagonal trimers, however only two are consistent with experiment. The high temperature phase IV is a hexagonal structure with alternate layers of freely rotating hydrogen molecules, and hexagonal trimers. The low temperature phase III is similar to the C2/c structure previously proposed. These structures are qualitatively different from previous work which introduced spurious features through finite size effects. The MD properly accounts for anharmonic effects and gives much better agreement with Raman data than lattice dynamics calculation. [Preview Abstract] |
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