Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session X38: Materials in Extremes: Hydrogen and SuperconductivityFocus
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Sponsoring Units: DCOMP GSCCM DMP Chair: Dominik Kraus Room: LACC 501A |
Friday, March 9, 2018 8:00AM - 8:36AM |
X38.00001: Relating DFT MD simulations of high-pressure hydrogen to experiment. Invited Speaker: Graeme Ackland There have been many experimental and theoretical studies of high |
Friday, March 9, 2018 8:36AM - 8:48AM |
X38.00002: What is the form of H in the Earth's inner core? Jorge Botana, Zhen Liu, Maosheng Miao, Frank Spera, Matthew Jackson Previous work on the possible presence of H in the Earth's inner corefocuses on FeH as the thermodynamically stable form of Fe-H compounds at the pressures of the Earth's core.1 In the present work we have carried out a systematic structure search of the Fe-H compounds at high pressure using a particle swarm optimization algorithm, as implemented in CALYPSO. Each structure has then been studied through ab initio calculations within the framework of the density functional theory, using VASP, and we have obtained the convex hull of the thermodynamically stable compounds. We have found that the Fe-rich compound Fe5H becomes thermodynamically stable at high pressure. This compound is structurally very different from FeH, but similar to the compounds Fe2-4H: it consists of an hcp-Fe lattice with H atoms arranged regularly in the octahedral interstices. |
Friday, March 9, 2018 8:48AM - 9:00AM |
X38.00003: Striking Isotope Effect on the Metallization Phase Lines of Liquid Hydrogen and Deuterium Rachel Husband, Mohamed Zaghoo, Isaac Silvera The insulator-metal transition in dense fluid hydrogen is of interest for both fundamental and planetary sciences. Almost all previous studies have treated hydrogen and deuterium without distinction. However, a study of their behavior at similar conditions can reveal the importance of ion dynamics. We have measured the metallization transition line of statically-compressed deuterium in the 1.2-1.7 Mbar range up to measured temperatures of ~3000 K. Compared to previous results on hydrogen, collected using the same experimental technique, deuterium is observed to metallize at substantially higher temperatures than hydrogen at the same pressure. This reveals a prominent isotopic shift in the location of the phase lines. The hydrogen molecule has larger zero-point energy than deuterium and is expected to dissociate at a lower temperature or pressure. Interestingly, the energetic difference in the free-molecule dissociation energies is comparable to the temperature (energy) difference of the phase transition lines. These results highlight the importance of nuclear quantum effects in the hydrogen isotopes at these conditions. |
Friday, March 9, 2018 9:00AM - 9:12AM |
X38.00004: Nuclear Quantum Effects in Metallic Hydrogen Jeffrey McMahon Describing the behavior of hydrogen over a wide range of thermodynamic conditions with quantitative accuracy is critical to many areas of physics. Dense and metallic hydrogen is especially interesting, because of the remarkable physics that it is expected to exhibit. The theory of hydrogen is challenging, however. The light nuclear mass, with large quantum motion, coupled with subtle effects in electronic structure are not easily handled. We have developed a computational method capable of rigorously accounting for these effects (in the atomic metallic phase) to an accuracy of better than 1%. In this presentation, this method will be described. Potential applications will be discussed. As an example, calculated zero-point energies of candidate structures of atomic metallic hydrogen will be presented. Implications for the phase diagram will be discussed. |
Friday, March 9, 2018 9:12AM - 9:24AM |
X38.00005: An Extended Binary Phase Diagram of Dense H2-He Mixture to 75 GPa Jinhyuk Lim, Choong-Shik Yoo Hydrogen and helium are two most fundamental quantum solids abundant in the Giant planets. The study of dense hydrogen-helium mixture is, therefore, importance to provide insights into the internal structure of the Giant planets as well as the chemistry between these fundamental solids. We have studied hydrogen-helium mixtures to 75 GPa at room temperature as a function of composition using diamond anvil cells and confocal micro-Raman spectroscopy. The results indicate that the binary phase diagram consists of various forms of hydrogen-rich and helium-rich phases, including a metastable H2-rich solid grown in a He-rich fluid and a structural phase transition of He lattice at ~52 GPa. These results therefore underscore a considerable level of miscibility in dense H2-He mixtures that can have a significant implication to the current layer structure of the Giant planets. |
Friday, March 9, 2018 9:24AM - 9:36AM |
X38.00006: Ternary compounds of hydrogen, oxygen and sulfur at high pressures Kien Nguyen-Cong, Joseph Gonzalez, Brad Steele, Ivan Oleynik The discovery of superconductivity in H3S with the highest Tc of about 200 K at 200 GPa has motivated extensive recent studies of various binary hydride compounds with the goal of achieving a higher Tc at lower pressures. However, the current studies of binary hydride compounds have not shown much promise. Therefore, there is an interesting scientific question whether three-element ternary compounds would improve upon binary systems including H3S. In this work, we examine a ternary system of hydrogen, sulfur and oxygen. The latter two elements are in the same group in periodic table, which might provide similar chemical bonding as well as improved superconducting properties. To test this hypothesis, we perform variable-composition first-principles evolutionary crystal structure search of HxSyOz ternary compounds at high pressure. Phase diagrams of the ternary system are constructed. The chemical bonding in the predicted ternary compounds is analyzed and its effect on resulting electronic and vibrational properties is discussed in connection to the possibility of finding superconductivity on this ternary system. |
Friday, March 9, 2018 9:36AM - 9:48AM |
X38.00007: Hydrogen-dominated materials under high pressure: clue and route to room temperature superconductors Tian Cui Metallic hydrogen under high pressure is believed to be a room-temperature superconductor. However, there are no experimental evidence for the predicted metallic state. As an alternative, hydrogen-dominated materials can metallize at lower pressures because of chemical pre-compressions, which are potential high temperature superconductors. Therefore, hydrogen-dominated materials are expected to become a new member of superconductor family: hydrogen-based superconductor. |
Friday, March 9, 2018 9:48AM - 10:00AM |
X38.00008: Novel Synthesis Route and Observation of Superconductivity in the Se-H System at Extreme Conditions Ajay Mishra, Maddury Somayazulu, Muhtar Ahart, Amol Karandikar, Russell Hemley, Viktor Struzhkin The recent observation of highest Tc ~ 203 K in the S-H system at high pressure by Drozdov et al. have inspired several theoretical studies for superhydrides with higher predicted Tc values. However there is scarcity of experimental observation of Tc in synthesized higher hydrides so far. We have chosen a novel route to synthesize higher hydride of Se, the closest analog of sulfur, using solid media and laser heating at pressure close to ~ 10 GPa. The synthesis of hydrogen rich van der Waals compound (H2Se)2H2 is confirmed using in-situ Raman spectroscopy. The synthesized compound shows metallic behavior on compression and superconducting transition temperature ~ 105 K has been observed using four probe technique at ~135 GPa. |
Friday, March 9, 2018 10:00AM - 10:12AM |
X38.00009: Synthesis and Characterization of Calcium Hydrides at High Pressure-Temperature Conditions Maddury Somayazulu, Ajay Mishra, Muhetaer Aihaiti, Hanyu Liu, Zachary Geballe, Maria Baldini, Yue Meng, Russell Hemley
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Friday, March 9, 2018 10:12AM - 10:24AM |
X38.00010: Synthesis and Stability of Lanthanum Superhydrides Zachary Geballe, Hanyu Liu, Ajay Mishra, Muhtar Ahart, Maddury Somayazulu, Yue Meng, Maria Baldini, Russell Hemley Recent theoretical calculations predict that megabar pressure stabilizes very hydrogen-rich simple compounds having new clathrate-like structures and remarkable electronic properties including room-temperature superconductivity. We report x-ray diffraction and optical studies demonstrating that superhydrides of lanthanum can be synthesized with La atoms in an fcc lattice at 170 GPa upon heating to ~1000 K. The results match the predicted cubic metallic phase of LaH10 having cages of thirty-two hydrogen atoms surrounding each La atom. Upon decompression, the fcc-based structure of LaH10 undergoes a rhombohedral distortion of the La sublattice. The superhydride phases consist of an atomic hydrogen sublattice with H-H distances of ~1.1 Å, which are close to predictions for solid atomic metallic hydrogen at these pressures. |
Friday, March 9, 2018 10:24AM - 10:36AM |
X38.00011: Dehydrogenation through pressure induced polymerization processes of PH3 Lin Wang, Ye Yuan PH3 is studied to understand the superconducting transition and responsible stoichiometry under high pressure by means of Raman, IR, and x-ray diffraction measurements, and theoretical calculations. It is found PH3 is stable up to about 8 GPa and then starts to dehydrogenate through two dimerization processes at room temperature as pressure up to 25 GPa. Two resulting phosphorus hydrides, P2H4 and P4H6, are verified experimentally and can be recovered to ambient pressure. On further compression above 35 GPa, P4H6 directly decomposes into elemental phosphorus. The superconductivity transition temperatures of P4H6 at 100 and 200 GPa have been predicted to be 13 and 67 K in agreement with reported results, suggesting it might responsible for the superconductivity at higher pressures. Our results clearly show that P2H4 and P4H6 are only stable P-H compounds between PH3 and elemental phosphorus, shedding light on the superconducting mechanism. |
Friday, March 9, 2018 10:36AM - 10:48AM |
X38.00012: Correlation between Inhomogeneity and Superconductivity in Cuprate Bi2Sr2CaCu2O8+d at High Pressure Yang Ding We report a discovery of the correlation between inhomogeneity and superconductivity in single-crystal Bi2Sr2CaCu2O8+d (Bi-2212) at high pressure, by using multiple synchrotron x-ray techniques. Our imaging and small-angle scattering measurements reveal a newly discovered ribbon phase as well as short-range charge ordering at nano and micron scales. We observe that both pressure and x-ray irradiation could alter the inhomogeneity, and the changes of the ribbon phase’s morphology coincide with the doom-shaped TC at high pressure. Our x-ray absorption, inelastic scattering, irradiation experiments imply that the inhomogeneity could be associated with an inhomogeneous distribution of oxygen holes. These findings provide a direct link between TC and inhomogeneity in cuprate Bi-2212 HTSC. |
Friday, March 9, 2018 10:48AM - 11:00AM |
X38.00013: Electron-hole balance and the anomalous pressure-dependent superconductivity in black phosphorus Jing Guo, Honghong Wang, Fabian Rohr, Yazhou Zhou, Zhe Wang, Shu Cai, Qi Wu, Tao Xiang, Robert Cava, Liling Sun Here we report the first in-situ high pressure (up to ~ 50 GPa) Hall effect measurements on single crystal black phosphorus. We find a strong correlation between the sign of the Hall coefficient, an indicator of the dominant carrier type, and the superconducting transition temperature (TC). Importantly, we find a change from electron-dominant to hole-dominant carriers in the simple cubic phase of phosphorus at a pressure of ~17.2 GPa, providing an explanation for the puzzling valley it displays in its superconducting TC vs. pressure phase diagram. Our results reveal that hole-carriers play an important role in developing superconductivity in elemental phosphorus, and the valley in TC near 17.2 GPa is associated with a Lifshitz transition. |
Friday, March 9, 2018 11:00AM - 11:12AM |
X38.00014: Novel Diamond Anvil Cell for Transport Measurement under High Pressure without Difficult Wiring Ryo Matsumoto, Aichi Yamashita, Hiroshi Hara, Shintaro Adachi, Hiroyuki Takeya, Yoshihiko Takano High pressure is a promising tool to obtain new functional materials which cannot appear under ambient pressure. For example, the discovery with great surprise of high-transition temperature superconductivity in H3S at ~200 K was recently reported under 150 GPa [1]. Diamond anvil cell (DAC) is most useful apparatus to generate high pressures, however, the resistivity measurement using DAC is quite difficult because it requires the small sample sizes (< 100 μm) and the hard electrodes. Moreover, an insulating layer should be inserted between the electrodes and a metal gasket, which is also broken by applying pressure. In this study, we focused on the boron-doped metallic diamond [2,3] and undoped diamond as a very hard electrode and an insulating layer, respectively. The resistivity measurements of Fe-based superconductor FeSe and very promising thermoelectric material SnSe single crystals have been demonstrated using the developed device under various pressures, and then the pressure effects were clearly observed. |
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