Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N59: Matter under Extreme Conditions II |
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Sponsoring Units: DCOMP DAMOP DCMP Chair: Stefanie Czischek, University of Ottawa Room: Room 301 |
Wednesday, March 8, 2023 11:30AM - 11:42AM |
N59.00001: Probing Asymmetric Dark Matter with Gravitational Waves Bartosz Fornal, Erika Pierre Models of asymmetric dark matter offer a simultaneous solution to two of the most intriguing open questions in particle physics: What is the nature of dark matter? What is the origin of the matter-antimatter asymmetry of the Universe? In this presentation, I will show how this class of models can be probed in gravitational wave experiments. I will concentrate on a theory with the Standard Model symmetry extended by an additional SU(2) group, under which the leptons and new fermionic partners form doublets. Interestingly, one of the new fermions satisfies the requirements for being the dark matter particle. The scale of breaking of this extra SU(2) symmetry is high and the model allows for a successful high-scale baryogenesis, i.e., explaining today's domination of matter over antimatter. This is achieved via a strong first order phase transition in the early Universe, which, in turn, results in the production of gravitational waves. The model predicts also the formation of topological defects like domain walls, also leading to the emission of gravitational radiation through their annihilation. As I will demonstrate, the expected gravitational wave spectrum of the model is within the reach of upcoming gravitational wave detectors, including DECIGO, Big Bang Observer, Cosmic Explorer and Einstein Telescope. This presents an entirely novel way of probing this type of theories, otherwise completely inaccessible in conventional particle physics experiments. |
Wednesday, March 8, 2023 11:42AM - 11:54AM |
N59.00002: Chemical interactions that govern the structures of metals Yuanhui Sun, Lei Zhao, Chris J Pickard, Russell J Hemley, Yonghao Zheng, Maosheng Miao Most metals adopt simple structures such as BCC, FCC, and HCP in specific groupings across the Periodic Table, and many undergo transitions to surprisingly complex structures on compression, not expected from conventional free-electron-based theories of metals. First-principles calculations have been able to reproduce many observed structures and transitions, but a unified, predictive theory that underlies this behavior is not yet in hand. Discovered by analyzing the electronic properties of metals in various lattices over a broad range of sizes and geometries, a remarkably simple theory shows that the stability of metal structures is governed by electrons occupying local interstitial orbitals and their strong chemical interactions. The theory provides a basis for predicting new structures in solid compounds and alloys over a broad range of conditions. |
Wednesday, March 8, 2023 11:54AM - 12:06PM |
N59.00003: Chemical templates that assemble the metal superhydrides Maosheng Miao, Yuanhui Sun The recent discoveries of metal superhydrides provide a new route to room-temperature superconductors. However, their structure trends and the chemical driving force needed to dissociate H2 and form H covalent network cannot be explained by direct metal-hydrogen bonds. Here, we show that the understanding of superhydrides formation needs a perspective beyond the traditional chemical bonds. By analyzing high-throughput calculation results of metals across the periodic table and in various lattices, we show that, after removing H, the remaining metal lattices exhibit large electron occupations of the nonatomic interstitial orbitals, which matches excellently to H lattices and their wavefunctions like a template. Furthermore, H lattices consist of 3D aromatic building units that are greatly stabilized by chemical templates of metals near the s−d border. This theory can naturally explain the stability and structure trends of superhydrides and greatly enhance the efficiency of predicting new materials, such as two-metal superhydrides. |
Wednesday, March 8, 2023 12:06PM - 12:18PM |
N59.00004: Core contributions to stopping powers in warm dense matter Alina Kononov, Thomas Hentschel, Stephanie B Hansen, Andrew D Baczewski Core electron excitations constitute a significant energy loss mechanism for ions traversing matter with velocities beyond the Bragg peak. However, little is known about the relative importance of contributions from different core shells, particularly at high temperatures, where modified binding energies and occupations alter the energetics and Pauli blocking of available transitions. Here, we use real-time time-dependent density functional theory (TDDFT) and a recently developed, cost-reducing scheme for optimizing projectile trajectories to compute temperature-dependent, velocity-dependent, and orbital-resolved contributions to proton stopping powers in warm dense lithium, sodium, and aluminum. We also evaluate techniques to calculate these core contributions from computationally efficient average atom methods. This work advances the understanding of fundamental mechanisms underlying stopping power in extreme conditions and the accuracy of materials models used in the design and interpretation of fusion experiments. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N59.00005: First-principles calculations of stopping powers in fusion-relevant mixtures Alexandra Olmstead, Alina Kononov, Thomas Hentschel, Stephanie B Hansen, Andrew D Baczewski During implosion of fusion capsules, instabilities at material interfaces can lead to mixing that impacts transport of fusion products through the fuel. Accurately predicting fusion yields and designing experiments accordingly therefore relies on accurate models of stopping powers in high energy density mixtures. Here, we calculate proton stopping powers in warm dense deuterium, carbon, and a deuterium-carbon mixture using real-time time-dependent density functional theory. First, we extend a recently developed method for selecting a single, representative projectile trajectory that reduces the need for averaging over multiple calculations to heterogeneous systems. Then, we investigate the validity of Bragg's rule of additivity and benchmark average atom and dielectric function approaches for this system. These efforts lay the foundation for further research on interface and mixing effects on stopping power in warm dense matter. |
Wednesday, March 8, 2023 12:30PM - 12:42PM Author not Attending |
N59.00006: Anharmonic thermodynamic properties and phase boundary across the post-perovskite transition in MgSiO3 Zhen Zhang, Renata M Wentzcovitch To address the effects of lattice anharmonicity across the perovskite to post-perovskite transition in MgSiO3, we conduct calculations using the phonon quasiparticle (PHQ) approach. The PHQ is based on ab initio molecular dynamics and, in principle, captures full anharmonicity. Free energies in the thermodynamic limit (N→∞) are computed using temperature-dependent quasiparticle dispersions within the phonon gas model. Systematic results on anharmonic thermodynamic properties and phase boundary are reported. Both the local density approximation (LDA) and the generalized gradient approximation (GGA) calculations are performed to provide confident constraints on these properties. Anharmonic effects are demonstrated by comparing results with those obtained using the quasiharmonic approximation (QHA). The inadequacy of the QHA is indicated by its overestimation of thermal expansivity and thermodynamic Grüneisen parameter and its converged isochoric heat capacity in the high-temperature limit. The PHQ phase boundary has a Clapeyron slope (dP/dT) that increases with temperature. This result contrasts with the nearly zero curvature of the QHA phase boundary. Anharmonicity bends the phase boundary to lower temperatures at high pressures. Implications for the double-crossing of the phase boundary by the mantle geotherm are discussed. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N59.00007: Predicting hot-electron free energies from ground-state data Federico Grasselli, Chiheb Ben Mahmoud, Michele Ceriotti Machine-learning interatomic potentials, while extremely successful in describing condensed phases, are usually trained on ground-state electronic-structure calculations depending exclusively on the atomic positions and ignoring the electronic temperature. Hence, they are limited in their ability to describe thermally excited electrons. We introduce a rigorous framework to calculate the finite-temperature electron free energy based exclusively on ground-state total energy and electronic density of states, while allowing to sample on-the-fly the electronic free energy at any temperature. Our physically-motivated approach facilitates modeling material properties in extreme conditions with a fraction of the usual cost. We demonstrate it by computing the equation of state and heat capacity of hydrogen at planetary conditions. This approach demonstrates the impact of a universal model describing structural and electronic properties inexpensively and its ability to enable more accurate and predictive materials modeling and design. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N59.00008: Superconductivity of MX2H8 (X= B or C) at low pressure Nisha Geng, Pratik Kumar Das, Katerina Hilleke, Eva D Zurek In the last decade several binary hydride compounds have been predicted to possess a high superconducting critical temperature, Tc, at high pressures. This includes an Fm-3m LaH10 phase, which was synthesized, and whose Tc was measured to be 250-260 K near 200 GPa. Currently, there is significant interest in designing superconducting ternary hydrides that can be quenched to mild pressures. One way in which such phases can be designed is by removing two hydrogen atoms from the Fm-3m MH10 phases and adding a p-block element that can form strong bonds. We theoretically studied such systems via high-throughput first-principles calculations. We identified dynamically stable MX2H8 compounds (M=alkali, alkaline or rare earth metal, X=B or C), and analyzed their superconducting properties and the factors that are responsible for them. Several phases are predicted with Tcs of over 100 K that can be quenched to mild pressures. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N59.00009: Pressure ionization and electron localization in solid silicon and cobalt under extreme pressure Md Mehdi Masud, Bradford A Barker, David A Strubbe Under extreme pressure, plasmas undergo pressure ionization, in which the atomic potential depth is reduced, and continuum lowering, in which the X-ray absorption onset shifts towards lower energy. We previously found by density functional theory (DFT) calculations that solid silicon shows pressure ionization but not continuum lowering because of Fermi-surface rising as in dense plasmas. Now we further investigate solids at low temperature but extreme pressure (~100 Mbar). Under these conditions, simple metals such as sodium become electrides (ionic-like insulators), and we found signatures of electride formation in diamond-structure silicon as well. The potential depth can be fit by common ionization models (ion-sphere, Debye-Hückel, modified Ecker-Kroll, and Stewart-Pyatt). We improve on our previous DFT and random phase approximation calculations with the GW/Bethe-Salpeter approach for more accurate electronic phase transitions and X-ray spectra. We also examine solid cobalt to see the effect of d orbitals in a transition metal, calculating potential depth, bandstructure, and X-ray spectroscopy, and look for signs of electride formation. This investigation gives insight into the connection between solid and plasma phenomena in extreme compression experiments. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N59.00010: Efficient calculations of equation-of-state data in the warm-dense matter regime Timothy J Callow, Eli Kraisler, Attila Cangi Equation-of-state (EoS) data — relating the pressure and internal energy to material density and temperature — is a key quantity in the warm dense matter regime, for example as input to hydrodynamics codes used to guide inertial confinement fusion experiments. The first-principles methods, density-functional theory and path-integral Monte–Carlo, are considered state-of-the-art approaches to calculate EoS data. However, both methods are computationally expensive, which motivates the development of low-cost approaches such as average-atom models. In the first part of this talk, we benchmark EoS results from an average-atom model against the extensive first-principles dataset from Militzer et al. (Phys. Rev. E 103, 013203). In the second part, we develop a neural-network surrogate model as a numerically feasible alternative to calculating EoS data. We train two neural networks to interpolate this dataset, with one being trained using average-atom outputs and the other without. We also compare the accuracy of the machine-learned and average-atom models using out-of-distribution data from other sources. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N59.00011: Temperature Measurements on Shocked Preheated Cerium Brian J Jensen, Thomas M Hartsfield, Robert Smalley Optical radiance and pyrometry methods are now available to measure temperature of shocked materials, and these have been used to study some metals including Sn and Ce. In this work, we have developed a preheated experiment configuration that incorporates velocimetry and optical radiance to simultaneously measure the longitudinal stress and temperature for materials shocked to states along an elevated temperature Hugoniot. This experimental method was used to study cerium metal preheated to approximately 200 Celsius and then shock compressed into the liquid phase. Stress-temperature data obtained in the shocked state and during release were used to determine the Hugoniot state, values for specific heat and Gruneisen gamma, and to obtain information about shock-melting. Details of the experimental methods, analysis, and results will be presented |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N59.00012: Extremely high energy dissipation capability of the ion-irradiated CNT mats Kailu Xiao, Edwin L Thomas Planar isotropic, highly porous multiwall carbon nanotube (MWCNT) mats were irradiated with high energy carbon ions to various doses to explore the effect of ion irradiation on high strain rate mechanical properties. The ions induce local bond damage as well as new covalent bonds within and between MWCNTs leading to additional deformation mechanisms beyond the localized tube-tube sliding and tension-failure modes of the pristine MWCNT mats. The energy dissipation capability of the ion-irradiated CNT mats was measured by laser-induced micro-projectile impact test (LIPIT) experiments. The specific penetration energy, Ep* increases over 200% compared to unirradiated mats, up to 28 MJ/kg, significantly higher than present armor materials. The post-mortem perforation morphologies were observed by scanning electron microscopy and show a relatively large network region around the impact site structure was cooperatively deformed, delocalizing, and dissipating the impact energy. Coarse-grained molecular dynamics (CGMD) simulations were also conducted to illuminate the influence of the structural changes from ion irradiation on MWCNT mat adiabatic heating effect after projectile impact. Simulations show higher adiabatic heating in the ion-irradiated MWCNT mats due to the extraordinary transfer of impact energy. Our present study provides an approach to improve the extreme rate dynamical performance of MWCNT mats. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N59.00013: Structure and pressure dependence of the Fermi surface of lithium Sabri Elatresh, Tushar Bhowmick, Audrey D Grockowiak, William A Coniglio, Mohammad Hossain, Elisabeth J Nicol, Stanley W Tozer, Shanti Deemyad There has been much interest in the phase diagram of lithium at both 1 atm and high pressure. We report first-principles calculations combined with Shubnikov–de Haas (SdH) oscillation measurements at 300 mK in external magnetic fields up to 35 T to map the Fermi surface of lithium. At 1 atm, our data reveal direct evidence for its spherical deformation. As the pressure increases, the deformation increases, but the Fermi surface remains mostly spherical up to 4.7 GPa. Finally, our data indicate that the electron effective mass does not deviate significantly under compression from its ambient pressure value. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N59.00014: X-ray photoemission and absorption spectroscopies as tools for ultrafast measurement of the "effective temperature" of nonequilibrium electrons. Oleh Matvyeyev, James K Freericks, Nicholas Sirica, Riccardo Comin, Andrij Shvaika Despite the fact that pump-probe spectroscopy is extensively applied to study the relaxation processes of nonequilibrium electrons, there remains a need to develop a robust and relatively simple method for effective thermometry of the nonequilibrium state. From our theoretical approach, we find a strong correlation between the shape-independent integrated weights of main and satellite peaks of the time-resolved X-ray photoemission (tr-XPS) and X-ray absorption (tr-XAS) spectra with the probabilities of the correlated thermal occupancies of electrons. This allows us to probe the energy of the electrons in the nonequilibrium state directly and therefore can serve as an effective ultrafast thermometer. Our finding gained an interest among experimentalists that has grown into collaboration. Since the model we apply in our study (the Falicov-Kimball model) is one of the simplest models of the strongly correlated electron systems, it is challenging to find the appropriate real material. Eventually, CeO2 compound was found as the best candidate for both tr-XPS and tr-XAS ultrafast experiments which are planned in near future. |
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