Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session P18: Materials Theory and ComputationFocus Session
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Sponsoring Units: DCOMP Chair: Silvina Gatica, Howard University Room: BCEC 156B |
Wednesday, March 6, 2019 2:30PM - 2:42PM |
P18.00001: Are most jammed packings of dry, frictionless grains similar? Pappu Acharya We study disordered jammed packings of frictionless disks interacting by either (one-sided) harmonic or Hertzian contact forces. We show that ensembles of such packings, in mechanical equilibrium, exhibit a very simple structure. In each case, we find that non-trivial fluctuations of the contact force network may be parameterised by a single dimensionless quantity for a large range of densities and disorder strengths. Surprisingly, a harmonic theory for displacement fluctuations in a crystal at thermal equilibrium is able to account for the statistics of these fluctuations. |
Wednesday, March 6, 2019 2:42PM - 2:54PM |
P18.00002: Percolation Around Structurally Disordered Sand Grains: A Dynamical Infiltration Study Donald Priour Percolation transitions, marking the boundary between configurations which admit the fluid or charge flow and those which are impermeable on large scales are salient phenomena for transport through porous materials where flow is through irregular spaces around impenetrable grains instead of well-defined linear channels. Using dynamical infiltration simulations involving virtual tracers moving in void regions, we calculate critical grain densities per unit volume where the inclusions are positionally and orientationally disordered. In addition, as a novel element, we also consider varying degrees of structural disorder, in which the shapes of grains are subject to random variation. In the case of ellipsoids, tetrahedrons, and rectangular solids we find that if expressed in units of the mean grain volume, the critical concentration is remarkably robust, with little variation for light to moderate disorder in the inclusion shapes. We also discuss scenarios in which in random variations in facet plane distances for solids such as dodecahedrons eventually yield non-dodecahedral fragments; with large scale dynamical infiltration simulations we seek to determine if percolation thresholds remain robust with increasing diversity in types of grain shapes or instead undergo a shift. |
Wednesday, March 6, 2019 2:54PM - 3:06PM |
P18.00003: From Birefringent Electrons to a Marginal or Non-Fermi Liquid of Relativistic Spin-1/2 Fermions: An Emergent Superuniversality Bitan Roy, Malcolm Kennett, Kun Yang, Vladimir Juricic In this talk, we present the quantum critical theory of an interacting nodal Fermi liquid of quasirelativistic pseudospin-3/2 fermions that have a noninteracting birefringent spectrum with two distinct Fermi velocities [1]. As we show, when such quasiparticles interact with gapless bosonic degrees of freedom that mediate either the long-range Coulomb interaction or its short range component (responsible for spontaneous symmetry breaking), in the deep infrared or quantum critical regime in two dimensions, the system is, respectively, described by a marginal- or a non-Fermi liquid of relativistic spin-1/2 fermions (possessing a unique velocity), and is always a marginal Fermi liquid in three dimensions. We consider a possible generalization of these scenarios to fermions with an arbitrary half-odd-integer spin, and conjecture that critical spin-1/2 excitations represent a superuniversal description of the entire family of interacting quasirelativistic fermions. |
Wednesday, March 6, 2019 3:06PM - 3:18PM |
P18.00004: Spatially-correlated Site Occupancy in the Nonstoichiometric Meta-stable ε-Al60Sm11 Phase during Devitrification of Al-10.2 at.% Sm Glasses Lin Yang, Feng Zhang, Fan-Qiang Meng, Lin Zhou, Yang Sun, Xin Zhao, zhuo ye, Matthew J. Kramer, Cai-Zhuang Wang, Kai-Ming Ho We examine a metastable ε-Al60Sm11 phase that appears during the initial devitrification of as-quenched Al-10.2 at.% Sm glasses. The phase is nonstoichiometric in nature since Al occupation is observed on the 16f Sm lattice sites. STEM images reveal profound spatial correlation of Sm content on these sites, which cannot be explained by the “average crystal” description from Rietveld analysis. Monte Carlo simulations based on a cluster-expansion model also give qualitatively different correlation functions from experiments. On the other hand, molecular dynamics simulations of the growth of ε-Al60Sm11 show that when the diffusion range of Sm is limited to ~ 4 Å, the correlation function of the as-grown structure agrees well with that of the STEM images. Our results show that kinetic effects, especially the limited diffusivity of Sm atoms plays the fundamental role in determining the nonstoichiometric site occupancies of the ε phase during the crystallization process. |
Wednesday, March 6, 2019 3:18PM - 3:30PM |
P18.00005: The interaction of carbon and boron nitride nanotubes as well as graphene with metals Christoph Rohmann, Michael P Zwolak The interaction of carbon nanotubes with metals is significant for a wide variety of applications. For example, the binding of tubes to transition metal nanoparticles plays a role in their catalytic growth, as well as in their nucleation observed by ETEM, HRTEM, STM or Raman measurement. We performed quantum chemical calculations to investigate (i) the binding strength and geometry of a variety of metals with carbon nanotubes and graphene (ii) the curvature dependence of the binding energy and lastly (iii) we offer an explanation as to why the reported metal-CNT/graphene binding strength varies widely in the literature. |
Wednesday, March 6, 2019 3:30PM - 3:42PM |
P18.00006: WITHDRAWN ABSTRACT
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Wednesday, March 6, 2019 3:42PM - 3:54PM |
P18.00007: Ab Initio Calculations of Partial Basal Dislocations in Bilayer Graphene Pavlos Mouratidis, Kenny Jolley, James McHugh, Malcolm Heggie, Patrick Briddon Graphite has been the material of choice in construction of nuclear reactors for many years due to its low neutron absorption cross-section and high scattering cross-section. The physical properties of a graphite moderator can greatly influence the cost, safety and lifespan of a reactor. Neutron collision damage in graphite results in the formation of basal dislocations. The subsequent interaction of basal dislocations with each other and the surrounding lattice causes severe dimensional changes along the basal direction. There has been a lot of interest recently in AB and AC stacking grain boundaries in bilayer graphene. Transition from AB to AC stacking can be described by the glide of basal dislocations resulting in expansion of dislocation cores and buckling of the bilayer. Herein we present a new model for the dimensional change of nuclear graphite which considers buckling and folding of graphene sheets due to the basal dislocations glide. Full ab initio and molecular dynamics calculations of oppositely sign on basal dislocations in bilayer graphene have been carried out. Analysis of dislocation cores and buckled sinusoidal harmonics has revealed absorbing results compared to previous theoretical works. |
Wednesday, March 6, 2019 3:54PM - 4:06PM |
P18.00008: Plasmonic capacitance and profiling the energy distribution of plasmonic hot electrons in planar metal-dielectric structures Abbas Goudarzi, Sahar Behpour, Yuri Rostovtsev, Oscar Garcia
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Wednesday, March 6, 2019 4:06PM - 4:18PM |
P18.00009: The effect of Ni impurities on the nucleation rates of undercooled Sn droplets Sitaram Panta, Eric J Cotts Although high purity Sn can undercool more than forty percent of its melting temperature, small amount of Ni in Sn decrease undercooling to 10 K. We report on measurements of the nucleation rate of undercooled Sn droplets as a function of temperature and Ni content, within the context of classical nucleation theory. The undercooling of these Sn-Ni alloys was found to decrease linearly up to 0.5at% of Ni. Analysis of the dependence of nucleation rates of Sn-Ni alloy on temperature revealed that the barrier height to nucleation systematically decreased with Ni concentration, by more than three orders of magnitude upon the addition of Ni. Such a huge increase in nucleation rate is difficult to explain with a simple picture of heterogeneous nucleation of Sn on Ni3Sn4 which eventually forms during solidification process. Previous work has revealed that Ni3Sn4 is a poor inoculant for Sn nucleation. In contrast, the huge increase in nucleation rate observed in this work would require very low wetting angles to explain with such a heterogeneous nucleation picture. The increase in nucleation rate and hence the decrease in energy barrier can be explained by a decrease in surface energy between liquid and nucleating solid. |
Wednesday, March 6, 2019 4:18PM - 4:30PM |
P18.00010: Generating amorphous structures by combining Reverse Monte Carlo and molecular dynamics and analyzing with graph theory algorithm Alec Mishkin, Jun Jiang, Maher Yazback, Kiran Prasai, Riccardo Bassiri, Martin Fejer, Hai-Ping Cheng We present results from atomistic modeling of amorphous zirconia-doped tantala with an aim to understand the sources of mechanical loss in its structure. This material is a candidate for future LIGO gravitational wave detector mirror coatings, where lower mechanical loss coatings are essential to reduce thermal noise. We use Reverse Monte Carlo (RMC) modeling, which is a common technique used to generate atomic models based on experimental data. Here we use pair distribution functions (PDFs) as the reference experimental data set for the RMC. However, the structural solutions from RMC based on PDFs are not unique, and other constraints are needed to rule out unphysical solutions. In this work, we use molecular dynamics as the additional constraint, and show that allowing the structure to perform ionic and volume relaxation in between RMC runs can generate models that are in good agreement with the PDF data and energetically favorable. We also present an analysis of the intermediate range order from these models. This analysis is achieved by converting amorphous structures into graphs, where atoms are vertices and bonds are edges, and analyzing the structures that are responsible for short and intermediate range segments of the PDF. |
Wednesday, March 6, 2019 4:30PM - 4:42PM |
P18.00011: Scaling of emergent symmetry at a first-order transition in the simplest classical model Jun Takahashi, Anders W Sandvik Emergent symmetry has attracted attention due to its possible connections with deconfined quantum criticality, where the phase boundary between a dimerized and a Neel phase is generically continuous, contrary to the standard Ginzburgb-Landau picture where a first-order phase transition is predicted. |
Wednesday, March 6, 2019 4:42PM - 4:54PM |
P18.00012: Magnetic Cooling for Nanoelectronics below 1 mK Yemliha Bilal Kalyoncu, Christian Scheller, Mario Palma, Dario Maradan, Anna V Feshchenko, Matthias Meschke, Dominik Zumbuhl Temperatures below 1 mK in quantum transport experiments could open the door for new physics such as novel nuclear spin phases, fragile fractional QH states, topological phases and unprecedented coherence. However, this is a formidable challenge since the thermal coupling becomes weak, making devices susceptible to heat leaks, microwaves and electronic noise. Our approach is to provide a separate nuclear refrigerator in each sample wire, cooling the device through the electronic degree of freedom. |
Wednesday, March 6, 2019 4:54PM - 5:06PM |
P18.00013: Compressive photoacoustic imaging in scattering media Yuning Guo, Xiaobo Yin, Baowen Li Nowadays optical imaging in highly scattering media is still challenging to meet the requirement for wide-field visualization with a high resolution across the physical and biomedical science. Photoacoustic imaging, which relies on the ultrasonic waves emitted by absorbing structures under pulsed light illumination via thermoelastic stress generation, provides an efficient way to overcome the optical diffusion limitation. Compressive sensing, an efficiently signal processing technique by finding solutions to underdetermined linear systems, is adapted to reduce the burden posed by traditional imaging requirements. It can be used to improve the trade-off between spatial resolution and acquisition time of sequential measurements, which can overcome the limiting of real-time applications to relative low resolutions. Based on compressive sensing, we design a photoacoustic imaging system that can achieve effective 3D imaging in scattering media with just a few sensors. It has the capability to image structured objects hidden in diffused media with a high resolution at a faster pace and works in the fields where the signal reduction is beneficial such as invasive bioimaging. |
Wednesday, March 6, 2019 5:06PM - 5:18PM |
P18.00014: Manipulating thin film properties by search for substrates over databases Pedram Tavadze, Lian Li, Cheng Cen, Aldo H Romero Substrates can have major effects on the growth direction, orientation, nucleation, morphology, field emission in carbon nanotubes, superconducticity, and etc. The influence of substrate on the thin film can be mechanical, electronic, or both. Specific applications require different substrates. In order to tune the characteristics of the thin film to ones needs, one has to explore a large set of possible substrates. As experimentally this work is almost impossible, one has to use computational methods to evaluate possible substrates. In this work we report a flowchart on how to search for optimal substrates and complement the selection by specific electronic structure characterization. We apply our methodology to FeSe, where the superconductor properties are very sensible to the substrate. We employ the available algebraic algorithm provided by MPInterfaces package to search for geometrical matches in the OQMD database and calculate the work-function of the matched substrates as the criteria to select a good substrate. The results from the geometrical matches are input to a machine learning algorithm to increase the search speed in the databases. |
Wednesday, March 6, 2019 5:18PM - 5:30PM |
P18.00015: A novel semi-metallic allotrope of carbon Joel Therrien, Michael Masaki, Purusottam Jena A previously unknown allotrope of 3-dimensional crystalline carbon has been synthesized via CVD. Formation occurs when specific hydrocarbons react with certain metal or metal-oxide catalysts such as copper or aluminum oxide at temperatures above 800°C. The material has been characterized by XRD, Raman, FTIR and XPS. Raman spectra indicate the material consists of a mixture of sp2 and sp3 bonded carbon. X-ray diffraction shows distinct peaks which do not correlate with graphite or diamond. Upon annealing at 1,100°C the diffraction peaks show considerable sharpening indicating the formation of larger domains. This is also reflected in the Raman spectrum which also shows a sharpening of the D and G carbon peaks. XPS analysis did not indicate the presence of any element beside carbon. The material has a high reflectivity from far UV to mid IR and visually appears mirror-like when deposited on smooth substrates. The temperature dependent conducitvity has a negative temperature coefficient suggesting the material is most likely a semi-metal as opposed to a true metal; something not unexpected with carbon. |
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