Bulletin of the American Physical Society
2021 Joint Spring Meeting of the Texas Sections of APS, AAPT and Zone 13 of the SPS
Volume 66, Number 2
Thursday–Sunday, April 8–11, 2021; Virtual
Session D08: APS: Condensed Matter and Plasma Physics II |
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Sunday, April 11, 2021 11:00AM - 11:12AM |
D08.00001: Long Particle Chains as Precursors to Ball Lightning? Karl Stephan While dozens of theories have been proposed to explain the rare atmospheric phenomenon known as ball lightning, few documented experiments have produced something resembling it. An experiment by Cawood (Nature, 124, 150 (1931)) involving electrically charged smoke reliably produced a spherical 20-cm-dia. cloud which consisted of long particle chains. One leading ball lightning theory (Abrahamson and Dinniss, Nature, 403, 519 (2000)) proposed that ball lightning consists of networks of silicon nanoparticles, but failed to specify how these particles would assemble. In experiments involving MgO smoke, we have demonstrated the ability of an electric field to produce long (up to 170 nm) smoke-particle chains, the first step in reproducing the Cawood experiment. The experimental setup used records video of an ultramicroscopic image of particles as they move in response to both gravity and an electric field, and obtains 3-D position data indirectly, allowing estimation of particle mass and mobility. [Preview Abstract] |
Sunday, April 11, 2021 11:12AM - 11:24AM |
D08.00002: Surface-bulk charge transfer and surface Luttinger arc in Weyl semimetals Osakpolor Obakpolor, Pavan Hosur Beyond our classification of materials based on their electrical conductivity; metals, insulators, semiconductors and semimetals, we have materials whose properties are unique due to their topology. Here, we study one example of these topological materials with promising applications ranging from fabrication of more efficient electronics to spintronic devices and photovoltaic applications; Weyl semimetals. Weyl semimetals are 3D materials in which non-degenerate conduction and valence bands cross at certain points in the Brillouin zone. Although theoretical predictions of this material started in 2011, it was not up until 2015 experimental discovery was made. On the surface of this material, there exist states called the Fermi arcs and the surface properties are different from those of the bulk. However, interestingly the surface and the bulk are coupled. In this work, we analyze one of the physical quantity that the consequence of this coupling shows up; the particle number on the surface of this material. We show that the bulk also contribute to to the particle number on the surface. Furthermore, we prove the existence of a new feature of this material which has been missed all these years; the Luttinger arc. [Preview Abstract] |
Sunday, April 11, 2021 11:24AM - 11:36AM |
D08.00003: Optimization of the U parameter in CoO groupings in ZnO (1010) and (1120) surfaces: a DFT$+$U and UPS study Kyle Stoltz, Mario Borunda Cobalt oxide groupings in ZnO surface structures were studied using density functional theory within the Hubbard-like U (DFT$+$U) formalism to calculate the total energy of several configurations of this system. We find the U parameter by fitting the calculated density of states (DOS) to ultraviolet photoelectron spectroscopy measurements of pristine and doped ZnO nanostructures. It was found that the most energetically favorable configuration in the Co-doped ZnO nanostructures are clusters of CoO. [Preview Abstract] |
Sunday, April 11, 2021 11:36AM - 11:48AM |
D08.00004: Annealing glasses by cyclic shear deformation and vibration modeled by a 2-D granular system: study of the effect of shear amplitude Francisco Lopez Gonzalez, Ana Maria Herrera Gonzalez, Fernando Donado Perez This work proposes a slightly tilted bidimensional vibrated hard-sphere system, periodically sheared via deformations, for modeling glass to crystal transitions. Specifically, the system, initially in random closed packed (RCP) state modeling an amorphous solid, rearranges into a hexagonal closed packed (HCP) crystal configuration. The vibration is fixed in amplitude and frequency, so it models a constant temperature. The shearing is achieved by periodical deformations of a deformable rhomboidal shape boundary based on a four-bar mechanism. To measure the time evolution of the annealing, the sixth-bond-orientational-order parameter $\psi_{6}\’$ is measured during 42 cycles of shearing. We report the results of 7 experimental cases where the maximum deformation shear amplitude is varied. We found correlations between shear amplitude with the average of the sixth-bond-orientational-order parameter. The results indicate complex oscillatory hexagonal order dynamics determined by the cyclic perturbation. These oscillations are analyzed by first and second-order linear regressions finding correlations between the sheared boundary's acceleration with the rate of change of $\psi_{6}\’$. Furthermore, images of the hexagonal crystal grains during its annealing are presented. [Preview Abstract] |
Sunday, April 11, 2021 11:48AM - 12:00PM |
D08.00005: A Novel Approach of Inducing Photoconductivity on GaN Thin Films Grown on Au Surfaces Phadindra Wagle, Aaron Austin, Elena Echeverria, Punya Mainali, Nathan Dice, Alex Bias, David Mcllroy Gallium Nitride(GaN) thin films were deposited on pristine and Au sputtered Si\textless 100\textgreater substrates by Atomic Layer Deposition(ALD). Photocurrent response of these GaN thin films were studied using 430nm, 505nm, and 660nm. The GaN thin films grown on pristine Si substrate were found to be responsive to aforementioned wavelengths whereas the GaN thin films grown on Au sputtered Si substrate did not show any photo-response. Interestingly, it was observed that growing layer of SiO2 on top of Au film leads way to photo responsive GaN. The photoresponse of these GaN thin films are believed to be originated from lattice mismatching between Si and GaN, where defects drive the photoconductivity. Moreover, X-ray photoelectron spectroscopy(XPS), X-ray diffraction(XRD), Scanning Electron Microscopy(SEM) were used to study stoichiometry, chemical bonding and morphology of the samples. [Preview Abstract] |
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