Bulletin of the American Physical Society
Spring 2017 Joint Meeting of the Texas Section of AAPT, Texas Section of APS, and Zone 13 of the Society of Physics Students
Volume 62, Number 3
Thursday–Saturday, March 9–11, 2017; San Antonio, Texas
Session C2: Condensed Matter Physics and Materials Research and Energy and the Environgment |
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Sponsoring Units: APS Chair: Heather Alexander Zakhidov, Texas State University Room: Oppenheimer OC 110 |
Friday, March 10, 2017 1:15PM - 1:27PM |
C2.00001: Rashba splitting, spin orbit corrections and their implications in organolead halide perovskites Eric Welch, Alex Zakhidov, Luisa Scolfaro CH3NH3PbI3 (MAPI) has become a benchmark light harvesting material in emergent, high-efficiency solar applications. It is a strongly absorbing, direct 1.6 eV bandgap, intrinsic semiconductor with balanced carrier mobilities, shallow defect levels, and a \textgreater 1-micron carrier diffusion length; all important metrics for high performing solar cell absorbers. In this work, first principles modeling is performed on the MAPI structure using density functional theory. Due to the presence of the heavy lead atom, spin orbit coupling (SOC) must be considered when doing \textit{ab-initio} calculations on the material. It has been shown previously that the GGA$+$U methodology with and without SOC allows to study the formation of polarons (a charge carrier together with its self-induced polarization) in the system.........$^{\mathrm{1}}$. Yet, the presence of SOC does qualitatively change the band structure of MAPI, lifting the conduction band degeneracies, and thus resulting in Rashba-type splitting. It can be shown that such spin-texture can lead to ultra-fast polarization dependent photocurrents in the absence of the external bias field. $^{\mathrm{\thinspace 1}}$E. Welch, L. Scolfaro, and A. Zakhidov, Density functional theory $+$u modeling of polarons in organohalide lead perovskites, \textit{AIP Adv.} \textbf{6}, 125037 (2016). [Preview Abstract] |
Friday, March 10, 2017 1:27PM - 1:39PM |
C2.00002: Ab initio study of structural and electronic properties of CuAlO$_{2}$ and AgAlO$_{2}$. James Shook, Luisa Scolfaro Transparent conducting oxides are an active area of research due to their applications in transparent electronics such as photovoltaic cells and flat panel displays. Of particular interest are XAlO$_{2}$ (X = Cu, Ag), two p-type oxides with band gaps in the optical range ($>$ 3.0 eV). These oxides are known to exist in three phases: two delafossite structures whose phase depends on stacking order (2H, 3R) and an orthorhombic crystal structure. How each phase compares to one another energetically is still not well understood. To that end, an ab initio study $-$ using Density Functional Theory based calculations with Generalized Gradient Approximation (GGA), GGA+U, with U being the Hubbard atomic potential for the d-orbital, and modified Becke-Johnson approximation for correlation and exchange potentials $-$ on the structural and electronic properties of XAlO$_{2}$ are presented. The 2H phase is modeled using an 8-atom hexagonal primitive cell while both a 4-atom rhombohedral primitive cell and 12-atom hexagonal unit cell are used to study the 3R phase. The orthorhombic phase is modeled using a 16-atom unit cell. The obtained band structures and density of states results are compared with those in literature and predictions about structural energies for each phase are presented. [Preview Abstract] |
Friday, March 10, 2017 1:39PM - 1:51PM |
C2.00003: Mapping the Non-Equilibrium Vortex Lattice Dynamics of MgB$_2$ Joseph Archer, Elizabeth De Waard, Nikolai Zhigadlo, Janusz Karpinski, Charles Dewhurst, Morten Eskildsen Small angle neutron scattering (SANS) studies of MgB$_2$~have discovered several metastable vortex lattice states, but so far the mechanism behind their metastability remains unknown. In this SANS study conducted at the Institut Laue-Langevin, MgB$_2$'s F and L phases are explored through heating and cooling across their phase transition temperature, and each metastable state is driven to its respective ground state using an AC magnetic field. Since the internal energy of a single vortex domain does not account for the presence of a L metastable state, jamming between vortex domains is explored as a possible explanation. Characteristically of jammed systems, a numerical solution for the probability distribution of inter-particle force magnitudes due to vortex-vortex interactions is found to obey a stretched exponential form for large radii. Several quantitative comparisons are also made between the ideal jamming models and experimental mapping of the metastable decay of the L phase that are suggestive of their close relation. [Preview Abstract] |
Friday, March 10, 2017 1:51PM - 2:03PM |
C2.00004: CsH$_{\mathrm{2}}$PO$_{\mathrm{4\thinspace }}$superprotonic phase stabilization attempts heber martinez, Juan Leal, Alan Goos, Israel Martinez, Alex Price, Cristian Botez CsH$_{\mathrm{2}}$PO$_{\mathrm{4}}$ (CDP) is one of the most promising electrolytes for proton exchange membrane fuel cells in the intermediate temperature range (200 - 400 ${^\circ}$C). One of the biggest challenges is the stabilization of the ``superprotonic'' phase present in CDP when it is heated above 231${^\circ}$C. We performed XRD and Impedance Spectroscopy (IS) on pure CDP and composites under ambient and humidified atmospheres. XRD confirmed the presence of the cubic phase of CDP with space group Pm-3m during a short interval of temperature and time. Although previously reported in the literature to appear only in the presence of a humidified atmosphere, IS showed the presence of the highly conductive phase also during a short time interval. Silica additive and a humidified atmosphere increase the stability of the superprotonic phase. [Preview Abstract] |
Friday, March 10, 2017 2:03PM - 2:15PM |
C2.00005: Tropospheric Ozone Measurements in Central Texas Paul Walter, Gary Morris The Tropospheric Ozone Pollution Program (TOPP) began in Houston in 2004 and recently expanded to Austin in 2016. We began launching weather balloons with payloads consisting of ozonesondes with radiosondes and GPS attached to measure ozone, relative humidity, temperature, and wind speeds throughout the troposphere. Undergraduate research students have helped with every aspect of the program from prepping and launching the ozonesondes to data analysis. Data from our 16 initial flights in 2016 is available at http://ir.stedwards.edu/natural-sciences/ozone. We present an overview of the project, student involvement, and current results. [Preview Abstract] |
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