Bulletin of the American Physical Society
2017 Fall Meeting of the APS Prairie Section
Saturday–Sunday, November 11–12, 2017; University of Illinois at Chicago, Chicago, Illinois
Session E1: Session E |
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Chair: Angel Yanguas-Gil, Argonne National Laboratory Room: UIC Student Center East 302 |
Sunday, November 12, 2017 1:00PM - 1:30PM |
E1.00001: Nanoporous materials for hydrogen and natural gas storage: in-situ neutron scattering observation of adsorbtion-induced structural changes Invited Speaker: Carlos Wexler Hydrogen and natural gas offer cleaner alternatives to gasoline to power automobiles with a much faster fill-up time compared to battery-powered systems. However, efforts to roll out these systems are hindered by the difficulty of storing gases at the required densities. Hydrogen, the ultimate fuel in terms of emissions (only water), is especially difficult; inventing ways to store a gas with a critical temperature of −239.95 °C (33.20 K) is a challenge of fundamental physics and chemistry. One promising system comprises the use of nanoporous materials to store the gas by physisorption. In this talk we will show investigations to the nature of these types of materials at the sub-nm scale, in particular whether these solids have structural changes during adsorption. Using in situ neutron scattering at the University of Missouri Research Reactor, we have observed an increase of the interlayer spacing in graphene oxide frameworks (GOF) for hydrogen, methane, and xenon at 0-150 bar and supercritical temperatures. We further observe an approximate law of corresponding states in this expansion and compare the experimental observations to molecular dynamics simulations of the system, which suggest possible structures for the GOFs. These observations may provide insight into the development of new materials optimized for gas storage or other applications. [Preview Abstract] |
Sunday, November 12, 2017 1:30PM - 1:42PM |
E1.00002: Modeling, analysis and ultrafast imaging of lattice dynamics in core-shell bimetallic nanocrystals Kiran Sasikumar, Mathew Cherukara, Jesse Clark, Thomas Peterka, Ross Harder, Subramanian Sankaranarayanan Energy transport via lattice vibrations play an important role in several applications such as heat dissipation in semiconductors, waste heat energy conversion via thermoelectric materials, and phase transitions in intensely heated nanofluids. Investigation of the temporal behavior of externally stimulated materials under severe thermal non-equilibrium conditions is, thus, crucial for energy research. Recently, advances have been made in experimental techniques to conduct time-dependent lattice dynamics measurements in nanomaterials. In particular, ultrafast laser pump and x-ray probe Bragg Coherent Diffraction Imaging (BCDI) has been used to directly image lattice distortions within nanocrystals. In particular, experiments on femtosecond laser heated bimetal (Au/Al) core-shell nanocrystals have revealed inhomogeneous effects in lattice breathing. Conventional theoretical models fail to explain the physics of the phenomena in such non-equilibrium environments, particularly in core-shell structures where interfacial effects can play an important role in phonon scattering. In this talk, we focus on multi-million-atom molecular dynamics (MD) simulations performed on core-shell bimetallic nanocrystals under the influence of extreme heat fluxes. We discuss how x-ray diffraction patterns are obtained from MD trajectories, which are directly compared with BCDI images to identify the origin of the inhomogeneous effects in lattice breathing. [Preview Abstract] |
Sunday, November 12, 2017 1:42PM - 1:54PM |
E1.00003: Nonlinear transport in semiconductor superlattices Martin Winslow The transport of electrons and holes within semiconductor superlattices are known to exhibit nonlinear behavior, such as negative differential conductivity. Using a \emph{full band ensemble monte carlo} simulation, this nonlinear behavior is observed when Umklapp scattering is included in the transport for both electrons and holes along the vertical growth direction. Our method allows for the analysis of a broad range of phenomena in superlattice transport due to the inclusion of the full (mini)band structure. Results for several superlattice designs utilized in high performance photodiode applications are presented, along with an overview of how an understanding of the electronic band structure and scattering processes (acoustic and optical phonon, alloy disorder, impact ionization) are utilized in a physical simulation. [Preview Abstract] |
Sunday, November 12, 2017 1:54PM - 2:06PM |
E1.00004: Structural study of manganese multiferroics in phase diagram Ba$_{\mathrm{1-x}}$Sr$_{\mathrm{x}}$Mn$_{\mathrm{1-y}}$Ti$_{\mathrm{y}}$O$_{\mathrm{3}}$. Kamal Chapagain, Omar Chmaissem, Stanislaw Kolesnik, Dennis Brown, Bogdan Dabrowski We have designed and synthesized unique manganese multiferroics exhibiting ferroelectricity and magnetism originating solely from Mn ion. Structural study shows large ferroelectric-type distortion, which are reduced by antiferromagnetism. Ti-substituted compounds with increase temperature and size of ferroelectric polarizations show an unusually large hysteresis of ferroelectric transitions and strong dependence of pressure. [Preview Abstract] |
Sunday, November 12, 2017 2:06PM - 2:18PM |
E1.00005: dc SQUID based Johnson Noise Measurements of a 3k$\Omega $ Resistor at mK temperatures Vidhi Shingla, Ethan Kleinbaum, Gabor Csathy Johnson noise measurement is a useful technique for primary thermometry of charge carriers. However, Johnson noise of k$\Omega $ resistors at mK temperatures is lower than typical noise of room temperature electronics. Therefore, lower noise amplifiers are needed to make such measurements. Low temperature amplifiers based on cooled High Electron Mobility Transistors (HEMTs) are often employed, however these offer low noise operation at MHz frequencies only. We present an alternative circuit which operates at low frequencies which is based on a dc SQUID. We demonstrate that our circuit does not contribute appreciable noise to the Johnson noise of a 3.25 k$\Omega $ resistor down to 16mK, enabling Johnson noise thermometry. [Preview Abstract] |
Sunday, November 12, 2017 2:18PM - 2:30PM |
E1.00006: Quantum Mechanism of Condensation and High Tc Superconductivity Shouhong Wang, Tian Ma We present a new quantum mechanism of condensates and superconductivity. First, we postulate that the quantum mechanical wave function $\psi=|\psi| e^{i \varphi}$ is the common wave function for all particles in the same class determined by the external potential $V(x)$, $|\psi(x)|^2$ represents the distribution density of the particles, and $\frac{\hbar}{m} \nabla \varphi$ is the velocity field of the particles. This is an entirely different interpretation from the classical Bohr interpretation, removes all absurdities. Second, we show that the key for condensation of bosonic particles is that their interaction is sufficiently weak to ensure that a large collection of boson particles are in a state governed by the same condensation wave function field $\psi$ under the same bounding potential $V$. The formation of superconductivity comes down to conditions for the formation of electron-pairs, and for the electron-pairs to share a common wave function. Based on the PID interaction potential of electrons and the average-energy level formula of temperature, these conditions for superconductivity are explicitly derived. Also we obtain both microscopic and macroscopic formulas for Tc, and obtain the field and topological phase transition equations for condensates. [Preview Abstract] |
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