Bulletin of the American Physical Society
2014 Annual Fall Meeting of the APS Prairie Section
Volume 59, Number 19
Friday–Saturday, November 21–22, 2014; Monmouth, Illinois
Session E1: Condensed Matter I |
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Chair: Ryan Gordon, Wester Illinois University Room: CSB 100 - Pattee Auditorium |
Saturday, November 22, 2014 2:00PM - 2:30PM |
E1.00001: Fractional Quantum Hall Effect in the Second Landau Level Invited Speaker: Ashwani Kumar A magnetic field applied perpendicular to the plan of a two-dimensional electron gas (2DEG) resolves the energy spectrum into discrete Landau levels. At low temperatures strong electron-electron interactions lead to the condensation of the 2DEG into the quantum fluid ground state responsible for the fractional quantum Hall effect (FQHE) and other exotic states. The nature of the FQHE states in lowest Landau level can be understood using conventional Laughlin-Jain theory. However the nature of FQHE states forming in second landau level (SLL) remains unknown. Our recent measurements of energy gap in SLL further raise the possibility of the non-conventional origin of these states. In this presentation I will talk about the transport studies of the newly established FQHE state at the Landau level filling factor $\nu =$ 3 $+$ 1/3. This and other odd-denominator states in SLL unexpectedly break particle-hole symmetry. Specifically, we find that the relative magnitudes of the energy gaps of the $\nu =$ 3 $+$ 1/3 and 3 $+$ 1/5 states from the upper spin branch are reversed when compared to the $\nu =$ 2 $+$ 1/3 and 2 $+$ 1/5 counterpart states in the lower spin branch. Our findings raise the possibility that the former states have a non-conventional origin.\\[4pt] In collaboration with Ethan Kleinbaum, Purdue University; L.N. Pfeiffer, Princeton University; K.W. West, Princeton University; and Gabor Csathy, Purdue University. [Preview Abstract] |
Saturday, November 22, 2014 2:30PM - 2:42PM |
E1.00002: Effect of Cadmium Selenide Nanoparticles on the Optical Band Gap of Lead Borate Glasses Nicholas Breslin, Saisudha Mallur, P.K. Babu The study of the variation of the optical band gap with composition in glasses gives information about the structure and electronic properties. Glasses containing nanoparticles is an interesting system to study due to its fundamental importance in mesoscopic physics and potential for technological applications. We studied lead borate glasses with the composition xPbO:(100-x)B$_{2}$O$_{3}$:1CdSe varying x between 29, 39, 49, 59, and 69 mol{\%}. Glasses were prepared by the usual melt-quench method. Starting materials were melted at 1000$^{\circ}$C and the melt was poured onto a brass plate. Glass pieces obtained through this quenching process were annealed for one hour at 400$^{\circ}$ C. Annealed glass pieces were polished using a lapping machine. Optical absorption measurements were carried out using a UV-VIS absorption spectrometer. The optical energy band-gaps were determined from the absorption edge data using Mott-Davis model. The optical band gap values are smaller and show unusual variation with PbO content compared to the binary lead borate glasses. In binary lead borate glasses, the absorption edge is due to direct forbidden transition whereas CdSe nanoparticles doped system initially shows indirect forbidden transition and with higher PbO content, it changes to indirect allowed transition [Preview Abstract] |
Saturday, November 22, 2014 2:42PM - 2:54PM |
E1.00003: Near-field spatial mapping of strongly interacting multiple plasmonic infrared antennas Yohannes Abate Near-field dipolar plasmon interactions of multiple infrared antenna structures in the strong coupling limit are studied using scattering-type scanning near-field optical microscope (s-SNOM) and theoretical finite-difference time-domain (FDTD) calculations. We monitor in real-space the evolution of plasmon dipolar mode of a stationary antenna structure as multiple resonantly matched dipolar plasmon particles are closely approaching it. Interparticle separation, length and polarization dependent studies show that the cross geometry structure favors strong interparticle charge--charge, dipole--dipole and charge--dipole Coulomb interactions in the nanometer scale gap region, which results in strong field enhancement in cross-bowties and further allows these structures to be used as polarization filters. The nanoscale local field amplitude and phase maps show that due to strong interparticle Coulomb coupling, cross-bowtie structures redistribute and highly enhance the out-of-plane (perpendicular to the plane of the sample) plasmon near-field component at the gap region relative to ordinary bowties. Preliminary results on using VO$_{2}$ film to tune infrared plasmonic antenna resonances will be presented. [Preview Abstract] |
Saturday, November 22, 2014 2:54PM - 3:06PM |
E1.00004: Molecular Dynamics of a Series of Self-Assembling Organic Monolayers: Selective Adsorption and Catalysis on 2D Molecular Sieves Alexander St. John, Carlos Wexler Spontaneous molecular self-assembly is a promising route for bottom-up manufacturing of two-dimensional (2D) nanostructures with specific topologies on atomically flat surfaces. Of particular interest is the possibility of selective lock-and-key interaction of guest molecules inside cavities formed by complex self-assembled host structures. Our host structure is a monolayer consisting of interdigitated 1,3,5-tristyrylbenzene substituted by alkoxy peripheral chains containing $n = $ 6, 8, 10, 12, or 14 carbon atoms (TSB3,5-C$n)$ deposited on a highly ordered pyrolytic graphite (HOPG) surface. Using \textit{ab initio} methods from quantum chemistry and molecular dynamics simulations, we construct and analyze the structure and functionality of the TSB3,5-C$n$ monolayer as a molecular sieve. Supported by ACS-PRF 52696-ND5. [Preview Abstract] |
Saturday, November 22, 2014 3:06PM - 3:18PM |
E1.00005: Interfering effects of localized electronic and nuclear spins on carrier transport in organic semiconductors Kevser Sahin Tiras, Yifei Wang, Nicholas J. Harmon, Markus Wohlgenannt, Michael E. Flatte Spin and magnetic-field effects in organic semiconductors have been intensively studied over the recent years. An interaction between electronic and nuclear spins (hyperfine interaction) is responsible for these magnetic-field effects. In organic semiconductor solid-state devices, a variety of such magnetic field effects have been observed. For example, magnetoresistance effects may be used for magnetic random-access-memory (MRAM). We experimentally and theoretically study the influence of radical doping on the transport characteristics in a conjugated polymer MEH-PPV in terms of magneto conductance (MC) and power conversion efficiency (PCE). We find that for initial doping the radical spins relax the mobile spins, thus reducing the magnetic field effect on magnetoresistance. For intermediate doping a dopant spin interacts with only one component of the radical pair. In this region, the MC is independent of the doping level and is reduced to half its undoped value. For further doping a galvinoxyl molecule interacts with both carriers that form a radical pair, the MC is completely quenched. We will also discuss the effect of galvinoxyl doping on photovoltaic PCE in the different regimes. [Preview Abstract] |
Saturday, November 22, 2014 3:18PM - 3:30PM |
E1.00006: Chemical disorder as an engineering tool for spin-polarization Stanislav Chadov, Lukas Wollmann, Sunil D'Souza, Claudia Felser In the field of the spin-polarized transport the disorder has been typically considered as a destructive mechanism, especially for the half-metallic ferromagnets, which are the materials with the highest possible spin-polarization. Since only few ab-initio electronic structure methods account for the important effects of broken translational symmetry, possible constructive role of disorder has been largely overseen. Here by means of the first-principles (KKR Green's function method + CPA + Kubo linear response formalism) we show that one can take an advantage of disorder by, e.g., increasing the spin-polarization of the electric current. Using the tetragonal Mn$_3$Ga non-half-metallic Heusler as a starting point and by introducing the special type of chemical disorder, we derive the materials with a high spin-polarization of the electric current. Our approach is based on the selective manipulation of conducting electrons mobilities in different spin channels, which becomes possible due to the peculiar electronic structure of Mn$_2$-based Heusler ferrimagnets. [Preview Abstract] |
Saturday, November 22, 2014 3:30PM - 3:42PM |
E1.00007: Structure and electronic properties of nanodiamond and its fluorination effect Kazuyuki Takai, Kenta Kogane, Hidekazu Touhara, Yoshiyuki Hattori Fluorination of nano-sized diamond (ND) is expected not only to stabilize the surface structure, but also to introduce functional groups on the surface, the conduction carriers, and so on. In this study, we evaluate the structure and magnetic properties of ND and fluorinated ND (FND) in order to consider the change in the electronic state and the surface structure by fluorination. Fluorination of ND was carried out by the direct reaction between gaseous fluorine (1 atm) and commercially available detonation diamond at 623 -- 873 K. X-ray Diffraction study reveals the structural stability of core part of ND during fluorination. X-ray photoemission spectroscopy exhibits F1s peak at the lower binding energy region than that for physisorbed molecular fluorine, indicating the formation of the chemical bonding between C and F in the sample. The Electron Paramagnetic Resonance results suggest that fluorination induces not only changes in the surface structure but also relaxation of defects in the core part. [Preview Abstract] |
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