Bulletin of the American Physical Society
Joint Fall 2010 Meeting of the APS Ohio Section and AAPT Appalachian and Southern Ohio Sections
Volume 55, Number 8
Friday–Saturday, October 8–9, 2010; Marietta, Ohio
Session C2: Condensed Matter Physics |
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Chair: Craig Howald, Marietta College Room: Rickey Science Center 166 |
Saturday, October 9, 2010 8:00AM - 8:12AM |
C2.00001: Theory of Coherent Perfect Absorption (CPA) applied to the layered polymer laser Michael Crescimanno, James Andrews, Guilin Mao Coherent perfect absorption (CPA) is a situation in which counterpropagating pump beams can be adjusted so that both beams are completely absorbed by the system. Using theory we delineate the conditions under which a CPA condition can be achieved in real polymeric laser films and remark on CPA's utility for enhancing these films utility. [Preview Abstract] |
Saturday, October 9, 2010 8:12AM - 8:24AM |
C2.00002: Scattering matrix elements for the nonadiabatic B + H$_{2}$ collision David Weeks, Luke Barger The 1$^{2}$A', 2$^{2}$A', and 1$^{2}$A'' adiabatic potential energy surfaces together with derivative coupling terms between the 1$^{2}$A' and 2$^{2}$A' electronic states are calculated at the multi-reference configuration-interaction level for the B+H$_{2}$ system. These surfaces and couplings are used to compute a set of effective potential energy surfaces that govern the dynamics of atomic boron and molecular hydrogen as they collide. Scattering matrix elements are calculated by propagating reactant wave packets on these surfaces with the split-operator method. The correlation function between the evolving reactant wave packets and stationary product wave packets is computed. A Fourier transformation of the correlation function is then used to calculate the scattering matrix elements using the channel packet method. These scattering matrix elements yield the probability that the B+H2 system will undergo fine structure, rotational, and vibrational transitions as a function of energy. [Preview Abstract] |
Saturday, October 9, 2010 8:24AM - 8:36AM |
C2.00003: Metastable Decay in the Square-Lattice Ising Model: Restriction to a Singe Droplet Howard L. Richards, James W. Howard For finite, regular, Euclidian lattices of Ising spins with nearest-neighbor ferromagnetic interactions, the ``metastable'' state, in which practically all spins are antiparallel to a weak magnetic field, can persist for a long time (measured in Monte Carlo steps per spin). Extensive previous studies have shown that the mechanism of decay depends on the relationships between the size of the lattice, the critical droplet radius, and the average distance between nucleating droplets. During the 2010 session of Marshall University's REU in Computational Science, we have used the Boost Graph Library to explore the effect of restricting the ``stable state'' to a single connected region. Such a restriction could simplify future studies of metastable decay on random graphs. However, the restriction produced some unexpected effects on the metastable lifetime, which we suspect are due to the entropic self-repulsion of the droplet boundary. [Preview Abstract] |
Saturday, October 9, 2010 8:36AM - 8:48AM |
C2.00004: Unique spin-polarized transmission effects in a QD ring structure Eric Hedin, Yong Joe Spintronics is an emerging field in which the \textit{spin} of the electron is used for switching purposes and to communicate information. In order to obtain spin-polarized electron transmission, the Zeeman effect is employed to produce spin-split energy states in quantum dots which are embedded in the arms of a mesoscopic Aharonov-Bohm (AB) ring heterostructure. The Zeeman splitting of the QD energy levels can be induced by a parallel magnetic field, or by a perpendicular field which also produces AB-effects. The combination of these effects on the transmission resonances of the structure is studied analytically and several parameter regimes are identified which produce a high degree of spin-polarized output. Contour and line plots of the weighted spin polarization as a function of electron energy and magnetic field are presented to visualize the degree of spin-polarization. Taking advantage of these unique parameter regimes shows the potential promise of such devices for producing spin-polarized currents. [Preview Abstract] |
Saturday, October 9, 2010 8:48AM - 9:00AM |
C2.00005: Temperature Dependence of the Contact Resistance of Copper and Silver to GaMnAs Khalid Eid, Noah Opondo, Bhim Paudel, Calford Otieno, Grant Riley, Xinyu Liu, Jacek Furdyna We will present our recent measurements and analysis of the specific contact resistance of silver and copper to the heavily p-doped ferromagnetic semiconductor GaMnAs. We employ the circular transmission line method (TLM) and four-point measurements to obtain both the specific contact resistance and the current transfer length as functions of sample temperature down to 20K. Our results clearly suggest that the dominant current transfer method at the ferromagnetic semiconductor/metal interface is field emission (i.e. tunneling), since there is very little variation of the contact resistance with temperature. Yet, a slight decrease of the contact resistance with lowering sample temperature below the GaMnAs Curie temperature indicates strong carrier recombination at the interface due to surface states. We found the specific contact resistance to be as low as 1x10$^{-7} \Omega $cm$^{2}$. Our results provide insight on the current flow mechanisms and might guide experiments on spin injection from GaMnAs into non-magnetic metals. [Preview Abstract] |
Saturday, October 9, 2010 9:00AM - 9:12AM |
C2.00006: Infrared studies of topological insulators Bi$_2$Te$_3$, Sb$_2$Te$_3$ and Bi$_2$Se$_3$ S.V. Dordevic, M.S. Wolf, N. Stojilovic, Hechang Lei, C. Petrovic, L.C. Tung Topological insulators are currently at the center of condensed matter physics research. These unusual materials are insulators in the bulk, but have conducting states on the surface. In this project we have used infrared spectroscopy to study the optical properties of topological insulators Bi$_2$Te$_3$, Sb$_2$Te$_3$ and Bi$_2$Se$_3$. In addition, we will report the results of magneto-optical measurements in magnetic fields up to 18 Tesla. Our results reveal unconventional charge dynamics and demonstrate the potential of infrared spectroscopy to provide insight into the unique properties of these novel materials. [Preview Abstract] |
Saturday, October 9, 2010 9:12AM - 9:24AM |
C2.00007: GaMnAs Ferromagnetic Single Electron Transistor Nano-devices Bhim Paudel, Leonidas Ocola, Calford Otieno, Noah Opondo, Grant Riley, Xinyu Liu, Jacek Furdyna, Khalid Eid Mn-doped GaAs (or GaMnAs) offers opportunities to demonstrate both new device concepts with added functionality and new phenomena in condensed matter physics, since it is both a ferromagnet and a semiconductor. We will present our recent results on fabricating and characterizing GaMnAs-based single electron transistor (SET) devices. The resistance of these deep-nanoscale devices can be manipulated either by varying the applied voltage or via an external magnetic field. The nano-devices were prepared using electron-beam lithography and wet chemical etching. The magnetoresistance of the devices was as high as 40{\%} at 4.2 K and the behavior was strikingly different from previous results reported in literature. [Preview Abstract] |
Saturday, October 9, 2010 9:24AM - 9:36AM |
C2.00008: Fluctuation Modes of a Bent-Core Nematic Liquid Crystal Madhabi Majumdar, Saonti Chakraborty, Yogesh Singh, James T. Gleeson, Antal Jakli, Samuel Sprunt We present a dynamic light scattering study of the bent-core nematic liquid crystal compound \textit{DT6Py6E6.} We utilize a ``dark'' scattering geometry, which allows us to search for fluctuation modes that are not purely associated with the uniaxial director. Indeed, we observe two modes (hydrodynamic and non-hydrodynamic) in addition to the expected twist-bend director mode. We present a model for the additional modes based on fluctuations of the biaxial order parameter, which leads to an estimate of 10-100 nm for the correlation length associated with these fluctuations. [Preview Abstract] |
Saturday, October 9, 2010 9:36AM - 9:48AM |
C2.00009: Positron Annihilation Lifetime Spectroscopy with a $^{68}Ge$ Positron Source Jason Calloo, Herbert Jaeger Positron annihilation lifetime (PAL) spectroscopy is a sensitive technique to probe the electronic environment of positrons in condensed matter. In particular, the lifetime of positrons in condensed matter depends mostly on the local electron density. Often PAL measurements are done with a $^{22}Na$ positron source because of its wide availability, convenient half life (2.6 y), and modest cost. One disadvantage of $^{22}Na$ is its low positron energy of E$_{max}$ = 540 keV, which limits penetration of positrons into the material under study. An alternative source of positrons is $^{68}Ge$. It decays by electron capture (T$_{1/2}$ = 271 d) to $^{68}Ga$ which in turn decays to $^{68}Zn$ and emits positrons with energies as high as 1.9 MeV, the highest positron energy of commercially available long-lived radioisotopes. Due to the lack of a prompt gamma emission signaling the begin of the positron$'$s lifetime, PAL measurements can only performed by detecting the emitted positrons directly. The design of a PAL spectrometer using a $^{68}Ge$ source will be discussed. [Preview Abstract] |
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