Bulletin of the American Physical Society
2009 Joint Spring Meeting of the Ohio Sections of the APS and AAPT
Volume 54, Number 3
Friday–Saturday, April 24–25, 2009; Ada, Ohio
Session C2: Condensed Matter and Nanomaterials |
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Chair: Mellita Caragiu, Ohio Nothern University Room: McIntosh Center Boardroom |
Saturday, April 25, 2009 8:16AM - 8:28AM |
C2.00001: Theoretical description of the white lines in 3d transition metals Kofi Nuroh The $3d \to 2{p_j}\;(j = 3/2,\;1/2)$emission lines in the 3d transition metals ${}^{21}Sc$ through ${}^{27}Ni$ have been studied using a theoretical model based on autoionization and characteristic decay events following electron impact ionization of a core electron in solids. The theory primarily hinges on the Bethe-Born formalism of inelastic scattering of electrons on atoms with the inclusion of correlation effects via many-body perturbation techniques. The $2{p^5}3{d^{\,n\, + 1}}$ intermediate resonant configuration is diagonalized to provide the multiplet splitting and their corresponding intensities. By analyzing the relative magnitudes of the electrostatic and magnetic interactions of the $2p$and $3d$electrons, it is found that $LK$ coupling is suitable for the systems Sc, Ti, and V, while $jK$ coupling is appropriate for Cr to Ni. Applying the dipole approximation to the Coulomb transition matrix elements, the calculated electron-energy-loss- spectra separate into two distinct manifolds that arise from the $2{p_{3/2}}$ and $2{p_{1/2}}$ levels, namely, the white lines, and the calculations compare very well with measurements for x-ray absorption spectra. Reference: K. Nuroh, Physical Review B 78, 245116 (2008). [Preview Abstract] |
Saturday, April 25, 2009 8:28AM - 8:40AM |
C2.00002: Dynamic Monte-Carlo Simulations of Diffusion in Polypropylenes: Possible Artifacts of Stereochemistry Ernst von Meerwall, Numan Waheed, Wayne Mattice We previously reported coarse-grained lattice-based dynamic Monte-Carlo (MC) simulations in polypropylenes (PP), as well as pulsed-gradient diffusion (D) experiments at 180 deg. C., to study the effects of stereochemistry. We had obtained three PP specimens, with probabilities of a meso dyad Pm = 0.02 (syndiotactic, ``sPP'', Mn = 12,300), 0.23 (atactic, ``aPP'', Mn = 5,300), and 0.89 (isotactic, ``sPP'', Mn = 9,900). New simulations copied the samples' Mn and Pm, and for iPP the polydispersity Mw/Mn = 1.24. The conversion factor K between MC steps and real time must be derived from experiment. It was found that K = 3300 MCS/ps for both sPP and aPP, but falls to 1600 for monodisperse iPP, falling further to 800 if polidispersity is coarsely included. As the lack of any M-dependence of K had been verified in our earlier work with n-alkanes and polyethylenes (PE), its Pm-dependence must either originate in a systematic error of the PE-calibrated GPC M values, or else be an intrinsic feature of our MC method. New dilute D measurements, consistent with the Flory M$^{-0.5}$ --dependence, point to the second possibility. [Preview Abstract] |
Saturday, April 25, 2009 8:40AM - 8:52AM |
C2.00003: Combined Zeeman and Aharonov-Bohm effects in a double quantum dot ring Abigail Perkins, Eric Hedin, Yong Joe A mesoscopic Aharonov-Bohm (AB) ring with a quantum dot (QD) embedded in each arm is investigated analytically to provide electron transmission characteristics. A parallel magnetic field provides Zeeman splitting of the QD energy levels. Combined Zeeman energy level splitting and AB-effects occur with a perpendicular field. The contour plots of the transmission as a function of electron energy and magnetic field are presented. Taking advantage of a unique parameter regime in which the AB-oscillations show extreme sharpening [1], the transmission characteristics can be tuned to produce spin-polarized currents. \\[4pt] [1] E. R. Hedin, Y. S. Joe, and A. M. Satanin, Jnl. of Computational Electronics, \textbf{7}, 280 (2008), and ``Online First,'' DOI: 10.1007/s10825-008-0201-y. [Preview Abstract] |
Saturday, April 25, 2009 8:52AM - 9:04AM |
C2.00004: Exploring the ferromagnetic phase diagram of Sb$_{2-x}$V$_{x}$Te$_{3}$ and Sb$_{2-x}$Cr$_{x}$Te$_{3}$ using hydrostatic pressure as an experimental variable Jeffrey Dyck, Matthew Bowers, Yi-Jiunn Chien, Ctirad Uher, Cestmir Drasar, Petr Lostak We report on the hydrostatic pressure dependence of the magnetotransport properties of ferromagnetic Sb$_{2-x}$V$_{x}$Te$_{3}$ and Sb$_{2-x}$Cr$_{x}$Te$_{3}$ with x $\le $ 0.15. Pressure significantly alters the carrier concentration in these diluted magnetic semiconductor compounds. Key to the understanding of the underlying mechanism of ferromagnetism is the role that both free hole and magnetic impurity concentration and type play in these materials. The evolution of Curie temperature with carrier concentration and average impurity separation, as tuned by pressure, will be compared to a simple model incorporating indirect exchange among impurity spins, mediated by the free holes. [Preview Abstract] |
Saturday, April 25, 2009 9:04AM - 9:16AM |
C2.00005: Monte Carlo Studies of Irreversibly Growing Droplets on Small-World Graphs Howard Richards For the Ising model on a regular, nearest-neighbor lattice of less than 6 dimensions, metastable decay occurs via the nucleation of critical droplets; subcritical droplets are biased toward shrinkage, whereas supercritical droplets are biased toward growth. The size of a critical droplet is governed by the competition between the coupling of the magnetic field to the volume $V$ of the droplet, which lowers the free energy, and the coupling of the droplet of the stable state to metastable state at the surface $S$ of the droplet, which increases the free energy. This competition between volume effects and surface effects makes the isoperimetric dimension $d$, defined by $(d-1)/d \! \equiv \! (V / S)({\rm d}S/{\rm d}V)$, relevant to metastable decay. The simulations show that for a moderate percentage of small-world connections, $d$ tends to saturate at 6, as should be expected from work on regular lattices. [Preview Abstract] |
Saturday, April 25, 2009 9:16AM - 9:28AM |
C2.00006: Current-voltage characteristics of a compressed carbon nanotube Evan Wilson, Ronald Cosby Current-voltage calculations for a compressed segment of a single-wall metallic carbon nanotube attached to copper electrodes are reported. Density functional theory is used for electronic structure computations. Currents through the 48-atom nanotube segment are predicted by applying a non-equilibrium Green's function technique. The conductance is predicted to increase linearly for small compressions. [Preview Abstract] |
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