Bulletin of the American Physical Society
Joint Fall 2009 Meeting of the Ohio Sections of the APS and AAPT
Volume 54, Number 9
Friday–Saturday, October 9–10, 2009; Delaware, Ohio
Session C2: Condensed Matter Physics and Materials Science |
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Chair: Brad Trees, Ohio Wesleyan University Room: Conrades-Wetherell Science Center 163 |
Saturday, October 10, 2009 8:00AM - 8:12AM |
C2.00001: Normal state charge dynamics of novel iron-based superconductor FeTe$_{0.87}$S$_{0.13}$ probed with infrared spectroscopy S.V. Dordevic, N. Stojilovic, Adam Koncz, Rongwei Hu, C. Petrovic We will present the results of our spectroscopic studies of novel iron-based superconductor FeTe$_{0.87}$S$_{0.13}$ with T$_c$ = 8 K. Infrared and optical measurements have been performed over a broad range of frequencies (50 - 50,000 cm$^{-1}$ and temperatures (10 - 300 K). Our results reveal unusual normal state: incoherent charge dynamics and absence of well defined quasiparticles. Unlike other iron-based superconductors, the structural and magnetic phase transitions at T$\simeq$ 30~K do not seem to have significant effect on optical properties of FeTe$_{0.87}$S$_{0.13}$. [Preview Abstract] |
Saturday, October 10, 2009 8:12AM - 8:24AM |
C2.00002: Experimental Characterization of Nonlinear Optical Materials Katie Knox, Chuan Yang, Zhiwen Liu An optical system based on a half-wave plate-polarizer attenuator was designed to determine the transmitted light through materials that behave nonlinearly in the presence of high-energy picosecond laser pulses. The sample's nonlinear absorbance of a frequency-doubled Nd:YAG laser was measured as the energy of the incident light was regulated by the rotation of a half-wave plate. The optical system was used to measure the absorption of two linear samples as well as a nonlinear liquid crystal. Experimental results revealed that the optical material, which was composed of gold nanospheres in the nonlinear liquid L34, behaved as expected in the presence of lower input energies, but the attenuated beam did not reach a high enough energy to observe the full limiting effects of the nonlinear material. [Preview Abstract] |
Saturday, October 10, 2009 8:24AM - 8:36AM |
C2.00003: Detection of Electronic Defects in Zircon and Hafnon using PAC Spectroscopy Herbert Jaeger, Sean McBride PAC spectroscopy is a nuclear technique for which a probe nucleus interacts with electric and magnetic fields due to extra-nuclear charges and spins. This interaction results in a precession of the nuclear spin, which in turn gives rise to a perturbation of the angular correlation of gamma rays that are emitted by the probes. This technique is well suited to detect phase transitions, but it is also very sensitive to dynamic processes, such as vacancy motion and electron trapping. We have used PAC spectroscopy to study phase changes upon annealing of radiation-damaged zircon as well as crystalline hafnon. Typical results of high-temperature measurements show periodic spin precession functions with little or no damping. At low temperature the amplitude of the spin precession function decreases indicating a smaller fraction of the probe nuclei being subject to the interaction prevalent at high temperature. We believe this is evidence of a trapped electronic defect, giving rise to a rapidly decaying high-frequency quadrupole interaction. At higher temperatures the defect detraps and no longer causes a reduction in the amplitude of the spin precession function. [Preview Abstract] |
Saturday, October 10, 2009 8:36AM - 8:48AM |
C2.00004: Thermodynamic properties of gold nanoparticles described by Sutton-Chen potential and Quantum Sutton-Chen potential Yongjin Park, Gustavo Carri Thermodynamic properties of gold nanoparticles ($<$1.6nm) have been investigated by atomistic Monte Carlo simulations with three different potential functions/parameterizations (Sutton-Chen potential, Sutton-Chen potential with Pawluk's parameterization, and Quantum Sutton-Chen potential). The melting temperature of gold nanoparticles is predicted and compared to other theoretical and experimental values. The agreement between the predicted melting temperatures and the experimental values was not satisfactory for any of the three potentials in the studied range of sizes. However, the Sutton-Chen potential showed very good agreement for nanoparticles larger than 1.3nm while the Quantum Sutton-Chen potential exhibited a trend of melting temperatures similar to the experimental one although it consistently overestimated the melting temperatures. [Preview Abstract] |
Saturday, October 10, 2009 8:48AM - 9:00AM |
C2.00005: Triangular Relations in Structural Glasses Karina E. Avila, Horacio E. Castillo, Azita Parsaeian Structural glasses exhibit the phenomenon of dynamical heterogeneity: different regions of the system present different dynamical behavior. To study this phenomenon, we analyze simulations of four models of structural glasses performed in the aging regime. We compute the triangular relations of the local and global two-time correlation functions, i.e., the mathematical relationships among correlators calculated for the time pairs (t1,t2), (t2,t3) and (t1,t3) with t1$>$ t2$>$ t3. We plot the triangular relations of the global and local correlations together to compare their behavior. We find that the probability distribution of local correlations is concentrated along the curve representing the global correlations. Our results provide evidence of time reparametrization invariance and also point toward universality in the aging fluctuations. [Preview Abstract] |
Saturday, October 10, 2009 9:00AM - 9:12AM |
C2.00006: Fluctuations in the relaxation of a strong glass Azita Parsaeian, Horacio E. Castillo, Katharina Vollmayr-Lee We present results of molecular dynamics simulations of amorphous silica, carried out by using the BKS inter-atomic potential. We quantify the evolution of fluctuations by studying the probability distributions of local observables such as individual particle displacements $\Delta x$ and local coarse grained intermediate scattering functions $C_r$. We test for universality by comparing the probability distributions with those in small molecule glasses and in polymer glasses. [Preview Abstract] |
Saturday, October 10, 2009 9:12AM - 9:24AM |
C2.00007: Fokker-Planck Dynamics in the Energy Domain Gcina Mavimbela, Horacio E. Castillo, Claudio Chamon We derive a Fokker-Planck Equation (FPE) in the energy domain for a system in an infinite heat bath by coarse-graining its microscopic Master Equation. The resulting FPE carries information on the dynamics through a function $\lambda(E)$, which is a sum over all possible transitions given a state of energy E. We investigate the effects of changing the assumptions about the transition rates without changing the Hamiltonian of the model. By determining the eigenvalues of the equivalent Schrodinger Equation (SE), we get the relaxation spectrum of the FPE. We find that in the thermodynamic limit the equivalent SE approaches the classical limit, and we use the WKB approximation to solve it. We illustrate the use of the method by applying it to a system of harmonic oscillators. [Preview Abstract] |
Saturday, October 10, 2009 9:24AM - 9:36AM |
C2.00008: Hysteretic synchronization of a spin-torque nano-oscillator to a microwave signal Sergei Urazhdin, Vasil Tiberkevich, Andrei Slavin We report measurements of phase-locking of oscillations in a current-driven spin-torque nano-oscillator (STNO) to a microwave magnetic field. Measurements were performed at T=5 K on magnetic point contacts on extended 3.5 nm thick Permalloy films, incorporated in a giant magnetoresistance structure. The locking is detected by a linear variation of the precession frequency f with the external signal frequency fext, and dramatic narrowing of the precession linewidth. When the amplitude of the locking signal hmw was sufficiently large and its frequency was close to unlocked oscillation frequency f0 we observed the predicted hysteretic phase-locking [1] but only when the microwave field hmw was perpendicular to the dc field H. In addition to locking at f=fext, we also observed locking at f=fext/n with other integer n. In case n=2, the locking also becomes hysteretic at sufficiently large hmw., but only when the microwave field is parallel to the dc field H. These results are consistent with the resonant linear excitation of magnetic precession for n=1, and parametric pumping for n=2. \\[4pt] [1] R. Bonin \textit{et al.}, Eur. Phys. Journal B 68, 221 (2009). [Preview Abstract] |
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