Bulletin of the American Physical Society
77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010; Baton Rouge, Louisiana
Session BC: Magnetism, Metal-Insulator Transitions, and Quantum Dots |
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Chair: Daniel Sheehy, Louisiana State University Room: Nicholson Hall 118 |
Thursday, October 21, 2010 8:30AM - 8:42AM |
BC.00001: Doping Dependence of Structural, Electrical and Magnetic Properties of Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ Single Crystals Biao Hu, Gregory T. McCandless, E.W. Plummer, Rongying Jin We have studied the doping dependence of structural, electrical and magnetic properties of Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ with 0.0$\le $x$\le $1.0. Our single crystal X-ray diffraction refinements show that the RuO6 octahedron rotates about 7$^{o}$ in undoped Sr$_{3}$Ru$_{2}$O$_{7}$. With the partial substitution of Ru by Mn, the rotation is gradually attenuated. Correspondingly, the electrical and magnetic properties of Sr$_{3}$(Ru$_{1-x}$Mn$_{x})_{2}$O$_{7}$ vary with x. We will discuss the correlation between structure and physical properties in this system. [Preview Abstract] |
Thursday, October 21, 2010 8:42AM - 8:54AM |
BC.00002: Magnetotransport Properties of Thin C-Fe Films Joseph Prestigiacomo, Kathie Lusker, Yimin Xiong, Shane Stadler, Amar Karki, David Young, Jayne Garno, Philip Adams The magnetotransport properties of C-Fe films formed by e-beam vapor deposition onto glass substrates are presented in the temperature region of 2 K to 300 K. Hall effect measurements exhibit a significant anomalous Hall voltage whose magnitude increases with increasing temperature. Measurements of the ordinary Hall coefficient in 10 nm-thick films give a charge carrier density ranging from n $\sim $ 3.0 x 10$^{29}$ m$^{-3}$ at 2 K to approximately half that value at 290 K. A comparison between anomalous Hall effect and parallel field magneto-optic Kerr effect measurements reveal a highly anisotropic coercive field with the easy direction lying in the plane of the film. The films have an isotropic linear positive magnetoresistance (LPMR) beyond their saturation magnetization. [Preview Abstract] |
Thursday, October 21, 2010 8:54AM - 9:06AM |
BC.00003: The Anomalous Hall Effect in Ultra-Thin Amorphous CNi3 Films Yimin Xiong, Philip Adams, Gianluigi Catelani The anomalous Hall resistance in homogeneous CNi$_3$ films with sheet resistance near the quantum resistance was studied. Tunneling measurements show that the saturation behavior is commensurate with the emergence of the 2D Coulomb gap, suggesting that e-e interactions mediate the high-disorder phase. The saturation of anomalous Hall resistance is associated with the crossover from the weak- localization regime to that of a 2D correlated insulator. In the weak-localization regime, where the sheet conductance G $\gg e^2/h$, the anomalous Hall resistance of the films increases with increasing disorder and the Hall conductance scales as G$_{xy} \propto G^\varphi$ with $\varphi$ = 1.6. However, at sufficiently high disorder the system begins to enter the 2D correlated insulator regime, at which point the Hall resistance R$_{xy}$ abruptly saturates and the scaling exponent becomes $\varphi$ = 2. The crossover is also clearly evident in the scaling behavior of the Hall conductivity as well as in the tunneling density of states. [Preview Abstract] |
Thursday, October 21, 2010 9:06AM - 9:18AM |
BC.00004: Structure and Magnetism of FeAl(110) Surface Phases Matthew Patterson, Orhan Kizilkaya, Challa Kumar, Richard Kurtz, Phillip Sprunger We have studied the correlation between FeAl(110) surface structures and surface ferromagnetism using X-ray absorption (XAS), X-ray magnetic circular dichroism (XMCD), and scanning tunneling microscopy (STM). FeAl(110) is cleaned by repeated cycles of Ne+ sputtering and annealing and exhibits a variety of surface reconstructions as a function of annealing temperature. Bulk magnetometry shows that single-crystal FeAl is paramagnetic at room temperature. However, it was found by XMCD measurements at the Fe L2,3 edge that the surface phase formed by sputtering without annealing exhibits ferromagnetism, and that the small induced magnetization vanishes both with oxidation of the surface and with reconstruction. The observed induced magnetization is discussed in light of STM measurements of the sputtered and oxidized surfaces and prior studies of the morphology of the FeAl(110) surface reconstructions. [Preview Abstract] |
Thursday, October 21, 2010 9:18AM - 9:30AM |
BC.00005: Nonreciprocal switching of VO$_{2}$ thin films on microstructured surfaces Charles Adams, Ismail Karakurt, Paul Leiderer, Johannes Boneberg, Richard Haglund Vanadium dioxide is a strongly correlated electron material that undergoes an insulator-to-metal transition at approximately 340~K, with a corresponding large change in its optical and electronic properties. By depositing a VO$_{2}$ thin film on a planar hexagonal close-packed array of 1.54~$\mu $m diameter silica microspheres, we constructed a laser-triggered thin film optical switch that exhibits different fluence thresholds for the insulator-metal transition (IMT) depending on the direction of illumination. The IMT was triggered by a ns Nd:YAG laser (532 nm) from two directions normal to the substrate while monitoring the transmission with a near-IR diode laser. Due to the focusing effects of the microspheres, the fluence required for switching the VO$_{2}$ was 2.4 times higher when the switching laser was incident from the film (top) side of the array than from the microsphere (bottom) side. Through both the experiments and simulations, we find evidence for strong nonlinear near-field absorption in the VO$_{2}$. [Preview Abstract] |
Thursday, October 21, 2010 9:30AM - 9:42AM |
BC.00006: Low-power laser induced metal-insulator transition in gold::vanadium dioxide nanoarrays Davon W. Ferrara, Evan R. MacQuarrie, Joyeeta Nag, Richard F. Haglund Vanadium dioxide (VO$_{2})$ is a strongly-correlated electron material with a well-known semiconductor-to-metal transition (SMT) that can be induced thermally, optically, or electrically. By coating lithographically prepared arrays of gold nanoparticles (NPs) of diameter 140 nm with a 60 nm thick film of VO$_{2}$ by pulsed laser deposition, hybrid Au::VO$_{2}$ structures were created. Due to the sensitivity of the Au particle-plasmon resonance (PPR), a temperature dependent shift in the PPR can be generated by switching the VO$_{2}$ from one phase to another, creating a tunable plasmonic metamaterial. To study the low-power switching characteristics of these structures, transient absorption measurements were made using a mechanically shuttered 785 nm pump laser, corresponding to the PPR resonance of the Au NPs, and 1550 nm CW probe. Results show that the presence of Au NPs significantly lowers the threshold laser power required to induce the SMT. Measurements on arrays of different grating constants (350 nm and 500 nm) support the hypothesis that the particles are acting as ``nano-radiators'' that absorb and redeposit thermal energy by scattering light back into the film. Finite element modeling was performed to better understand the complex thermodynamics of the structure. [Preview Abstract] |
Thursday, October 21, 2010 9:42AM - 9:54AM |
BC.00007: Cu/CuOx Nanoclusters on ZnO(1010): Electronic, Catalytic, Morphological Structure Ziyu Zhang, Matthew Patterson, Maoming Ren, Yaroslav Losovyi, John Flake, Richard Kurtz, Phillip Sprunger ARUPS, STM, and EELS has been used to study the electronic, atomic and chemical structure of Cu and CuO nanoclusters on non-polar ZnO(1010) surface. Within the backdrop of developing high performance CO2 reduction catalyst (methanol production), our studies show that higher yield rate are found for Cu(I) surface species. ARPUS results from nanocluster CuOx/ZnO reveals that the oxidation process is highly dependent on the cluster size (smaller size. Moreover, CO adsorption (BE and vibrational) are distinctly different between Cu and CuOx nanoclusters supported on ZnO. Reaction studies confirm that methanol production is 4 times higher on partially oxidized Cu nanoclusters. Photoemission shows a small amount of Cu(II) even upon repeated oxidation/annealing processes, indicating a preferential stability of Cu(I) in the supported nanoclusters, due to interfacial effects with the substrate. This talk will include results from EELS/TPD and STM/AFM studies to better elucidate the chemical adsorption and intermediates as a function of CuOx size and structure. [Preview Abstract] |
Thursday, October 21, 2010 9:54AM - 10:06AM |
BC.00008: Kondo temperature in a quantum dot Seungjoo Nah, Michael Pustilnik The dependence of the Kondo temperature in a quantum dot on the gate voltage is studied in the Coulomb blockade regime. Due to the finite size of the quantum dot, the Kondo temperature is greatly enhanced compared with that in the Anderson impurity model. [Preview Abstract] |
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