Bulletin of the American Physical Society
2007 Ohio Section APS/SOS/AAPT Joint Fall Meeting
Volume 52, Number 15
Friday–Saturday, October 19–20, 2007; Oxford, Ohio
Session C2: Condensed Matter Physics |
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Chair: Michael Pechan, Miami University Room: Culler Hall 220 |
Saturday, October 20, 2007 8:30AM - 8:42AM |
C2.00001: Effect of Carbon-Black Filler and Processing Oil on Ultrasound Devulcanization of Isoprene Rubber Ernst von Meerwall, Ximei Sun, Tirtha Joshi, Avraam Isayev In support of a novel approach to rubber recycling, we continue our investigation of the effects of intense ultrasound on isoprene rubber by studying molecular and segmental mobilities of the host rubber vulcanized in the presence of 35 phr carbon-black filler with and without 10 phr plasticizing processing oil. We measured wide-line transverse NMR relaxation (T$_{2})$. The magnetization decays followed a bimodal distribution, distinguishing physical and chemical network (short T$_{2})$ from lighter sol, dangling chain ends, and trace oligomers (long T$_{2})$. Pulsed-gradient diffusion measurements failed because the high melt molecular weight contained insufficient longer-T$_{2}$ sol components. It was found that, corrected for oil where present, chemically extractable sol fractions were reduced to about 2/3 of those in unfilled vulcanizates at equal ultrasound exposure. Black filler modestly decreased all segmental mobilities, whereas processing oil slightly increased them. This relative insensitivity to additives supports earlier conclusions that the efficiency of the ultrasound method is uncompromised by the solid filler and extender oils used in rubber-based industrial products. [Preview Abstract] |
Saturday, October 20, 2007 8:42AM - 8:54AM |
C2.00002: Broad-band Cryogenic Microwave Filtering Scheme for Operating Devices at Sub 0.1 Kelvin Temperatures Kristen Herrmann, Andrei Kogan We developed compact low-pass filters for transport experiments with single-electron devices at temperatures below 0.1 Kelvin. The filter assembly consists of a coil made of a long thin copper wire placed in a chamber filled with stainless still powder. The transmission of the filter at frequencies between 40 MHz and 20 GHz was measured using a Vector Analyzer (Anritsu Lightning) with a characteristic impedance of 50 Ohm. Our designs show significant reduction of the test signal at frequencies 2 GHz and above. The filter design, construction, and selection of the optimal parameters will be discussed. [Preview Abstract] |
Saturday, October 20, 2007 8:54AM - 9:06AM |
C2.00003: Quartet condensation of fermions. Aseem Talukdar, Michael Ma, Fu-Chun Zhang We investigate quartet condensation in fermion systems with four internal states. This is the generalization of the well known BCS superconductor formed by Cooper pair (CP) condensation. Physical examples include spin-3/2 fermionic atoms, bi-layered systems with electrons and holes, quadra-layer spin polarized electron hole system, and two band electronic system. We derive the Landau Ginzberg (LG) free energy for such system in terms of the CP amplitudes. The LG free energy is found to contain attractive interactions among different types of CP's. This will allow them to form bound states of CP's called Cooper quartets (CQ). Using a variational calculation based on the Bogoliubov inequality, we find that CQ condensation may be favored over pair condensation at low temperature. We also study the pairing structures in such systems when pair condensation is preferred. [Preview Abstract] |
Saturday, October 20, 2007 9:06AM - 9:18AM |
C2.00004: Determination of crystallization conditions of nano-crystalline soft magnetic ribbons Michael Titus Many soft magnetic nano-crystalline materials exhibit properties of high magnetic induction, low coercivity and low losses. These properties are key for many electrical device applications in the frequency range of 15-30 kHz. The material obtained for the current study belongs to the Finemet family FeCuNbSiB and was grown as amorphous ribbons using rapid solidification methods. The amorphous ribbons are crystallized into the nano-crystalline state through suitable heat treatment. This presentation will describe studies for determining appropriate heat treat conditions using temperature dependent x-ray crystallography, magnetization tests and micro-structural analysis. [Preview Abstract] |
Saturday, October 20, 2007 9:18AM - 9:30AM |
C2.00005: Incipient ordering of Nd in La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ at low temperatures Katherine Wooley, Erica Carlson We consider a new possible spin order in a lanthanum-based cuprate superconductor La$_{1.6-x}$Nd$_{0.4}$Sr$_x$CuO$_4$ that is known to have charge and spin stripe order coexisting, and indeed somehow related, with superconductivity. In lanthanum-based cuprates, it is commonly assumed that the effective spin coupling between the CuO planes averages to zero. In this case, at low temperatures, the Nd moments will mimic the ordering of those Cu moments that they are directly coupled to through the Cu-O-Nd bonds, and the Nd ordering is then used to infer the stripe ordering. However we argue that due to the tilting of the oxygen octahedra in the LTT phase, the Nd are symmetry-allowed to couple to both their neighboring CuO planes, thus mediating a spin coupling between the CuO planes. We show that ferromagnetic moments along the stripes are the signature of this Nd coupling. Thus this new spin order could be detected by a peak near the ferromagnetic point (0,0) in an elastic neutron scattering experiment and may also affect the intensity of the third harmonic peak of the Cu spin order. [Preview Abstract] |
Saturday, October 20, 2007 9:30AM - 9:42AM |
C2.00006: Effects of inter-dot tunnel coupling and magnetic flux on an Aharonov-Bohm ring with double quantum dots Chunghee Roh, Eric Hedin, Yong Joe We analyze the novel quantum transmission through parallel-coupled double quantum dots (QD) in an Aharonov-Bohm (AB) ring by employing an exactly solvable tight-binding formalism. Contour plots of the transmission as a function of energy levels in the dots, which can be controlled by applied gate voltages [1], are shown for different inter-dot coupling strength and magnetic flux. For zero flux and inter-dot coupling, we find a sharp anomaly of suppressed transmission (T=0) when the two QDs have the same energy value with opposite sign. However, tuning the magnetic flux in this system enhances the transmission and changes the widths of a Breit-Wigner and a Fano resonance. In addition, the periodicity of the transmission and the swing of the Fano resonance are also observed to be modulated by the magnetic flux. Finally, we discuss an intersection of resonances and a doubling of the periodicity in the transmission for fixed magnetic flux in the case of coherent tunneling between two QDs (non-zero inter-dot coupling). [1] A.W. Holleitner \textit{et al}, PRL \textbf{87}, 256802 (2001). [Preview Abstract] |
Saturday, October 20, 2007 9:42AM - 9:54AM |
C2.00007: Long Term Thermal Stability of ZrB$_{2}$/SiC and Ni/SiC Schottky Contacts Sara Schaefer, Tom Oder Wide band gap semiconductors such as silicon carbide (SiC), group III-nitrides and zinc oxide (ZnO) have properties that make them excellent for fabricating electronic devices for high temperature applications. A key component in many of these devices is the Schottky metal contact, which should remain stable in the high temperature environment. We have fabricated SiC Schottky diodes using zirconium boride (ZrB$_{2})$ and nickel as the Schottky contacts. These diodes were subjected to long term thermal stressing at 500 $^{\circ}$C for several hours. The electrical properties of the diodes were characterized by determining the Schottky barrier heights and the ideality factor from the current-voltage measurements. The barrier height value of 1.58 eV was obtained for the diodes with ZrB$_{2}$, and this remained roughly unchanged after stressing at 500 $^{\circ}$C for 20 hours. The ideality factor however varied from 1.1 to 1.6. Our results so far indicate that the diodes made with ZrB$_{2}$ contacts have better stability when compared to those made with Ni contacts. [Preview Abstract] |
Saturday, October 20, 2007 9:54AM - 10:06AM |
C2.00008: Improved SiC Schottky Diodes using ZrB$_{2}$ Deposited at High Temperatures Tom Oder, Pamela Martin, Adetayo Adedeji, Tamara Isaacs-Smith, John Williams Results on ZrB$_{2}$ Schottky contacts deposited on n-type SiC by DC magnetron sputtering at temperatures between 20 $^{\circ}$C and 800 $^{\circ}$C are presented. The Schottky barrier heights determined by current-voltage measurements, increased with the deposition temperature from 0.87 eV for contacts deposited at 20 $^{\circ}$C to 1.07 eV for those deposited at 600 $^{\circ}$C. The RBS spectra of these contacts revealed a substantial decrease in oxygen peak with increase in the deposition temperature and showed no reaction at the ZrB$_{2}$/SiC interface. The barrier heights of the contacts annealed in nitrogen for 20 mins at 200 $^{\circ}$C to 500 $^{\circ}$C using a rapid thermal processor revealed only a slight increase. These results indicate improvement in the electrical properties and thermal stability of ZrB$_{2}$ on n-type SiC when the contacts are deposited at elevated temperatures, making them attractive for high temperature applications. [Preview Abstract] |
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