Bulletin of the American Physical Society
Fall 2015 Joint Meeting of the Texas Section of the AAPT, Texas Section of the APS and Zone 13 of the Society of Physics Students
Volume 60, Number 15
Thursday–Saturday, October 29–31, 2015; Waco, Texas
Session C2: Condensed Matter Physics I |
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Chair: Jason Slinker, University of Texas, Dalls Room: A.108 |
Friday, October 30, 2015 10:45AM - 10:57AM |
C2.00001: Vortex dynamics in the YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-d\thinspace }}$Superconductor with In-plane Columnar Defects Introduced by Irradiation Andra Petrean, Lisa Paulius, Valentina Tobos, Heather Cronk, Wai-Kwong Kwok We report on the effects of introducing columnar defects by irradiation in clean single crystals of YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7-d\thinspace }}$in a direction \textit{parallel} to the ab-plane. The defects were introduced by bombarding the samples with $^{\mathrm{208}}$Pb$^{\mathrm{56+}}$ ions at an energy of 1.4GeV. We find that the defects suppress the first order melting transition for magnetic fields aligned parallel or at small angles relative to the defects. The columnar defects \textit{inhibit} vortex motion of vortices parallel to the defects, while the vortices experience less pinning when they are perpendicular to the defects. Our results suggest that the pinning anisotropy is increased, at least for magnetic fields up to the matching field dose of 1T. [Preview Abstract] |
Friday, October 30, 2015 10:57AM - 11:09AM |
C2.00002: A Magnetic Nanorod Array on a Superconducting Thin Film Wonbae Bang$^{1}$, K. D. D. Rathnayaka$^{1}$, I. F. Lyuksyutov$^{1}$, W. Teizer$^{1,2}$, D. G. Naugle$^{1}$ We have fabricated a magnet-superconductor hybrid (MSH) by using electron beam lithography, thermal evaporation, and electroplating. The MSH is composed of a magnetic nanorod array on top of a superconducting thin film. The array is insulated from the thin film. We have studied temperature and external magnetic fields dependence of electrical resistivity near the MSH’s critical temperature. We have observed strong hysteresis and enhanced superconductivity when the array is magnetized by an external magnetic field. [Preview Abstract] |
Friday, October 30, 2015 11:09AM - 11:21AM |
C2.00003: Development of Ag nanoparticle enhanced textured-powder Bi-2212/Ag wire Joshua Kellams, Peter McIntyre, Nathaniel Pogue, Jacob Vandergrifft, Kyle Shores A new approach to the preparation of cores for Bi-2212/Ag wire is being developed. Nanoparticle Ag is homogeneously dispersed in Bi-2212 fine powder, and the mixture is uniaxially compressed to form highly textured, cold-sintered core rods. The rods are assembled in a silver matrix, drawn to form monofilament wire, and restacked and drawn to form multifilament wire. Preliminary studies using tablet geometry demonstrate that a non-melt heat treatment produces densification, grain growth, intergrowth among grains, and macroscopic current transport. The status of the development is reported. [Preview Abstract] |
Friday, October 30, 2015 11:21AM - 11:33AM |
C2.00004: Effects of Salt Additives in the Performance of iridium-based LEC devices Lyndon Bastatas, Melanie Bowler, Yulong Shen, Kristin Jeannette Suhr, Matthew Darren Moore, Brad Holliday, Jason Slinker Light-emitting electrochemical cells (LECs) are low-cost, promising alternatives of organic light emitting diodes (OLEDs). Their single-layer architecture circumvents the multi-layer deposition requirement of state-of-the-art OLED devices. They are solution-processable so it also offers wider applicability. Recent studies have reported that addition of salt additives enhances the turn-on time and maximum brightness of LEC-based devices. So we investigated the effect of LiPF6 in iridium-based LECs by performing impedance spectroscopy coupled with device study. From this analysis we model the device to an equivalent circuit and extracted some parameters such as the electrical resistance of the active layer and bulk ionic resistances of the device. We find that there is a correlation between the resistances, salt concentration and characteristics of the device. The over-all resistance decreases as the salt concentration is increased, reaching to a certain threshold where addition of more ions only adversely affects the device. Our result highlights that there is an optimal salt concentration where the performance of the device is enhanced. [Preview Abstract] |
Friday, October 30, 2015 11:33AM - 11:45AM |
C2.00005: Chip-Based Synthetic Biology to Track Anticancer Drug Activity$\backslash $fs20 Dimithree Kahanda, Jason Slinker, Gaurab Chakrabarti, David Boothman It is advantageous to develop systems that represent significant complexity of biological systems, while maintaining control over specific factors involved in a particular process. We have established a chip-based electrochemical platform for following the repair of DNA damage produced by a redox-cycling anticancer drug, beta-lapachone($\beta $-lap). These chips, which possess key features to reproduce the cellular environment, drug cofactors, and base-excision repair (BER) enzymes tracked DNA damage repair activity with redox probe-modified DNA monolayers on gold. We were able to observe drug-specific changes in the square wave voltammetry at therapeutic drug concentrations with high statistical significance over drug-free control. We also demonstrate high correlation of this change with the specific drug cycle through rational controls. Thus, this chip-based platform enabled tracking of drug-induced damage repair processes when biological criteria were met, providing a unique synthetic platform for uncovering activity normally restricted to inside cells. [Preview Abstract] |
Friday, October 30, 2015 11:45AM - 11:57AM |
C2.00006: Surface probe measurements of mix conductor Kuo-Yao Lin For the past few decades, the research and industrial application of solid state lighting has been very active. Besides widely-used light emitting diodes (LED) and well-known organic light emitting diodes (OLED), considerable research also focuses on light-emitting electrochemical cells (LEECs) due to their great efficiency, high luminance, and long life time from a simple device architecture. Efficient LEEC devices can be fabricated from a single layer of an ionic transition metal complex (iTMC) between two electrodes, considerably simpler than conventional OLEDs. Ruthenium and iridium complexes are two common iTMC materials used for LEEC devices, with iridium complexes yielding higher efficiency devices. The underlying physics of LEEC devices is not fully understood yet, and researchers have proposed both electrodynamic and electrochemical models to interpret LEEC dynamics. Additional measurements need to be done on LEEC devices to collect enough information to support either model. Scanning Kelvin Probe Microscopy (SKPM) of LEEC devices would reveal the surface potential profile and clarify the physics behind LEECs. Only ruthenium iTMC device surface potential profile measurements have been done before. This talk will focus on SKPM of iridium LEECs to study the physics behind the device. [Preview Abstract] |
Friday, October 30, 2015 11:57AM - 12:09PM |
C2.00007: Superfluidity of magnons in ferromagnetic films Chen Sun, Thomas Nattermann, Valery Pokrovsky The magnon Bose-Einstein condensation in Yttirum Iron Garnet films at room temperature was discovered by the M\"{u}nster experimental group (S.O. Demokritov) in $2006$. Since the magnon condensate is coherent the natural question is whether the condensate is superfluid. Though the normal magnon density exceeds the condensate density in about $100$ times, the velocity of the superfluid part is by $5$-$7$ decimal orders larger than that of the normal part at the same field gradients. Thus, the spin current is dominated by the condensate, i.e. superfluid. A deeper obstacle is that the phase trapping is inconsistent with the free motion whose phase linearly depends on coordinate. The superfluidity can start only after submission of a finite (threshold) energy to the condensate by an external source. At energy close to threshold, the phase on long intervals of length remains close to the trapped values and changes by $2\pi$ on a comparatively short intervals (phase solitons). The superfluid velocity remains almost zero between solitons and acquires finite value inside solitons. Thus, the current and number of magnons are not conserved locally transferring the spin momentum to the lattice, but they are conserved globally. All these phenomena are due to the dipolar forces. [Preview Abstract] |
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