Bulletin of the American Physical Society
2012 Annual Meeting of the California-Nevada Section of the APS
Volume 57, Number 13
Friday–Saturday, November 2–3, 2012; San Luis Obispo, California
Session H2: Condensed Matter III: Superconductors |
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Chair: Nilgun Sungar, Cal Poly San Luis Obispo Room: Business 003 0112 |
Saturday, November 3, 2012 2:00PM - 2:12PM |
H2.00001: Improvement of Physical Properties in High Tc Superconductors with Pb-doping Maria Zarefakis, Sandy Lavito, Paulo Costa, Johnathan Johnson, Martin Morales-Avendano, David De LaCruz, Dominique Davenport, Sukhwinder Kaur, Marcella Santos, Tory Bear, Lu Rose Zhang Almost all of the high Tc superconductors (HTS) that have been explored up until now have low critical current densities, and because of this, these HTS have seen limited applications. Increasing the critical current density is of great importance if HTS are to attain wide-spread use. Previous studies have shown that Pb doping, within a certain range, can increase a superconductor's critical current density without altering the structure of the material. In order to better understand what the exact optimal lead doping range is, various ranges of Pb in superconducting $Bi_{2-x} Pb_x Sr_2 Ca_2 Cu_3 O_{11-\delta } $ compounds were prepared by the solid-state reaction method with $x$ ranging from 0.1-0.6. HTS within this optimal lead doping range have a more stabilized crystal structure, which reduces annealing time and improves their magnetic properties, and as a result, improves their manufacturability for commercial applications. When the Pb doping process through which superconductivity is enhanced is better understood, we will be able to focus on studying physical properties of Pb-doping optimized superconductors. Any findings in this direction will contribute to the selection of superconductors that are reproducible and suitable for commercial use in electric power transportation and other high-magnetic-field applications. [Preview Abstract] |
Saturday, November 3, 2012 2:12PM - 2:24PM |
H2.00002: Specific Heat of Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{4}$Sb$_{12}$ Banchong Somsanuk, Hank Anderson, Pei-Chun Ho, M. Brian Maple, Tatsuya Yanagisawa The filled skutterudite compound, PrOs$_{4}$Sb$_{12}$, displays unconventional superconductivity at a relatively low critical temperature Tc$=$1.85K. The underlining physics behind this heavy fermion superconductor compound is largely unknown. To gain better insight into the underlining physics, we need to study the effect of ferromagnetism on unconventional superconductivity by using Neodymium-doped compounds, Pr$_{\mathrm{1-x}}$Nd$_{\mathrm{x}}$Os$_{4}$Sb$_{12}$. One of the parameters to study is the differences in their thermodynamic property. The specific heats of these compounds were measured using finite heat pulse relaxation calorimetry in an 11K cryocooler system. This presentation will report on the progress of the specific heat measurement of the doped compound Pr$_{\mathrm{1-x.}}$Nd$_{\mathrm{x}}$Os$_{4}$Sb$_{12}$ (x$=$1, 0.5) and the physics behind measuring heat capacity. [Preview Abstract] |
Saturday, November 3, 2012 2:24PM - 2:36PM |
H2.00003: Pseudogap Precursors in Optimal Doped EuBCO R. Schwartz For the pseudogap phase, an important feature of cuprate superconductivity, Varma et al. predict the existence of loop currents. By means of Maximum Entropy analysis, we investigate transverse field $\mu $SR data of optimal-doped EuBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (T$_{\mathrm{c}} =$ 93 K). To search for precursor effects, and for predicted pseudogap loop currents, our focus is on a temperature interval between T$_{\mathrm{c}}$ and T*. An extra drop in normal-state frequency indicates demagnetization effects, possibly caused by short-living Cooper-pairs in the Cu-O$_{2}$ planes. In sum, our results suggest magnetic roots of cuprate superconductivity. [Preview Abstract] |
Saturday, November 3, 2012 2:36PM - 2:48PM |
H2.00004: A real time, continuously operating, fluxlocked superfluid interferometer Aditya Joshi, Richard Packard Interferometers are widely used in basic and applied sciences. These instruments using sound, light or de Broglie matter waves, have an output amplitude (e.g., the Josephson critical current in a dc SQUID), which is a sinusoidally varying function of some variable of interest (magnetic flux in the case of the SQUID). To achieve widespread practical utility, it is very useful to have a method to linearize the instrument's response. We report here a real-time flux locking technique using thermal counter flow to linearize the output of a superfluid He-4 quantum interference device (SHeQUID), an analogue of the superconducting dc SQUID. A continuously changing rotation flux through the interferometer sense loop of the SHeQUID produces a changing phase-difference in the sense loop. This change is canceled via continuous negative feedback using the phase shift caused by a thermally driven superflow. The feedback signal (injected heater power) is then a linear measure of rotation flux and is used to track the rotation signal in real time. [Preview Abstract] |
Saturday, November 3, 2012 2:48PM - 3:00PM |
H2.00005: Measurements of the Critical Casimir Effect and Superfluid Density in $^4$He Films John Abraham, Gary Williams, Konstantin Penanen We report the results of experiments on $^4$He films in the vicinity of the bulk superfluid transition temperature $T_\lambda$. A novel experimental apparatus allows measurements of film thinning due to the critical Casimir effect as well as the superfluid density of the film via third sound measurements. The temperature where the the Casimir film thinning begins to occur is found to be very close to the Kosterlitz-Thouless superfluid transition temperature in the film. Additionally, a new film-thickening effect is observed at $T_\lambda$ when the temperature is swept extremely slowly. [Preview Abstract] |
Saturday, November 3, 2012 3:00PM - 3:12PM |
H2.00006: Odd-Frequency Triplet Josephson Current Through an Exchange Spring Adam Moke, Thomas Baker, Adam Richie-Halford, Andreas Bill The existence of an odd-frequency long range triplet component in the order parameter of a proximity system with singlet superconductors is a recent prediction that has garnered great interest. The experimental fingerprint of this phenomenon is difficult to establish. We investigate a hybrid structure in which the emergence of the long range triplet component may be measured and identified. We consider a superconductor - exchange spring - superconductor Josephson junction as a function of increasing twist of the magnetic domain wall in the exchange spring. We show that as the domain wall is generated the long range triplet component emerges and modifies the current flowing through the Josephson junction. The critical temperature is also affected by the increased twist of the domain wall. The calculations lead us to propose an experiment where the long range triplet component can unequivocally be identified. [Preview Abstract] |
Saturday, November 3, 2012 3:12PM - 3:24PM |
H2.00007: Phase separation instabilities and modulated coherent pairing states in Bi-based cuprates Armen Kocharian, Kun Fang, Gayanath Fernando, Alexander Balatsky, Kalum Palandage There is growing evidence that the unconventional spatial inhomogeneities and structural changes in the doped high-Tc superconductors are accompanied by the pairing of electrons, subsequent quantum phase transitions (QPTs), and condensation in coherent states. We show that these superconducting coherent pairing with mediated opposite spin coupling are driven by phase separation instabilities near the quantum critical points. We examine electron coherent and incoherent pairing instabilities using our results on exact diagonalization in pyramidal and octahedron Hubbard-like clusters under variation of chemical potential (or doping), interaction strength, temperature and magnetic field. We also evaluate the behavior of the energy gap in the vicinity of its sign change in a real space as a function of out-of-plane position of the apical oxygen atom, due to vibration of apical atom and variation of inter-site coupling. Our results show direct correlation between the size of the energy gap characterizing the coherent superconducting state and a modulation of the structural positions of apical atom. These results provide a transparent microscopic explanation of (electron correlation induced) supermodulation of the coherent pairing gap observed recently in scanning tunneling microscopy. [Preview Abstract] |
Saturday, November 3, 2012 3:24PM - 3:36PM |
H2.00008: Investigation of Fermi {\&} Luttinger surfaces in Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$ using ARPES Simon Bell, Gey-Hong Gweon, Jianqiao Meng, K.H. Kim, H.G. Lee, S.I. Lee The electronic structure {\&} occupancy of doped cuprate superconductors Ca$_{2-x}$Na$_{x}$CuO$_{2}$Cl$_{2}$ of various doping levels is probed using angle-resolved photoemission spectroscopy (ARPES). The Fermi surface investigated shows that the Luttinger sum rule involving only the Fermi surface fails to account for the particles sum rule. Instead, the Luttinger rule that involves both the Fermi surface and the Luttinger surface seems necessary. We argue that such a generalized sum rule indicates the importance of very strong electron correlations. [Preview Abstract] |
Saturday, November 3, 2012 3:36PM - 3:48PM |
H2.00009: High resolution ARPES spectroscopy on topological insualtors Ahram Kim, Jian-Qiao Meng, Genda Gu, Gey-Hong Gweon We report new angle resolved photoelectron ARPES spectroscopy (ARPES) results on topological insulators, Bi2Se3 and Bi2Te3. Our data are characterized by unprecedentedly small Dirac point binding energy and the near absence of bulk conduction band near the Fermi energy, therefore, implying that our samples are closer to the ideal topological state than previously known samples. We also discuss the self energy extracted from the ARPES data and the line shapes, and compare them with those known for strongly correlated electron materials such as high temperature superconductors, with emphasis on high temperature. While our results agree with previous results known for topological insulators, in that they signify very weakly correlated and conventional electronic structure, thereby proving a nice reference case, we also point out some intriguing feature in the data. [Preview Abstract] |
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