Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session H39: Focus Session: Superconductivity-Josephson Junctions and Pairing State Symmetry |
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Sponsoring Units: DCMP Chair: Mac Beasley, Stanford University Room: Baltimore Convention Center 342 |
Tuesday, March 14, 2006 11:15AM - 11:27AM |
H39.00001: Tunneling spectroscopy studies of the interplay between $s$- and $p$-wave pairings in a Ru microdomain embedded in bulk single-crystal Sr$_2$RuO$_4$ Zhenyi Long, Chrysafis Andreous, Zhiqiang Mao, Yoshiteru Maeno, Ying Liu We have performed detailed tunneling spectroscopy measurements on In-Ru/Sr$_2$RuO$_4$ junctions prepared by pressing freshly cut pure In wire onto Sr$_2$RuO$_4$ single crystals containing Ru microdomains (the 3-K phase). We have observed a superconducting transition with a $T_c$ = 0.5 K and an energy gap of 0.08 meV, both of which correspond to those of the bulk Ru. We have also observed a Josephson coupling between In and Ru, suggesting that conventional $s$-wave pairing is present in the Ru microdomains. On the other hand, a zero bias conductance peak (ZBCP) in the tunneling spectrum and an enhanced critical magnetic field over the bulk value for Ru were observed as well, indicating that $p$-wave pairing exists simultaneously in the Ru microdomain. The temperature and the magnetic field dependences of the tunneling spectrum suggest a non-trivial interplay of the $s$- and $p$-wave pairings and a novel phase modulation of the order parameter at the boundary of the Ru microdomain. We observed an oscillation of the Ru energy gap as the magnetic field is applied along the c axis of the Sr$_2$RuO$_4$ crystal. Such oscillation was not observed with the field applied along the ab plane. We will discuss the implication of the above observations in this unique superconducting system. [Preview Abstract] |
Tuesday, March 14, 2006 11:27AM - 11:39AM |
H39.00002: Probing the configuration and dynamics of order parameter domains in Sr$_{2}$RuO$_{4}$ by Josephson interferometry Francoise Kidwingira, Joel Strand, Dale Van Harlingen, Yoshiteru Maeno We observe anomalous features in the magnetic field dependence of the critical current of Josephson junctions formed between conventional superconductors and the ruthenate superconductor Sr$_{2}$RuO$_{4}$, including magnetic hysteresis, switching noise, and a wide variation of qualitatively different diffraction pattern shapes.~ All of this behavior can be explained by assuming a complex p-wave order parameter of the form p$_{x}$+ip$_{y}$ that supports a dynamical structure of domains of different chirality and orientation.~ To test this hypothesis, we are studying the effects of magnetic field cooling on the junction critical current.~ We find a substantial enhancement of the critical current in field cooled samples, consistent with chiral domains that couple to an applied magnetic field. [Preview Abstract] |
Tuesday, March 14, 2006 11:39AM - 11:51AM |
H39.00003: Phase-sensitive tests of the pairing state symmetry in Sr$_2$RuO$_4$ Igor Zutic, Igor Mazin Exotic superconducting properties of Sr$_2$RuO$_4$ have provided strong support for an unconventional pairing symmetry. However, the extensive efforts over the past decade have not yet unambiguously resolved the controversy about the pairing symmetry in this material. While recent phase-sensitive experiments using flux modulation in Josephson junctions consisting of Sr$_2$RuO$_4$ and a conventional superconductor have been interpreted as conclusive evidence for a chiral spin- triplet pairing [1], we propose here an alternative interpretation [2]. We show that an overlooked chiral spin- singlet pairing is also compatible with the observed phase shifts in Josephson junctions and propose further experiments which would distinguish it from its spin-triplet counterpart. Supported by the US ONR and the National Research Council. \newline \newline [1]K. D. Nelson,Z. Q. Mao, Y. Maeno, and Y. Liu, Science {\bf 306}, 1151 (2004); T. M. Rice, Science {\bf 306}, 1142 (2004). \newline [2] I. Zutic and I. Mazin, Phys. Rev. Lett. {\bf 95}, 217004 (2005). [Preview Abstract] |
Tuesday, March 14, 2006 11:51AM - 12:27PM |
H39.00004: The Phase-sensitive $c$-Axis Twist Experiments on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ and Their Implications Invited Speaker: There are presently three sets of $c$-axis twist experiments on Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ (Bi2212)\footnote{R. A. Klemm, Phil. Mag. {\bf 85}, 801-853 (2005).}: the bicrystal experiments of Li {\it et al.}\footnote {Q. Li, Y. N. Tsay, M. Suenaga, R. A. Klemm, G. D. Gu, and N. Koshizuka, Phys. Rev. Lett. {\bf 83}, 4160 (1999).}, the artificial cross-whisker experiments of Takano {\it et al.}\footnote{Y. Takano {\it et al.}, Phys. Rev. B {\bf 65}, 140513 (2002); Physica C {\bf 408-410}, 296 (2004), etc.}, and the natural cross-whisker experiments of Latyshev {\it et al.}\footnote{Yu. Latyshev, A. P. Orlov, A. M. Nikitina, P. Monceau, and R. A. Klemm, Phys. Rev. B {\bf 70}, 094517 (2004).} We summarize these experiments and the extensive theoretical analyses of their possible implications, so that reliable conclusions can be inferred. The theoretical discussion includes the allowable order parameter symmetries, the twist theorem for the $c$-axis critical current of $d$-wave superconductors across a 45$^{\circ}$ twist junction, treatments of weak, first-order $c$-axis tunneling with coherent and incoherent components, and effects of the Fermi surface, strong coherent tunneling, orthorhombicity, nanoscale disorder, and OP twisting near the physical twist junction. As a minimum, all three experiments can only be understood in terms of a substantial $s$-wave superconducting order parameter component in Bi2212 for $T\le T_c$. An anisotropic $s$-wave order parameter can fit all three experiments quantitatively. The bicrystal and natural cross-whisker experiments are also consistent with the preponderance of other data that the $c$- axis tunneling in Bi2212 is strongly incoherent, so that all of the $c$-axis critical current arises from the $s$-wave order parameter component. These three sets of experiments appear to rule out a purely repulsive pairing interaction. [Preview Abstract] |
Tuesday, March 14, 2006 12:27PM - 12:39PM |
H39.00005: Josephson effect with d+ip superconductors Brigitte Leridon, Tai-Kai Ng, C. M. Varma Two different experiments, namely ARPES with circularly polarized photons and neutron diffraction have observed a time-reversal and inversion symmetry breaking in the pseudogap state of the cuprates. This phase had actually been predicted in the framework of a general model for the normal and superconducting state of high-Tc superconductors. This symmetry breaking should also affect the superconductive symmetry and lead to the admixture of a p-wave component to the dominant d-wave order parameter. We show here that this allows to make specific predictions for the Josephson effect between a ``d+ip'' superconductor and an ordinary s-wave superconductor, or between two ``d+ip'' superconductors, according to the orientation of the surface. We propose a set of experiments where, for some particular orientations, an anomalous Josephson effect should be observed whenever a pseudogap is present. [Preview Abstract] |
Tuesday, March 14, 2006 12:39PM - 12:51PM |
H39.00006: Direct test of pairing fluctuations in the pseudogap phase of an underdoped cuprate Nicolas Bergeal, Jerome Lesueur, Marco Aprili, Brigitte Leridon, Giancarlo Faini, Jean-Pierre Contour In underdoped cuprates, many experiments have provided evidence for the presence of a gap-like structure in the electronic excitations spectrum, in a region above the critical temperature and below a characteristic temperature T*. The origin of this so-called pseudogap is still hardly debated and the answer to this question turns out to be essential for the understanding of high-T$_{c}$ superconductivity. One doesn't know if the pseudogap is related to superconductivity or to an order in competition. In the former case, it has been suggested that superconducting pairing fluctuations may be responsible for the partial suppression of electronic excitations. This remains to be tested experimentally, but most of the probes used to investigate the pseudogap are not sensitive to pairs and therefore cannot provide such a test. Here, we report for the first time on a direct test of pairing fluctuations in the pseudogap regime using a Josephson-like experiment. Our results shows that fluctuations survive only in a restricted range of temperature close to T$_{c}$ (T-T$_{c}<$15K), well below T*, and therefore cannot be responsible for the opening of the pseudogap at high temperature. [Preview Abstract] |
Tuesday, March 14, 2006 12:51PM - 1:03PM |
H39.00007: Josephson (001) tilt grain boundary junctions of high temperature superconductors Gerald Arnold, Richard Klemm We calculate the Josephson critical current $I_c$ across in- plane (001) tilt grain boundary junctions of high temperature superconductors. We solve for the electronic states corresponding to the electron-doped cuprates, two slightly different hole-doped cuprates, and an extremely underdoped hole- doped cuprate in each half-space, and weakly connect the two half-spaces by either specular or random Josephson tunnelling. We treat symmetric, straight, and fully asymmetric junctions with $s$-, extended-$s$, or $d_{x^2-y^2}$-wave order parameters. For symmetric junctions with random grain boundary tunnelling, our results are generally in agreement with the Sigrist-Rice form for ideal junctions that has been used to interpret ``phase-sensitive'' experiments consisting of such in- plane grain boundary junctions. For specular grain boundary tunnelling across symmetric junctions, our results depend upon the Fermi surface topology, but are usually rather consistent with the random facet model of Tsuei {\it et al.} [Phys. Rev. Lett. {\bf 73} 593(1994)]. Our results for asymmetric junctions of electron-doped cuprates are in agreement with the Sigrist- Rice form. However, our results for asymmetric junctions of hole- doped cuprates show that the details of the Fermi surface topology and of the tunnelling processes are both very important, so that the ``phase-sensitive'' experiments based upon in-plane Josephson junctions are less definitive than has generally been thought. [Preview Abstract] |
Tuesday, March 14, 2006 1:03PM - 1:15PM |
H39.00008: Josephson junctions and arrays fabricated via nanolithography and ion damage Shane Cybart, John Clarke, Robert Dynes, Ke Chen, Yi Cui, Qi Li, Xiaoxing Xi In the years to come, the size and cost of cryo-coolers will get smaller and the demand for a VLSI Josephson junction technology will increase. One possible candidate to fill this need is the ``ion-damage'' Josephson junction. These junctions are fabricated by using ion bombardment to create localized narrow regions of defects in the plane of a thin film of superconductor. These regions have a superconducting transition temperature lower than that of the bulk film and act as hysteretic Josephson junctions. The advantage of these junctions over other technologies is that they have no interfaces between different materials, and can be placed over 10 times closer to each other in comparison to competing techniques. Individual junctions and series arrays were fabricated from YBCO and magnesium diboride. Junction current-voltage characteristics near the critical temperature follow the resistively shunted junction model however at lower temperatures the barrier becomes strongly coupled and flux flow behavior is evident. Series arrays of up to 20 junctions have been fabricated with sufficient parameter uniformity to achieve giant Shapiro steps under microwave radiation. [Preview Abstract] |
Tuesday, March 14, 2006 1:15PM - 1:27PM |
H39.00009: Quantum dynamics of a d-wave YBCO Josephson junction Floriana Lombardi, Thilo Bauch, Tobias Lindstr\"{o}m, Francesco Tafuri, Giacomo Rotoli, Tord Claeson We present direct observation of macroscopic quantum properties in an all high critical temperature superconductor d-wave Josephson junction. Although dissipation caused by low energy excitations is expected to strongly suppress macroscopic quantum effects we demonstrate macroscopic quantum tunneling [1] and energy level quantization [2] in our d-wave Josephson junction. We have investigated specific YBCO grain boundary Josephson junction's geometry, where tunneling in the node of the order parameter sensibly contributes to the transport properties. In such a case the Josephson current-phase relation is significantly modified and we have found that the fundamental state of the junction is doubly degenerate. The results indicate that the role of dissipation mechanisms in high temperature superconductors has to be revised, and may also have consequences for the class of solid state ``quiet'' quantum bit with superior coherence time. [1] T. Bauch \textit{et al}., \textit{Phys. Rev. Lett.} \textbf{94}, 087003 (2005). [2] accepted for publication in Science [Preview Abstract] |
Tuesday, March 14, 2006 1:27PM - 1:39PM |
H39.00010: Biot-Savart correlations in anisotropic superconductors Kumar Raman, Vadim Oganesyan, Shivaji Sondhi We study the normal-superconducting phase transition of layered type II superconductors in the limit of very weak Josephson coupling. By extending previous renormalization group treatments we investigate the importance of interlayer Biot-Savart interactions for three dimensional correlations near the transition and the recent weak-field magnetization experiments in BSSCO. [Preview Abstract] |
Tuesday, March 14, 2006 1:39PM - 1:51PM |
H39.00011: Electromagnetic wave generation by mesoscopic intrinsic Josephson junctions of single crystal $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$ Kazuo Kadowaki, Takuya Yamazaki, Itsuhiro Kakeya, Takashi Yamamoto It is known that the junction resistance $R_c$ of mesoscopic intrinsic Josephson junctions of single crystal $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$ in a sweeping magnetic field parallel to the $ab$-plane exhibits a strong quantum oscillating behavior with periods of a unit of magnetic quantum flux $\phi_0$ or $\phi_0/2$, which penetrate through each insulating layer between superconducting $\mathrm{CuO_2}$ layers of $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$ above or below a certain magnetic field $H^*$, respectively. This happens only at low level of currents, whereas at high currents this oscilating behavior fades away and $R_c$ becomes rather smooth saturation behavior. In such a condition it is expected that the collective motion of Josephson vortices would generate Josephson plasma in a junction, which may continuously emit the coherent THz electromagnetic waves. In reaching a current levels at $\sim$0.3-0.7$J_c$ in rather low fields, we were indeed able to detect electromagnetic radiation emitted from the junctions by a bolometer detecter located near the junction. The power observed is very large, reaching a few 100 W/cm$^2$, and is extremely efficient, showing 3-7\% of the total input current energies. This is compared with the other methds such as cascade lasers using quantum dots and parametric oscillators using laser mixing in a non-linear optical materials. [Preview Abstract] |
Tuesday, March 14, 2006 1:51PM - 2:03PM |
H39.00012: Magnetic oscillations of critical current in Josephson-junction stacks Alexei Koshelev We consider magnetic oscillations of critical current in stacks of Josephson junctions, which are realized in mesas fabricated from layered high-temperature superconductors. Depending on the stack lateral size and magnetic field, oscillations may have either period of half flux quantum per junction (large-size regime) or one flux quantum per junction (small-size regime). We study in detail the crossover between these two regimes. In the small-size regime the lattice structure experiences periodic series of phase transitions between aligned rectangular configuration and triangular configuration. Triangular configurations in this regime realize only in narrow regions near magnetic-field values corresponding to integer number of flux quanta per junction. This work was supported by the U.\ S.\ DOE, Office of Science, under contract \# W-31-109-ENG-38. [Preview Abstract] |
Tuesday, March 14, 2006 2:03PM - 2:15PM |
H39.00013: Effects of topological excitations in Josephson junction arrays. Said Sakhi We study the zero-temperature physics of planar Josephson junction arrays in the self-dual approximation in the presence of external offset charges and magnetic fluxes. We introduce a new Landau-Ginzburg formulation to describe both types of topological excitations (electric and magnetic) that determine the quantum phase structure of the model. Through the condensation of the boson fields, this approach captures with ease various phases of Josephson junction arrays including the superconducting phase, the insulating phase, in addition to a novel quantum Hall phase that results from the condensation of composites formed by electric and magnetic topological excitations. [Preview Abstract] |
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