Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session W34: Superconducting Nanowires |
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Sponsoring Units: DMP Chair: Zhili Xiao, Argonne National Laboratory Room: 404 |
Thursday, March 19, 2009 11:15AM - 11:27AM |
W34.00001: Current-induced anomalous negative magnetoresistance in Zn nanowires. Yu Chen, Stephen Snyder, Allen Goldman Quasi-one dimensional superconducting Zn nanowires, connected with wide Zn electrodes, were fabricated using electron-beam lithography. The Zn was deposited with the substrates held at liquid nitrogen temperature. At temperatures well below the nanowires' transition temperature, four-terminal measurements of resistance showed an anomalous negative magnetoresistance when applying a current slightly higher than its critical current in zero magnetic field. The magnitude of this negative magnetoresistance can be as large as 50 percent even with applied field as low as few Oersted. This effect was found over a narrow range of temperatures, which depended upon the applied current. At this writing, the origin of the effect is unclear. [Preview Abstract] |
Thursday, March 19, 2009 11:27AM - 11:39AM |
W34.00002: ABSTRACT WITHDRAWN |
Thursday, March 19, 2009 11:39AM - 11:51AM |
W34.00003: Electronic structure of quasi-one-dimensional edge-sharing cuprate LiCu$_{2}$O$_{2}$ single crystals measured by angle-resolved photoemission spectroscopy K.-D. Tsuei, C.-M. Cheng, J.-Y. Yuh, K.W. Yeh, M.K. Wu We have carried out a high resolution angle-resolved photoemission study on edge-sharing quasi-one-dimensional (1D) chain cuprate LiCu2O2 single crystals at room temperature. The low energy electron diffraction of cleaved (001) surfaces show a well ordered (2x1) pattern with single domain. Absence of photon energy dependence of high lying peaks just below the Fermi energy in the normal emission spectra suggests localization within the ab-pannar layers. One can identify three dispersive bands between 0.5 eV and 2 eV binding energies along the high symmetry directions along with the off-normal spectra. The highest energy peak is observed at the Y-point with a binding energy 0.55 eV bearing a $d_{xy}$ symmetry based on a polarization dependent selection rule, and can be associated with a hybridized state of primarily Cu 3$d_{xy}$ and O 2$p $orbitals, in agreement with a LDA band calculation. We observed no indication of a band maximum at half integral position along GY, predicted by a 1D $t-J$ model. Another peak at 1.3 eV shows a strong dispersion along GX, normal to the chain direction. Its identity will also be discussed. [Preview Abstract] |
Thursday, March 19, 2009 11:51AM - 12:03PM |
W34.00004: Synthesis and characterization of superconducting, single-crystal Al nanowires using template based electrodeposition Meenakshi Singh, Jian Wang, Mingliang Tian, Alexis Pereira, Nitesh Kumar, Thomas Mallouk, Moses Chan Al nanowires (ANW) have been fabricated using template based electrodeposition at room temperature for the first time. An anhydrous electrolyte comprised of AlCl$_{3}$ and LiAlH$_{4}$ in tetrahydrofuran with a Pt anode and Ag cathode was used to electrodeposit Al in an anodic aluminum oxide template. X-ray diffraction and electron diffraction show that the ANW are single crystal with (110) as the growth direction. Transmission electron microscopy shows that the wires have uniform diameters with an oxidation layer a few nanometers thick around them. Four electrode transport measurements on a single $70$ nm thick ANW have shown significant enhancement in the critical temperature and the critical field and decrease in the critical current density from the bulk value. [Preview Abstract] |
Thursday, March 19, 2009 12:03PM - 12:15PM |
W34.00005: Resistance in Superconducting Epitaxial Niobium Nanowires and Films Timothy McArdle, Allison Dove, Kevin Inderhees, Mitrabhanu Sahu, Alexey Bezryadin, Paul Goldbart, James Eckstein The thermally activated phase slip (TAPS) description of resistance in one-dimensional superconducting wires is unable to explain additional resistance observed in extremely narrow nanowires well below the critical temperature. We fabricate nanowires using electron beam lithography from single-crystal niobium films grown by ultra-high vacuum molecular beam epitaxy. Since the resulting wires are single crystal and homogenous, the role of disorder is reduced and neither weak links nor grains are present. The epitaxial films are 10 to 30 nm thick, while the finished wires range in length from 1 to 10 $\mu $m, and in width from 35 to 200 nm. Transport measurements on the nanowires of varying widths show a range of distinct temperature dependencies below the critical temperature that cannot be accounted for by the single exponential form of the TAPS model. [Preview Abstract] |
Thursday, March 19, 2009 12:15PM - 12:27PM |
W34.00006: Two superconducting transitions and periodic magnetoresistance oscillations in the crystalline Au nanowire with superconducting electrodes Jian Wang, Chuntai Shi, Mingliang Tian, Jainendra Jain, Qi Zhang, Nitesh Kumar, Meenakshi Singh, Thomas Mallouk, Moses Chan Transport measurements were made on individual crystalline Au nanowire with four focused ion beam (FIB) deposited tungsten (W) electrodes, which are superconducting below 5 K. It was found that the 1.2 microns long (between the inner edges of the two voltage electrodes) Au nanowire is superconducting. Instead of a single sharp drop to zero resistance as seen in usual superconductors, here the resistance drops in two steps. Below TC, with a magnetic field applied perpendicular to the axis of the nanowire, we found ``magnetoresistance mini-gaps'' in low field regime. In addition, clear periodic magnetoresistance oscillations in the superconducting to normal transition region were observed. The 1 micron and 1.9 microns Au nanowires were also investigated to further reveal the anomalous superconductivity we found. [Preview Abstract] |
Thursday, March 19, 2009 12:27PM - 12:39PM |
W34.00007: Vortex blockade and conductance fluctuations of superconducting strips in magnetic fields Paul Goldbart, Gil Refael, David Pekker Recent experiments on the conductance of a thin, narrow superconducting strip found periodic fluctuations as a function of the perpendicular magnetic field, with the period corresponding to approximately two flux quanta per strip area [1]. Using vortex-charge duality, we explore the possibility that the superconducting strip is the dual of a quantum dot, with vortices playing the role of the electrons, the magnetic field appearing as the gate voltage, and the applied current replacing the source-drain voltage. As with a quantum dot, extrema of the conductance are obtained when configurations with $n$ and $n+1$ vortices have equal energy; in the bias-current versus magnetic-field plane, the conductance displays blockade diamonds. Furthermore, we find that there is a simple relation between the linear-response conductance and the critical current, as they are both set by the barrier to vortex tunneling on to and off of the strip. [1] A. Johansson et al. Phys. Rev. Lett. 95, 116805 (2005). [Preview Abstract] |
Thursday, March 19, 2009 12:39PM - 12:51PM |
W34.00008: Tuning of the critical current of superconducting nanowires by application of voltage pulses Thomas Aref, Alexey Bezryadin The critical current of superconducting nanowires may be dependent on a number of factors such as dimensions of the nanowire, the wire's normal resistance or the presence of magnetic impurities. Determining which factors are most important is key to developing a detailed understanding of the underlying physics of 1D superconductivity. It is experimentally difficult to alter and probe such properties in situ at cryogenic temperatures. We have developed a method for tuning the critical current of a nanowire in situ inside a helium cryostat by the application of short, high bias voltage pulses. These pulses alter the critical current of the nanowire in a controlled manner by annealing or electromigration. Thus, for a single nanowire, we can vary critical current and normal resistance in situ. This process may have applications in developing future superconducting nanowire circuitry such as qubits where precise control of the nanowire's critical current is required. We also investigate the dependence of the critical current on the normal resistance of the wire and compare to existing theories. [Preview Abstract] |
Thursday, March 19, 2009 12:51PM - 1:03PM |
W34.00009: Flux-quantization effect in superconducting niobium loops Suhong Yu*, Zhili Xiao*, Alexandra Imre, Jiong Hua*, Ulrich Welp, Wai-Kwong Kwok Superconducting loops have periodical oscillation of critical temperature $T_{c}$ as a function of applied perpendicular magnetic field $H$ The corresponding periodicity is related to superconducting flux quantization, $h/2e$, due to size constraint. When the loop size shrinks, however, new phenomena can appear. For example, the oscillation can show a $h$/e rather than $h/2e$ periodicity if the hole diameter is comparable to the superconducting coherence length. We present experimental investigation of flux-quantization effect in mesoscopic superconducting niobium loops. We developed a new approach to fabricate high quality loops by combining electron-beam lithography with focused-ion-beam (FIB) milling techniques. Periodic oscillations were observed in both the $H-T$ phase diagram and the magnetoresistance. Analysis of the data with various theories will be presented [Preview Abstract] |
Thursday, March 19, 2009 1:03PM - 1:15PM |
W34.00010: Anisotropic magnetoresistance of a one-dimensional superconducting niobium strip Jiong Hua*, Zhili Xiao*, Alexandra Imre, Suhong Yu*, Umesh Patel*, Leo Ocola, Ralu Divan, Alexei Koshelev, John Pearson, Ulrich Welp, Wai-Kwong Kwok We investigated confinement effects on the resistive anisotropy of a superconducting niobium strip with a rectangular cross-section. When the strip's transverse dimensions are comparable to the superconducting coherence length, we find the angle dependent magentoresistances at a fixed temperature can be scaled as R($\theta $, H) = R(H /H$_{c\theta })$ where H$_{c\theta }$ = H$_{c0}$ (cos$^{2}\theta +\gamma ^{-2}$sin$^{2}\theta )^{-1/2}$ is the angular dependent critical field, $\gamma $ = w/d is the width to thickness ratio of the strip, and H$_{c0}$ is the out-plane critical field at $\theta $ = 0\r{ }. Our results can be understood in terms of the anisotropic diamagnetic energy of a one-dimensional superconductor in a magnetic field. [Preview Abstract] |
Thursday, March 19, 2009 1:15PM - 1:27PM |
W34.00011: Quasi-reentrant resistive behavior in Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{x}$ whiskers Sevda Avci, Umesh Patel, Suhong Yu, Zhili Xiao, Ralu Divan, Ulrich Welp, Wai-Kwong Kwok, Milind Kunchur BSCCO (2212) whiskers were fabricated via a melt-quench-growth method and their morphology was characterized with scanning/transmission electron microscopy and atomic force microscopy. Four-probe magneto-transport measurements were conducted as a function of temperature and current. In low magnetic fields and currents, the resistance decreases monotonically and vanishes at a temperature of $\sim $ 80 K. However, at large currents and magnetic fields the resistance shows a non-monotonic dependence on temperature, even showing values that are higher than the normal state resistance for certain ranges of the parameters We attribute the observed behavior to the brick-wall morphology of the whiskers leading to a competition between normal and superconductive tunnelings that is known to take place in granular superconductive systems. [Preview Abstract] |
Thursday, March 19, 2009 1:27PM - 1:39PM |
W34.00012: Quenching of Meissner Diamagnetism in Superconducting Nanocrystals Helena Moreira, Irene Resa, Benoit Mahler, Benoit Dubertret, Herve Aubin We developed a new chemical synthesis for the preparation of high quality monodisperse superconducting Lead (Pb) nanocrystals. They are obtained from the alcohol reduction of Lead carboxylates in a hot organic solution and lead to colloids stabilized and protected from oxidation by organic ligands. Large quantities of nanocrystals with tunable diameter (8 to 30 nm) can be obtained. This new material allows the study of the effects of quantum confinement on superfluid response with unprecedented size resolution. Magnetic susceptibility measurements show that the large critical field of the particles increases from 2 to 5 T as the diameter is reduced down to 16 nm. This critical field results from the competition between the kinetic energy for Cooper pairs and superfluid condensation energy. Below the diameter of 16 nm, no Meissner effect remains in the particles, but only the signature of residual superconducting fluctuations. Remarkably the size scale below which the superfluid response disappears (16 nm) is significantly larger than the value expected from Anderson criterion. This implies that, in the regime of quantum confinement, there are distinct size-scales for the formation of Cooper pairs and the establishment of the superfluid response. [Preview Abstract] |
Thursday, March 19, 2009 1:39PM - 1:51PM |
W34.00013: Thin Superconducting Rings and Cylinders in a Magnetic Field Robert Beaird, Daniel E. Sheehy, Ilya Vekhter We examine the magnetic field dependence of the critical temperature ($T_c$) for a thin superconducting ring and thin- walled superconducting cylinder (of radius $R$), in the presence of a magnetic field ($B$). We include both the orbital effect and the Zeeman splitting of the quasiparticle bands. We derive a Ginzburg-Landau free energy functional and allow for the appearance of the spatially-modulated (Fulde-Ferrell-Larkin- Ovchinnikov) state. We explore the competition between the orbital effect and Zeeman splitting as a function of the ratio of $R$ to the superconducting coherence length, the orientation of $B$ with respect to the plane of the ring, and the Maki parameter (the ratio of the orbital and paramagnetic critical fields). We focus on the interplay of the periodicity and the overall suppression of $T_c$ with applied $B$. [Preview Abstract] |
Thursday, March 19, 2009 1:51PM - 2:03PM |
W34.00014: Order and Creep in Flux Lattices and CDWs Pinned by Planar Defects Aleksandra Petkovic, Thomas Nattermann The influence of randomly distributed point impurities \emph{and} planar defects on the order and transport in type-II superconductors and related systems is considered theoretically. For random planar defects of identical orientation the flux line lattice exhibits a new glassy phase with diverging shear and tilt modulus, a transverse Meissner effect, large sample to sample fluctuations of longitudinal magnetic susceptibility and an exponential decay of translational long range order. The flux creep resistivity for currents $J$ parallel to the defects is $\rho(J)\sim \exp-(J_0/J)^{\mu}$ with $\mu=3/2$. Strong disorder enforces an array of dislocations to relax shear strain. [Preview Abstract] |
Thursday, March 19, 2009 2:03PM - 2:15PM |
W34.00015: Crossed Andreev reflection dominated subgap transport in normal metal/superconducting hybrid structures Andreas Kleine, Andreas Baumgartner, Jelena Trbovic, Christian Schonenberger We report on a systematic study of the non-local Andreev process (also called cross Andreev reflection = CAR) in planar mesoscopic N-S devices that consist of a superconducting (S) Al wire with several normal metal (N) fingers contacting the superconductor via tunneling barriers. We measure the non-local voltage appearing at a N (detector) contact located outside the current path, while a bias current is driven from another N (injector) contact to the S wire. This non-local differential signal has been studied as a function of bias and temperature for several samples with different N-S contact transparencies. In addition to CAR, elastic co-tunneling (EC) and charge imbalance (CI) appears in the measurements. We ob-serve a systematic dependence of the relative magnitude of CAR, EC and CI. Most strikingly, CAR can dominate the subgap transport for all energies below the superconducting gap for a certain kind of sam-ple. If the tunneling resistance R$_t$ is increased, EC starts to dominate over CAR. This contribution is limited to small subgap biases, whereas CAR remains dominating at higher subgap biases. This de-pendence is explained by Coulomb blockade that becomes more prominent for increasing R$_t$. [Preview Abstract] |
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