Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session U38: 1-D Superconductors and Organics |
Hide Abstracts |
Sponsoring Units: DCMP Chair: Andrei Lebed, University of Arizona Room: Baltimore Convention Center 341 |
Thursday, March 16, 2006 8:00AM - 8:12AM |
U38.00001: High-Tc superconductivity in entirely end-bonded carbon nanotubes Junji Haruyama, Izumi Takesue, Naoki Kobayashi, Shohei Chiashi, Shigeo Maruyama, Toshiki Sugai, Hisanori Shinohara One-dimensional (1D) systems face some obstructions that may prevent the emergence of superconductivity(SC), e.g., a Tomonaga-Luttinger liquid (TLL) and Peierls transition. A carbon nanotube (CN) is one of the best candidates for investigating a possibility of 1D SC and its interplay with such obstructions. Only two groups have experimentally reported SC in ropes of single-walled CNs (SWNTs) and very thin SWNTs [1] to date. In addition, those interplay with 1D phenomena have never been clarified. Some theoretical papers also predicted strong correlation between TLL states and SC for SWNT ropes and importance of electron-phonon interaction for thin SWNTs [2]. Here, we report that entirely end-bonded multi-walled CNs (MWNTs) can show SC with the T$_{c}$ as high as 12K [3] (about 50-times larger than T$_{c}$ in former of [1]). We find that emergence of this SC and its interplay with TLL states are highly sensitive to junction structures of Au electrode/MWNTs. Only MWNTs with optimal numbers of electrically activated shells realized by the entire end-bonding can allow the SC due to intershell effects. \textbf{Refs.} \textbf{1.}M. Kociak, et al., PRL 86, 2416 (2001); Z. K. Tang, et al., Science 292, 2462 (2001), \textbf{2}.J.Gonzalez, PRL 88, 076403 (2002); R.Barnett, et al., PRB 71, 035429 (2005), \textbf{3}.J.Haruyama et al., PRL Accepted [Preview Abstract] |
Thursday, March 16, 2006 8:12AM - 8:24AM |
U38.00002: Superconductivity of granular Bi nanowires fabricated by electrochemical deposition at ambient condition Mingliang Tian, Jinguo Wang, Tianheng Han, Yoji Kobayashi, Nitesh Kumar, Shengyong Xu, Ying Liu, Thomas Mallouk, Moses Chan Rhombohedral bulk Bi is a semimetal which is not superconducting down to low temperatures under ambient pressure. Amorphous Bi films and bulk Bi subjected to high pressure can be superconducting. We report here the observation of superconductivity of Bi nanowires (the diameter ranges from 40 to 100 nm) fabricated by electrochemical deposition at room temperature under atmospheric pressure. The superconducting transition temperature Tc, depending on the sample morphology, can be either of 3.7 K, 7.2 K or 8.3 K, which correspond exactly to the Tc's reported for the three high pressure Bi phases (II, III and V). However, structural studies showed that these superconducting Bi nanowires showed granular morphology consisting of rhombohedral Bi particles oriented along the [001] direction. Because the superconducting Bi wires did not show any detectable diamagnetic signature, the observed superconductivity might be related to the interfacial structures of the granular wires. Further studies are in progress. \textit{This work is supported by }\textit{ the Center for Nanoscale Science (Penn State MRSEC) funded by NSF under grant DMR-0213623.} [Preview Abstract] |
Thursday, March 16, 2006 8:24AM - 8:36AM |
U38.00003: Enhancing superconductivity: Magnetic impurities and their quenching by magnetic fields Tzu-Chieh Wei, David Pekker, Andrey Rogachev, Alexey Bezryadin, Paul M. Goldbart Magnetic fields and magnetic impurities are each known to suppress superconductivity. However, it has recently been found theoretically that in superconducting films with magnetic impurities the critical temperature can be raised by applying a magnetic field ($H$) [1]. Here, we extend the Eilenberger-Usadel formalism and use it to investigate this interplay of magnetic fields and magnetic impurities. Hence, we are able to compute the critical current ($J_c$) of a thin superconducting wire, in addition to its critical temperature ($T_c$). We find three regimes of wire parameters. In one, both $T_c$ and $J_c$ simply decrease with $H$; in a second, both $T_c$ and $J_c$ first rise and then fall with $H$; and in a third, $T_c$ simply decreases with $H$ but, at sufficiently low temperatures, $J_c$ first rises and then falls [2]. Our results are consistent with recent experiments on thin superconducting wires [3]. \newline [1] M.\ Kharitonov and M.\ Feigel'man JETP Lett. {\bf 82}, 473 (2005). \newline [2] T.-C.\ Wei et al.\ cond-mat/0510476. \newline [3] A.\ Rogachev et al.\ (manuscript in preparation). [Preview Abstract] |
Thursday, March 16, 2006 8:36AM - 8:48AM |
U38.00004: Anomalous behavior of the critical current in superconducting MoGe nanowires exposed to high magnetic fields. A. Rogachev, T.-C. Wei, D. Pekker, A.T. Bollinger, P.M. Goldbart, A. Bezryadin At low temperatures the critical current of superconducting MoGe nanowires with diameters 6-10 nm shows an unusual initial growth with increasing magnetic field, and reaches a maximum at the field 3-5 T. The non-monotonic behavior is present both in parallel and perpendicular field orientations and disappears at high temperatures. We suggest that the effect is caused by magnetic impurities, which suppress superfluid density in the nanowire at low fields but, due to partial polarization in the applied magnetic field, become less efficient pair-breakers in high fields. We compare our data with the microscopic theory that considers this competition of the reduced depairing by localized spins and the increasing depairing by the orbital effects [1]. The theory reproduces all experiential observations and suggests that magnetic impurities reside on a surface of a wire. [1] T.-C. Wei, D. Pekker, A. Rogachev, A. Bezryadin, and P.M. Goldbart, cond-mat/0510476. [Preview Abstract] |
Thursday, March 16, 2006 8:48AM - 9:00AM |
U38.00005: Confined Vortices in NbSe$_2$ Nanowires Abram Falk, Mandar Deshmukh, Amy Prieto, Andrea Jones, Hongkun Park Superconducting NbSe$_{2}$ nanowires have been studied with electrical transport. The cross-sectional dimensions are smaller than the London penetration depth, and signatures of confined magnetic vortices have been observed. The critical current shows non-monotonic behavior as the external magnetic field is increased, including periodic features corresponding to matching fields. In the vicinity of the critical current, we observe several peaks in the differential resistance as a function of bias current, consistent with the plastic flow of vortices. These observations are discussed in the context of theoretical London model studies and experiments in thin-film superconductors and bulk NbSe$_{2}$. [Preview Abstract] |
Thursday, March 16, 2006 9:00AM - 9:12AM |
U38.00006: Growth Mechanism of EuBa$_{2}$Cu$_{3}$O$_{7-\delta }$ Whiskers and Their superconducting properties for Intrinsic Josephson Junction Applications A.T.M. Nazmul Islam, T. Kawae, Y. Tachiki, S. Watauchi, Y. Takano, T. Hatano, T. Yamashita, I. Tanaka We have grown Eu-123 single-crystal whiskers by annealing of precursor pellets containing Ca and Te. Microstructural and compositional analysis was performed on the longitudinal cross-section and the area of origin of a whisker to elucidated some aspects of the growth mechanism from bulk precursor. Sub-micron sized junctions fabricated by focus ion-beam etching on Eu-123 whiskers showed clear multi-branch with hysteresis structure in the I-V curve, which suggest excellent crystalline quality both of as-grown and high pressure annealed whiskers. We have also doped Er and Tm having a smaller ionic radius in single crystalline whiskers of (Eu,R)-123 (R= Er, Tm) and observed that Eu-rich whiskers, which require higher temperature to be grown, are more susceptible to oxygen deficiencies and structural instabilities. Our results shows that the carrier doping can be systematically controlled from highly underdoped to slightly overdoped range by suitable choice of average ionic radius of rare-earth elements in as-grown whiskers. The critical current density J$_{c}$ of a Eu-123 whisker (T$_{c}$=45K) was estimated to be 1.43 $\times$ 10$^{5}$ A/cm$^{2}$ at 4.2K , twice as much as observed for Y-123 having a similar T$_{c}$. [Preview Abstract] |
Thursday, March 16, 2006 9:12AM - 9:24AM |
U38.00007: Evidence for Current-Driven Phase Slip Lines in Submicron High-$T_c$ Superconducting Wires P. Morales, J.Y.T. Wei We present superconducting current-voltage characteristics of submicron YBa$_2$Cu$_3$O$_{7-\delta}$ wires. The submicron-wide wires were fabricated using a chemical-free technique based on selective epitaxial growth. Pulsed current-biased and voltage-biased measurements were made between 4.2 K and $T_c$ and as a function of an applied magnetic field. The current-voltage characteristics exhibit distinctive behaviour suggesting that the current-driven or voltage-driven transition of our submicron high-$T_c$ wires into the resistive state is through the formation of phase slip lines. [Preview Abstract] |
Thursday, March 16, 2006 9:24AM - 9:36AM |
U38.00008: Quantum phase slips in the presence of finite-range disorder Leonid P. Pryadko, Sergei Khlebnikov To study the effect of disorder on quantum phase slips (QPS) in superconducting nanowires, we consider the plasmon-only model where disorder can be incorporated into a first-principles instanton calculation. We consider weak but general finite-range disorder and compute the formfactor in the QPS rate associated with momentum transfer. We find that the system maps onto dissipative quantum mechanics, with the dissipative coefficient controlled by the wave (plasmon) impedance $Z$ of the wire and with a superconductor-insulator transition at $Z_{\rm c}=6.5$ kOhm. The usual Ohmic resistivity of the wire at the transition point is non-universal. Its value depends on both the strength and the correlation length of disorder, and in the considered regime is much smaller than the normal-state resistivity. We argue that the system will remain in the same universality class after resistive effects at the QPS core are taken into account. [Preview Abstract] |
Thursday, March 16, 2006 9:36AM - 9:48AM |
U38.00009: Magnetization controlled superconductivity in a Pb film on a perpendicular array of ferromagnetic Co nanowires Zuxin Ye, Daya Rathnayaka, Wenhao Wu, Haidong Liu, Hong Zhang, Donald Naugle, Igor Lyuksyutov, Joseph Ross Jr. We report the studies of superconductivity in a Pb film on a perpendicular array of ferromagnetic Co nanowires. We first evaporate a Pb film of 300nm in thickness on a 60$\mu $m-thick porous Al$_{2}$O$_{3}$ membrane as the cathode for electroplating. Cobalt nanowires 100nm in diameter were electrochemically deposited in the pores starting from the Pb film. Scanning electron microscopy images showed uniform distribution of cobalt nanowires. The magnetization of the individual Co nanowires should be oriented perpendicular to the Pb film due to the high aspect ratio of the Co nanowires. We have observed significant difference in the superconducting behavior of the Pb film between zero-field cooled experiments and field-cooled experiments. In field-cooled experiments, the samples are cooled from room temperature to 20 K in fields of 1-5 T applied along the direction of the Co nanowires. This field aligns the magnetization of the Co nanowires, and as a result, enhances the superconducting transition temperature by 1.5-2.0 K in comparison to zero-field cooled experiments in which case the magnetization of the nanowires is not aligned. These experimental data support recent theory by I. F. Lyuksyutov et al. [PRL \textbf{81}, 2344(1998)]. [Preview Abstract] |
Thursday, March 16, 2006 9:48AM - 10:00AM |
U38.00010: Current carrying edges in unconventional superconductors Rahul Roy While the bulk of a p or d wave superconductor does not carry any current, a current can run along the edges of a sample even in the absence of a magnetic field, unlike the case of a s wave superconductor. Such a current is often quantized and is independent of the magnitude of the gap. However, the existence of such a current violates Bloch's theorem. Here, we examine, by computation and analytic calculation, the question of the edge current in p and d wave superconductors in various geometries and the connection with the Bloch argument. The computation of the edge current also allows us to shed some light on the angular momentum paradox in the A phase of Helium 3. [Preview Abstract] |
Thursday, March 16, 2006 10:00AM - 10:12AM |
U38.00011: The coherence conundrum in BEDT-TTF superconductors; how does interlayer transport die as temperature rises? John Singleton, Paul Goddard, Arzhang Ardavan, Stan Tozer, Ross McDonald, John Schlueter Recent attention has focused on ``bad metals'', systems which appear to be Fermi liquids at low temperatures ($T)$, but whose conductivity falls below the minimum metallic limit as $T$ rises. A key question concerns the coherence of the electron orbitals, and whether, as suggested by Anderson and others, it is destroyed by thermal fluctuations as $T$ rises. To address this, we have studied magnetic-field-orientation-dependent transport in the organic superconductor (BEDT-TTF)$_{2}$Cu(NCS)$_{2}$ at temperatures of up to 45 K in magnetic fields of up to 45 T. This material was chosen because its Fermi surface (FS) is well characterized by experiment. We find that the angle-dependent magnetoresistance oscillations (AMROs) due to orbits on the quasi-one-dimensional (Q1D) and Q2D FS sections are suppressed by rising $T$, with a $T$ dependence suggesting phonon scattering. The coherence peak in the resistivity seen in exactly in-plane fields, and other signatures of a 3D FS, remain to values of $T$ that exceed the proposed Anderson criterion for incoherent transport by a factor of order 80! The implications of these data for currently-held ideas about bandstructure will be discussed. [Preview Abstract] |
Thursday, March 16, 2006 10:12AM - 10:24AM |
U38.00012: Interplane penetration depth in $\kappa $-(ET)$_{2}$Cu[N(CN)$_{2}$]Br Russell Giannetta, Z. Shi, T.A. Olheiser, A. McCormick, D.D. Lawrie, R. Prozorov, J.A. Schlueter, A.M. Kini, U. Geiser We report measurements of the interplane penetration depth $\lambda _{\bot }$(T)$_{ }$ in the organic superconductor $\kappa $- (ET)$_{2}$Cu[N(CN)$_{2}$]Br\textbf{ (}T$_{C}$ = 11.9 K). At low temperatures, the superfluid density $\rho _{\bot }$= [$\lambda _{\bot }$(0)/ $\lambda _{\bot }$(T)]$^{2} \quad \propto $ 1-AT$^{N}$ with N = 1.3 -- 1.5, close to the exponent measured for the in-plane superfluid density. This result adds support to a d-wave picture, but with transport between planes more coherent than is observed in similarly anisotropic copper oxide superconductors. [Preview Abstract] |
Thursday, March 16, 2006 10:24AM - 10:36AM |
U38.00013: London penetration depth in fully deuterated $\kappa $-(ET)$_{2}$Cu[N(CN)$_{2}$]Br T.A. Olheiser, R.W. Giannetta, D.D. Lawrie, R. Prozorov, J.A. Schlueter, A.M. Kini, U. Geiser We report measurements of the London penetration depth, $\lambda $, for different magnetic field and crystal orientations in fully deuterated $\kappa $ (ET)$_{2}$Cu[N(CN)$_{2}$]Br\textbf{, }an organic superconductor with T$_{C}$ = 11.9 K. $\lambda $ increases dramatically with deuteration and develops a strong magnetic field dependence. The superfluid density exhibits a power law temperature dependence indicative of a nodal order parameter. We discuss possible connections to nanoscale antiferromagnetic domains. [Preview Abstract] |
Thursday, March 16, 2006 10:36AM - 10:48AM |
U38.00014: Pauli limiting in the superconductor $\kappa$-(ET)$_2$Cu(NCS)$_2$ under pressure Kyuil Cho, Braunen Smith, Chris Rea, Mike Viotti, Charles Agosta, John Schlueter We have strong evidence that the organic superconductor $\kappa$-(ET)$_2$Cu(NCS) $_2$ is Pauli limited when it is compressed with a small ($< 2$~ kbar) amount of pressure. A superconductor is considered Pauli limited when the magnetic energy, $ \mu_bH$, overcomes the binding energy of the Cooper pairs to destroy superconductivity. In most situations superconductivity is destroyed by the formation of vortices. At ambient pressure, $\kappa$-(ET)$_2$Cu(NCS)$_2$ shows some behavior that is reminiscent of a Fulde Ferrell Larkin Ovchinnikov state, although no direct evidence of a transition into this state has been measured. Through a series of penetration depth measurements using a tunnel diode oscillator under pressure, we can show the evolution of the ambient pressure state to the clearly Pauli limited state at 1.75 kbar. We will also discuss the design of our new plastic, gas charged pressure cell that has allowed us to make these measurements in dc and pulsed magnetic fields. We acknowledge support from the DOE \#ER46214 and the NSF \#DMR- SGER-0331272. [Preview Abstract] |
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