Symposium Organizers
Claudia Cantoni Oak Ridge National Laboratory
Amalia Ballarino European Organization for Nuclear Research
Kaname Matsumoto Kyushu Institute of Technology
Vyacheslav Solovyov Brookhaven National Laboratory
Haiyan Wang Texas A&M University
VV3: Poster Session: New Superconductors -- Properties and Synthesis
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
VV1: Role of High-Tc Superconductors in the Future Society
Session Chairs
Tuesday PM, April 26, 2011
Room 2020 (Moscone West)
9:30 AM - **VV1.1
SuperCities, SuperSuburbs and SuperGrids: Superconducting Materials Challenges Confronting the Energy Society of the Future.
Paul Grant 1
1 , W2AGZ Technologies, San Jose, California, United States
Show AbstractThis year, 2011, celebrates the 100th anniversary of the discovery of superconductivity, as well as the quarter century since the emergence of "high temperature" materials in 1986. Post-discovery hopes in the decades following each forecast significant applications of superconductivity to electric power would ensue, and, indeed, dozens of successful prototype demonstrations of rotating machinery, cables and conditioning equipment have taken place from the 1960s to the present. Yet, massive application to the power industry has yet to take place or even be inserted into utility long-range planning cycles. Thus, this talk will address the role of superconductivity in a revolutionary future energy society based on its symbiosis with nuclear, hydrogen and non-eco-invasive renewable, especially the impact new superconducting materials, more robust and with higher transition temperatures, might have to realize this vision.
10:00 AM - **VV1.2
Superconductors for Superconducting Magnets – the ``New" Old Driver for HTS Conductors.
David Larbalestier 1
1 National High Magnetic Field Laboratory, Florida State University, Tallahassee , Florida, United States
Show AbstractDevelopment of conductors of High Temperature Superconductors (HTS) has been largely driven by the prospect of new applications impossible for low temperature superconductors. HTS materials, especially YBCO can offer magnetic field capability well above any Nb conductor and temperature capabilities well above the liquid helium range. But they still have to face the cruel test of any new technology: that it compete effectively with the older and the known, or offer something quite new so that there is no competition. I will describe applications for HTS conductors – principally YBCO coated conductors and round wire, multifilament Bi-2212, that serve the traditional major market for superconductors -the magnet market. If electric utility applications of HTS are, only temporarily we hope, stepping back, magnet applications of HTS conductors can indeed offer some real prospects as I will try to review in my talk.
10:30 AM - **VV1.3
Superconducting Magnetic Energy Storage (SMES) System for GRIDS.
Qiang Li 1
1 , Brookhaven National Lab, Upton, New York, United States
Show AbstractDeveloping affordable, large-scale energy storage systems would be a game-changing advance for the U.S. electrical grid. In particular, energy storage will be crucial in enabling the widespread use of two key renewable energy sources: wind and solar power. Superconducting Magnet Energy Storage (SMES) systems use magnetic fields in superconducting coils to store energy with near-zero energy loss, and have instantaneous dynamic response and nearly infinite cycle life. SMES systems have come a long way since their inception in the 1970s. Previous SMES’s were usually used as short-term power devices designed to compensate for fluctuations in electrical power system. Making them into a grid-scale energy storage solution is a completely new ballgame. To achieve our goals, the performance of each of the individual subsystems that make up the GRIDS-SMES system will have to be propelled far beyond the present state-of-the-art. In this presentation, I will discuss the effort on the grid-scale SMES research currently carried out at Brookhaven National Laboratory and some critical issues involved, particularly, the required performance of superconducting wires. The need for accelerated research in superconducting materials will be highlighted.
11:30 AM - **VV1.4
High Current AC Cables from Coated Conductors.
Wilfried Goldacker 1 , Sonja Schlachter 1
1 Institute for Technical Physics, Karlsruhe Institute of Technology, Eggenstein-Leopoldahafen Germany
Show AbstractThe success of Coated Conductors in applications will crucially depend on the availability of high current low AC loss cables as Roebel bars or Rutherford cable. Roebel bars are shown to be the most promising solution for the transport current class up to 5 kA (DC, 77 K, self field). We report on the achieved progress in development of Roebel cables, as current carrying behaviour, AC losses, current transfer and current redistribution properties. The progress applying striations by means of laser grooving to the CC strands for further reduced AC losses and advanced methods for low resistive current transfer to the cables will be presented. For specific future applications in very large devices as fusion reactors like the future DEMO facility, or large power generators and accelarator magnets, operation currents of a few tens kA are requested. Rutherford cables with Roebel strands are a possible design of such conductors. A subsize Rutherford cable is under development in our laboratory with a systematic approach to solve all technical hints for the successful realisation. The status of the strand preparation and the cable assembling challenge will be reviewed. An outlook in competition to possibly alternative concepts will be discussed, the possible roadmap and required boundary conditions producing and applying high current carrying AC cables from coated conductors will be outlined.
12:00 PM - **VV1.5
From HTS Material Optimization to System Manufacturing - First Commercial FCLs from Nexans SuperConductors.
Joachim Bock 1 , Achim Hobl 1 , Mark Rikel 1
1 , Nexans SuperConductors GmbH, Huerth Germany
Show AbstractNexans SuperConductors GmbH (NSC) has successfully designed, built and tested the first three HTS Fault Current Limiter (FCL) systems that were sold on a commercial basis. The systems are dedicated to different application cases in Europe and two of these are live in the customer grids since last quarter of 2009. One of the FCLs is protecting the house load of a brown coal power station - the first HTS device operating in a power station worldwide.These events sum up a long development period that started in early nineties with establishing technologies for producing the melt-cast processed (MCP) BSCCO-2212 bulk material; tuning its electrical and mechanical properties to a level suitable for FCL applications; designing and testing FCL elements and stabilizing their high-yield production; assembling these elements in modular FCL systems that meet the customer requirements. NSC is now able to cover the whole production chain from raw materials to the final system also integrating the auxiliary equipment for cooling and control. In this contribution, we will overview the current status of HTS materials used at NSC for FCL applications and their further development, present the design of the delivered commercial systems, their testing and first experiences with field operation, and describe the currently running projects for the realization of FCL systems based on coated conductor tapes.
VV3: Poster Session: New Superconductors -- Properties and Synthesis
Session Chairs
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - VV3.1
Enhanced Superconducting Properties by Self–assembled Fe3O4 Nanoparticles in Epitaxial FeSe Thin Films.
Li Chen 1 , Chen-Fong Tsai 1 , Yuanyuan Zhu 1 , Zhenxing Bi 2 , Haiyan Wang 1 2
1 Materials Science and Engineering Program, Texas A&M University, CollegeStation, Texas, United States, 2 Department of Electrical and Computer Engineering, Texas A&M University, CollegeStation, Texas, United States
Show AbstractIn this paper we report epitaxial tetragonal Iron Selenide (FeSe) thin films grown on single crystal SrTiO3 (STO) (100) and MgO (100) substrates by a pulse laser deposition (PLD) technique. The superconducting properties were characterized using resistivity-temperature (R-T) measurement in a physical property measurement system (PPMS). Deposition temperature and annealing process were found to be critical for achieving tetragonal phase and the optimum superconducting properties of the films. The critical transition temperature of the thin films ranges from 2 K to 11.5 K depending on the deposition temperature and annealing conditions. The samples with higher critical temperatures all show self-assembled Fe3O4 nanoparticles (~15nm in average size) in the films according to X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis. It suggests that the formation of Fe3O4 might assist the formation of the stoichiometric FeSe tetragonal phase with enhanced superconducting properties.
6:00 PM - VV3.2
Synthesis and Characterization of Superconductor Thin Films Using Microwaves Oven.
Claudio Carvalho 1 , Joao Silveira 1 , Guilherme Torsoni 1 , Elton Souza 1 , Vivian Rodrigues 1 , Victor Solano Reynoso 1 , Gisele Souza 1
1 Physics and Chemistry, Universidade Estadual Paulista - UNESP, Ilha Solteira, SP, Brazil
Show AbstractHTS have been prepared by conventional process and submitted to different thermal treatments using electrical furnaces to improve some specific superconducting phases. However those processes or methodology are expensive and spend a lot of time to get pure phases. In this work we have prepared thin films of BSCCO system (2212) using microwave ovens (2.45 GHz, - 900 W) and a fine superconductor powder (less than 38 µm). The powder was obtained using the polymeric precursors process. The BSCCO films grown on crystalline substrate of LaAlO3 (100) showed crystalline structure. The films exhibited an x-ray diffraction pattern with c-axis perpendicular to the substrate and showed an onset superconducting transition temperature around of 91 K, In this measurements was used a Shimadzu diffractometer model XRD-6000 with copper filter Kα and the electrical resistance versus temperature measurements were carried out from room to below liquid nitrogen temperature (300 K - 65 K), using the four-probe dc method. This measurements were carried out by an automatic system, using a programmable voltage/current source model 228A, a nanovoltmeter model 2182, a high performance DMM model 2000, all of them from Keithley Instruments Inc. and a DT 470 sd temperature sensor from Lake Shore Cryotronics, Inc. Atomic force microscope measurements to study the film topology, alternative thermal treatments to get high quality phase, and also magnetic measurements are in progress.
6:00 PM - VV3.3
Improvement of Ferropnictide Superconductors through Novel Synthesis Techniques.
Jeremy Weiss 1 , Jianyi Jiang 1 , Eric Hellstom 1
1 Applied Superconductivity Center, Florida State University, Tallahassee, Florida, United States
Show AbstractBulk Co-doped BaFe2As2 (Ba-122) material has been synthesized from the elements in a single-step, hot isostatic pressing (HIP) technique. These bulk materials are relatively pure but still contain Fe-As and BaO phases. Using this synthesis technique we have made targets that were used to grow high-quality, epitaxial thin films by pulsed laser deposition by or collaborators at the University of Wisconsin-Madison. These films have transition temperatures at zero resistivity Tc,ρ=0 = 21.5K, transition widths as small as ΔTc= 1.3 K, and critical current density as high as 4.5MA cm-2 (4K SF). Here we report a novel two-step synthesis technique plus a study of reaction pathways in the Ba-Fe-As system aimed at understanding how the superconducting Ba-122 phase forms and eliminating impurity phases. The new technique significantly reduces the impurity phases in our bulk Ba-122 samples. We have expanded this new technique to synthesize other ferropnictides such as K-doped Ba-122 and SmFeAs(Fx,O1-x) and compare key differences between samples produced by our single-step and new two-step processes. This work is supported by NSF DMR-1006584.
6:00 PM - VV3.4
In-field Characterization of Fe-based Superconductor Epitaxial Thin Films with Enhanced Superconducting Properties.
Paolo Mele 1 6 , K. Matsumoto 1 7 , I. Nagayoshi 1 , H. Fujita 1 , Y. Yoshida 2 7 , Y. Ichino 2 7 , A. Ichinose 3 7 , T. Kiss 4 7 , M. Mukaida 4 7 , B. Maiorov 5 , F. Balakirev 5 , S. Baily 5 , L. Civale 5
1 , Kyushu Institute of Technology, Kitakyushu Japan, 6 , Hiroshima University, Hiroshima Japan, 7 , IST-TRIP, Tuskuba Japan, 2 , Nagoya University, Nagoya Japan, 3 , CRIEPI, Yokosuka Japan, 4 , Kyushu University, Fukuoka Japan, 5 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractAlmost with three years, four new families of Fe-based superconductors with layered structure similar to the cuprates were discovered. So far there is a wealth of reports on sintered iron-based superconductors samples, but in order to enlighten their fundamental physical properties and to disclose them to applications a development of research on epitaxial thin films is greatly desired. We recently reported [1,2] on growth of epitaxial Fe-Te-S thin films by pulsed laser deposition at 400 °C on SrTiO3 (100) (STO) and MgO (100) single crystal substrates. Films reached zero resistance condition: Tc0 = 3.54 K on STO and 5.37 K on MgO. The sample deposited on MgO was characterized at high pulsed magnetic fields (up to 40 T) and low temperatures (until 0.5K). Using 90% of the normal state resistance (Tc(ρn=0.9) ≈7 K and ΔT ≈ 2K) the upper critical field was evaluated as Hc2//(0) ≈ 27 T [3]. Furthermore, varying the angle between the applied field and c-axis of the sample, Hc2 was found as almost isotropic. However, Jc is just 104 A/cm2 (2 K, self field) for the sample deposited on MgO. At least 106 A/cm2 is required for practical applications at selected temperatures. We are now working to enhance the transport properties of Fe-Te-S, as well as Fe-Te-Se, Fe-Se and Fe-Te films by nano-engineering approach. The order of magnitude of ξ(0) in the films belonging to Fe-based superconductor family suggests that the introduction of nanometric artificial defects for the pinning of quantized vortices should significantly increase Jc, similarly to the case of YBCO. Possible approaches can be the modulation of interfacial strain by introduction of oxide buffer layers and the insertion of artificial pinning centers by means of surface-modified targets. New results obtained on nano-engineered doped Fe-based superconductor films will be reported at the conference.References [1] Mele et al. APEX 2 (2009) 073002 [2] Mele et al. SuST 23 (2010) 052001 [3] Maiorov et al. (2010), in preparationFunding from BES and JST-TRIP is acknowledged
6:00 PM - VV3.7
Superconductivity Under Pressure in NaAlSi with Iron-pictinide ``111" Structure.
Jennifer Schmitt 1 , Leslie Mareike Schoop 1 , Vadim Ksenofontov 1 , Sergey Medvedev 2 , Frederik Casper 1 , Juergen Nuss 3 , Martin Jensen 3 , Mikhail Eremets 2 , Claudia Felser 1
1 Chemistry, Inorganic and analytical chemistry , Mainz Germany, 2 , Max Planck Institute for Chemistry, Mainz Germany, 3 , Max Planck Institute for Solid State Physics of Solids, Stuttgart Germany
Show AbstractThe layered ternary sp conductor NaAlSi, possessing the iron-pictinide "111" structure, has a superconducting transition temperature Tc = 7 K. The superconducting properties in NaAlSi have been investigated by DC measurements of the magnetic susceptibility and measurements of electrical transport under pressure. These measurements indicate that NaAlSi is a type-II-superconductor, whose transition temperature increases with the applied pressure.
Symposium Organizers
Claudia Cantoni Oak Ridge National Laboratory
Amalia Ballarino European Organization for Nuclear Research
Kaname Matsumoto Kyushu Institute of Technology
Vyacheslav Solovyov Brookhaven National Laboratory
Haiyan Wang Texas A&M University
VV4: Mechanisms for High-Tc and the Quest for New Superconductors I
Session Chairs
Wednesday AM, April 27, 2011
Room 2020 (Moscone West)
10:00 AM - VV4.2
A DFT (LDA+U) Study of the Electronic Properties of Square-planar Coordinated Copper Monoxide Structures.
Paul Grant 1
1 , W2AGZ Technologies, San Jose, California, United States
Show AbstractIt is now 25 years and three months since Georg Bednorz observed the onset of high temperature superconductivity in copper oxide perovskites, and yet its origin remains still largely unresolved. However, it quickly became evident the phenomenon was restricted to those structures possessing a common feature -- square planar coordinated "sheets," or "layers" of copper monoxide, now believed essential to the existence of superconductivity in these materials. We examine the structural stability and electronic properties of both “sheets” and “tubes” of CuO in such coordination as a function of Hubbard U within the DFT (LDA+U) framework , and for those values which yield metallic band structures, their fermiology and hole/electron-phonon coupling, and where applicable, Landauer-Buettiker ballistic transfer. Although such compounds do not, as yet, exist, we consider their study via DFT as proxies to aid eventual general understanding of superconductivity in layered copper oxide perovskites.
10:15 AM - **VV4.3
Stripes and Superconductivity in Layered Cuprates.
John Tranquada 1
1 Condensed Matter Physics & Materials Science Dept., Brookhaven National Laboratory, Upton, New York, United States
Show AbstractStudies of the original high-temperature superconductor, La2-xBaxCuO4, continue to yield surprises. For x = 1/8, we have known for quite some time that the bulk superconducting transition temperature, Tc, is strongly depressed and that coupled density modulations of antiferromagnetic spins and of doped carriers, commonly called stripes, develop below a temperature of ~ 50 K. Experiments over the last few years have provided evidence that d-wave superconductivity coexists with the stripe order in individual Cu-O planes, but is not coupled coherently between layers. To explain the frustrated interlayer coupling, theorists have proposed the existence of another superconducting state whose phase is spatially modulated and intertwined with the stripe order. New work has focused on a sample at x = 0.095 with Tc = 32 K and rather weak intrinsic stripe order. Measurements of the anisotropic resistivity in a magnetic field perpendicular to the planes reveals the existence of a novel state with zero resistivity parallel to the planes but no superconducting phase order between the planes. It appears that field-induced stripe order may help to pin vortices within the planes, thus stabilizing this phase.This work is supported by the Office of Basic Energy Sciences, Division of Materials Science and Engineering, U.S. Department of Energy, through Contract No. DE-AC02-98CH10886 and through the Center for Emergent Superconductivity, an Energy Frontier Research Center.
10:45 AM - VV4.4
Reassessment of Under-doped T’- and Infinite-layer Cuprates by MBE.
Yoshiharu Krockenberger 1 , Hideki Yamamoto 1
1 , NTT BRL, Atsugi Japan
Show AbstractThe Mott insulating ground state of high-Tc cuprates is a predominate consideration. However, for the parent compounds of electron-doped superconductors superconductivity as high as 30 K has been reported recently [1]. Electron-doped cuprates adopt the Nd2CuO4 or T’ structure resulting in square-planar coordinated copper sites. The contradiction between earlier reported and our present results originates from the complicated oxygen chemistry in these materials. As-grown specimens contain a fair amount of interstitial oxygen. The removal of interstitial oxygen by post-reduction while simultaneously preserving regular oxygen sites occupied, is an exigency to obtain superconductivity. Empirically, preserving regular oxygen sites occupied while interstitial sites are evacuated, becomes a more difficult task to be accomplished for lower doping levels x. In this study, we systematically investigated the post-reduction process of T’- and infinite layered cuprates. Thin films of Sr1-xNdxCuO2 and T’-Pr2CuO4 films have been synthesized by MBE. For T’-Pr2CuO4 films a two-step annealing process has been applied while infinite layer Sr1-xNdxCuO2 films were annealed in a single-step process. We were able to alter the electronic properties of T’-Pr2CuO4 and infinite layer Sr1-xNdxCuO2 films systematically. The highest superconducting transition temperature was Tc = 26-27 K for T’-Pr2CuO4 films. Superconducting infinite layer Sr0.95Nd0.05CuO2 films have been also obtained after an optimized reduction process. The specially designed post-reduction processes enable a nearly ideal oxygen configuration and therefore intrinsic properties of the parent compounds are unveiled in agreement to recent calculations indicating that the parent compounds of T’-structure cuprates are not Mott insulators [2]. [1] O. Matsumoto et al., Phys. Rev. B 79 (2009) 100508(R); Physica C 469 (2009) 924.[2] C. Weber, K. Haule, G. Kotliar, Nature Physics 6, 574 (2010).
11:30 AM - VV4.5
Antiferromagnetic Coupling between Cu and Mn Spin at the LSMO/LSCO Interface and its Relationship with Cu-spin Moment in Cuprate Superconductors.
Gabriella Maria De Luca 1 , Giacomo Ghiringhelli 2 , Marco Moretti Sala 2 , Sergio Di Matteo 3 , Maurits W. Haverkort 4 , Helmuth Berger 5 , Julio Criginski Cezar 6 , Nicholas Brookes 6 , Mark Huijben 7 , Gertjan Koster 7 , Guus Rijnders 7 , Marco Salluzzo 1
1 Department of Physics, CNR-SPIN, Napoli Italy, 2 Dipartimento di Fisica, Politecnico di Milano, CNR-SPIN, Milano Italy, 3 Universitè de Rennes, Equipe de Physique des Surfaces et des Interfaces, Institut de Physique de Rennes, UMR CNRS-UR1, Rennes France, 4 , Max Planck Institute for Solid State Research, Stuttgart Germany, 5 , Institut de Physique de la Matière Condensée, Ecole Polytechnique Féderale de Lausanne, Lausanne Switzerland, 6 , European Synchrotron Radiation Facility, Grenoble France, 7 , Faculty of Science and Technology and MESA+ Institute for Nanotechnology, Enschede Netherlands
Show AbstractSince the discovery of high temperature superconductors (HTS), the close proximity between superconductivity and magnetism in their phase diagram was regarded as an indication of a magnetic origin of the effective electron-electron interaction leading to superconductivity in a hole doped antiferromagnetic Mott insulator. Different experimental techniques, like nuclear magnetic resonance [1] muon spin resonance [2] inelastic neutron scattering [3] and resonant inelastic x-ray scattering [4] demonstrated the persistence of antiferromagnetic short-range correlations and of magnetic collective excitations (magnons and bi-magnons) within the CuO2 planes of undoped and superconduting cuprates. However, the effective role of magnetic interaction in the superconducting phenomena remains unclear. A related issue is the mechanism of the magnetic coupling at the interface between cuprate and manganite (ferromagnetic) oxides, which is reported to be quite exotic. In particular, Chackhalian et al. found an effective antiferromagnetic (AFM) coupling between Mn and Cu spin at the superconducting(S)/ferromagnetic (F) interface in YBCO/LCMO multilayer’s [5]. Since YBCO contains two copper sites an ambiguity still exist whether the Cu moment appear in the CuO chains or in the CuO2 planes. Moreover the result was not yet confirmed in other S/F oxide interfaces.In this contribution, we report a systematic study, by Cu L2,3 edge X-ray Magnetic Circular dichroism (XMCD), of the magnetic moment within the CuO2 plane of undoped (La2CuO4 (LCO)), underdoped, and optimally doped La2-xSrxCuO4 (LSCO), NdBa2Cu3O7-δ (NdBCO) and YBa2Cu3O7-δ (YBCO) compounds. Additionally here we report data concerning the effective coupling between Cu and Mn spin moment in La0.7Sr0.3MnO3 (LSMO)/LSCO multilayer’s, where Cu is located only in the CuO2 planes.The experimental results show that, in undoped, underdoped and even in superconducting and optimally doped cuprates, the Dzyaloshinskii-Moriya (DM) interaction within the CuO2 planes survives and gives rise to the well-known out of plane spin canting, which create a spin component perpendicular to the CuO2 planes aligned by an external magnetic field [6]. In LSMO/LSCO multilayer, on the other hand, at low fields (<0.5 Tesla), we detected the presence of a magnetic dichroism at the Cu edge, with main (unique) contribution from the CuO2 planes at the interfaces. The associated magnetic moment is found opposite to the overall Mn spin moment of the ferromagnetic LSMO layers, confirming the earlier report [5].[1] V.F. Mitrovic et al. Phys. Rev. B 67,220503 (R) (2003)[2] C. Panagopoulos et al. Phys. Rev. B 66, 064501 (2002)[3] B. Lake et al. Nature (London) 415, 299 (2002)[4] L. Braicovich et al. Phys. Rev Lett. 104, 077002 (2010)[5] J. Chakhalian, et al. Nature Physics 2, 244 (2006)[6] G. M. De Luca et al. submitted to Phys. Rev. B
11:45 AM - **VV4.6
Substitutional Doping in Fe-based Superconductors.
Athena Safa-Sefat 1
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractKey properties of the three families of iron- superconductors (1111, 122, 111) will be presented upon chemical substitutions. Doping-dependent phase diagrams, neutron results, and structural effects will be discussed, and in relation to copper-based superconductors.
12:15 PM - **VV4.7
Revealing the Electronic Structure of the Iron Pnictides with Electron Energy-loss Spectroscopy.
Juan Idrobo 1 2 , Wu Zhou 1 2 , Matthew Chisholm 2 , Micah Prange 1 2 , Athena Safa-Sefat 2 , Michael McGuire 2 , Brian Sales 2 , Stephen Pennycook 2 1 , Sokrates Pantelides 1 2
1 Physics and Astronomy, Vanderbilt University, Nashville, Tennessee, United States, 2 Materials Science and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractThe new iron-based family of high-T
C superconductors has generated interest in the scientific community because the materials exhibit properties reminiscent of both classical BCS and cuprate high-T
C superconductors. Iron pnictides, quaternary compounds of the form LnFeAsO (Ln=rare-earth elements), become superconductors between 26 K to 56 K both when fluorine (electron) doped and in the presence of oxygen vacancies (hole doped). They also present structural and magnetic phase transitions between 120 K to 150 K. It is known that, when the materials are doped, the structural and magnetic phase transitions disappear, suggesting that magnetic fluctuations bind the Cooper pairs and therefore give rise to superconductivity. [1]
In this talk, we report real-space and momentum transfer-dependent electron energy-loss spectroscopy (EELS) studies of the parent compounds (LnFeAsO, Ln=La, Ce, Pr, Nd, Sm, Gd) using (scanning) transmission electron microscopy. We find that all the studied parent compounds LnFeAsO present a Fe L-edge fine structure closer to that of metallic iron than iron oxides. In particular, we determined the Fe valence state of all the LnFeAsO from the Fe EELS fine structure. We find that apparent Fe valence state of all the LnFeAsO is smaller than any other iron oxide and even smaller than metallic iron. Moreover, we observe a direct correlation between the Fe valence state and TC, i.e. the smaller the calculated Fe valence state, the larger is the TC for that compound. We also find an anomalous crystallographic orientation-dependence of the Ln M-edge fine structure. In particular, we find difference in the apparent crystal field splitting of Ce and Gd f-bands when the spectra are collected in plane (parallel to the c-axis) and out of plane (perpendicular to the c-axis). The results will be discussed using a combination of experiments and total-energy first-principles calculations within density functional theory.
Reference:I. Mazin, Nature 464, 183 (2010).
This research was partially supported by the National Science Foundation under Grant No. DMR-0938330 (J-CI, WZ), by ORNL's Shared Research Equipment (SHaRE) User Facility, which is sponsored by the Office of Basic Energy Sciences, U.S. Department of Energy (J-CI) and the Office of Basic Energy Sciences, Materials Sciences and Engineering Division, U.S. Department of Energy (MC, AS-S, MAM, BCS & SJP), DOE grant DE- F002-09ER46554 (MP, STP), and by the McMinn Endowment (STP) at Vanderbilt University.
12:45 PM - VV4.8
Fe1+y SexTe1-x Superconductors: Synthesis, Crystal Growth, Structural, Superconducting and Magnetic Properties, Isotope Effect.
Kazimierz Conder 1 , Ekaterina Pomjakushina 1 , Markus Bendele 2 3 , Rustem Khasanov 3 , Vladimir Pomjakushin 4
1 Laboratory for Developments and Methods, Paul Scherrer Institute, Villigen Switzerland, 2 Physik-Institut, University of Zürich, Zürich Switzerland, 3 Laboratory for Muon Spin Spectroscopy, Paul Scherrer Institute, Villigen Switzerland, 4 Laboratory for Neutron Scattering, Paul Scherrer Institute, Villigen Switzerland
Show AbstractThe effect of nominal stoichiometry on the phase purity of FeSe1-x samples and the superconducting transition temperature TC were investigated. It was found that in the Fe-Se system a stable phase exhibiting superconductivity at TC~8K exists in a narrow range of selenium concentration (FeSe0.974±0.005) [1]. Chemical stability measurements of FeSe1-x and studies of doping (on both Fe and Se-sites) introducing chemical pressure in the system will be also presented. Iron-chalcogenide single crystals Fe1+ySexTe1-x were grown by the Bridgman method. Crystal quality was checked by X-ray diffraction, microscopy and X-ray micro fluorescence spectrometry. For the crystals of the composition FeSe0.5Te0.5 and a transition temperature of TC≈14.6 K structural and anisotropic superconducting properties were investigated by means of single crystal X-ray, neutron powder diffraction, SQUID and torque magnetometry, and muon-spin rotation [2]. The magnetic penetration depth at zero temperature was found to be 491(8) and 1320(14) nm in the ab-plane and along the c-axis, respectively. The zero-temperature value of the superfluid density obeys the empirical Uemura relation [2].For single crystals with variable Se/Te ratio and fixed y=1.03, three regimes of behaviour were found: (i) commensurate magnetic order for x≤0.1, (ii) bulk superconductivity for x≥0.5, (iii) superconductivity coexisting with incommensurate magnetic order in a range x≈0.25-0.45 [3].The Fe isotope effect on the transition temperature TC and the crystal structure was studied in the FeSe0.95 by means of magnetization and neutron powder diffraction. The substitution of natural Fe (containing 92% of 56Fe) by its lighter 54Fe isotope leads to an increase of TC of 0.22(5) K, giving αFe = 0.81(15) [4].[1] E. Pomjakushina et al., “Synthesis, crystal structure, and chemical stability of the superconductor FeSe1-x”, Phys. Rev. B, 80 (2009) 024517[2] M. Bendele et al., “Anisotropic superconducting properties of single-crystalline FeSe0.5Te0.5”, Phys. Rev. B, 81 (2010) 224520[3] R. Khasanov et al., “Coexistence of incommensurate magnetism and superconductivity in Fe1+ySexTe1−x”, Phys. Rev. B, 80 (2009) 140511(R)[4] R. Khasanov et al., “Iron isotope effect on the superconducting transition temperature and the crystal structure of FeSe1-x”, New J. Phys., 12 (2010) 073024.
VV5: Mechanisms for High-Tc and the Quest for New Superconductors II
Session Chairs
Wednesday PM, April 27, 2011
Room 2020 (Moscone West)
2:30 PM - **VV5.1
The Promise and Limitation of High Pressure to Novel Superconductors with Higher Tc.
C. Chu 1
1 , University of Houston, Houston, Texas, United States
Show AbstractHigh pressure has played an important role in the study of superconductivity science and technology. Recently, there is a surge of interest in the search for novel superconductors with higher Tc and better performance, culminating in the inaugural US/China Workshop on Novel Superconductors in Bijing, September 27-29, 2010. While the physical phase space of exploration in novel superconductors is vast, we believe that to delocalize the localized state in solids with high degree of covalent bonding via physical and/or chemical means and to stabilize the unstable high Tc phase can be most effective. The application of high pressure is one of such means. The successful synthesis of unstable of unstable cuprate superconductors with a Tc up to 126 K at ~ 6 GPa and the successful advancement of the Tc of cuprate superconductors up to 164 K under ~ 30 GPa are just two among the examples. Even the Tc of elemental superconductors has been enhanced to 25 K for Li under ~ 40 GPa. Unfortunately, a pressure induced superconducting to semiconducting transition was detected recently in Li at ~ 70 K. We have decided to examine if cuprate HTS will meet similar fate. Single crystalline samples of optimally doped YBCO have thus been investigated up to 30 GPa. Indeed, a pressure induced superconducting to semiconducting transition was observed as evident by the appearance of activation energy at pressures above ~ 24 GPa. The results will be presented and the implications discussed.* Work has been supported in part by AFOSR, DoE, CONTACT and TcSUH
3:00 PM - VV5.2
Basic Properties of the Actinide Based Oxipnictide Compound: NpFeAsO.
Tomasz Klimczuk 1 2 , Ross Springell 3 , Helen Walker 4 , Eric Colineau 1 , Jean-Christophe Griveau 1 , Daniel Bouexiere 1 , Rachel Eloirdi 1 , Piotr Gaczynski 1 , Robert Cava 5 , Roberto Caciuffo 1
1 , Institute for Transuranium Elements, JRC, EC, Karlsruhe Germany, 2 , of Applied Physics and Mathematics, Gdansk University of Technology, Gdansk Poland, 3 , London Centre for Nanotechnology and Department of Physics and Astronomy, London United Kingdom, 4 , European Synchrotron Radiation Facility, Grenoble France, 5 , Department of Chemistry, Princeton University, Princeton, New Jersey, United States
Show AbstractWe report on the synthesis of NpFeAsO, the first 1111-type actinide based oxipnictide. This new compound is isostructural to the REFeAsO system (RE=Rare Earth), possessing lattice parameters, Fe-As interatomic distances, and Fe-As-Fe bond angles falling within the empirical ’optimum’ for the observation of the highest superconducting transition temperatures. A series of bulk measurements performed on the parent compound, including susceptibility, heat capacity and resistivity, show no evidence for the expected spin density wave (SDW) formation, nor antiferromagnetic (AFM) ordering of the iron sublattice. Instead, the distinct antiferromagnetic ordering occurs at TN = 57 K, which is four times higher in temperature than the highest TN observed in the REFeAsO (RE=Pr) family. We attempted doping the iron and the oxygen sites by cobalt and fluorine, respectively. The changes of the lattice parameters and the unit cell volume, are consistent with those published for REFe1-xCoxAsO and REFeAsO1-xFx, and indicate that the doping was successful. The subtle changes of the interatomic distances, due to chemical doping, will be discussed. There is no hint of superconductivity transition observable in the susceptibility and specific heat data for the F-doped or Co-doped NpFeAsO samples down to 2 K. This observation, together with the lack of both SDW and AFM ordering of the iron ions in the parent material, are in agreement with the scenario that the same magnetic interactions are responsible for both antiferromagnetism and superconductivity in 1111 systems.
3:15 PM - VV5.3
Influence of the As-Fe-As Angle on the Critical Temperature of Superconducting Iron Pnictides.
Ruben Weht 1 , Gaston Garbarino 2 , Manuel Nunez Regueiro 3
1 Department of Physics, CNEA, San Martin Argentina, 2 , European Synchrotron Radiation Facility (ESRF), Grenoble France, 3 Institut Néel, CNRS & Université Joseph Fourier, Grenoble France
Show AbstractThe discovery of superconductivity in layered iron based compounds, with superconducting critical temperatures (Tc) reaching up to 56K, has strongly refreshed the interest in high temperature superconductors. In particular, in search of a common pattern for high temperature superconducting compounds, the similarities and differences between cuprates and pnictides are been now deeply investigated. One example is to analyse the influence of the angle between cations and anions in the active planes, CuO2 and FeAs, that optimize the critical temperature. For cuprates the rule of thumb says that flatter Cu-O-Cu buckling angles give, in general, higher Tc's. For pnictides it has been proposed that regular tetrahedral angles yield the highest superconducting temperatures. To study in more detail this relationship we are conducting a systematic research of the behaviour of different pnictides using pressure as an external parameter. In this work we will present measurements of the electrical resistivity and the crystalline structure and calculations of the electronic properties, obtained from the actual atomic positions, of the compound SmFeAsO0.81F0.19 up to pressures ∼ 20 GPa. The correlation between the pressure dependence of the superconducting transition temperature and the crystallographic parameters on the same sample clearly shows that a regular FeAs4 tetrahedron maximizes Tc, through the optimization of carrier transfer to the FeAs planes, as indicated by the evolution of the electronic band structures.
3:30 PM - **VV5.4
Local Structural Investigation of High Temperature Iron-based Superconductors.
Lorenzo Malavasi 1 2
1 Physical Chemistry, University of Pavia, Pavia Italy, 2 , INSTM, Pavia Italy
Show AbstractIA strong revitalization of the field of high temperature superconductivity (HTSC) has been produced recently by the discovery of TC around 26 K in F-doped LaFeAsO iron pnictides. Starting from this discovery a huge amount of experimental data have been accumulated. This important corpus of results will allow the development of suitable theoretical models aimed at describing the basic electronic structure property and nature of superconducting states in these new fascinating systems. A close correlation between structural features and physical properties in the normal and superconducting states has already been demonstrated in the current literature. Advanced theoretical models are also based on the close correlation with structural properties and in particular with the Fe-As tetrahedral array. As for other complex materials a deeper understanding of their structure-properties correlation requires a full knowledge of the atomic arrangement within the structure. Here we report the results of an extensive investigation of the local structure in the SmFeAsO1-xFx and Ba1-xKxFe2As2 system carried out by means of x-ray total scattering measurements and Pair Distribution Function (PDF) analysis. The results presented indicate that the local structure of these HTSC significantly differs from the average structure determined by means of traditional diffraction techniques, in particular the distribution of Fe-As bond lengths. In addition, a model to describe the observed discrepancies between local and average structure is presented.
4:30 PM - **VV5.5
Superconductivity Generated at Interfaces between Insulators.
Jochen Mannhart 1 , Thilo Kopp 1
1 , Center for Electronic Correlations and Magnetism, Augsburg Germany
Show AbstractThe interface between the two insulators LaAlO3 and SrTiO3 has been found to be superconducting with a Tc of 300 mK [1,2]. In the presentation we will present surprising properties of this two-dimensional, superconducting system and examine the possibility to achieve high transition temperatures by using related interfaces.[1] N. Reyren et al., Science 317, 1196 (2007) [2] A. Caviglia et al., Nature 456, 624 (2008)
5:00 PM - **VV5.6
Superconducting Phase Diagram of the LaAlO3/SrTiO3 Interface System.
Stefano Gariglio 1 , Nicolas Reyren 1 , Andrea Caviglia 1 , Claudia Cancellieri 1 , Toni Schneider 2 , Jean-Marc Triscone 1
1 DPMC, University of Geneva, Geneva Switzerland, 2 Physikinstitut, University of Zurich, Zurich Switzerland
Show AbstractLaAlO3/SrTiO3 interfaces display a superconducting ground state [1] that can be controlled by an electric field [2]. In this presentation, we will first discuss the dimensionality of the superconducting state for different doping levels investigated by magneto-transport in perpendicular and parallel magnetic fields [3]. We will then examine the transition from the superconducting state to the “normal” state induced by magnetic field across the phase diagram. These measurements allow us to determine the system phase diagram in three dimensions (temperature, electric field, magnetic field). Using a scaling analysis of the critical behavior of the superconducting transition temperature, we obtain information on the class of the quantum phase transitions and the electronic phases surrounding the superconducting dome.
[1] N. Reyren et al. Science 317, 1196 (2007).[2] A. Caviglia et al. Nature 456, 624 (2008).[3] N. Reyren et al. Appl. Phys. Lett. 94, 112506 (2009).
5:30 PM - VV5.7
Violation of the Pauli Paramagnetic Limit and Intrinsic Spin-orbit Coupling in Symmetric Delta-doped SrTiO3 Heterostructures.
Minu Kim 1 , Yusuke Kozuka 2 , Christopher Bell 1 3 , Hikita Yasuyuki 1 , Harold Hwang 1 4 5
1 Department of Advanced Materials Science, The University of Tokyo, Kashiwa, Chiba, Japan, 2 Institute for Materials Research, Tohoku University, Sendai, Miyagi, Japan, 3 , Japan Science and Technology Agency, Kawaguchi, Saitama, Japan, 4 Department of Applied Physics, Stanford University, Stanford, California, United States, 5 Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, California, United States
Show AbstractElectron-doped SrTiO3 is a crucial material for oxide electronics, and highly interesting as the lowest-density superconductor [1], as well as being a high-mobility d-electron semiconductor [2]. However, many of the fundamental parameters defining its transport properties are unclear at this time. In this study, we present violation of the Pauli paramagnetic limit and intrinsic spin-orbit coupling of SrTiO3 heterostructures. By selective doping inside a SrTiO3 host down to a few nanometers [3], analogous to semiconductor delta-doped structures, the orbital pair-breaking is geometrically suppressed. Using this technique the spin-orbit coupling of SrTiO3 is exposed by the robustness of the superconductivity to magnetic fields parallel to the dopant plane, exceeding the Pauli limit by factor of four in the thinnest sample. The nature of our heterostructure means that we can maintain much higher mobilities in the thin limit than conventional superconducting thin films [4]. Additionally, unlike the LaAlO3/SrTiO3 interface where asymmetric potential can induce Rashba spin-orbit coupling [5,6], this spin-orbit coupling observed is intrinsic in SrTiO3 due to the preservation of structural inversion symmetry. These results shed light on potential application to spintronics and new possibility to study novel unconventional superconductivity.[1] J. F. Schooley et al., Phys. Rev. Lett. 12, 474 (1964).[2] O. N. Tufte et al., Phys. Rev. 155, 796 (1967).[3] Y. Kozuka et al., Nature 462, 487 (2009).[4] X. S. Wu et al., Phys. Rev. Lett. 96, 127002 (2006).[5] M. Ben Shalom et al., Phys. Rev. Lett. 104, 126802 (2010).[6] A. D. Caviglia et al., Phys. Rev. Lett. 104, 126803 (2010).
Symposium Organizers
Claudia Cantoni Oak Ridge National Laboratory
Amalia Ballarino European Organization for Nuclear Research
Kaname Matsumoto Kyushu Institute of Technology
Vyacheslav Solovyov Brookhaven National Laboratory
Haiyan Wang Texas A&M University
VV7: Transport Properties in New High-Tc and Cuprates Superconductors
Session Chairs
Thursday AM, April 28, 2011
Room 2020 (Moscone West)
9:30 AM - **VV7.1
Comparative Vortex Dynamics in Oxide, Iron-arsenide and MgB2 Superconductors.
Leonardo Civale 1
1 Superconductivity Technology Center, Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractVortex physics has been a topic of continuous interest since the discovery of the oxide high temperature superconductors (HTS). The complex vortex phenomenology in these materials, such as their rich temperature vs. magnetic field (T-H) phase diagram and their fast non-equilibrium dynamics, arises from the strong influence of thermal fluctuations, which is a consequence of the small superconducting coherence length (ξ) and the large crystalline anisotropy (γ). Although this behavior strongly contrasts with the much simpler vortex phenomenology in conventional low temperature superconductors (LTS), there is no sharp boundary between vortex physics in LTS and HTS. The discovery of the iron-arsenide superconductors provided a perfect opportunity to “bridge the gap” by investigating vortex matter in a whole new family of materials spanning a broad range of transition temperatures. While the small ξ in some of these induces large fluctuation effects similar to those found in the oxides, such as the appearance of vortex liquid phases and fast dynamics (large flux creep rates), the multi-band superconductivity in the FeAs-based compounds introduces a new level of complexity, requiring a re-evaluation of the concept of anisotropy in the vortex behavior. Valuable information can also be obtained from studies in MgB2, a chemically simpler two-band superconductor where ξ and γ can be modified by doping. In this talk I will discuss some of our recent studies of vortex matter in thin films and single crystals of oxide, iron-arsenide and MgB2 superconductors. Experimental results were obtained by a variety of tools including magnetization, transport, and vortex visualization by magnetic force microscopy, covering large portions of the T-H plane. I will present a comparative analysis of the vortex dynamics and the characteristics of the depinning excitations in these materials.
10:00 AM - **VV7.2
Single Crystals of Iron Pnictides: Investigations of Basic Properties Relevant for Applications.
Janusz Karpinski 1 , Nikolai Zhigadlo 1 , Serguy Katrych 1 , Zbigniew Bukowski 1 , Philip Moll 1 , Roman Puzniak 1 , Krzysztof Rogacki 1 , Bertram Batlogg 1 , Stephen Weyeneth 2 , Hugo Keller 2 , Mauro Tortello 3 , Renato Gonnelli 3 , Fedor Balakirev 4
1 Laboratory for Solid State Physics, ETH, Zurich Switzerland, 2 Institute of Physics, University of Zurich, 8057 Zurich Switzerland, 3 Dipartimento di Fisica, Politecnico di Torino, 10129 Torino Italy, 4 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractInvestigations of intrinsic properties of LnFeAsO (Ln=La, Pr, Nd, Sm, Gd) oxide high Tc superconductors require single crystal studies. LnFeAsO single crystals were grown from flux at high-pressure of 30 kbar. An overview of the basic superconducting properties measured on single crystals of LnFeAsO will be presented. Superconductivity in LnFeAsO has been induced by partial substitution of O by F, Sm by Th, Fe by Co or As by P. Single crystal structure investigation show structure modification due to substitutions, which is linked to superconducting properties. By comparing our experimental data for Sm1-xThxFeAsO, SmFeAsO1-xFy and SmFeAs1-xPxO compounds with other Fe-based pnictides it was found that the pnictogene height is a key factor that determines critical temperature. Our detailed study of the transport properties of SmFeAs(O,F) single crystals reveals a promising combination of high (> 2 106 A/cm2) and nearly isotropic critical current densities. LnFeAs(O,F) compounds show the highest Tc, highest upper critical fields, high electronic anisotropy and broadening of the resistive transition in magnetic fields. The penetration depth anisotropy γλ and upper critical field anisotropy γH were studied as a function of temperature for various substitutions. The penetration depth anisotropy γλ and upper critical field anisotropy γH are different and temperature dependent, what indicates multigap electronic structure. Point-Contact Andreev-Reflection spectroscopy studies show the existence of two gaps in the SmFeAsO1-xFx and SmFeAs1-xPxO crystals, which energy varies with doping level.
10:30 AM - **VV7.3
Critical Current Density and Scaling Behavior of Oxypnictide Thin Films.
Martin Kidszun 1 , Silvia Haindl 1 , Jens Haenisch 1 , Alexander Kauffmann 1 , Ludwig Schultz 1 , Bernhard Holzapfel 1
1 IMW, IFW Dresden, Dresden, Sachsen, Germany
Show AbstractThe successful growth of epitaxial LaFeAs(O,F) and SmFeAs(O,F) thin films opens the way to study intrinsic properties of this novel superconductors. Exploring the magnetic phase diagram up to 42 T we were able to investigate the temperature dependence and anisotropy of the upper critical field as well as the irreversibility field in this iron oxypnictide. The anisotropy of the irreversibility field was determined using a combination of resistive measurements in high magnetic fields and critical current density measurements. A substantial report about the anisotropy and the vortex matter will be given in this contribution.
11:30 AM - VV7.4
The Properties of Co-doped BaFe2As2 Single-crystalline Thin Films Grown by Template Engineering.
Sanghan Lee 1 , Chung Wung Bark 1 , Seung Hyub Baek 1 , Chad Folkman 1 , Chang-Beom Eom 1 , Jianyi Jiang 2 , Jeremy Weiss 2 , Chiara Tarantini 2 , Anatolii Polyanskii 2 , Eric Hellstrom 2 , David Larbalestier 2 , Yi Zhang 3 , Xiao Qing Pan 3
1 , UW-Madison, Madison, Wisconsin, United States, 2 , Florida State University, Tallahassee, Florida, United States, 3 , University of Michigan, Ann Arbor, Michigan, United States
Show AbstractUnderstanding new superconductors requires high-quality epitaxial thin films to explore intrinsic electromagnetic properties, control grain boundaries and strain effects, and evaluate device applications. So far superconducting properties of ferropnictide thin films appear compromised by imperfect epitaxial growth and poor connectivity of the superconducting phase. Here we report novel template engineering using single-crystalline intermediate layers of (001) SrTiO3 and BaTiO3 grown on various perovskite substrates that enables genuine epitaxial films of Co-doped BaFe2As2 with high transition temperature (Tc, ρ=0 of 21.5K), small transition widths (1.3K), superior Jc of 4.5 MA/cm2 (4.2K, self field) and strong c-axis flux pinning. Implementing SrTiO3 or BaTiO3 templates to match the alkaline earth layer in the Ba-122 with the alkaline earth-oxygen layer in the templates opens new avenues for epitaxial growth of ferropnictides on multi-functional single crystal substrates. Beyond superconductors, it provides a framework for growing heteroepitaxial intermetallic compounds on various substrates by matching interfacial layers between templates and thin film overlayers.
11:45 AM - VV7.5
Current Limiting Effect of Individual Grain Boundaries in Practical YBa2Cu3O(7-δ) Coated Conductors.
Dmytro Abraimov 1 , Pei Li 1 , Ron Feenstra 2 , David Larbalestier 1
1 Applied Superconductivity Center, National High Magnetic Field Laboratory, Tallahassee, Florida, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractGrain boundaries (GB) of different types significantly limit the critical current density Jc in modern YBa2Cu3O(7-δ)(YBCO) coated conductors. To understand the contribution of each GB type to such current limiting, we calculate the two major disorientation components, the in-plane (IP) and the out-of-plane (OOP), using standard Euler angle data generated by Orientation Imaging Microscopy (OIM). To detect critical current densities of numerous individual GBs we use Low Temperature Laser Scanning Microscopy (LTLSM) applied to precisely patterned Focused Ion Beam (FIB) quasi-1D links. Together, this approach allows us to correlate Jc with the OOP and IP components of more than 50 GBs in three different types of YBCO thin film grown by an ex situ BaF2 technique, by pulsed laser deposition (PLD), and in a real coated conductor made by the ex situ Metal Oxide Decomposition (MOD) route. All films were grown on rolling-assisted, biaxially-textured substrates (RABiTS). The template for the first YBCO film has almost equivalent IP and OOP tilts with x-ray pole figure FWHM values Δφ and Δω ~5o, while the templates for the second and third has a significantly improved OOP texture. For the first two films, the GBs follow the template GBs quite closely and we find that almost no grain boundary is of either simple IP or OOP tilt character. The third film has numerous meandering GBs with dominant OOP component. We also find that the OOP components form a continuous GB network in the YBCO deposited on the less textured template (first), while the continuous network is more dominated by the IP components for the better textured templates. For YBCO CCs grown on worse-textured RABiTS, we find that the OOP and IP misorientations affect Jc similarly. In the well textured MOD CC we detect two clusters of high Jc GBs: those with similar OOP and IP components but also a larger cluster with IP ≤1o and OOP components up to ≈6o. Additional microstructural analysis is necessary to find causes of such behavior. These data emphasize that grain boundaries grown on RABiTS are more complex and may be less sensitive to misorientation than those of pure character grown on SrTiO3 bicrystals.
12:00 PM - **VV7.6
Robust Grain Boundary Nature in Iron Pnictide Superconductors.
Takayoshi Katase 1 , Yoshihiro Ishimaru 2 , Akira Tsukamoto 2 , Hidenori Hiramatsu 1 , Toshio Kamiya 1 , Keiichi Tanabe 2 , Hideo Hosono 1
1 , Tokyo Institute of Technology, Yokohama Japan, 2 , International Superconductivity Technology Center, Tokyo Japan
Show AbstractGrain boundaries in high critical temperature (Tc) cuprate superconductors largely influence properties of their practical applications such as superconducting wires and tapes1; i.e., crystallites of cuprate superconductors must be highly textured to minimize the deterioration of intergrain critical current density through misoriented grain boundaries (GBs) (JcGB) because a misalignment of adjacent grains largely deteriorates JcGB, which follows an exponential decay of JcGB(θ) = Jc0exp(-θ/θ0) with the misorientation angle θ.Superconducting phases in the newly-found iron pnictide superconductors2 have the tetragonal (not orthorhombic) symmetry, and anisotropy of the physical properties looks rather smaller than those of the cuprates. In this paper, we report that iron pnictide superconductors are more robust against the grain boundary problems than the cuprates. The transport properties of well-defined GBs are examined for Co-doped BaFe2As2 (BaFe2As2:Co) epitaxial films.The GBs were formed by using [001]-tilt bicrystal substrates of MgO and (La,Sr)(Al,Ta)O3 (LSAT) with varied θ from 3 to 45o. The BaFe2As2:Co films were deposited on these bicrystal substrates by pulsed laser deposition with a 2ω Nd:YAG laser at 850 oC3. The BaFe2As2:Co GBs showed a high JcGB of ~2 MA/cm2 in a self-field at 4 K even at the critical angle of θc = 9o, which is twice larger than that of the cuprates. At θ > θc, JcGB(θ) exhibited a nearly exponential decay with the slope coefficient θ0 = 9o, which is much gentler than θ0 = 4o of YBCO. These results substantiate that BaFe2As2:Co has robust grain boundary nature for superconductivity compared to the cuprates, and are expected for high Jc superconducting wires and tapes even produced by a simple and low-cost process without severe texturing. At θ ≥ 16o, Josephson current dominated the supercurrent through the GBs4, and 45o-tilted GBs exhibited a clear Fraunhofer pattern and Shapiro steps. We discuss similarity and differences between BaFe2As2:Co and the cuprate superconductors based on these results as well.1D. Larbalestier et al., Nature 414, 363 (2001).2Y. Kamihara et al., J. Am. Chem. Soc. 130, 3296 (2008).3H. Hiramatsu et al., Appl. Phys. Lett. 93, 162504 (2008), Appl. Phys. Express 1, 101702 (2008). T. Katase et al., Appl. Phys. Express 3, 063101 (2010)4T. Katase et al., Appl. Phys. Lett. 96, 142507 (2010).
12:30 PM - VV7.7
Current Transport in high Jc, Macroscopically Untextured Bi2212 Polycrystals.
Fumitake Kametani 1 , J. Jiang 1 , E. Hellstrom 1 , D. Larbalestier 1 , Y. Huang 2 , H. Miao 2 , M. Rikel 3
1 Applied Superconductivity Center, National High Magnetic Field Laboratory, Tallahassee, Florida, United States, 2 , Oxford Superconducting Technology, Carteret, New Jersey, United States, 3 , NEXANS, Hurth Germany
Show AbstractAlmost all high Tc superconductors such as YBCO, Bi-2223 or the recently discovered pnictides possess grain boundaries that tend to block current. In the case of planar grain boundaries, an exponential decay of the critical current density Jc with increasing misorientation angle θ is observed. For polycrystalline versions of these materials to have high Jc we must develop a uni- or biaxial textured architecture. However there is one interesting exception to this rule, Bi2212. Macroscopically untextured Bi2212 round wire can achieve a high Jc of ~105 A/cm2 at 4.2 K and 45 T. In order to explore how such a high Jc is possible where many high angle grain boundaries occur in the round wires, we have been combining high resolution SEM imaging, EBSD-OIM, and FIB-extraction to local Jc measurements. Firstly the experiments have been carried out on much denser Bi2212 bulk with high intergrain Jc. By measuring the V-I characteristics of extracted individual filaments, we certainly can see that weak-link-free current paths exist in filaments and we are now focusing on individual grain boundaries of varied misorientation angles. The goal of our experiments is to understand those factors which make Bi2212 grain boundaries special. Our hope is that such information will enable better grain boundary current transfer in other high Tc materials such as YBCO.
12:45 PM - VV7.8
Flux Pinning of MOD and PLD Y1-xRExBa2Cu3O7-δ with Trace Amounts of RE = Nd and Tb Additions.
Joshua Reichart 1 , Yongli Xu 2 , Xueyan Song 3 , Timothy Haugan 1 , Victor Maroni 4 , Zhijun Chen 4 , Haiyan Wang 5 , Michael Sumption 6 , Paul Barnes 1
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , UES, Dayton, Ohio, United States, 3 , West Virginia University, Morgantown, West Virginia, United States, 4 , Argonne National Laboratory, Argonne, Illinois, United States, 5 , Texas A & M University, College Station, Texas, United States, 6 , Ohio State University, Columbus, Ohio, United States
Show AbstractThe doping of YBa2Cu3O7-δ (YBCO) with rare earth (RE) elements was studied to determine the effects on critical current density (Jc) and microstructure. Pulsed laser deposition (PLD) and metal-organic deposition (MOD) were performed to create thin films of (Y1-xREx)Ba2Cu3O7-δ with RE = Nd and Tb. Through previous research efforts it was shown that both Nd and Tb have a similar optimal range of doping concentration for PLD films. Additional measurements of Jc were made for angular Jc(θ) and magnetic Jc(H,T) for comparison to undoped YBCO. Initial results reveal that minutely doped samples made by MOD processing resulted in lower Jc then for PLD films; however, optimization of the process is necessary. Microstructure was analyzed by cross sectional TEM and Raman Spectroscopy. The TEM revealed differences between the Nd and Tb doped films. The Nd doped films have a very straight lattice structure while the Tb doped films are plane buckled. The research presented here demonstrates that these two different dopants are incorporated differently into the YBCO lattice while having similar effects on the films performance.
VV8: Role of Strain and Defects in Pinning
Session Chairs
Thursday PM, April 28, 2011
Room 2020 (Moscone West)
2:30 PM - **VV8.1
Nanostrain and Vortex Pinning in TFA-YBCO Nanocomposites.
Teresa Puig 1 , Xavier Obradors 1 , Anna Llordes 1 , Anna Palau 1 , Jordi Arbiol 1 , Jaume Gazquez 1 , Roger Guzman 1 , Alberto Pomar 1 , Felip Sandiumenge 1 , Susagna Ricart 1 , Fernando Martinez 1 , Manuela Erbe 1 , Mariona Coll 1 , Shuan Ye 1 , Daniel Chataigner 2 , Varela Maria 4 , Guy Deutscher 3
1 , ICMAB-CSIC, Bellaterra Spain, 2 , CRISMAT, Caen France, 4 , ORNL, Oak Ridge, Tennessee, United States, 3 , Tel Aviv University, Tel Aviv Israel
Show AbstractVortex pinning landscape engineering is the path towards tuning high performance YBCO coated conductors at high fields to match with specific application requirements. Many processing routes have been investigated and in particular, solution-derived nanocomposites with randomly oriented second phase nanoparticles have been shown to be an excellent option. The huge isotropic pinning forces encountered make this low cost material extremely valuable for HTS power applications and therefore they have motivated strong interest within this community. In this presentation, we will show our latest results on YBCO-TFA nanocomposites with different concentrations of BaZrO3, Y2O3 and BaCeO3 second phase nanoparticles, which evidence that these nanocomposties do experience a highly effective novel pinning mechanism, coupling superconducting pairing to lattice strain. The nanoscale strain evaluated from X-ray diffraction line broadening, correlates with the enhancement of the vortex pinning force and when this becomes isotropic leads to a vanishing anisotropy of the vortex pinning landscape. Still we demonstrated that the YBCO intrinsic mass anisotropy is preserved as was evidenced by high field Hc2(T) measurements. TEM investigation evidences a ramified shape of inhomogeneously distributed nanostrained regions associated to a highly dense defect structure (mainly stacking faults and partial dislocations interacting with twin boundaries), which is promoted by the non-coherent interfaces between randomly oriented nanodots and the epitaxial YBCO matrix. We envisage that the nanostrained regions inhomogeneously distributed within the superconducting matrix could suppress Cooper pair formation and hence promote vortex pinning according to a Bond Contraction Pairing model. Still the effects on the YBCO matrix strain due to particular issues like size, morphology, composition and density of the nanoparticles needs further investigation and for that purpose also Sn and Ta additions are being investigated and the corresponding results will be presented. In addition, the use of colloidal solutions with pre-formed nanoparticles should enables us to further control size, morphology and crystalline state of the nanoparticles and the progress achieved in this route in the last year will also be discussed.* We acknowledge financial support from MICINN (MAT2008-01022), Consolider Nanoselect, Generalitat de Catalunya (Pla de Recerca SGR-770 and XaRMAE), EU (NESPA)
3:00 PM - **VV8.2
Strain Tuning of Cuprate Superconductors.
Judith Macmanus-Driscoll 1 , Giorgio Ercolano 1 , Stuart Wimbush 1 , Lata Sahonta 1 , Haiyan Wang 2 , Sophie Harrington 1
1 Materials Science and Metallurgy, University of Cambridge, Cambridge United Kingdom, 2 Department of Electrical and Computer Engineering, Texas A and M University, Houston, Texas, United States
Show AbstractOwing to the extreme sensitivity of electron interactions to bond length and bond angle, in strongly correlated transition metal oxides strain plays a dominant role in tuning the properties. In this talk we propose possible novel ways to utilize strain effects to enhance Tc’s of cuprate superconductors. We also discuss the role of strain in tuning the pinning landscape and, by implementing our design rules, we demonstrate excellent critical current performance exceeding BZO.
3:30 PM - VV8.3
Peculiarities of REBCO Films Growth on Single Crystalline Substrates.
Constantin Tretiatchenko 1 , Victor Flis 1 , Vassily Svetchnikov 1 , Volodymyr Pan 1
1 Department of Superconductivity, G.V.Kurdyumov Institute for Metal Physics, Kiev Ukraine
Show AbstractStructural investigations show that REBCO films usually consist of columnar domains separated with low-angle dislocation boundaries irrespective of a deposition technique and a substrate. This is due to high anisotropy of perovskites, in particular, highly anisotropic growth rate in different crystallographic directions. This results in that formation of first atomic layers does not determine a nanostructure of the whole film. However, many imperfections once formed reproduce themselves in upper layers of the film. The substrate–film interface is important but its significance should not be overestimated. We used to develop a model and to simulate phenomena occurring at the surface during deposition, which lead to adjustment of the nanostructure of growing film to the substrate. The model takes into account highly anisotropic structure of layered copper oxides making a difference compared with numerous existing models developed for almost isotropic crystalline materials.Mismatch between the film and the substrate crystal lattices is the main source of defects. There are two essentially different ways to reduce the free energy of mismatched interface – by formation of misfit dislocations and by rotational relaxation of strains with formation of threading dislocations. In the first case atoms of the film are displaced longitudinally along the principal crystallographic direction. Just spacing between them becomes non-uniform. However, when chemical binding within the forming layer is much stronger than interaction between adatoms and the substrate, the film atoms may displace transversally. As a result, the film lattice rotates around the c-axis and divides into domains to reduce the free energy. In order to determine conditions, under which one or another mechanism takes place, to estimate the domain size and distribution, we developed an analytical model describing both misfit dislocations and rotational relaxation.Taking into consideration that the most of defects are metastable we made also a dynamic computer simulation. Our computer model deals with certain units of which the film consists rather than with individual atoms. The model is continuous and accounts for many aspects, such as anisotropy of chemical binding, surface and volume diffusion. We can simulate addition of impurity compounds and formation of nanoparticles. An interplay of a large number of factors results in a great variety of columnar and plate-like forms and morphologies, which can dramatically change even at small variations of temperature, deposition rate, and time of deposition. The computed patterns are consistent with the observed nanostructures and distribution of BaZrO3 nanoparticles. We propose new experiments, which can provide a further insight into growth mechanisms and nanostructure of high-Tc superconducting cuprate films.This work is supported by STCU through Project P424, by NAS of Ukraine and by the Ministry of Education and Science of Ukraine.
3:45 PM - VV8.4
The Challenging Microstructure of Trifluoracetate-YBa2Cu3O7-δ Nanocomposites.
Jaume Gazquez 1 , Jordi Arbiol 1 , Roger Guzman 1 , Patricia Abellan 1 , Felip Sandiumenge 1 , Maria Varela 2 , Anna Llordes 1 , Susagna Ricart 1 , Teresa Puig 1 , Xavier Obradors 1
1 , Institut de Ciència de Materials de Barcelona-CSIC, Bellaterra, Barcelona, Spain, 2 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
Show AbstractYBa2Cu3O7-δ-BaZrO3 (YBCO-BZO) nanocomposites grown by chemical solution deposition have recently shown a remarkable improvement in critical current density and record pinning forces at high magnetic fields. The functionality of these films is highly dependent not only on the morphology of the nanostructures but also on the strain and local composition of the interfaces between the two component oxides. Here we present a detailed investigation of the microstructure of such films by means of Z-contrast scanning transmission electron microscopy (Z-STEM) in combination with electron energy loss spectroscopy (EELS). The addition of BZO precursors to the initial solution leads to the formation of YBCO epitaxial films with two nanoparticle populations, epitaxial particles nucleated at the substrate-precursor interface, and a major population of non-coherent BZO particles randomly distributed in the YBCO matrix. The presence of such nanoparticles changes drastically the microsctructure of the YBCO matrix, generating incoherent interfaces, which ultimately promote lattice disorder and defects homogeneously distributed all over the film. Z-contrast imaging allowed us to unveil these defects unambiguously. We observe the presence of high density of intergrowths consisting of an extra Cu-O chain layer, which can form an ordered array of Y2Ba4Cu8O16. Occasionally, even two extra Cu-O chains are added, this causes a severe bending of (001) planes, which may extent up to several unit cells, and major distortion along a and b axes. The result is a non-uniform field strain, in the range of nanometers, that might give rise to the increased critical current density. This microstructural study will be extended to other YBCO nanocomposites with different second phase nanoparticles.* Research sponsored by MICINN (MAT2008-01022), Consolider Nanoselect, Generalitat de Catalunya (Pla de Recerca SGR-770 and XaRMAE), EU (NESPA) and the European Research Council Starting Investigator Award program. Research supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Materials Sciences and Engineering Division (MV).
4:30 PM - VV8.5
Systematic Studies of Flux Pinning of Y-Ba-Cu-O Superconductor with Varying Nanoparticle Additions.
Timothy Haugan 1 , Joshua Reichart 1 , Margaret Ratcliff 1 , Matthew Mullins 1 , Francisco Baca 2 , Eric Brewster 1 , Paul Barnes 1
1 AFRL/RZPG, U.S. Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States
Show AbstractMethods to enhance the flux pinning and critical current density (Jc) of YBa2Cu3O7-x (Y-Ba-Cu-O or YBCO) superconductor by addition of varying nanosize defects have been studied world-wide by many research teams in recent years. Thus far, nanoadditions to YBCO have optimized Jc for additions typically at 2-10 Vol%, which is different from low-temperature metallic superconductors such as NbTi where increasing additions up to 25 Vol% correlate with increasing Jc. The reasons for the differences between NbTi and YBCO are not fully understood yet. Herein we present further studies on nanoparticle additions to YBCO, particularly focusing on understanding how to increase and optimize the volume percent additions. Only select phases were chosen for systematic studies with varying lattice mismatches and epitaxy growth, including M = Y2O3, BaZrO3 and Y2BaCuO5 (Y211). Thin films of (YBCO+M) were deposited on single-crystal substrates by pulsed-laser deposition, and processing parameters were varied to optimize Jc(H,T,theta) include deposition temperature from 775°C to 840°C, additions from 0 to 20 Vol%, and different methods including (M/YBCO)N multilayer and (YBCO)1-xMx single-target methods. The processing conditions and microstructures that maximize Jc for varying operation temperature T = 5K to 77K and magnetic field H = 0-14T, and orientation theta = 0 to 90° will be presented. We have found that several phases, including Y211 and BaSnO3, can achieve much higher additions > 15 Vol% without reducing Tc or Jc(77K,self-field) significantly. This is contrast to other common phases such as Y2O3 which had surprisingly serious degradation for only > 8Vol%. The comparisons for the different systematic studies of M phase additions to YBCO will be shown and discussed.
4:45 PM - VV8.6
BYZO Nanopancakes in HTS YBa2Cu3O7-δ Films: Effect on Critical Current Density and Nonlinear Microwave Response.
Constantin Tretiatchenko 1 , Victor Flis 1 , Vassily Svetchnikov 1 , Oleksa Kalenyuk 1 , Oleksandr Kasatkin 1 , Viacheslav Moskaliuk 1 , Andrey Rebikov 1 , Volodymyr Pan 1
1 Department of Superconductivity, G.V.Kurdyumov Institute for Metal Physics, Kiev Ukraine
Show AbstractWe have studied nanostructure, electric transport and microwave properties of HTS YBa2Cu3O7-δ films prepared by pulse laser deposition on LaAlO3 single crystal substrates using targets doped with BaZrO3. Two essentially different types of nanoparticles are revealed by HREM: “nanopancakes” and “nanorods”. A variable composition of nanopancakes corresponds to BaxY1-xZrOy (BYZO). They are 1-4 nm in ab-plane and only few atomic layers thick. Nanopancakes are surrounded with strongly deformed area and a system of numerous edge dislocations in all directions, which are well seen in HREM pictures after Fourier filtering. Tiny particles are suggested to be coherently coupled with YBCO matrix, generate numerous dislocations being additional flux pinning centers, and retard thermally activated relaxation of the dislocation nanostructure. Thus, nanopancakes seem to be responsible for usually observed Jc enhancement in Zr doped films.At higher substrate temperatures and/or slower deposition elastic strains relax by a slight inclination (~3°) of the c-axis of nanoparticles. Nanopancakes evolve to much wider (20−40 nm) and longer nanorods, which are often considered as a stack of self-assembled nanoparticles. Dislocations almost disappear. Thus, relaxation of elastic strains leads to more ordered structure, but reduces the number of dislocations. If the concentration of nanorods would be high enough and their diameter would be less, they could serve as pinning centers themselves. However, for Zr additions a temperature increase and slower deposition essentially reduce Jc. The I-V curves measured for the films containing 1.5% BZO have been found to be well approximated by a dependence E = Ecexp(−J0/J)μ rather than by a power law E = Ec(J/Jc)n. The exponential law is typical for a regime of collective vortex creep or superconductors with extended linear or planar defects. The μ exponent is found to be about unity in perpendicular applied field and μ ≈ 3/2 in the parallel field. Therefore, at perpendicular field vortex pinning and creep is determined mainly by extended c-oriented linear defects (dislocations and nanorods), whereas at parallel orientation pinning seems to occur at planar defects such as stacking faults with partial dislocations surrounding them.Linear and nonlinear microwave properties of the YBCO (BZO) films turned out to be qualitatively similar to that of pure YBCO films without nanoparticles and the defect nanostructure associated with them. A microwave response of HTS films is linear up to certain RF current amplitude – a nonlinearity threshold Ib. BZO nanoparticles appreciably improve microwave properties of the YBCO films. Ib of YBCO film containing 3% BZO is about 3 times greater than for the pure film. Moreover, a faster raise of nonlinear surface resistance is observed in the pure film above the threshold. This work is supported by STCU through Project P424, by NAS of Ukraine and by the Ministry of Education and Science of Ukraine.
5:00 PM - VV8.7
Strain-driven Oxygen Deficiency in REBCO Films with Self-assembled BaZrO3 Nanocolumns.
Claudia Cantoni 1 , Yanfei Gao 2 3 , Sung Hun Wee 1 , Eliot Specht 1 , Jaume Gazquez 4 , Jianyong Meng 3 , Stephen Pennycook 1 , Amit Goyal 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Computer Science and Mathematics Division, Oak Rlidge National Laboratory, Oak Ridge, Tennessee, United States, 3 Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee, United States, 4 Dept. Fisica Aplicada III, University Complutense of Madrid, Madrid Spain
Show AbstractWe present direct observation of nanoscale c-axis strain modulation within the YBCO matrix surrounding BZO nanocolumns by aberration-corrected Z-contrast STEM. The strain originating by the large REBCO-BZO lattice mismatch is partially relieved by arrays of misfit dislocations which generate large local atomic displacements and hinder proper REBCO oxygenation. EELS maps and line scans show that the oxygen deficient REBCO stretches over a region of outer diameter equal to 3-4 times the BZO rod diameter, explaining the observed Tc reduction for large BZO concentrations. The direct strain measurements provide a picture that reconciles XRD experiments with analytical and finite element strain simulations.
5:15 PM - VV8.8
Strain-mediated Self-assembly of Nanostructures in YBCO Films: Modeling and Experiment.
Judy Wu 1 , Jack Shi 1 , Rose Emergo 1 , Javier Baca 2 , Timothy Haugan 3 , Paul Barnes 3
1 Physics and Astronomy, Univ. of Kansas, Lawrence, Kansas, United States, 2 , Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 3 Propulsion Directorate, U.S. Air Force Research Laboratory, WPAFB, Ohio, United States
Show AbstractStrain-mediated self-assembly of impurity nanostructures has been extensively applied to generate pinning centers in YBa2Cu3O7-δ (YBCO) films. While remarkable enhancement of critical current density Jc has been obtained, the need to precisely design a 3-dimensional pinning landscape arises in order to provide optimal Jc as function of magnetic field H and its orientation for specific applications. To address this issue, an interactive approach has been developed involving theoretical modeling of the elastic strain in a doped YBCO film and experimental exploration of controllable growth of nanostructures in YBCO. Excellent agreement between theory and experiment has been obtained. Using several oxides as example including BaZrO3 (BZO), BaSnO3 (BSO) and Y2O3, we show their geometries in YBCO film can be controllably generated via strain engineering at nanoscales. Using strain engineering, a 3D landscape of BZO nanorods has been demonstrated in YBCO films up to several micrometer thickness. Significantly enhanced Jc has been observed in the entire range of magnetic field orientations at H up to 5T.
5:30 PM - VV8.9
Reversible Shift in the Superconducting Transition for BaFe1.8Co0.2As2, La1.85Sr0.15CuO4 and YBCO Using Piezoelectric Substrates.
Sascha Trommler 1 , Huehne Ruben 1 , Kazumasa Iida 1 , Silvia Haindl 1 , Patrick Pahlke 1 , Thomas Thersleff 1 , Ludwig Schultz 1 , Bernhard Holzapfel 1
1 , IFW Dresden, D-01171 Dresden Germany
Show AbstractIt is known that the application of strain has a significant influence on the properties of superconducting materials. Typically, thin films are prepared on substrates with different lattice misfits inducing a biaxial tensile or compressive strain to study this effect. Unfortunately, this approach is often restricted to very thin films. Additionally, it is difficult to correlate strain and superconductivity directly, as the preparation conditions and the resulting microstructure may severely affect the superconducting properties. An alternative approach is the use of single crystalline piezoelectric substrates enabling a dynamical variation of the induced strain by applying an electric field on the substrate. This approach is used to study the strain dependence of superconducting properties. Therefore, thin epitaxial YBCO, La1-xSrxCuO4 and BaFe2-xCoxAs2 films were prepared on piezoelectric (001) Pb(Mg1/3Nb2/3)0.72Ti0.28O3 (PMN-PT) substrates. Depending on the material, additional buffer layers are required to achieve an epitaxial growth and good superconducting properties in the deposited layers. The structural as well as the electrical properties of the grown films were characterized in detail. It was verified that the strain is transferred into the superconducting layer. A reversible shift of the superconducting transition was observed for all layers investigated with a value of 0.44 K for La1.85Sr0.15CuO4 and 0.2 K for BaFe1.8Co0.2As2 for a biaxial strain of 0.022% and 0.017%, respectively.1) 1)S. Trommler et al, 2010, New J. Phys. 12, 103030
Symposium Organizers
Claudia Cantoni Oak Ridge National Laboratory
Amalia Ballarino European Organization for Nuclear Research
Kaname Matsumoto Kyushu Institute of Technology
Vyacheslav Solovyov Brookhaven National Laboratory
Haiyan Wang Texas A&M University
VV9: Vortex Pinning
Session Chairs
Friday AM, April 29, 2011
Room 2020 (Moscone West)
9:45 AM - VV9.2
On the Large Isotropic Pinning Effects of BaZrO3 Nanorods as the Temperature is Lowered and the Field Increased in REBa2Cu3O7-δ Coated Conductors.
Aixia Xu 1 , Jan Jaroszynski 1 , Alexander Gurevich 1 , Yan Xin 1 , Fumitake Kametani 1 , David Larbalestier 1 , Yimin Chen 2 , Yi-yuan Xie 2 , Selvamanickam Venkat 3 , Sung-Hun Wee 4 , Amit Goyal 4
1 , Applied Superconductivity Center, Tallahassee, Florida, United States, 2 , SuperPower, Schenectady, New York, United States, 3 Department of Mechanical Engineering and the Texas Center for Superconductivity, University of Houston, Houston, Texas, United States, 4 , Oak Ridge National Laboratory, Oak ridge, Tennessee, United States
Show AbstractBaZrO3 nanorods are well known to produce strong correlated c-axis pinning at high temperatures. Surprisingly, however, recent studies of BZO-containing samples at 4 K show no signs of c-axis correlated pinning, even though the critical current densities are largely enhanced. Here we show that the dominant 4 K pinning characteristic, valid up to at least 31 T, is isotropic and can be fit to a standard anisotropic mass scaling except near the ab-plane where correlated pinning by the CuO layers enhances Jc. By measuring the angular-dependent current density Jc(θ) over a wide range of field and temperature, we observe that this isotropic pinning is valid only below ~30 K. We conclude that these low temperature isotropic pins are largely point pins induced by the strain fields of the BZO nanorods and that they are easily thermally depinned at higher temperatures, leaving the strong correlated c-axis pins then quite evident. At 4 K, however, the point pins contribute almost half of the Jc.
10:15 AM - **VV9.4
Enhancement in Flux-pinning and Jc via Incorporation of Double Perovskite Structured Pinning Additives in YBCO Films.
Sung Hun Wee 1 , Yuri Zuev 2 , Claudia Cantoni 1 , Eliot Specht 1 , Amit Goyal 1
1 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Physics, University of Tennessee, Knoxville, Tennessee, United States
Show AbstractNanoscale defects or imperfections (chemical or structural) within YBa2Cu3O7-δ (YBCO) superconductor play a central role in “pinning” or immobilizing magnetic flux-lines (or vortices), the motion of which yields dissipative current and reduces the critical current density, Jc. Hence, we have conducted extensive research to improve the pinning and Jc via controlled introduction of various nanoscale, insulating, nonsuperconducting defects in the superconducting films. In this talk, we will discuss our recent progress on finding of rare earth barium tantalates and niobates as new classes of additives for superior flux-pinning of YBCO films. Optimization of the growth conditions of YBCO samples with these pinning additives resulted in superior field and angular Jc performance with the highest Fp(max) among all samples with engineered columnar defects, including BaZrO3. Detailed structural and superconducting properties of the YBCO films will be presented. This research was sponsored by the U.S. DOE Office of Electricity Delivery and Energy Reliability - Superconductivity Program for Electric Power Systems Advanced Cables and Conductors.
10:45 AM - VV9.5
Synthesis and Characterization of YBa2Cu3Ox Thin Films Incorporating BaSnO3 Length-controlled Nanorods.
Kaname Matsumoto 1 , Paolo Mele 1 , Yasutaka Honda 1 , Isamu Tanaka 1 , Yutaka Yoshida 2 , Yusuke Ichino 2 , Ataru Ichinose 3
1 , Kyushu Institute of Technology, Kitakyushu Japan, 2 , Nagoya University, Nagoya Japan, 3 , CRIEPI, Yokosuka Japan
Show AbstractMultilayered films alternating pure YBCO layers and YBCO+BSO layers were prepared on STO substrates by alternating ablation of YBCO and YBCO+4 wt% BSO targets. BSO nanorods can be systematically changed into nanoparticles by controlling the BSO nanorod length (15 nm ~ 300 nm in the present experiment). Several combinations were obtained (YBCO+BSO layers length / pure YBCO layers length = 15 nm/60 nm, 30 nm/60 nm, 60 nm /60 nm, 30 nm /30 nm and 30 nm /90 nm) All the multilayered films presented high values (2~3 MA/cm2) of self-field Jc. In-field Jc is high (about 0.26 MA/cm2 at B=5 T, B//c) for samples which the ratio between YBCO+BSO layers and pure YBCO layers is around 0.25, then in the angular dependence Jc (B//c) > Jc (B//ab). When the ratio becomes close to the unit, opposite behaviour appears and Jc (B//ab) > Jc (B//c). The intensity of Jc peak in the c-axis direction on the angular dependence of Jc becomes strong gradually as the ratio between YBCO+BSO layers and pure YBCO layers shortens. The control of nanorod length is the powerful tool to deepen understanding of flux pinning by APCs.
11:30 AM - VV9.6
Potential for a Chemical Addition with ``Universal” Pinning Enhancement in RBCO Coated Conductors.
Dean Miller 1 , Nestor Zaluzec 1 , Victor Maroni 1 , Zhijun Chen 1 , Jeremy Kropf 1 , Tolga Aytug 2 , Miriappan Paranthaman 2 , Eliott Specht 2 , Yimin Chen 3 , Venkat Selvamanickam 3
1 , Argonne National Laboratory, Argonne, Illinois, United States, 2 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 3 , SuperPower, Inc., Schenectady, New York, United States
Show AbstractImproving flux pinning through chemistry modifications in RBCO high temperature superconducting (HTS) tapes is currently a major research focus. In this work, we present microstructural characterization of tapes with one or more chemical additions, including Zr, Ce, Ho, and Nb, prepared using pilot-scale MOCVD process equipment. In one part of this work, we explored the synergistic effect between Zr additions and (Y,Gd) content in (Y,Gd)BCO tapes. Our characterization of these samples revealed an interplay between Zr-based columnar defects and ab-plane aligned rare-earth oxide precipitates that can explain less than optimal changes in H//ab and H//c pinning depending on the ratio of Zr to (Y,Gd). We also studied alternate additions, such as Ce, Ho, and Nb in order to establish the chemistry and microstructure of the pinning landscape induced by these additions. The rare-earth additions primarily induce ab-plane aligned defects similar to those attributed to Y and Gd in (Y,Gd)BCO tapes. However, Nb induced both ab-plane aligned defects and columnar defects similar to those associated with Zr, leading to superior performance for all field orientations. Through this work, we have developed a more enlightened understanding of how these additions influence pinning behavior.Research supported by the U.S. Department of Energy, Offices of Electricity Delivery and Energy Reliability and Office of Science. The Electron Microscopy Center at Argonne is supported by the Office of Science.
11:45 AM - VV9.7
Studies Towards Enhanced Performance and High Throughput MOCVD-YBCO Films.
Tolga Aytug 1 , M. Paranthaman 1 , E. Specht 1 , F. List 1 , Y. Zhang 1 , Y. Zuev 1 , C. Cantoni 1 , A. Goyal 1 , D. Christen 1 , Y. Chen 2 , V. Selvamanickam 2 , V. Maroni 3 , D. Miller 3 , Z. Chen 3 , A. Kropf 3 , N. Zaluzec 3
1 , Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States, 2 , SuperPower, Inc, Schenectady, New York, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States
Show AbstractA research-scale metal-organic chemical vapor deposition (MOCVD) system has been used to investigate and understand the effects of Nb addition/substitution on the micro-structural properties and flux pinning performance of these films. Systematic variations in doping have revealed trends in the resulting performance/property correlations, as characterized by coordinated analyses of electrical transport, x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. In particular, the minimum Jc values of the samples showed substantial improvement compared to undoped counterparts. From detailed microstructural investigations, the angular enhancement of Jc is found to be due to the formation of both self-assembled columnar-like defects and Nb-incorporated high density strings of precipitates parallel to ab-planes in the YBCO matrix. The chemical nature of these bi-directional defects will be discussed based on microscopy analysis combined with x-ray diffraction, Raman microscopy, and x-ray absorption spectroscopy studies. In addition, we will introduce ultraviolet (UV)-assisted MOCVD-REBCO film growth capability at ORNL.