Suppressed Superconductivity of the Surface Conduction Layer in Bi2_2Sr2_2CaCu2_2O8+x_{8+x} Single Crystals Probed by {\it c}-Axis Tunneling Measurements

We fabricated small-size stacks on the surface of Bi$_2$Sr$_2$CaCu$_2$O$_{8+x}$ (BSCCO-2212) single crystals with the bulk transition temperature $T_c$$\simeq$90 K, each containing a few intrinsic Josephson junctions. Below a critical temperature $T_c'$ ($\ll$ $T_c$), we have observed a weakened Josephson coupling between the CuO$_2$ superconducting double layer at the crystal surface and the adjacent one located deeper inside a stack. The quasiparticle branch in the $IV$ data of the weakened Josephson junction (WJJ) fits well to the tunneling characteristics of a d-wave superconductor($'$)/insulator/d-wave superconductor (D$'$ID) junction. Also, the tunneling resistance in the range $T_c'$$<$$T$$<$$T_c$ agrees well with the tunneling in a normal metal/insulator/d-wave superconductor (NID) junction. In spite of the suppressed superconductivity at the surface layer the symmetry of the order parameter appears to remain unaffected.Comment: 13 pages, 6 figure

Properties of electrospun superconducting and magnetoresistive nanowires

Supraleitende Nanofasern und magnetoresistive Nanodrähte wurden durch Elektrospinnen und entsprechende Temperaturbehandlung hergestellt. Der Mechanismus des Elektrospinnens wird vorgestellt. Die Kernpunkte der Herstellung von Nanobändern und die Idee des Auffangens von parallelen Nanofasern werden demonstriert. Um supraleitende oder magnetoresistive Phasen unter Erhalt der Faserstruktur zu erzeugen, wird die Temperaturbehandlung basierend auf einer thermogravimetrischen Analyse vorgeschlagen. Die Untersuchung der supraleitenden Nanofasern basiert auf den zwei Kuprat- Supraleitern La1.85Sr0.15CuO4 und Bi2Sr2CaCu2O8 (Bi-2212). Ein Vergleich der supraleitenden Eigenschaften zwischen La1.85Sr0.15CuO4 Nanodrähten und Nanobändern wird vorgestellt. Die magnetischen und elektrischen Eigenschaften der Bi-2212 - Netzwerke, mit reiner Bi-2212 Phase, aber auch Pb - und Li - dotierten Phasen, werden präsentiert. Das erweiterte Bean-Modell des kritischen Zustandes wird zur Bestimmung der kritischen Stromdichte angewendet und ein Modell eines Netzwerks bestehend aus Josephson-Kontakten wird vorgeschlagen, um die einzigartigen elektrischen Eigenschaften zu erklären. In einem eigenen Abschnitt werden die Eigenschaften einer einzelnen, dicken Bi-2212 Faser demonstriert. Die Eigenschaften von magnetoresistiven Nanodrahtnetzwerken werden anhand des Perowskits La1−xSrxMnO3 untersucht. Der Einfluss des Dotierungsgrads von Sr auf die magnetischen und magnetoresistiven Eigenschaften wird diskutiert. Zum Schluss werden die Eigenschaften von hybriden La1.85Sr0.15CuO4/La0.7Sr0.3- MnO3 - Nanodrahtnetzwerken präsentiert.Superconducting nanofibers (nanowires and nanoribbons) and magnetoresistive nanowires were fabricated by the electrospinning technique accompanied with appropriate thermal treatment. The mechanism of electrospinning is introduced. The key points of producing nanoribbons and the idea of parallel nanofiber collection are demonstrated. To obtain the superconducting or magnetoresistive phases while maintaining the fiber structure, a thermal treatment based on the thermal gravity analysis is proposed. The investigation of the superconducting nanofibers is based on two cuprate superconducting materials: La1.85Sr0.15CuO4 and Bi2Sr2CaCu2O8 (Bi-2212). A comparison of the superconductivity between La1.85Sr0.15CuO4 nanowires and nanoribbons is presented. The magnetic and electric properties of the Bi-2212 nanowire networks are presented, including a comparison between pure Bi-2212, Pb-doped Bi-2212, and Li-doped Bi-2212 nanowire networks. The extended critical state model is applied for the critical current density estimation, and a Josephson junction network model is proposed to explain the unique features of the electric properties. As a special section, the properties of a single Bi-2212 thick fiber are also demonstrated. The characterization of the magnetoresistive nanowire networks is based on the perovskite materials La1−xSrxMnO3. The influence of the Sr doping level on the magnetic properties and magnetoresistance is discussed. At the end, the properties of La1.85Sr0.15CuO4/La0.7Sr0.3MnO3 hybrid nanowire networks are presented

Proceedings of the 4th International Conference and Exhibition: World Congress on Superconductivity, Volume 2

This document contains papers presented at the 4th International Conference Exhibition: World Congress on Superconductivity held June 27-July 1, 1994 in Orlando, Florida. These documents encompass research, technology, applications, funding, political, and social aspects of superconductivity. The areas covered included: high-temperature materials; thin films; C-60 based superconductors; persistent magnetic fields and shielding; fabrication methodology; space applications; physical applications; performance characterization; device applications; weak link effects and flux motion; accelerator technology; superconductivity energy; storage; future research and development directions; medical applications; granular superconductors; wire fabrication technology; computer applications; technical and commercial challenges; and power and energy applications

Vortex pinning and critical current control and enhancement by magnetic structure and artificial arrays in YBa2Cu3O7-δ superconductor thin films

Superconductivity provides revolutionary solutions to practical applications, such as magnetic resonance imaging, fault current limiters, and unsurpassable sensitivity and characteristic for electronics and quantum computing, which to date are unattainable by more conventional technologies. The is still a lot can be improved in making superconductors cheaper, more reproducible and robust to enable even easier and broader paths into our everyday lives. One of the most versatile superconductor with strong potential for many types of technologies and corresponding applications is YBa2Cu3O7-δ (YBCO), a high temperature superconductor (HTS) ceramic material. This material can be manufactured in the form of high quality single-crystalline epitaxial films, not only on small chips for electronic devices, but also on large area wafers and tapes over a hundred meters long for cellular communication filters and electric power generation, handling and transmission. They suffer, however from the relatively low degree of reproducibility of their functional characteristics, especially for devices required for electronics and quantum computation, for which highly accurate and reproducible functionalities are required. This reproducibility problem stems from the fact that YBCO has four elements in its crystal structure, which are rather difficult to grow in a perfectly ordered fashion

Superconductor

This book contains a collection of works intended to study theoretical and experimental aspects of superconductivity. Here you will find interesting reports on low-Tc superconductors (materials with Tc 30 K). Certainly this book will be useful to encourage further experimental and theoretical researches in superconducting materials

Transport measurements on NdCeCuO thin films

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1992.Title as it appears in the M.I.T. Graduate List, June 1992: Transport properties of NdCeCuO thin films.Includes bibliographical references (leaves 125-131).by Andreas Kussmaul.Ph.D

Superconductors at the Nanoscale

By covering theory, design, and fabrication of nanostructured superconducting materials, this monograph is an invaluable resource for research and development. Examples are energy saving solutions, healthcare, and communication technologies. Key ingredients are nanopatterned materials which help to improve the superconducting critical parameters and performance of superconducting devices, and lead to novel functionalities. Contents Tutorial on nanostructured superconductors Imaging vortices in superconductors: from the atomic scale to macroscopic distances Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy STM studies of vortex cores in strongly confined nanoscale superconductors Type-1.5 superconductivity Direct visualization of vortex patterns in superconductors with competing vortex-vortex interactions Vortex dynamics in nanofabricated chemical solution deposition high-temperature superconducting films Artificial pinning sites and their applications Vortices at microwave frequencies Physics and operation of superconducting single-photon devices Josephson and charging effect in mesoscopic superconducting devices NanoSQUIDs: Basics & recent advances intrinsic Josephson junction stacks as emitters of terahertz radiation| Interference phenomena in superconductor-ferromagnet hybrids Spin-orbit interactions, spin currents, and magnetization dynamics in superconductor/ferromagnet hybrids Superconductor/ferromagnet hybrid

A study of three transition metal compounds and their applications

The La5/8-yPryCa3/8MnO3 with colossal magnetoresistance (CMR) effect has a rich phase diagram and is well studied for its electronic phase separation phenomenon, where the ferromagnetic (FM) metal order co-exists and competes with the charge-ordered (CO) insulator phase. High Pr doping will favor the CO order, leading a sharp FM to CO dominated phase transition around Pr concentration of 0.3 and above. Hydrostatic pressure favors FM metallic order without damaging the sample and can be tuned continuously. In this study, pressurized-magnetic and resistivity measurements was done on a La0.25Pr0.375Ca0.375MnO3 single crystal. The sample, at first sitting in CO dominated phase, changed into FM upon a small amount of pressure. This transition was verified both by magnetic and resistivity measurement results. FeSe1-x is one of the newly discovered iron-based superconductors. As a binary transition metal compound, it is of great research interest due to the simple stacking 2d-layered structure. The itinerant or localized nature of the electrons in Fe2+ ion has been debated but not concluded. In this research, Raman scattering measurements on FeSe0.97 were applied within a temperature range from 5 K to 300 K. The excitation near 185 cm-1 was assigned to B1g phonon excitation. Broad and intensive excitation peaks were found in a wide region between 200 cm-1 and 700 cm-1, and they are classified as the Fe2+ crystal field excitations. These excitations suggest a low Hund coupling constant and thus support the itinerant nature of 3d electrons in Fe2+ ion indirectly. Evanescent wave was discovered to be able to tunnel through a negative reflectance index material and gets strengthened inside an alternating metal-high K material 1d photonic crystal structure. Where the regular light eventually fails in sub-micron photolithography due to diffraction limit, evanescent wave can carry the information of small structure below diffraction limit. In our study, HfO2, a transitional metal oxide widely used in IC fabrication, was used as the high-K material to construct a sub-wavelength length imaging device for nano scale photolithography applications

Review on Superconducting Materials

Short review of the topical comprehension of the superconductor materials classes Cuprate High-Temperature Superconductors, other oxide superconductors, Iron-based Superconductors, Heavy-Fermion Superconductors, Nitride Superconductors, Organic and other Carbon-based Superconductors and Boride and Borocarbide Superconductors, featuring their present theoretical understanding and their aspects with respect to technical applications.Comment: A previous version of this article has been published in \" Applied Superconductivity: Handbook on Devices and Applications \", Wiley-VCH ISBN: 978-3-527-41209-9. The new extended and updated version will be published in \" Encyclopedia of Applied Physics \", Wiley-VC