1. Estudio de la evolución y técnica de regulación de la corriente presistente en anillos superconductores de YBCO - Quelle, Iria; González Jorge, H.; Romaní, L.; Domarco, G.
En este trabajo se realiza un estudio de la evolución de corriente en función de la densidad de vórtices atrapados y se presenta una técnica para regular la corriente partiendo del valor crítico, en anillos superconductores de YBCO. Para generar una corriente persistente en los anillos se utiliza un método de tipo inductivo, denominado field cooling, que combinado con campos magnéticos en sentido contrario al inductor permite disminuir la densidad de vórtices atrapados y se logra también disminuir el decaimiento de corriente. Una vez que se ha inducido la corriente crítica en los anillos una zona muy localizada de éstos se...

2. Niobium Nitride / Aluminium Nitride Superconductor / Insulator Multilayers and Tunnel Junctions - Niobium Nitride,Aluminium Nitride,Superconductor Insulator,Zoe H. Barber,Mark G. Blamire
INTRODUCTION The fabrication of artificial superconductor / insulator (SI) multilayer structures offers the possibility of observing novel superconducting phenomena and properties. Possible applications based on such multilayers and Josephson superlattices include practical devices such as flux flow oscillators [1] and particle and photon detectors [2], novel device structures [3],[4] and high density packaging of devices and circuits. Multilayer Josephson junctions have been used to study dimensional crossover phenomena in superconductors and localization and interaction effects [5]. Information on the interlayer coupling of a system such as niobium nitride, which has a superconducting coherence length intermediate between that of metallic superconductors, such as niobium, and the high T c oxides, is of particular interest for...

3. Síntesis y caracterización del superconductor antiferromagnético RuSr2GdCu2O8 - Flórez, M.; Uribe L., M. A.; Landínez Téllez, D.A.; Roa-Rojas, J.
Reportamos la síntesis del óxido superconductor RuSr 2 GdCu 2 O 8 . Análisis de difracción de rayos X (DRX) permitieron determinar que este material cristaliza en una estructura tetragonal de tipo perovskita. En mediciones de resistividad eléctrica se observó una transición al estado superconductor con temperatura crítica T c =35,5 K. Mediciones de magnetización permitieron observar una transición entre estados paramagnético y antiferromagnético, con una temperatura de Néel T N =132,7 K, evidenciándose la coexistencia de superconductividad y antiferromagnetismo en T
4. Modos electromagnéticos colectivos en superconductores de capas en estado de vórtices - Vega Monroy, R.; Pacheco Martínez, P.; Montoya Morrón, C.
Se estudian diferentes tipos de modos colectivos electromagnéticos en superconductores de capas en estado de vórtices. La ley de dispersión de este tipo de modos presenta un corrimiento de frecuencia a diferencia de modos similares en superconductores convencionales.

5. Efecto del confinamiento geométrico sobre las propiedades críticas de anillos superconductores - Calero, J.M.; Porras-Montenegro, N.; Segovia Ch., Francis A.; Granada E., Juan Carlos
En el marco de la teoría de Ginzburg-Landau se examina el estado superconductor en un anillo mesoscópico de espesor despreciable en presencia de un campo magnético perpendicular al plano del anillo, para el caso cuando el borde interno del anillo contacta con un medio caracterizado por un parámetro de de Gennes b finito. Se muestra que para valores pequeños de b existen estados superconductores de borde sólo para campos magnéticos mayores que cierto valor crítico que de-pende de b. Esto implica una reducción de las regiones en el diagrama de fases donde existe el efecto Meissner paramagnético.

6. Superconductividad de borde en anillos superconductores mesoscópicos bajo diferentes condiciones de frontera - Segovia Ch., Francis A.; Granada E., Juan Carlos
In the framework of the Ginzburg-Landau theory, in the linear approach, we study the critical behavior of a mesoscopic superconducting ring with negligible thickness, in the presence of an applied magnetic field perpendicular to the plane of the ring. Special attention is devoted to the influence of the different materials, contacting the inner and external edges of the superconductor, on the features of the phase diagram and of regions where the paramagnetic Meissner effect exists.

7. Caracterización de muestras superconductoras de YBCO - Durand Niconoff, J. Sergio

8. Authors - Superconductor Device; Mikio Iizuka; Masashi Tachiki; Hisashi Nakamura
Terahertz wave (0.3-10THz) technology is unexplored and promising area for key infrastructure technology in the next generation. Bottleneck for the development of terahertz technology is a lack of light source for continuous terahertz waves. We have carried out a large-scale simulation of a high-temperature-superconductor device generating terahetz waves to develop a new light source for continuous terahertz waves. This simulation needs high-performance computational resource, because the phenomena, generating terahetz waves in high-temperature-superconductor is strong nonlinear and complex system in multiscale of time and space. Thus, the Earth Simulator is needed for performing the simulation effectively. By the last year, we...

9. Properties of a magnetic superconductor with weak magnetization : application to ErNi₂B₂C - Ng, Tai-Kai; Leung, Wai-Tak
Using a Ginsburg-Landau free energy functional, we study the H - T phase diagram of a weak magnetic superconductor, where the magnetization from the magnetic component is marginal in supporting a spontaneous vortex phase in absence of external magnetic field. In particular, the competition between the spiral state and spontaneous vortex phase is analysed. Our theory is applied to understand the magnetic properties of ErNi₂B₂C.

10. Ag doped (Bi1.6Pb0.4)Sr2CaCu2O8+ä textured rods - Madre, M.A.; Amaveda, H.; Mora, M.; Sotelo, A.; Angurel, L.A.
Se han preparado polvos cerámicos de composición (Bi1.6Pb0.4)Sr2CaCu2O8+d + x % Ag en peso (con x = 0, 1 y 3) mediante un proceso sol-gel. Estos polvos se han utilizado para fabricar precursores que se texturaron por medio del método de fusión zonal flotante. Se ha encontrado un gran cambio en la microestructura cuando se compara con muestras de composición pura Bi2Sr2CaCu2O8+d. Tanto la resistividad eléctrica a temperatura ambiente, como la corriente crítica, así como la resistencia a flexión se mejoran cuando la Ag se adiciona a estas muestras dopadas con Pb, mientras que no se observa cambio en la...

11. Superconductor-Insulator Transition - Sergey I. Knysh
Introduction In recent years, a lot of work has been concentrated on explorations of electronic systems. It is believed that understanding of the physics in 2D will give an insight into the problem of Hi-Tc superconductivity. The dimension d=2 turns out to be critical for both superconductivity and localization. Disorder-driven superconductor-insulator transition is governed by this two important effects. The impossibility of long-range order in d 2 was proven by Hohenberg 1 and Mermin and Wagner. Here is the general idea of a proof for Bose condensation. The static response function s A;B (k; k) satisfies the axioms of scalar product and an upper bound s A;A y (k) (fi=2)C A;A y(k) where C is the equal-time...

12. DIRECT DEPOSITION OF C-AXIS TEXTURED HIGH-TC YBCO SUPERCONDUCTING THICK FILMS UNORIENTED METALLIC SUBSTRATES - Wen, Xuejun
In this thesis, first two chapters give brief introduction to several aspects of superconductivity, including the concepts, history and applications of superconductivity, and fabrication techniques for long and uniform high-temperature superconductors tapes/wires. Last four chapters present detail information about my research in developing c-axis textured high-Tc YBCO superconducting thick films on unoriented metallic substrates Previous work in the development of YBCO superconducting wires and tapes has been focused on the deposition of YBCO on buffered metallic substrates. Although such an approach has proved successful in terms of achieving grain texturing and high transport current density, critical issues involving continuous processing...

13. Nonequilibrium Dynamics in Mesoscopic Superconductor-Semiconductor-Superconductor Junctions - Konrad W. Lehnert
Mesoscopic superconductor-semiconductor-superconductor junctions show an anomalous half-integer Shapiro step, which persists to high temperatures in the absence of a critical current. The temperature and bias dependence of this effect demonstrate that it is caused by nonequilibrium ac supercurrents flowing at twice the usual frequency. Because the spectrum of states in the normal metal depend on #, the superconducting phase difference, a dc voltage across the junction causes the states to oscillate in time. This in turn causes the electrons in the normal metal to fall out of equilibrium. The nonequilibrium electron population carries supercurrent at much higher temperature and over...

14. Weak-Localization-Like Effects in Superconductor--Ferromagnet--Superconductor Structures - M D Lawrence,N Giordano
. We report measurements of the resistance as a function of temperature and magnetic field in structures containing a narrow (#2 m) ferromagnetic strip connecting two superconducting films. The low-field magnetoresistance has a general appearance similar to that expected for weak localization, but the magnitude is much too large to be accounted for in terms of this mechanism. In zero field the resistance exhibits behaviour well below the critical temperature of the superconductor which cannot be attributed to the usual proximity effect. Certain features of the results suggest that this behaviour may be associated with electron phase coherence. Studies of electron transport in small structures have revealed a...

15. SURFACE RESISTANCE OF HIGH TEMPERATURE SUPERCONDUCTOR BY THE RESONANT CAVITY METHOD - KARKI, BHISHMA R.
The cavities of high temperature superconductor were prepared and oxygenated Q measurements made.TM 010 modes were chosen for the measurements since they are independent of the cavity height. Resonant frequencies of the cavities were theoretically calculated and the corresponding S 11 parameters were measured by sweeping the Network Analyzer over the corresponding frequency range. Measurements were taken at a range of temperature from 10 K to 90 K in step of 10 K. Both unloaded Q-factor (Q 11 ) and loaded Q–factor (Q L ) were then calculated using the experimental data. A series of plots of Q vs. T...

16. Flux Tube Dynamics in the Dual Superconductor - Melissa Lampert
INTRODUCTION 't Hooft [1] and Mandelstam [2] proposed long ago that quark confinement in QCD would come about as the result of the confinement of color electric flux into flux tubes, and that such flux tubes would form in a dual superconductor. One possible pathway to formation of this dual superconductor was offered later by 't Hooft [3]. He showed that an Abelian projection of a non-Abelian gauge theory contains magnetic monopoles. Though the effective interaction among these monopoles is hard to calculate, it is not unreasonable to suppose that they form a condensate like that of the Cooper pairs in a superconductor. This magnetic condensate would then...

17. Flux Tube Dynamics in the Dual Superconductor - Melissa A. Lampert
We study plasma oscillations in a flux tube of the dual superconductor model of 't Hooft and Mandelstam. A magnetic condensate is coupled to an electromagnetic field by its dual vector potential, and fixed electric charges set up a flux tube. An electrically charged fluid (a quark plasma) flows in the tube and screens the fixed charges via plasma oscillations. We investigate both Type I and Type II superconductors, with plasma frequencies both above and below the threshold for radiation into the Higgs vacuum. We find strong radiation of electric flux into the superconductor in all regimes, and argue that this invalidates the use of the simplest dual...

18. Cintas superconductoras multicapa preparadas mediante deposición de disoluciones químicas - Obradors Berenguer, Xavier; Puig Molina, Teresa; Sandiumenge Ortiz, Felip; Piñol Vidal, Salvador; Mestres Andreu, Narcís; Pomar Barbeito, Alberto; Castaño Linares, Óscar; Cavallaro, Andrea; Coll Bau, Mariona; Gázquez Alabart, Jaime; González González, Juan C.; Gutiérrez Royo, Joffre; Palau Masoliver, Anna; Hassini, Awatef
Referencia OEPM: P200500702.-- Fecha de solicitud: 23/03/2005.-- Titulares: Consejo Superior de Investigaciones Científicas (CSIC).

19. Superconductor-Insulator transition in 2D Disordered Films - Ke Dong
Introduction: the role of disorder Dirty Superconductor Anderson[2] argued that superconductivity is insensitive to perturbations that do not destroy time-reversal invariance. For s-wave superconductors, because the interaction between the two electrons in a Cooper pair is attractive, it will be energetically favorable if these two electrons stay close, therefore their spin must be in the singlet state, and the electrons have opposite spins ~ oe 1 = Gamma ~ oe 2 ; it can also be shown that the largest binding energy occurs for electrons diametrically opposite to each other around the Fermi surface, in other words ~ k 1 = Gamma ~ k 2 . As we know, under time-reversal transformation, both...

20. Superconductor: WIRES AND CABLES: MATERIALS AND PROCESSES - Peter J. Lee
Introduction The phenomenon of superconductivity was first observed in 1912 in the laboratory of Heike Kamerlingh Onnes, at the University of Leiden (Holland). At low temperatures certain materials (about 800 superconducting compounds have been recently tabulated by Poole and Farch, 2000) suddenly lose their resistance to the flow of electricity on cooling. The phenomenon remained a laboratory curiosity until 1954 when G. B. Yntema at the University of Illinois, made the first successful superconducting magnet and even at that point magnet performance fell well below that predicted by the properties of the superconductor. The slow progress can be partially attributed to the difficulty in obtaining the extremely low temperatures required, and the lack...

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