bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of varying debris cover thickness on ablation: a case study for Koxkar Glacier in the Tien Shan
Authors: Juen M. , Mayer C. , Lambrecht A. , Han H. , Liu S.
Published: March 2014

Abstract. To quantify the ablation processes on a debris covered glacier, a simple distributed ablation model has been developed and applied to a selected glacier. For this purpose, a set of field measurements was carried out to collect empirical data. A morphometric analysis of the glacier surface enables us to capture statistically the areal distribution of topographic features that influence debris thickness and consequently ablation. Remote-sensing techniques, using high-resolution satellite imagery, were used to extrapolate the in situ point measurements to the whole ablation area and to map and classify melt-relevant surface types. As a result, a practically applicable method is presented that allows the estimation of ablation on a debris covered glacier by combining field data and remote-sensing information. The sub-debris ice ablation accounts for about 24% of the entire ice ablation, while the percentage of the moraine covered area accounts for approximately 32% of the entire glacierized area. Although the ice cliffs occupy only 1.7% of the debris covered area, the melt amount accounts for approximately 12% of the total sub-debris ablation and 2.5% of the total ablation respectively. Our study highlights the influence of debris cover on the response of the glacier terminus in a particular climate setting. Due to the fact that melt rates beyond 0.1 m of moraine cover are highly restricted, the shielding effect of the debris cover dominates over the temperature and elevation dependence of the ablation in the bare ice case.
Nuevas tecnologías y aprendizaje significativo de las ciencias
Authors: Romero Ariza Marta , Quesada Antonio
Published: March 2014

Este trabajo pretende fomentar la reflexión sobre el potencial de la tecnología educativa para promover el aprendizaje significativo de las ciencias. Con este propósito se recurre a la literatura especializada, para mostrar algunos resultados de investigación sobre la aplicación de las TIC a la enseñanza de las ciencias (herramientas de adquisición de datos, programas de modelización, simulaciones, laboratorios virtuales…). El valor formativo de dichas aplicaciones se discute desde los actuales conocimientos acerca de cómo los individuos aprenden, mostrando el potencial de estos recursos para superar los obstáculos específicos asociados al aprendizaje efectivo de las ciencias (ideas previas, falta de contextos significativos, grado de abstracción de modelos y teorías…). No obstante, también se ofrece una visión crítica señalando riesgos y limitaciones.
La importancia de las habilidades cognitivo-lingüísticas asociadas al estudio de la Astronomía desde la perspectiva del profesorado
Authors: García Barros Susana , Martínez Losada Cristina
Published: March 2014

El trabajo pretende conocer cómo valora el profesorado de Primaria y Secundaria en ejercicio y formación una serie de habilidades cognitivo-lingüísticas (descripción de hechos/fenómenos, de modelos, definición…). También se pretende conocer si los docentes establecen diferencias entre las habilidades expresadas genéricamente y en términos astronómicos, y si existen diferencias entre los grupos de docentes. Así mismos se analiza si los profesores identifican y valoran estas habilidades en actividades concretas. Los resultados muestran que los docentes valoran positivamente las habilidades, apreciándose diferencias entre las enunciadas genéricamente y en términos astronómicos y entre grupos de profesores. Los participantes tienen dificultades para identifican la habilidad cognitivo-lingüística exigidas en las actividades.
Concepciones del profesorado universitario acerca de la ciencia y su aprendizaje y cómo abordan la promoción de competencias científicas en la formación de futuros profesores de Biología
Authors: Martínez Galaz Carolina Paz , González Weil Corina Úrsula
Published: March 2014

Esta investigación indaga en las concepciones de un grupo de profesores universitarios chilenos. Nuestro objetivo fue relacionar sus visiones acerca de qué es la ciencia y cómo esta se aprende. También se analizó información acerca de las competencias científicas que declaran promover los docentes, y su relación con las concepciones señaladas. La investigación es mixta, y mediante la aplicación de un cuestionario y la realización de entrevistas se recoge información de las variables en estudio. Los resultados evidenciaron una relación positiva entre la visión empirista de ciencia y la visión de transmisión-recepción del aprendizaje; también la existencia de una relación positiva entre la visión constructivista del aprendizaje y la declaración del fomento de competencias.
Niveles de algebrización de la actividad matemática escolar. Implicaciones para la formación de maestros
Authors: Godino Juan D. , Aké Lilia P. , Gonzato Margherita , Wilhelmi Miguel R.
Published: March 2014

El desarrollo del razonamiento algebraico elemental desde los primeros niveles educativos es un objetivo propuesto en diversas investigaciones y orientaciones curriculares. En consecuencia, es importante que el profesor de educación primaria conozca las características del razonamiento algebraico y sea capaz de seleccionar y elaborar tareas matemáticas adecuadas que permitan la progresiva introducción del razonamiento algebraico en la escuela primaria. En este trabajo, presentamos un modelo en el que se diferencian tres niveles de razonamiento algebraico elemental que puede utilizarse para reconocer características algebraicas en la resolución de tareas matemáticas. Presentamos el modelo junto con ejemplos de actividades matemáticas, clasificadas según los distintos niveles de algebrización. Estas actividades pueden ser usadas en la formación de profesores a fin de capacitarlos para el desarrollo del sentido algebraico en sus alumnos.
Fabrication of Cu2SnS3 solar cells by screen-printing and high-pressure sintering process
Authors: Nomura Takeshi , Maeda Tsuyoshi , Wada Takahiro
Published: March 2014

Cu-poor Cu2−

x
SnS3 (CTS) powders with x = 0.0–0.3 prepared by mixing the elemental powders and post-heating at 600 °C in N2 gas were analyzed by X-ray diffraction and ultraviolet–visible–near-infrared (UV–vis–NIR) spectroscopy. The area of the solid solution region in the Cu-poor side of CTS was quite small in the Cu2S–SnS2 pseudo-binary system. We deposited CTS films by a screen printing and high-pressure sintering (PHS) process and post-annealing at 575 °C for 10 min under a 1% H2S/N2 gas atmosphere. The solar cells were fabricated with a device structure of Ag/indium tin oxide (ITO)/i-ZnO/CdS/Cu2SnS3 (CTS)/Mo/soda-lime glass. The CTS solar cell with x = 0.1 showed maximum efficiency of 1.03%. Then, we prepared Cu1.9SnS3 powders by mixing the elemental powders and post-heating at various temperatures. The CTS solar cell with Cu1.9SnS3 powder prepared by post-heating at 300 °C showed an efficiency of 1.38% with V
oc of 182 mV, J
sc of 21.7 mA/cm2, and FF of 0.350.
XPS Study of Chemical Bonding and Valence Band Structures in High-Tc Superconductors (Y, Sc, Ba)-Cu-Oxides
Authors: Mori N. , Takano Y. , Ozaki H.
Published: March 2014

An XPS study was carried out to know the chemical bonding states and valence band structures in (Y,Sc,Ba)-Cu-Oxides. Two types of samples were prepared; one of them is a high-Tc (∼90K) superconductor, while the other shows no superconductivity. The XPS signal of the Cu2p state consists of three peaks corresponding to Cu1+, Cu2+ and Cu3+ for both types of samples, but their peak ratios and chemical shifts are different. No large peak was observed in the density of states near the Fermi level for both types of samples.
Spin-Lattice Relaxation in the Normal and Superconducting States of a High Tc Superconductor: La1.83Sr0.17CuO4
Authors: Lee M. , Yudkowsky M. , Halperin W. P. , Thiel J. , Hwu S.-J. , Poeppelmeier K. R.
Published: March 2014

Polycrystalline samples of La1.83Sr0.17CuO4 were studied by pulsed NMR on the copper nucleus up to 70K. An extremely broad spectrum was observed. A Korringa constant of 14±± Ks and an energy gap of 2Δ/kBTc=1.3 were found. Homogeneous line narrowing was observed in the superconducting state. T2 data are presented for YBa2CuO7 as well.
AC Complex Susceptibility of Superconducting La–Sr–Cu–O and Y–Ba–Cu–O Systems
Authors: Oda Yasukage , Nakada Ichiroh , Kohara Takao , Fujita Hiroshi , Kaneko Tetuyuki , Toyoda Haruhisa , Sakagami Eiji , Asayama Kunisuke
Published: March 2014

The complex susceptibility x'-ix” of the superconducting La–Sr–Cu–O and Y–Ba–Cu–O systems were measured together with their electrical resistance. The recent best specimen of Y1Ba2Cu3O7-α shows the complete Meissner effect in the temperature width less than 1.7 K at Tc=91 K (mid-point). This specimen was found to be distorted to the orthorhombic structure by about 1.5%. This specimen was studied both in powdered and in recompressed into a pellet style. It is found that the semiconductive behavior in the electrical resistance comes from the grain boundary. DC susceptibility and ESR measurements of this specimen were carried out.
High Tc Superconductors of the Perovskite Structure Oxides
Authors: Hikami Shinobu , Matsuda Yuji
Published: March 2014

Y–Ba–Cu oxide and Ho–Ba–Cu oxide are discovered to be high Tc superconductors. Other related high Tc superconducting materials with similar perovskite structures are also found. The effects of Ni and Mn on these materials are investigated by the measurement of the resistivity.
High Tc Magnetic Superconductors in Rare Earth (R) Barium Copper Oxide RBa2Cu3O7-δ
Authors: Yang K. N. , Dalichaouch Y. D. , Ferreira J. M. , Hake R. R. , Lee B. W. , Neumeier J. J. , Torikachvili M. S. , Zhou H. , Maple M. B.
Published: March 2014

Superconductivity with critical transition temperature Tc near 90 K has been found in RBa2Cu3O7-δ compounds where R = Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu, and with Tc=56 K for R = La by electrical resistivity and low field magnetic susceptibility measurements. All compounds (except La) form in the orthorhombic, layered perovskite structure which is isomorphic to YBa2Cu3O7-δ. The lattice parameters of the compounds decrease in accordance with the metallic radii of the R trivalent ions. The electrical resistivity of the compounds studied (except for R = Nd) decreases with decreasing temperature and exhibit a sharp superconducting transition. Upper critical magnetic field Hc2 of the heavy R compounds (R from Dy to Yb) were measured and the highest initial slope |dHc2/dTc|Tc yet found for above 90 K superconductors was exhibited in TmBa2Cu3O7-δ with a value of 2.8 tesla/K.
Magnetic Properties of the High Tc Y–Ba–Cu–O System
Authors: Song S. N. , Hwu S. J. , Poeppelmeier K. , Mason T. O. , Ketterson J. B.
Published: March 2014

The superconducting properties of a series of Y–Ba–Cu–O compounds were studied. The d.c. susceptibility data are used to establish part of the phase diagram and the volume fraction of the superconducting phase scales accordingly. Based on the resistivity, magnetization and critical field measurements, various parameters which characterize these superconductors were derived.
High-Tc Superconductivity and Phase Diagram of (La1-xBax)2CuO4-y
Authors: Fujita Toshizo , Aoki Yuji , Maeno Yoshiteru , Sakurai Junji , Fukuba Hitoshi , Fujii Hironobu , Okamoto Tetsuhiko , Kumagai Kazuo , Kurisu Makio , Kadomatsu Hideaki , Fujiwara Hiroshi
Published: March 2014

The lattice, magnetic and superconducting properties of the oxides, (La1-xMx)2CuO4-y (M=Ba,Ca), were extensively investigated as a function of both temperature T and Ba-concentration x. For x > 0.025 the compounds show a superconducting transition, with which two different types of phase transitions were found to compete in the T-x plane; crystal distortion from a tetragonal to an orthorhombic lattice and antiferromagnetic ordering. External hydrostatic pressure tends to depress the magnetic ordering and to enhance superconductivity.
Temperature-Dependent EXAFS Spectra of YBa2Cu3O7-δ
Authors: Gygax S. , Crozier E. D. , Alberding N. , Bauchspieß K. R. , Seary A. J.
Published: March 2014

We present EXAFS data on YBa2Cu3O7-δ taken at four temperatures: 80 K, 112 K, 170 K, and 297 K. Spectra from both the Y edge and Cu edge are analyzed for the mean distances to near neighbors and the mean square relative displacements, σ2. The distances show small temperature dependences. The σ2's are unusal, decreasing more strongly at low temperature (112 K to 80 K) than at high temperature (300 K to 170 K). This could indicate some softening of the bond strengths and may indicate a phase transition.
Superconductivity in YM2Cu3O7-δ (M=Ba, Sr) Family
Authors: Oda Migaku , Murakami Toshiaki , Enomoto Youichi , Suzuki Minoru
Published: March 2014

The relation of the superconducting transition temperature (Tc) to the structure in YBa2Cu3O7-δ samples and the Sr substitution effect on the Tc are examined. From these studies, it is found that the superconductivity in YM2Cu3O7-δ (M=Ba, Sr) family is sensitive to the structural change which is caused by the difference in both the amount and the distribution of the oxygen vacancies in the Cu plane between the Ba planes.
Correlations among Thermal Processing, Superconducting Properties, and Microstructure in La1.85Sr0.15CuO4
Authors: Christen D. K. , Thompson J. R. , Sekula S. T. , Boatner L. A. , Sales B. C. , Pennycook S. J.
Published: March 2014

For various thermal processing conditions, measurements of the electrical transport and superconducting magnetic properties have been correlated with the microstructure as determined by X-ray diffraction and transmission electron microscopy. We find the largest critical current densities Jc are associated with the presence of coherent second-phase precipitates, and are significatly higher than for materials containing only grain boundaries or dislocations as flux pinning sites. Low-temperature annealing in oxygen results in nearly perfect, defect-free grains, separated by clean, planar grain boundaries. We conclude that the temperature-dependent diamagnetic response below Tc cannot be explained by the observed gross microstructure.
Superconductivity in High Tc Rare Earth–Ba–Cu Oxide
Authors: Murakami Masato , Teshima Hidekazu , Morita Mitsuru , Matsuda Shoichi , Hamada Hiroki , Matsuo Munetsugu , Inuzuka Takayuki , Suyama Ryuji , Snuzuka Masaaki , Sawano Kiyoshi , Kubo Hiroshi , Abe Mitsunobu , Nagumo Michihiko
Published: March 2014

We report the superconductivity in rare earth–Ba–Cu–O system and the identification of the phase responsible for superconducting behavior. The Tc offset for the La compound is comparable to that observed for Y–Ba–Cu–O. We also found that mixed rare earth compounds are high Tc superconductors. Some results on magnetic properties are also given.
Flow Visualization Study on Large-Scale Vortex Ring in He II
Authors: Murakami Masahide , Hanada Masaya , Yamazaki Tsutomu
Published: March 2014

The behavior of large-scale vortex rings in He II is studied by the application of the method of flow visualization. A vortex ring is formed by pushing a piston and the resulting flow field is visualized with neutrally buoyant hydrogen-deuterium particles as tracers. The development and the translational motion of rings are examined from sequential still pictures.
Temperature Dependence of Electrical Resistance in (La1-xSrx)2CuO4 Superconductors between 4.2 K and 1000 K
Authors: Mori Katsunori , Isikawa Yosikazu , Kobayashi Koichi , Sato Kiyoo
Published: March 2014

The temperature dependence of electrical resistance, R(T), for (La1-xSrx)2CuO4 system was measured in the temperature range from 4.2K to 300K. Especially, for the sample x=0.075 the measurement was extended up to 1000K and it was found that for R(T)∝Tn, the value of n was about 1.1.
High Tc Superconductivity in Metallic Oxide Compounds
Authors: Bánkuti J. , Gál M. , Horáth G. , Kirschner I. , G.-Sólymos K. , Torkos K.
Published: March 2014

Different preparation techniques were elaborated for obtaining La–Ba–Cu–O, La–Sr–Cu–O, Y–Ba–Cu–O, Y–Sr–Cu–O, Y–La–Ba–Cu–O and Y–La–Ba–Sr–Cu–O metallic oxide superconductors. Physical and chemical properties of them were analysed by thermogravimetry, powder X-ray, SEM, electron microprobe and SIMS which hint at a multiple-phase structure of the compounds in question. Tc for one part of samples is higher than 50 K and for the other part falls into liquid nitrogen temperature range above 90 K. Superconductivity was confirmed by magnetic measurements too. A change in Fermi-surface topology due to the increasing additive material content and a supplementary percolation process can be treated as the main effects for high-Tc superconductivity.
Influence of Chemical Pressure on the Superconductivity of La1.8Sr0.2CuO4
Authors: Grover A. K. , Dhar S. K. , Paulose P. L. , Nagarajan V. , Sampathkumaran E. V.
Published: March 2014

The influence of Ca in place of Sr and Eu in place of La on the superconducting and normal state behaviour of La1.8Sr0.2CuO4 has been investigated. Both the substituents tend to depress the superconducting transition temperature, whereas the degree of semiconducting (localization)-like behaviour in resistance for the air-annealed specimens in the normal state are widely different. The data are discussed in terms of possible size and charge mismatch effects.
Electron Impact Excitation and Ionization of 4He Clusters
Authors: Buchenau H. , Northby J. A. , Winkler C. , Toennies J. P.
Published: March 2014

Neutral 4He clusters have been produced in a low temperature nozzle expansion and studied in a high resolution TOF apparatus. They are observed by electron impact ionization followed by quadrupole mass analysis. It is possible to distinguish charged fragments resulting from cluster ionization from those derived from the unclustered beam component by their differing arrival times at the detector. In addition, a metastably excited neutral product has been observed. Appearance potential experiments suggest that the metastable species is not simply related to the metastable excitations previously observed in the bulk liquid.
Lattice Dynamics of BaPb0.75Bi0.25O3
Authors: Reichardt Winfried , Weber Werner
Published: March 2014

The phonon dispersion curves and the phonon density of states for superconducting BaPb0.75Bi0.25O3 have been measured by neutron scattering. Almost all phonon branches could be mapped out. However, we could not detect the band of `breathing' type vibrations of O octahedra which was expected to show strong coupling to the conduction electrons. Instead, defect type modes are found near 42 meV. These modes are interpreted as local `breathing' type vibrations, associated with static distortions of O octahedra.
Sound Propagation in High Temperature Superconductors
Authors: Lüthi B. , Wolf B. , Kim T. , Grill W. , Renker B.
Published: March 2014

Measurements of the temperature dependence of longitudinal and transverse sound velocities in high temperature superconductors are presented and discussed.
Suppression of the Critical Current and Transition Temperature of Superfluid 3He in a Single Submicron Cylindrical Channel
Authors: Pekola J. P. , Davis J. C. , Packard R. E.
Published: March 2014

The flow of superfluid 3He through a single cylindrical channel of 0.7 micron diameter is studied. Suppresion of the transition temperature and of the depairing critical current density are observed indicating that the boundary condition at the wall is that for diffuse quasiparticle scattering. The suppresions agree reasonably well with model calculations for this geometry using the diffuse scattering boundary conditions.
Some evidence for dissipation of superflow due to thermal activation of 2π phase slips of the order parameter inside the channel is seen.
Sputter-Deposited Films of Perovskite Compound and Nb–Si–O System
Authors: Ōgushi Tetsuya , Hakuraku Yoshinori , Ōtawa Toshiyuki , Suresha G. N. , Honjo Yutaka , Ōzono Yoshihisa , Kawano Iwazo , Numata Tadashi
Published: March 2014

One of the authors of this manuscript has reported a resistance anomaly of very thin Nb–Si films. The anomaly is marked by a sudden drop in the resistance by a factor of ∼103 at a temperature (TD) ∼180K. This behavior bears many resemblance to that of a superconductor. It became apparent to us that the presence of oxygen during sputtering remarkably improved the stable yield of the films with this anomaly and the highest TD obtained is ∼250K. These might be attributable to that in the ceramic superconductor.
I-V Characteristics of (La1-xSrx)2CuO4 Superconducting Films and Infrared Irradiation Effects
Authors: Moriwaki Kazuyuki , Enomoto Youichi , Murakami Toshiaki
Published: March 2014

Superconducting (La1-xSrx)2CuO4 (LSC) films have been fabricated using a sputtering method. Both the (100)-preferred polycrystalline films and the (103)-plane single crystalline films are found to exhibit I–V characteristics similar to those by weak-link type JJs which could be apllied to highly sensitive infrared detectors. The I–V characteristics for the LSC films might be ascribed to the layered structure with perovskite and rock salt repetition. Voltage shift in the I–V curve through infrared irradiation on the single crystalline LSC films is measured. The responsivity is on the order of 103 V/W at a 1.3 micrometer wavelength.
Anisotropy Effects upon the Magnetic Properties of High-Tc Superconductors
Authors: Kogan Vladimir G. , Clem John R.
Published: March 2014

All known high-Tc superconductors are strongly anisotropic. We use the mass tensor formulation of the Ginzburg-Landau theory to discuss the effects of anisotropy upon various magnetic properties of single- and polycrystals. We also consider the influence of anisotropy upon the width of the resistive transition as a function of field.
Theory of the Magnetization of Granular Superconductors: Application to High-Tc Superconductors
Authors: Clem John R. , Kogan Vladimir G.
Published: March 2014

We calculate the dc magnetization of a three-dimensional array of weakly Josephson-coupled superconducting grains whose dimensions are of the order of the intragranular weak-field penetration depth. Because of significant flux penetration into small grains, the initial slope of the magnetization versus applied field not only is smaller than that for very large grains of the same shape, but also decreases with increasing temperature and vanishes at the critical temperature. The same behavior is expected for the ac susceptibility versus increasing temperature in a sample cooled in zero field. The dc magnetization is found to exhibit a corresponding size-dependent suppression for all fields up to the upper critical field.
Mechanism of High-Tc Oxide Superconductors
Authors: Soda Toshio
Published: March 2014

The mechanism of recently discovered high Tc Y–Ba type copper oxide superconductors is proposed by the two conduction band model of heavier and lighter electrons, taking into account of the infrared divergent effect due to the Fermi surface of the lighter electrons. The interaction between two heavy electrons, via a screened Coulomb interaction between a heavier and a lighter electrons, turns out to be attractive when their relative momentum is the Fermi momentum, though modified largely by the on site and screened Coulomb interaction but slightly by the Ruderman-Kittel-Yosida type spin-spin interaction between them. Tc is estimated to be of the order of one hundred degree Kelvin, depending on the magnitudes of the two band widths.
Upper Critical Field of High Tc Superconducting Oxides
Authors: Kobayashi Norio , Sasaoka Takaaki , Oh-Ishi Katsuyoshi , Sasaki Takako , Kikuchi Masae , Noto Koshichi , Syono Yasuhiko , Muto Yoshio
Published: March 2014

The upper critical field of the superconducting oxide La2-xSrxCuO4-y was studied as a function of the Sr concentration by electrical resistance measurements under magnetic fields up to 26 T. The slope of upper critical field near Tc and the electrical resistivity show anomalous concentration dependences. The results are related to the orthorhombic-to-tetragonal phase transition.
Normal and Superconducting State Properties of La2-xSrxCuO4
Authors: Kwok W. K. , Crabtree G. W. , Hinks D. G. , Capone D. W.
Published: March 2014

The resistivity, magnetoresistance, superconducting transition temperature, and critical fields for La2-xSrxCuO4 were measured as a function of x. We find systematic behavior in the transition temperatures and critical field slopes, but not in the resistivities.
Preparation, Structure, Transport Properties and Photoemission Studies of the High-Tc-Superconductors YBa2Cu3O4-δ and La1-xSrxCuO4
Authors: Schindler W. , Grassmann A. , Schmitt P. , Ströbel J. , Niederhofer H. , Adrian G. , Saemann-Ischenko G. , Adrian H.
Published: March 2014

Single-phase bulk-YBa2Cu3O9-δ was prepared by solid-state reaction under oxygen atmosphere as well as exclusively in air, observing a transition from semi- to superconducting behaviour depending on the preparation. Low temperature powder x-ray diffraction from 300K down to 10K was carried out to investigate the structure. The upper critical field is estimated to Bc2 (T=0) = 110T (Tc-midpoint), critical current densities of up to 180A/cm2 are determined at different temperatures in magnetic fields up to 7T. Photoemission experiments show, that grains are only coupled by semiconducting interfaces and reveal a strong hybridization between O-2p and Cu-3d states.
Superconducting Wires of High Tc Oxides
Authors: Ohmatsu Kazuya , Ohkura Kengo , Takei Hiromi , Yazu Syuji , Hitotsuyanagi Hajime
Published: March 2014

Superconducting wires of Y–Ba–Cu–O system have been investigated. Wires were fabricated by powder method. The wires were successfully reduced to a small diameter. Wires of Y1Ba2Cu3O7 exhibit zero resistance at 90 K.
Ultrasound Attenuation due to Order Parameter Fluctuations in Impure p-Wave Superconductors
Authors: Monien Hartmut , Tewordt Ludwig , Scharnberg Kurt
Published: March 2014

The peak in the attenuation of longitudinal ultrasound in UBe13 and UPt3 below the superconducting transition has been taken as evidence for unconventional superconductivity. By studying two particular p-wave states and their collective degrees of freedom in the presence of finite quasiparticle mean free paths ℓ we show that such an interpretation of the attenuation peak is indeed feasible. Even in the hydrodynamic limit qℓ≪1 and for sound frequencies ωs/2π much less than typical collective mode frequencies, real order parameter fluctuations yield attenuation peaks in reasonable agreement with experiment, if an energy dependent normal state density of states is assumed, as seems appropriate for heavy fermion systems.
Pauli Enhancement of Hc2 of a Triplet Superconductor
Authors: Jaffe John E.
Published: March 2014

For a triplet superconductor in a magnetic field, a phase is predicted in which spins in only one direction are paired, as in the Al phase of 3He. The upper critical field Hc2(T) separating this phase from the normal state is larger than the Hc2 one would have in the absence of the Pauli paramagnetism responsible for the new phase. The effect depends on the derivative of the density of states at the Fermi energy and is reduced but not destroyed by spin-orbit coupling. Comparison is made to the superconducting phase diagram of UPt3 measured by V. Muller et. al. [Phys. Rev. Lett. 58, 1224 (1987).]
Current-Carrying States in Anisotropic Superconductors at T=0
Authors: Choi C. H. , Muzikar Paul
Published: March 2014

There is much speculation that the heavy fermion superconductors may have order parameters with a nontrivial k-dependence. Thus, the expected properties of superconductors with such order parameters are of great interest. Here we discuss states with a nonzero vs, for two such order parameters, a triplet gap of the A phase from, and a singlet gap with a particular d-wave symmetry. We compute supercurrent, magnitude ofthe order parament, and density of states, all as functions of vs; We work at T=0, and inculed the effect of impurity scattering. Both the impurities and the supercurrent strongly affect the spectrum of low energu excitations.
Stable Superconducting State in the Presence of Spin Density Waves in URu2Si2
Authors: Kato Masaru , Machida Kazushige , Ozaki Masa-aki
Published: March 2014

We investigate theoretically a stable superconducting state in the presence of the spin density wave (SDW). First we enumerate possible pairing states both with odd- and even-parity under two-dimensional square symmetry and classify them into two classes less competitive and competitive witn SDW. Setting up a model Hamiltonian with imperfect nesting Fermi surface, we calculate physical properties of these states. Experimental relevance to URu2Si2 is briefly discussed. It is concluded that the state developed is highly unlikely to be isotropic singlet pairing and should be anisotropic state with even or odd parity.
The Magnetic Phase Transition of the Magnetic Superconductor TmRh4B4
Authors: Willekers R. W. , Bosch W. A. , Meijer H. C. , Postma H.
Published: March 2014

Measurements of the electrical resistivity, the ac susceptibility and the specific heat of the magnetic superconductor TmRh4B4 have revealed a magnetic phase transition in zero field at 0.49±0.01 K, and at 0.415±0.015 K for fields between 0.36 and 0.86 T.
Hysteresis phenomena and a rapid variation of susceptibility with field suggest a metamagnetic transition. Some results of measurements on Tm0.7Y0.3Rh4B4 are given.
Analysis of Mixed State in Metamagnetic Superconductors
Authors: Wong On , Whitehead J. P. , Umezawa H.
Published: March 2014

The application of the boson method of superconductivity to ferromagnetic superconductors [1,2,3] is extended to examine a particular class of magnetic systems which, at low temperature, exhibit a field induced transition from an antiferromagnetic state to a ferrimagnetic state at a critical field H3. The method is self-consistent and the flux quantisation condition satisfies automatically.
Coexistence of Antiferromagnetism and Superconductivity
Authors: Teraoka Yoshihiro
Published: March 2014

A coexistence of antiferromagnetism and superconductivity has been investigated theoretically in Cr and its alloys with many defects. By use of the interacting virtual state approach, we have calculated the sublattice magnetization and the density of states at the Fermi energy in the antiferromagnetic state. The strongly enhanced density of states leads us to the superconductivity with a relative high Tc.
Superconducting Behavior of Cu1.8Mo6S8 at High Pressures
Authors: Janawadkar M. P. , Sastry V. Sankara , Hariharan Y. , Radhakrishnan T. S.
Published: March 2014

Low temperature electrical resistance measurements on the Chevrel phase compound (CPS) Cu1.8Mo6S8 upto a quasihydrostatic pressure of 60 kbar are reported. These measurements show a negative dTc/dP, increase in the width ΔTC to several Kelvin, and suppression of the structural phase transition seen at ambient pressures.
Magnetization Measurements on the Reentrant Superconductor ErxY1-xRh1.1Sn3.6
Authors: Blank D. H. A. , Flokstra J.
Published: March 2014

We performed magnetization measurements on the reentrant magnetic superconductor ErxY1-xRh1.1Sn3.6 (x = 0.8, 0.9, 1) using a SQUID magnetometer in a 3He-4 He dilution refrigerator. The temperature was varied between 50 mK and 2 K and different background fields were used.
The experiments were concentrated on the behaviour of the magnetic flux within the samples. The flux is frozen at the superconducting transition temperature when the sample is cooled from the paramagnetic region and reaches the value for the ferromagnetic state when superconductivity is destroyed. The hysteretic behaviour of the flux with decreasing and increasing temperature gives information about the critical fields and currents of the compounds.
Transverse Surface Impedance of Normal and Superfluid 3He
Authors: Einzel D. , Hirschfeld P. J. , Wölfle P.
Published: March 2014

We present a variational calculation of the transverse surface impedance for normal and superfluid 3He which includes, through a microscopic boundary condition, a general class of boundary scattering laws for thermal excitations. Particularly, we study the consequences of specular, backward and (for superfluid 3He–B) Andreev scattering.
Thermal Diffusive Conductivity of Dilute Superfluid 3He–4He Mixtures
Authors: Chui T. C. P. , Lipa J. A.
Published: March 2014

We describe a new technique for measuring the effective thermal conductivity of superfluid 3He–4He mixtures. Our results confirm the large departures from hydrodynamic theory reported previously. Our analysis suggests that the measured conductivity is the finite thermal diffusive conductivity of superfluid helium in the absence of counterflow. This conductivity need not diverge in the limit of small 3He concentration.
Metallic Glassy Behavior and Superconductivity in Ion-Beam-Sputtered Nb Films
Authors: Kuwasawa Yoshinori , Kobayashi Yasushi , Nakano Shigeru
Published: March 2014

We report the findings of the metallic glass like behavior to superconducting transition on the highly disordered Nb films, fabricated by high voltage ion beam sputtering. We have measured the temperature dependence of electrical resistance from 1.5 to 300 K and the magnetoresitance at low temperture. In all samples, the temperature coefficient of resistivity becomes negative and tends to be more negative with increasing the resistivity ρ(300K) which depends upon the substrate temperature during deposition. The upper critical field Hc2(T) for superconducting samples was greatly enhanced over that of crystalline Nb films.
“Dissipative” Phase Transition in Granular Superconductors
Authors: Panyukov S. V. , Zaikin A. D.
Published: March 2014

Superconducting phase transition in disordered granular films with the normal state resistance caused by quasiparticle tunneling is studied within the framework of the percolation model. The value of the “critical” dimensionless normal state conductance αc between individual grains becomes larger for larger values of disorder. In the vicinity of the percolation transition point, αc is independent of the grain charging energy and αc∼(p-pc)-1, pc being the “critical” probability.
Upper Critical Field of the Anisotropic Organic Superconductors, (TMTSF)2CIO4
Authors: Murata Keizo , Tokumoto Madoka , Anzai Hiroyuki , Kajimura Koji , Isiiiguro Takehiko
Published: March 2014

The anisotropy of the upper critical field, H
C2, of the organic superconductor, (TMTSF)2CIO4 was determined. The principal axes of H
C2 were associated with the axes of the lattice. From the temperature dependence of H
C2, Pauli (Clogston) limited behavior was apparent when the magnetic field was parallel to the a-axis, which suggests the singlet superconductivity. Coherence lengths of two samples were calculated and found to be strongly dependent on T
C.
Mechanism of Superconductivity in Organic Superconductors
Authors: Yamaji Kunihiko
Published: March 2014

Strong interactions between the HOMO level and totally symmetric intramolecular vibration modes in the TTF-analog molecules is pointed out to lead to important attractive interactions between electrons in the organic metals composed of these molecules. A model taking account of them and also of the Coulomb interaction etc. is solved to give the superconducting transition temperature Tc, which proves to have 8 K in the reasonable parameter range for the β-(BEDT-TTF)I3 superconductor. This mechanism is claimed to work also for the (TMTSF)2X salts. No appearance of CDW and the spin amplitude of SDW in the latter salts become understandable in the present scheme.
Superconductivity of Mo/Si Multilayer Films
Authors: Nakajima H. , Fujimori H. , Ikebe M. , Muto Y.
Published: March 2014

Multilayered Mo/Si thin films have been prepared by a dual rf-magnetron sputtering technique. X-ray diffractometry shows that the multilayer films with the modulation wavelength λ longer than 30 Å are composed of bcc Mo and amorphous Si, while with λ shorter than 30 Å are both amorphous. In the multilayers with d(Mo)=d(Si) (λ=d(Mo)+d(Si)), a maximum of Tc is 6.10 K for λ=23 Å. Tc decreases to 5 K with decrease of λ , which is close to Tc of amorphous Mo56Si44 alloy. Tc also decreases with increase of λ, which is explained by the proximity effect due to crystalline Mosublayers. The superconductivity of this multilayer films is concluded to result from amorphous MoSi phase. The anisotropy ratio, Hc2///HC2⊥, is 1.5–1.6 for λ shorter than 40 Å. This value of the anisotropy ratio is interpreted by the surface superconductivity. Thus, the superconductivity is 3-dimensional in this range of λ. The anisotropy increases to 29.0 for λ=234 Å. The large anisotropy is attributed to interlayer decoupling due to the amorphous Si and crystalline Mo.
Syntheses of A15 Nb3(Si, Ge) Films by Alternated Sputtering Technique
Authors: Nakamura Toshiyuki , Yamamoto Hiroshi , Tanaka Masaichi
Published: March 2014

A Nb-Ge-Si film was prepared by an alternated sputtering technique to examine the stable growth of Nb3Si with a single A15 phase. The film with a compositionally graded structure was deposited. The composition of the layer was changed from Nb-rich (Nb84Ge9Si7) of the base layer toward the stoichiometry (Nb75Ge2Si23) at the surface. The optimum sputtering condition and aiso the value of the compositional gradient were investigated for syntheses of high-Tc layers. As a result, the value of Tcon attained up to above 19 K in the Nb-Ge-Si film which contained Ge as little as 2 at.% at the stoichiometry and had a single A15 phase. The maximum Tc observed is the highest of all Nb-Si compounds.
Cu63 NMR Study of Superconducting Cu/Nb Superlattice
Authors: Aoki R. , Zheng G-Q. , Kohori Y. , Oda Y. , Asayama K. , Wada S. , Obi Y.
Published: March 2014

Nuclear spin lattice relaxation time T1 of Cu63 was measured for Cu/Nb multilayered sample, in each 50 layers of Cu and Nb with thicknesses of 400 Å and 245 Å. The superconducting transition was observed by magnetic induction at Tc=4.6 K. As temperature T is lowered below Tc, the relaxation rate T1
-1 is once increased and then decreased exponentialy. This behavior is characterized by the existence of superconducting energy gap 2Δ=0.96 meV=2.4 kBTc in Cu. For further lowering of T below 0.8 K, the rapid decreasing in T1
-1 was replaced by a gradual change almost proportional to T.
Commensurate Vortex States of the Infinite Superconducting Microladder
Authors: Fink Herman J. , López A. , Rodrigues D.
Published: March 2014

The second order phase boundary of an artificial structure such as the microladder is shifted to higher temperatures when the order parameter is spatially modulated by a wave vector q compared to no modulation (q = 0). Commensurate solutions exist when q=π/m where m is an integer \geqslant2. For these solutions the relative order parameter, its phase and the current patterns along the ladder are calculated near the phase boundary. We found that the period of the phase is twice as large as that of the modulus of the order parameter and that of the vortex current pattern. When m is an even integer every m-th transverse branch contains a null of the order parameter across which the phase flips by π with no current passing through these branches.
Quasi-Two-Dimensional Superconductivity
Authors: Mishima Akiomi
Published: March 2014

The superconductivity of the quasi-two-dimensional (2D) electron system with the nearest-neighbor transfer energy T1 and the next-nearest-neighbor transfer energy T2 on a square lattice is studied as a model of the superconductivity in Ba(Sr)-La-Cu oxides within the mean field theory. It turns out that the superconducting critical temperature Tc and the superconducting energy gap at T=0 Δ0 are not exponential below the critical value of the coupling constant λ. The value of Tc is 42 K and 2Δ0/kBTc≃3.58 (kB, is the Boltzmann constant) for T2/T1=0.2, λ/2T1=0.17 and 2T1=1 eVc.
Shear Modulus Softening of a Lattice of Superconducting Vortices
Authors: Tang X.-M. , Racine G.-A. , Leemann Ch. , Martinoli P.
Published: March 2014

The critical currents of superconducting films, in which the vortex lattice is exposed to the pinning field created by a periodic thichness modulation, show an unusual non-monotonic temperature dependence near the superconducting transition. This anomalous feature, which is observed when the flux lattice is commensurate with the periodic film structure, is consistent with a softening of the shear modulus of the vortex lattice due to anharmonic “phonon-phonon” interactions.
The Influence of Epitaxy on the Critical Current Densities of Evaporated Nb Films
Authors: Oya Gin-ichiro , Komukai Tetsuro , Sawada Yasuji
Published: March 2014

Critical current densities Jc and corresponding global pinning forces per unit volume Fp (in transverse magnetic field, at k.2K) for high-quality epitaxial single-crystal Nb films are extensively investigated in relation with the crystallinity of the films, compared with those of polycrystalline Nb films. It is observed that the single-crystal films with very smooth surfaces have much higher Jc (above 2×109 A/m2) at low fields than the polycrystalline films with less smooth furfaces. The increase in Jc at low fields for the single-crystal films is found to be caused by the shift of the position of the peak in Fp(b) to lower reduced magnetic field b and the increase in hight of the peak, without producing much change in Fp(b) at high b in perpendicular and parallel field orientations. The high Jc for the single-crystal films may predominantly be due to the existence of surface barriers (predicted by Bean and Livingston) on the films.
Grain Boundary Pinning in Polycrystalline NbN Films
Authors: Pruymboom A. , Hoondert W. H. B. , Zandbergen H. W. , Kes P. H.
Published: March 2014

An approximate closed form expression for the elementary pinning force of a grain boundary is used to evaluate the bulk pinning force, in the isolated vortex regime, of a type-II superconductor with grain sizes smaller than the flux line spacing. A comparison is made with experimental results on NbN films.
Heat Transfer Investigations of Superconductors in Pressurized He II
Authors: Ruppert Udo , Yang W. Z. , Lüders Klaus , Funaki K. , Takata Y. , Takeo M. , Irie F.
Published: March 2014

Measurements of steady state and transient heat transfer on bare superconducting NbTi-wires in pressurized super fluid helium were performed. Results of the extreme thermal stability of the cooling, which explains the vanishing propagation velocity under these conditions, are reported.
Superconductivity and Field Effect Transistors
Authors: Kleinsasser A. W. , Jackson T. N.
Published: March 2014

A gate-controlled semiconductor-coupled proximity effect weak link acts as a superconducting field effect transistor (FET). In this paper we present a semi-quantitative analysis of the static electrical properties of such a device, comparing theory and available experimental measurements. We emphasize that the critical current-resistance product, an important figure of merit for potential applications, is often significantly larger than that expected from theory. We offer an explanation for this discrepancy and describe experiments in progress to test it. Our analysis can be used to discuss the feasibility, advantages, and disadvantages of these devices, both for scientific investigations and for applications, allowing comparison of the potential of superconducting FETs with more familiar normal FETs.
Reduced Density Matrices and Two-Fluid Model for Fermi Superfluid
Authors: Visoottiviseth K. , Thiankusol P.
Published: March 2014

From the assumption of the off-diagonal long-range order (ODLRO) in the reduced density matrices (RDM) and the neglect of long range three-particle correlation, the equation of motion for the time dependent macroscopic pair wave function ϕ (x,y) in Fermi superfluid has been derived, clearly showing the gauge invariance. The normal (noncondensate) density and super (condensate) density have thus been defined. The wave equation then leads to the setting up a “two-fluid” hydrodynamics for Fermi superfluid, probably in superconductors.
Critical States for Fluxon Dynamics in Long Josephson Junctions
Authors: Pace Sandro , Cirillo Matteo , Pagano Sergio
Published: March 2014

We have studied in an analytical way the static configurations of the superconducting phase in long one-dimentional Josephson junctions in the presence of both an external magnetic field and a uniform bias current. Under some conditions unstable static states can be generated by the reflection of a fluxon at the junction edges. An analysis of such unstable configurations can provide information on the stability of the various dynamical states in the junction.
Reflection Properties of Fluxon in a Josephson Transmission Line
Authors: Akoh H. , Sakai S. , Takada S.
Published: March 2014

Direct observation is reported of fluxon reflections in a Josephson transmission line (JTL) using a Josephson sampler. It is found that a single fluxon, an antifluxon, and multi-antifluxons are reflected depending on the bias current at the end of the JTL. The observed reflection properties, including the interaction between reflected antifluxons, can be satisfactorily explained by numerical simulations taking account of the nonlinear shunting loss and the surface loss.
Current-Phase Relation for Flow of an S-Wave Paired Superfluid through a Cylindrical Channel of Finite Length
Authors: Hook J. R.
Published: March 2014

The Ginzburg-Landau equations are used to investigate superflow through a cylindrical orifice of radius R and length L. The order parameter is taken to be a complex scalar ψ, appropriate to an s-wave paired superfluid. It is assumed that ψ=0 on the surfaces of the orifice and that rigid boundary conditions may be employed at the ends of the tube. The use of a variational form for the radial variation of ψ reduces the problem to a one dimensional one. The critical value of L for each value of R has been calculated at which changeover from a single-valued to a multivalued current-phase relation occurs. The maximum supercurrent for tubes of various geometries has also been calculated.
Thermal Fluctuations in Magnetic Field and the Josephson Supercurrent in Pb–Ag–Pb (SNS) Junction
Authors: Nagata Shoichi , Taniguchi Satoshi
Published: March 2014

The effect of thermal fluctuations on the critical current of Pb-Ag-Pb (SNS) Josephson junctions has been studied. When the critical current goes to zero in the magnetic field (around the minimum positions of the Fraunhofer pattern), the effect of thermal fluctuations is significantly enhanced. In the presence of strong fluctuations, the envelope of the maximum in the Fraunhofer pattern is proportional to 1/H2, which is quite different from the form of 1/H in the absence of fluctuations.
Knudsen Flow and Effective Shear Viscosity of Liquid 3He
Authors: Einzel D. , Parpia J. M.
Published: March 2014

We present new torsional oscillator data on the shear viscosity of liquid 3He at low temperatures. They are analyzed with a theory of Poiseuille flow, which is also applicable in regimes of temperature and pressure where the Knudsen number, characterizing the flow of the thermal excitations, may become large.
Observed Transition from a Weak Link to a Tunnel Josephson Junction
Authors: Ohta Hiroshi , Takahata Mitsuhiro , Yamada Yasuharu , Takahashi Yoshiaki
Published: March 2014

Electrolytical anodization can change short weak links of niobium into small-area tunnel Josephson junctions. The critical current of anodized weak links can have either temperature dependence of a short weak link calculated by Kulik & Omel'yanchuk or that of a tunnel junction given by Ambegaokar & Baratoff. These observations agree with the recent general theory presented by D.B.Arnold which explains the temperature dependenceof the critical currents both of metallic weak links and tunnel Josephson junctions consistently.