bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared and Light Absorption Spectra of High-Tc Superconducting Oxides: La–Ba–Cu–O, La–Sr–Cu–O, and Y–Ba–Cu–O
Authors: Ogita Norio , Udagawa Masayuki , Ohbayashi Kohji
Published: March 2014

Infrared absorption spectra of (La1-xBax)2CuO4, (La1-xSrx)2CuO4, (La1-xSrx)2NiO4, (La1-xNdx)2CuO4, and Y-Ba-Cu-O systems have been measured. In (La1-xBax)2CuO4, and (La1-xSrx)2CuO4, an absorption peak at about 680 cm-1 has been found disappear at concentrations where the superconductivity is observed. In (La1-xSrx)2NiO4, no such change has been observed. In (La1-xNdx)2CuO4 a considerable decrease of 680 cm-1 peak intensity has been found with an increase of x. In Y-Ba-Cu-O system, no specific infrared absorption peak has been observed in the energy region of 400 - 4000 cm-1. In all materials we measured, we could not detect any clear visible light absorption spectrum.
Spectral Studies on the High Tc Superconductors
Authors: Tanaka Jiro , Shimizu Masaaki , Kamiya Koji , Shimada Michihiro , Tanaka Masashi
Published: March 2014

Optical spectra of high Tc superconductors were investigated in the far-infrared, infrared and visible region, which showed several elementary excitations and their interactions. The temperature dependence of the reflection spectra as well as the Raman spectra were investigated above and below the transition temperatures. A possibility of an electron and an exciton interaction is considered.
NMR Study of Motion of 3He in Adiabatic Flow of He II
Authors: Okuyama Mineo , Satoh Toshimi , Satoh Takeo , Fukuda Kohji
Published: March 2014

With a new-type mutual friction force introduced by us recently to explain the temperature distribution along the capillary of adiabatic flow of HeII, the normal fluid velocity vn has been calculated. It shows a very remarkable behavior in the net mass flow velocity dependence. In order to confirm the result, a NMR technique is applied to obtain the velocity of 3He atoms, v3, added to the system. It is found that there is a close similarity in the net mass flow velocity dependence between vn and v3. This supports the validity of our thermohydrodynamic description of adiabatic flow with a new-type mutual friction force.
Experimental Electronic Structure Studies of the High-Temperature Superconductors La2-xSrxCuO4 and Ba2GdCu3O7-y
Authors: Nücker N. , Fink J. , Renker B. , Ewert D. , Weijs P. J. W. , Fuggle J. C.
Published: March 2014

X-ray induced photoelectron spectroscopy (XPS), bremsstrahlung-isochromat spectroscopy (BIS), and electron energy-loss spectroscopy (EELS) were used to investigate the electronic structure of La2-xSrxCuO4. The samples with x=0 show near the Fermi energy a smeared out gap or very low density of states in a region of ∼2 eV. Upon replacement of La by Sr, this gap is filled with defect states, the intensity of which is proportional to x. Similar spectra were observed for Ba2GdCu3O7-y (TC=94K). This may indicate, that the density of states near EF in this compound may be related to defects on the O sites too.
Capillary Flow of Superfluid 3He–4He Mixtures
Authors: Mudde R. F. , Beelen H. van
Published: March 2014

Thermal counterflow in a 100 µm glass tube is investigated. The complex temperature profiles, registered along the flow path also in the regime of laminar flow, are analysed.
Anomalous Magnetism of the High-Tc Superconductors with Rare-Earth and/or Transition Element Ions–Static Susceptibility with Resistivity–
Authors: Minami Hidetoshi , Masumi Taizo , Hikami Shinobu
Published: March 2014

A series of the high-Tc superconductors Y–Ba–Cu–O system substituted Y– by rare earth ions Eu–, Gd–, Ho– or/and –Cu– by transition element ions –Mn–, –Ni– have been studied at 4.2∼120K from a stand-point of magnetism by using a microwave SQUID at 9 GHz. Anomalous coexistence of the magnetic phase with perfect diamagnetism in Ho–Ba–Cu–Oxide has been observed, whereas substitution of –Cu– by transition element ions yields delicate effects on superconductivity.
Superconductivity In Ba2Ln(Lanthanoids)Cu3O9-x Compounds
Authors: Yamada Tomoaki , Kinoshita Kyoichi , Matsuda Azusa , Watanabe Takao , Asano Yoshihiro
Published: March 2014

Superconductivity has been observed in Ba2LnCu3O9-x compounds with Ln=La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb. However, Pr, Ce, Tb and Lu compounds have not shown superconductivity. Lattice constants of these compounds which have an oxygen defect perovskite structure show definite relation to ionic radii of Ln. The effect of the crystal structure on superconductivity is discussed.
Identification of Novel High-Tc Superconducting Phase X1Ba2Cu3O7+d (X=Y, La; -0.5<d<1)
Authors: Semba Kouichi , Tsurumi Shigeyuki , Hikita Makoto , Iwata Tsunekazu , Noda Juichi , Kurihara Susumu
Published: March 2014

A novel high-Tc superconducting phase is found in the oxide X–Ba–Cu–O (X=Y, La). A sample with the composition Y1Ba2Cu3O7+d shows a sharp superconducting transition at 92.6 K (at the midpoint) with a width as narrow as 0.8 K. By means of X-ray powder pattern analysis and Electron Probe Micro Analysis, we have identified the high-Tc superconducting phase as the almost tetragonal oxygen-defect perovskite (ODP) with the unit-cell composition Y1Ba2Cu3O7+d (-0.5<d<1).
We found that the ODP phase also exists in the La–Ba–Cu–O system. Even in the ambient pressure, the Tc(end point) = 63 K was obtained. This Tc is about three times as high as that observed in K2NiF4 phase. This suggests that the ODP structure may be crucial for high-Tc superconductivity X–Ba–Cu–O system.
Production of “Fast” and “Exotic” Negative Ions in He II
Authors: Williams Charles D. H. , Hendry Philip C. , McClintock Peter V. E.
Published: March 2014

The “fast” negative ion provides, in principle, the basis for a determination of the Landau critical velocity for roton creation in HeII under its SVP; but precise measurements will require a more reliable ion source than those reported hitherto. It is known that a glow discharge above the liquid surface is necessary, but not sufficient, for the production of large fluxes of “fast” or “exotic” ions. Several new electrode geometries have been tested with HeII at 1.03K with variable results which are discussed. We report the new observation that the discharge must be white (rather than the more usual violet) for “fast” or “exotic” ions to be generated.
Superconductivity and Magnetism of the (La, Y)–Cu–O System
Authors: Takano Yoshiki , Tasaki Seiji , Takigami Hiroyuki , Sekizawa Kazuko
Published: March 2014

Superconductivity with the transition temperature of about 35 K observed in the La–Cu–O system is attributed to La2CuO4-δ phase with the orthorhombic K2NiF4 type crystal structure. Single phase La3Cu2O7 was synthesized under high pressure oxygen (5 atm. O2 at 650 °C). Single phase (La0.6Y0.4)3Cu2O7 was also synthesized in air at 1000 °C. Both of them, however, have the K2NiF4 type (not Sr3Ti2O7 type) structure and are semiconductive down to 4.2 K.
Superconductivity Studies on the High Tc Phase in the Y–Ba–Cu–O System
Authors: Rao G. V. Subba , Varadaraju U. V. , Thomas K. A. , Vijayashree R. , Raju N. P. , Srinivasan R. , De U. , Janaki J. , Radhakrishnan T. S.
Published: March 2014

Synthesis, characterization and superconducting behavior of the phases (i) Y2-xBaxCu2O5 (0\leqslantx\leqslant1.6) and (ii) YBa2Cu3+xO7+y (0\leqslantx\leqslant2.0) are reported. The composition YBa2Cu4O7+y shows a Tc (zero resistance) of 94K.
Superconductivity of the Ba–Y–Cu–O System in the Liquid Nitrogen Temperature
Authors: Zhao Zhao , Bairu Bairu , Shi Shi , Yinhuan Yinhuan , Lu Lu , Yong Yong , Wang Wang , Huisheng Huisheng , Zhao Zhao , Yuying Yuying , Li Li , Lin Lin
Published: March 2014

The oxide compounds of BaxY1-xCuO3-y (x=0.3–0.5) have been successfully prepared. The zero resistance temperature of the samples is at 91.5K, with Tc onsets higher than 100K. ac magnetic susceptibility measurements show that the superconducting phase at 82K is not less than 85% in volume.
High Tc Superconductivity in La1.8M0.2CuO4 (M=Ca, Sr, Ba) and (Y1-xBax)2CuO4
Authors: Yakhmi J. V. , Gupta L. C. , Gopalakrishnan I. K. , Umarji A. M. , Iye R. M. , Vijayaraghavan R.
Published: March 2014

Resistivity investigations have been carried out in La1.8M0.2CuO4 (M = Ca, Sr and Ba) which single phase materials with K2NiF4 structure. La1.8Sr0.2CuO4 exhibits a superconducting transition at T
c=34.2K with the width of transition ΔTc=2.5K. Tc for Ca1.8Ca0.2CuO4 is 20K. Barium doped material exhibits the onset of superconductivity in the neighbourhood of 30K. Adding Gd-impurity in the material, La1.75Gd0.05Sr0.2CuO4, broadens the transition considerably. Detailed investigations on the multiphase material (Y1-xBax)2CuO4 clearly shows that its superconducting behavior strongly depends upon the heat treatment. A single phase sample with chemical composition YBa2Cu3O6+x, prepared using a special heat treatment, exhibits zero resistance state at 107K.
Superconductivity in La1.85-xNdxSr.15CuO4
Authors: Kwok W. K. , Crabtree G. W. , Umezawa A. , Alp E. E. , Morss L. , Soderholm L.
Published: March 2014

The effect of magnetic impurities on the high Tc superconductor La1.85Sr.15CuO4 was investigated by replacing La with Nd. We find a depression of Tc and dHc2/dT with increasing Nd concentration which does not follow predictions of the pairbreaking effects due to magnetic impurities. We attribute our experimental results to a density of states effect.
Calculations of the Superconducting Properties of Cu–O Based Perovskite-Like Structures
Authors: Papaconstantopoulos D. A. , Pickett W. E. , Krakauer H. , Boyer L. L.
Published: March 2014

We have used the results of first principles local density band structure calculations to calculate the McMillan-Hopfield parameter η in a series of ordered cubic perovskite and layered perovskite structures of the form MxNyCuOz, where M and N are La, Ba, and Cs. We find relatively low values of η compared to those of transition metal superconductors, but within a range of soft oxygen phonon modes the resulting electron-phonon coupling strength λ is large (λ∼2.5). This strength appears to be sufficient to explain the high transition temperatures Tc=30-40 K in these materials within the usual electron-phonon mechanism.
Cooperative Bipolaron Tunneling in High Tc Copper Oxide Compounds and Superconductivity
Authors: Kamimura Hiroshi
Published: March 2014

Based on a new mechanism of the Jahn-Teller distortion mediated bipolaron tunneling as an origin of high Tc superconductivity, important key-factors to give a measure of Tc are investigated. It is suggested that Tc is determined by a pair-breaking temperature of a bipolaron and thus it does not depend on the electron-lattice interactions. Means to increase covalency will lead to the discovery of higher Tc materials.
Low Temperature Specific Heat in La2CuO4 and the High Temperature Superconductor La1.85Sr0.15CuO4-y
Authors: Gutsmiedl P. , Andres K. , Amberger E. , Rietschel H.
Published: March 2014

At lowest temperature the specific heat of La1.85Sr.15CuO4-y and La2CuO4 is dominated by a large T-2-term arising from a nuclear specific heat contribution. When attributing this to the quadrupole splitting of either the La or Cu nucleus unusually large electric field gradients (1018-1019 V/cm2) are obtained. The alternative of an antiferromagnetic ground state of the Cu ions is discussed. Above 2 K all samples show a T3-term corresponding to rather low Debye temperatures of 130 - 200 K. To fit the total specific heat for La2CuO4 an additional linear term must be assumed whereas for superconducting La1.85Sr.15CuO4 a phenomenological T1/2-behaviour gives the better description for the additional contribution.
Lattice Vibrations at the Metal-Semiconductor Transition in BaPb1-xBixO3
Authors: Sugai Shunji
Published: March 2014

Comprehensive Raman studies of lattice vibrations in oxide superconductors BaPb1-xBixO3 are presented. In order to explain consistently the Raman and infrared data a dimerization model is proposed for the appearance of the semiconducting state in this system. The transfer-integral, on-site Coulomb repulsion and electron-molecular-vibration coupling constant are presented as a function of Bi concentration. The calculated activation energy is in good agreement with the experimental data.
Acoustic Property Measurement of the Oxide Superconductor (La1-xSrx)2CuO4 by the Sphere Resonance Method
Authors: Yoriwaki Ryozo , Hikata Takeshi , Han Taesu , Iwazumi Toshiaki , Sawada Hldeaki , Sakudo Tunetaro , Suzuki Tetsuro , Matsuura Etsuyuki
Published: March 2014

Acoustic-property of sintered (La1-xSrx)2CuO4-y sample has been measured by a sphere-resonance method. Softening of elastic modulus has been ooserved for the samples with x=0.05, 0.075 and 0.1, and not observed for a x=0.2 sample. The softening temperature increased with decreasing x, and was found to be related to an antlferrodlstortlve transition temperature in La2CuO4-y (x=0). The correlation between the superconducting transition temperature and the softening is discussed.
Anisotropic Properties of Superconducting Single Crystals (La1-xSrx)2CuO4 and Ba2YCu3O7+y
Authors: Hidaka Yoshikazu , Enomoto Youichi , Suzuki Minoru , Oda Migaku , Katsui Akinori , Murakami Toshiaki
Published: March 2014

Resistivity and the second critical field Hc2 have been measured for superconducting (La1-xSrx)2CuO4 and Ba2Cu3O7+y single crystals grown from the melt. The Hc2 along the basal plane is estimated to be larger than that along the c-axis by a factor of more than 5. These anisotropy due to crystallographic structure is briefly discussed.
Far Infrared Detector Using Boundary Josephson Junctions
Authors: Enomoto Youichi , Noda Juichi
Published: March 2014

A cryogenic optical detector has been fabricated by using a polycrystalline thin film of an oxide superconductor, BaPb0.7Bi0.3O3(BPB). For a wide detective area, the BPB detector was patterned into a shape of meander line, which consists of a great number of Josephson junction serially connected through the grain boundary. As a result of accumulation effect of Josephson junction arrays, the optical responsivity for the BPB detector with the detection area of 1×1 mm2 is obtained up to about 104 V/W, which is larger than that of InSb hot electron detector in 100 µm wavelength region.
Shapiro Steps in I-V Curves of Josephson Point Contacts Made of Ba–Y–Cu–O Ceramics
Authors: Yamashita Tsutomu , Kawakami Akira , Nishihara Takaharu , Takata Masasuke
Published: March 2014

Using BaYCuO ceramics having Tc(zero)=86K, point-contact Josephson devices have been fabricated. The devices were made of lead-ceramics and ceramics-ceramics point-contacts. X band radio frequency power was applied to the devices to measure rf induced voltage steps (Shapiro-steps) in I–V curves. Clear Shapiro-steps were observed at 4.2K in the lead-ceramics devices. By using the ceramics-ceramics devices Shapiro-steps were observed at 77K (in liquid nitrogen). The observed step-voltage VO and applied frequency f satisfied the relation VO=n(h/2e)f, where h and e are respectively, the Planck constant and electron charge and n is an integer.
Superconductivity at 93 K in Single-Phase YBa2Cu3O7
Authors: Kadowaki K. , Huang Y. K. , Sprang M. van , Menovsky A. A.
Published: March 2014

Evidence of a stable and reproducible high-Tc superconductivity above 90 K is reported in the single-phase YBa2Cu3O7. It is confirmed that this YBa2Cu3O7 phase is responsible for high-Tc superconductivity. A Curie-Weiss law in the dc-susceptility is observed above the superconducting transition temperature. The importance of the amount of the oxygen containing in this system to realize the superconductivity above 90 K is emphasized in relation to the crystal structure.
Superconductivity Enhancement due to Density Wave Instability in (La, M)2CuO4 and Related Materials
Authors: Machida Kazushlge , Kato Masaru
Published: March 2014

It is shown theoretically that superconducting transition temperature Tc can rise due to the presence of the spin (SDW) or charge density wave (CDW) instability. We demonstrate that within a simple imperfect nesting model in two dimensions Tc can exceed by an order of magnitude higher than that in the absence of the SDW (or CDW) transition under certain conditions. The SDW can enhance the anisotropic singlet pairing while the CDW does the isotropic singlet pairing state. We discuss its implication in the light of recent high Tc superconductors (La, M)2CuO4 and related materials.
Upper Critical Field Measuremennts of High-Tc Superconducting Oxides under a Pulsed Magnetic Field up to 70 Tesla
Authors: Okuda Kiichi , Noguchi Satoru , Yamagishi Akio , Sugiyama Kiyohiro , Date Muneyuki
Published: March 2014

Upper critical fields of high-Tc superconducting oxides with the constitutions La1.85Sr0.15CuO4-δ, Y0.4Ba0.6CuOy and YBa2Cu3O7-δ were measured by magnetoresistance method under a pulsed magnetic filed up to 70 tesla in a temperature region from 4.2 K to the superconducting transition temperature Tc. The Hc2 (0) at zero temperature defined by the midpoint of the resistive transition are estimated to be 40,90 and 148 tesla, for La1.85Sr0.15Cu4-δ, Y0.4Ba0.6Cuy and YBa2Cu3O7-δ, respectively.
Magnetization of Superconducting Ba (Y, Nd, Sm, Gd, Dy., Er, Yb) CuO Systems
Authors: Nam Sang Boo
Published: March 2014

The high temperature superconductors Ba(Y, Nd, Sm, Gd, Dy, Er, Yb)CuO were independently made via the solid reaction method, and their magnetizations were measured by using the BTi SQUID susceptometer. My main findings are that the Meissner effect was observed in the range of 78–92K, the fluxoids were found to be trapped during the field cooling case at all temperatures, the transition temperatures Tc were found to be sensitive to the colling rates of samples during their syntheses, and that the majority of samples were found to have layered perovskite X-ray diffraction patterns. The magnetization M(T) can be understood within the frame work of the BCS theory. The 2Δ(0)/kBTc was deduced to be 3 - 4.4. However, I found the magnetic hysteresis present even in low field 30G range at 10K and that M(T) near Tc was sensitive to thermal fluctuations.
Magnetic Field Effects in High-Tc Superconductors
Authors: Nakao Masao , Nemoto Masaaki , Yuasa Ryohkan , Mukaida Hiromi , Terakado Shingo , Shikichi Kazuaki , Mizukami Atsuo
Published: March 2014

Superconducting and structural properties of high-T
c superconductors RE-Ba-Cu-O (RE = Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb) were investigated. Each compound with nominal composition, RE1Ba2Cu3O7-δ, displayed superconductivity around 90 K. Magnetic field effects on resistance suggested that each compound was almost single phase except La-Ba-Cu-O. An X-ray study showed that the 90K-range superconducting phase is an orthorhombic perovskite common to all systems. Compounds of tetravalent rare earth elements (Ce, Pr, Tb) were found nonconducting under the same preparation conditions.
The Electrical and Magnetic Properties in the Isostructural Superconducting Alloys of YBa2Cu3O9-δ
Authors: Horng H. E. , Lin J. H. , Yang H. C.
Published: March 2014

In this study, a series of isostructural alloys of YBa2Cu3O9-δ has been synthesized. A comparison of the resistivity data, ac magnetic susceptibility and critical current density measurements exhibits a compositional dependence of the superconducting transition temperatures TC and critical currents JC. Causes are discussed.
Critical Field and Current of the High-Tc Superconductor YBa2Cu3O7
Authors: Apfelstedt I. , Flükiger R. , Küpfer H. , Meier-Hirmer R. , Obst B. , Politis C. , Schauer W. , Weiss F. , Wühl H.
Published: March 2014

We report on resistive and inductive measurements of the upper critical field Bc2 and the critical current jc of YBa2Cu3O7. The strong field dependence of the resistively and inductively measured superconductive transition is explained by a strong anisotropy of Bc2. After grinding the sample the critical current density exceeds 106 A/cm2 in the grain, whereas in the sintered bulk sample this value is three orders of magnitude smaller.
Static Magnetization of High-Tc Superconductors
Authors: Gould C. M. , Friedman L. J. , Bozler H. M.
Published: March 2014

We have measured the total magnetization of a series of compounds in the classes La2-xSrxCuO4 in the temperature range 5 K to 400 K and field range 0 to 4 T. In the superconducting state we observe an essentially complete Meissner effect below Hc1. We do not observe persistent currents on a macroscopic length scale. In the normal state we find the magnetization is only roughly temperature independent. The dependence correlates well with sample composition.
Fast Neutron Damage Studies of La1.85Sr0.15CuO4
Authors: Sekula S. T. , Christen D. K. , Kerchner H. R. , Thompson J. R. , Boatner L. A. , Sales B. C.
Published: March 2014

The effect of fast neutron damage on the superconducting transition temperature Tc and the critical current density jc of the compound La1.85Sr0.15CuO4 has been investigated. Irradiation to a fluence of 1.3×1018 n/cm2 (E > 0.1 MeV) resulted in a decrease of Tc of about 3 K while jc at 4.2 K and H = 2 T increased by a factor of two to 1.2×104 A/cm2.
Study of the Upper Critical Field Hc2 for High-Tc Superconductors in Pulsed High Magnetic Fields
Authors: Nakao Koichi , Miura Noboru , Uchida Shin-ichi , Takagi Hidenori , Tanaka Shoji , Kishio Kohji , Shimoyama Jun-ichi , Kitazawa Koichi , Fueki Kazuo
Published: March 2014

The magnetoresistance and the magnetization in high-Tc superconductors Y–Ba–Cu–O and Ln–Ba–Cu–O (Ln=Er and Ho) were measured in pulsed high magnetic fields up to 40T. The values of dHc2/dT are estimated to be -1.8, -1.8 and -1.2T/K for Y, Er and Ho compounds, respectively. The magnetization of the Er and Ho compounds show a paramagnetic behavior at high magnetic fields even below Tc, but a considerable deviation from the free ion magnetizations was observed.
Magnetic Field Studies of the La2-xMxCuO4 and Ba2Y1Cu3O7 High Tc Superconductors
Authors: Fuller W. W. , Osofsky M. S. , Toth L. E. , Qadri S. B. , Lawrence S. H. , Hein R. A. , Gubser D. U. , Francavilla T. L. , Wolf S. A.
Published: March 2014

We have prepared and characterized high Tc single phase samples of La2-xMxCuO4 (where M = Sr, Ba, or Ca and x = 0.1, 0.2, or 0.3) and Ba2Y1Cu3O7. We report on the dc susceptibility, magnetization, and magnetoresistance. We have extracted many of the critical superconducting and normal state parameters from the data.
The Collective Modes of Superfluid 3He–A
Authors: Ling Renzhi , Saunders J. , Dobbs E. R.
Published: March 2014

The attenuation of zero sound in superfluid 3He–A has been measured for eight frequencies in the range 24–94 MHz at a pressure of 29.3 bar. The clapping mode resonance was studied at all frequencies, the re-entrance of the normal flapping `mode' was observed for the first time at both 34.2 and 44.2 MHz, and attenuation due to pair breaking alone was measured by suitable orientation of the superfluid texture. Comparison with numerical evaluation of the sound attenuation from theory has given information on strong coupling effects away from T

c
and evidence of weak ℓ=3 pairing fluctuations.
Superconducting Properties of Y–Ba–Cu–O System
Authors: Watanabe Hirohito , Kasai Yuji , Mochiku Takashi , Sugishita Akimitsu , Iguchi Ienari , Yamaka Eiso
Published: March 2014

We report the measurements of superconducting properties of Y–Ba–Cu–O compound, particularly the critical current and the gap structure. X-ray diffraction shows that the sample has strong c-axis orientation perpendicular to the pressed surface of bulk material. Temperature dependence of critical current is found to be in good agreement with the Ginzburg-Landau theory near T=Tc. Single particle tunneling between a sintered bulk Y–Ba–Cu–O compound and a Pb film yields a series of gap structures. The observed value of 2Δ/kBTc at low temperatures is about 10 when Δ is estimated at the gap bump voltage and 6–7 when estimated at the point where superconducting and normal tunnel resistances become equal. It is pointed out that the latter method does not apply in the case of d-wave superconductors even at T = 0.
Superconducting properties of Y–Ba–Cu–O Compounds
Authors: Wenger L. E. , Chen J. T. , Logothetis E. M. , Win W. , McEwan C. J. , Soltis R. , Hurley M.
Published: March 2014

Superconducting properties of Y–Ba–Cu–O compounds have been studied by resistivity, current-voltage characteristics, ac susceptibility, x-ray diffraction, and reverse ac Josephson effect measurements. The results are described in terms of granular superconductivity with the Josephson coupling depending upon composition and annealing conditions. In several mixed phase compounds, the presence of Josephson coupled grains have been detected at 240 K by the reverse ac Josephson effect.
Superconducting Properties and Characterization of High-Tc Oxides
Authors: Sadakata N. , Ikeno Y. , Sugimoto M. , Nakagawa M. , Kohno O. , Ohara K. , Kaiho K. , Agatsuma K.
Published: March 2014

Superconductivity in La–Sr–Cu oxide and M–Ba–Cu oxide where M=Y, Yb, Er, Sm was investigated. Critical temperature at zero resistance was found to be 37K for La1.85Sr0.15CuO4-y Deviation from this composition resulted degradation of superconductivity. Y0.33Ba0.67CuO3-y exhibited zero resistance at 90K, however, superconductivity in this system depended heavily on heat-treating condition. Yb–Ba–Cu oxide and Er–Ba–Cu exhibited zero resistance at 86K and 89K, respectively. Sm–Ba–Cu oxide had relatively low critical temperature.
Preparation of High Tc Oxide Superconducting Filaments Using the Method of Solution Spinning
Authors: Gotō Tomoko , Horiba Iwao , Kada Masahiro , Tsujihara Masanori
Published: March 2014

This paper describes the preparation of the high Tc Y–Ba–Cu–O system superconducting filaments utilizing a low cost textile fiber spinning technology for alumina fiber. Two precursor techniques of a spinning of viscous solution and an extrusion of slurry were examined for the formation of long filaments. The precursor to the Y–Ba–Cu oxide containing poly(vinyl alcohol) (PVA) was extruded as a filament, dried and subjected to heat treatment to remove volatile components and to generate the oxide in the appropriate phase and grain size. The long filament more than 20 µm in diameter was obtained and was a polycrystalline with grain size of 200–400 nm and had a layered perovskite structure. The filaments were so brittle that they were pressed into a pellet and the Tc of the pellet was measured by the resistive method. The onset temperature was observed at 90.5 K and a zero resistivity state at 85.4 K.
Fermi Surface Anisotropies in Heavy-Fermion Superconductors
Authors: Rauchschwalbe U. , Steglich F. , Sparn G. , Bredl C. D. , Fulde P. , Maki K.
Published: March 2014

We present evidence that at the superconducting transition temperature Tc of the Heavy-Fermion-Superconductors CeCu2Si2 and UBe13, the order parameter is formed only on part of the Fermi-surface. In UBe13, at least part of the Fermi-surface that does not participate in superconductivity at Tc≃0.9K develops an order parameter in the accessible temperature range, i.e. at 0.55K. The effect can be sharply enhanced by doping UBe13 with a few at% Th, leading to a second phase transition within the superconducting state. In CeCu2Si2, those parts of the Fermi-surface which do not participate in superconductivity down to the lowest temperatures carry a small effective mass. The influence of impurities on the Fermi-surface anisotropy is discussed.
195Pt NMR Study of Heavy Fermion Superconductor UPt3
Authors: Kohori Yoh , Kohara Takao , Shibai Hirofumi , Oda Yasukage , Kaneko Tetsuyuki , Kitaoka Yoshio , Asayama Kunisuke
Published: March 2014

195Pt NMR in UPt3 in both normal and superconducting state has been observed. The spectrum has large negative shift and is quite anisotropic. In 4.5kOe, the negative shift does not change down to the lowest temperature 85mK. This means that the conduction electron spin susceptibility does not decrease in the superconducting state. The result does not contradict the possibility of anisotropic p-wave superconductivity of UPt3. The nuclear spin lattice relaxation rate, T1
-1 is proportional to T (T1 T=980µ secK) in 0.5-4.2K range indicating the Fermi liquid nature of the system in this temperature range.
Specific Heat of the Heavy Fermion Superconductor UPt3 at Very Low Temperatures
Authors: Schuberth E. , Gutsmiedl P. , Gross F. , Andres K. , Bucher E.
Published: March 2014

The specific heat of a single crystal sample of UPt3 has been measured as grown and after a brief heat treatment down to temperatures of 35 and 15 mK respectively. While the heat treatment changes the superconducting fraction of the sample, an additional low temperature increase of c/T is seen which seems to be independent of superconductivity.
Measurement of Critical Velocity in 3He A1 Phase
Authors: Ruel R. , Kojima H.
Published: March 2014

Superflows in 3He A1 phase were generated by applying magnetic field gradient along 25 µm channels. For sufficiently large ramping rate of the field gradient the superflow saturated. This saturation was interpreted as a critical velocity and it was measured as a function of temperature. The critical velocity was found to be 0.2 mm/sec independent of temperature in the reduced temperature range between 4×10-4 and 8×10-3.
Superconducting and Magnetic Properties of CeRh4B4 and PrRh4B4
Authors: Ooyama T. , Kumagai K. , Nakajima H. , Shimotomai M.
Published: March 2014

CeRh4B4 and PrRh4B4 with CeCo4B4 structure were successfully synthesized with high pressure up to 9.0 GPa and high temperature. The superconducting transition temperatures, Tc, of CeRh4B4 and PrRh4B4 are 0.29 and 4.6K, respectively. The effective moment of 3.10µB and the Curie-Weiss temperature of -2.6K are obtained by the susceptibility measurement, suggesting the antiferromagnetic interactions of Pr moments. The large peak of heat capacity at 1.6K in PrRh4B4 indicates that the antiferromagnetic order coexists with superconductivity below 1.6 K. Any Kondo-like behavior of the electrical resistance and the enhancement of heat capacity at low temperature were not observed in CeRh4B4. The lattice parameters of CeRh4B4 indicate that the valence of Ce is 3.4. The large reduction of Tc is considered to be attributed to the valence fluctuations of Ce moments.
Evidence for Lattice Softening in α-Uranium from Specific Heat Measurements under Pressure
Authors: Vahldiek Frank , Eichler Andreas
Published: March 2014

The low-temperature α-phase of uranium is known to exhibit a peculiar variation of the superconducting transition temperature with pressure, rising from values below about 0.1 K to a maximum near 2 K at 11 kbar and decreasing again to higher pressures. From specific heat measurements under high pressure we find that the initial increase in Tc is accompanied by a distinct decrease of the Debye temperature. This behaviour is discussed, also in comparison to lanthanum, to which it shows some similarities.
Specific Heat of Heavy-Fermion CeCu6: Effect of Pressure and Magnetic Field
Authors: Fisher R. A. , Lacy S. E. , Marcenat C. , Olsen J. A. , Phillips N. E. , Flouquet J. , Amato A. , Jaccard D.
Published: March 2014

The specific heat, C, of a single crystal of CeCu6 has been measured between 0.06 and 20K to pressures, P, of 8.8 kbar, and between 0.3 and 20K in magnetic fields, H, to 7.5T. At zero H and P, a minimum in C/T is observed near 8K. Below that temperature C/T increases, and below 1K is linear in T, C/T=1.67-0.67T J/mole K2. No maximum in C/T is found. This increase in C/T is reduced by a factor of three at 8.8 kbar and virtually completely suppressed for H = 7.5T along the [001] axis. With H ∥ [100] and [010] axes the effect on C is small.
Comment on Phonon-Mediated Pairing Interaction in the Dense Kondo Systems
Authors: Jin B. , Matsuura T. , Kuroda Y.
Published: March 2014

Using the one-dimensional periodic Anderson model coupled to a linear harmonic chain, we derive a phonon-mediated attractive interaction for Cooper pairs and calculate the superconducting transition temperature for various types of Cooper pairs rather quantitatively based on the first principle calculation. The result shows that because of the strong Kondo volume collapse effect as observed the phonon-mediated effective attraction can overcome the intra-atomic Coulomb repulsion and stabilize the spin-singlet Cooper pairing state when the heavy electron's band width is rather wide.
Electrical Resistance and Specific Heat of Magnetic-Field-Induced-Superconductors, Eu0.8Sn0.2Mo6S7-ySey
Authors: Kawamata Shuichi , Kobayashi Norio , Ikebe Manabu , Muto Yoshio
Published: March 2014

The electrical resistance under magnetic fields up to 23T and the specific heat under fields up ,to 6T of the compounds Eu0.8Sn0.2Mo6S7-YSeY(0≤Y≤0.7) have been measured. The specific heat shows Schottky contribution due to Eu2+ ions in 8S7/2 state, which have magnetic moments. We have observed the hysteresis of the electrical resistance in the field range where Superconductive-Normal-Superconductive transitions appear. Analysis of the hysteresis provides a direct evidence that the magnetic field induced superconductivity of these samples is caused by the Jaccarino-Peter compensation mechanism.
Spin Disorder Resistivity and Bare Curie Temperature in the Ferromagnetic Superconductor ErRh4B4
Authors: Kwok W. K. , Middleton S. P. , Hall L. N. , Dunlap B. D. , Joss W. , Crabtree G. W. , Hinks D. G.
Published: March 2014

Low temperature AC magnetoresistance measurements on a single crystal of ErRh4B4 were made to determine the bare Curie temperature and the spin disorder resistivity. A `crossed field' technique was used to suppress the superconductivity in order to probe the normal state properties. The bare Curie temperature was found to be 1.07K and the spin disorder resistivity extrapolates to a finite value at T=0K.
Specific Heat Study of Body Centered Tetragonal ErRh4B4
Authors: Iwasaki Hideo , Ikebe Manabu , Kobayashi Norio , Muto Yoshio
Published: March 2014

Specific heat of ErRh4B4 with bct structure was measured in the temperature range between 0.3 K and 30 K. The specific neat takes a λ type anomaly at 0.62 K showing the antiferromagnetic order. The entropy of the magnetic system is calculated to be ∼ R1n2 by performing an integration of the specific heat below 1.3 K. This value indicates that the crystal field ground state of Er is doublet and the excited levels are at least above 3 K and is quite different from the result (R1n4) of ErRh4B4 with pt structure. The discrepancy between bct and pt ErRh4B4 comes from the arrangements of Rh4B4 units in both crystal structures.
Cooling of TbMo6S8 by Adiabatic Magnetization
Authors: Rogacki Krzystof , Poppe Ulrich , Pobell Frank
Published: March 2014

Adiabatic magnetization cooling of the antiferromagnetic superconductor TbMo6S8 has been investigated between 0.2 K and 2 K in magnetic fields up to 2.5 kOe. It was found that the cooling occurs only in the antiferromagnetic phase and is largest (80 mK/kOe) at temperatures which are about a factor of two below the Neél point. The observed dependence of the temperature on the magnetic field is qualitatively reproduced by a combination of spin-wave theory and Ginzburg-Landau theory. The results obtained for TbMo6S8 and those from our previous work for GdMo6S8 are compared.
The Specific Heat of ErxY1-xRh1.1Sn3.6 for x=0.4, 0.8 and 1
Authors: Willekers R. W. , Bosch W. A. , Meijer H. C. , Bakker S. J. M. , Postma H. , Flokstra J.
Published: March 2014

Specific heat measurements between 50 and 800 mK of the three magnetic superconductors ErxY1-xRh1.1Sn3.6 With x = 0.4, 0.8 and 1, respectively, are presented. For these compounds broad anomalies with maxima at 245, 360 and 435 mK, respectively, were observed. No sharp peaks were detected. This means that magnetic short-range order gives the main if not the full contribution to the specific heat. A low-lying doublet is responsible for the magnetic behaviour below 1 K. The results are compared with some theories.
Superconducting and Magnetic Phase Transitions in RExY1-xRh1.1Sn3.6 (RE=Er, Ho)
Authors: Pasch A. W. M. van de , Lazaro F. J. , Blank D. H. A. , Houwman E. P. , Flokstra J.
Published: March 2014

The superconducting (Tc and magnetic ordering (Tm) critical temperatures in RExY1-xRh1.1Sn3.6 (RE = Er, Ho) have been determined by magnetic measurements. For RE = Er superconductivity appears for any value of x, and reentry to a magnetically ordered state for x \gtrsim 0.6, while for RE = Ho the compound becomes either superconducting or magnetically ordered, and is expected to remain paramagnetic for x near 0.5. Theories of Abrikosov-Gorkov and Roshen-Ruvalds are used to explain Tc(x) , leading to I2N(0)G=0.23 K and 0.8 K for Er and Ho respectively. Comparison of Tm(x) with the theory of Oguchi-Obokata gives respectively J = 0.30 K and 0.96, using a Heisenberg model with z = 6.
Superconductivity and Antiferromagnetism of Cr–Ru and Cr–Re Alloys
Authors: Nishihara Yoshikazu , Murata Keizo , Tokumoto Madoka , Yamaguchi Yuji
Published: March 2014

Cr–Ru and Cr–Re alloys with bcc structure exhibit superconductivity in Ru and Re concentrations higher than ∼17 at.%. The magnetic susceptibility of the superconducting alloys shows a peak at 160∼170 K. Below this temperature, the temperature derivative of electrical resistivity becomes slightly large with decreasing temperature. The resistivity shows no clear hump around this temperature. The result suggests that in the superconducting alloys only a very small portion of the Fermi surface contributes to form the gap of spin-density wave or the antiferromagnetic ordering is different from that of Cr-type spin-density wave.
Magnetic and Transport Properties of CexTaS2 and (Ce2S3)xTaS2
Authors: Suzuki Kazuya , Kojima Norimichi , Ban Toshiro , Tsujikawa Ikuji
Published: March 2014

Transport and magnetic properties of Cex TaS2 have been studied. The susceptibility as a function of temperature exhibits a diverging anomaly at 2.3K and the resistivity decreases below this temperature, indicating the appearance of a magnetic ordering with a spontaneous magnetization. The dependence of the magnetization on magnetic field applied parallel to the c-axis shows the meta-magnetic phase transition at 2kOe. Above 45kOe, the magnetization seems to be saturated, but the effective magnetic moment is 0.6µB per Ce atom even at 45kOe which is quite small compared with that of the free Ce3+ ion. It is discussed whether the f-electron in this compound has the localized nature or the itinerant one.
Magnetization and Superconductivity of Impurity-Doped Y9Co7
Authors: Yamaguchi Yuji , Nishihara Yoshikazu , Ogawa Shinji
Published: March 2014

Magnetic and superconducting transition temperatures of pure and impurity-doped Y9Co7 are summarized. Doping of Al, Sc, Zr and Gd extremely enhances the ferromagnetism and suppresses the superconductivity, while doping of La, Lu and 3d transition metals influence moderately. The result suggests that the introduction of randomness into the lattice has crucial influence on the magnetism and the superconductivity. Superconductivity of Y9Co7 is suggested to coexist with a very large spin fluctuation of one dimensional ferromagnetism.
Depairing Critical Mass- and Spin-Superflows in Superfluid Fermi Liquids
Authors: Jacak Lucjan
Published: March 2014

The dependence of the critical velocity and depairing superflow on a1 Landau amplitude (on b1 for spin-superflow) is determined in the framework of weak coupling microscopic approach for superconductors. The superflow instability phenomenon is described for s-paired Fermi liquid and coordinates of the tricritical point, vs. a1 parameter, are determined by application of the bifurcation theorem. The relation to the local limit for superconductors type II upon magnetic field is indicated. The similar considerations for p-paired superfluid Fermi liquid is also contained with relevance to charged p-paired systems. The super flow instability for BW-2D and 2D-normal phase transitions of p-paired systems is described.
The Variation of Tc with Resistivity and the Disappearance of Global Superconductivity near the Metal-Insulator Transition
Authors: Zhang Y. Z. , Kunchur M. , Tsuboi T. , Lindenfeld P. , McLean W. L.
Published: March 2014

By changing the deposition parameters 3D granular aluminum (Al-Al2O3) can be prepared with different variations of Tc as a function of resistivity. As the metal-insulator transition is approached Tc decreases gradually to a limiting value independent of the deposition, beyond which complete superconducting transitions are no longer observed. The behavior in Al-Al2O3 is quite different from that observed in Al-Ge (with grain sizes 4 or 5 times larger), where Tc drops abruptly and reaches much lower values. The difference is in accord with the considerations of Deutscher, Goldman, and Micklitz of the competition between localization and percolation.
Resistive State of the Superconducting Metallic Glass Zr78Co22 in Longitudinal Magnetic Fields
Authors: Zhang Zhang , Qirui Qirui , Zhou Zhou , Xianyi Xianyi , Wang Wang , Jinsong Jinsong , Guan Guan , Weiyan Weiyan
Published: March 2014

When the temperature is far from Tc, it is discovered that two types of voltage steps appear on the I-V or H-V curves of the metalic glass Zr78Co22 under longitudinal magnetic fields. The large steps are related with the existing superconducting phase separation in the sample. But the small steps overlapping the large steps originate from phase-slip-centers.
Correlations between Controlled Structural Inhomogeneities, Superconductivity and Transport Properties in Amorphous Films of (Mo0.4Ru0.4)0.85Bo0.15 and Zr1-xSix
Authors: Hensel B. , Lippert M. , Adrian H.
Published: March 2014

In this paper we present a method to prepare amorphous thin films with controlled structural in-homogeneities on a length scale just above the short range order (10–100 Å). The influence on transport properties and superconductivity of the systems (Mo0.6Ru0.4)0.85B0.15 and Zr1-xSix is discussed in the framework of a structure model obtained from SAXS and RPHS-computer simulation.
Superconducting Transition of Quench-Condensed Ultrathin Films
Authors: Kawaguti T. , Shinozaki B. , Fujimori Y.
Published: March 2014

The condition of the onset of superconductivity in highly homogeneous ultrathin Bi and Pb films has been investigated by measuring the temperature dependence of the sheet resistance R□. The experimental results suggest that highly homogeneous metal films with R□ lower than ∼6 k Ω could be superconducting, while those with R□ greater than ∼6 k Ω are insulating at zero temperature, in agreement with the condition of the onset of global superconductivity in granular films. The superconducting transition temperature Tc shows a remarkable decrease with increasing the normal-state sheet resistance, unlike the results of granular films.
Fluctuation-Induced Conductivity of Superconducting Films with the Overdeposition of Gold
Authors: Kobayashi T. , Kojima S. , Okamoto K. , Ohtsuka M.
Published: March 2014

The intrinsic pair-breaking mechanisms in the superconducting metal films were investigated with respect to the fluctuation-induced conductivity (FIC) above the transition temperature. The tin
and aluminum sample films were overdeposited with gold (about 1 atomic layer in averaged thickness). The measured FIC is well explained by the traditional superconducting theory with the pair-breaking parameter δ. The experimental relation δ=a+b
R
n
□ holds, where R
n
□ is the normal sheet resistance. The values of δ for gold-overdeposited samples are larger than those for unoverdeposited ones. This is considered to be due to the spin-orbit scattering effect owing to the existence of gold.
Temperature Dependence of Pair-Breaking Parameter δ near Superconducting Transition Temperature Tc of Thin Aluminum Films
Authors: Shinozaki Bunju , Rinderer Léo
Published: March 2014

The pair-breaking parameter δ has been determined by two different methods for films with sheet resistance R□, 12Ω/□<R□<200Ω/□. One of them, δM, is estimated from the relation δ=π\hbar/8KBTτin, where τin is the inelastic scattering time obtained by the analysis of the magnetoconductance. The other, δF, is determined by fitting the theory to the experimental data of the excess conductance due to fluctuations at zero field. It has been shown that: l) the temperature dependence of δM near Tc agrees well with the theory of Brenig et al.,; 2) for clean films, δF analysed by adding the correction term to the Maki-Thompson contribution shows almost the same temperature dependence as δM. In the film with R□≃200Ω/□, however, a discrepancy between them remains.
Superconductivity of (Pb, Sn, Ge)Te Semiconductor Film with a Little Pb Inclusion
Authors: Takaoka Sadao , Sugita Tatsuya , Murase Kazuo
Published: March 2014

The superconductivity (SC) behaviors of PbTe films containing Pb inclusion are observed below Tc of Pb (7.2K) in spite of a small amount of pb precipitate (1 at.%). In these films, random arrays of small Pb particles are considered to be coupled as Josephson junctions through host PbTe. Further a search for enhancement of Tc due to non-phonon mechanism by interactions between superconducting metal particles and excitons of narrow gap semiconductor in Pb1-xSnxTe and (or) Ge-ion motion in Pb1-xGexTe are undertaken. No enhancement of Tc is observed.
Critical Exponents for Breakdown in Two-Dimensional Percolating Superconducting-Insulating Composites
Authors: Octavio Miguel , Octavio Alfredo , Aponte Juan , Medina Rodrigo , Lobb Christopher J.
Published: March 2014

We present numerical simulations of the critical exponents for breakdown in superconducting-insulating mixtures. We calculate exponents for both lattice and continuum models assuming that the elements in the networks are either one-dimensional wires or Josephson-like weak-links. The exponents for Swiss-Cheese, Inverse Swiss Cheese and lattice models are found to be in good agreement with theoretical calculations.
Depairing Critical Current for Spin Singlet-Triplet States of Superfluid Fermi Liquid
Authors: Krzyźanowski I. H.
Published: March 2014

The unitary states of superfluid neutral Fermi liquid with d-singlet and p-triplet pairing interaction are investigated in the framework of weak coupling approximation. The pair breaking current is calculated at zeroth temperature. The dependence of the depairing critical mass-superflow on a1 Landau amplitude is determined. The mixed-type spin singlet-triplet state BS (a mixture of Balian-Werthamer state with d-wave state) and 2 DS (a mixture of triplet planar with d-wave state) are found to be stable for certain region of the superfluid velocity vs.
Dynamical Properties of Superelastic Percolating Systems
Authors: Burton D. , Lambert C. J.
Published: March 2014

A natural extension of scalar percolation models of, for example granular superconductors, are superelastic vector models in which nearest neighbour sites with more than one degree of freedom are coupled by infinitely strong central force bonds with probability P and unit strength bonds with probability (1-P). We present results for the density of vibrational states of such a system, obtained from a numerical simulation of a two dimensional triangular network. As the superelastic rigidity percolation threshold is approached from below, the density of states becomes fracton-like and is characterized by a spectral dimensionality \tilded which is greater than the Euclidean dimension of d=2. This behaviour is explained using single parameter scaling, which predicts a value for \tilded slightly greater than our numerical result of \tilded=2.9. No sharp features in the density of states at phonon-fracton cross-over are observed.
Anomalous NMR Relaxation Rate in the High-Tc State of β-(BEDT-TTF)2I3
Authors: Maniwa Yutaka , Takahashi Toshihiro , Takigawa Masashi , Yasuoka Hiroshi , Saito Gunzi , Murata Keizo , Tokumoto Madoka , Anzai Hiroyuki
Published: March 2014

An anomalous enhancement of the NMR relaxation rate T1
-1 was observed in the high-Tc superconducting state of the titled material at zero field, by using a field-cycling technique. The enhancement of T1
-1 starts to pronounce below Tc∼6.2K, which was determined by AC susceptibility measurements on the same run. A peak of relaxation rate was observed much below Tc. The enhancement is suppressed by the external field, which evidences a close relation to the superconductivity.