bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconductivity in β-(BEDT-TTF)2AuI2
Authors: Oshima Kokichi , Saito Gunzi , Sakai Fumlko
Published: March 2014

The superconducting properties in β-(BEDT-TTF)2AuI2 is experimentally Investigated by the conductivity and the low field magnetization measurement. The temperature dependence of Hc2 shows the paramagnetic limited behaviour at low temperatures indicating the spin singlet superconductivity.
Two kinds of Tc are obtained and ascribed to the impurity effect due to sample preparation process. Samples which become partially superconducting are studied, and we speculate the nonsuperconducting part is of layered structure. Low Tc and high Tc states are discussed in contrast to the case in the I3 salt. Possible contribution of phonon mode related to the superlattice formation is considered.
Superconductivity and Surrounding Phase of Organic Conductor, (DMET)2Au(CN)2
Authors: Kikuchi Koichi , Murata Keizo , Klkuchi Mikio , Honda Yoshiaki , Takahashi Toshihiro , Oyama Teruo , Ikemoto Isao , Ishiguro Takehiko , Kobayashi Keiji
Published: March 2014

Organic conductor, (DMET)2Au(CN)2, (DMET = dimethyl (ethylenedithio) diselenadithiafulvalene), based on a new donor, which is asymmetric, was found to undergo superconducting transition around 0.7 - 0.8 K under a pressure of 5 kbar. Below 2 kbar, metal-insulator transition was observed. Preliminary study by means of EPR and NMR on the possible low temperature insulating phase is presented.
Superconducting Fluctuations above the Transition Temperature in the Mercury-Chain Compound Hg3-δAsF6
Authors: Okamoto Kiyomi
Published: March 2014

We calculate the critical behavior of the electrical conductivity, the specific heat and the diamagnetic susceptibility in the mercury chain compound Hg3-δAsF6 above its superconducting transition temperature Tc on the basis of the model recently proposed by Sugiyama, Gutfreund and Weger. In contrast to their result, the electrical conductivity behaves as 1/\surdε with ε=ln
(T/Tc), which is characteristic of three dimensional systems. The other two quantities also behaves as 1/\surdε. The contribution of the superconducting fluctuation to the specific heat is enhanced in comparison with the usual superconductor case. On the other hand, the magnetic susceptibility is either suppressed or enhanced according to the direction of the applied field. The correlation length, the linearized TDGL equation and the GL free energy density up to |Δ|2 are also obtained.
Observation of the “Bloch Oscillations” in Granular Films of Oxidized Tin Particles
Authors: Yoshihiro Kazuo , Kinoshita Joji , Inagaki Katsuya , Yamanouchi Chikako , Kobayashi Shun'ichi , Karasawa Takeshi
Published: March 2014

Experimental observation of the “Bloch oscillations” which are predicted theoretically in small Josephson junctions, resulting from their macroscopic quantum nature, has been made in superconducting granular tin films, the sheet resistance of which ranges from 3 to 12 kΩ at 4.2 K. We show that the values of 2ef obtained from the experimental V - I characteristics and a relationship I = 2ef are in agreement to within 0.3 % with those calculated using the frequency f of the microwave fields applied. It is one of the important conditions to observe the “Bloch oscillations” in the junction network that the number of parallel paths connecting two current electrodes is a few hundreds or less.
Periodic Voltage-Charge Relation in Small Tunnel Junctions
Authors: Tamura Hirotaka , Hasuo Sinya , Okabe Yoichi
Published: March 2014

A static relation between voltage and charge in a non-superconducting tunnel junction with capacitance C is obtained by using a classical statistical calculation, neglecting the quantum-mechanical size effect in the electrode. The junction behaves as a non-linear capacitor with a periodic voltage-charge relation if e2/(2C)≫kT. The response of the junction to dc and ac signal is obtained. The field effect in series-connected tunnel junctions are also calculated.
Temperature Dependence of Macroscopic Quantum Tunneling
Authors: Grabert Hermann , Olschowski Peter , Weiss Ulrich
Published: March 2014

The rate of decay of metastable states of Josephson systems is determined for a wide range of parameters. The temperature extends from the region where the decay is thermally activated down to very low temperatures where the system decays by macroscopic quantum tunneling. The range of damping parameters extends from weakly damped to heavily overdamped motions. It is found that the transition between thermally activated decay and tunneling occurs near a cross over temperature T0 which decreases with increasing damping strength. Well above T0 the rate follows the classical Arrhenius law where the preexponential factor is affected by the frequency dependent damping. As T0 is approached, quantum corrections to the classical rate become increasingly important. In the vicinity of T0 the rate follows a scaling law describing the crossover between thermally activated and quantum mechanical decay. In the region below T0 the decay rate can be determined analytically only in limiting cases. For systems described by the resistively shunted junction model, numerical calculations are presented. The results are compared with recent experimental data on the decay of the zero-voltage state in current biased Josephson junctions and on fluxoid quantum transitions in SQUID rings.
Resistive Transition of Sierpinski Gasket Arrays of Weak Josephson Junctions
Authors: Lee Hu Jong , Forrester M. G. , Tinkham M. , Lobb C. J.
Published: March 2014

We present the results of measurements of transport properties of 6th order Sierpinski gasket arrays of weak Josephson junctions. The system shows a broad fluctuation-dominated resistive transition. The temperature dependence of the resistance, however, does not fit the existing theory of fluctuation effects for dimension d=l, d=2, or d=1.585, the fractal dimension of the gasket. The current-voltage characteristics exhibit power-law behavior, but with the exponent varying smoothly with temperature, in contrast to those of 2D arrays. The sample voltage as a function of magnetic field reveals dilation invariance as the field axis is expanded by a factor of 4, reflecting the self-similar geometry of the gaskets.
Macroscopic Quantum Tunneling in SQUID
Authors: Kawamoto Hiroshi
Published: March 2014

The macroscopic quantum tunneling in a SQUID coupled to an external heat bath is studied. The heat bath is modeled in which equilibrium noise current in the resistor (resistance R) exerts a random force on a SQUID system. This model has been very successful in the classical theory of I–V characteristics. The potential energy of a SQUID is of symmetric double-well when an applied magnetic flux φapp=1/2·(h/2e). In the present work, the temporal evolution of a wave packet initially localized in one well of this potential, is studied by using the well-known damping theory. For φ0
2/hR≪1, where φ0 is a flux quantum, the influence of the noise current is summarized into two parts. One is the usual dissipative effect with the damping constant ∼(φ
O

2/hR)/τc and the other is the seesaw motion of the potential bottoms with the frequency ∼(φ
O

2/hR)1/2/τc. Here, τc is the correlation time of the noise current. The tunneling frequency is enhanced by the seesaw motion, the case φ0
2/hR\gtrsim1 can not be treated in the damping theory because the time scale of the motion must be larger than τc in this method.
A-B Phase Transition of Superfluid 3He Confined in Specular and Diffusive Pore Geometry
Authors: Takagi Takeo
Published: March 2014

The structure of the order parameter and the free energy of the superfluid 3He confined in the pore, whose radius is comparable to the coherence length of the superfluid is studied. In this situation the gradient energy plays a crucial role to determine the structure of the order parameter and/or condensation state. The superfluid A and B phases are examined for the boundary condition of specular and diffusive scattering at the wall, which shows that the A phase becomes more stable than the B phase under the condition the pore radius R being smaller than some critical radius Rc the specular wall boundary condition even in the weak coupling limit. The critical radius Rc is calculated to be ∼100nm. So this size effect seems to give one of the possible mechanism of nucleation in the B→A phase transition.
Influence of Temperature and Friction on Macroscopic Quantum Coherence in SQUID-Rings
Authors: Weiss Ulrich , Grabert Hermann , Linkwitz Sebastian
Published: March 2014

The dynamics of an almost symmetrical double-well system coupled to an Ohmic heat bath is studied. This case is of potential relevance to the problem of quantum coherence in SQUID rings. The coherent quantum oscillations characteristic for isolated systems are shown to be strongly affected by dissipation. We report on recent analytical results describing the influence of thermal fluctuation and biasing forces. The range of parameters in which quantum coherence survives is determined and the time evolution of the occupation probabilities in the two wells is calculated.
Effect of the Subgap Conductance on the Metastable States in a Josephson Tunnel Junction
Authors: Cristiano R. , Pagano S. , Silvestrini P. , Gray K. E. , Liengme O.
Published: March 2014

An investigation of the decay rate of metastable states in Josephson tunnel junctions in presence of thermal noise is presented. We have observed that, in the extremely underdamped regime, there is an exponential temperature dependence of the best fit value for the shunt conductance. Such a
dependence shows a close relation with the temperature dependence of the subgap conductance, suggesting that the effective conductance for the escape from the metastable states obeys to a quasiparticle thermal activation mechanism. The introduction of this effective conductance into the lifetime expression for the zero-voltage states leads to significant changes in the width of the switching current distributions. A comparisons of the experimental data with the proposed model is reported.
Effect of Quantum Fluctuations on the Chaos in Josephson Junctions
Authors: Hida Kazuo
Published: March 2014

The quantum effect on the onset of chaos in the Josephson junction is studied by numerical simulation and the scaling theory using the semiclassical quantum Langevin equation. It is found that the effect of the quantum noise has the same universal property as the classical noise in the critical region of period doubling cascade and intermittency.
Decay of a Dissipative Object by Quantum Noise
Authors: Eckern Ulrich , Lehr Walter
Published: March 2014

The decay time, τ, of a dissipative object out of the metastable minimum of a (cubic) potential due to quantum noise is determined by a numerical investigation of the quasiclassical Langevin equation. In the zero temperature limit, and for moderate to large damping (γ\gtrsimω
o
), we find that σ=ln
(ω
o
τ/2π) can be approximated by a σ≃κ·γΔV/\hbarω
o

2 where the constant κ is κ≃3.20. This is in good agreement with an analytic treatment of the Langevin equation, but about a factor three smaller than the result obtained by Caldeira and Leggett by the instanton method.
Macroscopic Quantum Shift of the Flux and Quantum Tunneling
Authors: Panyukov S. V. , Zaikin A. D.
Published: March 2014

Quantum fluctuations in Josephson junctions and SQUIDs are studied. The quantum shift of the flux in SQUIDs, i.e. the quantum average between classical and measured values of the flux <δφ> is predicted and calculated. The value of <δφ> depends on temperature, dissipation strength and the external flux. The effect of the junction finite size is also examined. Our theory gives a natural quantitative explanation of the experimental results [1] consenting macroscopic quantum tunneling in a SQUID with a highly damped Josephson junction.
Simultaneous Bloch and Josephson Oscillations, and Resistance Quantizations in Small Superconducting Double Junctions
Authors: Likharev K. K. , Zorin A. B.
Published: March 2014

A structure comprising three superconducting electrodes separated with two small Josephson junctions has been analyzed. It has been assumed that a dc voltage V̄ is applied to the external electrodes of the structure, and a dc current Ī is fed to its middle electrode. The analysis has proved that the supercurrent flowing through the structure should oscillate simultaneously with the Josephson frequency fJ=2eV̄/h and the Bloch frequency fB=Ī/2e. Mutual phase locking of these oscillations leads to quantization the ratio R=V̄/Ī in units RQ=h/(2e)2.
Measurement Scheme for the Macroscopic Quantum Coherence Experiment
Authors: Tesche C. D.
Published: March 2014

An experimental strategy to test for macroscopic quantum coherence in a rf SQUID is described. The back action of broadband noise sources in a conventional dc SQUID magnetometer measurement system destroy the coherent state. A novel measurement scheme is suggested in which the rf SQUID is weakly coupled to an intermediate bistable system. This system consists of a pair of dc SQUIDs biased below threshold. The combined rf and dc threshold SQUID system is described by a single potential. The form of this potential is varied by changes in the external bias to the dc SQUIDs at the moment in which the measurement is to occur. This causes a transition in the dc SQUID system which serves to freeze the coherent oscillations. Amplification by a conventional SQUID linear amplifier chain then follows.
Measurement of the Anisotropies of the Viscosity and Superfluid Density for 3He–A
Authors: Hook J. R. , Hall H. E. , Gould S. G. , Faraj E
Published: March 2014

Measurements have been made of the frequency and damping of a torsional oscillator containing a disc of 3He–A 105µm thick as the orbital texture is manipulated by applying magnetic fields of varying strength and direction relative to the disc. By comparing these results with theory we deduce the two principal values of the superfluid density tensor and three of the five viscosity coefficients with good accuracy, and obtain rough estimates of the other two viscosity coefficients.
Flux Quantization in Nonperiodic Superconducting Networks
Authors: Wang Y. Y. , Steinmann R. , Chaussy J. , Rammal R. , Pannetier B.
Published: March 2014

We present measurements of the superconducting phase transition line Tc(H) of various non periodic wire arrays prepared by electron beam lithography. In the Sierpinski gasket, a fractal phase transition line is observed over 5 levels of hierarchy. Quantitative comparison with recent renormalization group calculations allows an accurate understanding of flux quantization effects on this fractal lattice. We have also observed flux quantization in fivefold Penrose tilings. Results in two none-quivalent tilings are discussed.
Are Josephson Networks Similar to Spin Glasses?
Authors: Rosenblatt J. , Raboutou A. , Peyral P. , Lebeau C.
Published: March 2014

The critical exponents of 3D X–Y system - a random array of Josephson junctions - differ from model calculations but are close to those found for spin glasses. Although in apparent contradiction with Harris's criterion, we ascribe this behaviour to randomness in coupling energies. The model gives very good agreement with the experimental results.
Positional Disorder in Real Josephson Junction Arrays
Authors: Forrester M. G. , Lee Hu Jong , Tinkham M. , Lobb C. J.
Published: March 2014

We present the results of measurements on proximity-effect arrays with deliberate positional disorder, characterized by a parameter Δ*. In measurements of resistance vs. perpendicular magnetic field, R(fo), we find strong evidence for a critical field, fc, beyond which phase coherence is destroyed. We find that fc∝1/Δ*, as predicted by Granato and Kosterlitz.
The Superconducting Phase Transition in Million Josephson Tunneling Element Arrays
Authors: Gordon James M. , Goldman A. M. , Bhushan M. , Cantor R. H.
Published: March 2014

Square arrays of one million Josephson junctions have been fabricated using the Selective Niobium Anodization Process (SNAP). Such arrays are nearly ideal examples of systems which can be described by the 2D X-Y model. In zero magnetic field we find clear evidence of the expected Kosterlitz-Thouless transition in the power law dependence of the voltage on current in the vicinity of and immediately below the transition temperature. In the regime above the transition, where the temperature-dependent resistance is determined by the free vortex density, only activated behavior is observed. This finding is in contrast with the results of measurements on thin films and proximity-coupled arrays where an exp
[-A(T-Tc)1/2] dependence of resistance on temperature is found.
Effect of Dissipation on Macroscopic Quantum Tunneling
Authors: Cleland Andrew N. , Martinis John M. , Clarke John
Published: March 2014

We report measurements of the escape rate from the zero-voltage state of a current-biased Josephson junction shunted by a normal-metal resistor. The critical current, capacitance, and resistance of the junction were measured in the classical regime. The escape rate was measured in both the high-temperature regime, where thermal activation dominates, and in the low-temperature regime, where macro-scopic quantum tunneling dominates. The measured escape rates are in good agreement with the predicted escape rates with respect to both the effect of dissipation and the existence of quantum corrections to thermal activation.
Reduction of the Superfluid Fraction of 3He in Sintered Silver
Authors: Kotsubo V. , Ditusa J. , Hall T. , Mihailovich R. , Parpia J. M.
Published: March 2014

We have measured the superfluid density of 3He liquid confined within the pores of a silver sinter plug. The silver was of nominal 70 nm size, and was packed to 54% of solid density. The mean pore size as measured was ∼200 nm. The plug was mounted on a torsional oscillator, and the superfluid density can be measured by studying the decrease of the resonant period. We have measured the pressure and temperature dependence of the period shift and find that the superfluid density is suppressed to ∼14% at 0 bar and is ∼53% of its bulk value at 29 bar. There is substantial temperature dependence even at the lowest values of T/T
c
(∼0.25) achieved in these experiments.
Fluctuation-Induced Diamagnetism above Tc in Nb/Si Multilayers
Authors: Obara Haruhiko , Uchinokura Kunimitsu , Tanaka Shoji
Published: March 2014

The fluctuation-induced diamagnetism above the superconducting critical temperature Tc was investigated in detail in the thin films of Nb/Si superconductive multilayers. Samples were prepared in an ultrahigh vacuum by electron-beam deposition method. When the Si layers were thick, two-dimensional behavior was observed and when they were thin, three-dimensional one was observed. An intermediate sample showed a crossover between the two- and three-dimensional behaviors. The experimental results were in good agreement with the theory of Gerhardts (Phys. Rev. B9 (1974) 2945).
3He Film Flow
Authors: Daunt J. G. , Harris-Lowe R. F. , Harrison J. P. , Sachrajda A. , Seeto T. , Steel S. C. , Turkington R. R. , Zawadzki P.
Published: March 2014

Following our earlier observation of 3He film flow, a new experiment has been designed to avoid possible temperature gradients along the 3He film. The film substrate, a 4 mm stainless steel tube, is physically separate from the level detectors, and the 3He both inside and outside the beaker is cooled with sinter. The onset of film flow is now below 1 mK, as distinct from ∼3 mK in our previous work. At our lowest temperature, 0.55 mK, the flow rate decreases almost exponentially with the height of the film, from ∼5 mm3/hour at the rim to ∼0.1 mm3/hour with the 3He 1.5 mm below the rim. As T approaches Tc the flow rate decreases. The present results suggest flow of the bulk or 3-D superfluid 3He, with the decrease in flow with height resulting from the suppression of the order parameter as the film thickness approaches the coherence length.
NMR Study of V/Ag Multilayered Supercondutors
Authors: Imai Takashi , Takigawa Masashi , Yasuoka Hiroshi , Mizutani Toshiyuki , Hosoito Nobuyoshi , Shinjo Teruya
Published: March 2014

The nuclear spin-lattice relaxation time T1 of 51V in V/Ag multilayered superconductors has been measured in zero magnetic field using the field cycling technique. The data indicate that the order parameter in the V layers increases up to 2Δ(0)=3.5kB Tc with decreasing temperature, irrespective of the existence of the proximity effect and the dimensional crossover in the multilayered films.
Metallic Superlattices with Monolayer Modulation
Authors: Makous John L. , Falco Charles M. , Vaglio Ruggero , Cucolo Annamaria
Published: March 2014

We report the preparation and characterization of sputtered Mo/Ta superlattices where the wavelengths are modulated by integer numbers of atomic monolayers. Resistivity and tunnel junction measurements on Mo/Ta superlattices with wavelengths in the range from 153 atomic planes each of Mo and Ta to the monolayer limit of 1 atomic plane of each are found to be consistent with their structural properties as determined by x-ray analyses. In addition, these results are consistent with earlier studies on the phonon structure of Mo/Ta using Brillouin scattering.
Order Parameter of 3He–B in Confined Geometries
Authors: Fetter A. L. , Ullah S.
Published: March 2014

The diagonal order parameter of superfluid 3He–B in confined geometries is found to differ qualitatively from the bulk form. The predicted depression of the critical current agrees well with experiment [1]. We solved the Ginzburg-Landau equations for the diagonal form of the order parameter in both slab and cylindrical geometries and the results for both cases are presented in detail.
Transient Phenomena during the Flux-Flow Onset in Thin-Film Superconductors
Authors: Buck Wolfgang , Parisi Jürgen
Published: March 2014

From time-resolved measurements of the flux-flow voltage detailed information can be derived about the spatial current distribution and the migration of flux domains across superconducting thin-film samples. Calculations based on the Gibbs-free-energy-barrier model achieve excellent agreement with the experimental voltage signal generated by a single flux domain. For a series of consecutive flux tubes the monopole-interaction model has to be included. In this case, the computer simulation of experimental voltage patterns reveals a damped oscillation of the number of flux quanta per domain. This number approaches an equilibrium value much smaller than the domain size in the case of a singularly existing flux tube. Flux flow in superconducting films turns out to be a convenient phenomenon for studying general properties of transient behaviour during its onset.
Elastic Correlations of the Pinned Fluxoid Lattice in a Superconductor
Authors: Yamafuji Kaoru , Matsushita Teruo , Toko Kiyoshi , Fujiyoshi Takanori
Published: March 2014

A formal theory of macroscopic pinning force FP is presented from a viewpoint that FP of is a value of Lorentz force FL at a bifurcation point, JT=Jc, above which a nondissipative state fluxoi'd lattice carrying a transport current with the density JT becomes unstable and a dynamic dissipative state called the flux flow appears. It is shown that correlation lengthes among pinned fluxoids diverge at the bifurcation point Jc, as these do in other bifurcation phenomena.
Heat Capacity of Dilute 3He–4He Mixtures
Authors: Owers-Bradley J. R. , Main P. C. , Batey G. J. , Church R. J. , Bowley R. M.
Published: March 2014

We have made measurements of the specific heat capacity of three dilute mixtures (2.6%, 1% and 0.5%) of 3He and of pure 4He. The 4He contribution to the specific heat of the mixtures is subtracted leaving only the 3He part. This is fitted to a theoretical expression over the whole temperature range from 10 mK to 700 mK. Assuming a dispersion relation of the form ε=\hbar2k2(1+γk2)/2m*, the fits yield the value of γ and the effective mass m* of each mixture. We find the effective mass in the limit of zero concentration is (2.24 ± 0.02)m3. This is compared to values deduced from other measurements.
Mechanism of Saturation and Nonsaturation of the Global Pinning Force in Superconducting Nb–Ti
Authors: Matsushita Teruo , Küpfer Heinz
Published: March 2014

The global pinning froce in Nb-49wt%Ti wires precipitated by heat treatment shows saturation at high fields. From the measurements of the Labusch parameter and the interaction distance in this regime, saturation is considered to be caused by a catastrophic instability of the pinned fluxoid lattice but not by the shearing deformation. The global pinning force increases largely by additional cold working of the wire. This enhancement is attained by stabilization of the defective fluxoid lattice by stronger pinning forces of the elongated precipitates.
Fluxoid Motion and Related Electromagnetic Phenomena in a Superconducting Disk in a Rotating Magnetic Field Geometry
Authors: Matsushita Teruo
Published: March 2014

Comparison is made from the viewpoint of relativity between the flux cutting process and the rotationally shearing fluxoid motion in a superconducting disk in a rotating parallel magnetic field. Two cases are treated: rotation of the external field and counterwise rotation of a superconducting disk in the stationary field. A remarkable discrepancy between two cases appears in the pin-free limit for the flux cutting process. The lack of the relativity is considered as serious defect in
the flux cutting model.
Investigation of the Critical Angle for Flux Cutting in Disks of Type II Superconductors
Authors: Lalonde R. , Sekerka J. , Leblanc M. A. R.
Published: March 2014

The critical angle for flux cutting is investigated by causing flux to enter at a fixed angle θo with respect to the flux line lattice of trapped flux.
Calculation of the Viscosity Coefficients of 3He–A
Authors: Shahzamanian M. A.
Published: March 2014

The fourth rank shear viscosity tensor of 3He–A is calculated by using the kinetic equation for Bogoliubov quasiparticle. The approximate collision integral of Wölfle et al for 3He–B is modified and used. In general only three of the five viscosity coefficients are independent.
New Results in the Theory of Collective Pinning
Authors: Brandt Ernst Helmut
Published: March 2014

Recent progress in the theory of collective pinning of flux lines in type-II superconductors is outlined: Its correction due to nonlocal theory of elasticity, its extension to films of finite thickness which yields the condition for dimensional crossover, and improved computersimulations. The observation of an abrupt reversible transition to a state with highly disordered flux-line lattice is commented. The meaning of the range and strength of pins in a periodic flux-line lattice is discussed.
Flux Pinning in A15 Superconductors
Authors: Osamura Kozo , Ochiai Shojiro
Published: March 2014

Global pinning force is influenced greatly by microstructures like grain size and third elements, when Nb3 Sn and V3 Ga superconductors are prepared by various different techniques. The structure dependence of flux pinning has been investigated in details. The main flux pinning center was attributed to the grain boundary. Accordinng to the modified shear model proposed by Evetts and Plummer (1985), the global pinning force has been analysed. It was found to have the same magnitude for both NB3Sn and V3Ga. The third elements influenced the specific force as well as the upper critical field. In and Ga made the pinning force increase, while the pinning force decreased by the addition of Ti or Zr. Generally, increasing the critical field resulted in the decrease of specific pinning force. This apparent result is suggested to relate with the change of the thermodynamic critical field. The effect of strain on the pinning force was not direct, but appeared through the change of critical field.
Flux Pinning Behavior in Amorphous MoSi Thin Films
Authors: Kubo Shugo
Published: March 2014

Pinning force densities Fps for amorphous Mo0.75Si0.25 films (200∼20 nm thick) for the use of memory devices utilizing Abrikosov vortices have been examined in the perpendicular and parallel fields. The maximum Fpmaxs in the perpendicular field decreased with decreasing film thickness. On the other hand, the Fpmaxx dependence on film thickness in the parallel field was found to have a peak at a thickness around 50 nm. Furthermore, Fp values for the thinner films in the parallel field became one order of magnitude larger than those in the perpendicular field. Pinning in these films, including the effect of a Si underlayer and overlayer for protection, was discussed.
Probing of Defects in Amorphous Superconducting Films via Collective Flux Pinning
Authors: Wördenweber R. , Pruymboom A. , Kes P. H.
Published: March 2014

Two-dimensional collective pinning in thin amorphous films is an useful tool to study defects on the scale of the coherence length. Our results obtained on sputtered NbxGe and MoxSi layers demonstrate a relation between the sputter conditions, the resulting defects and the pinning behavior. A classification of the defects is given and estimates on their size and density are derived, which are in excellent agreement with other (direct) observations.
Superconducting Coil Application to Power Frequency –50 k VA Coil Development–
Authors: Shimizu Eriko , Ito Daisuke
Published: March 2014

In order to study stability and a. c. losses in a. c. superconducting coils, the authors have developed a 50kVA coil and operated it at 50Hz. The coil was wound with an ultra-fine multifilamentary superconducting 42 strand cable. The conductor has 15367 NbTi filaments, 0.42µm in diameter with 1.1mm twist pitches. To prevent wire motions, the cable was embedded in grooves on coil formers and was wound under a large tension. The coil was quenched at 173A r.m.s., which was about 90% of the critical current, and central peak field was 1.54T. The measured a. c. losses were 2.2W/coil, when the coil was operated at 163A r.m.s., 1.45T. From a. c. loss measurements, it was shown that inter-strand coupling loss was very small, compared with inter-filament coupling loss.
Fluxon Fluctuations in Long Josephson Junctions
Authors: Han B. S. , Lee B. , Symko O. G. , Zheng D. J.
Published: March 2014

Fluctuations of a long Josephson junction biased at current steps lead to telegraph noise where the mean lifetime between two steps depends on the bias conditions. The origin of such fluctuations is the thermal noise inside the junction.
Radiation from NB3Ge Nanobridges: Experiments and Comparison with Theory
Authors: Mück M. , Rogalla H.
Published: March 2014

High-κ nanobridges were structured from Nb3Ge thin-films and their radiation was measured at 10.5 GHz. The measured power levels and linewidths are about 10-13 W and 300 MHz, respectively. Series connected bridges show a much smaller linewidth. This indicates a coherent behaviour which can be observed in the de-characteristics, too. The experimental results are compared with a theoretical model and characteristical times are extracted.
Optimization of a DC SQUID with Complete Flux Transformer Circuits
Authors: Knuutila Jukka , Kajola Matti , Sepä Heikki , Mutikainen Risto , Salmi Jorma
Published: March 2014

The design of a complete DC SQUID is discussed, taking the effects of the flux coupling circuits and resonances caused by parasitic capacitances into account. Our analysis and practical considerations suggest coupling via an intermediary transformer. A model is developed to optimize the structure: it describes the whole circuit with the help of a suitably modified autonomous SQUID. Following these design principles we have built a DC SQUID, primarily for use in biomagnetic research but also well suited for other applications. The lowest measured noise of our SQUID is 1×10-6 φ0/√Hz, indicating the success of the design.
Bunching of Solitons in Long Josephson Junctions
Authors: Sakai Shigeki
Published: March 2014

An analytic method for getting bunched two-soliton states in long Josephson junctions is proposed. The theory is based on assuming the junction current-phase relation to be of a triangular sawtooth shape. In the presence of the surface impedance losses, if the bias current is larger than a critical value, there are plural solutions at any bias current, but if not, there is no solution. Numerical experiments using a finite difference method are also performed, and we conclude that solutions are stable when two solitons take the first- and the third-nearest configurations, but unstable when they take the second- and fourth-nearest ones.
“Regular” Barrier Nonuniformities in Optically Controlled Josephson Tunnel Junctions
Authors: Camerlingo C. , Janawadkar M. P. , Russo M.
Published: March 2014

Josephson junctions with a photoconducting artificial barrier exhibit a light-sensitive behavior of both the quasiparticle and pair tunneling regimes. Moreover a shaping of the critical current density profile may occur as a consequence of nonuniformities either in the illumination or in the barrier film morphology. In this framework a novel procedure to fabricate tunnel junctions with a variable thickness barrier is reported. Effects due to a “regular” modulation of the thickness have been experimentally investigated by light-induced critical current vs. external magnetic field measurements. Preliminary results on “small” overlap structures are discussed.
Chaos in Josephson Junctions Induced by Picosecond Current Pulses
Authors: Sobolewski Roman , Dykaar Douglas R. , Hsiang Thomas Y. , Vanneste C. , Chi C.-C.
Published: March 2014

We report studies of intermittent chaos in hysteretic Josephson junctions induced by ultrashort electrical pulses. Substantial changes in the junction dc I-V characteristics, including an excessive low frequency noise, a novel re-entry state wherein the dynamics became chaotic at low dc bias, but returned to the zero-voltage state at higher biases, and a complicated behavior for very high amplitude input pulses were experimentally observed. The threshold switching curve was different from that in the static limit. The experimental findings are in good agreement with numerical simulations based on the resistively and capatively shunted junction model.
Oscillating DC-Characteristics of the Quasiparticle Current Injected into a Superconductor under Joule Heating Conditions
Authors: Hahn Artur , Hümpfner Klaus
Published: March 2014

DC-characteristics measured on Ag/Ta metallic microcontacts show the oscillatory behavior previously accounted for by interference effects of quasiparticles Andreev-reflected from the NS phase boundary. In a magnetic field the effect is more pronounced and more than fourty orders of interference are observable. The “melting depth”, i.e. the radius of the normal region below the contact, varies linearly with the dissipated power U2/RN.
Artificial Microstructure and Quantum Interference of Supercurrents
Authors: Fink Herman J. , Loo J. , Roberts S. M.
Published: March 2014

Multiply connected branches in a superconducting micronetwork may show quantum interference of supercurrents in the presence of an applied magnetic field without Josephson junctions (JJ). A microloop could be a suitable direct current (dc) superconducting quantum interference device (SQUID) without JJs provided its size is chosen properly. We have calculated the persistent current density, JB, which gives rise to the magnetic moment of a microloop as a function of magnetic flux threading the loop for various ring sizes at externally injected current densities of about 1/2 the critical current of a long straight wire. The corresponding order parameters at various points in the circuit are shown as a function of JB for two ring sizes. We find that such a circuit behaves like a dc SQUID.
Phase Transition and Dissipation by Quasiparticle Tunneling in Arrays of Josephson Junctions
Authors: Kampf Arno , Schön Gerd
Published: March 2014

Arrays of Josephson junctions show different phase transitions depending e.g. on the dimensionality of the network. The dynamics associated with the charging of the superconducting islands introduces quantum mechanical effects. We investigate the influence of the dissipative quasiparticle tunneling currents on the quantum effects and the phase transitions.
Microscopic Calculation of the Heat Transfer between an Isotropic Superfluid and a Granular Structure
Authors: Hughes G. D. , Hui V. C. , Lambert C. J.
Published: March 2014

We introduce a new model of a sintered metallic powder in which neighbouring grains are either fused together with probability P or weakly coupled with probability (1-P). A new selective renormalization technique is used to compute the density of vibrational states ρ(ω) at wavelengths λ greater than or of order a typical grain size L. For λ≫L, ρ(ω) is Debye-like, whereas for λ>L, a cross over to fracton-like behaviour is observed, consistent with recent experimental results. BCS theory is employed to yield an expression for the heat transfer Q between sinter modes and 3He-B quasi-particles. This expression is combined with ρ(ω) to yield for the first time a fully microscopic evaluation of the temperature dependence of \dotQ.
Image Frequency Termination of the Superconducting Quasiparticle Mixer
Authors: Feldman Marc J. , Face Dean W.
Published: March 2014

A simple analytic expression is derived from the quantum theory of mixing ignoring all reactances, which predicts that a smaller image termination conductance always increases the range of parameter values which produce infinite available gain in the superconducting quasiparticle mixer. An exactly short circuited image is anomalous in that infinite gain is strictly prohibited, except for one special case. Including the nonlinear quasiparticle reactance, the calculated gain contours for real junction I-V curves, displayed on a Smith chart of image termination impedance, are symmetrical about an axis rotated counterclockwise from the real axis. This rotation implies that the predominant effect of the nonlinear reactance is a time delay. This time delay may be related to the average time delay in the quasiparticle response function.
Elimination of Image Fields in Magnetometer Flux Transformers
Authors: Dummer D. , Weyhmann W.
Published: March 2014

We present a feedback scheme which avoids errors in the measurement of magnetization due to the image field created by the induced current in a flux transformer. The scheme has been tested on the superconducting transition of indium and proven to be very effective.
Quasiperiodicity in Long RF-Biased Josephson Junctions
Authors: Guerrero Luis E. , Octavio Miguel
Published: March 2014

We present and discuss numerical simulations, using a modified sine-Gordon equation, of long Josephson junctions in a magnetic field and in the presence of rf radiation. Quasiperiodicity arises from the coexistence of the frequency of the driving force and the natural frequency of an oscillating spatial structure of soliton-like character. The quasiperiodic regime presents subharmonic response at either of those frequencies.
Measurements of Noise Characteristics of a dc SQUID with a Resistively Shunted Inductance
Authors: Ohkawa N. , Noguchi T. , Tsukada N.
Published: March 2014

We experimentally demonstrate that energy sensitivity of a dc superconducting quantum interference device (SQUID) with large β=2LsIo/φo is lowered by connecting a damping resistor across the loop inductance of the SQUID, where Ls is the loop inductance of the SQUID, Io is the critical current of each Josephson junction, and φo is the flux quantum. This is due to the considerable increase of the flux-to-voltage transfer function of the SQUID.
A Microscopic Approach to Nonlinear Sound Propagation in Superfluid 3He–B
Authors: Namaizawa Hiroshi
Published: March 2014

A microscopic approach to nonlinear sound propagation observed in 3He–B will be given. Using the eigen-solution of the real squashing modes we define the quasi-spin operators from the triplet-pairing order-parameters and study the coupling between the quasi-spin and the zero-sounds. The resulted nonlinear equations are shown equivalent to those encountered in optical two-level systems.
Low-Temperature Scanning Tunneling Microscopy of Superconducting Materials
Authors: Ishigame Y. , Morita S. , Mikoshiba N.
Published: March 2014

For the measurement at low temperature, we constructed a small and rigid tunnel unit. Using this tunnel unit, we obtained the STM image of Ag plate without a vibration isolation system. We also calibrated the piezoelectric constants of the tube scanner by measuring the STM image of the barrier layer of the aluminum oxide.
Self-Field Effects in Josephson Junctions Coupled with n-InAs and the Surface Inversion Layer on p-InAs
Authors: Inoue Koh , Kawakami Tsuyoshi
Published: March 2014

Magnetic properties and electrode geometrical effects in planar-type Josephson junctions coupled with n-InAs and the surface inversion layer of a two-dimensional electron gas (2DEG) on p-InAs are studied. For n-InAs coupled junctions, the magnetic field dependences of the critical currents show a strong self-field limitation accompanying the electrode geometrical effect, and they are well explained by the “large” junction theory. However, for 2DEG coupled junctions, the properties reveal “small” junction behavior, and they are inconsistent with the Josephson penetration depth estimated from the critical current density.
Collective Excitations in p- and d-Wave Superconductors
Authors: Hirashima Dai S. , Namaizawa Hiroshi
Published: March 2014

We study the collective excitations in p- and d-wave superconductors. For both cases we develop a theory of response in a gauge invariant way taking account of the collective degrees of freedom. Further we find that in the d-wave phases there also exist collective modes as in the p-wave phases. Effects of crystal anisotropy on the collective modes are also discussed.
Investigation of the Magnetic Refrigerant for the Ericsson Magnetic Refrigerator
Authors: Hashimoto T. , Kuzuhara T. , Matsumoto K. , Sahashi M. , Inomata K. , Tomokiyo A. , Yayama H.
Published: March 2014

In the temperature range above ∼20 K, the Ericsson magnetic refrigeration cycle has to be adopted instead of the Carnot cycle, because the lattice entropy becomes no longer negligible as compared with the magnetic entropy. Moreover, in this range since the thermal agitation energy ∼kT of spin also increases, the ferromagnetic materials have to be used for the refrigerant to obtain large entropy change enough to refrigerate. However, temperature variation of the magnetic entropy change of ferromagnetic material is not suitable for the Ericsson cycle.
In the present paper we will give the answers to the following questions; (1) what kinds of ferromagnets must be used for the refrigerant? (2) what kind of method to compose the refrigerant using those ferromagnets is promising?
Bulk Superconductivity of Silver at Millikelvin Temperatures Induced by the Proximity Effect
Authors: Mota A. C. , Visani P. , Pollini A.
Published: March 2014

Measurements of the effective field penetration depth λ, breakdown field, Hb, supercooling field, Hsc, and superheating field, Hsh, are used to investigate the superconducting properties of silver caused by the proximity of niobium in the temperature range 5 mK<T<9.5 K. An analysis of the Hb data yields the coherence length ξN=α/T with α=1.46 µm K. This value is in very good agreement with the theoretical value \hbarvF/2πk=1.70 µm K.
Long Time Relaxation Process in MOSFET Devices
Authors: Porjesz Tamás , Kovács György , Kirschner István , Kármán Tamás , Zsolt Gábor
Published: March 2014

Transistor characteristics in implanted MOSFET structures were measured up to higher drain voltages. Applying a drain voltage above a critical value we observed a decreasing drain current at constant drain and gate voltages. The decrease of the current has shown an exponential-like behaviour having a time constant of 15 minutes. After swithching off the drain voltage the current, or better to say, the conductivity started to increase with a time constant somewhat higher than the decreasing one. The critical drain voltage depends on the temperature and on the gate voltage as well. At room temperature the critical voltage in the range of 30 volts while at helium temperatures it is in the range of 10 volts. For all of the measurements a gate voltage near the threshold was used to avoid the sample heating by the higher drain current. The effect could be explained by slowly depleting and filling traps in the insulating layer. The measurements gave similar results for n- and p-channel insulated gate MOSFET-s.
Low-Temperature High-Pressure Apparatus with Large-Capacity Pressure Cell
Authors: Kogure Yoshiaki , Hiki Yosio
Published: March 2014

An apparatus has been constructed to generate hydrostatic pressures up to 2 GPa at temperatures 4.2 K - 300 K in a high pressure cell with the capacity of 2 cm3. The cell was a piston-cylinder type one with using the teflon capsule technique. An oil press equipped with a pressure control system was used to apply a constant load on the high pressure piston. Some ultrasonic and related measurements are planned to be performed with this apparatus by utilizing the merit of the large-capacity cell.
Experimental Study of Low-Temperature Long-Time Relaxation in Epoxy Resin
Authors: Sahling S. , Sahling A. , M. KOláč M. KOláč
Published: March 2014

The power \dotQ(T1, To, t) released after rapid temperature change from T1 (1.1K≤T1≤25K) to To (1.1K≤To≤4.2K) for 0.2h≤t≤700h was measured. At T1, To<2K results agree with the standard tunnelling theory with a distribution parameter of two-level systems Pm=1.0·1039/Jg. The heat release for T1>2K, To≤1.3K leads to the assumption of the existence of a maximum energy Ef/kB=16.5K in the distribution fuction. For To>1.3K, experiments indicate that the tunnelling parameters are temperature dependent.
Frequency Stabilization of a Sapphire Resonator Oscillator Using an Acoustic Modulation Technique
Authors: Lusher C. P. , Hardy W. N.
Published: March 2014

We are developing a microwave oscillator using a sapphire resonator contained in a superconducting cavity as the frequency determining element. We present a technique for keeping a free-running oscillator at the centre of one of the microwave resonances in the sapphire. In this technique the sapphire is excited at one of its acoustic modes of free vibration using an ultrasonic transducer. The resulting periodic distortion of the sapphire causes a periodic variation in the microwave resonance frequencies, which are determined by the size of the sapphire. This introduces sidebands onto a reflected microwave reference carrier and these sidebands can be used to keep the carrier at the exact centre of a microwave resonance in the sapphire.
Basic Discussion on Low Temperature Power Electronics
Authors: Murakami Yoshishige , Kimura Hideo
Published: March 2014

The low temperature power electronics are needed for the interface between the superconducting energy system and the conventional power system, since the latter has been developed for the high voltage and low current, and for the alternating current, while the former has been oriented for the high current and low voltage, and for the direct current.
As for the power switching devices for the converter between ac(conventional technology) and dc(superconducting technology), we have experimented the semiconductor unipolar and bipolar devices and their models for the computer simulation have been derived. The unipolar devices among which power MOS FET's represent the capability of low loss and high density current conduction in the liquid nitrogen temperature, although in the liquid helium temperature the freeze out of carriers has been observed. However the bipolar devices have the problem of the freeze out of carriers in low temperatures.
The computer simulation based on the derived model are in good agreement with the experimental results and the optimal design parameters have been discussed. The operation in the liquid nitrogen temperature of power switching devices will be well consistent with the high temperature superconductors which have been recently discovered.