bluuebunny/crossref_metadata_2025 huggingface dataset:
LOW TEMPERATURE AND THE ORIGIN OF CRYSTALLINE SYMMETRY
Authors: RADIN CHARLES
Published: November 2004

This is a status report on the classical problem of determining the origins of crystalline symmetry in low temperature matter.
FOURIER TRANSFORMS AND STRUCTURAL ANALYSIS OF SPIRAL LATTICES
Authors: FAN XUDONG , BURSILL L. A. , PENG JU LIN
Published: November 2004

Elementary properties of spiral lattices are evaluated in reciprocal space. The relative merits of direct space object data, Fourier transforms and power spectra (diffraction patterns) are discussed and applied to the identification of the radial law for three distinct naturally-occurring spiral structures.
THE ELECTRONIC STRUCTURE AND SUPERCONDUCTIVITY OF THE HIGH Tc COPPER OXIDES
Authors: SCHLUTER M.
Published: November 2004

The electronic structure and possible superconductivity mechanisms of the new high Tc copper oxides are discussed. The conventional band picture is contrasted with the localized orbital Mott-Hubbard picture for the electronic groundstate. The nature of quasiparticles introduced by doping of the insulating parent compounds depends on assumptions made for the underlying groundstate. Possible pairing mechanisms of these particles that have been proposed to lead to high temperature superconductivity are analyzed.
EFFECTIVE ACTION OF A TWO-DIMENSIONAL ANTIFERROMAGNET
Authors: IOFFE L. B. , LARKIN A. I.
Published: November 2004

In the limit of weak quantum fluctuations an effective long-wave action of the Heisenberg quantum antiferromagnet is obtained which allows one to get a spectrum, spin, and statistics of long-wave fluctuations. In the vicinity of the point of instability of an antiferromagnetic state quantum fluctuations result (at zero temperature as well) in a paramagnetic phase of a spin liquid.
INFLUENCE OF CARBON ON AMORPHOUS HYDROGENATED CARBON SILICON TIN ALLOY
Authors: DEMICHELIS F. , KANIADAKIS G. , TAGLIAFERRO A. , TRESSO E. , DELLA MEA G. , PACCAGNELLA A.
Published: November 2004

A systematic experimental investigation on different sets of a-SiSn:H and a-CSiSn:H films prepared in similar conditions has been made. A correlation among the elemental composition (obtained from RBS, nuclear reaction and ERDA analysis), the chemical bonding (from IR absorption measurements), the optical and electrical parameters (from transmittance, reflectance and conductivity measurements) of the two types of alloy leads to a more fundamental understanding about the influence of carbon in amorphous hydrogenated silicon tin and about the possibility of optimizing its physical properties by incorporating convenient carbon contents.
SPECIFIC HEAT OF THE HIGH Tc SUPERCONDUCTOR Bi-Sr-Ca-Cu-O
Authors: YUAN S. L. , LI J. W. , WANG W. , RAN Q. Z. , ZHENG G. G. , GUAN W. Y. , ZHENG J. Q.
Published: November 2004

The Bi-Sr-Ca-Cu-O superconductors with the nominal composition (1113) were prepared. An orthorhombic unit cell (a = 0.544 nm , b = 0.543 nm , c = 3.07 nm ) was determined by X-ray diffraction. The resistance transition curve shows that the sample has an onset around 110 K and the zero resistance temperature at 85 K. The mutual inductance measurement also shows a two-step transition which correspond to two superconducting phases as well as that in the resistive transition. The specific heat measurement was performed in the range of 56 K to 130 K by the continuous scanning method. A simple extrapolation of the curve was made from below and from above Tc to yield ΔC = 45 mJ/g.K and ΔC/Tc = 0.49 mJ/g.K .2 From these values, the Sommerfeld constant γ and the Debye temperature θ D were estimated.
THE NEUTRAL HIGGS PHENOMENA FOR THE HUBBARD HAMILTONIAN
Authors: SCHMELTZER D.
Published: November 2004

Using a functional integral method we show that the Hubbard model coupled weakly in the third dimension is equivalent to an XY model (the phase fluctuation of the charged singlets) coupled to a neutral Higgs field induced by the spinon fluctuations. The analysis is performed for the non half-filled band case. The critical behaviour is similar to the three dimensional type II superconductor.
A WEAK COUPLING THEORY FOR La2CuO4: ln2–PARQUET APPROACH
Authors: Dzyaloshinskii I. E. , Yakovenko V. M.
Published: November 2004

In the model of two-dimensional electrons with a square Fermi surface , ln 2-parquet equations are derived and numerically solved. It is suggested that this model can describe La 2 CuO 4 in the weak coupling limit. The main result is a strong difference between the Hubbard model with one charge and the model with four effective charges, describing an interaction of a general form.
PAIRING OF HOLES INDUCED BY MAGNETIC INTERACTIONS
Authors: Schmeltzer D.
Published: November 2004

We consider a planar Hubbard model with three sites per primitive cell. This model is mapped into a magnetic Hamiltonian. The charged holes interact via the magnetic interaction. The effect of this interaction is to create a magnetic background for the holes. Defining new quasi-particles we find that the many-body interaction becomes attractive and gives rise to conventional superconductivity. At large hole concentrations the critical temperature is determined by the antiferromagnetic exchange between copper-copper. In addition, the Increase of hole concentration reduces the exchange coupling which vanishes at some critical values. At small hole concentrations the critical temperature is determined by the Bose Einstein condensation temperature.
LANDAU FREE ENERGY FUNCTIONAL FOR BIPOLARONIC SUPERCONDUCTOR
Authors: KOPEĆ T. K.
Published: November 2004

The Landau free energy functional with two competing order parameters is derived from microscopic considerations for bipolaronic superconductor.
EFFECT OF LOW CRYSTAL SYMMETRY ON ELECTRON-PHONON COUPLING IN PEROVSKITE SUPERCONDUCTORS
Authors: Mazin I. I. , Rashkeev S. N.
Published: November 2004

The electron-phonon coupling for La 2 CuO 4-type superconductors is calculated in frameworks of rigid-muffin-tin approximation by two ways: first, in spherical approximation of Gaspari-Gyorffy and, second, taking into account the proper local symmetry. In the second case electron-phonon coupling is a few times stronger than in the first one. We conclude that low local symmetry, especially on O I sites is to a great extent responsible for the strong electron-phonon coupling in perovskites.
NUMERICAL SIMULATION OF THE HIGH-Tc SUPERCONDUCTORS
Authors: Morgenstern I.
Published: November 2004

Monte Carlo simulations based on the Trotter-Suzuki transformation were carried out using 6 × 6 and 12 × 12 lattices and the single-band Hubbard model with intermediate-range repulsive interaction. The absence of the "minus-sign problem" for sufficiently low temperatures and appropriate doping indicates bosonic behavior reminiscent of superconductivity. It was found that holes prefer to pair on next-nearest-neighbor sites while nearest neighbors are suppressed. Additional electron-phonon coupling in the form of the breathing mode not only preserves this symmetry but strengthening of the bosonic background indicates the possibility of superconductivity.
GROUND-STATE PROPERTIES AND ELEMENTARY EXCITATIONS OF THE ONE-DIMENSIONAL HUBBARD MODEL
Authors: Carmelo J. , Baeriswyl D.
Published: November 2004

The ground state of the one-dimensional Hubbard Hamiltonian is discussed on the basis of the Bethe ansatz solution of Lieb and Wu. A simple analytical representation of the distribution functions for charge and spin degrees of freedom is derived. The elementary excitations are associated with electron-hole pairs of two pseudo-fermion systems, one for the charge, the other for the magnetic excitations. Spinons and holons correspond to ground state configurations of odd-numbered rings. It is argued that holons will form bound pairs in weakly coupled chains.
Electronic structure and charge fluctuations in YBaCu3O7−δ from EELS, XPS and Auger spectroscopies
Authors: Balzarotti A. , De Crescenzi M. , Motta N. , Patella F. , Sgarlata A.
Published: November 2004

Electron energy loss, x-ray photoemission and Auger spectroscopies have been used to study the valence states and the Cu 2p and 01 s core levels of YBa 2 Cu 3 O 7−δ as a function of the oxygen concentration δ. Evidence is found of dynamic charge fluctuations on the oxygen sublattice giving rise to a greater concentration of trivalent copper at the Cu(1) sites with respect to that determined by the analysis of neutron diffraction data. The lowest final states configurations of Cu 2+ and Cu 3+ are found to be c3d10L and c3d10L2, respectively, where c and L denote core holes on copper and oxygen atoms. Oxygen holes have high mobility and a Hubbard correlation energy less than 2 eV, a signature of their delocalization.
PHOTOINDUCED I.R. ABSORPTIONS IN THE 1-2-3 SYSTEM
Authors: TALIANI C. , RUANI G. , ZAMBONI R. , MATACOTTA F. C.
Published: November 2004

The infrared photoinduced absorption (PA) spectrum of the semiconducting tetragonal phase of YBa 2 Cu 3 O 7−y ( y = 0.79 ÷ 0.85) is investigated in the 3200–350 cm −1 spectral range at low temperature (34 k). A broad electronic band is observed at 0.13 eV and is attributed to long lived metastable hole states generated by photoexcitation.

Two PA phonon bands observed at 435 and 510 cm −1 correspond to totally symmetric modes of 1-2-3 involving Cu-O vibrations parallel to c axes. A vibronic activation mechanism is proposed in order to account for their IR activity and the nature of the .13eV midgap hole state is discussed in this framework.
NONSUPERCONDUCTING PHASES AT GRAIN BOUNDARIES IN YBa2Cu3Ox SUPERCONDUCTORS
Authors: WANG KEGUANG , ZHANG TINGJIE , ZHOU LIAN , ZHANG PINGXIANG , WANG SUQIAN , HUANG HANLIANG
Published: November 2004

The morphology, composition and phases of grain boundaries in YBa 2 Cu 3 O x superconductors have been investigated by SEM, TEM and AES. The results show that some impure phase particles present at the grain boundary in the samples sintered at 940°C for 26 hours, which grow to be a shell around the grain as the sintering temperature increases to 970°C. No such particle has been found at the grain boundaries in the sample sintered at 920°C for 26 hours by SEM, Jc is the highest in our studied samples. AES and TEM analyses indicate that the grain boundaries are complex multilayer structures consisting of barium-rich, copper-rich, carbon-rich, yttrium and oxygen-deficient impure phases. The dominant impure phases harmful to Jc at the boundary are the mixtures of BaCO 3, Cu 2 O , BaC 2, Y 2 C 3 and an amorphous material.
REPRODUCIBLE TECHNIQUE FOR DEPOSITION OF Y–Ba–Cu–O THIN FILM FROM RF SPUTTERING
Authors: JIA Q. X. , REN D. , ANDERSON W. A.
Published: November 2004

The composition of Y–Ba–Cu–O thin films deposited by RF sputtering was found to depend strongly on the substrate location and accumulated sputtering time, if a stoichiometric compound target was used. The film is seriously off-stoichiometric, with Ba being deficient, and Cu and Y in excess not only for the centered substrate, but also for the off-centered substrate. However, after prolonged sputtering, stable conditions can be obtained and a right film composition achieved for the off-centered substrate. A more powerful technique for obtaining stoichiometry in as-deposited thin films can be realized by arranging the substrate perpendicular to the target. The accumulated sputtering time for obtaining reproducible stoichiometric, as-deposited films is directly related to the substrate location. A stoichiometric thin film was obtained during the first deposition from a new target and repeated in many following runs.
SUPERCONDUCTING PROPERTIES OF HTSC THIN FILMS PREPARED IN SITU BY SINGLE TARGET DEPOSITION
Authors: GEERK J. , Xi X.X. , LI H.C. , GUAN W.Y. , KUS P. , HÖBEL M. , LINKER G. , MEYER O. , RATZEL F. , SCHULTHEISS C. , SMITHEY R. , STREHLAU B. , WESCHENFELDER F.
Published: November 2004

Thin films of ReBaCuO (Re=Y, Gd) and of BiCaSrCuO have been deposited onto A1 2 O 3, MgO , SrTiO 3, Si and ZrO 2 substrates by planar and inverted cylindrical magnetron sputtering. The main advantage of this preparation technique is the high reproducibility allowing detailed and systematic studies of the film properties as a function of deposition parameters. Optimum deposition parameters were a high oxygen partial pressure of 2×10−1 Torr in an oxygen-argon mixture and substrate temperatures near 800°C. Except for the substrate Si the films grow highly textured on all substrates. For the 1–2–3 material zero resistance is obtained near 90 K for the case of textured growth. For Si the best film showed zero resistance near 84 K. High critical currents between 4×105 and 5.5×106 A/cm 2 were determined for films of the 1–2–3 material on the substrates MgO , ZrO 2 and SrTiO 3. On films SrTio 3 tunnel junctions with Pb and In counterelectrodes could be prepared which showed a gap-like feature in their current-voltage characteristic. These junctions could be prepared with great reproducibility and experimental arguments could be provided which show that this gap-like feature is due to a superconducting density of states effect. Finally, first results are presented on YBaCuO thin films which were deposited by a novel ablation device which uses a pulsed electron beam instead of the laser beam.
HOLONS WITH SPINON CLOUD IN THE DOPED RVB STATE
Authors: MORI HIROYUKI
Published: November 2004

The effect of interactions between holons and spinons in doped resonating valence bond states is investigated. In particular, we focus on those interactions through which a holon emits or absorbs spinons, and we study the influence of these interactions on the effective mass of a holon along the slave boson treatment in the mean field approximation. Our result asserts that the spinon cloud scarcely affects the effective mass of a holon in both s- and d-wave states.
THE HEAT CAPACITY OF THE ONE-DIMENSIONAL MODEL OF QUASIPERIODIC BINARY ALLOY
Authors: SALEJDA WŁODZIMIERZ
Published: November 2004

The temperature dependence of the heat capacity [Formula: see text] of the harmonic model of quasi-periodic binary chain of atoms is studied numerically. It is shown that [Formula: see text] at T RED =k B T/E max ≲10−2, where A is a constant depending on the model parameters and E max denotes a maximal eigenenergy of the dynamic matrix. At high temperatures, [Formula: see text] approaches the Dulong-Peti limit.
THEORETICAL STUDIES OF SMALL COPPER OXIDE CLUSTERS AND POSSIBLE RELEVANCE TO SUPERCONDUCTIVITY
Authors: WULFMAN CARL E. , CURTISS LARRY A.
Published: November 2004

Ab initio molecular orbital computations indicate that in a [ CuOH 2]3+ complex oxygen hole (pπ type orbital) formation is favored over Cu 3+ formation. In contrast, it is found that in a [ Fe(H 2 O )]3+ complex oxygen hole formation is much less favorable, thus, suggesting a reason for the depression of T c upon Cu substitution by Fe in YBa 2 Cu 3 O 7−x. Computations on a symmetrical [ Cu(H 2 O )4]3+ cluster indicate that it has a degenerate unrestricted Hartree-Fock (UHF) ground state in which the oxygen hole is strongly coupled adiabatically to nuclear motions. The electronic repulsion energy of the ground state is, as a result, lowered by a combination of vibrational and electronic correlation effects. The relevance of these observations to the existence of high temperature superconductivity in cuprates is discussed.
A STEP-BY-STEP APPROACH TO INTEGRABILITY
Authors: HANSEL DAVID , MAILLARD JEAN-MARIE , RUJÁN PÁL
Published: November 2004

We try to elucidate the role played by different symmetries in simple models of statistical mechanics. Starting with obvious symmetries for the partition function and combining them with duality relations we obtain a set of constraints on the possible algebraic varieties relevant for the integrable manifolds and the phase diagram of the lattice model. When imposing in addition the inversion relation special polynomials are obtained, which are close and sometimes identical to the set of equations defining the parameter subspace of the integrable models. Our procedure is detailed on the q-state chiral Potts models on a square lattice, in particular for q=3 and 4.
Phenomenological Constraints on Theories for High Temperature Superconductivity
Authors: Varma C.M.
Published: November 2004

This is an attempt at a coherent view of the normal and superconductive state properties of the high-temperature superconducting materials. The discussion is organized as follows:

Phenomenology of the Normal state anomalies, where it is shown that a single hypothesis about the charge and spin polarizability is enough to understand essentially all their properties.

Phenomenology of the Superconductive state.

Lessons from the Phenomenology.

Phenomenology for the choice of a Microscopic Model.

Comparison of the Bi-O family with the Cu-O family.

Speculations on the Physics of the Magic Polarizability.
EQUIVALENCE OF QUANTUM BOLTZMANN EQUATION AND KUBO FORMULA FOR dc CONDUCTIVITY
Authors: CHEN LIAO-YUAN , SU ZHAO-BIN
Published: November 2004

We present a derivation of the quantum Boltzmann equation for linear dc transport with a correction term to Mahan-Hansch's equations and derive a formal solution to it. Based on this formal solution, we find the electric conductivity can be expressed as the retarded current-current correlation. Therefore we explicitly demonstrate the equivalence of the two most important theoretical methods: quantum Boltzmann equation and Kubo formula.
UNIVERSAL CONDUCTANCE AT THE SUPERCONDUCTOR-INSULATOR TRANSITION
Authors: WEN X. G. , ZEE A.
Published: November 2004

Invoking a duality picture we used earlier to describe semion superconductivity, we suggest an explanation of the universal conductance measured in thin films at the superconductor-insulator phase transition.
MAGNETIC RELAXATION EFFECTS IN ZERO FIELD COOLED Y–Ba–Cu–O
Authors: HASANAIN S. K. , MUMTAZ A. , ALI T. , HUSAIN M. , BHATTI G. S.
Published: November 2004

Results of the magnetic relaxation in 1:2:3 superconductors initiated by a very slow field reversal, are reported. We find that the relaxation at earlier times follows a stretched exponential type function, while at longer times it has a logarithmic behaviour. The onset time of ln t behaviour depends on the applied field. The data is interpreted in terms of a two-stage relaxation process.
MODIFIED TIGHT-BINDING APPROXIMATION AND ELECTRON-PHONON SPECTRAL FUNCTION FOR TRANSITION METALS
Authors: KUZEMSKY A.L. , ZHERNOV A.P.
Published: November 2004

The modified tight-binding approximation has been analyzed in detail and is applied to the derivation of an expression for electron-phonon spectral function (EPSF) which enters the strong coupling equations of superconductivity. Numerical calculations of the EPSF and the electron phonon coupling parameter λ for five transition metals, V, Nb, Mo, W, Ta have been performed.
HUBBARD MODEL AND ANYON SUPERCONDUCTIVITY: A REVIEW
Authors: BALACHANDRAN A. P. , ERCOLESSI E. , MORANDI G. , SRIVASTAVA A. M.
Published: November 2004

Several different models have recently been proposed to explain high temperature superconductivity.

This is a review of two such proposals, namely the Hubbard and anyon models. There is a belief that they are actually interrelated and not mutually exclusive, although a convincing demonstration of any such connection is yet to be found.

The choice of these topics as subjects of our review is dictated by our common interests. It is also dictated by our conviction of their physical importance regardless of their role in the study of the novel superconductors.
THE THIRD LAW OF THERMODYNAMICS
Authors: MIĘKISZ JACEK , RADIN CHARLES
Published: November 2004

We consider a very general class of discrete classical one dimensional statistical mechanical models and prove that generic finite range interactions have crystalline zero temperature ensembles, and in particular satisfy the third law of thermodynamics.
FORMAL CONSTRAINTS ON SERIES ANALYSIS ON THE POTTS MODEL
Authors: HANSEL D. , MAILLARD J.M.
Published: November 2004

It is shown that the low temperature expansion of the partition function, magnetization and nearest neighbour correlation functions of the q-state checkerboard Potts model in a magnetic field drastically simplify on a very simple algebraic variety. These four formal constraints on the expansions are also analysed in the framework of the resummed low temperature expansions and the large q expansions. These exact results are generalized straightforwardly to higher dimensional hypercubic lattices and also to some random problems.
ARE THE NEW HIGH TEMPERATURE SUPERCONDUCTORS STRONG COUPLING SYSTEMS?
Authors: WEINSTEIN M.
Published: November 2004

Under certain circumstances the excitations of a superconductor will not be those predicted by BCS theory, but rather electron bag states. A variational calculation is used to establish this regime in which such collective states form. The fact that such bags may bind more than one electron implies the existence of more than one peak in the plots of dI/dV versus VP obtained in Giaever tunneling experiments. The estimate of the number and ratios of voltages associated with such peaks is in qualitative agreement with recent experimental results.
SUPERFLUIDITY AND THERMODYNAMICS OF A CONDENSED SOLITON SYSTEM
Authors: FRIEDBERG R. , LEE T.D.
Published: November 2004

Technical details of the new proposal that nontopological solitons might be relevant to high Tc superconductivity are presented. Energy levels, thermodynamics, the phase transition and superfluidity are calculated.
MICROSCOPIC MODEL FOR OXYGEN VACANCY ORDERING IN YBaCuO
Authors: MATTIS DANIEL C.
Published: November 2004

We discuss the oxygen vacancy ordering in Y 1 Ba 2 Cu 3 O 7. This ordering is known to cause the observed orthorhombic distortion, and it is associated with the existence of high-Tc superconductivity. We construct a model which reflects the competition between a dichotomous chemical bond and the Coulomb potential and show how, in principle, this may provide the key to electronic differences between tetragonal and orthorhombic phases. Experimental support is cited for this model.
A TEM STUDY OF Y-Ba-Cu-O SUPERCONDUCTOR MATERIAL PREPARED BY PLASMA SPRAYING
Authors: LU J. , QIAO G.W.
Published: November 2004

A transmission electron microscopy (TEM) study was made on Y-Ba-Cu-O superconductors prepared by plasma spraying which is a useful technique in forming and manufacturing of brittle materials. Amorphous region and transitional phases with certain orientation relationship were found between YBa 2 Cu 3O7−x grains.
ON THE NATURE OF HIGH Tc SUPERCONDUCTIVITY IN OXIDES WITHOUT RE: A-O CHAINS INSTEAD OF Cu-O CHAINS?
Authors: YIN D. , GAN Z. , HAN R.
Published: November 2004

In view of the recently determined lattice parameters and the structural models of the new high Tc oxide phases without rare-earth elements, the mechanism of high Tc superconductivity in these new materials is considered very similar to that of the earlier YBa2Cu3O7 . Since both the oxides of Bi and Tl are semiconductor-like and similar to CuO, Bi-O and Tl-O chains can be formed on the A2O2 type layers and play the similar role of the Cu-O chains in the YBa2Cu3O7 .
STUDIES OF NEW SUPERCONDUCTING Bi-Sr-Ca-Cu-O SYSTEM BY INFRARED AND RAMAN SPECTROSCOPY
Authors: LIU JINGQING , YAN YIFENG , ZHOU TANG , CHE GUANGCAN , CHANG DAWEI , CHEN WEI , WANG YANYUN , ZHAO ZHONGXIAN
Published: November 2004

We report both infrared transmission and Raman scattering results on the new superconducting Bi-Sr-Ca-Cu-O system. Because of its layered structure along c axis, some very thin and transparent slices have been got. In the infrared spectrum there is an absorption band around 500cm−1 with a width of about 300cm−1, and a vibrational mode at 840cm−1, higher frequency than those of phonon modes in Y-Ba-Cu-O system, has also been observed. The Raman scattering spectrum shows similar results, but the scattering signals are very weak because of the strong absorption in visible of this system.
SCALING IN THE STEADY STATE OF A REVERSIBLE AGGREGATION
Authors: HAYAKAWA HISAO
Published: November 2004

The steady state of the reversible aggregation is analyzed using the method of the most probable size distribution. A scaling solution is obtained in the case of λ−α<1, where λ and α are the homogeneity of the coagulation and fragmentation kernels. It is found that gelation occurs for λ−α>1.
SUPERCONDUCTIVITY IN Tl-Ca-Ba-Cu-O COMPOUNDS
Authors: POLITIS C. , LUO H.L.
Published: November 2004

We report the constitution, characterization and superconducting temperatures of the novel high-Tc superconductor Tl-Ca-Ba-Cu-O. For the nominal composition of Tl 2 Ba 2 Ca 2 Cu 3O10, Tc onset up to 130K (midpoint: 120K, zero resistivity: 118.5K) have been found.
CAP FORMATION BY PROTEINS ON THE CELL MEMBRANE: EXCLUDED VOLUME EFFECTS
Authors: WIEGEL F.W. , GOLDSTEIN B.
Published: November 2004

We study the lateral diffusion of proteins in the outer membrane of a biological cell. The “Bretcher” lipid flow field can sweep these particles together into a single cap, provided the flow is strong enough. We analyze the effect of the excluded volume of the proteins on the structure of the cap.
REMANENT EFFECTS AND GRANULAR JOSEPHSON TUNNELLING IN 1:2:3 MICRO-BRIDGE JUNCTIONS
Authors: BOWDEN G.J. , HEALY S.A. , DOU S.X. , BOURDILLON A. , LIU H.K. , ZHOU J.P. , SORRELL C.C.
Published: November 2004

A study has been made of supercurrent in a 1:2:3 micro-bridge or slot-junction. It is shown that the maximum supercurrent through a slot-junction is strongly dependent on temperature, applied magnetic field, and magnetic history. In addition, inter-granular Josephson tunnelling has been observed using field-modulation techniques.
THE 110 K SUPERCONDUCTING TRANSITION IN Bi-Ca-Sr-Cu-O SYSTEM
Authors: GREEN S.M. , MEI YU , JIANG C. , LUO H.L. , POLlTIS C.
Published: November 2004

Large resistive transitions with strong diamagnetic signals have been achieved in the Bi-Ca-Sr-Cu-O system. The fractional drop in resistivity at 110K is found not to correlate with the strength of the diamagnetic signal. For samples with nominal composition BiCaSrCu 2 O y containing two superconducting phases, greater than 50% of the susceptive transition can be associated with the 110K phase.
SUPERCONDUCTIVITY IN THE Tl-Ca-Ba-Cu-O SYSTEM: SYNTHESIS, CHARACTERIZATION AND MECHANISM
Authors: GANGULI A.K. , SWAMY K.S. NANJUNDA , SUBBANNA G.N. , RAJUMON M.K. , SARMA D.D. , RAO C.N.R.
Published: November 2004

Synthesis and characterization of some of the members of the Tl-Ca-Ba-Cu-O system are presented. T c in both the TlCa n−1 Ba 2 Cu n O 2n+3 and Tl 2 Ca n−1 Ba 2 Cu n O 2n+4 series increase with the number of Cu-O layers, n; T c in the latter series with two Tl-O layers are generally higher than in the former with a single Tl-O layer. Tl in the cuprates is in the 3+ state while Cu is in the 1+ and 2+ states, showing the importance of oxygen holes. The concentration of these holes seems to increase with the number of Tl-O layers.
THERMODYNAMIC STUDY ON YBa2Cu3C7−x
Authors: TOCI F. , SCHUERENKAEMPER A. , TOUSSAINT N. , CAMBINI M. , MANES L.
Published: November 2004

Results are related to ordering of oxygen vacancies in the YBa 2 Cu 3 O 7−x lattice.

The concentration and ordering of oxygen in the lattice of YBa 2 Cu 3 O 7−x are fundamental for its superconducting properties.

Partial free energies, enthalpies and entropies of YBa 2 Cu 3 O 7−x have been obtained from oxygen standard potential measurements performed between 700 and 1100 K, by means of a miniaturized solid state galvanic cell. The oxygen molar content of the phases investigated was between 6.65 and 6.95.

Oxygen diffusion kinetics was also studied by means of the same apparatus, by following the depolarization of the electrode after a coulometric titration.

Structural characterization was performed by X-ray powder diffraction, metallography and scanning electron microscopy.
ULTRASONIC ATTENUATION MEASUREMENTS ON LuBa2Cu3O7 AND HoBa2Cu3O7
Authors: SUN KEUN J. , LEVY MOISES , SARMA BIMAL K. , KU H.C. , YANG H.D. , SHELTON R.N. , McCALLUM R.W. , KLAVINS P.
Published: November 2004

HoBa 2 Cu 3 O 7 and LuBa 2 Cu 3 O 7 show very different ultrasonic attenuation behavior at temperatures below 220 K. The Ho sample exhibits a broad maximum in attenuation at around 220 K, while the Lu sample shows a minimum followed by a plateau below 140 K. At T c , the Ho sample shows a decrease in attenuation; there is no evidence for such a change in the Lu sample.
A NOTE ON FLUX TRAPPING AND SUPERCONDUCTIVE GLASS STATE IN HIGH-Tc SUPERCONDUCTORS
Authors: DATTA T. , ALMASAN CARMEN
Published: November 2004

We have shown that the power law behavior of H versus T*, attributed to a de Almeida-Thouless criticality in a high temperature superconductor, may be due to shielding effects and critical currents. We calculate a hitherto unrecognized scaling of T* with J0 and specimen size. Verification of these predictions will favor the conventional Type II model over the glass model for these systems.
PROCESS LEADING TO THE DISCOVERY OF POSSIBLE SUPERCONDUCTIVITY WITH ZERO RESISTANCE UP TO 162 K IN A MULTIPHASE Tl-Ca-Ba-Cu-O SYSTEM
Authors: WU P.T. , LIU R.S. , LIANG J.M. , HUANG Y.T. , CHEN L.J.
Published: November 2004

The process leading to the discovery of possible superconductivity with zero resistance up to 162 K for multiphase samples with nominal composition TlCa 4 Ba 3 Cu 6 O x is briefly reviewed. The discovery was made during the deliberate course to fabricate superconducting compounds with more than three Cu-O layers interposed between Tl-O layers.
THE ROLE OF HOP-ON, HOP-OFF INTERACTIONS IN MIXED PHASE CERAMIC SUPERCONDUCTORS
Authors: LAM C.C. , FUNG P.C.W. , CHENG P.K.
Published: November 2004

We propose a superconductor Hamiltonian model which consists of several major contributions: (i) intra-band interactions among electrons in both the valence and conduction bands, forming Cooper pairs as mediated by phonons; (ii) “hop-on”, “hop-off” interactions between bipolarons and Cooper pairs in the two bands, especially those in the valence band. Using the U-matrix theory, which is equivalent to the Bogoliubov transformation under the c-number approximation in this case, we derive the Bogoliubov ground state and ground state energy. This model can explain certain crucial features of mixed phase ceramic superconductors.
TUNNELLING MEASUREMENTS IN THE Bi SUPERCONDUCTORS
Authors: ESCUDERO R. , MORALES F. , ESTRADA F. , BARRIO R.
Published: November 2004

Tunnelling experiments made on a crack junction of Bi 2( Sr 0.56 Ca 0.39 Bi 0.05)3 Cu 2 O y show reproducible features in the I-V characteristic. Accurate measurements of the temperature dependence of these features show close agreement with the BCS behavior of the gap. Possible tunnelling processes in this material are discussed in connection with the experimental data.
HEAT CAPACITY OF YBa2Cu3O7−δ NEAR Tc
Authors: INDERHEES S.E. , SALAMON M.B.
Published: November 2004

The exceptionally short Ginzburg-Landau coherence length of the high temperature superconductor YBa 2 Cu 3 O 7−δ makes possible the observation of fluctuation effects near the transition from the normal to the superconducting state. At the time of this writing, observations of fluctuation contributions to the electrical conductivity,1 magnetic susceptibility2 and thermopower3 have been reported. Excess contributions to the heat capacity (C fl ) due to thermal fluctuations, though far more difficult to observe, have been noted by several researchers.4 The heat capacity measurements are of particular interest, as a comparison of C fl above and below T c may elucidate the number of components of the Ginzburg-Landau (GL) order parameter and hence the nature of the pairing. The behavior of the heat capacity in an applied magnetic field is distinctly different from that of an ordinary superconductor.5 We summarize here our results on heat capacity measurements in zero field and in an applied magnetic field.
PERCOLATION AND GLASS BEHAVIOR IN CERAMIC SUPERCONDUCTORS: OXYGEN EFFECTS
Authors: CIVALE L. , SAFAR H. , DE LA CRUZ F.
Published: November 2004

It is shown that small variations of oxygen content in La 1.8 Sr 0.2 CuO 4−δ can be used to control the reversible and irreversible magnetization temperature dependence of the superconducting state. A grain bond model is appropriate to describe the superconducting response of the ceramics. The study of the temperature dependence of the magnetization and the resistive transition temperature, in a slightly deoxygenated sample, show that the reversible superconducting state is strongly correlated to superconducting percolation. Deoxygenation has been shown to be an excellent technique to study the time evolution of metastable states induced by currents in the bonds and or in the grains. It is shown that superconducting grains are not correlated to ceramic grains.
CHARGED PARTICLE ENERGY LOSS IN LAYERED MEDIA
Authors: KRESIN V.Z. , MORAWITZ H.
Published: November 2004

In contrast to isotropic three-dimensional metals, charged particle (electron or positron) losses in layered conducting materials depend strongly on temperature. It is demonstrated that this effect arises from specific features of the plasmon band in such systems. This prediction can be checked experimentally.
JOSEPHSON EFFECTS IN A Y1Ba2Cu3O7 BREAK JUNCTION AT 77 K
Authors: ZHAO S.P. , TAO H.J. , CHEN Y.F. , CHE G.C. , YANG Q.S.
Published: November 2004

Josephson effects in a Y 1 Ba 2 Cu 3 O 7 break junction at 77 K are reported. The I-V characteristics show clear Shapiro steps under microwave radiation and magnetic dependence of the critical current is of the typical Fraunhofer diffraction pattern. Estimate of the magnetic penetration depth is given. Discussions of the I-V curve concerning nonstationary processes are presented.
COMPOSITION DEPENDENCE OF SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE IN La(Ba1−xCax)2Cu3O7−y SYSTEM
Authors: CAO N. , ZHENG J.Q. , SHAO X.Y. , CHEN X.S. , GUAN W.Y.
Published: November 2004

The composition dependence of superconductivity and crystal structure in La ( Ba 1−x Ca x)2 Cu 3 O 7−y system was determined by the resistivity measurements and X-ray diffraction analysis. The superconducting transition temperature is raised with the increase of Ca content till x=0.6, at which the zero resistance temperature of the sample is 81.5 K. In the meanwhile, the crystal structure of the sample changed from tetragonal (x=0) to orthorhombic structure (x=0.2, 0.4, 0.6). With further increase of Ca content, the superconductivity decrease for the sample of x=0.8 with mixed phases including the orthorhombic oxygen-deficient perovskite-like (ODP) structure and no superconducting transition is found at 4.2 K for the sample of x=1 without the ODP structure. A possible explanation of these experimental results is given.
SUPERCONDUCTIVITY IN Pb-DOPED Bi-Ca-Sr-Cu-O SYSTEM
Authors: XIA J.S. , FAN M.H. , HE Z.H. , ZHANG Q.R. , CHEN J. , CHEN Z.Y. , QIAN Y.T.
Published: November 2004

A new superconducting transition near 100 K was observed in the Pb -doped Bi-Ca-Sr-Cu-O samples. Compared with the 107 K and 65 K phases, the volume fraction of this superconducting phase is very small, but forms an effective connection between the grains of other two phases. It is suggested that the new phase plays an important role for T c above 100 K in the Bi 2−x Pb x Ca 2 Sr 2 Cu 3 O y system.
HREM STUDIES OF THE SUPERCONDUCTING PHASE Tl2Ba2Ca2Cu3Ox
Authors: ZHENG J.G. , CHEN J. , JIANG J.G. , LIANG Y.H. , DING S.Y. , YU Z. , LI Q. , FENG D.
Published: November 2004

The superconducting phase Tl 2 Ba 2 Ca 2 Cu 3 O x (Tl2223) has been identified in high-T c superconducting ceramics with nominal composition of Tl 2 Ba 2 Ca 2 Cu 3. The configurations of grains and grain boundaries have also been observed directly by high resolution electron microscopy [HREM]. The small angle grain boundaries are mixed with both translation and orientation characteristics. The boundary regions are nearly parallel to (100) to (010) in crystal state, While in amorphous state, they are nearly parallel to (001). There also exists large angle grain boundaries in TlBaCaCuO superconductor.
PREPARATION AND FORMATION OF HIGH-Tc PHASE IN Bi2−xPbxSr2Ca2Cu3Oy SYSTEM
Authors: LIU H.B. , ZHAN X.N. , MAO Z.Q. , ZHANG W.J. , ZHOU L. , LU J. , ZHOU G.E. , LI B.Y. , PENG D.K. , CAO L.Z. , RUAN Y.Z. , CHEN Z.J. , ZHANG Y.H.
Published: November 2004

With the aim of preparing a single, high-T c phase in the Bi 2−x Pb x Sr 2 Ca 2 Cu 3 O y system, optimization of the composition and heat treatment have been studied. It was found that the composition at which the more high-T c phase forms, was x=0.4 and in condition (3). For sample 3 (x=0.4), specific heat anomaly indicates that the superconductivity of high-T c phase was bulk phenomenon. This means there is more volume fraction of high-T c phase in this sample.
FILM FABRICATION AND OPTICAL PROPERTIES OF AMORPHOUS THIN-FILM OF MODIFIED BNN (Ba2NaNb5O15) SYSTEM
Authors: TSUKIOKA MASAYUKI , MASHIO TASUKU , SHIMAZU MASAJI , NAKAMURA TAKESHI
Published: November 2004

For the first step of making highly aligned BNN thin-film, transparent and colorless amorphous thin-films of modified BNN system were successfully prepared either on silicon oxide layer formed on (111) plane of a polished silicon wafer of 500×0.3 mm or on polished glass ceramic plate of 50×50 mm by rf-sputtering technique. Sputtering targets, whose chemical composition was proposed by K.G. Barraclough as the congruently melting one, were used. Refractive indices and thickness of the films at several positions on these thin-films were measured by prism-coupling technique, and they were about 2.35 and 1.93 μm, respectively over the entire film surface.
TEMPERATURE DEPENDENCES OF Y2Cu2O5 ESR SPECTRA
Authors: GIPPIUS A.A. , MOSHCHALKOV V.V. , KOKSHAROV YU. A. , TIKHONOV A.N. , MILL B.V. , ZOUBKOVA Y.
Published: November 2004

Temperature dependences of the ESR spectrum in Y 2 Cu 2 O 5 compound are studied for both polycrystalline and single crystal samples. The g-factors along the main axes are found to be ga=2.099, gb=2.048, and gc=2.21 at room temperature, T=293 K . As temperature decreases, the linewidth ΔH increases in agreement with the Huber’s formula ΔH=A(T N /(T−T N ))β+B(θ/T+1) with the following parameters: A=1513±10 Oe , B=509±10 Oe , T N =7±1 K , θ=18±2 K , β=1.3±0.3. In the vicinity of the Neel Temperature, T N , the ESR spectrum has a very complicated form indicating the existence of clusters with different internal magnetic fields. Below T N , a single line symmetrical ESR spectrum is recovered.
ALGEBRAIC ANALYSIS OF THE ELECTROMAGNETIC WAVE INTERACTION WITH THE TWO-LEVEL SYSTEM WITH TWO-FOLD DEGENERATED STATES
Authors: RUSTAMOV K.A.
Published: November 2004

Algebraic properties of the analytical model, describing electro-magnetic weak interaction with the two-level system with two-fold degenerate state are considered. The expressions for the coherent states and Green function of the system are obtained.
DONOR GENERATION IN PLASMA TREATED SILICON
Authors: KUSMARTSEVA O.E. , SENCHUKOV F.D.
Published: November 2004

An inversion of the conduction type of the p-silicon surface layer by gas discharge plasma treatment was observed. It was found that this conduction inversion was conditioned by donor center formation. Donor behavior are discussed. Some plasma treatment regimes to induce the donor centers in silicon are reported.
PREPARATION OF SUPERCONDUCTING THICK FILMS OF YBa2Cu3O7 BY DEPOSITION OF A SUPERCONDUCTING PRECURSOR INK
Authors: DABROWSKI B. , HINKS D.G.
Published: November 2004

A simple and reliable method of producing good quality superconducting thick films of YBa 2 Cu 3 O 7 with zero resistance above 87 K is presented. The method consists of dipping, spraying or painting a superconducting precursor ink on a substrate (of arbitrary dimensions) with subsequent sintering in flowing oxygen at temperatures close to the melting temperature of YBa 2 Cu 3 O 7. Superconducting transition temperatures (T c ) as a function of substrate material, firing temperature and nature of the precursor ink are discussed. BeO was found to be the best substrate for our process.
BEHAVIOR OF DOUBLE JUNCTION SQUID OF Y-Ba-Cu-O BULK SUPERCONDUCTOR
Authors: KATARIA N.D. , TOMAR V.S. , OJHA V.N. , KUMAR MUKESH , REDDY G.S.N. , GUPTA A.K.
Published: November 2004

A dc SQUID like geometry with a ring and a pair of constrictions is carved out of bulk Y-Ba-Cu-O superconductor. The I—V curves exhibit hysteresis arising due to trapping of the self fields. The V—Φ curves show multiple flux periodicities with unequal amplitudes. There is twenty fold rise in the amplitude of voltage modulation in cooling from 77 to 4.2 K. The complications of presence of series and parallel arrays of granular junctions are attributed respectively to large and small periodicities observed in V—Φ curves. The modulation structure gets more resolved at 4.2 K due to reduction in thermal noise effects.
HIGH-FIELD AND MICROSTRUCTURE STUDIES OF SUPERCONDUCTING nYBa2Cu3Oy:AgO COMPOSITES
Authors: HUANG C.Y. , TAI H.H. , WU M.K.
Published: November 2004

We have measured the resistance of superconducting n YBa 2 Cu 3 O y: AgO (n=2,3,4, and 5) composites above 77 K for magnetic field up to 20 T. The data reveal that the resistance is zero even at 80 K and 20 T. The temperature dependence of the critical field near T c (91.6 K) is very strong, and critical fields at 0 K are thus expected to be very high. Our results of scanning electron microscopy and polarized light microscopy have shown that the presence of silver results in the growth of very large grains (~0.5 mm) with silver dispersed in the grains, giving rise to strong pinning and, hence, large superconducting critical current densities.
STATIONARY REGIMES AND THEIR MANIFESTATIONS IN BIRTH-DEATH PROCESSES
Authors: BATUNIN A.V.
Published: November 2004

The necessary conditions for the existence of stationary regimes in birth-death processes — with polynomial dependence of coefficients on the number of particles — are found. Possible manifestations of stationary regimes in hadron physics are discussed.
THE DYNAMICS OF THE ORDERING PROCESS WITH LONG-DISTANCE HOPPING
Authors: ENOMOTO YOSHIHISA , KAWASAKI KYOZI
Published: November 2004

We study the asymptotic behavior of the ordering process of quenched systems with long-distance hopping. Based on a newly proposed computer model of such systems, two dimensional simulations are performed to investigate the scaling law for the scattering structure function.
SYNTHESIS AND CHARACTERIZATION OF LARGE STABLE QUASICRYSTALS IN THE Al-Cu-Ru SYSTEM
Authors: POLITIS C. , KRAUSS W. , LEITZ H. , SCHOMMERS W.
Published: November 2004

We report the synthesis, the growth morphology and the characterization of stable quasicrystalline materials in the ternary Al-Cu-Ru system. Quasicrystalline materials have been prepared by melting, solid state reaction and mechanical alloying techniques. In particular, large quasicrystals (size: ~1.2 mm) with the composition Al 68 Cu 22 Ru 10 were prepared by arc melting. According to the investigations by X-rays, electron diffraction and differential thermal analysis, the observed quasicrystals are stable up to the melting point at 1014°C. The quasicrystallinity, represented here, is obviously the thermodynamically stable state.
SUPERCONDUCTIVITY IN Bi1.9−xPbxSb0.1Sr2Ca2Cu3Oy COMPOUNDS (x=0.1, 0.2, 0.3, 0.4)
Authors: CAO L.Z. , LIU H.B. , ZHOU L. , MAO Z.Q. , ZHANG W.J. , LI B.Y. , LI X.X. , ZHANG Y.H.
Published: November 2004

Superconducting properties of Bi1.9−xPbxSb2Ca2Cu3Oy have been investigated with x=0.1, 0.2, 0.3, and 0.4. The diamagnetic signals of three samples (x=0.2, 0.3, 0.4) indicated that three superconducting transitions (140 K, 11 K, 80 K) exist in three multiphase compounds.
FORMING PROCESS OF 110 K HIGH-Tc PHASE IN Bi-Pb-Sr-Ca-Cu-O SYSTEM
Authors: WANG Y.G. , WANG N.L. , JIAO X.P. , WANG J.S. , HAN G.C.
Published: November 2004

The effect of heat treatment on the forming process of the high-Tc phase in the cast-annealing samples has been discussed. Experiments show that the high-Tc phase is formed based on the low-Tc phase. Adding Pb to Bi-Sr-Ca-Cu-O system can increase the forming rate and proportion of the high-Tc phase. X-ray powder diffraction indicates that some samples contain mostly the high-Tc phase. EDAX analyses suggest that Pb cations substitute partially for Sr cations rather than Bi cations in the superconducting grains.
ON THE HIGH TEMPERATURE SUPERCONDUCTIVITY IN THE 124-CLASS OF SUPERCONDUCTORS
Authors: APOSTOL M.
Published: November 2004

The critical temperature of the 124-class of high temperature superconductors is investigated by employing the model of charge carriers interacting with the oxygen-displacive modes of the lattice. The role played by the fixed stoichiometry in entailing a relatively narrow range of critical temperature is emphasized.
GRASSMANNIAN APPROACH TO THE RESONATING-VALENCE-BOND STATE OF THE 2D HEISENBERG ANTIFERROMAGNET
Authors: SHAPIR YONATHAN , BLUM THOMAS
Published: November 2004

A systematic representation of the resonating-valence-bond state of the 2D spin-1/2 Heisenberg antiferromagnet in terms of anticommuting Grassmann variables is derived. This representation is extended to the dilute case and the holon statistics are considered. Independent phase fluctuations on each valence-bond yield a U(1) gauge theory with low-lying gapless excitations in accordance with other approaches.
OBSERVATION OF SPECTRA BY RAMAN SCATTERING ON a-Si:H/a-SiNx:H SUPERLATTICES
Authors: LIU GUO-GAO , ZHANG XING-KUI , CHENG GUANG-XU , XIA HUA , CHEN KUN-JI
Published: November 2004

Raman scattering has been performed on a- Si:H /a- SiN x: H superlattices in this letter. We have observed the zone-folding effects on longitudinal acoustical phonons in a- Si:H /a- SiN x: H superlattices. The experimental results confirm the theoretical expectation. Additionally, we have observed the modes of interface between the air and samples.
THIN LANTHANUM OXIDE AND RARE-EARTH OXIDE FILMS BY PECVD OF β-DIKETONATE CHELATE COMPLEXES
Authors: WEBER A. , SUHR H.
Published: November 2004

A method for the deposition of lanthanum oxide and rare-earth (Re) oxide films using the tris[2,2,6,6-tetramethyl-3,5-heptanedionato] chelate complexes is reported. The films were characterized by metal analysis, carbon analysis, FTIR spectra, XPS and SEM micrographs. The film composition strongly depends on experimental parameters. Films deposited in an oxygen plasma at a substrate temperature of 400°C and a power density of 1.5 W/cm 2 are amorphous, transparent and show carbon contents of < 2%. If argon or hydrogen is used as carrier gas, films contain ≈ 5% carbon. With substrate temperatures < 400° C or power densities < 1.5 W/cm 2, films containing trivalent Re metal ions and considerable contamination by polymeric material are formed.
SPUTTERING DEPOSITION OF Tl–Ca–Ba–Cu–O THIN FILMS WITH ZERO RESISTANCE AT 101 K
Authors: YAN S. L. , HU X. J. , SONG Q. X. , CAO H. L. , YAN J. , YANG X. M. , PEI G. W. , ZHANG Q. M. , ZHOU X. D.
Published: November 2004

Superconducting Tl–Ca–Ba–Cu–O thin films have been prepared by dc magnetron sputtering from a pair of Tl 2 Ca 1 Ba 3 Cu 4 O y bulk targets. The post-annealing films on ZrO 2 ceramic substrates exhibit an onset temperature of about 125 K and zero resistance as high as 101 K. SEM showed a smooth terraced surface structure. The XRD analysis proved that the films were polycrystalline and were not single phase superconducting material.