bluuebunny/crossref_metadata_2025 huggingface dataset:
ELECTRON THEORY OF THE SUPERCONDUCTIVITY AND CRITICAL TRANSITION POINT Tc OF Ba2YCu309−d(d=2) BY THE APPLICATION OF THE EMPIRICAL ELECTRON THEORY OF SOLIDS AND MOLECULES
Authors: Ruihuang S.H. Yu
Published: November 2004

Application of “the empirical electron theory of solids and molecules” to the analysis of crystal structure obtained by Siegrist and his colleagues of Ba2YCu3O9−d(d≈2) directly yields the covalent bond electron structure of the crystal. The interpretation of the half oxygen vacancy in Cu-O4-O5 layers gives the necessity of the existence of empty thoroughfares for the superconductivity at low temperature crystal. Thermal agitation together with the fluctuation of the fractional covalent bonds render Ba atoms to rotate and to throw 04, 05 atoms to the thoroughfares to destroy the superconductivity. The calculated Tc agrees with the experimental value rather satisfactorily. The twinning observed by R. Beyers and his colleagues at IBM research centers further gives evidence for the thoroughfares existence.
SUBMILLIMETER CONDUCTIVITY AND DIELECTRIC CONSTANT OF La1.8Sr0.2CuO4 CERAMIC
Authors: Gorshunov B.P. , Goncharov Yu. G. , Kozlov G.V. , Prokhorov A.M. , Prokhorov A.S. , Volkov A.A.
Published: November 2004

The temperature dependence of conductivity and dielectric function of the superconducting La1.8Sr0.2CuO4 ceramic is measured using backward-wave oscillator technique at the frequency 15 cm −1 and in the temperature range 5–300K. The temperature behavior of the parameters is found to be close to the classical one at frequencies lower than superconducting energy gap.
ON THE COEXISTENCE OF PHONON AND NON-PHONON (PLASMON) MECHANISMS IN NEW HIGH Tc SUPERCONDUCTORS
Authors: Kresin Vladimir Z.
Published: November 2004

An analysis of recent experimental data shows that high T c is due to the coexistence of phonon and non-phonon mechanisms.
MAGNETIC AND STRUCTURAL PROPERTIES OF SOME ABa2Cu3O7−δ SUPERCONDUCTORS
Authors: Causa M.T. , Dutrús S.M. , Fainstein C. , Nieva G. , Salva H.R. , Sánchez R. , Steren L.B. , Tovar M. , Zysler R.
Published: November 2004

We report here normal and superconducting properties of ABa 2 Cu 3 O 7−δ (with A=Y, Gd, Dy, and Er) and of Fe doped YBa2Cu3O7−δ . Results from X-ray powder diffraction, electrical resistivity, magnetic susceptibility, ESR, and specific heat measurements are presented, leading to a characterization of the magnetic properties of these materials. The effect of structural modifications of the lattice on the superconducting properties and the relative insensitivity of Tc to the presence of magnetic moments is discussed.
HIGH-DENSITY EXPANSION FOR THE EXTENDED HUBBARD MODEL
Authors: BARTKOWIAK M.
Published: November 2004

The Green’s-function diagrammatic high-density expansion technique for Hubbard’s operators is constructed and applied to the extended Hubbard model. The electron Green’s functions and the band structure of the ground state for arbitrary electron density are calculated in the zeroth-order in 1/z. The phase diagram, staggered magnetic susceptibility and the Néel temperature for the half-filled band case are derived in the first order of the high-density expansion. Connections of the high-density and linked cluster expansions are also discussed.
ATOMIC STRUCTURE OF THE DECAHEDRAL PHASE
Authors: ROMEU D.
Published: November 2004

Under the unique assumption of decagonal growth and starting form a decahedral seed, a stable physical quasicrystalline structure can be produced closely matching most T phase experimental observations. Different associated structures with the same overall symmetry can be obtained by the same mechanism.
PHYSICAL PROPERTIES OF HIGH Tc OXIDES
Authors: UCHIDA S.
Published: November 2004

A brief review is given on the current status of experimental research for the high Tc superconductors in Japan. Based upon the recent experimental investigation, the variation of electronic states is discussed for three classes of oxides, BaPb 1−x Bi x O 3, ( La 1−x Sr x)2 CuO 4 and YBa 2 Cu 3 O 7−y with the change of compositions x and the oxygen vacancies y.
EVIDENCES OF JOSEPHSON WEAK LINK NETWORK IN SINTERED BULK Y1Ba2Cu3O7−x OXIDE
Authors: QIAN YONGJIA , QIU JINGWU , CHEN KAIYUAN , ZHOU BING , MIAO BAICAI , CAI YIMING , TANG ZHIMING
Published: November 2004

Measurements of point-contact tunneling, AC susceptibility vs transport current, zero voltage supercurrent under microwave irradiation and critical current as a function of temperature have been carried out on high Tc oxide superconductor Y 1 Ba 2 Cu 3 O 7−x. The results of these measurements can be interpreted by the assumption of existence of Josephson weak link network in the oxide.
HIGH-DENSITY EXPANSION FOR THE SPINLESS FERMION MODEL I: FIRST ORDER IN 1/z AND HORWITZ-CALLEN RENORMALIZATION
Authors: BARTKOWIAK M. , MÜNGER P. , MICNAS R.
Published: November 2004

A diagrammatic technique for Hubbard's operators is employed to perform systematically the high-density expansion for the three-dimensional spinless fermion model. The molecular field theory is obtained by the zero-order renormalization of blocks. Summation of the first order diagrams is carried out in both selfconsistent and correctional way. It turns out that the charge ordering parameter, calculated self-consistently, has a jump for a certain medial temperature. We have also shown, that the Horwitz-Callen renormalization leads to the first or second order phase transition, depending on t/W and fails when this ratio is large enough. The phase diagrams of the system for the half-filled band case, derived in both unrenormalized and renormalized first order of high-density expansion are presented.
THE EFFECT OF RVB FLUX CONFIGURATION ON THE SUPERCONDUCTING STATE
Authors: BASKARAN G. , TOSATTI E. , YU L.
Published: November 2004

The RVB state is a singlet quantum liquid which can support periodic or fluid-like quantum circulation around the elementary plaquette in two dimensions. In the s + id phase there is a half flux quanta of circulation in every elementary plaquette. We show that the holons in the presence of this lattice of circulation have a two-valley structure, as opposed to "s"or "d" states, which have a single valley. Using an effective holon Hamiltonian, we study the mean-field properties of the two-valley holon condensate, and compare its energy with the single valley case. A transition from the "d" to the "s + id" state is predicted with increasing hole concentration for sufficiently large Hubbard U. Some speculations are offered about the general case of a fluid-like distribution of flux quanta.
MAGNETIC POLARONS IN THE HUBBARD MODEL WITH INTERSITE INTERACTIONS
Authors: Khveschenko D. V. , Pokrovsky V. L. , Uimin G. V.
Published: November 2004

A possible formation of magnetic polarons and bipolarons of small sizes in copper oxides is discussed in the framework of the Hubbard model. The long-range Coulomb interaction prevents the phase separation and stabilizes bipolarons. Magnetic bipolarons have an orbital momentum perpendicular to copper-oxide planes. They can produce a superconducting state. A small concentration of such polarons is sufficient to suppress antiferromagnetism. Exchange interaction of polarons imitates the Pauli paramagnetism.
PAIRING MECHANISM FOR OXYGEN HOLES IN PLANAR CuO2 SYSTEMS
Authors: SASAKI Ken , BETSUYAKU Hiroshi
Published: November 2004

Effects of antiferromagnetic fluctuations on the pairing of holes produced on oxygen ions by doping are investigated theoretically for the planar CuO 2 systems in the spin-density-wave (SDW) background. Explicit expressions for singlet and triplet effective interactions are obtained within the random-phase approximation, which predicts great possibilities of singlet pairing. It is shown that the pairing is multiplicatively enhanced by the coexistence of p− and d-holes near the SDW instability.
THERMODYNAMIC CHARACTERISTICS OF Y–Ba–Cu–O TYPE COMPOUNDS IN THE MODEL OF STRONG ELECTRON–PHONON COUPLING
Authors: Golubov A. A.
Published: November 2004

Based on recently measured phonon density of states of Y–Ba–Cu–O an investigation of the strong electron-phonon coupling model is carried out. The numerical solutions of the real axis Eliashberg equations are obtained for a number of phonon spectra parameters. Isotope shifts of T c , spectral behavior of the pairing energy Δ(ω) and the ratio 2Δ g / T c (where Δ g is the gap edge) are calculated. The model gives a very small oxygen isotope shift for rather moderate values of the electron-phonon coupling constant λ ~ 3. The results strongly suggest the weak coupling with high frequency phonon modes and strong coupling with low frequency modes.
ELECTRONIC TRANSFER OF LOCAL PAIRS AND SUPERCONDUCTIVITY IN METAL OXIDE COMPOUNDS
Authors: KULIK I. O.
Published: November 2004

We propose that two-electron centers (local pairs) are formed at oxygen atom(s) which preexist superconductivity. Due to the interaction of these with the conduction band electrons (presumably those at Cu – O layers) the local pairs (which are supposed to be peroxide species, [Formula: see text], in perovskite high-Tc compounds) gain kinetic energy and become mobile. Superconductivity scenario is that of local pair condensation accompanied by BCS-like ordering of conduction band electrons. Consequences of the model concerning gap (or, rather, gaps) formation, pecularities of IR absorption and tunneling effect, and transport properties in the normal state are discussed.
NUMERICAL SIMULATION OF THE 1D AND 2D HUBBARD MODELS: FERMI LIQUID BEHAVIOR AND ITS BREAKDOWN
Authors: Sorella S. , Tosatti E. , Baroni S. , Car R. , Parrinello M.
Published: November 2004

The ground state of the 1D and of the 2D (square lattice) finite-size Hubbard model is investigated for variable filling using a novel quantum simulation method. We have studied up to 256 sites for both 1D and 2D. Away from half filling the 2D antiferromagnetic order is initially destroyed, albeit without any clear sign of a Fermi liquid behaviour. A metallic jump in n(k) appears only very far from half filling. In the 1D case, by contrast, a Fermi liquid-like jump in n(k) is obtained even very close to half filling.
NONCOLLINEAR MAGNETIC STRUCTURES IN ANTIFERROMAGNETIC La2CuO4
Authors: Borovik-Romanov A. S. , Buzdin A. I. , Crotov S. S. , Kreines N. M.
Published: November 2004

Weak-noncollinear antiferromagnetic structure of La 2 CuO 4 (space symmetry D 2h 18) is determined on the basis of symmetry analysis. The transition of the first order in the magnetic field into weak ferromagnetic phase is possible, the corresponding reconstruction of antiferromagnetic structure being predicted.
Reformulation of pairing theory
Authors: GULACSI Miklos , GULACSI Zsolt
Published: November 2004

The original Cooper pairing theory is reformulated for electrons confined in a layer. This analysis is motivated by the quasi-two-dimensional character of the oxidic superconductors, in case of which the extension of the initial (3D) Cooper framework is practically impossible. By considering the electrons moving in a flat box, due to quantum size effect the properties of these oxidic superconductors can be explained in a natural way. In this short communication we will concentrate to the variation of the critical transition temperature due to the layer thickness and to the number of conduction (Cu-O) planes. The results are confirmed by the experiment. This being an evidence for the presence of the charge confinement effect in the oxidic superconductors.
TWO-DIMENSIONAL VERTEX MODEL WITH LOCAL FRICTION COEFFICIENT
Authors: ENOMOTO YOSHIHISA , KAWASAKI KYOZI , NAGAI TATSUZO
Published: November 2004

Time evolution of two-dimensional cellular structures is studied in the context of a deterministic vertex model. Simulating this model for long time periods we discuss two typical aspects of cellular structures. One is the asymptotic growth law of cell size and the other is concerned with the topological properties such as the cell shape distribution.
PHOTOELECTROCHEMICAL EFFECT ON YBa2Cu3O7 SINGLE CRYSTALS
Authors: HAMPEL M. , GRABNER E. W. , BACHTLER M. , LORENZ W. J.
Published: November 2004

Electrochemical dc and transient measurements in the system YBa 2 Cu 3 O 7/ acetonitrile + tetrabutylammonium-perchlorate (as a supporting electrolyte) at T = 298 K showed a significant photoeffect on single crystal electrodes after irradiation with chopped white or monochromatic light under cathodic polarization conditions. The effect could not be observed on polycrystalline electrodes and on single crystals under anodic polarization conditions. Under potentiostatic control, the photoreduction current increased nearly exponentially with decreasing electrode potential. Obviously, an enhanced reduction of copper oxide components at the surface takes place during illumination. The photoeffect was found to depend on both the photon energy and the adjustment of the (twinned) single crystals and may be explained assuming a significant band gap in c-direction and an intrinsic photo-excitation of electrons from the valence band to the conduction band of the p-type conducting material.
FIRST ORDER RAMAN SCATTERING FROM SEMICONDUCTOR QUANTUM DOTS
Authors: RODRIGUES P.A.M. , CERDEIRA HILDA A. , CERDEIRA F.
Published: November 2004

We develop a model appropriate for describing the Raman spectrum of samples, containing a collection of semiconductor quantum dots with and without dispersion in their linear dimensions. These nanometer size crystallites are assumed to have the same atomic arrangement as that of the bulk material and to be embedded in a host material made up of a different semiconductor of the same crystal structure. The results from our calculations are compared to previous models for polycrystalline materials.
NONPHONON MECHANISM OF SUPERCONDUCTIVITY IN COMPOUNDS OF TRANSITION METALS
Authors: IVANOV V.A. , ZAITSEV R.O.
Published: November 2004

The kinematical mechanism of superconductivity is applied to the Emery-Hirsch model for the CuO 2 and BiO 3 layers. A superconducting region due to strong kinematic interaction of p- and s, d-electrons are determined as a function of np and ns,d-degrees of non-filling of 2p6, 6s2, 3d10 shells of O 2−, Bi 3+, Cu +. The T c is calculated taking into account the spin flip relaxation time. Magnetostatic properties of a superconducting state in a weak magnetic field are investigated. Coefficients of the Ginzburg-Landau equation are calculated. The ground state energy of the Emery-Hirsch model is also calculated.
AN EXACTLY SOLVABLE TWO-FOLD CAYLEY TREE MODEL
Authors: DELALE CAN F.
Published: November 2004

A two-fold Cayley tree graph with fully q-coordinated sites is constructed and the ferromagnetic Ising model on the constructed graph is solved exactly. It is shown that a phase transition results in zero field at the critical Bethe temperature with spontaneous magnetization below the critical Bethe temperature.
THE EXPONENT MODEL CALCULATION OF REDUCED TEMPERATURE IN LIQUID-SOLID PHASE TRANSITION
Authors: AHMED K. , KHWAJA FARID A. , TARIQ-UR-RAHMAN
Published: November 2004

The classical theory of nucleation for crystallization from the liquid to the solid phase, is reviewed. By extending the present theory of specific rate of nucleation in supercooled liquids a relation for diffusion activation energy in terms of the nucleation temperature is obtained. The empirically found constant ratio (reduced temperature) T*/Tm is derived using a model based on exponent. The fitting of the experimental data for the reduced temperature yields interesting physical features on nucleation in this simple framework.
ON THE INSTABILITY OF THE FERROMAGNETIC STATE IN THE U=∞ LIMIT OF THE HUBBARD MODEL
Authors: Douçot B. , Rammal R.
Published: November 2004

The U=∞ limit of the Hubbard model is studied using a variational approach in which the spins are in a static coherent state. We find that the Nagaoka Ferromagnetic state is no longer the ground state as soon as two holes are present, and this for various geometries. We suggest that this instability also remains for a finite density of holes.
VARIATIONAL STUDY OF THE PAIR HOPPING MODEL
Authors: Fazekas P.
Published: November 2004

We study the ground state of a Hamiltonian introduced by Kolb and Penson for modelling situations in which small electron pairs are formed. The Hamiltonian consists of a tight binding band term, and a term describing the nearest neighbour hopping of electron pairs. We give a Gutzwiller-type variational treatment, first with a single-parameter Ansatz treated in the single site Gutzwiller approximation, and then with more complicated trial wave functions, and an improved Gutzwiller approximation. The calculation yields a transition from a partially paired normal state, in which the spin susceptibility has a diminished value, into a fully paired state.
NEUTRAL EXCITATIONS IN QUASI-1D STRONGLY CORRELATED ELECTRON SYSTEMS
Authors: Klein D.J. , García-Bach M.A. , Valentí R.
Published: November 2004

Novel neutral spin-0 excitations for quasi-1D systems with one electron per site are obtained within a localized scheme. Our ground state wave-function is defined by a variational localized - site cluster - expanded ansatz and these excitations are naturally built upon it. All computations are easily carried out by a transfer matrix technique that enables explicit inclusion of electron - correlation effects and, at the same time, provides a quasi—particle band—theoretic picture of these excitations. This treatment is applied, in particular, to a polyphene strip. At k=0 the energy gap corresponds to a dipole-allowed transition in the visible region, our result compares fairly well with observed decreasing transitions for finite polyphene strips.
COMPUTATIONALLY EFFICIENT MODELING OF BLOCK COPOLYMER AND BENARD PATTERN FORMATIONS
Authors: OONO Y. , SHIWA Y.
Published: November 2004

Computationally efficient discrete space-time models of spatially-ordered pattern formation dynamics (e.g., block copolymer phase separation dynamics) are proposed. Models are simple but can give sufficiently realistic spatial patterns, and their time evolution.
Y-BA-CU-O SUPERCONDUCTING CERAMICS
Authors: TIAN SHUNBAO , LI XIAOFEI , WEN TINGLIAN , LIN ZUXIANG , LI SHICHUN , YU HUIJUN
Published: November 2004

Polycrystalline Y-Ba-Cu-O superconducting materials have been studied. It was found that chemical composition and processing condition may play an important role in the final structure and superconducting properties.

The density has been determined and compared with the calculated value according to the structure model reported by Bell Labs. The grain size and the morphology of the materials were observed by SEM.
A NEW MECHANISM OF HIGH Tc SUPERCONDUCTIVITY BY ANTIFERROMAGNETIC SPIN WAVES
Authors: SOGO KIYOSHI
Published: November 2004

New mechanism of superconductivity is presented, which utilizes antiferromagnetic spin waves. It is found that for the case of Ising like anisotropy the spin wave coherence strongly enhances the superconductive coupling constant, which gives rise to a rather high critical temperature. Sloppy spin wave mechanism is also suggested.
DYNAMICAL STARK EFFECT IN AN AMPLITUDE MODULATED FIELD
Authors: JOSHI A. , PURI R.R. , LAWANDE S.V.
Published: November 2004

The analytic solution of the Bloch equations in the secular approximation for a two level atom driven off-resonance by an intense amplitude modulated field is presented. The dependence of the atomic population inversion on the longitudinal and transverse lifetimes is investigated.
MAGNETIC ORDERING IN A TWO-DIMENSIONAL HUBBARD MODEL
Authors: NIE HUI-QUAN , ZHAO BAO-HUA , ZHANG KAI-YI , Chao K.A. , MICNAS R.
Published: November 2004

We have used the fourth order perturbation expansion to construct the magnetic phase diagram of the two-dimensional Hubbard model. To the contrary of the three-dimensional case, a stable antiferromagnetic phase is found at the limit of (t/U)≃0 if the electron density n lies in the region 0.95<n<1.05. Our results for n=0.9 are compared to the recent indecisive Monte-Carlo investigation on the magnetic structure factor regarding the antiferromagnetic ordering.
THE RELATION BETWEEN SUPERCONDUCTIVITY AND CRYSTAL STRUCTURE OF Tl-Ba-Ca-Cu-O SYSTEM
Authors: LIANG J.K. , HUANG J.Q. , ZHANG Y.L. , XIE S.S. , ZHENG D.N. , CHEN X.R. , JIA S.L. , CHE G.C. , LIU H.B. , NI Y.M. , YANG Q.S. , ZHAO Z.X.
Published: November 2004

It was found that the same compositional samples showed different superconducting behavior and diffraction patterns due to different heat treatment. It is interesting to note that there exist at least three superconducting phases in Tl-Ba-Ca-Cu-O system. All of them belong to the space group [Formula: see text]. They have the same lattice constant a but different lattice constant c. The transition temperature Tc is closely related with the lattice constant c. The superconducting phase with bigger lattice constant c has higher Tc. A structure model, which can generalize all of the structure of high Tc superconductors, is proposed.
POTASSIUM SUBSTITUTION FOR BARIUM IN RBa2Cu3O7(R=Y, Eu, Pr): ITS EFFECT ON SUPERCONDUCTIVITY, OXYGEN DEFICIT AND CRYSTAL STRUCTURE
Authors: FELNER I. , KOWITT M. , LEHAVI Y. , EDERY D. , BEN-DOR L. , WOLFUS Y. , NOWIK I.
Published: November 2004

We have studied the crystal structure, magnetic susceptibility, and oxygen concentration in single-phase samples of high TcR Ba 2−yKyCu3Ox (where y=0 to 1 for R=Y and Eu), and in nonsuperconducting PrBa 2−y K y Cu 3 O x (y=0 to 1.5). The YBa 2−y K y Cu 3 O x samples all have the same orthorhombic structure and almost the same Tc, even though x=6.1 for y=1. EuBa 2−y K y Cu 3 O x evolves from orthorhombic to tetragonal structure, and Tc progressively drops, with increasing y; for y=1 it is no longer superconducting. The mixed-valent Pr in PrBa 2 Cu 3 O 7 becomes tetravalent in the presence of K + ions substituted for Ba ++. The decrease in cation charge reduces both the oxygen concentration and the average valency of the Cu in all three systems.
STRUCTURAL CHARACTERISTICS OF THE NEW HIGH-Tc SUPERCONDUCTING PHASE Bi2Sr2Ca Cu2O8+x
Authors: Carrillo E. , Orozco E. , Fuentes-Maya J. , Mendoza A. , Gasga J. Reyes , Martínez L. , Pérez R. , García A. , Schabes P.S. , Acosta D. , José-Yacamán M.
Published: November 2004

A structural characterization of the superconducting phases in Bi 2 Sr 2 Ca Cu 2 O 8+x is carried out. X-Ray measurements are in agreement with recently reported diffraction patterns indicating an orthorhombic structure with large c-axis parameter (≈30Å). Twin boundaries which are commonly found in high-T c superconducting compounds based on Y or rare earths are however not frequent in these new type of superconductors. Transmission Electron Microscope images show a layered type of structure and electron diffraction patterns which confirm the orthorhombic structure. The resistivity measurements show a large drop at 100°K with a Tc of the order of 76°K.
ON THE THEORY OF SUPERCONDUCTIVITY IN THE HUBBARD MODEL
Authors: PLAKIDA N.M. , STASYUK I.V.
Published: November 2004

A pairing mechanism caused by the kinematical interaction in the Hubbard model is considered. On the basis of equations of motion for two-time Green functions with anomalous pairings taken into account, equations are derived for the superconducting gap of an extended S-type and T c .
X-RAY DIFFRACTION STUDY OF THE MODULATED STRUCTURE IN SUPERCONDUCTING SINGLE-CRYSTAL Bi2Sr2CaCu2Oy
Authors: CHU X. , MAI Z.H. , YAN Y.F. , WANG J.H. , ZHENG D.N. , LI C.Z. , YANG Q.S. , ZHAO Z.X.
Published: November 2004

X-ray precession technique1 has been utilized to study the reciprocal space of the superconducting single crystal Bi 2 Sr 2 CaCu 2 O y. An average structure with space group of Pnnn and a real structure with the superspace group of [Formula: see text] or [Formula: see text] have been found for this one dimensional modulated incommensurate material. As well, a basic structure with the space group of Fmmm is derived from the experimental data.
A STUDY OF CRYSTALLIZATION BEHAVIOR OF METGLASS Fe80B20 ALLOY BASED ON RESISTIVITY MEASUREMENTS
Authors: SHAMIM A. , ABBAS T. , SULEMAN M. , MATEEN A. , AHMAD A. , NAWAZ M. , ZAFAR M.S.
Published: November 2004

Crystallization behavior of amorphous Fe 80 B 20 alloy has been studied using resistivity measurements. Other phase transitions after crystallization have also been studied.
HIGH-TEMPERATURE RESISTIVITY AND IMPURITY (Mg, Pb OR Sb) SUBSTITUTION EFFECTS OF Bi1Sr1Ca1Cu2Oy
Authors: SUGAWARA K. , OKIBAYASHI K. , KATAOKA S.
Published: November 2004

High-temperature resistivity (R4) measurements of Bi 1 Sr 1 Ca 1 Cu 2 O y (BSCCO) revealed that R4 increases almost linearly with temperature up to about 800°C and sharply increases above 870°C. The interface resistivity between BSCCO sample and electrodes (Pt) revealed anomalous increments at around 650°C and 800°C, a possible indication of some kind of crystal instability in BSCCO. Impurity ( Mg, Pb or Sb ) substitution effects were also studied. The superconducting properties of BSCCO are sensitively affected by Pb and Sb substitutions, but less sensitively by Mg substitution.
ELASTIC PROPERTIES AND DEBYE CHARACTERISTIC TEMPERATURE OF PARTIALLY MELTED YBa2Cu3O7−x SUPERCONDUCTOR
Authors: LEE D.F. , SALAMA K.
Published: November 2004

The quasi-isotropic elastic constants are measured in a 85% dense partially melted YBa 2 Cu 3 C 7−x superconductor in the temperature range 80–300 K. The room temperature values of the longitudinal and shear moduli of the void-free material are found to be 168 and 59 GPa respectively, and no decrease in these constants is observed during the transition from normal to superconducting states. The Debye temperature is found to be 426 K which is comparable to that of the tetragonal phase polycrystalline BaTiO 3 (429 K).
THE RESOLUTION OF SUPERCONDUCTING COMPOUNDS IN THE PARAMETRIC SYSTEM TlxBa2Ca2Cu3Oy
Authors: EIBSCHÜTZ M. , VAN UITERT L.G. , GRADER G.S. , GRODKIEWICZ W.H. , KYLE T.R. , ZYDZIK G.J.
Published: November 2004

A parametric representation of critical temperature (T c ) vs Tl/Cu for the crossection Tl x Ba 2 Ca 2 Cu 3 O y shows evidence of all known superconducting compounds and two additional phases as well. Peaks in T c vs Tl/Cu fit expected Tl/Cu values within a few percent using weight analysis.
(0001) AND $(11\bar{2}0)$ FACETTING OF ALUMINA UNDER ELECTRON IRRADIATION
Authors: PENG J.L. , BURSILL L.A.
Published: November 2004

(0001) and [Formula: see text] polar surface facetting of sapphire and ruby is observed directly at atomic resolution under electron irradiation. For atomically clean surfaces, monolayers of spinel-type A1 3 O 4 structure have been identified using computer modelling and image-matching. For surfaces precoated with thin amorphous layers there is no irradiation-induced rearrangement and simple metal atom surface terminations have been identified. The results are discussed in terms of alternative surface depolarization mechanisms, which should be relevant to electronic, catalytic and ceramic applications of alumina.
THIN FILMS OF BARIUM, YTTRIUM, EUROPIUM, ERBIUM, AND COPPER OXIDES PREPARED BY PLASMA — ENHANCED CVD
Authors: HOLZSCHUH H. , OEHR C. , SUHR H. , WEBER A.
Published: November 2004

Thin films of BaO , Y 2 O 3, Eu 2 O 3, Er 2 O 3 and CuO have been prepared by plasma-enhanced CVD using the heptanedionato- and pentanedionato-complexes of the metals as precursors.
THERMOELECTRIC POWER OF Tl2Ba2(Ca1−xMgx)2Cu3Oy SUPERCONDUCTORS
Authors: YAN S.S. , CHEN T. , ZHANG H.B. , SHEN Z.H. , TONG L.T. , ZHANG H.
Published: November 2004

Thermopower of a series of Tl 2 Ba 2( Ca 1−x Mg x)2 Cu 3 O y superconductors has been measured in a temperature range of 77–300 K. The data are analysed on the assumption that there are two regions in the samples: metallic and semiconductive. It is found that the diffusion thermopower of the metallic region, which is the normal state of the superconductive phase in the sample, is proportional to the temperature and has a small as well as negative value.
DIODE CHARACTERISTICS OF YBa2Cu3O7/n- TYPE SILICON CONTACTS
Authors: HÄCKEL S. , DONEIT J. , PINKOWSKI A. , LORENZ W.J.
Published: November 2004

The temperature dependences of diode characteristics were measured on high-T c -superconducting YBa 2 Cu 3 O 7 (polycrystalline)/n-type silicon (monocrystalline) contacts using a common two-pole-technique at low frequencies. The non-superconducting p-type semiconductor YBa 2 Cu 3 O 6.5 (polycrystalline) served as a reference substance. The temperature coefficients of the diffusion voltage, the diffusion current and the saturation current were found to be finite at T>T c , but almost zero at T≤T c . At T=78 K , the diffusion voltage of the diode YBa 2 Cu 3 O 7/n-type silicon was about 200 mV lower as compared to that of the reference diode YBa 2 Cu 3 O 6.5/n-type silicon.

The observed phenomena are explained in terms of different charge carrier behavior in the superconducting ceramics above and below T c .
PHONON DENSITY OF STATES IN THE SUPERCONDUCTING Y-Ba-Cu-O SYSTEM
Authors: RUAN J.H. , YU A.S. , QIN J. , GOU C. , YANG T.H. , LIN J. , NIU S.W. , YAN Q.W. , SHEN Z.G.
Published: November 2004

The generalized phonon density of states for the high-T c superconductor YBa 2 Cu 3 O 7.1 with high Meissner effect (50%) and for its retreated sample with low Meissner effect (15%) at T=300 K and T=86 K respectively was measured by using inelastic neutron scattering method. The density of states of the superconductor YBa 2 Cu 3 O 7.1 at temperatures of both 300 K and 86 K shows a similar energy spectrum below 95 meV. However, above this energy there are evident softening of modes at 86 K. In addition, a large decrease of 92 meV peak in the density of states for a sample with lower Meissner effect was observed, this effect is supposed to be a result of an increase of vacancies on O 4 site.
EFFECTS OF PLASMA OXIDATION ON TRANSPORT PROPERTIES OF SPUTTERED Y-Ba-Cu-O FILMS
Authors: NOJIMA T. , AWAJI S. , MAENO Y. , FUJITA T.
Published: November 2004

Effects of plasma oxidation on superconducting and normal properties were studied for rf-sputtered Y-Ba-Cu-O films. The plasma oxidation was performed in a mixture gas of Ar-50%O 2 both before and after annealing. The oxidation enhances superconducting transition temperature, T c , and improves metal-like behavior of normal resistance as well. Typical films obtained after the oxidation exhibited the transition with an onset at 94 K and with zero resistance below 82 K. The improvement was found to hold for more than 30 days after oxidation.
LATTICE DYNAMICS OF TRANSITION METAL OXIDE MnO USING THREE BODY FORCE SHELL MODEL
Authors: MOHAN S.
Published: November 2004

The phonon dispersion curve for the transition metal oxide viz. manganese oxide at room temperature has been calculated for the first time, assuming Mn ++ and O −− ions are highly polarisable. The three body force shell model employed here takes care of the effect of many body interactions in the lattice potential. The aim of this paper is to treat the various interactions between the ions in a more general way without making them numerically equal. The values of the phonon frequencies evaluated by the new approach are in general, in good agreement with the experimental values.
POSSIBLE ROLE OF Pb IN Bi2−xPbxSr2Ca2Cu3Oy SYSTEM
Authors: YUAN S.L. , JIN S.Z. , ZHU B. , WANG W. , ZHENG J.Q. , ZHENG G.G. , GUAN W.Y.
Published: November 2004

The preliminary study on the electron spin resonance (ESR) for the Bi 2−x Pb x Sr 2 Ca 2 Cu 3 O y system has been made at room temperature. It is found that no significant ESR signal appears for Pb-substituted BiPbSrCaCuO system at RT, but a strong ESR signal was found for BiSrCaCuO system with 90 K superconducting transition under the same experimental conditions. These might be attributed to the Cu 3+/ Cu 2+ ratio in the bismuth based systems. A possible role of Pb in the Bi 2−x Pb x Sr 2 Ca 2 Cu 3 O y system is discussed.
CRITICAL CURRENTS AND MAGNETIC PROPERTIES OF CERAMIC HIGH-Tc SUPERCONDUCTORS
Authors: BLATTER G. , DERSCH H. , DUPRÉ T. , RHYNER J. , ZELLER H.R.
Published: November 2004

Experiments on critical current and magnetic properties of ceramic YBa 2 Cu 3 O 7−δ are discussed and analyzed in terms of an adapted critical state model.
RAMAN SCATTERING ON PHONONS IN Nb-Cu METALLIC SUPERLATTICE
Authors: ZHANG X.-K. , XIA HUA , HU AN , ZHANG M.-S. , YUAN X.-Y. , CHEN QIANG , ZHU S.-N.
Published: November 2004

We present Raman scattering results on transverse acoustic phonons in metallic superlattice and have verified most expectations regarding acoustic phonon folding as in semiconductor superlattices. Raman folded peaks up to seventh order can be observed which agree closely with elastic continuum prediction in frequency. Owing to metal high optical absorption, phonon momentum nonconserving have caused increasing linewidth and disorder-activated transverse-acoustic mode scattering.
A NEW SUPERCONDUCTING MATERIAL IN A Y-Ba-Cu-O AND Bi-Ca-Sr-Cu-O MIXED SYSTEM
Authors: DISSANAYAKE M.A.K.L. , TENNEKONE K. , ILEPERUMA O.A. , SAMARAPPULI S.H.S.P.
Published: November 2004

A new superconducting phase has been found in a mixed system prepared from the YBa 2 Cu 3 O 7−δ and Bi 2 CaSr 2 Cu 2 O 9−δ high-T c materials. The new compound shows an onset of resistivity transition at ~100 K and zero resistivity below ~50 K. Powder X-ray diffraction pattern of the new compound differs completely from those of YBa 2 Cu 3 O 7−δ and Bi 2 CaSr 2 Cu 2 O 9−δ. The materials prepared using a mixture of the oxides and carbonates with identical cation stoichiometric ratios, on the other hand, does not exhibit superconductivity.
ON THE SPECIFIC HEAT ANOMALIES IN THE TEMPERATURE RANGE 200 K TO 240 K IN CuO AND YBa2Cu3O7−δ(YBCO)
Authors: SLASKI M. , ÆGREID T.L. , NES O.M. , FOSSHEIM K.
Published: November 2004

Specific heat anomalies in YBa 2 Cu 3 O 7−δ (YBCO) and CuO were investigated in the temperature range 200 K to 240 K. It was found that small amounts of CuO contained as a separate phase in YBCO produce easily observable anomalies caused by two consecutive antiferromagnetic (AF) transitions at 211.6 K and 228.3 K in CuO. The anomalies hence were observed in both pure CuO and YBCO samples containing some free CuO. The anomalies found here are of a different character than the broad peak we observed earlier around 220 K in pure ceramic YBCO. This lends support to the earlier interpretation of the 220 K anomaly as a structurally related one.
COLD FUSION IN CONDENSED MATTER: IS A THEORETICAL DESCRIPTION IN TERMS OF USUAL SOLID STATE PHYSICS POSSIBLE?
Authors: SCHOMMERS W. , POLITIS C.
Published: November 2004

The interaction potential between two deuterons (d+) in solid palladium has been estimated using a theoretical picture which is well known in the physics of liquids. On the basis of this potential, the essential experimental results of Fleischmann and Pons (J. Electroanal. Chem.261 (1989) 301) and Jones et al. (preprint) can be explained qualitatively. Thus, in our opinion, the description of cold fusion in condensed matter by means of usual solid state physics should not be excluded.
EXPERIMENTAL STUDY OF THE HIGH Tc SUPERCONDUCTOR Y-Ba-Cu-O SYSTEM
Authors: NAQVI S.M.M.R. , ALAM JAWAID , AHMAD FIROZ , KHAN MUSHEER HASAN
Published: November 2004

Two batches of Y-Ba-Cu-O superconductors have been prepared. The zero resistance temperature is 90 K with Tc onset at 93 K and 95 K, respectively. Susceptibility measurements show superconducting phase at LN2. X-ray diffraction results indicates single phases.
ORTHORHOMBIC TO TETRAGONAL STRUCTURAL TRANSITIONS IN YBa2−xLaxCu3O7±δ
Authors: UMARJI A.M. , SOMASUNDARAM P. , SENBHAGARAMAN S.
Published: November 2004

In YBa 2−x La x Cu 3 O 7±δ(x=0.0 to 1.0), the structure becomes tetragonal (3a=c) when x>0.35 and the Tc of the orthorhombic phase decreases. The oxygen content increases with trivalent La partially substituting for bivalent Ba, but the perovskite triple cell is still maintained along ‘c’ direction. The additional oxygen, probably occupying O5 position, is less labile and consequently the orthorhombic to tetragonal (3a≠c) transition (accompanied by loss of oxygen) is pushed up from 610°C for x=0.0 to > 900°C for x=0.25.
THEORY OF POINT CONTACT SPECTRA FOR SYSTEM METAL TIP-SUPERCONDUCTOR WITH INTERNAL JOSEPHSON JUNCTION
Authors: KUPKA M. , HUDÁK O.
Published: November 2004

We report on the calculations of current-voltage characteristics and dynamical resistivity for a model system (series connected point contact metal — superconductor and Josephson junction of the S-N-S type) as a function of applied voltage. Calculated shape of dV/dI as a function of V shows some qualitative agreement with measured curves on real low-resistivity point contacts of the type metal tip – ceramic superconductor (LaBaCuO, YBaCuO). Method for determination of the energy gap is proposed.
HIGH TEMPERATURE SUPERCONDUCTOR GdBa2Cu3O7−x INVESTIGATION BY OPTICALLY THERMOSTIMULATED EXOEMISSION (OTSEE) METHOD
Authors: CHRZANOWSKI J. , SUJAK B. , BENZAR I. , ZALESKI A. J. , CISZEK M. , OLEJNICZAK J.
Published: November 2004

Measurements of optically-thermostimulated electron emission from the high temperature superconductor GdBa 2 Cu 3 O 7−x were performed for the temperature range of 65–300 K. Changes in the intensity of the emitted electrons with temperature were observed. OTSEE peak at about 230 K is ascribed to structural changes in the sample, which are reflected at surface layer.
SOLIDIFICATION CHARACTERISTICS OF YBaCuO COMPOUNDS AND THE TEXTURED CRYSTALS GROWN BY LASER FLOATING ZONE MELTING
Authors: JIANG X. P. , ZHANG J. S. , HUANG J. G. , JIANG M. , GE Y. L. , QIAO G. W. , HU Z. Q. , LI Y. Y. , SHI C. X.
Published: November 2004

The partial vertical sections of Y–Ba–Cu–O phase diagram have been studied. The results show that Y 1 Ba 2 Cu 3 O 7−x (123) phase melts incongruently around 1010ºC with a peritectic reaction and melting in growing single or in a great difficulty in growing single or directed crystal of 123 phase from melt by using normal solidification technologies. The new laser floating zone melting technique has been applied for manufacturing crystal rod of YBaCuO compound with diameter near 1.5 mm. The grown crystal can be changed into superconductor of single 123 phase with T c above 90 K and with certain texture feature following suitable heat treatments. It is also found that oriented crystal of 123 phase can be obtained directly from YBa 2 Cu 12 O y composition below 1010°C via eutectic reaction, and they may form composed superconductor wire with T c near 85 K after suitable heat treatment.
THE KRAMERS TURNOVER PROBLEM: RECROSSING EFFECTS AND THE ENERGY DIFFUSION DESCRIPTION OF THERMAL ACTIVATION
Authors: DEKKER H.
Published: November 2004

Kramers' Brownian motion model for escape from a metastable potential well is reconsidered in terms of the particle's energy and the action variable near the peak of the barrier. The pertinent phase space density ρ(ε, s) is uniquely determined (i) by means of a spectral analysis and (ii) upon specifying the energy distribution of (re-)entering particles. The ensuing decay rate Γ goes to zero in the low as well as in the high friction limit according to Kramers' original formulae. The nature of the intermediate turnover regime is critically discussed — and a comparison with related recent work by Büttiker, Harris and Landauer, Mel'nikov and Meshkov, and Grabert is made — while a problem with the underlying density is pointed out.
INTENSITY OF X-RAY (222) LINE IN InSb AT 77 K UNDER PRESSURE
Authors: OKAI BIN , TAKANO KAORU J. , YOSHIMOTO JIICHIRO , TAKAHASHI HIROKI , IZAWA ATSUSHI , TSUJI KAZUHIKO
Published: November 2004

The intensity of X-ray (222) line in InSb was measured at liquid nitrogen temperature up to the transition pressure. No abrupt decrease at ca. 3 GPa as reported by Yoder-Short, Colella and Weinstein was observed at 77 K, indicating that a smearing of the bonding charge is not responsible for the structural transition of InSb.
THE SPHEROMAK AS AN AXISYMMETRIC SPHERICAL DYNAMO: CLARIFICATION OF AN OLD AMBIGUITY
Authors: SALINGAROS N. A.
Published: November 2004

An elementary result in magnetostatics clarifies a fundamental ambiguity in the theory of the Spheromak (which is a compact toroidal plasma without the external poloidal windings of a Tokamak). A free Spheromak (without an external equilibrium field) is shown to possess intrinsic rotational self-forces that amplify its toroidal current, and hence its poloidal magnetic field. This result explains the experimentally observed increase of toroidal current in free compact toroidal plasmas. The possibility of an axisymmetric spherical dynamo that generates its own dipole-like self-field is mentioned.
DYNAMIC JAHN-TELLER COUPLING, ANHARMONIC OXYGEN VIBRATIONS AND HIGH-Tc SUPERCONDUCTIVITY IN OXIDES
Authors: JOHNSON K. H. , CLOUGHERTY D. P. , McHENRY M. E.
Published: November 2004

A universal dynamic Jahn-Teller (DJT) mechanism for superconductivity and its applications to CuO and BaBiO 3 high-T c oxides are reviewed. Dynamical interconversion between the shallow "double-well" potentials of degenerate delocalized oxygen-oxygen "pπ-bonds" at the Fermi energy (E F ) induces anharmonic oxygen vibrations, lattice-electron coupling, and Cooper pairing. This mechanism yields high T c 's and small-to-vanishing isotope shifts for cuprates, where O (pπ)- O (pπ) bond overlap at E F is promoted by Cu (dπ*)- O (pπ) hybridization. It yields lower T c 's and larger isotope shifts for BaBiO 3's, where O (pπ)- O (pπ) overlap is small. For vanishing bond overlap at E F , DJT coupling reduces to harmonic phonon coupling in BCS theory. Simple formulae for calculating T c and isotope shifts for any superconductor from the "real-space" chemical bonding at E F are presented, yielding (T c ) max ≈ 230 K .
CONVENTIONAL AND CORRELATED FLUX FLOW RESISTIVITY FEATURES IN AN Y BASED SUPERCONDUCTOR
Authors: HASANAIN S. K. , HUSSAIN M.
Published: November 2004

The resistive behavior of a polycrystalline Y 1 Ba 2 Cu 3 O 7−x superconductor has been studied in the field range 0 < H < 10 KOe , as a function of current and temperature (T > 77 K ). We find nonlinear I – V characteristics V ∝ In at 77 K, in the presence of an applied field. The exponent n is found to be field dependent. At higher temperature, linear flux flow features are evident. The viscosity coefficient for flux flow is obtained, and is seen to be non-constant over the field range. Small differences between (J ‖ H) and (J ⊥ H) behavior are observed.
TWO-BAND FIBONACCI QUASICRYSTAL WITH HYBRIDIZATION: EXACT LOCAL GREEN’S FUNCTION USING THE RENORMALIZATION-GROUP METHOD
Authors: CHAKRABARTI A. , KARMAKAR S.N. , MOITRA R.K.
Published: November 2004

In this paper we present a study of the electronic properties of a one-dimensional Fibonacci chain with two hybridizing bands. Our study is motivated by recent experiments with quasicrystals in which transition metal atoms occupy positions of icosahedral symmetry. Using a recently proposed real space renormalization group scheme we make an exact analytical study of the two-band problem. We examine the effect of hybridization on the energy spectrum, the wave functions and the density of states of the Fibonacci chain. We find that the spectrum continues to remain a Cantor set even in the presence of hybridization. We conclude therefore this property of the spectrum is a purely structural effect. We present our results on the electronic density of states and show how hybridization produces additional structures in the energy spectrum.
RECENT ADVANCES IN THE SURFACE STUDIES BY ANGLE-RESOLVED X-RAY PHOTOELECTRON DIFFRACTION
Authors: POON H.C.
Published: November 2004

Intensity data of X-ray photoelectron spectroscopy usually show strong spatial modulations due to diffraction of photoelectrons by the surrounding atoms of the emitter. Some of the theoretical aspects and recent developments in the surface analysis by this diffraction technique will be reviewed.
FORMATION REACTIONS OF THE Tl2Ca2Ba2Cu3O10 AND Tl2Ca1Ba2Cu2O8 PHASES
Authors: HUANG T.W. , HUNG M.P. , CHIN T.S. , KU H.C. , HSU S.E.
Published: November 2004

Solid state formation of the superconducting phases in the Tl–Ca–Ba–Cu–O system has been studied by DTA, TGA , and XRD analyses. It was found that the formation reaction of the high Tc Tl 2 Ca 2 Ba 2 Cu 3 O 10 and the low Tc Tl2Ca1Ba2Cu2O8 phases takes place at around 900°C and 840°C respectively, within a reaction time of 30 minutes. Activation energies of these reactions are found to be 50 kcal/mol and 35 kcal/mol, respectively. The use of precursor Ca 3 BaCu 3 O x yielded superconducting materials with superior characteristics as compared to those prepared from the direct mixture.
GROWTH OF UNCRACKED BARIUM-SODIUM NIOBATE CRYSTALS
Authors: TSUKIOKA MASAYUKI , KUROIWA SHINICHIRO , TANOKURA YASUO , KOBAYASHI MICHIKO , SHIMAZU MASAZI , TSUTSUMI SADAO
Published: November 2004

It is known that cracking occurs in Barium-Sodium Niobate, Ba 4 Na 2 Nb 10O30 (BNN), during Czochralski (cz) growth. This is due mainly to lattice distortions associated with the ferroelectric phase transition. We have studied the cz crystal growth condition for BNN without cracking, and found that high quality single crystals of BNN without cracking can be grown by using Gd-doped starting melt, i.e., Ba 4 Na 2 Nb 10O30-Ba3NaGdNb10O30 solid solution. In order to confirm the effect of Gd doping on the crystalline quality, Gd concentrations were measured by ICP for both the cz single crystal sample and the starting powder material.

Gadlinium concentration in the as-grown crystal was about 0.195 mol %, nearly the same as that (2.0 mol %) in the starting material.

Dielectric constant along c-axis, ε33, was measured at temperatures from 300 K to 870 K. The experimental result revealed that ε33 of the single crystal is about two times larger than that of BNN single crystal without Gd impurity in the temperature range from 300 K to 650 K.
GENERALIZED SPHEROIDAL WAVE EQUATIONS FOR IMPURITY STATES IN A HETEROSTRUCTURE
Authors: SHAN YUEH
Published: November 2004

Within the framework of effective mass theory, a set of generalized spheroidal wave equations for the exact treatment of a shallow donor impurity in a semiconductor-semiconductor heterostructure is obtained from the relevant Schrödinger equation by the method of separation of variables in prolate spheroidal coordinates. The way of calculating the eigensolutions of these wave equations is briefly discussed.
DYNAMICS OF QUASIPARTICLES IN CuO2 PLANES
Authors: MATTIS DANIEL C.
Published: November 2004

At 5 electrons per cell, planar CuO 2 is an antiferromagnetic insulator rather than a Fermi liquid. We consider the effects of adding a few electrons or holes into such an insulator and derive a relation between the insulating energy gap and effective mass m* of the added carriers. We find [Formula: see text]to differ from [Formula: see text], with both being temperature dependent.
DIRECT OBSERVATION OF A STRUCTURE TRANSFORMATION OF 3-ATOM Ir CLUSTERS ON Ir SURFACES
Authors: TSONG TIEN T. , CHEN CHONG-LIN
Published: November 2004

A 3-atom Ir cluster on the Ir (111) or (001) surface can assume either a 1-D chain-like or a 2-D island-like structure. On the (111), the ln(p1D/p2D) vs 1/T plot is linear where p1D and p2D represent respectively the probability of observing the cluster in the 1-D or in the 2-D structure. The 2-D structure is more stable with a lower cluster binding energy of ΔE12=−0.098±0.004 eV. On the (001), the 1-D structure is more stable with ΔE12=+0.335±0.015 eV. In addition, the plot deviates significantly from the simple linearity at low temperatures, indicating the entropy factor is temperature dependent.
ICON SEMANTICS — A FORMAL APPROACH TO ICON SYSTEM DESIGN
Authors: CHANG SHI-KUO
Published: November 2004

A generalized icon is an object with the dual representation of a logical part (the meaning) and a physical part (the image). We describe a formal approach to specify icon systems. Iconic operators are presented, which constitute an icon algebra to construct complex icons and define icon semantics. The Chinese character formation rules can then be explained in a unified way. Applications of this methodology are discussed.