bluuebunny/crossref_metadata_2025 huggingface dataset:
THE THUE-MORSE APERIODIC CRYSTAL, A LINK BETWEEN THE FIBONACCI QUASICRYSTAL AND THE PERIODIC CRYSTAL
Authors: RIKLUND ROLF , SEVERIN MATTIAS , LIU YOUYAN
Published: November 2004

The electronic spectrum and eigenstates of a one-dimensional aperiodic Thue-Morse crystal isstudied with an on-site tight-binding model. The relation between the constructing elements andthe hierarchical splitting of the bands into subbands is analysed. The eigenstates are shown to be much more similar to those of a periodic crystal than those of a Fibonacci quasicrystal. We thus claim that the Thue-Morse aperiodic crystal is a link between the Fibonacci quasicrystal and theperiodic crystal, and that the study of non-Fibonaccian aperiodic crystals is a promising steptowards the desired unified theory of disordered, aperiodic and periodic systems. Since the experimentally studied MBE-grown aperiodic crystals typically has 5% fluctuation in layer thickness, we also investigate the density of states and eigenstates for a model system withfluctuating site-energies.
SUPERCONDUCTORS WITH HIGH ZERO-RESISTANCE TEMPERATURE IN Ln-Ba-Cu-O SYSTEM (Ln=Gd, Dy, Ho, Er, Tm, Yb, and Lu)
Authors: Huang Yuzhen , Chen Genhua , Chen Liquan , Mai Zhenhong , Chu Xi , Yang Qiansheng , Ni Yongming , Liu Guirong , Wang Lianzhong , Tang Ruming , Bi Jianqing , Wang Changqing , Jia Shunlian , Cui Changgeng , Guo Shuquan , Li Shanlin , Zhao Zhongxian
Published: November 2004

The new superconductors with zero-resistance temperature around 90K in Ln-Ba-Cu-O system (Ln=Heavy rare earth elements with the exception of Tb) have been synthesised. It has been shown that the nominal composition and preparation procedure for various heavy rare earth compounds are different from each other.
Thermal characterization and superconductivity of the Th5−xBaxPb2−0.5xCu5O13+y
Authors: Zhang Yuling , Xie Sishen , Cheng Xiangrong , Li Kesheng , Yang Qiansheng , Ni Yongming , Liu Guirong , Liang Jingkui
Published: November 2004

We report the phase transition behavior of the samples Th5−xBaxPb2−0.5xCu5O13+y(x=2.75-3.75) between 20°C and 1300°C, and the effect of heat treatment on the superconductivity. The specific heat, DSC and DTA as well as TGA investigations have been performed.

The second-order-like transition around 240°C was observed by DTA and Spesific heat determination. The results are shown in Fig.1 and Fig.2.
HIGH MAGNETIC FIELD HALL EFFECT AND MAGNETORESISTANCE STUDIES OF Y-Ba-Cu-O: A HIGH Tc SUPERCONDUCTOR
Authors: Hettinger J.D. , Swanson A.G. , Brooks J.S. , Ma Y.P.
Published: November 2004

We have measured the transition temperature, critical field, magnetoresistance, and Hall effect for the high temperature superconductor Y-Ba-Cu-O in magnetic fields up to 23T in the temperature range 4.2 to 125K. Meissner studies at zero magnetic field were also performed in some cases. We find a strong dependence of these parameters on the relative percentage of the correct phase of Y-Ba-Cu-O in the sample. We report new results on magnetoresistance and Hall effect in these materials.
POSITRON ANNIHILATION STUDY OF HIGH Tc SUPERCONDUCTOR YBaCuO IN THE REGION NEAR TRANSITION TEMPERATURE
Authors: TENG Ming-kang , SHEN De-xun , CHEN Ling , YI Chuan-yuan , WANG Guang-hou
Published: November 2004

The lifetime parameters of positrons annihilating in the high Tc superconductor YBaCuO are first reported to show the anomalies at the transition temperature region, indicating the abrupt decrease of local electron density at the positron site, possibly due to the lattice relaxation or due to the interaction between crystallites of nomal state and that of the superconducting state, which coexist at the phase transition period.
UPPER CRITICAL FIELD OF HIGH Tc SUPERCONDUCTING OXIDES
Authors: CUI Changgeng , GUO Shuquan , LI Shanlin , CHEN Lie , DONG Cheng , XU Xianting , LIANG Jingkui
Published: November 2004

Upper critical fields Bc2(T) near Tc have been measured for the samples of Ba2YCu3Ox and Ba2GdCu3Ox. The upper critical field slope (dBc2dT)Tc and the upper critical field Bc2(O) have been calculated by using the least squares filling of straight line and using WHH expression in dirty limit respectively. The results show that Bc2(O) can be reach 114T and 127T for the samples of Ba2YCu3Ox and Ba2GdCu3Ox respectively.

It is observed that there is a upwards curvature near Tc in the curves of B(T) vs.T. The main reason might be a proximity type effect in which a small amount of high Tc materials is able to raise the effective Tc of the samples, However such an effect could be suppressed at high field.
ANTIFERROMAGNETIC ORDERING IN Y-BA-CU-PT-O
Authors: Kovachev V.T. , Vlakhov E.S. , Nenkov K.A. , Lovchinov V.A. , Gospodinov M.M. , Stojanova A.K. , Dimitrov D.A.
Published: November 2004

A high temperature superconducting Y-Ba-Cu-Pt-O compound has been investigated. The results on magnetization and magnetic susceptibility of the compound are presented. A hysteresis of the magnetic moment at 4.2K is observed. This hysteresis occures, most probably, due to an antiferromagnetic ordering in the material. The Curie asymtotic temperature and Nèel temperature of the material are reported.
TEMPERATURE AND MAGNETIC FIELD DEPENDENCE OF CRITICAL CURRENT OF YBaCuO JOSEPHSON JUNCTIONS
Authors: Gao Peng , Fan Hongchang , Yao Xixian , Yu Zheng , Ding Shiying , Jing Xiunian , Shi Kexin , Yan Jialie
Published: November 2004

Josephson junctions were fabricated using high Tc superconductor. The I-V characteristics of the junctions were measured at liquid N2 temperature. The temperature and magnetic field dependence of the critical current were obtained and compared with theories.
A Physical Model For High Tc Superconductivity Of The Oxygen Deficient Perovskite Y-Ba-Cu-O
Authors: Zi-zhao Gan , Dai Yuan-dong , Han Ru-shan
Published: November 2004

The high Tc superconductivity of the oxygen deficient perovskite Y1Ba2Cu3O7 has closed relation to the ordering distribution of the cations with various valences and the oxygen vacancies in this structure. The special electronic structure related to such ordering distribution lead to the phonon softening and the excitonic mechanism for superconducting pairing. These effects provide a physical model to understand the high Tc superconductivity in this material.
THE EFFECT OF LOCAL MODE ON Tc OF THE OXIDE SUPERCONDUCTORS
Authors: Zou Nanzhi , Wang Zidan , Pang Jinzhong , Gong Changde
Published: November 2004

Although there may exist a large intrasite Coulomb repulsion, the local mode can still induce a attractive interaction between electrons through oxygen breathing mode. This interaction plays an imporatnt role in raising Tc. The result approaches that of experiment by a combination of the local mode and the Van Hove singularity.
Structural Relationships in High Temperature Superconductors
Authors: Schuller Ivan K. , Segre C.U. , Hinks D.G. , Jorgensen J.D. , Soderholm L. , Beno M. , Zhang K.
Published: November 2004

The recent discovery of two types of metallic copper oxide compounds which are superconducting to above 90K has renewed interest in the search for new high temperature superconducting materials. It is significant that both classes of compounds, La2−xSrxCuO4−y and YBa2Cu3O7−δ are intimately related to the extensively studied perovskite family. Both compounds contain highly oxidized, covalently bonded Cu-O sublattices, however, they differ in geometry. In this paper we discuss the relationship of these features to the superconducting properties.
Model for High Tc-Superconductivity
Authors: Bennemann K.H.
Published: November 2004

A model for high Tc-superconductivity in La2−xMxCuO4 and YBa2Cu3O7 systems is discussed. We argue that in La2CuO4 systems superconductivity results partly from electron-phonon coupling, but in YBa2Cu3O7 presumably dominantly from attractive coupling of the Cu2+ outer d-electron to the oxygen p-holes.
AUTOMATIC FORMATION OF SUPERCONDUCTIVE PHASE IN THE Y–Ba–Cu–O COMPOUND SYSTEM
Authors: Hua Z.Y. , Cheng H.S. , Jia C.L. , Jiang A.R. , Miao B.C.
Published: November 2004

Real compositions and structures of various samples of Y-Ba-Cu-O compound have been studied by Rutherford backscattering (RBS), nuclear reaction, electron probe microanalysis (EPMA), high-resolution electron microscopy (HREM) and X-ray diffraction. Results show that in this system all superconductive samples with different nominal compositions have a tendency to form a superconductive phase of perovskite-like YBa2Cu3O7 (Phase A), and the remaining constituents are gathered to another phase (Phase B). Therefore the chemical compositions of this compound system are insensitive to Tc and the superconductor is relatively easy to be prepared.
RAMAN AND INFRARED STUDY OF YBa2 Cu3 O7
Authors: Mihailović D. , Čopič M. , Zgonik M. , Novak A.
Published: November 2004

We have measured Raman and far-infrared spectra of YBa2 Cu3 O7 as a function of temperature. No significant changes are observed in the Raman spectra as with temperature. Far-infrared transmission measurements show a band at 100 cm −1 broadening at Tc .
KINETIC EQUATIONS FOR DENSE GASES A REVIEW OF PHYSICAL AND MATHEMATICAL RESULTS
Authors: BELLOMO N. , LACHOWICZ M.
Published: November 2004

This review paper deals with the analysis of a class of nonlinear kinetic equations derived on the basis of the Enskog theory for dense gases. The physical problem of the derivation of the equation and the mathematical problem of the analysis of the existence and uniqueness of the solutions to the initial value problem are both reviewed and discussed in details. Some new results are also given.
LOCAL APPROACH TO VARIATIONAL METHOD FOR ELECTRON CORRELATION IN NARROW BAND SYSTEMS
Authors: WEI GUO-ZHU , NIE HUI-QUAN , ZHANG KAI-YI , CHAO K.A.
Published: November 2004

Using the local approach, we have performed a third order perturbation calculation to investigate the electron correlation effect in extended Hubbard model with both positive and negative intraatomic and interatomic correlation energies. We found the significant third order correction over the second order terms. Consequently, all published results, especially the phase diagrams which were derived with the second order perturbation calculation are not reliable.
PHONON AND PHASON STRAIN IN DECAGONAL QUASICRYSTALS
Authors: GÓMEZ A. , PÉREZ-RAMÍREZ J.G. , CASTAÑO V.M. , JOSÉ-YACAMÁN M.
Published: November 2004

The phason model for quasicrystals of Socolar et al. is generalized for the case of an arbitrary quasicrystal. The formalism is applied to the experimental data for pentagonal quasicrystals of Al16Mn14 . It is shown that the general phason model explains most of the experimentally observed features on the electron microscope images, such as an observed 12.6/2 Å frange shift across boundary domains. It is shown that the microdomains introduced by the phasons can also explain the X-ray correlation length observed experimentally by Bancel et al.13
CLASSICAL DIFFUSION AND QUANTAL LOCALIZATION OF A KICKED PARTICLE IN A WELL
Authors: COHEN AVRAHAM , FISHMAN SHMUEL
Published: November 2004

The classical and quantal behavior of a particle in an infinite potential well, that is periodically kicked is studied. The kicking potential is K|q|α, where q is the coordinate, while K and α are constants. Classically, it is found that for α > 2 the energy of the particle increases diffusively, for α < 2 it is bounded and for α = 2 the result depends on K. An approximate formula for the diffusion coefficient is presented and compared with numerical results. For quantum systems that are chaotic in the classical limit, diffusive growth of energy takes place for a short time and then it is suppressed by quantal effects. For the systems that are studied in this work the origin of the quantal localization in energy is related to the one of classical chaos.
SUPER-RADIATION IN THE TWO-COMPONENT TWO-LEVEL SYSTEM
Authors: KADANTSEVA E. P. , SHUMOVSKY A. S. , YUKALOV V. I.
Published: November 2004

An exact hierarchy of equations for atomic averages is constructed for a multicomponent super-radiative system. By an example of a two-component system it is shown that the correlations between components arising from the interaction with a common field of radiation change the process qualitatively in comparison with the case of two independent components. In particular, two successive super-radiation pulses may appear in the system that initially had only one excited component.
SUPERCONDUCTIVE CERAMICS OBTAINED WITH SOL–GEL METHODS
Authors: ARCANGELI G. , FAVA R. , MASCI A. , NARDI A. , VATTERONI R. , ZONDINI C.
Published: November 2004

Several sol–gel routes have been considered, studied and developed to produce large quantities of granulates which can be processed to obtain ceramics having good superconducting characteristics. In the considered process a mixture of commercial nitrates is atomized, at room temperature, in a solution 1:1 of Primene JMT and benzene, and a pale blue gel of the starting elements is suddenly formed. The granulates obtained are free flowing, very reactive and well suited for pressing. For their intrinsic characteristics they could be very good precursors for the production of large quantities of superconductive ceramics in different forms. The precipitated gel is dried, calcined, pressed in the form of cylindrical pellets which are sintered up to 960°C. No grinding or different thermal treatments are needed. The sintered material has low electric resistance, shows a clear Meissner effect and has a transition temperature of between 91 and 95 K.
ISING MODEL IN THE MAGNETIC FIELD iπkT/2
Authors: LIN K. Y. , WU F. Y.
Published: November 2004

It is shown that the free energy and the magnetization of an Ising model in the magnetic field H = iπkT/2 can be obtained directly from corresponding expressions of these quantities in zero field, provided that the latter are known for sufficiently anisotropic interactions. Using this approach we derive explicit expressions of the free energy and the magnetization at H = iπkT/2 for a number of two-dimensional lattices.
SUPERCONDUCTIVITY IN THE NEARLY HALF–FILLED HUBBARD MODEL WITH STRONG ON SITE CORRELATION
Authors: Das A. N. , Choudhury P. , Ghosh B.
Published: November 2004

Superconductivity in a nearly half-filled Hubbard model with large on-site repulsion has been studied following the Hubbard's approximation. At T = 0, the Fermi energy touches the top of the lower Hubbard subband for n = 1, one electron per site in the system. For a particular density of states, sharply peaked at the centre of the band, the superconducting transition temperature is zero for n = 1 (zero hole concentration) and becomes maximum at a hole concentration of 1/3. The high temperature thermoelectric power of the oxide superconductors has been discussed, which indicates the strong correlation in the system.
QUANTUM FLUCTUATIONS ON THE GUTZWILLER APPROXIMATION OF THE HUBBARD MODEL
Authors: LAVAGNA M.
Published: November 2004

Many experimental results seem to relate the superconducting oxides to the phenomenon of Mott localization in strongly correlated systems. We will give a brief review of the different theories developed until then to treat the Mott localization in the Hubbard model: variational Ansatz of Gutzwiller or RVB Ansatz, leading to fundamentally different ground states.

In this context, we propose a new approach which consists to take account of the quantum fluctuations around the mean-field solution provided by the Gutzwiller approximation. We show how to understand the ground state in terms of a resonance (split by the Mott gap in the almost-localized regime) in complete analogy with the Abrikosov-Suhl resonance of the Kondo problem — heavy fermions. Superconductivity appears as induced by the constrained intersite correlations developed by quantum fluctuations around this resonant state.
ELECTRONIC PROPERTIES OF STRONGLY CORRELATED SYSTEMS
Authors: RICE T. M. , ZHANG F. C.
Published: November 2004

The observation that the energy scale of the magnetic excitations determined by the Heisenberg coupling constant ( J ≈ 0.1eV ) is much smaller than the charge excitation energies (≳ 2eV ) places the stoichiomatic Cu-oxides with formal valence Cu 2+ in the class of Mott insulators. Holes introduced into the CuO 2 layers can therefore be described by an effective Hamiltonian which contains a hopping term for holes between nearest neighbor CuO 4-squares (matrix element, t ) in addition to the Heisenberg term1). This effective Hamiltonian is restricted to the Hilbert subspace with one or less electrons in the Wannier orbital on each CuO 4 square. The Wannier orbital is made up from the [Formula: see text] Cu-orbital and a combination of the 2p O-orbitals with the same symmetry. The hybridization energy is maximized for a hole by forming a spin singlet combination of these orbitals so that the form of the effective Hamiltonian does not differ in form2) from that of a single band Hubbard model in the strongly correlated limit. The inclusion of O-O hopping does not change this conclusion3). Estimates of the parameter t , give a value t ≈ 0.5eV so that the ratio J/t ≪ l .
MAGNETISM AND SUPERCONDUCTIVITY IN DOPED PLANAR CuO2 SYSTEMS
Authors: Aharony Amnon , Birgeneau R. J. , Kastner M. A.
Published: November 2004

We present a model for the magnetic phases and superconductivity in doped planar CuO 2 systems. Electronic holes on the oxygens introduce local ferromagnetic exchange coupling between the Cu spins. The resulting frustration destroys the antiferromagnetic state characterizing the undoped planes, and generates a new spin glass phase. This frustration also yields an attractive interaction between the holes, whose range decreases with increasing doping. Arguing that transport is via the non-bonding in-plane oxygen orbitals, we use the BCS approximation to obtain an excellent estimate of the superconducting transition temperature T c (x) , for La 2−x Sr x CuO 4.
PERTURBATION THEORY OF THE PERIODIC ANDERSON LATTICE AND SUPERCONDUCTIVITY
Authors: Geertsma W.
Published: November 2004

In this paper I develop a perturbation calculation of the second and fourth order interparticle interaction in band states, based on the Periodic Anderson Lattice. I show that 4th order interparticle interactions giving rise to the wellknown Kondo effect vanish in the superconducting ground state. This term survives in the presence of a magnetic field. Pair excitations can only give rise to an appreciable attractive contribution when the d states are less than half filled and the pair energy is near the Fermi level. The only important attractive interaction comes from the normal fourth order terms.
SPIN-POLARON PAIRING AND HIGH-TEMPERATURE SUPERCONDUCTIVITY
Authors: Kamimura Hiroshi
Published: November 2004

In this paper a review is given on the mechanism of high temperature superconductivity recently developed by Kamimura, Matsuno, and Saito. In this mechanism spin-polarons associated with itinerant holes in the e v band (Cu dz 2- Op π band) are created in CuO 2 layers by strong intra-atomic exchange interaction (Hund's coupling) with localized dx 2− y 2 holes. Then the interplay of Hund's coupling and superexchange between Cu 2+( dx 2− y 2) spins gives rise to an attractive exchange interaction between spin-polarons, which leads to the formation of spin-singlet spin-polarons pairs. This contributes to high temperature superconductivity. Further the s-wave pairing reproduces the observed x dependence of T c as well as the right magnitudes of T c in ( La 1−x Sr x )2 CuO 4 satisfactorily.
SIMPLE SPIN-HOLE MODEL FOR MAGNETIC CORRELATIONS IN COPPER-OXIDE SUPERCONDUCTORS
Authors: Robledo A. , Varea C.
Published: November 2004

A simple model of spins and holes for weakly coupled CuO 2 layers is constructed to study the temperature-concentration phase diagrams of doped La 2 CuO 4 and YBa 2 Cu 3 O 6. Addition of holes, localized on the O sites, induces a transformation of spin correlations similar to that produced in an antiferromagnet when it is diluted with ferromagnetic impurities. The insulator-metal (I-M) transition occurs when the correlations in the paramagnetic phase switch from antiferromagnetic to ferromagnetic character and the correlation length vanishes. Repulsions between holes inhibit or suppress the appearance of ferromagnetic long-range order.
ON PHONON MECHANISM OF HIGH TC SUPERCONDUCTIVITY
Authors: Liu Fu-sui , Wang X. Q. , Mangkorntong P.
Published: November 2004

This paper explains simultaneously dTc/dP > 0, dλ/dP < 0 and the isotope effect observed for Y1Ba2Cu3O6.9 and La1.85Sr0.75CuO4 in terms of unified parameters in phonon mechanism of superconductivity.
ON THE RELEVANCE OF THE CONVENTIONAL BAND THEORY IN CASE OF HIGH-Tc SUPERCONDUCTORS: OPTICS OF La2−xSrxCuO4
Authors: Maksimov E. G. , Mazin I. I. , Rashkeev S. N. , Savrasov S. Y. , Uspenski Yu. A.
Published: November 2004

We discuss the question of the applicability of conventional band structure calculation to superconducting copper oxides. We show that optical spectra of La 2−x Sr x CuO 4 are reasonably described by LMTO band structure calculations. In fact, 20% reduction of calculated plasma frequency and introducing interband relaxation makes theoretical reflectivity spectra to reproduce essentially all features of single-crystal experimental reflectivity.
PAIRING IN Cu-O SYSTEMS: RENORMALIZATION GROUP AND EXACT DIAGONALIZATION RESULTS
Authors: Alascio B. , Gagliano E. , Avignon M. , Balseiro C. A.
Published: November 2004

We model the Cu-O high T c compounds by a generalized Hubbard Hamiltonian that includes an intersite Coulomb repulsion G. We use a real space renormalization group approach to calculate effective interactions and gap energies in infinite chains. The results indicate attraction between added holes in these systems. The magnitudes of these attractive energies are compared with exact results obtained by the Lanczos method for finite clusters.
BINDING OF HOLES WITHIN THE EFFECTIVE SINGLE-BAND HAMILTONIAN FOR CuO2 LAYERS
Authors: Bonča J. , Prelovšek P. , Sega I.
Published: November 2004

We have performed an exact numerical diagonalization of the effective single-band Hamiltonian for CuO 2 layers on a square lattice with 16 cells. Our results for one and two holes indicate in a range of exchange energies J/t on a possibility of pairing between holes, showing up in the binding energy and in the hole density correlations.
A NEW APPROACH TO CALCULATION OF ENERGY OF S = 1/2 HEISENBERG ANTIFERROMAGNET USING VARIATIONAL GUTZWILLER WAVE FUNCTION
Authors: GOCHEV I. G. , IVANOV N. B. , Kh. IVANOV P.
Published: November 2004

A new method for calculation the energy of S = 1/2 Heisenberg antiferromagnet /AFM/ in Gutzwiller state is developed. The method is analogous to low-temperature expansion /LTE/ in statistical physics
POSSIBLE SUPERCONDUCTIVITY ON THE JUNCTION SURFACE OF DIELECTRIC La2CuO4
Authors: Brazovskii S. A. , Yakovenko V. M.
Published: November 2004

It is possible to Induce excess charge on the surface of dielectric La 2 CuO 4 by the field effect or in the Schottky junction. The superconductivity can be observed in this two-dimensional system.
A NEW EFFECT ON THE CRITICAL TEMPERATURE IN NON RARE EARTH CERAMIC SUPERCONDUCTORS
Authors: Chela-Flores J. , Martin P. , Rodriguez Nuñez J. J.
Published: November 2004

We argue from the experimental evidence that interlayer effects underlie the phenomenon of high- T c superconductivity in the non rare earth oxide ceramics.
SPECIFIC HEAT IN MONO-CRYSTAL YBCO: λ-LIKE ANOMALIES AT 90K AND 229K
Authors: Fossheim K. , Nes O. M. , Lægreid T. , Darlington C. N. W , O'Connor D. A. , Gough C. E.
Published: November 2004

The specific heat, C p , has been measured with high precision in a mono-crystal of YBa 2 Cu 3 O 7−δ (YBCO) superconductor in the temperature range 55K-300K. The measurements provide data with a relative resolution Δ C p / C p of approximately 5 · 10−4. The main conclusions are:

1) Close to the superconducting transition the specific heat shows influence of fluctuations.

2) A reversible second order or weakly first order phase transition is found to occur at T o = 229 K .
NUCLEAR MAGNETIC RESONANCE STUDY OF 205Tl IN MULTIPHASE Tl-Ba-Ca-Cu OXIDE SUPERCONDUCTORS
Authors: Mihály L. , Tompa K. , Bakonyi I. , Bánki P. , Zsoldos É. , Pekker S. , Oszlányi G. , Hutiray Gy.
Published: November 2004

Several batches of T l- Ba - Ca - Cu oxide superconductors have been synthesized and characterized by resistivity, magnetic susceptibility and X-ray diffraction measurements. The 205 T l NMR line snifts (K), the spin-lattice and spin-spin relaxation times have been measured at room temperature. The temperature dependence of the spin-lattice relaxation rate is also reported. The resonance around K = 0.25 % has a composite line shape indicating the presence of two T l sites. The two sites are tentatively assigned to thallium atoms in the (2223) and (2212) T l- Ba - Ca - Cu phases.
QUANTUM NETWORK SIMULATIONS OF HIGH Tc CERAMIC SUPERCONDUCTORS
Authors: JEFFERY MARK , GREEN CHARLES , TYAGI SOMDEV , GILMORE R.
Published: November 2004

Microwave absorption measurements of the high T c ceramic superconductors reveal reproducible features in weak magnetic fields. These features are qualitatively explained by a quantum network model of these superconducting oxides. The ceramic superconductors are modeled as a set of one-dimensional wires weakly coupled at random nodes. The magnetoconductance, magnetization and susceptibility are computed from the network S-matrix.
SUPERCONDUCTIVITY AND STRUCTURES OF MBa2Cu3O7−x (WITH M = Y, Eu AND Yb) OXIDES
Authors: KHAN M. N. , Al-DALLAL S. , MEMON A.
Published: November 2004

We have prepared and observed that the zero-resistance temperature transition occurs in the chemical system MBa 2 Cu 3 O 7 (M = Y, Eu and Yb). The highest T c (ρ = 0) is 92.50 K for Y, 93.80 K for Eu and 96.00 for Yb. The X-ray diffraction analysis shows that these compounds correspond to a single phase which is an orthorhombic perovskite structure. The results of the infrared (IR) studies on orthorhombic and tetragonal phases of some of these compounds provide evidence for the oxygen rearrangement on going from the orthorhombic to the tetragonal phase.
FINITE TEMPERATURE ENTROPY OF THE ANTIFERROMAGNETIC POTTS MODEL
Authors: CHEN X. Y. , PAN C. Y.
Published: November 2004

Monte Carlo simulation is used to deal with the finite temperature entropy of the q-state antiferromagnetic Potts model which is the extension of the general q-color problem (at zero temperature). The finite temperature entropy of the model in two and three dimensions is obtained which is consistent with the zero temperature results. A possible universal relation of the model to determine when the order-disorder transition happens is proposed.
Q-COLOR PROBLEM IN D DIMENSIONS
Authors: PAN C. Y. , CHEN X. Y.
Published: November 2004

Two methods are introduced to deal with the general q-color problem on a d-dimensional hypercubic lattice: one is the cell-growth method which gives an approximative solution of the problem in two and three dimensions, another is to combine the cell-growth method with the Monte Carlo simulation which leads to a recursion formula for the problem in d-dimensions. The results of both methods are in excellent agreement with Lieb's exact solution for the case of q = 3 in two dimensions and support Mattis' conjecture in the case of q > d, improve it in the case of 2 < q ≲ d. The validity of the recursion formula is supported by a Monte Carlo simulation up to four-dimensions.
SYMBOLIC DYNAMICS OF UNIMODAL MAPS REVISITED
Authors: HAO BAI-LIN , ZHENG WEI-MOU
Published: November 2004

Symbolic dynamics of unimodal maps has been recast into a more natural and down-to-numbers way. The median itineraries are built without such artificial constructions as "antiharmonics" and "harmonics" by making use of the newly established periodic window theorem. A generalized composition rule extends the *-composition introduced by Derrida, Gervois and Pomeau. Periodic as well as chaotic orbits are described systematically. The location of all superstable periodic orbits and band-merging points may be calculated by solving equations obtained directly from the corresponding symbolic sequences.
INTERGROWTH AND OTHER MICROSTRUCTURE FEATURES IN BCSCO SUPERCONDUCTOR
Authors: WEN SHULIN , FENG JINGWEI , LI CHENGEN
Published: November 2004

Three compositions of Bi-Ca-Sr-Cu-O superconducting ceramics were studied and characterized by X-ray, EDS and HREM.

In addition to the basic lattice structure A1 with unit-cell of 5.41 Å, B = 5.44 Å and c = 30.8 Å, other 3 kinds of perovskite-related structures A0, A3 and A4 were found.

Furthermore, a prominent structural phenomenon, the intergrowth between A1 and other perovskite-related structures (A0, A2 and A4) were found in abundance. We had some difficulties isolating pure 120 K phase; the intergrowth may be an obstacle factor.
DEFECT STRUCTURE OF YBa2Cu3O7−δ
Authors: BLINOVSKOV Ya. N. , VORONIN V. I. , VERKHOVSKII S. V. , DAVYDOV S. A. , KARKIN A. E. , KOZHEVNIKOV V. L. , LEONIDOV I. A. , MIRMELSHTEIN A. V. , SERIKOV S. S. , Ya. NOVAK P. , FLYATAU E. E. , CHESHNITSKII S. M.
Published: November 2004

From the analysis of NQR spectra for Cu and on the basis of investigations of high-temperature electrical conductivity and thermal e.m.f. depending on oxygen pressure and temperature it is shown that in YBa 2 Cu 3 O 7−δ there are pair correlations of the oxygen atoms which lead to formation of the ( O 2)z− pairs, the charge of which is determined by deviation from stoichiometry.
PROPERTIES OF SOLIDS WITH PORES AND CRACKS
Authors: YUKALOV V. I.
Published: November 2004

A model of solids with pores and cracks or other regions of disorder is constructed. Stability conditions for such a solid are considered in the case of an effective attraction between particles and without external fields. The possibility of the appearance of the phonon-photon superradiance in the ensemble of charged cracks is discussed. The relative variation of the Mössbauer-effect probability for partially disordered systems, compared with completely ordered ones, is calculated and found to be in a very good agreement with experimental results.
EFFECTIVE SPINON-SPINON AND HOLON-HOLON INTERACTIONS IN RVB MODELS OF HIGH-Tc SUPERCONDUCTIVITY
Authors: VAN HIEU NGUYEN
Published: November 2004

The interaction between the bosonic excitations as well as between the fermionic ones in the RVB systems with the (extended) Hubbard Hamiltonian were studied by means of the slave boson technique and the perturbation theory. The corresponding effective Hamiltonians have been found. It was shown, in particular, that in the RVB system with two interpenetrating sublattices there exists the effective attraction between two holons of different kinds as well as between two spinions of different kinds in the singlet state.
THICK FILMS OF YBaCuO FROM PRECALCINED POWDERS
Authors: MADHAVRAO L. RAO , RAJAGOPALAN RAJ
Published: November 2004

Preparation and some of the chemical and microstructural aspects of thick films of the YBa 2 Cu 3 O 7−x superconductors (herein designated as YBaCuO) using precalcined YBaCuO powders and a colloidal method are described. Films on alumina substrates were made from calcined YBaCuO powders dispersed in hexane using a commerical dispersant which acts as a steric stabilizer and binder. The additive decomposes without residues at relatively low temperatures, and structurally stable and uniform films are obtained for proper dosage of the dispersant. Scanning electron microscopy has been used to examine the microstructure, quality and sinterability of the films. An example of the use of other additives to improve sintering and adhesion of the film to the substrate is also described. Substrate/film interaction has been studied by compositional mapping using an electron probe microanalyzer. The results show a substantial reaction layer (1−2μm) of barium aluminate and a significant diffusion distance (of several microns) of aluminum into the film.
ON THE UBIQUITY OF 1/f NOISE
Authors: WEST BRUCE J. , SHLESINGER MICHAEL F.
Published: November 2004

A generic mechanism for the ubiquitous phenomenon of 1/f noise is reviewed. This mechanism arises in random processes expressible as a product of several random variables. Under mild conditions this product form leads to the log-normal distribution which we show straightforwardly generates 1/f noise. Thus, 1/f noise is tied directly to a probability limit distribution. A second mechanism involving scaling is introduced to provide a natural crossover from log-normal to inverse power-law behavior and generates 1/fα noise instead of pure 1/f noise. Examples of these distributions and the transitions between them are drawn from such diverse areas as economics, scientific productivity, bronchial structure and cardiac activity.
MODIFIED KORTEWEG-DE VRIES EQUATIONS ON EUCLIDEAN LIE ALGEBRAS
Authors: KUPERSHMIDT B.A.
Published: November 2004

For any finite-dimensional Euclidean Lie alegebra [Formula: see text], a commuting hierarchy of generalized modified Korteweg-de Vries equations is constructed, together with a nonabelian generalization of the classical Miura map. The classical situation is recovered for the case when [Formula: see text] is abelian one-dimensional. Localization of differential formulae yields a representation of the Virasoro algebra in terms of elements of the current Lie algebra associated to [Formula: see text].
ON ANYON SUPERCONDUCTIVITY
Authors: CHEN YI-HONG , WILCZEK FRANK , WITTEN EDWARD , HALPERIN BERTRAND I.
Published: November 2004

We investigate the statistical mechanics of a gas of fractional statistics particles in 2+1 dimensions. In the case of statistics very close to Fermi statistics (statistical parameter θ=π(1−1/n), for large n), the effect of the statistics is a weak attraction. Building upon earlier RPA calculation of Fetter, Hanna, and Laughlin for the case n=2, we argue that for large n perturbation theory is reliable and exhibits superfluidity (or superconductivity after coupling to electromagnetism). We attempt to describe the order parameter for this superconducting phase in terms of “spontaneous breaking of commutativity of translations” as opposed to the usual pairing order parameters. The vortices of the superconducting anyon gas are charged, and superconducting order parameters of the usual type vanish. We investigate the characteristic P and T violating phenomenology.
THE FIBONACCI QUASICRYSTAL RECONSIDERED: VARIETY OF ENERGY SPECTRA FOR CONTINUOUS SCHRÖDINGER EQUATIONS WITH SIMPLE POTENTIALS
Authors: THOMAS U. , KRAMER P.
Published: November 2004

The continuous Schrödinger equation is considered on a Fibonacci string of finite length with piece-wise constant potentials or δ-potentials. Using for the calculation of the band structure a well-known map we find that the band splitting depends critically on the energy and system parameters; for appropriately chosen parameters quasi-continuous parts exist in the energy spectra up to high Fibonacci numbers.
EXACT SOLUTIONS FOR A 4-SPIN-INTERACTION ISING MODEL ON THE d=3 PYROCHLORE LATTICE
Authors: BARRY J.H. , WU F.Y.
Published: November 2004

The pyrochlore lattice is a three-dimensional (d=3) periodic array of corner-sharing regular tetrahedra. An Ising model is defined upon this lattice as having a 4-spin “volume” interaction among the corner Ising spins of each elementary tetrahedron. The model is solved exactly and shown to be devoid of any finite-temperature phase transition, thereby remaining in a disordered (high-temperature) phase. Exact solutions are found for all multisite correlations which are then used to obtain exact solutions for specific heat, initial and non-linear parallel magnetic susceptibilities as well as initial perpendicular susceptibility, inelastic neutron scattering function, and the joint configurational probabilities of the Ising spins. All solutions are simple algebraic functions of K and tanh K (K being the multispin coupling parameter) and exhibit such behaviors as rounded extrema, crossing points, sigmoidal curves having non-vertical inflection points, and the like. Despite their “analytical quiescence”, most of these simple solutions are evidently the first exact explicit expressions for the selected physical quantities to appear in the literature for classical and quantal d=3 Ising models having multispin “volume” interactions, with the prospect of offering some guidance and insights upon a larger class of multisite-interaction model systems.
PHASE TRANSITION IN THREE-DIMENSIONAL ISING SYSTEMS WITH QUENCHED NON-MAGNETIC IMPURITIES: A REVIEW OF MONTE CARLO STUDIES
Authors: BRAUN P. , STAADEN U. , HOLEY T. , FÄHNLE M.
Published: November 2004

A review is given of Monte Carlo simulations for the phase transition in simple cubic Ising ferro-, ferri-, and antiferromagnets with quenched non-magnetic impurities of concentration x. Special emphasis is given on the description of a fully vectorized multispin coding program and on the problems related to the analysis of the Monte Carlo data. The following three subjects are discussed: 1) For ferro- and antiferromagnets, the critical behaviour of the order parameter is different from the one of the corresponding pure system, in agreement with the prediction of the Harris criterion. The possibly effective exponent β depends on x, whereas for ferrimagnets no such concentration dependence is revealed by the present study for x=0, 0.1, and 0.2.2) For strongly diluted systems, there is a maximum for the Kouvel-Fisher exponent γ(T) of the order-parameter susceptibility outside the critical regime, in accordance with the predictions of the correlated molecular field theory. 3) For the diluted antiferromagnet (x=0.5), a cusp emerges at T c for the uniform susceptibility, in agreement with the theory of Fishman and Aharony.
SPIN-1/2 TWO-DIMENSIONAL ANISOTROPIC HEISENBERG ANTIFERROMAGNETS
Authors: PAN C.Y.
Published: November 2004

A real space renormalization group method is applied to study the spin-1/2 two-dimensional anisotropic Heisenberg antiferromagnets. We carry out the calculation on a 5×5 cluster by using a variational approach. The ground-state energy per site is estimated as e0=−0.6845±0.0005 which is in good agreement with other numerical estimates. We also calculate the different ground state energies when anisotropy changes. By comparing with 3×3 cluster calculation the resulting threshold for long range order drops and the curve of the renormalization group parameter vs. anisotropy shows no hint of discontinuity over a wide range of anisotropic parameters. Hence, our calculation suggests that long-range order exists for the ground-state of the spin-1/2 Heisenberg antiferromagnets in two dimensions.
TEMPERATURE AND INITIAL CONDITIONS ON STRANGE REPELLERS
Authors: PALMORE JULIAN , McCAULEY JOSEPH L.
Published: November 2004

Chaotic maps generate symbol sequences whose lattice disorder may be described by a Gibbs distribution. In particular, the Gibbs distribution describes the frequency with which intervals are visited in chaotic motion on a multifractal. One of us pointed out earlier that the inverse temperature implies a choice of initial conditions of a map from a subset of the fractal that is typically unknown in advance. We show here that, for maps that generate strange repellers, almost all initial conditions belong to the infinite temperature distribution. Finite temperature Gibbs distributions therefore correspond to a set of symbol sequences that occur with measure zero.
STRUCTURED HIERARCHICAL NEURAL NETWORK
Authors: DOTSENKO VIKTOR , TIROZZI BRUNELLO
Published: November 2004

The spatially structured hierarchical neural network which can store ultrametrically correlated patterns is considered. The patterns belonging to a common ancestor state in the two-level hierarchical tree are supposed to be strongly correlated.

The models with both uncorrelated and strongly correlated classes of patterns are considered. In the framework of replica symmetric theory the free energy is calculated and in the low-temperature limit the maximum capacity is found.
AES STUDY OF THE INTERFACE FORMATION IN PECVD SiO2-InSb STRUCTURES
Authors: VALCHEVA E.P. , GERMANOVA K.G. , GEORGIEV S.S.
Published: November 2004

Semiconductor-insulator structures prepared on InSb substrates by plasma-enchanced chemical vapour deposition of SiO 2 are investigated by means of Auger electron spectroscopy. The chemical composition of the oxide layer and the insulator-InSb interface formation are studied as a function of the deposition temperature. The conditions for the presence of native oxide in the interfacial region are estimated and discussed.
RAMAN AND INFRARED STUDY OF PHASE TRANSFORMATION IN CRYSTALLINE HYDROGEN IODIDE AND DEUTERIUM IODIDE HI AND DI
Authors: TSE W.S. , FANG C.S. , ANDERSON A. , TORRIE B.H.
Published: November 2004

Raman and infrared spectra of polycrystalline HI and DI in the region of lattice and internal modes for all three phases have been recorded over the temperature range 18 K to the melting point. The temperature dependent Raman and infrared results are consistent with the X-ray and neutron work that two phase transitions occur at HI and DI involving reorientation of the HI and DI molecules as a whole.
NUMERICAL STUDY OF THE t−J MODEL: EXACT GROUND STATE AND FLUX PHASES
Authors: Hasegawa Y. , Poilblanc D.
Published: November 2004

Strongly correlated 2D electrons described by the t–J model are investigated numerically. Exact ground state for one and two holes in a finite cluster with periodic boundary conditions are obtained by using the Lanczos algorithm. The effects of Coulomb repulsion of the holes on the nearest neighbor sites are taken into account. Commensurate flux phases are investigated for the same size of clusters. They are shown to be a good approximation for the ground state specially in the intermediate value of J/t.
Two Quantum Liquids
Authors: Wheatley Joseph
Published: November 2004

We describe a theory of the two dimensional Heisenberg-Hubbard model working in the spin and hole fermion representation based on the use of a singular gauge transformation on the spins. We are motivated by a new mean field theory for a system of strongly coupled fermions and bosons which is also described. In the latter case we obtain the bose condensed—fermi liquid phase; in the former we obtain equations governing generalized flux phases. We do not find superconducting solutions to these equations in the atomic limit, J=0. If solutions exist for finite J case then it is argued that an energy gap is present in that case.
ANTIFERROMAGNETIC ORDERING IN THE HUBBARD MODEL: SLAVE BOSON APPROACH, PATH-INTEGRAL FORMULATION
Authors: Wróbel Piotr , Kopeć Tadeusz K.
Published: November 2004

The magnetic phase diagram (temperature versus doping) for the Hubbard model in the large U/t limit has been constructed by using the path-integral method. The antiferromagnetic order parameter has been represented in terms of fermion operators which correspond to neutral, spin one-half quasi-particles, spinons. Numerical calculations have been performed for the two-dimensional square lattice. A stable antiferromagnetic phase for the half-filled band has been found below a critical temperature TC=J where J=4t2/U is the superexchange interaction. It has been shown that antiferromagnetism is destroyed by doping with about 15% of holes for t/J=10. The results are discussed in the light of recent experiments for high TC oxides.
U=∞ HUBBARD MODEL: TOWARDS THE EXACT SOLUTION IN d=∞
Authors: Janiš Václav
Published: November 2004

We investigate the U=∞ Hubbard model. Using a Grassmann-integral representation, we transform this model to a Grassmann field theory with two degrees of freedom per site and with a local quartic interaction. An external inhomogeneous field is introduced so that the linked-cluster expansion be applicable. All 1-loop contributions from this expansion are summed up and an exact expression for the inhomogeneous grandcanonical potential dependent on the auxiliary external field in d=∞ is found.
FERMIONS ON A LATTICE IN HIGH DIMENSIONS
Authors: Müller-Hartmann E.
Published: November 2004

The limit of high dimensions of lattice fermion models has soon met great interest after its recent introduction by Metzner and Vollhardt. Fermion models are greatly simplified in high dimensions. The simplifications achieved are, however, much more subtle and diverse than those known for spin models. In the present contribution I present some of my own work as well as a short review of some other work on this new promising subject.
INCOMMENSURATE CRYSTAL MODEL FOR OPTICAL TRANSMISSION IN Rb2ZnBr4
Authors: WAHLSTRÖM G. , CHAO K.A.
Published: November 2004

We have calculated the optical transmission spectrum of Rb2ZnBr4 using a three-dimensional tight binding model with modulation along one direction. Our calculation reproduces very well the observed change of spectrum across the normal-to-incommensurate transition at 355 K.
CRYSTAL STRUCTURES AND DEFECTS IN PHASES EXISTING IN Ba3Y2Cu5O15−x
Authors: LI D.X. , SUI M.L.
Published: November 2004

Crsytal structures and defects of the phases existing in Ba3Y2Cu5O15−x have been investigated with SAED, CBED and HREM. Sample A was furnace cooled and is a high Tc superconductor whereas sample B is air cooled and not superconducting at 77.35K. Both samples contain predominantly the so called superconducting phase with the space group Pmmm (a=0.386, b=0.389 and c=1.16 nm) and a minor phase, called phase-II with the space group Pbam (a=1.23, b=0.740 and c=0.571 nm). In sample B, the other three minor phases are: phase-III: orthorhombic, a=0.892, b=0.639 and c=0.535 nm; phase-IV: BCC, a=1.82 nm and phase-V: hexagonal, a=b=0.526, c=0.635 nm.

The positions of the Ba, Y and Cu atoms can clearly be seen in the structural image viewed along the [100] direction of the superconducting phase. The contrast increment of the bright spots on the basal plane was perhaps related to the oxygen vacancies. Lattice distortion, (010) and [Formula: see text] domain boundaries in the superconducting phase, microdomains and twins in phase-III have been observed. High resolution electron micrographs of both phase-II and phase-IV were also presented. The amount of the superconducting phase and defects in the crystal structure may affect the superconductivity of the Ba3Y2Cu5O15−x oxide significantly, the former being bene-ficial and the latter harmful.
HIGH Tc SUPERCONDUCTIVITY OF Sr-La-Cu-O AND Ba-Y-Cu-O THIN FILMS
Authors: ZHAO B.R. , LI L. , LU Y. , WANG H.S. , SHI Y.H. , ZHAO Y.Y. , YUAN C.W. , GAO J.
Published: November 2004

In a very short time after it was reported1 that perovskite-type Ba-La-Cu oxide system could have high temperature superconductivity, many new results were reported.2,3 Later, Y was substituted for La to form Ba-Y-Cu oxides and the Tc rose to the liquid nitrogen region.4 In this report we describe the results obtained with the Sr-La-Cu-O and Ba-Y-Cu-O thin films.
PHASE SOLITONS IN THE PEIERLS-FROLICH MODEL AND E-E INTERACTION
Authors: Balatsky A.V. , Matveenko S.I.
Published: November 2004

The electric charge of the phase soliton in the Peierls dielectric is calculated when e-e interaction is present. It is shown that the value of the charge is connected with the change of the phase of the charge density wave on the soliton ∆æ by the relationship q=∆æ/2π(1 +δ) where δ is a constant of scattering forward.
STAGGERED SYMMETRY AND SINGLE AVERAGE MAGNETIZATION IN DILUTE SYSTEMS
Authors: GALAM SERGE
Published: November 2004

Mean field treatment of the dilute Ising antiferromagnet in a field is discussed. It is shown that to consider one average single magnetization does indeed account for the staggered symmetry of the model by including implicitly the effects of next nearest neighbor interactions which are not present in the initial Hamiltonian. The dependence of the equation of state on the dilution concentration is also discussed.
EQUILIBRIUM THERMODYNAMICS OF SIMPLE HYDRODYNAMIC TYPE SYSTEM
Authors: SANKOVICH D.P.
Published: November 2004

A generating thermodynamic functional for the one-dimensional, one-component hydrodynamic type system with the Hamiltonian density au2+bu4is determined. Correlation functions of this model are considered.