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IMPORTANCE-SAMPLING MONTE CARLO APPROACH TO CLASSICAL SPIN SYSTEMS
Authors: HUANG HSING-MEI
Published: November 2004

A new approach for carrying out static Monte Carlo calculations of thermodynamic quantities for classical spin systems is proposed. Combining the ideas of coincidence countings and importance samplings, we formulate a scheme for obtaining Γ(E), the number of states for a fixed energy E, and use Γ(E) to compute thermodynamic properties. Using the Ising model as an example, we demonstrate that our procedure leads to accurate numerical results without excessive use of computer time. We also show that the procedure is easily extended to obtaining magnetic properties of the Ising model.
THE EVOLUTION OF SEMICONDUCTOR SUPERLATTICES AND QUANTUM WELLS
Authors: ESAKI L.
Published: November 2004

Following the past nearly twenty-year evolutionary path in the interdisciplinary research of semiconductor superlattices and quantum wells, significant milestones are presented with emphasis on experimental achievements in the physics of reduced dimensionality made possible with the advance in heteroepitaxy.
HOMOCLINIC AND HETEROCLINIC INTERSECTIONS IN THE PERIODICALLY FORCED BRUSSELATOR
Authors: NI WAN-SUN , TONG PEI-QING , HAO BAI-LIN
Published: November 2004

The homoclinic and heteroclinic intersections of the stable and unstable manifolds of the fixed and periodic points in the Poincaré maps of the periodically forced Brusselator have been studied by direct integration of the system using periodic-orbit following technique. Since the free limit cycle oscillator does not possess any saddle points where one may start the construction of invariant manifolds, one has to look into the Poincaré sections in the extended phase space with the time axis included. We have followed a series of homoclinic and heteroclinic crossings and the one-piece chaotic attractor appears to be the envelope of unstable manifolds of all orders.
SYNTHESIS AND CHARACTERIZATION OF HIGH-Tc SUPERCONDUCTORS IN THE Tl–Ca–Ba–Cu–O SYSTEM
Authors: BANSAL NAROTTAM P. , FARRELL D. E.
Published: November 2004

In an effort to synthesize the high-T c superconducting phase in the thallium system, two nominal compositions, Tl 2 Ca 2 Ba 2 Cu 3 O 10 and Tl 1 Ca 3 Ba 1 Cu 3 O 8.5, have been investigated for superconductivity as a function of the sintering temperature, time, atmosphere, and quench rate. Samples have been characterized by electrical resistivity measurements, X-ray diffraction, and scanning electron microscopy. Samples of starting composition Tl 2 Ca 2 Ba 2 Cu 3 O 10 fired in air at 860–900°C and rapidly quenched showed T c (R = 0) of 96–107 K. In contrast, specimens of starting composition Tl 1 Ca 0 Ba 1 Cu 3 O 8.5 when baked at 900°C and slow cooled in oxygen were superconducting at ≥ 116 K and consisted of Tl 2 Ca 2 Ba 2 Cu 3 O 10+x as the dominant phase. Our results also show that, in contrast to the case of YBa 2 Cu 3 O 7−x, doping with a small concentration of fluorine sharpens the resistive transition and produces large T c increase in thallium-based superconductors.
INDUCTANCE TECHNIQUE FOR MEASURING TRANSITION TEMPERATURES OF SUPERCONDUCTING POWDERS
Authors: VETHANAYAGAM T. K. , SCHULZE W. A. , TAYLOR J. A. T. , SNYDER R. L.
Published: November 2004

A simple technique to measure T c of superconducting powder samples is evaluated. Inductance of the sample is used as the indicator to determine the behavior of the material as it goes to the superconducting state. The effect of particle size and sample size on the measured parameters has been investigated. The main advantages of this technique are the absence of electrical contacts and the elimination of the need for sintered bars. The technique has the potential to measure the amount of superconducting phases as well as the critical current density.
MULTIFRACTAL DESCRIPTION OF THE STATISTICAL EQUILIBRIUM OF CHAOTIC DYNAMICAL SYSTEMS
Authors: McCAULEY JOSEPH L.
Published: November 2004

In this review, we apply the method of backward iteration to chaotic maps of the interval to illustrate how both the f(α) spectrum and its underlying statistical mechanics follow directly from the dynamics in statistical equilibrium. The sizes of intervals in the coarse-grained phase space are expressed directly in terms of finite-time average Liapunov exponents, representing the reverse of the information flow that is the underlying cause of deterministic chaos. The transfer matrix formulation follows directly from the method of backward iteration when addresses generated from symbolic dynamics are assigned to tree-branches. The inverse temperature is interpreted in terms of classes of initial data of the dynamical system. Finally, the usefulness of the thermodynamic formalism is illustrated by showing how the pore distribution of sandstone can be modeled by a certain two-scale Cantor set on an octal tree.
TOPOLOGICAL CONSTRAINTS FOR QUASICRYSTALS
Authors: KALUGIN P.A. , LEVITOV L.S.
Published: November 2004

Topological constraints necessary for the existence of icosahedral quasicrystals having continuous phasons are found. As a result of application of these constraints a model of a new type for icosahedral quasicrystals is constructed. The “atomic surfaces” in R6 in this model are free of discontinuities, i.e. the displacements of atoms are continuous as functions of a phason shift. The positions of atoms in the physical space R3 from 60 interpenetrating rhombohedral lattices. The model exhibits diffraction properties of an ideal quasiperiodic structure and has perfect icosahedral symmetry.
MAGNETIC PROPERTIES OF RBa2Cu3O7−x(R=Y, Eu, Dy) IN THE WELL-ORDERED AND QUENCHED STATES
Authors: MEI YU , GREEN S.M. , JIANG C. , LUO H.L. , POLITIS C.
Published: November 2004

Magnetic susceptibility between 6 and 300 K and magnetization measurements at 6 and 30 K were conducted on a sequence of RBa 2 Cu 3 O 7−x (R=Y, Eu, Dy) materials including a set of well-annealed and hence properly oxygenated samples and two sets of quenched specimens (from 700° and 950°C). Corresponding to the three heat treatments, samples demonstrated respectively superconducting transitions at ~95 K, ~50 K and general semiconducting behavior.
NOVEL PATH INTEGRAL APPROACH TO EFFECTIVE FIELD THEORIES FOR D-DIMENSIONAL QUANTUM SPIN SYSTEMS
Authors: ANGELUCCI ANTIMO , JUG GIANCARLO
Published: November 2004

We present a novel path integral formulation for the effective field theory describing d-dimensional quantum spin models. The new approach avoids the coherent states representation, but at very low temperatures reproduces all known results obtained with the latter technique for describing excitations of the Neél state. The possibility of exploring higher-temperature, unbroken-symmetry state excitations (such as those appropriate for the quantum spin-liquid state) within this method is illustrated.
VALENCE STATES AND LOCAL ENVIRONMENT OF THALLIUM AND COPPER IONS IN SOME NEW HIGH Tc SUPERCONDUCTORS BY XAS
Authors: STUDER F. , RETOUX R. , MARTIN C. , MICHEL C. , RAVEAU B. , DARTYGE E. , FONTAINE A. , TOURILLON G.
Published: November 2004

The valence states of cations inside four high T c thallium superconductors have been investigated by X-ray absorption spectroscopy at thallium LIII , LI and copper K-edges. The thallium ions are observed on LIII and LI edges in the Tl(III) valence state (empty 6s levels) in spite of large Tl-O distances in the (a, b) plane of the structure as deduced from X-ray diffraction. The presence of two types of Tl-O distances have been well established on XANES spectra and the F.T. of EXAFS have shown the presence of two very short Tl-O bonds (2.03 Å). The copper K-edges are characterized by the absence of Cu(I) state (3d10 line).
MICROWAVE AND MILLIMETERWAVE STUDIES OF THE TWO-DIMENSIONAL ELECTRON GAS IN HETEROSTRUCTURES AND MOSFETs
Authors: KUCHAR F.
Published: November 2004

Experimental techniques for studying the two-dimensional electron gas in semiconductor heterostructures and MOSFETs at microwave and millimeterwave frequencies are reviewed. The phenomena described concern electrical conductivity, carrier mobility, cyclotron resonance, quantum Hall effect, depolarisation effects, and electron spin resonance.
STABILITY AND BIFURCATION PROPERTIES OF SOLUTIONS OF EVOLUTION EQUATIONS FOR THE SUPERRADIATING SYSTEM
Authors: BAKASOV A.A. , NARBAEV B.M. , SHUMOVSKY A.S.
Published: November 2004

Evolution equations describing a previously inverted system of two-level atoms have been strictly investigated. Solutions obeying the most necessary physical conditions are found to be stable. It implies physically that there are no such initial conditions at which the regime of radiation changes step-wise. Particularly, the transition from spontaneous radiation to superradiation proceeds continuously. It is also shown that the superradiation can serve as an example of a system with a dynamical long-range ordering which is not, however, a nonequilibrium phase transition.
SYMBOLIC DYNAMICS ANALYSIS OF SYMMETRY BREAKING AND RESTORATION
Authors: ZHENG WEI-MOU , HAO BAI-LIN
Published: November 2004

A bifurcation theory and symbolic dynamics analysis of symmetry breakings and restorations in antisymmetric mappings is carried out. The fact that symmetry breakings are precursors to period-doubling happens to be a natural consequence of word ordering in symbolic dynamics. Symbolic dynamics also provides the selection rule for such bifurcations to occur and helps to locate the symmetry restoration point in the chaotic region. When the inverse branches are known explicitly the analysis may be made detailed enough to determine the bifurcation structure with high precision.
LATTICE DYNAMICS OF MBa2Cu3O7(M=Y, Gd) and YBa2Cu3O6
Authors: QIN JIE , JIANG YIMIN
Published: November 2004

We have presented a lattice dynamical calculation of phonon dispersion curves and one-phonon density of states for the high-T c superconducting MBa 2 Cu 3 O x (M=Y, Gd : x=7, 6) compounds. The model we used is in the framework of a rigid-ion model which includes long-range Coulomb potential and a short-range overlap. The results of calculation give quite good agreement with the available Raman and infrared data, and the measurements of phonon density of states. These results therefore can serve as a guide for further experimental investigations of the phonon properties in M-Ba-Cu-O (M=rare earth atom) system.
MICROSTRUCTURAL SELF-ORGANIZATION IN IRRADIATED SYSTEMS
Authors: ABROMEIT C.
Published: November 2004

Irradiated metals and alloys are examples of open, dissipative systems far away from thermal equilibrium. In several cases they show self-organization of the microstructure resulting from non-linear reactions of the migrating point defects, i.e. vacancies and interstitials. In this review, the various published theoretical approaches to radiation-induced self-organization are discussed using a rate equation description. Two different mechanisms of defect interaction with the microstructure are possible origins for the occurrence of periodic fluctuations: (i) A diffusion-controlled reaction coupling involving biased constructive and destructive reactions and (ii) the coupling of atomic fluxes to interstitial and vacancy fluxes which are induced by the recombination reaction. Using an adiabatic approximation in a linear stability analysis, the conditions for the formation of radiation-induced periodic structures are obtained. The symmetry of the geometrical arrangements are deduced from an extension into the weakly non-linear regime. The results are compared with experimental observations. It is demonstrated that the radiation-induced defect wall structures and void lattice formation can well be explained as a self-organization process in an open, dissipative system.
ISING MODEL FOR INTERSTITIAL ALLOYS AND SUPERCONDUCTING OXIDES
Authors: HAUCK J. , HENKEL D. , MIKA K.
Published: November 2004

The interstitial alloys MZx with Z= H, C, N, O etc. at octahedral or tetrahedral sites of the fcc or bcc M lattice are analysed for nearest and next-nearest neighbor Z-Z interactions. Many compounds have repulsive interactions close to the borderline of maximum separation, which is characterized by Pauling’s electrovalence rule. There are also borderlines for attractive interactions, e.g. cluster formation or segregation. The new superconducting oxides Ba 2 YCu 3 O x, La 2 CuO 4, Bi 2 Sr 2 Ca n−1 Cu n O 2n+4 can be viewed as bcc M= Ba, Cu, Bi etc. lattice with Z= O atoms at octahedral sites. The low T c compounds Nbo , NbC x, TiO x, TiN x, PdH x, etc. have Z= C, N, O, H atoms at octahedral sites of the fcc M= Nb, Ti, Pd lattice.
GROUND-STATE ENERGY OF THE SPIN-1/2 TWO-DIMENSIONAL ANTIFERROMAGNETIC HEISENBERG MODEL
Authors: PAN C.Y.
Published: November 2004

The ground-state energy of the spin-1/2 two-dimensional antiferromagnetic Heisenberg model is obtained by a real space renormalization group method. A relative larger cluster (5×5) is used to improve the accuracy and a boundary theory is applied to extrapolate to the result which is in good agreement with the finite-size calculation and in fairly good agreement with the other available numerical estimates. How to further improve the calculation is discussed.
ELECTRONIC STRUCTURE AND PROPERTIES OF LaTiO3 AND LaNiO3
Authors: MATHI JAYA S. , SUBRAMONIAM G. , JAGADISH R. , RAO R.S. , ASOKAMANI R.
Published: November 2004

The band structures of the perovskite oxides LaTiO 3 AND LaNiO 3 calculated for the first time are reported here. The band structures were done using the Linear Muffin Tin Orbital (LMTO) method. The Fermi energy, density of states at the Fermi energy and the number of electrons in the conduction band were all determined. These quantities were used to calculate the electronic specific heat coefficient and the Pauli paramagnetic susceptibility. The Stoner parameter with regard to the enhancement in the Pauli susceptibility is calculated in the Thomas-Fermi approximation and is compared with the χ expt /χ bs value.
RANDOM FIELD AND OTHER SYSTEMS DOMINATED BY DISORDER FLUCTUATIONS
Authors: NATTERMANN THOMAS , RUJAN PAUL
Published: November 2004

Spin-models in random fields (RFs) are good representations of many impure materials. Their macroscopic collective behaviour is dominated by the fluctuations in the random fields which accumulate on large scales even if the local field is arbitrarily small. This feature is shared by other weakly disordered models, like flux lines or domain walls in random media. We review some of the main theoretical attempts to describe such systems. A modification of Harris’ argument demonstrates that at the critical point the RF disorder is relevant and that (hyper)scaling must be changed. A domain argument invented by Imry and Ma shows that long-range order is not destroyed by weak RFs in more than d=2 dimensions. This result is supported both by a more refined treatment of the domain argument and by considering the roughness of an isolated domain wall due to the randomness. The wall (or flux line) becomes rough due to disorder but if d>2 the wall remains a well-defined object in RF systems. Different approaches are used to calculate the roughness exponent ζ for walls and lines. Some applications of ζ for the description of type-II superconductors and incommensurate systems are given.

More detailed calculations are possible for one-dimensional, Bethe-lattice or the hierarchical Dyson model systems, which confirm as a rule the more approximate treatment of the other sections. In one dimension there is an interesting relation between the statistical mechanics of these models and nonlinear dynamics.

Non-classical critical behaviour occurs in RF systems for d<6 and is determined in general by three independent exponents which fulfil certain inequalities. The new exponent θ≡yJ>0 is related to the violation of conventional hyperscaling and is determined by the energy ~H0ξ0 of a correlated region of size ξ. In a renormalization group treatment, the temperature T turns out to be a (dangerous) irrelevant variable which is the most prominent property of the systems considered in this review.

The irrelevance of thermal fluctuations on large scales produces metastability and hysteresis effects both in the transition region and in the ordered phase, only briefly considered here. These features occur also in other systems with a disordered T=0 fixed point like in the ordered phase of a spin-glass.
ON ANTIFERROMAGNETIC INSTABILITY IN THE HUBBARD MODEL
Authors: WRÓBEL PIOTR , KOPEĆ TADEUSZ K.
Published: November 2004

A functional integral method applied to the Hubbard model has been used to construct the magnetic phase diagram (temperature versus doping) for large U/t. The antiferromagnetic order parameter has been represented in terms of fermion operators which correspond to neutral, spin one-half quasi-particles i.e. spinons. Static approximation has been applied. Numerical calculations have been performed for the two-dimensional square lattice. A stable antiferromagnetic phase for the half-filled band has been found below the critical temperature TN=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.
ALGORITHM FOR CALCULATING FUNCTIONS IN METHOD OF SUCCESSIVE APPROXIMATIONS
Authors: YUKALOV V.I.
Published: November 2004

A new algorithm is proposed for constructing unknown functions with the help of their several approximate expressions. The algorithm is illustrated by calculating the ground-state energy of anharmonic oscillator. Different variants of the method are analysed, and it is shown that the accuracy of the calculations can be carried to 0.1%.
NUMERICAl STUDY OF THE 2D HUBBARD MODEL AT HALF FILLING
Authors: Sorella S. , Parola A. , Parrinello M. , Tosatti E.
Published: November 2004

The ground state of the 2D (square lattice) finite-size Hubbard model is studied at half filling with a newly developed Quantum Monte Carlo method. We have studied square cells from 18 to 242 sites for U=3 with high statistical accuracy to perform a reliable size scaling analysis. The results confirm that the system is an antiferromagnetic insulator. The finite size scaling results are discussed in detail, focusing on the behaviour of magnetization, and most particularly of momentum distribution.
Generalized Pairing and Commensurability Effects in High Temperature Superconductors
Authors: Baskaran G.
Published: November 2004

The strong correlation in CuO based superconductors may prevent pairing of real electrons in the planes, in particular, for small density of holes. It is suggested, based on some simple arguments, that a generalized ‘pairing’ involving certain number of singlet pairs and holes may take place in this system. This leads to some interesting commensurability effects even in the absence of chiral symmetry breaking and makes the [Formula: see text] filled t-J model and Large U Ilubbard filled t-J model and Large U Ilubbard model special having enhanced pairing correlation and large gain in the kinetic energy.
On the Projected Fermion Description of Anisotropic S=1/2 Antiferromagnets
Authors: HSU THEODORE C.
Published: November 2004

In this paper we consider anisotropic S=1/2 antiferromagnets through a projected fermion description. The success of projected fermion methods for the isotropic system is reviewed. We present an analytical approximation to Gutzwiller approximation and illustrate it’s use by showing that it is consistent with the SU(2) symmetry of projected fermions. The anisotropic antiferromagnet is written in terms of a fermion mean field. We consider the case of Ising anisotropy and show that in the Ising limit a procedure of minimizing the post-projection energy of a fermion mean field state gives the correct Ising ground state.
RANDOM JOSEPHSON NETWORKS AND SPIN GLASSES
Authors: FEIGEL’MAN M.V. , IOFFE L.B. , LARKIN A.I. , VINOKUR V.M.
Published: November 2004

The phase transition into a spin glass-like state is predicted for the system of superconductive wires connected by Josephson links and placed into the magnetic field. History-dependent equations of state for T<Tc are derived and diamagnetic response to the variation of the magnetic field is predicted. The experiments that can solve the discrepancy between the analytical theory and the numerical simulations on the existence of the phase transition in the vector spin glasses are discussed.
SIMULATION OF THE DYNAMICS OF A MACROMOLECULE IN A RANDOM CONSTRAINT CAGE
Authors: GEURTS BERNARD J. , WIEGEL FREDERIK W.
Published: November 2004

We determine the centre of mass diffusion coefficient D and the chain relaxation time T of a macromolecule diffusing through a random constraint cage. This cage models the average topological constraints on the motion of a particular polymer, imposed by the other polymers in the system. The constraint cage consists of regularly spaced constraint lines on a cubic lattice which are “active” with a probability p and absent with a probability 1−p. To a good approximation D≈A(p)N−α(p) and T≈B(p)Nβ(p) if N≫1. The exponents α and β show two regions of very rapid change at pc,1≈0.30 and at pc,2≈0.98.
QUASI-CRYSTALLINE TO CRYSTALLINE TRANSFORMATION IN (Ti1−xVx)2Ni ALLOYS
Authors: ZHANG Z. , KUO K.H.
Published: November 2004

The transformation of quasicrystal in (Ti1−xVx)2Ni alloys, x=0.0–0.3, to the equilibrium Ti2Ni and TiNi phases on heating in-situ in an electron microscope has been studied. Twins occurred frequently in the fcc Ti2Ni across {111} planes and fivefold twins sometimes can be obtained. The electron diffraction patterns of fivefold twins and quasicrystal are similar but distinctly different. A parallel orientation relationship existed between the fcc Ti2Ni and the ordered bcc TiNi.
A STUDY OF YBa2Cu3O9−δ TYPE SUPERCONDUCTING SINGLE CRYSTALS
Authors: LU H.X. , WU J. , ZHANG X.Y. , GAO X.K. , LI X.J. , HU M.S. , MAO X.Y. , WANG T.X. , XIN H.Q. , SHI Y.B.
Published: November 2004

Single crystals of Y-Ba-Cu-O type superconductors having the typical dimension 0.5 to 1 mm in the plane of the plate have been prepared. The analysis of composition show that they correspond to YBa2Cu3O9−δ. Laue photographs, which prove the samples to be single crystals, show some diffraction spots instead of rings. The measurement of susceptibility and other measurements have been performed.
SPINOIDAL DECOMPOSITION NEAR A LIFSHITZ POINT
Authors: MARKIEWICZ R.S.
Published: November 2004

Near a Lifshitz point, there is a deep minimum of the electronic energy. This minimum can lead to a spinoidal decomposition for carrier concentrations near the Lifshitz point. Such a two-phase mixture would be an ideal candidate for excitonic superconductivity.
SPIRAL LATTICE CONCEPTS
Authors: Bursill L.A. , Lin Peng Ju , Fan Xudong
Published: November 2004

The concept of a spiral lattice is introduced, and some mathematical properties derived. This is relevant to the prediction and characterization of states of matter intermediate between crystals, quasicrystals and glasses.
SURFACE MODES IN SEMI-INFINITE FERROELECTRICS
Authors: SANTOS A.R. DOS , OLIVEIRA F.A.
Published: November 2004

We evaluate the response function for a ferroelectric with a perfect flat surface and a simple cubic structure.
NONSTOICHIOMETRIC DEFECTS IN YBa2 Cu3O7−δ
Authors: BURSILL L.A. , GOODMAN P. , TAYLOR K.N.R.
Published: November 2004

Controlled injection of planar defects offers a possible means for optimizing the superconducting properties of Y-Ba-Cu-oxide sinters. High resolution electron microscopic examination of yttrium-rich superconducting preparations show c-plane intergrowth defects, together with twinning involving a 90° rotation of the c-axis.
CRYSTAL STRUCTURE AND SUPERCONDUCTIVITY OF Bi2Sr2CaCu2O8 COMPOUND
Authors: LIANG J.K. , XIE S.S. , CHE G.C. , HUANG J.Q. , ZHANG Y.L. , ZHAO Z.X.
Published: November 2004

The crystal structure of the ideal compositional compound Bi2Sr2CaCu2O8 with superconducting transition temperature Tc(0)=81.4K has been determined by X-ray powder diffraction method. The basic structure of this compound has the tetragonal symmetry with the lattice constants a=3.825Å, c=30.82Å. The most possible space group is [Formula: see text]. Each unit cell contains two chemical formulae. The arrangements of atoms in the unit cell are as follows:

2Ca cations occupy 2(a) equivalent point position

4Sr, 4Bi and 4Cu cations occupy the same equivalent point position 4(e) with respective parameters z=0.1, 0.3, 0.45.

16O anions respectively occupy 8(g) (z=0.45) and two 4(e) equivalent point positions (z=0.2 and z=0.385).

The crystal structure of Bi2Sr2CaCu2O8 can be derived from Aurivillius type structure. The other possible superconducting phases in the Bi-Sr-Ca-Cu-O system can be considered as the structure having different stacking on the basis of Aurivillius phase.
FINITE-SIZE SCALING ANALYSIS OF THE DECAY OF AN UNSTABLE STATE DURING A FIRST ORDER PHASE TRANSITION
Authors: VIÑALS JORGE , JASNOW DAVID
Published: November 2004

We extend standard finite-size scaling methods to study the dynamical evolution of an unstable state far from equilibrium as the system undergoes a first order phase transition. We suggest that the nonequilibrium structure factor S(q, t, L), at late times and for large enough lattice sizes, scales as S(q, t, L)=LdF(qL, t1/x/L). L is the linear dimension of the system and 1/x is the domain growth exponent. We obtain x=2 in the case of the kinetic Ising model with a nonconserved order parameter. For a critical quench in a system with conserved order parameter, scaling of the peak of the structure factor gives 1/x≈0.27. Higher wavenumbers, however, are more consistent with x=3.
X-RAY DIFFRACTION STUDY ON THE CRYSTAL STRUCTURE OF Sm1+xBa2−xCu3O7−y
Authors: ASANO H. , YOKOYAMA Y. , NISHINO M. , KATOH H. , AKINAGA H. , TAKITA K.
Published: November 2004

Crystal structures in solid solution of Sm 1+x Ba 2−x Cu 3 O 7−y (X = 0 - 0.4) have been investigated by Rietveld analysis of X-ray powder diffraction data. The structure changes from orthorhombic to tetragonal at x=0.2. With the increase of x, Tc decreases monotonically from 90 K and the compound becomes semiconducting at x=0.4.
STUDY ON THE SUPERCONDUCTIVITY OF Ba2(Y1−xLax)Cu3O7−y
Authors: DONG C. , LIANG J.K. , CUI C.G. , LI S.L. , NI Y.M. , JIA S.L. , ZHAO Z.X.
Published: November 2004

A series of samples with the nominal composition Ba 2( Ba 1−x La x) Cu 3 O 7−y, (0≤x≤1), was synthesized by solid state reaction. An X-ray diffraction study showed that a continuous solid solution exists between Ba 2 YCu 3 O 7−y and Ba 2 LaCu 3 O 7−y and there is a composition induced order-disorder transition from an orthorhombic to a tetragonal structure when x value is near 0.9. All the samples with orthorhombic crystal structure are superconductors with Tc onset above 90K. The transition midpoint temperature decreases smoothly when La content increases. The samples with x≥0.9 have a tetragonal structure and show semiconductor behavior with an exception of the x=1.0 sample which is a superconductor. Based on our previous and present studies, we concluded that the low dimensional character of the crystal structure and the mixed-valence state of copper or oxygen are necessary conditions for high-Tc superconductivity in copper-containing oxides.
HIGH-TEMPERATURE SUPERCONDUCTIVITY IN 123 AND OTHER CUPRATE PHASES OBTAINED IN AN EFFORT TO INVESTIGATE INTERGROWTH STRUCTURES
Authors: VIJAYARAGHAVAN R. , RAM R.A. MOHAN , GANAPATHI L. , RAO C.N.R.
Published: November 2004

In an effort to synthesize copper oxides involving intergrowth structures, we have found several compositions giving rise to high-temperature superconductivity, most of them containing the 123-type phase. A novel 123 superconducting phase is found in the Y-Sr-Cu-O system. More interestingly, an oxide of the Y-Ba-La-Cu-O system showed zero resistivity around 210K. Existence of extra Cu-O layers in some of the intergrowth structures may also lead to high-Tc superconductivity.
DIFFERENCE OF VARIATION OF UNIT CELL VOLUME V AND Tc WITH OXYGEN CONTENT IN YBa2Cu3O7−x AND LaBa2Cu3O7+x
Authors: CHE G.C. , XIE S.S. , LIANG J.K. , LI K.S. , ZHENG D.N. , NI Y.M. , JIA S.L. , ZHAO Z.X.
Published: November 2004

In YBa 2 Cu 3 O 7−x, the more the oxygen content is the higher is the Tc, the smaller is the lattice parameter c and the unit cell volume V. But in LaBa 2 Cu 3 O 7+x the less the oxygen content is, the higher is the Tc, the larger are c and V. These may be due to oxygen content being less than 7.0 in YBa 2 Cu 3 O 7−x and more than 7.0 in LaBa 2 Cu 3 O 7+x. These results give some informations regarding superconducting mechanism and show that the one-dimensional chain plays an important role.
C-AXIS TEXTURE IN YBaCuO SUPERCONDUCTING THIN FILMS
Authors: BAO Z.L. , WANG F.R. , JIANG Q.D. , WANG S.Z. , YE Z.Y. , WU K. , LI C.Y. , YIN D.L.
Published: November 2004

YBaCuO superconducting thin films with zero resistance temperature above 77K have been prepared by e-beam multilayer deposition. The texture of C -axis normal to substrate in the thin films on Al 2 O 3, MgO and ZrO 2 substrates were observed, and conditions and reasons inducing the texture were studied.
DYNAMIC THEORY OF ELECTRON TRANSFER PROCESS
Authors: ZHEN YIN
Published: November 2004

Based on time-dependent Hartree-Fork approximation, we have developed a new technique for dealing with non-adiabatic electron transfer process and also obtained the formula for finding consistently the effective adiabatic parameter and the transition probability. Comparing to Landau-Zener theory our results indicate that the transition probability is greatly influenced by the coupling between the electron and the heat-bath. As the initial state of the electron is in the ground state, interaction between the electron and the heat-bath reduces the transition probability between the electron states. This can be explained that the transition probability from covalent to ionic state in a solute reaction system goes down due to the influence of the solvent. As the initial state of the electron is in the excited state, the coupling to the heat-bath acts to enhance the transition probability between the electron states. This can elucidate that desorption probability decreases in the process of the electron stimulated desorption in virtue of the heat-bath.
ELECTROCHEMICAL BEHAVIOR OF YBa2Cu3O7
Authors: BACHTLER M. , LORENZ W.J. , SCHINDLER W. , SAEMANN-ISCHENKO G.
Published: November 2004

The corrosion behavior of the high-Tc-superconductor YBa2Cu3O7 in aqueous solutions was studied at room temperature by electrochemical dc and ac methods and surface analysis. The oxidic ceramics is found to be more stable in alkaline than in acid media. The surface stability decreases with the time of contact to the electrolyte and depends strongly on the polarization conditions. Segregation and decomposition effects are observed. Ageing effects are related to an increase of the ohmic resistance of the surface layers. A relatively positive reduction peak in cyclic voltammograms is correlated to the reduction of a formal Cu(III)-oxide species, which may be better explained in terms of a Cu(II)-peroxide species as [Cu2+ -O−]+ . The high-Tc-superconductor YBa2Cu3O7 does not act as a special electrocatalyst for the anodic oxygen evolution reaction. The superconductivity of the samples is a bulk property and remains even after electrochemical surface treatment.
THE QUADRATIC STARK EFFECT AND ONE-PHOTON SELF-INDUCED TRANSPARENCY
Authors: ZABOLOTSKII A.A.
Published: November 2004

The self-consistent Maxwell-Bloch Eqs. containing linear detuning and nonlinear frequency shift are considered. The soliton solution is found and discussed. The new regimes of self-induced transparency are predicted.
LARGE WAVE NUMBER FEATURES OF FORM FACTORS FOR PHASE TRANSITION KINETICS
Authors: OONO Y. , PURI S.
Published: November 2004

Porod’s law and Tomita’s sum rule are two universal features expected for form factors of systems undergoing phase ordering processes, but have never been conclusively observed in numerical experiments. We demonstrate the drastic effect of finite thickness of interfaces on these asymptotic laws. Our results strongly suggest that the form factor obtained by Ohta, Jasnow and Kawasaki is asymptotically accurate, if not exact.
SPECIFIC HEAT OF THE HIGH Tc SUPERCONDUCTOR Bi-Sr-Ca-Cu-O
Authors: YUAN S.L. , LI J.W. , WANG W. , RAN Q.Z. , ZHENG G.G. , GUAN W.Y. , ZHENG J.Q.
Published: November 2004

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

In this letter, the recent developments of the spin bag mechanism are summarized.
TOPOLOGICAL TERM OF THE ANTIFERROMAGNETIC HEISENBERG MODEL IN 2+1 DIMENSION
Authors: WU KE , YU LU , ZHU CHUAN-JIE
Published: November 2004

It is shown in this note that the two different ways2,4 of introducing the topological term in the discussion of the spin 1/2 antiferromagnetic Heisenberg model are identical to each other.
SUPERCONDUCTIVITY ASSOCIATED WITH THE GRANULAR STRUCTURE IN Ba2YCu3O7−δ
Authors: ZHAO YONG , ZHANG QIRUI , GUAN WEIYAN , XIA JIANSHENG , HE ZHENHUI , CHEN ZUYAO , QIAN YITAI , PAN GUOQIANG
Published: November 2004

The dependence of the resistance on the magnetic field and the current-voltage characteristics of the single phase Ba 2 YCu 3 O 7−δ have been measured. The nonmonotonic behavior and a hysteresis of R(H) and the current-voltage characteristics suggest that the granular superconductivity exist in this material, and it plays an important role in transport properties.
MAGNETIC PROPERTIES OF Bi2Sr2CaCu2Oy SINGLE CRYSTAL
Authors: YIN H. , CUI C.G. , WU K.C. , LI S.L. , ZHANG J.L. , YAN Y.F. , WANG J.H.
Published: November 2004

The lower critical fields of single crystal Bi 2 Sr 2 CaCu 2 O y at 77 K have been found to be 99.0 G and 19.8 G for the field parallel and perpendicular to c-axis respectively. From H c2 −T curve, the slope d H c2 / d T near T c has also been estimated by linear estimation. The results exhibit an anisotropy of the sample. The observation of Meissner and shielding effect shows that the sample is bulk superconductor.
ISING MODEL WITH STRONGLY CORRELATED RANDOM FIELDS
Authors: HORIGUCHI T. , GONCALVES L.L.
Published: November 2004

We investigate the Ising models with strongly correlated random fields, taking the values ±h0 and 0, on the square lattice and on the linear chain. The models present long range order and these results are consistent with the lower critical dimensionality obtained by the domain wall argument.
SCALING PROPERTIES OF VALENCE-BOND-SOLIDS WITH A LINEAR STRUCTURE
Authors: ISKE P.L. , CASPERS W.J.
Published: November 2004

In this work we will prove that the degeneracy of the ground state of linear Valence-Bond-Solids (VBS) structures is independent of the size of the lattice. We show that the ground states of VBS systems with different sizes can be mapped onto each other.

In this letter we will develop a scenario to construct such an isomorphism and we will apply it to calculate the correlation length for two cases.
POINT-CONTACT PROPERTIES OF YBa2Cu3O7−δ AND SmBa2Cu3O7−δ
Authors: REIFFERS M. , SAMUELY P. , KUPKA M. , HUDÁK O. , DIKO P. , CSACH K. , MIŠKUF J. , KAVEČANSKÝ V. , PONOMARENKO N.M.
Published: November 2004

The I-V characteristics and their derivatives on the point-heterocontacts of Y(Sm)Ba 2 Cu 3 O 7−δ Cu(Ag) are presented. Three types of dependences were observed. The observed deviations from classical tunneling behavior are explained. The phonon energies were determined from the classical PC tunneling spectra.
SYMMETRY OF THE HOLE STATES IN BiCaSrCuO HIGH-Tc SUPERCONDUCTORS
Authors: BIANCONI A. , CASTRUCCI P. , DE SANTIS M. , DI CICCO A. , FABRIZI A. , FLANK A.M. , LAGARDE P. , KATAYAMA-YOSHIDA H. , KOTANI A. , MARCELLI A. , ZHAO Z.X. , POLITIS C.
Published: November 2004

Polarized Cu L3-edge X-ray absorption spectra (XAS) of oriented film of Bi 2 Sr 2 Ca 1 Cu 2 O y have been measured to determine the symmetry of the orbital of the electronic holes. The states with the configuration 3d9L (L indicates ligand holes) have been detected. The holes d in superconducting materials are found to be in the antiferromagnetic band with b1 symmetry, derived by the Cu 3dx2 - y2 orbital, but also in a second band with a1 molecular symmetry, derived by Cu 3dz2 - r2 orbital at the Cu site. Our results can be rationalized with the formation of both d (b1) L and d (a1) L states in the ground state of this high-T c superconductor.
GLASSY BEHAVIOR OF YBa2Cu3O7
Authors: SAHLING A. , SAHLING S.
Published: November 2004

Long time power released in YBa 2 Cu 3 O 7 after rapid cooling from equilibrium temperature T1 (2.35 K≤T≤15.11 K ) to T0=1.5 K and heat capacity (1.2 K ≤T≤100 K ) were measured. The observed time and temperature dependence of the power release is similar to those of amorphous solids. The resulting density of states of two-level systems is close to the values obtained from heat capacity and acoustic measurements.
FORMATION OF COOPER PAIRS IN THE HUBBARD MODEL
Authors: Bogoliubov N.M. , Korepin V.E.
Published: November 2004

It is shown that Cooper pairs of electrons are formed in the one dimensional Hubbard model.
MONTE CARLO SIMULATION OF METHANOL GLASS
Authors: VISHNU KAMATH P. , CHANDRASEKHAR J. , RAO C.N.R.
Published: November 2004

Monte Carlo simulation studies predict a glass transition in methanol around 180K (experimental Tg, 160K). Methanol exists mainly in the form of linear hydrogen bonded polymers with an average of 10 molecules per polymeric unit in the glass at 180K compared to 6 molecules per unit in the liquid at 298K. There is a considerably greater preponderence of the polymeric. species in the glass relative to the liquid. There is a small change in the distribution of the hydrogen bonded species at Tg, but a significant breaking down of the polymeric species occurs above 220K. The average coordination number as well as the gmin/gmax ratios show a change around 220K instead of at Tg. The simulated distribution of hydrogen bonded species is comparable to the results obtained from infra-red spectroscopy.
ON THE DIMERIZATION OF LINEAR POLYMERS
Authors: DE CARVALHO C. ARAGÃO
Published: November 2004

We use the continuum limit of the Su-Schrieffer-Heeger model for linear polymers to construct its effective potential (Gibbs free energy) both at zero and finite temperature. We study both trans and cis-polymers. Our results show that, depending on a renormalization condition to be extracted from experiment, there are several possibilities for the minima of the dimerized ground state of cis-polymers. All calculations are done in the one-loop approximation.
STUDY ON THE SPECIFIC HEAT OF Bi2Sr2CaCu2Oy SINGLE CRYSTAL
Authors: ZHENG D.N. , YANG H.S. , CHEN Z.J. , WANG J.H. , YAN Y.F. , Ni Y.M. , CHEN G.H. , WANG K.Q. , JIA S.L. , ZHAO Z.X.
Published: November 2004

The specific heat of Bi 2 Sr 2 CaCu 2 O y has been measured using non-adiabatic method between 10 K and 130 K. No specific heat jump related to superconducting transition was observed around T c . This may be due to the defects and disorder of atoms existed in the single crystal.
AN INFRARED VIEW OF HIGH Tc SUPERCONDUCTORS
Authors: TANNER D.B. , TIMUSK T.
Published: November 2004

Studies of the infrared properties of the high T c superconductors are reviewed, with particular emphasis on attempts to determine the energy gap by far infrared spectroscopy and on the properties of the strong absorption that occurs in the mid infrared. We argue that this mid-infrared absorption is a direct particle-hole excitation rather than a Holstein emission process. In addition, we conclude that although the energy gap is not easily observed, several recent experiments place it in the weak to moderate strong coupling range.
PREPARATION AND CHARACTERIZATION OF UNUSUAL LEVITATION Tl-Ba-Ca-Cu-O SAMPLES
Authors: SHENG Z.Z. , LIU Y.H. , FEI X. , SHENG L. , DONG C. , HARTER W.G. , HERMANN A.M. , VIER D.C. , SCHULTZ S. , OSEROFF S.B.
Published: November 2004

A preparation procedure for the Tl-Ba-Ca-Cu-O superconducting samples which can be levitated above or beneath a magnet is described. X-ray powder diffraction data for these samples are presented and discussed. Their electronic and magnetic properties are presented. The explanation for the unusual levitation is briefly discussed.
SLIDING FRICTION IN VISCOUS HYDRODYNAMICS: THE ROUGH SURFACE AS VORTICITY SOURCE
Authors: DEKKER H.
Published: November 2004

Basset’s collective friction coefficient for a viscous fluid flowing past a rough solid surface is obtained — analytically — as an intrinsic consequence of the Navier-Stokes equations by treating the surface as a source of vorticity.
THERMODYNAMIC PROPERTIES OF 3-SPIN HEISENBERG ANTIFERROMAGNET
Authors: FLOREK W.S.
Published: November 2004

The energy levels for 3-spin Heisenberg magnet with near-neighbor interaction are fully determined, therefore the thermodynamic properties of this system can be examined. We consider only the case of antiferromagnetic exchange (spins are frustrated). The results are in agreement with Affleck prediction and with Peierls-Marshall theorem (for integer spin).
EFFECTS CAUSING RESONANCES IN TUNNELLING CURRENT OF HIGH-Tc SUPERCONDUCTORS
Authors: TAKÁCS S.
Published: November 2004

Two models (localization of carriers in normal regions, bag-like excitations of the superconducting condensate) are given for possible explanation of additional structure in the tunnelling current of high-T c superconductors above the gap voltage.
PREFERABLE ORIENTATION OF CRYSTALLINE THIN-FILM OF MODIFIED BNN SYSTEM
Authors: TSUKIOKA MASAYUKI , MASHIO TASUKU , SHIMAZU MASAJI , NAKAMURA TAKESHI
Published: November 2004

Using rf-sputtering method, modified BNN ( Ba 2 NaNb 5 O 15) thin-films, which are highly aligned, were prepared on a polished surface of a stainless steel plate and on a polished silicon wafer. It was found that preferably aligned thin-films were successfully obtained only when modified Nb-rich BNN target was used. Preferable orientation of these thin-films was confirmed by X-ray diffraction measurement.

In order to find the correlation between preferable orientation and separation from plasma center, X-ray measurement was carried out at several points on the thin-film sputtered on a long stainless steel substrate (5×100 mm ). The result indicated that preferable orientation was dominant near the position of plasma center. In order to distinguish whether the strong X-ray peak observed in the preferably aligned BNN thin-film is due to (200) peak of Nb 2 O 5 or (440) peak of BNN, X-ray measurements and the following quantitative analyses; fluorescent X-ray, ICP (Induced Coupled Radio Frequency Plasma) and an Atomic Absorption Method, were carried out for films sputtered from Nb-rich BNN target. The results reveal that the thin-films include considerable quantity of barium and sodium. This suggests that the highly aligned thin-film is composed of modified BNN and not Nb 2 O 5.
GROUP VELOCITY MEASUREMENT FROM THE PROPAGATION OF THE IONIZATION FRONT IN A SURFACE-WAVE-PRODUCED PLASMA
Authors: COTRINO J. , GAMERO A. , SOLA A. , LAO C.
Published: November 2004

During the first instant, previous to steady-state in a surface-wave-produced plasma, an ionization front advance front the launcher to the plasma column end. The velocity of the ionization front is much slower than the group velocity of the surface wave, this give a reflection of the incident signal on the moving ionization front. In this paper, we use this effect to calculate the surface wave group velocity.
CRYSTAL STRUCTURE AND SUPERCONDUCTIVITY OF TlBa2Ca2Cu3O8.5
Authors: LIANG J.K. , ZHANG Y.L. , HUANG J.Q. , XIE S.S. , CHE G.C. , CHENG X.R. , NI Y.M. , JIA S.L.
Published: November 2004

The crystal structure of TlBa 2 Ca 2 Cu 3 O 8.5(Tc=112 K) has been determined by means of X-ray powder diffraction method. It belongs to primary tetragonal symmetry with lattice parameters: a=3.847 Å, c=15.89 Å. Its space group is [Formula: see text]. Each unit cell contains one chemical formular unit. The arrangements of ions in a unit cell are as follows:

1Tl cation occupies 1(b) equivalent point position. 2Ca and 2Ba cations occupy 2(h) equivalent point positions with respective atomic parameters z=0.100 and 0.320. 3Cu occupy 1(a) and 2(g) (z=0.200) equivalent point positions. 8.50 anions occupy 1(d), 2(f), 2(g) (z=0.325) and 4(i) (z=0.200) equivalent point positions respectively. (Occupation factor is 0.945.)

The crystal structure of TlBa2Ca2Cu3O8.5 is quite similar to those of the other superconducting phases. All cations are distributed at positions of (0,0,z) and (1 /2,1 /2,z) alternatively. The oxygen deficient pseudo-perovskite unit Ba-Cu-Ca-Cu-Ca-Cu-Ba is separated by double Tl-O layers in the crystal structure of Tl 2 Ba 2 Ca 2 Cu 3 O 10. However, the oxygen deficient pseudo-perovskite unit Ba-Cu-Ca-Cu-Ca-Cu-Ba is separated by single Tl-O layer in the crystal structure of TlBa 2 Ca 2 Cu 3 O 8.5. The relations among the crystal structure of the superconducting phases as well as the relation between the crystal structure and superconductivity are discussed.
CORRELATION BETWEEN THERMAL STABILITY AND SUPERCONDUCTIVITY IN YBa2Cu3−xMx (M=Co, Zn)O7−y SYSTEM
Authors: ZHANG H. , ZHAQ Y. , CHEN Z.Y. , ZHANG Q.R.
Published: November 2004

A series of single-phase samples YBa 2 Cu 3−x M x (M=Co, Zn)O 7−y (x=0.025, 0.05, 0.075 and 0.1) were prepared, and their thermal decomposing temperature and superconducting critical temperature were determined. It was found that the thermal decomposing temperature as well as the Tc of the system decrease almost linearly as the value of x increases. Careful analysis shows that there is a close relationship between the thermal stability and superconductivity.
CRYSTAL STRUCTURE OF HIGH-Tc SUPERCONDUCTORS AND THE VALENCE OF THEIR CONSTITUENT ATOMS
Authors: MODRAK P. , OLSZEWSKI S.
Published: November 2004

Crystal structure of a high temperature superconductor and Pauling’s radii are used to calculate the valence of the constituent atoms. The simple considerations lead to the conclusion that the basic as well as the supplementary oxygen atoms are equally charged negative ions with the ionization degree about -2, and that there are two kinds of Cu atoms: one is the neutral atoms and the other is positive ions with the ionization degree about 3.5.
SUPERCONDUCTIVITY STUDIES ON (Ln1−xLux)Ba2Cu3O7, Ln=La, Sm
Authors: BALAKRISHNAN R. , VARADARAJU U.V. , SUBBA RAO G.V.
Published: November 2004

In the system Sm 1−x Lu x Ba 2 Cu 3 O 7, single phase orthorhombic perovskite is formed for x≤0.5 above which a multiphase material is obtained with the predominant 123 phase. All the phases except when x=1.0, exhibit superconductivity with Tc,zero in the range 87–90 K. Pure LaBa 2 Cu 3 O 7 is tetragonal and shows a Tc,zero of 73 K. Orthorhombic distortion and a Tc,zero of 79 K can be induced for x=0.1 in La 1−x Lu x Ba 2 Cu 3 O 7. In the latter system, single phase materials are obtained for x≤0.5. However, all phases exhibit superconductivity with Tc, zero=90±2 K for 0.2≤x≤0.8.
CALCULATED DIELECTRIC PARAMETERS OF BARIUM TITANATE-POTASSIUM NIOBATE COMPOSITES AS A FUNCTION OF COMPOSITION AND FREQUENCY
Authors: SARKAR S.K.
Published: November 2004

Some dielectric parameters e.g. dielectric constant, resistivity, dielectric strength, loss tangent, and saturation polarization of barium titanate-potassium niobate composites have been calculated as a function of composition and frequency, assuming a very simplified model and a 3–0 connectivity pattern. Most of the parameters have been found to vary linearly with composition at a given frequency.