bluuebunny/crossref_metadata_2025 huggingface dataset:
GEOMETRY OF TYPE II SUPERSTRINGS AND THE MODULI OF SUPERCONFORMAL FIELD THEORIES
Authors: CECOTTI S. , FERRARA S. , GIRARDELLO L.
Published: November 2004

We study general properties of the low-energy effective theory for 4D type II superstrings obtained by the compactification on an abstract (2,2) superconformal system. This is the basic step towards the construction of their moduli space. We give an explicit and general algorithm to convert the effective Lagrangian for the type IIA into that of type IIB superstring defined by the same (2,2) superconformal system (and vice versa). This map converts Kahler manifolds into quaternionic ones (and quaternionic into Kahlerian ones) and has a deep geometrical meaning. The relationship with the theory of normal quaternionic manifolds (and algebras), as well as with Jordan algebras, is outlined. It turns out that only a restricted class of quarternionic geometries is allowed in the string case. We derive a general and explicit formula for the (fully nonlinear) couplings of the vector-multiplets (IIA case) in terms of the basic three-point functions of the underlying superconformal theory. A number of illustrative examples is also presented.
SUPERCONFORMAL SYMMETRY AND SUPERSTRING COMPACTIFICATION
Authors: SCHWARZ JOHN H.
Published: November 2004

Various topics in conformal field theory and the theory of Kac-Moody algebras are presented. In particular, the Goddard-Kent-Olive construction is used to derive various conformal and superconformal theories, including a large class of N=2 models recently discovered by Kazama and Suzuki. The relationship between compactification of extra dimensions and the description of internal degrees of freedom by a conformal field theory is discussed. Various approaches to compactification based on exactly soluble conformal field theories, including Gepner’s proposal for using the N=2 minimal models, are sketched. Recent progress in understanding N=2 models and Calabi-Yau spaces using mathematical techniques of singularity theory is described. It is argued that a classical solution could be a useful first approximation to a quantum ground state even though it is known that string theory is strongly coupled and the perturbation expansion diverges.
A GENERALIZED BÄCKLUND TRANSFORMATION FOR THE (SUPER SYMMETRIC) SELF-DUAL YANG-MILLS FIELDS
Authors: CHAU L.-L. , SHAW J.C. , YEN H.C.
Published: November 2004

We derive a Bäcklund transformation for the self-dual Yang-Mills fields by using the method of special Riemann problem with one zero, in which the moving poles in the complex parameter plane are incorporated. This BT is more general than a previously given one and is capable of generating in one step monopole or instanton solutions from a vacuum solution. We further extend this result to the case of the supersymmetric self-dual Yang-Mills fields.
QUANTUM NONDEMOLITION MEASUREMENTS FROM PATH INTEGRAL
Authors: GOLUBTSOVA G.A. , MENSKY M.B.
Published: November 2004

The path integration method is applied to continuous quantum nondemolition (QND) measurements. Direct and indirect QND measurements are considered. It is shown that an observable is QND variable then and only then if the equation of motion for this observable due to a special “effective Hamiltonian” coincides with the classical equation of motion for this observable. The method is developed for finding a class of QND variables in the case of quadratic Hamiltonian.
THE CANONICAL STRUCTURE OF THE MANIFESTLY SUPERSYMMETRIC STRING
Authors: ALLEN THEODORE J.
Published: November 2004

Both the Green-Schwarz and Siegel strings are presented in canonical form. Both systems are shown to describe the same number of physical degrees of freedom. The apparent extra symmetries of the Siegel string are not true symmetries but are combinations of second-class constraints. A formal quantization procedure is outlined and the problems of quantization are discussed.
ISSUES OF SYMMETRIES IN THE GROSS-NEVEU MODEL
Authors: MORENO E. , SCHAPOSNIK F.A.
Published: November 2004

We study the chiral Gross-Neveu model using a path integral approach. After showing how U (1) massless excitations decouple we investigate the SU (N) sector of the theory. One then finds that for certain values of the coupling constant, the original (vector SU (N)) symmetry is enlarged to a chiral SU (N), giving rise to a conformally invariant model.
GRAVITON AMPLITUDES, EFFECTIVE ACTION AND STRING GENERATING FUNCTIONAL ON THE DISC
Authors: TSEYTLIN A.A.
Published: November 2004

We discuss some issues related to computation and renormalization of closed string amplitudes and effective action on the disc. The general expression for the O (ln ε) term in the string theory and effective field theory generating functionals for the S matrix is found. It is emphasized that in order to establish the correspondence between the string theory and the effective field theory it is necessary to compare the total coefficients of all (“local” plus “modular” and “N-dependent” plus “N-independent”) infinities present in the amplitudes. The regularized expression for the N=3 graviton amplitude on the disc is explicitly computed and it is suggested that a proper regularization is a key to a resolution of a paradox discussed previously in the literature.
AKUTZU-WADATI LINK POLYNOMIALS FROM FEYNMAN-KAUFFMAN DIAGRAMS
Authors: GE MO-LIN , WANG LU-YU , XUE KANG , WU YONG-SHI
Published: November 2004

By employing techniques familiar to particle physicists, we develop Kauffman’s state model for the Jones polynomial, which uses diagrams looking like Feynman diagrams for scattering, into a systematic, diagrammatic approach to new link polynomials. We systematize the ansatz for S matrix by symmetry considerations and find a natural interpretation for CPT symmetry in the context of knot theory. The invariance under Reidemeister moves of type III, II and I can be imposed diagrammatically step by step, and one obtains successively braid group representations, regular isotopy and ambient isotopy invariants from Kauffman’s bracket polynomials. This procedure is explicitiy carried out for the N=3 and 4 cases. N being the number of particle labels (or charges). With appropriate symmetry ansatz and with annihilation and creation included in the S matrix, we have obtained link polynomials which generalize the definition of the Akutzu-Wadati polynomials from closed braids to any oriented knots or links with explicit invariance under Reidemeister moves.
THE F-SPIN STRUCTURE OF THE NEUTRON-PROTON INTERACTING BOSON MODEL: HAMILTONIAN AND ELECTROMAGNETIC OPERATORS
Authors: DE COSTER C. , HEYDE K.
Published: November 2004

We study the F-spin structure of a general proton-neutron interacting boson model Hamiltonian and of the corresponding electromagnetic operators, using a separation into parts which are symmetric and antisymmetric under the interchange of proton and neutron degrees of freedom. We also use a formal procedure in which we couple proton and neutron operators to a given F-tensor rank. We deduce conditions of F-spin symmetry and F-spin invariance for the Hamiltonian, as well as selection rules for electromagnetic transition matrix elements. We use first order perturbation theory to obtain the (F, Fz)-dependence of the energy and wave functions, when F-vector and F-tensor (rank 2) parts are added to an “unperturbed” Hamiltonian, which is F-spin invariant.
EXTENDED CONFORMAL GROUP, SUPERSYMMETRY, AND GEOMETRICAL PROPERTIES OF HADRONS
Authors: BANDYOPADHYAY PRATUL , GHOSH PRADIP
Published: November 2004

We have studied the interrelation among conformal symmetry, internal symmetry and super-symmetry and have shown that extended conformal group which includes, apart from conformal transformation, space, time and conformal reflection can give rise to internal symmetry algebra as well as supersymmetry algebra. To achieve this result, we have dealt with conformal spinors which are taken to be the constituents of the hadrons and these split into two Cartan semispinors or Dirac spinors in the Minkowski space, giving rise to the particle and antiparticle configurations. Supersymmetry is broken here just by the mass term and as such no massless hadron can exist in nature. The internal symmetry arises from the discrete symmetry of reflection. The most significant feature of this formalism is that the symmetry structure helps us to explain the meson-baryon mass difference in an elegant way and the role of fictitious superpartners is completely avoided. Again, any baryon number nonconserving process like proton decay is found to be forbidden by the Lorentz invariance. Finally, it is noted that though the discrete symmetry of reflection is taken to be the origin of the internal symmetry, topological nontrivial structures like strings do not appear here and this also avoids the possibility of the nonconservation of global charge.
LAGRANGIAN OF SIX-DIMENSIONAL N = 4b CHIRAL SUPERGRAVITY
Authors: KAVALOV AN. R. , MKRTCHYAN R. L.
Published: November 2004

The supersymmetry and α-symmetry of the complete Lagrangian of pure d = 6 N = 4b supergravity are proved.
SEARCHING FOR SUPERSYMMETRY AT e+e− SUPERCOLLIDERS
Authors: BAER HOWARD , BARTL A. , KARATAS DEBRA , MAJEROTTO W. , TATA XERXES
Published: November 2004

We study the signals resulting from the production and subsequent decays of heavy sleptons, sneutrinos and all the charginos [Formula: see text] and neutralinos [Formula: see text] at ultrahigh energy e+e− colliders. In contrast to existing studies that assume that supersymmetric particles directly decay to the lightest supersymmetric particle (taken here to be the lightest neutralino, [Formula: see text]) which then escapes detection, we incorporate realistic decay patterns using the minimal supersymmetry model as a guide for the masses and mixing angles in the gaugino-Higgsino sector. We show that very heavy sleptons and sneutrinos often decay into heavier charginos and neutralinos which themselves often decay into real W and Z0 bosons and lighter [Formula: see text]'s and [Formula: see text]'s. This results in a considerably softer missing transverse momentum [Formula: see text] spectrum than would be expected if sparticles decayed directly to the [Formula: see text] so that [Formula: see text] is not necessarily a viable signature for very heavy sparticles. We show that the optimal signature for supersymmetry in very high energy e+e− collisions depends on the model parameters. Whereas [Formula: see text] is a viable signature for lighter sleptons and sneutrinos (m ~ 0.3 TeV ), the production of very heavy sparticles is signalled by events with two or more large angle W and Z0 bosons and often a very hard electron. We discuss strategies for extracting the SUSY signal and argue that it can be separated from standard model backgrounds over the whole of parameter space.
ON THE RELATION BETWEEN MULTIPLICITY AND TRANSVERSE ENERGY IN HIGH ENERGY HADRON-HADRON AND NUCLEUS-NUCLEUS COLLISIONS
Authors: WU YUANFANG , LIU LIANSHOU
Published: November 2004

The relation between multiplicity and transverse energy in high energy h-h and A-A collisions is investigated using a Monte Carlo generator of nondiffractive processes. The width of multiplicity fluctuation D/ for fixed E⊥ is found to be small and approximately constant for a wide range of E⊥.
EXCEPTIONAL GROUPS IN STRING THEORY
Authors: LÜST DIETER , THEISEN STEFAN
Published: November 2004

We review the occurrence of exceptional groups in string theory: their dual role as gauge symmetry and as a symmetry unifying space-time, superconformal ghost and internal degrees of freedom. In both cases the relation to the extended world-sheet supersymmetries is discussed in detail. This is used to construct the supermultiplet structure of the massless sectors of all supergravity theories possible in string theory, in even space-time dimensions between four and ten.
SOME FUNDAMENTAL ASPECTS OF SEMICLASSICAL AND QUANTUM GRAVITY
Authors: PADMANABHAN T.
Published: November 2004

Some recent developments in the study of quantum gravity and its semiclassical limit are reviewed. The discussion includes the role of constraint equations in quantization, the definition of 'time' in the semiclassical limit, the various forms of 'backreaction' in semiclassical gravity and the role of vacuum fluctuations in quantum gravity.
DUALITY AND CONFINEMENT IN THREE DIMENSIONAL YANG-MILLS THEORY
Authors: ARAGÃO de CARVALHO C. A. , MARINO E. C. , MARQUES G. C. , GOLDMAN de CASTRO M.
Published: November 2004

We exploit the order-disorder duality existing between the Wilson loop operator W(c) of an SU (N) Yang-Mills theory, and a local complex scalar field ϕ of a theory with global Z(N) symmetry in 2 + 1 dimensions, in order to establish a general method for the computation of the correlation functions of W(c) within the framework of the dual ϕ field theory. An explicit operator realization of W(c) in terms of ϕ is obtained. An effective dual Lagrangian, Lϕ, is proposed to account for the long distance properties of the theory. It is shown that, for N = 2, 3, 4, 5 this dual theory is always in a completely broken Z(N) symmetry phase. An explicit computation shows that for these values of N  has an area type behavior for the whole range of the parameters, meaning that the static quarks will be permanently confined.
ON A PHASE STRUCTURE OF A TWO-DIMENSIONAL (φ2)2 FIELD THEORY
Authors: EFIMOV G. V.
Published: November 2004

Two models of scalar fields with the interaction Lagrangians gφ4 and [Formula: see text] are considered in ℝ2. There are phase transitions in these models for a certain g = gc. It is shown that the spontaneous symmetry breaking takes place for g > gc. The description of the two phases for g < gc and g > gc is given. The effective coupling constants in perturbation series are less than unity for both the phases so that these models describe the systems with weak coupling. In the second model the "Goldstone" particles have nonzero masses in the phase g > gc.
FRACTALS AND THE QUANTUM THEORY OF SPACETIME
Authors: NOTTALE LAURENT
Published: November 2004

We review in this paper the first results obtained in an attempt at understanding quantum space-time based on a new extension of the principle of relativity and on the geometrical concept of fractals. We present methods for dealing with the nondifferentiability and the infinities of fractals, as a first step towards the definition and intrinsic description of a fractal space. After having recalled that the Heisenberg relations imply a transition of spatial coordinates of a particle to fractal dimension 2 about the de Broglie length λ = ħ/p, it is suggested that a similar transition occurs for temporal coordinates about the de Broglie time τ = ħ/E. We then investigate the hypothesis that the microstructure of space-time is of fractal nature, and that the observed properties of the quantum world at a given resolution result from the smoothing of curvilinear coordinates of such a spacetime projected into classical spacetime. Along this road, we successively study the link of fractal dimension 2 to spin, we give first hints on the expected behavior of families of fractal geodesics, and we exhibit a general class of fractal structures which is assumed to yield a lowest order description of the quantum vacuum. The links between the new approach and both special and general relativity are touched upon. We finally suggest that the anomalous peaks recently observed in the spectra of positrons from supercritical heavy ion collisions may be understood in this context.
DIFFEOMORPHISM GROUPS, QUANTIZATION, AND SU(∞)
Authors: HOPPE JENS
Published: November 2004

A method of relating infinite dimensional Lie algebras to basis dependent sequences of finite dimensional Lie algebras is introduced. Diff A S2 and Diff A T2 are shown to be N → ∞ limits of SU(N), with a limiting procedure, and " SU (∞)'s", that differ from the usual Kac Moody ones. After a detailed presentation of these two 'principal' examples, the general construction is outlined, which seems to work for the Poisson algebra of more or less any homogenous symplectic manifold.
APPLICATIONS OF CHIRAL SUPERSYMMETRY FOR SPIN FIELDS IN SELF-DUAL BACKGROUNDS
Authors: GY. FEHER L. , HORVATHY P. A. , O'RAIFEARTAIGH L.
Published: November 2004

Due to chiral supersymmetry the (nonzero mode) spectral and symmetry properties of a 4-dimensional, self-dual Dirac-Yang-Mills operator [Formula: see text] can be recovered from those of the corresponding scalar Laplacian D2. It is shown that a similar result holds for higher spins, and that in the 4-vector case the supersymmetric partners are − D214 and the fluctuation operator. The reduction to D2 is used to simplify previous analyses of the (nonzero mode) spectrum of [Formula: see text] and of the fluctuations for a BPS-monopole, and to explain the Kepler and su (2/2) (super)symmetries of a system studied recently by D'Hoker and Vinet.
ASPECTS OF SPIN AND STATISTICS IN GENERALLY COVARIANT THEORIES
Authors: ANEZIRIS C. , BALACHANDRAN A. P. , BOURDEAU M. , JO S. , SORKIN R. D. , RAMADAS T. R.
Published: November 2004

In this paper, we explore the consequences of diffeomorphism invariance in generally covariant theories. Such theories in two and three dimensions are known to admit topological excitations called geons. It is shown by specific examples that a quantum state of two identical geons may not be an eigenstate of the geon exchange operator, which means that a geon may have no definite statistics. As shown before by Sorkin and as discussed further here, it may also happen, for instance, that in 3 + 1 dimensions a tensorial (spinorial) geon obeys Fermi (Bose) statistics, while in 2 + 1 dimensions an "integral-spin" geon can obey "fractional statistics". Thus ideas on spin and statistics borrowed from Poincaré invariant theories are not always valid in quantum gravity, at least without further physical inputs. Previously, it was shown by Friedman and Sorkin that pure gravity in three space dimensions may admit spinorial states. This result is extended to two dimensions where pure gravity is shown to admit "fractional spin" geons.
MICROSTRUCTURAL STUDY OF HIGH TcY-Ba-Cu-O
Authors: Zhang J. , Gu H. , Xu J. , Gai S. , Yin D.
Published: November 2004

High Tc Y-Ba-Cu-O material with zero resistance above 90K were studied by TEM and X-ray anayses. Crystalline structure, grain boundaries and dislocations have been shown and discussed.
SUPERLATTICE STRUCTURE IN HIGH-TEMPERATURE SUPERCONDUCTING Y-Ba-Cu-O SYSTEM
Authors: Godwod K. , Górecka J. , Majewski J.
Published: November 2004

A set of superconducting samples with different superconducting phase concentration was investigated. The superlattice structure /2xa, 2xb, 2xc/ in the orthorhombic superconducting YBa2Cu3Oy was revealed. The relationship between superconducting property and the superlattice presence was found.
DC SUSCEPTIBILITY OF HIGH Tc SUPERCONDUCTORS Y-Ba-Cu-O SYSTEM
Authors: ZHANG SHIYUAN , WHANG HAO , ZHOU NINGSHENG , WANG ZIJUN , MA XIANG
Published: November 2004

This paper reports the results of dc susceptibility and magnetization loop of a ring sample on the high Tc denser superconductors with nominal concentration YBa2Cu3O9−x and Y0.4Ba0.6CuO3−x in our laboratory.
The Josephson Effect in Ceramic Bridge at Liquid Nitrogen Temperature
Authors: Wu P.H. , Cheng Q.H. , Yang S.Z. , Chen J. , Li Y. , Ji Z.M. , Song J.M. , Lu H.X. , Gao X.K. , Wu J. , Zhang X.Y.
Published: November 2004

Bridge junction can be made by cutting a bulk ceramic superconductor into the right sizes. Using this sort of bridge, both dc and ac Josephson effects are confirmed in liquid nitrogen . We have observed microwave induced steps at either nhf/2e or 2nhf/2e where n is an integral, as well as the oscillation of critical supercurrent with the increase of microwave power or externally applied magnetic field.
HIGH Tc Ba-Y-Cu-O COMPOUND "HOLE" CONDUCTIVITY PROPERTY
Authors: Shi Wanquan , Chai Zhang , Li Biqin , Liu Shixiang , Liu Xuejun , Hu Zhongbo
Published: November 2004

This paper proved that high Tc Ba-T-Cu-O compound have “hole” conductivity property like P-type semiconductor by hot probe measuring. We suposed that high Tc Ba-Y-Cu-O compound is “hole pair” conductivity in superconductivity state.
HIGH-TEMPERATURE OXIDE SUPERCONDUCTORS: STRUCTURE, STOICHIOMETRY AND THE MECHANISM OF SUPERCONDUCTIVITY
Authors: RAO C.N.R.
Published: November 2004

Magnetic susceptibility data show La2CuO4 to be antiferromagnetic. Oxides of the K2NiF4 structure of the general formula (La1−y Lny)2−x Srx(Bax)CuO4 show superconductivity in the 15-40K range, the Tc becoming maximum at a specific value of x or of the a-parameter. Superconductivity in La3−xBa3+xCu6O14 and La4−xBa1+xCu5O13 systems has been investigated besides that in the Y-Ba-Cu-O system. Role of oxygen in the superconductivity of YBa2Cu3O7−δ is discussed. The problem of rationalizing macro and microstructures of YBa2Cu3O7−δ is indicated. Infrared spectra of the superconducting oxides and their marginal metallicity in the normal state are examined. Based on electron spectroscopic studies, it is shown that holes are likely to be on oxygen rather than on copper, giving rise to peroxide-like species; Copper is present in the 1+ state (besides the 2+ state).
HIGH Tc SUPERCONDUCTIVITY: A MODEL BASED ON ANTIFERROMAGNETIC FLUCTUATIONS
Authors: Schmeltzer D.
Published: November 2004

The system X–La–Cu–O is described as a Fermi liquid with antiferromagnetic interaction. This interaction gives rise to two types of fluctuations, magnetic and superconducting. As a result, we find a free energy which contains two order parameters which at high temperature give rise to superconductivity and at low temperature to reentry-like paramagnetism. For two-dimensional systems, topological effects give rise to fractional statistics and as a result superconductivity appears when the topological angle θ gives rise to a Bose statistic.
ISING MODELS ON TWO-DIMENSIONAL QUASI-CRYSTALS: SOME EXACT RESULTS
Authors: CHOY T. C.
Published: November 2004

Exactly soluble Z-invariant (or Baxter) models of statistical mechanics are generalised on two-dimensional Penrose lattices based on the de Bruijn construction. A unique soluble model is obtained for each realization of the Penrose lattice. Analysis of these models shows that they are soluble along a line in parameter space which intersects the critical surface at a point that can be determined exactly. In the Ising case, critical exponents along this line are identical with the regular two-dimensional Ising model thus supporting the conventional picture of the universality hypothesis.
MIXED VALENCE COPPER OXIDES: RELATIONSHIPS BETWEEN CRYSTAL CHEMISTRY AND SUPERCONDUCTIVITY
Authors: RAVEAU B. , MICHEL C. , MAIGNAN A. , HERVIEU M. , PROVOST J.
Published: November 2004

The influence of different factors — mixed valence of copper, coordination of this element, low dimensionality of the structure, phase transition and non-stoichiometry — upon superconductivity is analyzed for the two families of higher Tc superconductors La 2 CuO 4 and YBa 2 Cu 3 O 7-type.
SOME ASPECTS OF HIGH-TEMPERATURE SUPERCONDUCTORS: A REVIEW
Authors: HUANG C. Y.
Published: November 2004

A brief history of the discovery of high-temperature superconductors is presented. Some salient properties (magnetism, Mössbauer effect, etc.) are reviewed. Some results obtained on recently discovered superconductors and super-high-temperature superconductors are also discussed.
THE ROLE OF OXYGEN IN YBa2Cu3O7−δ
Authors: GOODENOUGH JOHN B. , MANTHIRAM A.
Published: November 2004

Five observations concerning the role of oxygen in the high-Tc superconductors YBa 2 Cu 3 O 7−δ are emphasized: (1) An internal electric field parallel to the c-axis constrains the redox reactions associated with the intercalation/disintercalation of oxygen primarily to the [ CuO 3−δ]3− layers located between Ba 2+ layers. (2) Intercalation of O 2− into the tetragonal YBa 2 Cu 3 O 6 phase results in an ordering onto one of the basal-plane axes of the Cu(1) layer, the b-axis of the orthorhombic phase. (3) Ordering between and within b-axis chains gives rise to discrete phases predicted to occur at O 6.875, O 6.75, O 6.5, O 6.25, and O 6.125. (4) An equilibrium oxidation state for the intercalation layer depends not only on the oxygen partial pressure and temperature, but also on the cations of the structure. (5) At higher oxidation states of the intercalation layer, any oxygen atom on the a-axis interacts with a near-neighbor oxygen on the b-axis to trap out holes in a peroxide ion ( O 2)2−.
INTERFACE ANALYSIS OF InSb MIS STRUCTURES
Authors: GERMANOVA K. G. , VALCHEVA E. P.
Published: November 2004

There exists an ambiguity in the interpretation of a peak structure in the interface state spectra of MIS structures on InSb as an interface state, or as a deep bulk level in the semiconductor. The structures are prepared by plasma enhanced chemical vapour deposition of SiO 2. An analysis is performed and conclusion is drawn that the peak structure is due to an interface state which might be connected with the oxygen sensitive phenomena at the InSb surface.
THE RVB CONDUCTOR AND THE FERMI LIQUID (GUTZWILLER-BRINKMAN-RICE) CONDUCTOR
Authors: Baskaran G.
Published: November 2004

The doped Mott insulator has, under some conditions, qualitatively different behaviour as compared to an ordinary Fermi liquid conductor. This difference is focussed and brought out by a simple renormalisation group analysis as well as reinterpreting the known canonical transformation method and other results. We argue that there exists a separate fixed point, different from the Fermi-liquid fixed point, which governs the long wavelength and long-time scale behaviour of an RVB conductor. Also we identify the disordered local moment phase of the Hubbard model (for non-half filling) with the RVB metal phase and locate the phase boundary between the two phases. At the end we study in detail a recent construction of Anderson and show that the novel quasi-particles of an RVB conductor, namely, holons and spinons are bosons and fermions respectively.
RESONATING VALENCE BONDS: A NEW STATE FOR MIXED VALENCE SYSYEMS?
Authors: Lee D. H.
Published: November 2004

In this paper, we briefly review the recent efforts to understand the novel resonating valence bond (RVB) state for the S = 1/2 antiferromagnetic (AFM) Heisenberg model. We propose a pair hopping mechanism which generates a new form of AFM superexchange, and argue that the RVB wavefunction is successful because it takes full advantage of this pair hopping. Finally, we will argue that the high T c copper oxides represent a new fixed point of mixed valence systems, in which the low energy charge transfer process is governed by pair hopping between copper and oxygen orbitals.
SUPERCONDUCTIVITY IN CHAIN-LIKE STRUCTURES
Authors: Noga M.
Published: November 2004

The copper-oxygen chains which can be responsible for superconductivity in high T c oxides of the type YBa 2 Cu 3 O 7−x are idealized by the Hubbard model in the strong coupling limit. A unitary transformation is found by which the large interaction term is exactly diagonalized. It is shown that a system which is open to fermion number fluctuations and described by the Hubbard model in the strong coupling limit behaves always as a superconductor.
STRONG ELECTRON-PHONON COUPLING AND THE ORTHORHOMBIC TO TETRAGONAL TRANSITION IN La2CuO4
Authors: Barišić S. , Batistić I.
Published: November 2004

It is proposed that the main contribution to the electron-photon coupling in ionic metals arises from the deformation induced variation of the crystal field on the ionic sites which are involved in conduction. The latter are assumed here to be the oxygen sites in the CuO 2 planes of the layered metal oxides. The coupling of holes on those sites to the tilting mode of the La 2 CuO 4 lattice is investigated in detail. Although the coupling is quadratic in small tilting displacement the large value of the corresponding coupling constant explains the destabilization of the tilted (orthorhombic) La 2 CuO 4 lattice on increasing the hole concentration. It is shown that the holes are suppressing the tilt locally, creating the regions of the tetragonal please, as observed recently in the photogeneration experiments. The stability of the corresponding small polarons (tiltons) is discussed in detail.
COMMON EXCITONIC MECHANISM FOR CuO2 AND BiO3 BASED PEROVSKITES
Authors: Nuñez Regueiro M. D. , Aligia A. A.
Published: November 2004

BiO 3 based high Tc oxides are studied and compared to CuO 2 based ones. Both are described by a general Hamiltonian and studied by perturbation theory in the hopping energy. It is shown that a common polarization mechanism can give rise to pairing of the O holes added to the antiferromagnetic or disproportionated semiconducting states. The necessary conditions are: proximity of the M(Cu or Bi) and O levels, a gap in the electronic spectrum of the system and important nearest-neighbor M-O repulsion.
SPUTTERING OF CERAMIC MATRIX AND PHONON SPECTRA
Authors: TOŠIĆ B. S. , ŠETRAJČIĆ J. P. , Dj. TIMOTIĆ U. , DJAJIĆ R. P. , Lj. MIRJANIĆ D
Published: November 2004

The model is formed based on the continual deformation of mass distribution by sputtering of thin films. It was shown that due to mass deformation acoustical phonons are eliminated. This can cause a higher critical superconductive temperatures. The agreement of theory and experimental data of ceramic oxides is satisfactory. It is expected that presented theory is at service for synthesis of new superconductive materials.
MEAN-FIELD THEORY FOR LAYERED HIGH-TEMPERATURE SUPERCONDUCTORS
Authors: Baeriswyl D. , Schneider T.
Published: November 2004

Using the mean-field approximation we study a model for quasi-two-dimensional layered superconductors. The interlayer coupling, assumed to be mediated by a small electron hopping term, is found to leave Tc practically unaffected. Consequently, a three-dimensional pairing mechanism is required to explain the observed dependence of Tc on the average interlayer spacing in the Bi and Tl compounds.
ENERGY GAP IN S- AND D-WAVE PAIRING SUPERCONDUCTORS
Authors: Dolgov O. V. , Golubov A. A.
Published: November 2004

The ratio 2Δ g / T c . where Δ g is the gap edge, T c is the critical temperature, is calculated in the framework of the model of strong electron-phonon coupling. Both isotropic and anisotropic pairing cases are considered. It is shown that the isotropic Eliashberg model can not account for the large values of the ratio 2Δ g / T c for the reasonable values of the electron-phonon coupling parameter λ, while anisotropic pairing can resolve this problem.
DISTRIBUTION OF SUPERCONDUCTING PHASES IN THE Bi2Sr2CuO6 – CaCuO2 SYSTEM
Authors: Pekker S. , Sasvári J. , Hutiray Gy.
Published: November 2004

Bi 2 Sr 2 CuO 6 – CaCuO 2 system is studied in a wide range of compositions by electrical resistivity and X-ray diffraction measurements. The T c = 80 K phase can be observed in all compositions except the Ca free Bi 2 Sr 2 CuO 6, while the T c = 110 K phase is characteristic to the high CaCuO 2 concentration range, with maximum intensity at the nominal composition of Bi 2 Sr 2 Ca 2 Ca 5 Cu 6 O 16. The distribution of 20 K, 80 K and 110 K T c phases is estimated from powder X-ray measurements.
SUPERCONDUCTIVITY OF THE Pr-SUBSTITUTED (Nd1−xPrx)Ba2Cu3O7−δ SYSTEM
Authors: KU H. C. , CHEN C. C. , HSU S. W.
Published: November 2004

Electrical, magnetic and crystallographic measurements have been carried out for the pseudoquaternary ( Nd 1−x Pr x) Ba 2 Cu 3 O 7−δ system. Orthorhombic phase persists from x = 0.0 up to x = 0.7 and transforms into the tetragonal structure only for x ≥ 0.8. Superconducting transition temperature T c decreases linearly from 92 K for x = 0.0 to below 10 K for x = 0.3 and extrapolated to 0 K around x = 0.35. Magnetic susceptibility data indicates that the valence of the Pr ion is close to 4+. Pr 4+ is a very powerful oxidizing agent and may distort or move oxygen away from the Cu-O chain and/or the CuO 2 planes and seriously suppress superconductivity.
PHENOMENOLOGICAL THEORY OF POLYMER MELT DYNAMICS
Authors: SKOLNICK JEFFREY , YARIS ROBERT , KOLINSKI ANDRZEJ
Published: November 2004

A particularly interesting problem in polymer physics is the mechanism by which an individual polymer chain moves in a polymer melt or concentrated polymer solution. The first rather successful model of polymer dynamics was the reptation model of de Gennes which asserts that due to the effect of entanglements a polymer finds itself confined to a tube. Thus, the dominant long wavelength motion of the chain should be slithering out the ends of the tube. In order to examine the validity of the reptation model, a series of dynamic Monte Carlo simulations were performed. Although the simulations are on chains sufficiently long that agreement with the experimentally observed scaling with degree of polymerization n of the self diffusion constant and terminal relaxation time is observed, reptation does not appear to be the dominant mechanism of long distance motion. Rather the motion is isotropic, with the slowdown from dilute solution behavior arising from the formation of dynamic entanglements — rare long lived contacts where a given chain drags another chain through the melt for times on the order of longest internal relaxation time. Motivated by the simulations results, a phenomenological theory for the diffusive and viscoelastic behavior is developed that is consistent with both simulations and experiment and which does not invoke reptation. The major conclusions arising from the theoretical approach are described, and comparison is made with experiment.
THERMODYNAMIC STABILITY OF THE TWO-DIMENSIONAL JELLIUM MODEL IN A STRONG MAGNETIC FIELD
Authors: TAO R. , WIDOM A. , TAO Z. C. , SIM HOCK-KEE
Published: November 2004

It is shown that two-dimensional jellium in a strong magnetic field is thermodynamically unstable. At filling factor v < 1, it produces a negative pressue and a negative compressibility, violating the second law of thermodynamics. The grand canonical partition function is convergent, but is not equivalent to the canonical ensemble. After Maxwell construction, the v < 1 state is a non-uniform phase-coexistent state. The application of this finding to the theoretical study of the fractional quantum Hall effect is also discussed.
THEORETICAL ANALYSIS OF THE OPTICAL-ABSORPTION TAIL IN AMORPHOUS SEMICONDUCTOR SUPERLATTICES
Authors: YONEZAWA FUMIKO , ISHIDA KEIKO , SATO FUMITOSHI
Published: November 2004

We propose a two-band tight-binding model Hamiltonian to describe the behaviour of electrons in amorphous semiconductor superlattices. Our model Hamiltonian is characterized by its off-diagonal terms υz in direction z which is perpendicular to layers in a superlattice; we define υz as a parameter which represents the dimension of well layers accompanying the change in a well-layer width Lw under the condition that a barrier-layer width is fixed. On the basis of this model, we calculate the density of states D(E) and the absorption spectra I(E), from which we estimate the exponential-tail widths E0 and Eu of D(E) and I(E), respectively. We discuss the ways in which these widths E0 and Eu are influenced (i) by the dimension of the system, (ii) by the dispersion of well-layer widths and (iii) by the degree of disorder. We also propose the possibility to improve the photovoltaic efficiency in solar cells composed of amorphous semiconductor superlattices.
THE LINEARIZED HUBBARD MODEL: DYNAMICAL SUPERALGEBRA AND SUPERSYMMETRY
Authors: MONTORSI ARIANNA , RASETTI MARIO , SOLOMON ALLAN I.
Published: November 2004

The dynamical superalgebras for the conventional Hubbard model and for its extension to a superlattice given by the union of two sublattices are considered. Self consistency equations are obtained for the relevant order parameters. Moreover the models are shown to be the linearized form of a class of supersymmetric models obtained from charges living in the fermionic sector of these superalgebras. The superconductive phase transition exhibited by these models is accounted for as a spontaneous breaking of supersymmetry.
SINGLE CRYSTAL GROWTH OF HIGH TEMPERATURE SUPERCONDUCTORS AND INVESTIGATION OF THEIR PHYSICAL PROPERTIES
Authors: TATARCHENKO V. A. , EMEL'CHENKO G. A. , ABROSIMOV N. V. , BORODIN V. A. , Ya. VINNIKOV L. , ZHARIKOV O. V. , ZHOKHOV A. A. , KONONOVICH P. A. , MASALOV V. M. , ROMANENKO I. M. , RYAZANOV V. V. , CHERNYSHOVA L. I.
Published: November 2004

Part of the phase diagram of the La 2 O 3- CuO system has been studied and single crystals of La 2 CuO 4, (LaSr) 2 CuO 4 (up to 20 × 8 × 6 mm 3), YBa 2 Cu 3 O 7−δ (up to 8 × 6 × 0.1 mm 3) and HoBa 2 Cu 3 O 7-(up to 3 × 2.5 × 1 mm 3) have been grown by the method of spontaneous crystallisation, using a rotational crucible. It has been established that thermal treatment of "123" single crystals under oxygen pressure to 10 bars improves their superconducting properties. Electrical, magnetic, optical properties, and the real structure of the single crystals produced have been studied.
THERMODYNAMICS OF SOLIDS WITH REGIONS OF DISORDER
Authors: KADANTSEVA E. P. , YUKALOV V. I.
Published: November 2004

A model of a solid with randomly distributed regions of disorder is considered. In particular cases these regions of disorder can be pores or cracks. It is shown that in the case of an effective repulsion between particles the system is stable thermally as well as mechanically. A detailed numerical investigation of main thermodynamical quantities as functions of temperature at several densities is presented.
STUDY OF HIGH-Tc SUPERCONDUCTING MATERIALS IN (Bi.Pb)-Sr-Ca-Cu-O SYSTEM
Authors: WANG YUGUI , JIAO XINPING , WANG JINSONG , WANG NANLING , HAN GUCHANG
Published: November 2004

The high-T c superconducting materials in (Bi.Pb)-Sr-Ca-Cu-O system with zero resistance temperature of 104 K have been made by solid state reaction. The system has been compared with BiSrCaCu 2 O y composition. The preliminary results show that Pb would make the superconducting polycrystalline grains grow smaller resulting in the separation of 100–110 K and 80 K superconducting crystalline grains and connectivity among the high-T c phase grains. By comparison, the proportion of superconducting phase is not increased in the Pb doped multiphase samples. The magnetization measurement indicates that all of them belong to the weak pinning superconductors.
THE INFLUENCE OF THE MAGNETIC IMPURITIES ON THE HTS CRITICAL TEMPERATURE
Authors: Ya. SHAPIRO B.
Published: November 2004

The transfer mechanism of holes in the 123 compounds between chains and layers by optical transverse boson mode is introduced. The critical temperature as a function of the magnetic impurity concentrations both in the planes and in the chains is obtained.

The critical temperature is determined by the difference of the concentrations in the chains and in the planes. The dependence strongly differs from the usual Abrikosov-Gor'kov behaviour.

The results are correct for any layered structure with two different types of layers.
PHASE DIAGRAM OF THE QUENCHED THREE-COMPONENT POTTS MODEL
Authors: BAKAEV A. V. , ERMILOV A. N. , KURBATOV A. M.
Published: November 2004

For the quenched Potts model in the ferromagnetic, antiferromagnetic and disordered phases the expression for the free energy is obtained. On the basis of this expression, the phase diagram of the Gaussian three-component Potts model is constructed. The phase diagram obtained is qualitatively different in some features from that of the quenched Ising model.
TWO-DIMENSIONAL ELECTRON CORRELATION IN A MAGNETIC FIELD — THE FRACTIONAL QUANTUM HALL EFFECT
Authors: TSUI D. C.
Published: November 2004

A review is given of recent experiments on the fractional quantum Hall effect. The emphasis is placed on the quasi-particle energy gap data, which provide a first quantitative test of theory, and on the observation of an even denominator fraction.
SOME PROPERTIES OF THE NONLINEAR PYROELECTRIC CURRENT IN EXTERNAL d.c. ELECTRIC BIAS
Authors: SAJOSCH H. J.
Published: November 2004

A simple expression for nonlinear pyroelectric current considering the nonlinearities caused by an external dc electric bias field is given. It was shown that the polarity of the dc bias field strongly influences the pyroelectric current. A threshold value for the sample thickness of a TGS crystal at which the total pyroelectric current starts to be nonlinear is given.
ON EXPLICIT SOLUTIONS OF A COUPLED KdV-mKdV EQUATION
Authors: Guha-Roy Chanchal
Published: November 2004

A coupled Korteweg de Vries (KdV)-modified KdV equation is presented, some explicit solutions of which are exhibited in terms of Jacobi elliptic functions.
RELAXATION OF THE MAGNETISATION IN SUPERCONDUCTING OXIDES
Authors: GABOVICH A.M. , MOISEEV D.P. , PANAITOV G.I. , POSTNIKOV V.M. , SIDORENKO A.S. , SIMONOV A. Yu.
Published: November 2004

Relaxation of the thermoremanent magnetisation M in oxide superconductors BaPb 0.75 Bi 0.25 O 3, YBa 2 Cu 3 O 7−δ, Bi 2 Sr 2 CaCu 2 O x and Bi 4 Sr 3 Ca 4 Cu 4 O x is measured at T=4.2 K by the SQUID magnetometer. It is well described by the law M(t)=M0- Sln t, where t is the time, M0 and S are constants. The dependence of the decay rate S on the external magnetic field H is investigated in detail for the ceramics BaPb 0.75 Bi 0.25 O 3 with a low first critical magnetic field H cl ~12 Oe .
OBSERVATION OF NOISE INDUCED THERMAL VOLTAGES AND NON-UNIFORM CURRENT TRANSPORT EFFECTS IN A GaAs-AlGaAs HETEROJUNCTION IN STRONG MAGNETIC FIELDS
Authors: REEDTZ G. MARULLO , BOELLA G. , RINAUDO G.
Published: November 2004

The dc voltage between two probes of a GaAs-AlGaAs heterojunction has shown zero-current oscillations as a function of the magnetic field B with a 1/B period close to the electron density determined from the Hall plateaus. A similar effect was observed when using an ac current.

Combining the ac current data corresponding to opposite polarities of B we were able to separate two contributions similar in behaviour to the different components of the thermopower tensor.

If thermal gradients are present, the current distribution in the two-dimensional channel of the heterojunction must be highly inhomogeneous. Further evidence in this direction is given.
TWISTED MAGNETS AND TWISTED SUPERFLUIDS
Authors: Chandra P. , Coleman P.
Published: November 2004

We present a quantum fluids approach to incommensurate magnetic structures, emphasizing the close analogies between spin and neutral superfluidity. In particular we show that in twisted magnets the spin superfluid phase stiffness determines the long-wavelength behavior, and that there exists the spin analogue of the roton. We conclude with a brief discussion of charge fluctuation effects, and the possibility of twisted superconductors with mixed parity pairs.
IMPORTANCE OF LOCAL SPIN-FLIP PROCESSES IN QUANTUM ANTIFERROMAGNETS
Authors: Oleś Andrzej M.
Published: November 2004

The variational wave function proposed by Bartkowski to treat the ground state of a quantum antiferromagnet is reexamined. The fundamental equations of this method, for the energy and magnetization, are formulated in terms of a linked cluster expansion. It is found that the energy which results from the numerical minimization of the formula derived by Bartkowski is lower than originally reported. The energy is further improved by including higher order linked diagrams, which gives the energy of E0=−0.3338J per bond and magnetization of 0.356 for the square lattice. The same wave function is next used to treat the motion of a single hole in a quantum antiferromagnet. Its motion becomes possible due to the local coupling to quantum fluctuations. It is found that the spectrum is dominated by the incoherent processes, but a coherent propagating mode may be also identified. The quasiparticle dispersion is only weakly modified by quantum fluctuations present on the neighbouring bonds.
SPIN-CARRYING SLAVE BOSON REPRESENTATION FOR STRONGLY CORRELATED FERMION SYSTEMS
Authors: Wölfle P.
Published: November 2004

We consider slave boson formulations of the Hubbard model, the t–J model and the Anderson model, in which spin and charge fermion degrees of freedom are represented by Bose fields. The approach has been applied to the Hubbard model generalizing the formulation of Kotliar and Ruckenstein. There the Gutzwiller solution is recovered as a saddle point. The method allows to find other types of mean field solutions in a systematic way. Dynamical correlation functions in mean field approximation as well as fluctuation contributions are also calculated.
Static properties of the 2D Hubbard model on a 4×4 cluster
Authors: Parola Alberto , Sorella Sandro , Baroni Stefano , Parrinello Michele , Tosatti Erio
Published: November 2004

A numerical study of the 2D Hubbard model at various fillings has been performed. The static properties of 10, 14 and 16 electrons on a 4×4 cluster have been studied by exact diagonalization at intermediate couplings. A simple “power method” has been used in order to minimize memory requirements. Spin-spin, charge-charge and hole-hole correlations have been computed together with the one particle density matrix. This computation provides the first exact results on such a system, which can be used as a test for existing simulation algorithms.
BINDING OF HOLONS-SEMIONS IN THE CHIRAL STATE
Authors: Schmeltzer D.
Published: November 2004

We show that in the chiral spin state the charged holons induce a magnetic field. The vector potential of this magnetic field is singular and depends on the holon density. Mapping the problem to a vortex lattice we find that for the semion case the charge neutrality condition implies that the electric charge can have two opposite vorticities [Formula: see text]. As a result the two vortices bind forming a boson of charge 2e. The critical temperature for binding is the Kosterlitz Thouless one.
MEAN SQUARE SIZE OF POLYELECTROLYTES: ANALOGY WITH THE POLARON PROBLEM
Authors: KHANDEKAR D.C. , BHAGWAT K.V. , WIEGEL F.W.
Published: November 2004

We point out that a formal analogy exists between the path integrals for the configuration sum of a polyelectrolyte and for the propagator of a polaron in a polar crystal. Using this analogy and some recent results in polaron theory we evaluate the mean square end-to-end distance  of the polyelectroyte. It is shown that for large polymers the electrostatic interaction does not change the behaviour of  from that of a free polymer.
SYNCHROTRON RADIATION STUDIES OF MBE FORMED SEMICONDUCTOR INTERFACES: Si-GaAs AND GaAs-Si
Authors: BACHRACH R.Z. , BRINGANS R.D. , OLMSTEAD MARJORIE A. , UHRBERG R.I.G
Published: November 2004

Studies of silicon on gallium arsenide and gallium arsenide on silicon interface formation will be described and used as examples of how synchrotron radiation excited photoemission is a powerful probe of surface and interface phenomena. The samples and interfaces studied in this work were prepared in-situ using thermal Ga and As MBE sources and a resistive Si evaporation source. The MBE capability has allowed us to explore atomic and electronic structural issues of interface formation during hetero-epitaxy. We have combined these techniques to explore Si and GaAs surfaces, the adsorbate interactions of Ga and As on Si, and interface formation of Si on GaAs and the inverse system, GaAs on Si. Several of these surfaces and interfaces yield model systems which can provide general insights. As an example, studies of arsenic terminated silicon (100) and (111) surfaces will be described. A specific focus of the paper will be the interfacial development of Si on GaAs(100). Si deposited at various coverages below 10 ml onto a room temperature substrate yields a disordered surface. For coverages below two monolayers, subsequent annealing at 450–600°C leads to a single domain 1×2 surface from either the As rich c(2×8) or Ga rich 4×6 reconstructions. While the periodicity is the same for the different starting surfaces, evidence is presented that the atomic arrangement in the unit cell is different.