bluuebunny/crossref_metadata_2025 huggingface dataset:
COMPLETE STRUCTURE OF Zn YUKAWA COUPLINGS
Authors: CASAS J.A. , GOMEZ F. , MUÑOZ C.
Published: November 2004

We give the complete twisted Yukawa couplings for all the Zn orbifold constructions in the most general case, i.e. when orbifold deformations are considered. This includes a certain number of tasks. Namely, determination of the allowed couplings, calculation of the explicit dependence of the Yukawa couplings values on the moduli expectation values (i.e. the parameters determining the size and shape of the compactified space), etc. The final expressions are completely explicit, which allows a counting of the different Yukawa couplings for each orbifold (with and without deformations). This knowledge is crucial to determine the phenomenological viability of the different schemes, since it is directly related to the fermion mass hierarchy. Other facts concerning the phenomenological profile of Zn orbifolds are also discussed, e.g. the existence of nondiagonal entries in the fermion mass matrices, which is related to a nontrivial structure of the Kobayashi-Maskawa matrix. Some theoretical results are also given, e.g. the non-participation of (1,2) moduli in twisted Yukawa couplings. Likewise, (1,1) moduli associated with fixed tori which are involved in the Yukawa coupling, do not affect the value of the coupling. We discuss the relevance of these facts for the supersymmetry breaking process.
TOPOLOGICAL GAUGE THEORIES FROM SUPERSYMMETRIC QUANTUM MECHANICS ON SPACES OF CONNECTIONS
Authors: BLAU MATTHIAS , THOMPSON GEORGE
Published: November 2004

We rederive the recently introduced N=2 topological gauge theories, representing the Euler characteristic of moduli spaces ℳ of connections, from supersymmetric quantum mechanics on the infinite-dimensional spaces [Formula: see text] of gauge orbits. To that end we discuss variants of ordinary supersymmetric quantum mechanics which have meaningful extensions to infinite-dimensional target spaces, and introduce supersymmetric quantum mechanics actions modeling the Riemannian geometry of submersions and embeddings, relevant to the projections [Formula: see text] and inclusions [Formula: see text] respectively. We explain the relation between Donaldson theory and the gauge theory of flat connections in three dimensions and illustrate the general construction by other two- and four-dimensional examples.
SPATIAL SYMMETRY, LOCAL INTEGRABILITY AND TETRAHEDRON EQUATIONS IN THE BAXTER-BAZHANOV MODEL
Authors: KASHAEV R.M. , MANGAZEEV V.V. , STROGANOV YU. G.
Published: November 2004

We show that the Baxter-Bazhanov model is invariant under the action of the cube’s symmetry group. The three-dimensional star-star relations, proposed by Baxter and Bazhanov as local integrability conditions, correspond to a particular transformation from this group. Invariant Boltzmann weights, parametrized in terms of the Zamolodchikov angle variables, apparently satisfy the tetrahedron equations.
PROTON SPIN WITHIN NONPERTURBATIVE QCD
Authors: DOROKHOV A.E. , KOCHELEV N.I. , ZUBOV YU. A.
Published: November 2004

A review of various approaches to the problem of the proton spin is presented. Arguments are given in favor of the idea that the answer to the “spin crisis” is to be found in fundamental nonperturbative properties of the QCD vacuum.
GROUND STATE CHARGE OF FERMION SOLITON SYSTEM IN 1+1 AND 3+1 DIMENSIONS
Authors: RAVENDRANADHAN M. , SABIR M.
Published: November 2004

Ground state charge of some fermion soliton system without C-invariance is calculated in 1+1 and 3+1 dimensions by a combination of adiabatic method and spectral flow analysis. Induced charge is calculated by evolving adiabatically the fields from a vacuum having a background field which has a zero energy state and spectral symmetry. The spectral flow is calculated by an analysis of the bound state spectrum. In 1+1 dimension our calculations are in agreement with the results already found in the literature. In 3+1 dimension we study the interaction of fermions with monopoles and dyons. In the case of monopoles, even though there is spectral asymmetry, ground state charge is found to be ±1/2. It is shown that ground state charge gets contribution only from the lowest angular momentum states and is discontinuous at the fermion mass.
COMMUTING QUANTITIES AND EXCEPTIONAL W ALGEBRAS
Authors: FREEMAN M.D. , HORNFECK K. , WEST P.
Published: November 2004

Sets of commuting charges constructed from the current of a U(1) Kac-Moody algebra are found. There exists a set Sn of such charges for each positive integer n>1; the corresponding value of the central charge in the Feigin-Fuchs realization of the stress tensor is c=13−6n−6/n. The charges in each series can be written in terms of the generators of an exceptional W algebra.
QUANTIZING SL(N) SOLITONS AND THE HECKE ALGEBRA
Authors: HOLLOWOOD TIMOTHY
Published: November 2004

The problem of quantizing a class of two-dimensional integrable quantum field theories is considered. The classical equations of the theory are the complex sl(n) affine Toda equations which admit soliton solutions with real masses. The classical scattering theory of the solitons is developed using Hirota’s solution techniques. A form for the soliton S matrix is proposed based on the constraints of S matrix theory, integrability and the requirement that the semiclassical limit is consistent with the semiclassical WKB quantization of the classical scattering theory. The proposed S matrix is an intertwiner of the quantum group associated to sl(n), where the deformation parameter is a function of the coupling constant. It is further shown that the S matrix describes a nonunitary theory, which reflects the fact that the classical Hamiltonian is complex. The spectrum of the theory is found to consist of the basic solitons, excited (or ‘breathing’) solitons, scalar states (or breathers) and solitons transforming in nonfundamental representations. For some region of coupling constant space only the original solitons are in the spectrum and so the S matrix is complete, in addition arguments are presented which indicate that in a more restricted region the theory is actually unitary. It is also noted that the construction of the S matrix is valid for any representation of the Hecke algebra, allowing the definition of restricted S matrices, which lie in the unitary and complete region.
WRONG-SIGN MUONS IN NEUTRINO(ANTINEUTRINO)-NUCLEON COLLISIONS
Authors: CHOBAN E.A. , ONIPCHUK A.B.
Published: November 2004

The contribution of the quasi-parton mechanism (a model of [Formula: see text] creation phenomenologically including nonperturbative effects) to the wrong-sign-muon production in the (anti)neutrino-nucleon scattering is calculated and compared with experimental data. The comparison shows that this contribution may be significant, and thus the wrong-sign-muon production could be used as the means of investigating the quasi-parton mechanism in the weak neutral-current interaction.
FROM INTEGRABILITY TO CONFORMAL SYMMETRY: BOSONIC SUPERCONFORMAL TODA THEORIES
Authors: HOU BO-YU , CHAO LIU
Published: November 2004

In this paper we study the conformal integrable models obtained from conformal reductions of WZNW theory associated with second order constraints. These models are called bosonic superconformal Toda models due to their conformal spectra and their resemblance to the usual Toda theories. From the reduction procedure we get the equations of motion and the linearlized Lax equations in a generic Z gradation of the underlying Lie algebra. Then, in the special case of principal gradation, we derive the classical r matrix, fundamental Poisson relation, exchange algebra of chiral operators and find out the classical vertex operators. The result shows that our model is very similar to the ordinary Toda theories in that one can obtain various conformal properties of the model from its integrability.
ALL SYMMETRIES OF NONEINSTEINIAN GRAVITY IN d=2
Authors: STROBL THOMAS
Published: November 2004

The covariant form of the field equations for two-dimensional R2-gravity with torsion as well as its Hamiltonian formulation are shown to suggest the choice of the light-cone gauge. Further a one-to-one correspondence between the Hamiltonian gauge symmetries and the diffeomorphisms and local Lorentz transformations is established, thus proving that there are no hidden local symmetries responsible for the complete integrability of the model. Finally the constraint algebra is shown to have no quantum anomalies so that Dirac’s quantization should be applicable.
STAR-SQUARE AND TETRAHEDRON EQUATIONS IN THE BAXTER-BAZHANOV MODEL
Authors: KASHAEV R.M. , MANGAZEEV V.V. , STROGANOV YU. G.
Published: November 2004

Spatially symmetrical Baxter-Bazhanov model’s Boltzmann weights are proved to satisfy the tetrahedron equation. The latter is a consequence of the “inversion” and “star-square” relations for the Boltzmann weight elementary building blocks.
SUPERSYMMETRIC QUANTUM MECHANICS APPLIED TO NONRELATIVISTIC QUARK MODELS
Authors: GAVIN E.J.O. , FIEDELDEY H. , LEEB H. , SOFIANOS S.A.
Published: November 2004

We examine the effect of changing the energy levels and normalization constants of bound states corresponding to baryons and mesons in nonrelativistic quark models. We do this by applying the transformations of supersymmetric quantum mechanics (SUSYQM) to the potentials used in these models. In particular, we fit the spectra and leptonic decay widths of [Formula: see text] and [Formula: see text] mesons by modifying several existing [Formula: see text] potentials by means of supersymmetric transformations. It is found that the potentials are unchanged beyond 2 fm, and that fitting the widths induces greater oscillations in the potentials than those generated by adjusting the energy levels only. Transformations of SUSYQM are applied to the hypercentral potential in order to accommodate the Roper resonance in the s-wave nucleon spectrum. The quark-quark potential found by inverting the transformed hypercentral potential via a new exact Abel transform differs significantly from the original potential up to 5 fm from the origin and violates the concavity requirement. The [Formula: see text] potential related to this potential by Lipkin’s rule does not reproduce the meson spectrum. As the Hall-Post lower bound is also accurate for baryons, the results of the application of supersymmetric transformations in this approximation scheme are also considered and compared to the upper bound of the hypercentral approximation.
QUANTUM AFFINE SYMMETRY IN VERTEX MODELS
Authors: IDZUMI MAKOTO , TOKIHIRO TETSUJI , IOHARA KENJI , JIMBO MICHIO , MIWA TETSUJI , NAKASHIMA TOSHIKI
Published: November 2004

We study the higher spin analogs of the six-vertex model on the basis of its symmetry under the quantum affine algebra [Formula: see text]. Using the method developed recently for the XXZ spin chain, we formulate the space of states, transfer matrix, vacuum, creation/ annihilation operators of particles, and local operators, purely in the language of representation theory. We find that, regardless of the level of the representation involved, the particles have spin 1/2, and that the n-particle space has an RSOS type structure rather than a simple tensor product of the one-particle space. This agrees with the picture proposed earlier by Reshetikhin.
PATH INTEGRATION IN RELATIVISTIC QUANTUM MECHANICS
Authors: REDMOUNT IAN H. , SUEN WAI-MO
Published: November 2004

The simple physics of a free particle reveals important features of the path-integral formulation of relativistic quantum theories. The exact quantum-mechanical propagator is calculated here for a particle described by the simple relativistic action proportional to its proper time. This propagator is nonvanishing outside the light cone, implying that spacelike trajectories must be included in the path integral. The propagator matches the WKB approximation to the corresponding configuration-space path integral far from the light cone; outside the light cone that approximation consists of the contribution from a single spacelike geodesic. This propagator also has the unusual property that its short-time limit does not coincide with the WKB approximation, making the construction of a concrete skeletonized version of the path integral more complicated than in nonrelativistic theory.
ONE-LOOP QUANTUM GRAVITY ON DE SITTER SPACE
Authors: VASSILEVICH D.V.
Published: November 2004

We demonstrate that being formulated properly all the approaches to de Sitter quantum gravity give the same one-loop path integral as was obtained by Taylor and Veneziano in a framework of the gauge fixed procedure.
AN INTRODUCTION TO NONCOMMUTATIVE DIFFERENTIAL GEOMETRY ON QUANTUM GROUPS
Authors: ASCHIERI PAOLO , CASTELLANI LEONARDO
Published: November 2004

We give a pedagogical introduction to the differential calculus on quantum groups by stressing at all stages the connection with the classical case (q→1 limit). The Lie derivative and the contraction operator on forms and tensor fields are found. A new, explicit form of the Cartan-Maurer equations is presented. The example of a bicovariant differential calculus on the quantum group GL q(2) is given in detail. The softening of a quantum group is considered, and we introduce q curvatures satisfying q Bianchi identities, a basic ingredient for the construction of q gravity and q gauge theories.
DYNKIN TBA’S
Authors: RAVANINI F. , VALLERIANI A. , TATEO R.
Published: November 2004

We prove a useful identity valid for all ADE minimal S-matrices, that clarifies the transformation of the relative thermodynamic Bethe Ansatz (TBA) from its standard form into the universal one proposed by Al. B. Zamolodchikov. By considering the graph encoding of the system of functional equations for the exponentials of the pseudo-energies, we show that any such system having the same form as those for the ADE TBA’s, can be encoded 011 A, D, E, A/Z2 only. This includes, besides the known ADE diagonal scattering, the set of all SU(2) related magnonic TBA’s. We explore this class systematically and find some interesting new massive and massless RG flows. The generalization to classes related to higher rank algebras is briefly presented and an intriguing relation with level-rank duality is signalled.
NEW SET OF FINITE AND ASYMPTOTICALLY FINITE GUTS
Authors: SHAPIRO I.L. , YAGUNOV E.G.
Published: November 2004

New set of one-loop finite GUT models is constructed. In particular there are some SU (N), N=5, 7, 9…models with two Higgs multiplets. The stability of finite solutions in UV and IR limits is investigated. The asymptotical behavior of the effective Yukawa and scalar couplings verify the asymptotical finiteness of the models. The renormalization group equations in curved space-time are also considered.
LOW-ENERGY CURRENT ALGEBRA APPROACH AT THE QUARK LEVEL
Authors: IVANOV A. N. , TROITSKAYA N. I. , NAGY M.
Published: November 2004

The low-energy theorem, derived by Terent'ev within the framework of current algebra, is proved at the quark level within the framework of the Extended Nambu–Jona-Lasinio model. The proposed method allows to evaluate a vacuum expectation value of any time-ordered product of QCD-hadronic currents in terms of constituent-quark loops and low-lying meson exchanges.
ANALYTIC EVALUATION OF LANDSHOFF TYPE INTEGRALS FOR AXIAL GAUGES
Authors: MILGRAM MICHAEL
Published: November 2004

It is demonstrated that it is possible to expand Feynman Integrals in axial gauges to arbitrary orders in a small mass-like parameter, and in so doing, replace ad hoc prescriptions by the limit of a gauge-fixing term imposed within the Lagrangian. Both the Landshoff and Principle Value prescriptions are related to the canonical form of the integrals and the expansions associated with them, and the values for a subset of the Landshoff Integrals are tabulated to second order in the mass-like parameter. The expansion technique relies 011 the method of Analytic Regularization, which includes Dimensional Regularization as one of a number of limiting cases.
MARINARI–PARISI AND SUPERSYMMETRIC COLLECTIVE FIELD THEORY
Authors: RODRIGUES JOÃO P. , VAN TONDER ANDRÉ J.
Published: November 2004

A field theoretic formulation of the Marinari–Parisi supersymmetric matrix model is established and shown to be equivalent to a recently proposed supersymmetrization of the bosonic collective string field theory. It also corresponds to a continuum description of super-Calogero models. The perturbation theory of the model is developed and, in this approach, an infinite sequence of vertices is generated. A class of potentials is identified for which the spectrum is that of a massless boson and Majorana fermion. For the harmonic oscillator case, the cubic vertices are obtained in an oscillator basis. For a rather general class of potentials it is argued that one cannot generate from Marinari–Parisi models a continuum limit similar to that of the d = 1 bosonic string.
NONLINEAR QUANTUM MECHANICS WITH NONCLASSICAL GRAVITATIONAL SELF-INTERACTION II: NONSTATIONARY SITUATION
Authors: POPOVA A. D. , PETROV A. N.
Published: November 2004

Quantum mechanics (first quantization) with self-consistent gravitational interaction, previously constructed for the stationary case, is extended to the general case. The two requirements for such a theory are realized: to obtain the theory maximally resembling a classical field theory and to achieve the invariance of the theory under the rescaling transformations of a wave function. The construction is not trivial, because it rejects the variational principles of extremality of any action and involves some principles of smoothed extremality which give relevant equations.
SPIN–STATISTICS THEOREMS WITHOUT RELATIVITY OR FIELD THEORY
Authors: BALACHANDRAN A. P. , DAUGHTON A. , GU Z.-C. , SORKIN R. D. , MARMO G. , SRIVASTAVA A. M.
Published: November 2004

Conventional proofs of the spin–statistics theorem either use relativistic quantum field theory or concern field theory solitons. We here construct new proofs of this theorem for spinning particles. They are extensions of previous work on spinless particles and require neither relativity nor field theory. They do, however, assume certain continuity conditions involving the existence of antiparticles. Non-Abelian statistics, such as parastatistics and braid statistics of order 2 or more, are excluded in our framework.
PHYSICAL NONLINEAR ASPECTS OF CLASSICAL AND QUANTUM q-OSCILLATORS
Authors: MAN'KO V. I. , MARMO G. , SOLIMENO S. , ZACCARIA F.
Published: November 2004

The classical limit of quantum q-oscillators suggests an interpretation of the deformation as a way to introduce nonlinearity. Guided by this idea, we considered q fields, the partition function, and compute a consequence on the specific heat and second order correlation function of the q-oscillator which may serve for experimental checks for the nonlinearity.
SPINORS, THE DIRAC FORMALISM AND CORRECT COMPLEX CONJUGATION
Authors: BASRI SAUL A. , BARUT A.O.
Published: November 2004

It is pointed out that in the Dirac formalism ψ†γ0ψ is not a correct spinorial expression and should be replaced by [Formula: see text] where C0 is a Lorentz-invariant quantity with different spinorial indices than γ0. Although [Formula: see text] has the same matrix value as γ0 in flat space-time, the two quantities are different in curved space-time. However, γ0 retains its role as the time component of a 4-vector, and as a factor in the parity and time reversal states.
POISSON BRACKETS ON PRESYMPLECTIC MANIFOLDS
Authors: DUBROVIN B.A. , GIORDANO M. , MARMO G. , SIMONI A.
Published: November 2004

The problem of defining Poisson brackets for a degenerate Lagrangian without introduction of canonical variables is discussed. More generally, we introduce and give a complete geometrical description of a class of Poisson brackets on a presymplectic manifold. The construction is illustrated by both finite-dimensional and field-theoretic examples.
BOSONIC SUPERCONFORMAL AFFINE TODA THEORY: EXCHANGE ALGEBRA AND DRESSING SYMMETRY
Authors: CHAO LIU , HOU BO-YU
Published: November 2004

We propose and investigate a new conformal invariant integrable field theory called bosonic superconformal affine Toda theory. This theory can be viewed either as the affine generalization of the so-called bosonic superconformal Toda theory studied by the authors sometime earlier, or as the generalization to the case of half-integer conformal weights of the conformal affine Toda theory, and can also be obtained from the Hamiltonian reduction of WZNW theory (with an affine WZNW group). The fundamental Poisson stracture is established in terms of the classical r matrix. Then the exchange algebra for the chiral vectors is obtained as well as the reconstruction formula for the classical solutions. The dressing transformations of the fundamental fields are found explicitly, and the Poisson-Lie structure of the dressing group is also constructed with the aid of classical exchange algebras, which turns out to be the semiclassical limit of the quantum affine group. The conformal breaking orbit of the model is also studied, which is called bosonic super loop Toda theory in the context. In addition, the quantum exchange relation and quantum group symmetry are discussed briefly.
THE RENORMALIZATION GROUP FLOW IN 2D N=2 SUSY LANDAU-GINSBURG MODELS
Authors: BIEŃKOWSKA JADWIGA
Published: November 2004

We investigate the renormalization of N=2 SUSY Landau-Ginsburg models with central charge c=3p/(2+p) perturbed by an almost marginal chiral operator. We calculate the renormalization of the chiral fields up to the gg* order and of the nonchiral fields up to the g(g*) order. We propose a formulation of the nonrenormalization theorem and show that it holds in the lowest nontrivial order. It turns out that, in this approximation, the chiral fields cannot get renormalized: [Formula: see text]. The β function then remains unchanged: β=∈g.
DETECTION OF SUSY HIGGS BOSONS AFTER RADIATIVE CORRECTIONS
Authors: CRUZ J.L. DIAZ , SAMPAYO O.A.
Published: November 2004

We study the detection of the Higgs bosons predicted in the minimal SUSY standard model (h0, H0, A0 and H±). We find that after radiative corrections are considered, there is a region of parameter space where h0 will be out of the LEP reach. Some portion of this region can be covered at hadron colliders using the mechanism of associated production [Formula: see text], with h0→γγ. Other decays that may help to detect the neutral Higgses (produced either inclusively or in association with [Formula: see text]) are H→ZZ*, W+W−/ZZ, A0→Z+H0. We find that H± may be detected also through the decays H±→W±h0 and the associated production of H± with [Formula: see text].
DYSON-SCHWINGER EQUATIONS IN TERMS OF RANDOM WALKS: FOUR-FERMION INTERACTIONS
Authors: JAROSZEWICZ T. , KURZEPA P.S.
Published: November 2004

Quantum field theories of interacting fermions have been recently formulated in terms of directed random walks. Using this formulation, we derive a hierarchy of equations for the correlation functions of scalar N-component four-fermion theories. These follow from an analysis of the underlying random process, and from geometric considerations. Our equations are, as we show, equivalent to the standard Dyson-Schwinger equations of motion, and are a convenient starting point for nonperturbative investigations of four-fermion theories. In particular, we discuss the physical interpretation of the gap equation in the language of random walks, and show that, in both the N→0 and N→∞ limits, an interacting theory can be obtained only for a finely tuned negative bare coupling constant.
φ2k OSCILLATOR IN THE STRONG COUPLING LIMIT
Authors: KORSUN L.D. , SISSAKIAN A.N. , SOLOVTSOV I.L.
Published: November 2004

A nonperturbative method for calculating functional integrals is proposed. Only Gaussian quadratures and only those types of diagrams which occur in the standard perturbation theory are used for the formulation of this method. The proposed approach is used for the consideration of the φ2k anharmonic oscillator in the strong coupling limit.
CONFORMALLY INVARIANT LAGRANGIANS IN METRIC-AFFINE AND RIEMANN-CARTAN SPACES
Authors: ZHYTNIKOV V.V.
Published: November 2004

Various types of generalized conformal transformations in non-Riemannian manifolds and corresponding transformation properties of the geometrical objects are reviewed. Possible structures of conformally invariant gravity and matter Lagrangians in arbitrary space dimensions are discussed. New electrovac exact solutions of R+R2+Q2 gravity with conformally flat Bertotti-Robinson metric and nonzero torsion have been found.
QUANTUM ANYON-LIKE SYSTEMS WITH TOPOLOGICAL CHARGES ON U(1) BUNDLES
Authors: IVANOV O.M. , SAVINKOV A.G.
Published: November 2004

We investigate some classes of locally Hamiltonian systems. To formulate a global Hamiltonian formalism a nontrivial principal U(1) bundle over a multi-particle dynamical space is constructed. Lift of dynamics to the total space is considered for the models. Absence of a transposition operator lifting to the bundle space forces us to review a statistics theme from a new standpoint. A topological invariant to characterize system properties is generalized by using geometrical methods and the anyon analogy.
THE LOW-TEMPERATURE SPECIFIC HEAT OF U(Pt, Pd)3
Authors: VAN DER MEULEN H. P. , FRANSE J. J. M. , DE VISSER A.
Published: November 2004

Specific-heat measurements on single-crystalline samples of U ( Pt 1− x Pd x )3 ( x = 0.00, 0.05 and 0.10) reveal anomalously large values for c/T at low temperatures. The data for UPt 3 have previously been analyzed by making use of the enhanced value of the low-temperature Grüneisen parameter. By this analysis, the heavy-electron contribution to the specific heat has been separated from the normal part that is largely due to the phonon term. Taking this latter term to be the same for all three compounds, the heavy-electron contribution has been evaluated for temperatures below 20 K. This contribution is compared with a spin-1/2 Kondo-type of specific heat. The resulting curves for the x = 0.00 and x = 0.10 alloys are very similar and mainly differ in the temperature at which the maximum is found. The effect of an applied magnetic field within the hexagonal plane, however, shifts the maximum to lower temperatures for x = 0.00 whereas for x = 0.10 a shift towards higher temperatures is found.
UNCONVENTIONAL SUPERCONDUCTIVITY IN UPt3: FREQUENCY DEPENDENT AC SUSCEPTIBILITY
Authors: KOZIOL Z. , FRANSE J. J. M. , MENOVSKY A. A.
Published: November 2004

A method has been developed for measuring and analysing the complex ac susceptibility of a metal undergoing a superconducting transition, in case there exists an interplay between the normal-state skin-effect and the response characteristic for the superconducting state. For the unconventional superconductor UPt 3, the study of the temperature and frequency dependence of the complex conductivity close to T c has resulted in predictions for the surface resistance and the radio-frequency susceptibility which are in a good qualitative agreement with published experimental results.
TRANSFORMATION OF THE U GROUND STATE IN UXTh1−XBe13 (1 > X > 0.07) COMPOUNDS
Authors: ALIEV F. G. , ANDREEV A. V. , GRISHCHENKO I. V. , MOSHCHALKOV V. V. , VILLAR R. , VIEIRA S.
Published: November 2004

A study of the low temperature heat capacity and Hall effect of U x Th 1− x Be 13 (1 > x > 0.07) compounds shows the transition from the "quasi" Kondo heavy fermion ground state in UBe 13 to the spin-fluctuating one for x < 0.9. The character of the temperature dependence of the electron term in the heat capacity for U 0.9 Th 0.1 Be 13 and U 0.64 Th 0.36 Be 13 indicates the possibility of a weak magnetic transition below 1K.
ANISOTROPIC MAGNETIC BEHAVIOR IN UPd2Al3
Authors: GRAUEL A. , BÖHM A. , KÖHLER R. , MODLER R. , GEIBEL C. , SATO N. , KOMATSUBARA T. , WEBER G. , STEGLICH F.
Published: November 2004

The magnetic phase diagram of the antiferromagnetically ordered heavy-fermion superconductor UPd 2 Al 3( T N = 14K , T c = 2K ) is highly anisotropic. Three different magnetic phases are only observed for magnetic fields applied in the easy basal plane of the hexagonal PrNi 2 Al 3 structure ( B ⊥ c ). For B || c , only one transition at the Néel temperature T N is found. A tetravalent ( 5f 2) uranium-configuration is inferred from a crystal-electric field analysis of the temperature dependence of the anisotropic paramagnetic susceptibility.
MAGNETIC PROPERTIES OF A SUPERCONDUCTOR WITH A TRICRITICAL POINT (UPt3)
Authors: FOMIN I. A.
Published: November 2004

Available experimental data indicate the existence of a tricritical point (tcp) on the line of transition of UPt3 into the superconducting state in the temperature-pressure plane. In particular, at normal pressure the transition has to be of the first order. The analysis of a phase diagram of a superconductor with the tcp in the temperature-magnetic field coordinates is presented here. The diagram does not conform either with the usual behavior of type I nor type II superconductors. The lines Hcm(T) and Hc2(T) intersect at a finite field. The line Hc1(T) branches from Hcm(T) at a finite field too. This diagram can be brought into agreement with that observed for UPt3. Both the existence of a tcp and the related magnetic properties are not accounted for by the weak coupling BCS theory.
THERMAL CONDUCTIVITY OF LAYERED SUPERCONDUCTORS
Authors: JIANG C. , CARBOTTE J. P.
Published: November 2004

We present results for the electronic thermal conductivity in the superconducting state for a layered structure. The electrons are assumed to be free in the xy plane with a hopping probability from plane to plane. Eliashberg theory adapted to this geometry. with full account of the corresponding anisotropy, is used to evaluate the thermal conductivity. It is found that anisotropy can profoundly affect its temperature dependence particularly at low temperature.
THEORETICAL AND EXPERIMENTAL EVIDENCES FOR A STRONG ELECTRON-PHONON COUPLING IN HIGH-Tc OXIDES
Authors: ZEYHER ROLAND
Published: November 2004

The present status of superconductivity-induced lattice properties and electron-phonon effects in electronic properties is discussed. It is argued that most of the experimental data can be understood if the dimensionless electron-phonon coupling constant λ is between 1 and 3 and the corresponding transport constant around λtr 1. An analysis of the temperature dependence of the heat conductivity based on the screened ionic model reveals that both the observed maximum below Tc as well as the change in slope at Tc are compatible with a strong electron-phonon coupling in contrast to previous conclusions. It is also pointed out that the presently available resistivity data in stochiometric high-Tc oxides can be understood as phonon-limited resistivities and yield no compelling evidence for exotic scattering mechanisms.
TUNNELLING SPECTROSCOPY OF HIGH-TC SUPERCONDUCTORS
Authors: BECHERER TH. , KOWALEWSKI J. , WOLF TH. , HUTH M. , ASSMUS W. , ADRIAN H.
Published: November 2004

Break junction tunnelling measurements were performed on YBa 2 Cu 3 O 7– and Bi 2 Sr 2 CaCu 2 O 8–single crystals and on polycrystalline ( Bi , Pb )2 Sr 2 Ca 2 Cu 3 O 10–samples. In the case of Bi 2 Sr 2 CaCu 2 O 8 the superconducting gap as evaluated from the peak-to-peak distance is Δab = (21.2 ± 2.8) meV , i.e. 2∆ab/kBTc = (5.5 ± 0.8). The differential conductance curves are similar to those of conventional strong coupling superconductors but with a much larger smearing, that cannot be explained with any of the theoretical models proposed so far. The measurements on YBa 2 Cu 3 O 7 show a strong linear background in the conductance. After subtraction of the background, peaks are discernible at ±21 meV, which yields 2∆ab/kBTc ≈ 2.8 if SIS tunnelling is assumed. The conductance curves of the ( Bi , Pb )2 Sr 2 Ca 2 Cu 3 O 10–polycrystals are dominated by the appearance of sharp minima below the superconducting transition temperature. The temperature dependence of these minima can be fitted well by the BCS behaviour.
DECOUPLING AND FLUX-LINE-DYNAMICS IN YBa2Cu3O7/PrBa2Cu3O7-SUPERLATTICES
Authors: JAKOB G. , HAHN T. , STÖLZEL C. , TOMÉ-ROSA C. , KLUGE T. , ADRIAN H.
Published: November 2004

We prepared YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7 superconductor/insulator-supetlattices of high quality and with high T c-values. Structural investigations show that even the best samples are not ideal in structure. The flux-line dynamics in this superlattices was found to be different from that of bulk YBa 2 Cu 3 O 7 and we discuss the different models for the flux-line-structure.
ELASTIC PROPERTIES OF STRAINED FCC AND HCP IRON
Authors: KRAFT T. , METHFESSEL M. , VAN SCHILFGAARDE M. , SCHEFFLER M.
Published: November 2004

Using the full-potential linear muffin-tin orbital method within the local spin-density approximation we analyse the influence of the nearest neighbour distance on fcc(111) or hcp(0001) iron layers. The LDA-LSDA error in describing ferromagnetic phases is determined to be at least 15 mRy/atom. As a consequence of this error, our calculations favour paramagnetic ground states. In this sense, the reported results have some model character. However, our analysis of the elastic energy cost under distortions should hold for transition metals in general. Allowing relaxations of the interplanar distance the fcc phase can become energetically favourable over the hcp phase at large lattice mismatches. The main reason for this behaviour is the enhanced stiffness of the hcp interplanar bonds due to the shortening of the axial c/a ratio.
ANNULAR EFFECT AND OTHER PATTERNS OF CURRENT DISTRIBUTION IN POINT CONTACTS
Authors: LYSYKH A. A. , ZASETSKY G. V. , BAGATSKY V. M. , YANSON I. K.
Published: November 2004

The experiments with point-contacts, containing type-II superconductors, gave possibility to study the conditions with different current density distributions in contact cross-section. The current density is constant over the cross-section of pure contacts with the ballistic electron transport: d < < li, where d is the contact diameter, li is the impurity (elastic) mean free path of electrons. A uniform current flow also occurs in contacts between pure electrodes separated with a thin layer of a metal (t < < d) having high resistivity.

In dirty contacts (d > > li) an annular effect is observed: the current density is low in the centre and the highest at the contact section periphery. The relative width of the annulus of the flowing current is proportional to li/d.

In contacts between two type-II superconductors in the zero external magnetic field, the current first flows over an annulus, whose width increases with the current. In the critical state preceding the superconductivity destruction in the contact, the current density reaches its highest value in the center and decreases towards the periphery as r−1/2.
OBSERVATION OF THE EXPONENTIAL TEMPERATURE DEPENDENCE OF THE TUNGSTEN SINGLE CRYSTAL MAGNETORESISTIVITY (PEIERLS' EXPONENT)
Authors: MARCHENKOV V. V. , CHEREPANOV A. N. , STARTSEV V. E.
Published: November 2004

The transverse magnetoresistivity of ultrapure tungsten single crystals in Corbino disk form was measured in the temperature interval 4.2–50 K in magnetic fields up to 14 T. The exponential temperature dependence of the electroconductivity, predicted by Peierls and caused by the intersheet electron-phonon Umklapp processes, is discovered in the magnetoconductivity. When the intersheet Umklapp processes are "frozen-out" the temperature dependence of the magnetoconductivity is a power function.
EXPERIMENTAL CONDUCTION ELECTRON SPIN-SPLITTING FACTORS IN MOLYBDENUM AND OSMIUM
Authors: OSTAPIAK O. Z. , PERZ J. M. , PLUZHNIKOV V. , STARTSEV V. E.
Published: November 2004

Conduction electron spin-splitting factors have been determined from spin-zeros in quantum oscillations in magnetostriction arising from orbits on the lenses in Mo, and from harmonic ratios of oscillations due to the zone 7 ellipsoids in Os. The Mo results are in qualitative disagreement with results of LMTO calculations; a possible explanation of the failure of the theory is proposed. The Os results are in good agreement with theoretical calculations of g factors and exchange-correlation enhancement.
FIRST-PRINCIPLES APPROACH TO ALLOY PHASE STABILITY
Authors: TURCHI P. E. A. , REINHARD L. T. , SLUITER M.
Published: November 2004

Order-disorder phenomena and structural transformations in substitutional alloys are studied with a proper combination of quantum mechanics and statistical thermodynamics. The methodology is briefly presented and its predictive capabilities are illustrated for various alloys, including the bcc-based Ti-V, Ti-Fe and Cr-Fe systems, in terms of electronic structure, ground-state and short-range order diffuse scattering properties, and finally phase diagram results.
ELECTRONIC STRUCTURE OF TRANSITION METAL COMPOUNDS
Authors: HÜFNER S.
Published: November 2004

The basic features of the electronic structure of transition metal oxides is discussed. It is found that the bands of the anions are well understood whereas the exact nature of the d-bands is still uncertain. There is a competition between local excitonic like excitations and excitations which reflect with some renormalization the band structure. The nature of gap states in NiO is discussed.
THERMOPOWER AND ELECTRICAL RESISTIVITY OF LaxY1−xAl2 ALLOYS
Authors: BURKOV A. T. , BAUER E. , GRATZ E. , RESEL R.
Published: November 2004

The electronic transport theory predicts linear temperature dependences for the thermopower (S) and the electrical resistivity (ρ) at elevated temperatures. However, the experimental data for La x Y 1− x Al 2 alloys reveal nonlinear dependences for both, S(T) and ρ (T) . We relate this disagreement to the density of states (DOS) structure in the vicinity of the Fermi level. Based on the linearised Boltzmann transport equation, we obtain from the experimental temperature dependences of ρ and S an electron dependent function ϕ(ε), reflecting the energy dependence of DOS and that of scattering processes. In the scope of Mott's s-d model the 1/ϕ(ε) function is proportional to the DOS near the Fermi level. A comparison of the 1/ϕ(ε) function with available band structure calculations shows good agreement for YAl 2 and LaAl 2. In the case of alloys, the structure of DOS may cause a temperature dependence of the impurity contribution to the resistivity but has only a minor effect on S(T) at evelated temperatures.
DETERMINATION OF SPIN STRUCTURES OF MAGNETIC MULTILAYERS BY POLARIZED NEUTRON REFLECTOMETRY
Authors: LOEWENHAUPT M. , HAHN W. , HUANG Y. Y. , FELCHER G. P. , PARKIN S. S. P.
Published: November 2004

The capabilities of spin–dependent reflectivity measurements with neutrons to determine the spatial arrangement of magnetic moments in magnetic multilayers are illustrated with two examples, Fe/Cr and Fe/Gd multilayers. The spin structure of sputtered films of [Fe30Å/Cr10Å]x30 was observed in the virgin state and after annealing in different conditions; the results were correlated to the progressive decrease of the magnetoresistivity. [Fe35Å/Gd50Å]x15 multilayers, with their antiparallel magnetization, show at low temperature evidence of a magnetic phase transition which is surface induced.
EXCHANGE COUPLING IN Fe/Pd/Fe TRILAYERS
Authors: NAIT-LAZIZ H. , BOUARAB S. , DEMANGEAT C. , MOKRANI A. , DREYSSE H.
Published: November 2004

The exchange coupling in Fe/Pd/Fe trilayers is investigated through self-consistent real-space description of the Hubbard Hamiltonian. For both ferromagnetic (F) and antiferromagnetic (AF) couplings between Fe layers, the Pd layers are shown to be polarized. However, the AF coupling between Fe layers reduces strongly the Pd polarization displayed in the case of F coupling. Also, the magnetic moments of the Fe atoms at the Fe/Pd interface are smaller in the AF coupling as compared to the F one. Up to five layers of Pd, the F coupling is found stable. For 6 layers of Pd, the AF coupling becomes more stable. This result compares qualitatively with the experiment of Celinski and Heinrich, but the number of layers neccessary to move from F to AF is smaller than that reported experimentally. The quantitative disagreement may be related to the relaxation at the interface, surface roughness or/and interdiffusion which are not considered in this study.
AB-INITIO BAND STRUCTURE CALCULATION FOR MAGNETIC MULTILAYERS
Authors: STICHT J. , HERMAN F. , KÜBLER J.
Published: November 2004

The magnetic properties of magnetic multilayers are studied using first principles total energy calculations. In this paper we present our results for bcc Fe multilayers with a (001) stacking direction. Using Nb as a spacer material we find an oscillating exchange coupling with a period of about 4.6 Å( ≈3 Nb monolayers). A detailed study of the magetic moments in the Nb spacer is given. Furthermore we discuss the dependence of the exchange coupling strength as a function of the thickness of the Fe slabs.
CONTINUOUS REORIENTATION TRANSITION OF THE MAGNETIZATION IN THIN FERROMAGNETIC FILMS
Authors: JENSEN P. J. , BENNEMANN K. H.
Published: November 2004

The change of the direction of the magnetization of very thin magnetic films from perpendicular at low temperatures to in- plane orientation at high temperatures is investigated. This transition is driven by the competition between uniaxial lattice anisotropy, favoring a perpendicular orientation, and the magnetic dipole interaction (shape anisotropy). The strong spin correlations in this two dimensional (2D) system have to be taken into account through a renormalization procedure. A continuous rotation of the magnetization and a vanishing long range ferromagnetic order around the reorientational temperature TR were observed experimentally. We propose that this may indicate a decomposition of the ordered 2D system into spin blocks. If the directional entropy of spin blocks near TR and higher order anisotropy terms are considered, a continuous perpendicular to inplane transition may result.
MAGNETIC TRANSITION IN QUASI ONE DIMENSIONAL WIRES AND THIN FILMS OF GADOLINIUM
Authors: ALI NAUSHAD , MASDEN J. T. , HILL PEGGY , CHIN ARTHUR
Published: November 2004

Thin wires of gadolinium metal have been fabricated using a step lithographic technique with cross-sectional areas from 0.87 × 10−11 cm 2 to 58 × 10−11 cm 2. The thin films of gadolinium were deposited in a ultra high vacuum system by thermal evaporation with the thickness of films in the range 200Å to 1200Å. Resistivity data of Gd thin wires does not show evidence of bulk transition at T c ≈ 293 K (bulk) at all. However, a phase transition manifested as a sharp drop in resistivity of Gd thin wires is observed around 20 K. Thin films of Gd deposited on glass and sapphire substrates were used to measure the magnetic properties using a SQUID magnetometer. Films of thickness > 500Å show ferromagnetic transition around 290 K (close to bulk) and a small peak in the magnetization around 20 K is also observed. For Gd films of thickness ~ 200Å there is no evidence of ferromagnetic transition, however, the magnetization data clearly shows a peak in the neighborhood of 20 K. It appears that in the case of very thin films and thin wires of Gd we are observing a magnetic transition around 20 K. This transition may be due to magnetic ordering of the surface which has a transition temperature much smaller than the bulk ferromagnetic T c of 293 K.
MAGNETOOPTIC MEASUREMENTS ON Gd/Nb/Gd SANDWICHES
Authors: PASCHEN U. , SÜRGERS C. , LÖHNEYSEN H. v.
Published: November 2004

Gd/Nb/Gd layered films were grown epitaxially in UHV by electron-beam evaporation on a 500-Å-thick Nb buffer layer (substrate: sapphire [Formula: see text]). The deposition temperature was 750° C for the Nb buffer layer and 300° C for the other films. The Gd films grow in (0001) and the Nb films in (110) orientation as determined by X-ray measurements. The magnetization curves of the Gd/Nb/Gd sandwiches (with a protective 50 Å Nb layer on top) were measured with the transverse magnetooptic Kerr-effect. The coercitive field of the sandwiches oscillates as a function of the Nb thickness indicative of an interaction between the two Gd films (thickness 100 Å) through the nonmagnetic Nb interlayer. These oscillations have a period of about 11 ± 2 Å (typical of the magnetic coupling through nonmagnetic transition-metal layers) and were observed for more than three periods in the Nb thickness range from 15 to 55 Å.
NMR IN FeNi/Co FILMS WITH COUPLED LAYERS
Authors: LESNIK N. A. , GOLUB V. O.
Published: November 2004

The observation of NMR on Co 59 nuclei in vacuum evaporated FeNi/Co films using spin-echo technique at room temperature is reported. The effect of layer interaction upon the enhancement factor and the nuclear relaxation rates have been found. Both the parameters and the induced anisotropy field decreased with the Co layer thickness decreasing. The obtained results are discussed. It seems the anistropy field change to be the main source of the observed NMR parameter behaviour.
GROUND-STATE PROPERTIES OF Mn2 AND Fe2 IN THE LOCAI-SPIN-DENSITY APPROXIMATION
Authors: PIECHOTA J. , SUFFCZYŃSKI M.
Published: November 2004

Ab initio self-consistent all-electron spin-polarized calculations have been performed for the ground-state properties of the Mn 2 and Fe 2 molecules using the local-spin-density approximation. The total energy, the binding energy, the equilibrium distance, vibrational frequency, and the ground-state configuration are reported for each of these dimers. While for Fe 2 the region near equilibrium distance, r e , is characterized by full-symmetry (D∞ h ) molecular orbitals, for Mn 2 the symmetry breaking is essential: The true, "antiferromagnetic", ground state can be obtained only if reduced, C∞ v , symmetry constraints are used. These results are compared with other calculations and experimental results, where available.
SIZE CHANGES OF LATTICE PARAMETERS IN SMALL PARTICLES OF PLATINUM, PALLADIUM AND NICKEL
Authors: GAMARNIK M. Y.
Published: November 2004

The character and nature of the structural size effect in Pt, Pd and Ni are investigated experimentally and theoretically. By precise X-ray determinations a decrease of lattice parameters for Pt and an increase of those for Pd and Ni are established in highly dispersed powders. The effects are explained by an excess (intracrystalline) pressure (positive or negative) in a small particle, stipulated by electrostatic interaction between elements of crystal charge lattice.
ITINERANT MAGNETISM IN SOLIDS
Authors: MOHN P. , SCHWARZ K.
Published: November 2004

Based on the spin-density functional theory we discuss the essential mechanism of spin-split itinerant electrons which cause the formation of spin-magnetic moments in a solid. The success and the difficulties of the Stoner model of itinerant magnetism is shown for hcp Co. The FSM (fixed spin moment) method allows us to compute the total energy as a function of volume and magnetic moment, E(M, V). These energy surfaces contain the crucial information about magneto-volume instabilities and related phenomena. At finite temperatures collective phenomena such as spin fluctuations are important which can be treated with a Landau—Ginzburg formalism. Results are given for the finite temperature properties of the strongly enhanced Pauli paramagnet fcc Pd and the metamagnetic system YCo2.
FUNCTIONAL INTEGRATION AND QUANTUM MONTE CARLO IN ITINERANT MAGNETS: THE BERRY PHASE AND THE SIGN PROBLEM
Authors: SAMSON J H
Published: November 2004

Itinerant magnets are widely studied by functional integration: a stochastic field {Δi(τ)} replaces the interaction in the Heisenberg and N-band Hubbard models, giving the partition function Z=ʃD3Δexp(–NβV[{Δi(τ)}]) as an integral over a time-dependent field. A difficulty in quantum Monte Carlo simulations is that some paths contribute negative weight to the integral. We consider the contribution exp(−NβV[{Δi(τ)}]) of an arbitrary path. The path has a phase, tending to a Berry phase for smooth paths in the low-temperature narrow-band limit (where spins follow fields adiabatically), and to zero in the high-temperature limit, recovering the static approximation. Time dependence can be integrated out in simple cases, yielding an effective static Hamiltonian Veff({Δi}). The weight exp[−NβVeff({Δi})] is real but not positive-definite.