bluuebunny/crossref_metadata_2025 huggingface dataset:
THE "NAIBEA" ACCELERATOR: AN IMPROVED INVERSE FREE ELECTRON LASER
Authors: HUSSEIN M. S. , PATO M. P.
Published: November 2004

The basic principles of linearly accelerating electrons with the aid of a laser combined with a static electric or magnetic field are discussed. The NAIBEA accelerator is then detailed. Predictions are made for future developments in the field of relativistic particle accelerators.
ANALYTIC EXPRESSIONS OF CROSS SECTIONS, ASYMMETRIES AND W DENSITY MATRICES FOR e+e− → W+W− WITH GENERAL THREE-BOSON COUPLINGS
Authors: GOUNARIS G. , LAYSSAC J. , MOULTAKA G. , RENARD F. M.
Published: November 2004

We establish explicit analytic expressions for the e+e− → W+W− cross sections, asymmetries and W± spin density matrix elements in terms of the complete set of anomalous three-boson couplings. This should be useful for performing a model-independent analysis of LEP 2 or future high energy collider data. Sensitivities to the various three-boson couplings are discussed and possible ways to disentangle their effects are proposed.
CHERN–SIMONS THEORIES WITH SUPERSYMMETRIES IN THREE DIMENSIONS
Authors: NISHINO HITOSHI , GATES S. JAMES
Published: November 2004

We study various Chern–Simons (CS) theories in three dimensions with extended super-symmetries. Starting with remarks on nonsupersymmetric cases, we give (i) N = 2 non-Abelian CS theories, (ii) N = 4 non-Abelian CS theory, (iii) conformal supergravity CS theories for general N ≥ 2 up to N = ∞, (iv) CS action in terms of composite gauge fields, based on the N = 1 supersymmetric SO (n + 1)/ SO (n) σ model, (v) relationship of CS theories with higher-dimensional supersymmetric theories, especially with ten-dimensional heterotic string theory, (vi) a prototype model yielding the N = 2 CS theories, (vii) N = 8M and N = 8M − 2 extended supersymmetric Abelian CS theories, and (viii) CS theories for graded Lie groups. Some remarks on anyon models and supersymmetric Jones polynomials are also given.
THE RENORMAUZATION GROUP FOR FLAG MANIFOLDS
Authors: RANDJBAR-DAEMI S. , STRATHDEE J.
Published: November 2004

The renormalization group equations for a class of nonrelativistic quantum σ-models targeted on flag manifolds are given. These models emerge in a continuum limit of generalized Heisenberg antiferromagnets. The case of the [Formula: see text] manifold is studied in greater detail. We show that at zero temperature there is a fixed point of the RG transformations in (2 + ε) dimensions where the theory becomes relativistic. We study the linearized RG transformations in the vicinity of this fixed point and show that half of the couplings are irrelevant. We also show that at this fixed point there is an enlargement of the global isometries of the target manifold. We construct a discrete non-Abelian enlargement of this kind.
THE Z4 × Z4 ORBIFOLD MODEL AT AN ENHANCEMENT POINT AND THE 26 MODEL
Authors: KOBAYASHI TATSUO , OHTSUBO NORIYASU , TANIOKA KAZUTAKA
Published: November 2004

We construct a "shifted" Z4 × Z4 orbifold model equivalent to a twisted Z4 × Z4 orbifold model at an enhancement point. It is proved that the N = 2 algebra of the 26 model is coincident with that of the "shifted" orbifold model. The correspondence between the Z4 × Z4 orbifold model and the 26 model is investigated with respect to massless spectra and Yukawa couplings. Also studied are Yukawa couplings and some other aspects of the models away from the enhancement point.
EARLY TIME PROPERTIES OF TIME EVOLUTION IN TWO-DIMENSIONAL SUBSPACE AND CP VIOLATION PROBLEM
Authors: URBANOWSKI K.
Published: November 2004

Approximate formulae are given for the effective Hamiltonian H||(t) governing the time evolution in a subspace ℋ|| of the state space ℋ. The properties of matrix elements of H||(t) and the eigenvalue problem for H||(t) are discussed in the case of two-dimensional ℋ||. The eigenvectors of H||(t) for the short time region are found to be different from those for the long time region. The decay law of particles described by the eigenvectors of H||(t) is shown to have the form of the exponential function multiplied by some time-independent factor, equal to 1 only in the case of the [Formula: see text]-invariant theory. Some general properties of the matrix elements of H||(t) are tested in the Lee model.
A TIME-DEPENDENT CLASSICAL SOLUTION OF c=1 STRING FIELD THEORY AND NONPERTURBATIVE EFFECTS
Authors: DHAR AVINASH , MANDAL GAUTAM , WADIA SPENTA R.
Published: November 2004

We describe a real-time classical solution of c=1 string field theory written in terms of the phase space density, u(p, q, t), of the equivalent fermion theory. The solution corresponds to tunnelling of a single fermion above the filled Fermi sea and leads to amplitudes that go as exp(−C/g str ). We discuss how one can use this technique to describe nonperturbative effects in the Marinari-Parisi model. We also discuss implications of this type of solution for the two-dimensional black hole.
PHOTOPRODUCTION OF WEAK VECTOR BOSONS IN A SPINOR THEORY
Authors: LEMKE E.H.
Published: November 2004

We put forward the hypothesis that the weak W boson be a compound of two 2-component Lorentz spinors. The resulting novel γWW vertex is no gauge field structure. Nevertheless, the Born amplitude of γγ→WLWL respects partial-wave unitarity. As in the Yang-Mills case, the amplitude consists of a direct term, a crossed term, and a sea-gull term, and no unobserved particles are to be involved to get the “good” high-energy behavior. This is due to an imaginary pseudoscalar γWW interaction term. Significant differences between angular distributions and total cross sections of the non-Abelian case and the case of the composite bosons are displayed. The unitarity constraint applied to the reaction γγ→WTWT leads to the prediction of the existence of a composite charged weak scalar Φ±. It constitutes the spin 0 state of the constituents forming W±. Furthermore, the existence of a second and heavy scalar-vector pair ω-X is predicted. These weak boson states are found to exclude the presence of a seagull graph. In the threshold region, the total cross section of γγ→WW in the compositeness case is smaller than in the non-Abelian case. In a broad intermediate energy region it can be larger. Upper unitarity mass-bounds are estimated. They suggest mΦ≈mw so that Φ± might be discovered by forthcoming experiments. The structure of the γΦW, γXW and γωW transition vertices can be inferred without making recourse to unitarity. However, unitarity requires that the mass relation mΦ/mW=mω/mX be valid.
A GEOMETRICAL APPROACH TO TIME-DEPENDENT GAUGE-FIXING
Authors: EVANS JONATHAN M. , TUCKEY PHILIP A.
Published: November 2004

When a Hamiltonian system is subject to constraints which depend explicitly on time, difficulties can arise in attempting to reduce the system to its physical phase space. Specifically, it is nontrivial to restrict the system in such a way that one can find a Hamiltonian time-evolution equation involving the Dirac bracket. Using a geometrical formulation, we derive an explicit condition which is both necessary and sufficient for this to be possible, and we give a formula defining the resulting Hamiltonian function. Some previous results are recovered as special cases.
THE LOW-LEVEL SPECTRUM OF THE W3 STRING
Authors: LU H. , POPE C.N. , NILSSON B.E.W. , STELLE K.S. , WEST P.C.
Published: November 2004

We investigate the spectrum of physical states in the W3 string theory, up to level 2 for a multiscalar string, and up to level 4 for the two-scalar string. The (open) W3 string has a photon as its only massless state. By using screening charges to study the null physical states in the two-scalar W3 string, we are able to learn about the gauge symmetries of the states in the multiscalar W3 string.
A VECTOR-LIKE LARGE N APPROACH TO ZERO-DIMENSIONAL SU(2) MATRIX MODELS
Authors: RODRIGUES JOĀO P. , WELTE ALEXANDER
Published: November 2004

The action of an SU(2) multimatrix model can always be rewritten as that of an SO(3) multivector model. In the context of a zero-dimensional model, we argue that all symmetry invariants can be expressed in terms of O(3) invariants and develop a systematic, vector-like [Formula: see text] approximation. This approximation has no interpretation in terms of subsets of Feynman diagrams of the original model.
THE CHIRAL APPROACH TO THE ELECTROWEAK INTERACTIONS
Authors: FERUGLIO F.
Published: November 2004

The effective Lagrangian approach is reviewed and applied to the case of electroweak interactions.
SL(2, Z) DUALITY AND MAGNETICALLY CHARGED STRINGS
Authors: SEN ASHOKE
Published: November 2004

The postulate of SL(2, Z) invariance of toroidally compactified heterotic string theory in four dimensions implies the existence of new string (dual string) states carrying both electric and magnetic charges. In this paper we study the interaction between these dual strings. In particular, we consider the scattering of two such strings in the limit where one string passes through the other string without touching it, and show that such scattering leads to the exchange of a fixed amount of electric and magnetic charge between the two strings.
SEARCH FOR ANOMALOUS SPIN-SPIN INTERACTIONS USING A PARAMAGNETIC SALT WITH A DC SQUID
Authors: NI WEI-TOU , PAN SHEAU-SHI , CHUI T.C.P. , CHENG BO-YUAN
Published: November 2004

We use a paramagnetic salt TbF3 with a DC SQUID to search for a possible anomalous spin-spin interaction of two rotating HoFe3 polarized bodies with the TbF3 paramagnetic salt. We set limits on the electron-electron spin interaction and the electron-nucleus spin interaction. In terms of a standard dipole-dipole form, the limits are (−2.1 ±3.5)×10−14 for the anomalous spin-spin interaction of electrons in terms of the interaction strength between the magnetic moments of the electrons, and (−2.1±3.6)×10−8 for the anomalous spin-spin interaction between the electron and the Ho-nucleus in terms of the interaction strength between the magnetic moments of the electron and the Ho-nucleus.
SYMMETRIES OF p-BRANES
Authors: PERCACCI R. , SEZGIN E.
Published: November 2004

Using canonical methods, we study the invariance properties of a bosonic p-brane propagating in a curved background locally diffeomorphic to M×G, where M is space-time and G a group manifold. The action is that of a gauged sigma model in p+1 dimensions coupled to a Yang-Mills field and a (p+1) form in M. We construct the generators of Yang-Mills and tensor gauge transformations and exhibit the role of the (p+1) form in canceling the potential Schwinger terms. We also discuss the Noether currents associated with the global symmetries of the action and the question of the existence of infinite-dimensional symmetry algebras, analogous to the Kac-Moody symmetry of the string.
INTRODUCTION TO VERTEX ALGEBRAS, BORCHERDS ALGEBRAS AND THE MONSTER LIE ALGEBRA
Authors: GEBERT REINHOLD W.
Published: November 2004

The theory of vertex algebras constitutes a mathematically rigorous axiomatic formulation of the algebraic origins of conformal field theory In this context Borcherds algebras arise as certain “physical” subspaces of vertex algebras. The aim of this review is to give a pedagogical introduction to this rapidly developing area of mathematics. Based on the machinery of formal calculus, we present the axiomatic definition of vertex algebras. We discuss the connection with conformal field theory by deriving important implications of these axioms. In particular, many explicit calculations are presented to stress the eminent role of the Jacobi identity axiom for vertex algebras. As a class of concrete examples the vertex algebras associated with even lattices are constructed and it is shown in detail how affine Lie algebras and the fake monster Lie algebra naturally appear. This leads us to the abstract definition of Borcherds algebras as generalized Kac-Moody algebras and their basic properties. Finally, the results about the simplest generic Borcherds algebras are analyzed from the point of view of symmetry in quantum theory and the construction of the monster Lie algebra is sketched.
SPHALERONS AT FINITE TEMPERATURE
Authors: BRAIBANT SYLVIE , BRIHAYE YVES , KUNZ JUTTA
Published: November 2004

We construct the sphaleron for several temperature-dependent effective potentials. We determine the sphaleron energy as a function of temperature and demonstrate that the sphaleron energy at a given temperature T is well approximated by the sphaleron energy at temperature zero scaled by the ratio of the vacuum expectation values of the Higgs field at temperatures T and zero. We address the cosmological upper bound on the Higgs mass.
CURRENT ALGEBRA AND CONFORMAL FIELD THEORY ON A FIGURE EIGHT
Authors: BALACHANDRAN A.P. , BIMONTE G. , GUPTA K.S. , MARMO G. , SALOMONSON P. , SIMONI A. , STERN A.
Published: November 2004

We examine the dynamics of a free massless scalar field on a figure eight network. Upon requiring the scalar field to have a well-defined value at the junction of the network, it is seen that the conserved currents of the theory satisfy Kirchhoff’s law, that is that the current flowing into the junction equals the current flowing out. We obtain the corresponding current algebra and show that, unlike on a circle, the left- and right-moving currents on the figure eight do not in general commute in quantum theory. Since a free scalar field theory on a one-dimensional spatial manifold exhibits conformal symmetry, it is natural to ask whether an analogous symmetry can be defined for the figure eight. We find that, unlike in the case of a manifold, the action plus boundary conditions for the network are not invariant under separate conformal transformations associated with left- and right-movers. Instead, the system is, at best, invariant under only a single set of transformations. Its conserved current is also found to satisfy Kirchhoff’s law at the junction. We obtain the associated conserved charges, and show that they generate a Virasoro algebra. Its conformal anomaly (central charge) is computed for special values of the parameters characterizing the network.
COMPETITION BETWEEN GAPPING OF THE ELECTRONIC SPECTRUM AND MAGNETIC ORDER IN CeNiSn
Authors: ALIEV F. G. , VILLAR R. , VIEIRA S. , LOPEZ DE LA TORRE M. A. , GANZIUK A. L.
Published: November 2004

From the study of the thermal expansion of CeNiSn, CeNi 0.9 Cu 0.1 Sn , Ce 1− x La x NiSn ( x = 0.03, 0.1) between 0.5K and 25K; and the transport (3 < T < 60K ) and magnetic (0.1 < T < 8K ) properties of CeNiSn, we conclude that the competition between the local and long-range antiferromagnetic Kondo-type interactions plays a basic role in the formation of the gapped ground state. We propose a simple picture for the electron spectrum near the Fermi level, which can describe the main low temperature properties of CeNiSn.
U(Pd1−xNix)2Al3: AN ALLOY BETWEEN TWO HEAVY-FERMION SUPERCONDUCTORS
Authors: SCHANK C. , JÄHRLING F. , TEGEL U. , GEIBEL C. , GRAUEL A. , BÖHM A. , BORTH R. , HELFRICH R. , JAECKEL D. , WEBER G. , STEGLICH F.
Published: November 2004

We present and analyze measurements of the electrical resistivity, the dc- and ac-susceptibility and the specific-heat of the quasi-binary alloy U ( Pd 1− x Ni x )2 Al 3 in the temperature range from 0.3K to 300K. All investigated properties indicate a continuous change from UPd 2 Al 3 to UNi 2 Al 3, with the exception of superconductivity, which dissappears for 0.12 ≤ x ≤ 0.95. The results stress the importance of crystal field effects.
PERIODICAL ANDERSON MODEL AND ELECTRON-PHONON INTERACTION
Authors: SANDALOV IGOR S.
Published: November 2004

The periodical Anderson model (PAM) is microscopically derived. It is shown that the PAM is a mean field theory for the electric potential. The mixing interaction (MI) consists of single- and two-particle contributions. The first is proportional to the overlap integral of localized and band wave functions and vanishes when band energies are on the Fermi surface. It leads to the absence of heavy-fermion effects in the theories based on the PAM with only this mixing term. Using the orthogonal basis this term vanishes only at zero temperature. Applicability of the Luttinger theorem to systems with strongly-correlated electrons (SSCE) is discussed. The phonon dynamic matrix and electron-phonon interaction (EPI) for SSCE are microscopically derived.
ON THE MAGNETOACOUSTIC OSCILLATIONS IN HEAVY FERMION COMPOUNDS
Authors: WOJCIECHOWSKI R. , KOWALEWSKI L.
Published: November 2004

Using the Green's function technique and MFA for the slave bosons approach, we consider the influence of the magnetic field on the oscillations of the sound velocity in cerium-based heavy fermion compounds. The quasiparticle-phonon interaction is assumed to result from the volume dependence of the spin fluctuation temperature T *. We obtain magnetic oscillations of the sound velocity at finite temperature. The mass enhancement and the renormalised Fermi energy are the same as those obtained for the magnetic de Haas-van Alphen effect.
RENORMALIZATION OF FERMI VELOCITY IN A COMPOSITE TWO DIMENSIONAL ELECTRON GAS
Authors: WEGER M. , BURLACHKOV L.
Published: November 2004

We calculate the self-energy Σ(k, ω) of an electron gas with a Coulomb interaction in a composite 2D system, consisting of metallic layers of thickness d ≳ a 0, where a 0 = ħ2∊1/ me 2 is the Bohr radius, separated by layers with a dielectric constant ∊2 and a lattice constant c perpendicular to the planes. The behavior of the electron gas is determined by the dimensionless parameters k F a 0 and k F c ∊2/∊1. We find that when ∊2/∊1 is large (≈5 or more), the velocity v(k) becomes strongly k-dependent near k F , and v ( k F ) is enhanced by a factor of 5-10. This behavior is similar to the one found by Lindhard in 1954 for an unscreened electron gas; however here we take screening into account. The peak in v(k) is very sharp (δ k/k F is a few percent) and becomes sharper as ∊2/∊1 increases.

This velocity renormalization has dramatic effects on the transport properties; the conductivity at low T increases like the square of the velocity renormalization and the resistivity due to elastic scattering becomes temperature dependent, increasing approximately linearly with T. For scattering by phonons, ρ ∝ T 2.

Preliminary measurements suggest an increase in v k in YBCO very close to k F .
POINT CONTACT SPECTROSCOPY IN ORIENTED YBa2Cu3O7−δ
Authors: HASS NIR , ILZYCER D. , DEUTSCHER G. , DESGARDIN G. , MONOT I. , WEGER M.
Published: November 2004

We report point contact spectroscopy measurements on YBa 2 Cu 3 O 7−δ thin films and textured bulk ceramics. The I(V) curves measured along the Copper-Oxygen (ab) plane direction are characteristic of the Andreev reflection phenomenon, with a sharp break at the gap edge. This allows a rather precise determination of the (in plane) gap, Δ = 20 mev . Subgap structure suggests the existence of a smaller gap for some orientations in the (ab) plane, of the order of 12 mev. The data also enabled us to set a lower bound to the inplane Fermi velocity in YBa 2 Cu 3 O 7−δ: v F ≥ 7 × 107 cm/sec . The value of v F has a crucial importance in the determination of the theoretical explanation for superconductivity in the High Temperature Superconductors. For out of plane measurements, only a weak zero bias anomaly is observed at energies up to 5 mev.
PINNING FORCE DENSITY IN YBa2Cu3O7-FILMS AND YBa2Cu3O7/PrBa2Cu3O7-SUPERLATTICES
Authors: SCHMITT M. , KLUGE T. , TOMÉ ROSA C. , JAKOB G. , WAGNER P. , HAHN T. , ADRIAN H.
Published: November 2004

The in plane critical current density jc (B, Θ, T) of dc-sputtered YBa 2 Cu 3 O 7-films and YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices was measured in dependence of the angle Θ between the magnetic field [Formula: see text] and the [Formula: see text]-axis of the films in two orientations: 1. The current direction is parallel to the axis of rotation (i.e. [Formula: see text] always). 2. The current flows perpendicular to the axis of rotation (i. e. [Formula: see text]). For low temperatures we do not find any difference between the two current orientations, and the critical current density [Formula: see text] behaves like jc (B cos Θ, 0°). For higher temperatures the two cases differ from each other for Θ near to the maxima in jc at 90° and 270° for the YBa 2 Cu 3 O 7-films whereas for YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices we hardly find any change for both experimental setups. We compare the behaviour of the experimental results for the two orientations for the YBa 2 Cu 3 O 7-films and YBa 2 Cu 3 O 7/ PrBa 2 Cu 3 O 7-superlattices and discuss the temperature dependence of the intrinsic pinning force density.
INVESTIGATIONS ON LOCKING OF DISPLACIVE MODULATION IN Bi-Sr-Ca-Cu-O SYSTEM BY T.E.M.
Authors: EZRAHNI M. , SURESH BABU D. , BROHAN L. , TILLEY R. J. D. , GANNE M.
Published: November 2004

We have investigated the effect of temperature, oxygen content and Bi/Ca substitution on the q vector, by T.E.M, on Bi-Sr-Ca-Cu-O system in order to explain the locking of displacive modulation along one or two directions. q value is independent of temperature and oxygen content but dependent on Bi/Ca substitution. The data suggests that the locking of displacive modulation is due to ordering of Bi atoms on Ca sites (4f) in commensurate space group Pnnn. We have obtained composition limits as Bi 2.2 Sr 2 Ca 0.8 Cu 2 O 8+d and Bi 2.04 Sr 2 Ca 0.96 Cu 2 O 8+d for one and two direction(s) of modulation respectively.
Tl-BASED HIGH-Tc SUPERCONDUCTOR WITH CUBIC SYMMETRY
Authors: VOLCOV V. A. , KOVALEV YU. G. , FOKINA N. P. , OVCHINNIKOV S. G. , CHERNOV V. K. , VASYLYEV A. D. , ALEKSANDROV K. S.
Published: November 2004

Ceramic samples of the system Tl-Pb-Sr-Ca-Ba-Cu-O-F have been prepared by modification of standard Tl-based ceramics by BaF 2. A cubic structure with parameter a = 6.04 A is found by powder X-ray analysis. Both electric and magnetic data reveal superconductivity with Tci = 117 K . Electron conductivity is found at T = 300 K .
LOW TEMPERATURE SPECIFIC HEAT OF YBa2Cu3O7
Authors: CASPARY R. , HELLMANN P. , WOLF T. , STEGLICH F.
Published: November 2004

We show specific heat data in magnetic fields to B = 8T on new polycrystals with different oxygen content and compare them with earlier results. The analysis reveals a field dependent residual linear term which is discussed within theoretical models of Bulaevskii and for a spin-glass.
OXYGEN VACANCY ORDERING AND THE DENSITY OF STATES IN YBa2Cu3O7−y
Authors: CRISAN V. , VERNES A. , NEUFELD Z. , MOSTIS K. , LUPULESCU A. , JANOSI A.
Published: November 2004

Using Haydock recursion method, the density of states for the ordered vacancies model of Alario-Franco for YBa 2 Cu 3 O 7−y, was computed. With the oxygen vacancies concentration, the changes of the shape of the density of states were observed. Due to isolated units of Cu-O-Cu from the chains, for y ≥ 0.25 at E-EF~4 eV a sharp peak in the density of states appeared in qualitative agreement with optical experiments.
LONG–RANGE MAGNETIC ORDER IN La2NiO4+δ UNDER SMALL OXYGEN EXCESS
Authors: POGORELOV YURY G.
Published: November 2004

Within a continuum model based on the microscopic magnetic symmetry of Ni 2+ ion (spin S = 1) in the metal-oxide compound La 2 NiO 4+δ, a theoretical analysis is made of the stability of antiferromagnetic long-range order under the effect of oxygen interstitials at δ ≪ 1. It is shown that the Néel temperature dicreases significantly with growing δ though does not become zero, in contrast to that in the structurally isomorhic compound La 2 CuO 4+δ (but Cu 2+ spin S = 1/2).
MAGNETIC FIELD DEPENDENCE OF THE POINT-CONTACT SPECTRA OF CeNi5
Authors: NAIDYUK Y. , REIFFERS M. , JANSEN A. G. M. , YANSON I. K. , WYDER P. , GIGNOUX D. , SCHMITT D.
Published: November 2004

The intermetallic compound CeNi 5, where Ce is not magnetic and in the maximum valence state, is an enhanced Pauli paramagnet in which spin fluctuations are present. For point contacts between a CeNi 5 single crystal and Cu, the second derivatives of the I-V characteristics reveal a maximum at low voltages (around 3 mV) which disappears in applied magnetic fields above 10 T. This behaviour in the point-contact spectra is ascribed to the quenching of spin fluctuations by the magnetic field.
POINT-CONTACT SPECTROSCOPY OF THE ELECTRON-PHONON INTERACTION IN SmNi5
Authors: REIFFERS M. , SZABO P. , GIGNOUX D. , SCHMITT D.
Published: November 2004

The measured point-contact (PC) spectra of the heterocontact between oriented hexagonal single crystal of SmNi 5 and Cu in ballistic and thermal regime are presented. The PC spectrum (the second derivative of I–V characteristic - d 2 I/dV 2( eV )) is directly proportional to the electron-quasiparticle interaction (EQI) function. The absence of the magnetic field effect on the energy position of the characteristic peaks until 10T is the confirmation of the phonon origin. The phonon part of the EQI function is similar to the electron-phonon interaction function for LaNi 5.
THEORY FOR SPIN–POLARIZED ELECTRON CAPTURE SPECTROSCOPY IN FERROMAGNETIC NICKEL
Authors: HÜBNER W. , FALICOV L. M.
Published: November 2004

A time-dependent many-body theory is developed for the study of spin-polarized electron capture spectroscopy. As a model system we choose the head-on collision of protons with a nickel atom. For the electronic part of the Hamiltonian we use the most general on-site interaction terms allowed by atomic symmetry. The total electronic many-body states are group-theoretically classified with respect to the conserved quantum numbers L, L z and S z. The time-dependent Schrödinger equation for this system is solved exactly. The zero-, one- and two- electron capture probabilities which are treated on the same footing are monitored along the trajectories of the scattering species on the femtosecond time scale. In good agreement with experiments on surfaces we find probabilities of 22% and 0.33% for one- and two-electron capture respectively and spin polarizations between -60% and -100%. The predominant capture of minority electrons is enhanced due to electronic correlations. This implies that the probing of magnetism occurs on a significantly longer time scale than the probing of single electron properties.
AN IMPROVED APPROACH TO SELF-CONSISTENT DIAGONALIZATION-FREETOTAL-ENERGY MINIMIZATIONS FOR METALS
Authors: OPPENEER P. M. , HIERSE W.
Published: November 2004

An improved method for the ab initio total-energy minimization and molecular-dynamics simmation of metallic systems is presented. In this method, the problem of fluctuating occupation numbers is dealt with in a new way. Proceeding from the steepest-descent ansatz, an iteration equation is derived which has the following important features: No re-orthonormalization of wave functions is needed after each iteration step, fluctuating occupation numbers are explicitly allowed, and no diagonalization of a Hamiltonian or Lagrange matrix is required. Furthermore, our method is especially suited for atom-centered basis functions.
CORRELATION EFFECTS IN NiO: COMPARISON OF NEAR THRESHOLD EXCITATION SPECTROSCOPIES
Authors: SCHEIPERS A. , MERZ H.
Published: November 2004

At UHV-cleaved single-crystal NiO(100) surfaces core electron energy loss spectra (CEELS) at low primary energy and soft x-ray appearance potential spectra (SXAPS) have been measured at the oxygen K-threshold: the near-edge fine-structures have been investigated up to 40 eV above the threshold. Both spectroscopic methods probe in different ways the structure of the lowest empty states. CEELS is closely related to x-ray absorption spectroscopy (XAS), in both cases the excited final configuration consists of one core hole and one additional electron near the Fermi level E F. In APS we can study correlation effects very directly because the excited system consists of one core hole and two additional interacting electrons in localized resp. delocalized states near E F.

The interpretation of the CEELS and SXAPS spectra at the oxygen K-edge is in agreement with a description of NiO as an intermediate valence system, where the charge-transfer gap is smaller than the Hubbard correlation energy. The comparison of our measured spectra with the experimental XAS of NiO shows the dominance of optically allowed channels in both spectroscopies.
EELS STUDY OF SINGLE CRYSTALLINE NiO(100)
Authors: GORSCHLÜTER A. , MERZ H.
Published: November 2004

A detailed EELS study of NiO(100) cleaved in UHV has been performed to obtain new information about the origin of the insulating gap and about the nature of weak excitations within the gap. The low loss intensity of the inneratomic d-d excitations within the gap is strongly dependent on the primary energy whereas the cross section for the first excitations across the gap is approximately constant. This can be explained by different types of O 2p- Ni 3d hybridization. We assume that the first transitions across the gap are due to excitations of localized electrons in the p-d orbitals of a Ni-O cluster.
MÖSSBAUER INVESTIGATIONS OF THE ANTIFERROMAGNETIC PHASE IN THE METASTABLE β–Fe2O3
Authors: WIARDA D. , WEYER G.
Published: November 2004

In order to clarify our PAC–measurements with 111 In probes in the metastable iron oxide β– Fe 2 O 3 Mössbauer investigations (MS) were done with 57 Fe . In the PAC–spectra two fractions due to the two cation sites had been observed in the paramagnetic phase. In the MS–spectra one fraction due to the α–phase (≈40%) and two fractions belonging to the β–phase (≈60%) are visible. Below the Néel–temperature of about 100K the MS signal belonging to the β–phase splits into two magnetic multiplets. The temperature dependence of these multiplet components was investigated and a critical exponent β of the antiferromagnetic phase transition of β = 0.39(1) was derived. It is in good agreement with the value of β = 0.365 expected for a three dimensional Heisenberg magnet.
PRESSURE AND FIELD DEPENDENCE OF THE RESISTIVITY IN RECO2 COMPOUNDS
Authors: GRATZ E. , BAUER E. , HAUSER R. , MAIKIS M. , HAEN P. , MARKOSYAN A.
Published: November 2004

Pressure and field dependent resistivity measurements have been performed for various RECo 2 compounds. These compounds exhibits a dramatic pressure dependent shift of the magnetic ordering temperature T c to lower temperatures. The first order type of transition does not change with pressure in the heavy RECo 2 ( RE = Dy , Ho, Er). A magnetic field, in contrast, increases T c in all RECo 2 compounds. If the transition is of first order, it changes to second order with increasing fields. Above T c the resistivity behaviour is determined by scattering processes of the conduction electrons on both, local moments and spin fluctuations.
NEW INTERMETALLIC COMPOUNDS IN THE TERNARY SYSTEM Yb-T-Al (T=Ag, Au, Pd, Pt)
Authors: CORDIER G. , HENSELEIT R.
Published: November 2004

Structural characteristics of a number of ternary rare earth/transition metal/aluminium compounds are hexagonal nets of the AlB 2-type, Kagomé nets and tetragonal pyramides. Crystal structures of the new compounds in the ternary Yb-T-Al systems contain units and sections of them.

Kagomé nets stacked in an ..ABAB.. sequence are observed in YbAg1.5Al0.5 ( MgZn 2-type). The crystal structure of Yb8Ag21Al45 is related to the BaHg 11-type. YbAu0.8Al3.2 ( CaZn 2 Al 2-type) contains tetragonal pyramides which are connected by common edges. Fragments of the AlB 2- and BaAl 4-type structure are present in Yb5Au15Al16. YbPdAl2 and YbPtAl2 ( YbPdAl 2-type) contain pentagonal prisms as the characteristic structural elements.
STRUCTURAL AND TRANSPORT PROPERTIES OF THE PSEUDO-BINARY SYSTEM Fe(Sb1−xTex)2 (0 ≤ x ≤ 1)
Authors: HARADA T. , NISHIMURA K. , MAKABE T. , NARITA T.
Published: November 2004

The electrical resistivity (ρ) and the thermoelectric power (S) of Fe ( Sb 1− x Te x )2 were studied to investigate the electrical properties of them. The ρ- T curves for all specimens measured show semiconductive properties. The results of the ρ-T and S-T curves suggest the existence of the narrow 3d-bands between ordinary covalent bands. From the X-ray analysis it is concluded that the crystal structures of the ternary system are distorted continuously from the orthorhombic structure to the monoclinic one.
SPECTROSCOPIC PROPERTIES OF [Ru(bpy)2(bpz)]2+
Authors: SCHMIDT J. , WUDY J. , HUBER P. , DOMEL H. , BRAUN D. , YERSIN H.
Published: November 2004

We report on the temperature and magnetic field dependence of the low-temperature emission and excitation spectra of [Ru(bpy)2(bpz)]2+ doped into [Zn(bpy)3](ClO4)2. We could identify, for the first time, the origins corresponding to the three lowest electronic states. They are assigned to be triplet sublevels of a Ru4d – (bpz)π* metal to ligand charge transfer (MLCT) excitation. The energies of these zero-phonon lines are 15804 cm −1 (line I), 15822 cm −1 (line II), and 15899 cm −1 (line III). These sharp electronic transitions (halfwidths ≈ 2 cm −1) are associated with broad emission bands, which result from superpositions of vibrational satellites and multi-phonon structures. In particular, it is shown that magnetic fields have a drastic influence on the lowest electronic transition (including the vibronic structure). This transition is strongly forbidden. Thus, at zero field the origin line I is only detected in emission (τ = 130 μ s ). However, application of magnetic fields of B ≥ 8 T leads to a growing in of the corresponding excitation line, being in resonance with the luminescence line. For B = 12 T, this lowest origin line exhibits a Zeeman red-shift of ≈ 4 cm −1. However, the associated broad emission maximum is blue-shifted by ≈ 400 cm −1, where the shift attains a saturation near B = 4 T. These results are explained by a field-induced mixing of the wavefunctions of the lowest excited states. The described effects result from the large differences in the vibronic radiative deactivation paths and the radiative rates of the involved states.
NONLINEAR MAGNETIC RESPONSE AT THE CRITICAL POINTS OF GRAPHITE COMPOUNDS INTERCALATED BY TRANSITION METAL CHLORIDES
Authors: HAGIWARA M. , KAWACHI M. , UCHIKOSHI M. , MATSUURA M. , FRANDROIS S.
Published: November 2004

Ordering of CoCl 2−, NiC1 2− and CrCl 3−graphite intercalation compounds (GIC) is studied by observing nonlinear magnetic response at weak AC excitation fields and at very low frequencies. The result for CoCl 2− and NiCl 2− GICs supports the two-step hierarchical spin ordering model by confirming the non-breaking of total magnetic symmetry between the upper and lower transition temperatures.
OSCILLATORY EXCHANGE COUPLING OF Fe LAYERS ACROSS Cr INTERLAYERS
Authors: LENG Q. , WOLF J. A. , GRÜNBERG P. , ZINN W.
Published: November 2004

The exchange coupling of Fe layers across Cr interlayers oscillates as a function of the Cr thickness with a short and a long period. The short period oscillations are only observed In samples with very good quality. In addtion to ferro- and antiferromagnetic type coupling there is also a contribution favoring a perpendicular magnetization alignment of neighbouring magnetic films. The temperature dependence of these couplings has been investigated .
MAGNETORESISTANCE OF Au-BASED MULTILAYERS WITH TWO MAGNETIC COMPONENTS: NiFe/Au/Co/Au
Authors: OKUYAMA T. , YAMAMOTO H. , DOHNOMAE H. , ANNO T. , ONO T. , SHINJO T.
Published: November 2004

Magnetoresistance properties of [NiFe/Au/Co/Au] multilayers prepared by ultrahigh vacuum deposition were investigated. An antiparallel alignment of magnetizations caused by the difference of the coercive fields of NiFe and Co layers is realized when d Au is larger than 50Å and a large enhancement of resistivity was observed.
THE ACTIVATION ENERGY OF MAGNETIZATION REVERSAL PROCESSES DUE TO VIBRATIONS OF WALLS
Authors: SCHMIDT W.
Published: November 2004

Our calculations concern an ultrathin film with perpendicular anisotropy, Co/Au, and a lattice of pinning defects. We consider a mechanism of the aftereffect where the walls are detached from the cavities by vibrations. Dependence of the activation energy on the external field is used to estimate the distance d between defects, the pinning force (or the radius of the pin cavity) and the stability time. From the obtained values d and the pinning force, the coercive force H c is calculated, when the aftereffect can be neglected.
PHOTON EMISSION FROM TRANSITION METAL SURFACES IN SCANNING TUNNELING MICROSCOPY
Authors: BERNDT RICHARD , GIMZEWSKI JAMES K.
Published: November 2004

Light emission from noble metal surfaces excited by a scanning tunneling microscope has been interpreted as arising from in elastic tunneling excitation of tip-induced plasmon modes. We have extended this work to study the adsorption of oxygen on Ti and have observed the formation of structures with subnanometer lateral dimensions which give rise to clear contrasts in STM topographs and photon intensity maps. The experimental results strongly indicate that these contrasts are due to oxygen-induced variations of the local density of states.
INTERFACIAL SEGREGATION IN α-IRON
Authors: LEJČEK PAVEL
Published: November 2004

Measurements of solute segregation to free surfaces and grain boundaries in well-defined samples of α-Fe-Si model alloys revealed pronounced differences. Segregation of C and P and depletion of Si are characteristic for grain boundaries. Cosegregation of Si and N resulting in formation of silicon nitrides prevails at the majority of free surfaces in samples containing nitrogen, but S segregation dominates at the surfaces of nitrogen free samples. The results are summarized from the viewpoint of the type of interface, alloy composition and segregation temperature.
AB-INITIO CALCULATION OF THE INITIAL- AND FINAL-STATE EFFECTS ON CORE LEVEL SHIFTS AT TRANSITION METAL SURFACES
Authors: HENNIG D. , METHFESSEL M. , SCHEFFLER M.
Published: November 2004

The surface core-level shift at a transition metal surface can be calculated in two different ways using the initial-state approximation or using a more involved approach which includes screening of the photo-created core hole. Our calculated results obtained using the full-potential LMTO method for the close packed surfaces of all 4d transition metals within the initial state picture can be well explained by standard arguments.
PHOTOEMISSION STUDY OF THE ELECTRONIC STRUCTURE OF SIZE-SELECTED Ptn — CLUSTERS DEPOSITED ON Ag(110)
Authors: ROY H.-V. , BOSCHUNG J. , FAYET P. , PATTHEY F. , SCHNEIDER W.-D.
Published: November 2004

We report on a photoemission study (XPS, UPS) of the evolution of the electronic structure with cluster size of Pt n ( n = 1-10) clusters deposited on a Ag(110) single crystal surface. The clusters are produced by Xe-ion bombardment of a Pt target. The ionized clusters are mass-selected by a quadrupole mass spectrometer and guided to the substrate by an RF-mode only quadrupole. The substrate is in the center of the analysis chamber allowing in-situ characterization of the supported clusters. Photoemission spectra taken on submonolayer quantities of mass-selected monodispersed Pt clusters indicate individual discrete electronic structure features of the Pt 5d emission. In the atomic-like limit virtual bound state formation with different 5d3/2 and 5d5/2 line broadening is observed which points to an energy dependent Vsd hopping matrix element in agreement with theoretical predictions. With increasing cluster size the splitting between the bonding-like and antibonding-like Pt 5d states reflects the Pt-Pt interaction. The shift of the center of gravity of the Pt 5d state towards the Fermi energy and their concomittant broadening indicate the trend to Pt-metal formation.
MAGNETIC BEHAVIOUR OF A Cr+1.6 at.% Si SINGLE CRYSTAL
Authors: LOURENS J.A.J. , ALBERTS H.L.
Published: November 2004

Measurements of thermal expansion and velocity of sound around the Néel temperature (TN) of a Cr+1.6 at.% Si single crystal are presented. A weak continuous transition superimposed on a sharp first-order discontinuity was observed in the thermal expansion near TN. The continuous component is accurately described by a critical exponent power law. The sound velocity diverges sharply near TN in contrast with theoretical predictions for Cr-like itinerant electron antiferromagnets.
THEORY OF OPTICAL AND MAGNETOOPTICAL PROPERTIES OF INVAR COMPOUNDS
Authors: HALILOV S.V. , FEDER R.
Published: November 2004

The frequency-dependent optical conductivity tensor for ferromagnetic transition metal compounds is determined in a theoretical framework, in which spin-orbit interaction and ferromagnetic exchange interaction are included on an equal footing. The interplay of the latter two mechanisms manifests itself in substantial modifications of the diagonal tensor components and the appearance of offdiagonal components, and thereby in optical and magnetooptical properties. Numerical calculations for Fe3Pt using a “high-spin” model yield a polar Kerr rotation angle in good agreement with experimental data, Results for the diagonal tensor components reveal very pronounced differences between assumed ”high-spin” and ”low-spin” models of Fe3Pt. We conclude that specific experimental studies should be able to provide more information on the still not completely resolved issue of the nature of the INVAR mechanism in Fe3Pt.
LANDAU DESCRIPTION OF MAGNETOVOLUME EFFECTS IN ITINERANT MAGNETIC SYSTEMS
Authors: SCHRÖTER M. , ENTEL P.
Published: November 2004

Recent band-structure calculations for Fe3Ni and Fe3Pt seem to confirm that these are indeed high-spin low-spin systems. Thus the anomalous low thermal expansion of INVAR at room temperature may be explained with the thermal excitation of the low-spin state, which has a lower volume than the high-spin state. To account for the negative thermal expansion at T=0, usually the existance of an antiferromagnetic state with almost vanishing excitation energy is postulated. We show that this need not be the case and that the existing bandstructure data, interpreted in terms of a classical Landau-like field theory, explain this low temperature effect and yield overall temperature dependencies, which are in reasonable agreement with experiments.
MAGNETIZATION DEPENDENCE OF PHONON EFFECT ON VOLUME OF AN ITINERANT ELECTRON FERROMAGNET
Authors: OSHIMA Masao , HAMAGUCHI Nobuhiro , FUKUMOTO Shinji , KIM D.J.
Published: November 2004

Volume behavior is often anomalous for T<Tc of an itinerant electron ferromagnet. Recently Kim pointed out that phonons also can be responsible for such anomalous behavior. Further to explore such possible role of phonons, in this paper we carry out a numerical calculation on the temperature dependences of phonon Debye temperature and Grüneisen constant of an itinerant electron ferromagnet by using a model electronic density of states. Our numerical results support our earlier conclusion and demonstrate the importance of taking into account the effect of the electron-phonon interaction in understanding the anomalous volume and elasticity behavior of an itinerant electron ferromagnet.
THE MAGNETOVOLUME EFFECT IN STRONG ITINERANT PARAMAGNETS
Authors: PANFILOV A.S. , SVECHKAREV I.V.
Published: November 2004

The results of investigations of the enhanced spin susceptibility of some transition metals and alloys under pressure are reviewed and discussed. The evaluated values of the volume derivative of the interaction parameter d In J/d In V unambiguously confirm the predominant role of the short-range electron correlations in these systems.
AB INITIO CALCULATION OF MAGNETIC MOMENTS, HYPERFINE FIELDS, MAGNETIC ANISOTROPY AND EXCHANGE INTERACTIONS IN RARE-EARTH INTERMETALLICS
Authors: HUMMLER K. , LIEBS M. , BEUERLE T. , FÄHNLE M.
Published: November 2004

The intrinsic magnetic properties of R2Fe14B (R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb) are calculated from first principles within the local-spin-density approximation and the linear-muffin-tin-orbital method in atomic-sphere approximation. The total magnetization is in excellent agreement with experimental data. The local magnetic moments of the crystallographically inequivalent Fe sites appear to be not proportional to the local hyperfine fields. It is shown that the rare-earth contribution to the magnetic anisotropy may be qualitatively related to the electrostatic interaction of the aspherical 4f charge density with the crystal field. The effective intersublattice exchange coupling is evaluated from the change of the total energy upon 4f spin reversion.
COMPOSITION DEPENDENCE OF MAGNETIC AND ANISOTROPY PROPERTIES OF YCo4B
Authors: HONG N.M. , THUY N.P. , HIEN T.D. , VOIRON J. , GRATZ E. , GRÖSSINGER R. , HILSCHER G. , HOLUBAR T. , LINDBAUM A. , HUNDERGGER P. , SASSIK H.
Published: November 2004

It turns out from our investigations on YCo4+δ B1−δ (δ=0, ±0.1, ±0.2) that the CeCo4B structure is stable for a considerable range of δ. Upon increasing the B content, the saturation magnetisation decreases, the spin reorientation temperature is nearly unchanged but the character of the spin reorientation process is strongly affected.
THEORETICAL AND EXPERIMENTAL INVESTIGATION OF THE MAGNETIC X-RAY DICHROISM IN DILUTED AND CONCENTRATED TRANSITION METAL ALLOYS
Authors: EBERT H. , AKAI H. , MARUYAMA H. , KOIZUMI A. , YAMAZAKI H. , SCHÜTZ G.
Published: November 2004

By combining the Coherent Potential Approximation with the spin polarized relativistic Korringa-Kohn-Rostoker method of band structure calculation it got possible to describe the electronic structure of disordered magnetic alloys in a fully relativistic way. This new development allowed us to extend our theoretical description of the magnetic X-ray dichroism (MXD), which is based on the spin polarized relativistic Green's function formalism, to deal not only with pure and impurity systems but also with this interesting class of materials. We demonstrate this by calculations of K- and L-edge MXD spectra in the alloy systems FexCo1−x, CoxPt1−x and FexPt1−x, which are found in a very satisfying agreement with corresponding experimental data. In addition the relationship of the integrated MXD-spectra with the calculated spin magnetic moments is discussed in short.
MARTENSITIC TRANSFORMATION AND MAGNETIC PROPERTIES OF Fe-Pd ALLOYS
Authors: GOTO T. , KASHIWAKURA A. , KOYAMA S.
Published: November 2004

The effects of martensitic transformation from fcc to fct structure on the magetic properties of Fe-Pd alloys are investigated by magnetization, magnetostriction and 57Fe Mössbauer effect measurements. In the composition range of 30–32.5 at .% Pd, in which the fcc-fct transformation occurs, the Curie temperature decreases sharply with decreasing Pd content and the magnetostriction vs. temperature curve has a broad maximum around the fcc-fct transformation temperature. The Mössbauer spectrum exhibits the difference between the internal field for fcc, and fct.
THE COMBINED ANALYSIS OF SPECIFIC HEAT AND THERMAL EXPANSION OF Nd1−xLuxMn2 COMPOUNDS
Authors: KIM-NGAN N.H. , BROMMER P.E. , FRANSE J.J.M.
Published: November 2004

Specific heat and thermal expansion measurements have been performed on Nd1−xLUxMn2 in the temperature range between 1.5K and 300K. Below 10K, anomalies are observed which are ascribed to a spin reorientation of the Nd sublattice. These anomalies are only slightly affected by the substitution of Nd by Lu. Large effects, however, are observed on the magnetic properties of the Mn sublattice. The antiferromagnetic order disappears for x exceeding 0.30. The data are analysed in terms of Grüneisen parameters. In the paramagnetic compound LuMn2, a spin-fluctuation contribution to the thermodynamic properties is observed. In the Nd-containing compounds, distinct contributions from the crystal field acting on the Nd ions can be distinguished. The variation of the magnetic properties of the Mn sublattice with the concentration of Lu is discussed.