bluuebunny/crossref_metadata_2025 huggingface dataset:
The Microscopic Model of Composite Particles for ν=1/m FQHE Edge Excitations, its Bosonization and the Chiral Condition
Authors: Zheng Wen-Jun
Published: October 2003

We derive a microscopic theory of the composite particles describing the low-lying edge excitations in the fractional quantum Hall liquid with ν=1/m. Using the composite-particle transformation, one finds that the edge states of the system in a disc sample are described by the Calogero–Sutherland model with other interactions between the composite particles as perturbations. The effects of both the interactions and the confinement potential are considered, and proved unable to change the exponent g=ν=1/m. We also obtain the important chiral condition at the mean field level, and as a result justify microscopically the Chiral Luttinger Liquid model of the FQHE edge states.
Deviations from Quantized Hall Conductivity and Current Density Distribution in Finite 2DEG Samples
Authors: Bartoš I. , Rosenstein B.
Published: October 2003

Simple expressions for local and total Hall conductivities in finite two dimensional electron systems under magnetic field are obtained from the Kubo formula. The deviations of the Hall conductivity from integer values are always negative and their magnitude is inversely proportional to the effective width of the sample and proportional to the slope of the Landau branch dispersion relation at the Fermi level, Eq. (22). We also calculate the local conductivity in finite samples. The conductivity density is constant in the bulk and sums up to an integer value. Its spatial distribution is terminated in the bulk in a universal manner. Illustrations for simple models of the confinement barrier, as well as relation to recent experimental data for quantum wires are given.
Edge States of Quantum Hall Fluid and Berry Phase
Authors: Basu B. , Bandyopadhyay P.
Published: October 2003

The edge states of Abelian and non-Abelian Hall Fluids have been studied in a unified way from topological aspects. It is shown that the edge current is related to the fact that the effective Berry phase of quasiparticles at the edge should be vanishing which leads to the anomaly cancellation.
Theoretical Models for the Optical Properties of Clusters and Nanostructures
Authors: Rubio Angel , Alonso J. A. , Blase X. , Louie Steven G.
Published: October 2003

Applications of the Time Dependent Density Functional Formalism to calculate the response of metallic and semiconducting nanostructures to static and time-dependent electric fields in the linear regime are reviewed. The paper focuses on the presentation of models of increasing sophistication for the cluster structure, ranging from the simple spherical jellium model to a fully ab initio description of the ionic structure. Simple models explain the main features of the spectrum. For instance the existence of a pronounced surface plasmon resonance in the absorption spectrum of alkali metal clusters, and its redshift with respect to the classical Mie resonance are well explained within the framework of the simple jellium model. However, the detailed understanding of the experimental optical spectra can only be achieved by complementary ab initio calculations. In fact, the optical spectrum appears to carry detailed information on the cluster structure. Details of the new theories and computational schemes to deal with the optical properties of complex systems are also presented: linear and nonlinear susceptibilities, quasiparticle excitations, core-polarization. These methods are of relevance in the physics of nanostructures and nanoscale technology.
Reflection and Transmission Coefficients for Two- and Three-Dimensional Quantum Wires
Authors: Razavy M.
Published: October 2003

The problem of a quantum wire connected smoothly on both sides to leads of variable cross section is studied. A method for solving this problem in terms of a set of nonlinear first order matrix differential equations for the variable reflection amplitude is discussed. The reflection coefficient obtained in this way is directly related to the conductivity, and is calculated as a function of the energy of the ballistic electrons. This formulation can be applied to three-dimensional as well as two dimensional quantum wires. For two specific cases the reflection coefficient is obtained as a function of the wave number of the incident electron, and the contribution of quantum tunneling to the transmission in each case is demonstrated. Also a model with a dissipative force is introduced and its effect on the transmission of the electrons is investigated.
Generalized Localized Matter Wavepackets
Authors: Baskoutas S.
Published: October 2003

Studying the system of the non-Hermitian (NH) generalized parametric oscillator, we use the Wei–Norman factorization method, as well as the biorthonormal basis formalism, in order to initiate a complex probability density. Generalizing the usual Yuen procedure for the calculation of the variances Δq, Δp in terms of the complex probability density, we obtain a reduction in the position and an increase in the momentum uncertainty, in discrete time intervals. In the framework of the macroscopic quantum tunneling (MQT) effect, such a suppression of the matter wavepacket spreading provides a mechanism to localize a quantum particle, and is responsible for its behavior as a macroscopic state, inhibiting the tunneling process. Applications of squeezed matter wavepackets can be found in the control of excited-state chemical reactions, in MQT for Josephson junctions, and in the tunneling of trapped atoms in optical crystals.
Word Problem and Decimation Procedure in the Ising Model on Infinite Hyperbolic Group Lattices
Authors: Regge Tullio , Zecchina Riccardo
Published: October 2003

An elaborate counting procedure for solving the Word Problem yields the free-energy of the Ising model defined over infinite hyperbolic group lattices Λp. Such structures are characterized by a local 2D geometry (2p-sided faces connected by bonds) and a tree-like skeleton responsible of macroscopic boundary effects. The comparison of the above solution with the one derived by decimation gives a simple geometrical interpretation for the renormalized bond activities in terms of a particular dimer covering generating function. The infinite order of the group-lattices and the absence of a thermodynamic limit procedure, leads to an anomalous entropic behaviour at low temperature which can be interpreted in terms of a recursive appearance of decoupled infinite regions.
Boundary Weights for Temperley–Lieb and Dilute Temperley–Lieb Models
Authors: Behrend Roger E. , Pearce Paul A.
Published: October 2003

We use a direct approach to obtain the general diagonal solutions of the boundary Yang–Baxter equation for the Temperley–Lieb and dilute Temperley–Lieb models and their elliptic extensions.
Jacobian Elliptic Wave Solutions for the Wadati–Segur–Ablowitz Equation
Authors: Teh C. G. R. , Koo W. K. , Lee B. S.
Published: October 2003

Jacobian elliptic travelling wave solutions for a new Hamiltonian amplitude equation determining some instabilities of modulated wave train are obtained. By a mere variation of the Jacobian elliptic parameter k2 from zero to one, these solutions are transformed from a trivial one to the known solitary wave solutions.1,2
Orbital Kondo-Effect From Tunneling Impurities
Authors: Zaránd G. , Vladár K.
Published: October 2003

The article reviews recent results for the low energy physics of fast tunneling centers in metallic environments. For strong enough couplings to the environment these tunneling centers display an orbital Kondo effect and give rise to a non-Fermi-liquid behavior. This latter property is explained by establishing a mapping of the tunneling center model to the multichannel Kondo model via the renormalization group transformation combined with a 1/Nf expansion. The case of M-state systems, the role of the splittings and the present experimental situation are also discussed.
Effective Hamiltonian in the Problem of a "Central Spin" Coupled to a Spin Environment
Authors: Tupitsyn I. S. , Prokof'ev N. V. , Stamp P. C. E.
Published: October 2003

We consider here the problem of a "giant spin", with spin quantum number S≫1, interacting with a set of microscopic spins. Interactions between the microscopic spins are ignored. This model describes the low-energy properties of magnetic grains or magnetic macromolecules (ferromagnetically or antiferromagnetically ordered) interacting with a surrounding spin environment, such as nuclear spins.

Our aim is to give a general method for truncating the model to another one, valid at low energies, in which a two-level system interacts with the environmental spins, and higher energy terms are absorbed into a new set of couplings. This is done using an instanton technique.

We then study the accuracy of this technique, by comparing the results for the low energy effective Hamiltonian, with results derived for the original giant spin, coupled to a macroscopic spin, using exact diagonalization techniques. We find that the low energy central spin effective Hamiltonian gives very accurate results (with increasing accuracy for large S), provided the typical coupling energies between the giant spin and the microscopic spins are not too large, and provided temperature and external field are sufficiently low. The essential limitation to the applicability of the low-energy effective Hamiltonian is just the semiclassical WKB approximation itself, which inevitably fails for very small S.

Our results thus justify previous use of this effective Hamiltonian in calculations of the effects of nuclear spins on the dynamics of nanomagnetic systems.
An Analytical Approach to the Fredrickson–Andersen Model in One Dimension
Authors: Schulz Michael , Trimper Steffen
Published: October 2003

The dynamics of a modified kinetic Ising model usual noted as Fredrickson–Andersen model (FAM) is formulated in terms of Pauli-operators using a Fock-space representation of the Master equation. The method is appropriate to study the cooperativity by including topological restrictions explicitly. Following the concept of the FAM the block distribution function of m+1 adjacent liquid-like (spin down) or solid-like (spin up) regions is analysed in one dimension. The hierarchy of evolution equations for those functions can be solved exactly at zero temperature leading to a double exponential decay and to a nonergodic behaviour. In case of nonzero temperatures, we are able to solve this set of infinite nonlinear first order differential equations only after a well motivated decoupling procedure. It results an implicit solution for the averaged density. For short time scale the system behaves like an ordinary Ising model with exponential relaxation. In the long time limit, we observe already in lowest order a crossover to an exponential screened algebraic decay with an universal exponent 3/2 and moreover, the relaxation time will be drastically enlarged.
Semiconductivity of Protein: The Saxon–Hutner–Luttinger Theorem in Biopolymers
Authors: Iguchi Kazumoto
Published: October 2003

We study semiconductivity of protein with a primary structure, where we use the transfer matrix method of the tight-binding model for electrons in a protein. We first introduce the model and the scheme for obtaining the spectrum. Second, we set up the transfer matrices in order to apply for a protein with an amino acid sequence. Third, we prove the Saxon–Hutner conjecture for the one-dimensional disordered polyatomic chains, and apply it to the protein system. We show that this theorem provides a good foundation for understanding the intriguing semiconductive character of the protein, which was first suggested by Szent–Györgyi a long time ago.
Some Remarks on Phase Transitions Generated by the Superposition of Multifractals
Authors: Chen H. J. , Tseng H. C. , Lai W. Y. , Chen W. D.
Published: October 2003

Emergence of novel second-order phase transitions by sums of multifractals was found by Radons and Stoop.1,2 Using the same method as Radons and Stoop but different support, we have found that the second-order phase transitions are suppressed.3 In this paper, we continue to extend the method to three multifractals, with the effect of the sums of the three multifractals being the sums of two identical multifractals and those of two different multifractals combined together. We have found that the resulted phase diagrams are more complicated, with second-order phase transitions either partially or completely suppressed.
Statistical Description of the Turbulent Mixing of Scalar Fields
Authors: Dopazo César , Valiño Luis , Fueyo Norberto
Published: October 2003

A formulation in terms of probability density function (PDF) transport equations is presented for inert and reactive scalar fields undergoing turbulen mixing. The PDF methodology is related to the classical moment equations. The hierarchy of PDF transport equations resembles the BBGKY equations in statistical mechanics. Closure hypothesis, approximating the molecular mixing term, are described and their predictions for simple systems are compared with direct numerical simulations (DNS). Solution algorithms in terms of Monte Carlo particles are also discussed.
The Influence of Lattice Vibrations on Spin-Correlated Crystal Fields I: An Intersite Mechanism for a Dynamic Lattice
Authors: Dixon J. M. , Kelly M.
Published: October 2003

The role of lattice vibrations in providing additional contributions to spin correlated crystal fields has been investigated in the context of the calculation of zero field splittings for S-state ions. A many-electron theory, due to Stevens, which was originally developed to study exchange interactions in magnetic insulators has previously been used to study inter-site modifications to spin-correlated crystal fields in a static lattice. The present paper develops a methodology for the incorporation of lattice vibrations using a similar technique and an iterative form of perturbation theory for effective operators.
Angular-Resolved Vleed from O-Cu(001): Valence Bands, Chemical Bonds, Potential Barrier, and Energy States
Authors: Sun Chang Q
Published: October 2003

It is shown that the VLEED, furnished with appropriate modelling approaches, is able to reveal comprehensive information about the details of a surface. Constructing Brillouin zones from the critical positions on the angular-resolved VLEED spectra yields information about valence bands and in-plane reconstruction of the O-Cu(001) surface. Decoding the fine-structure features with new models [J. Phys. Chem. Solids58 903 (1997) and J. Phys.: Condens. Matt., C9, 5823 (1997)] rewards us with consistent understanding of the bond formation and its consequences. It is interpreted that the bond forming results in the dislocation of surface atoms, the variation of energy states, the nonuniformity and anisotropy of the potential barrier, and the reduction in both work function and inner potential of the surface.
Lecture on SUSY Gauge Theories and Integrable Systems
Authors: Marshakov A.
Published: October 2003

I consider main features of the formulation of the finite-gap solutions to integrable equations in terms of complex curves and generating 1-differential. The example of periodic Toda chain solutions is considered in detail. Recently found exact nonperturbative solutions to [Formula: see text] SUSY gauge theories are formulated using the methods of the theory of integrable systems and where possible the parallels between standard quantum field theory results and solutions to the integrable systems are discussed.
Discrete Hirota's Equation in Quantum Integrable Models
Authors: Zabrodin A.
Published: October 2003

The recent progress in revealing classical integrable structures in quantum models solved by Bethe ansatz is reviewed. Fusion relations for eigenvalues of quantum transfer matrices can be written in the form of classical Hirota's bilinear difference equation. This equation is also known as the completely discretized version of the 2D Toda lattice. We explain how one obtains the specific quantum results by solving the classical equation. The auxiliary linear problem for the Hirota equation is shown to generalize Baxter's T-Q relation.
P∞ Algebra of KP, Free Fermions and 2-Cocycle in the Lie Algebra of Pseudodifferential Operators
Authors: Orlov A. Yu. , Winternitz P.
Published: October 2003

The symmetry algebra P∞=W∞⊕ H ⊕ I∞ of integrable systems is defined. As an example the classical Sophus Lie point symmetries of all higher KP equations are obtained. It is shown that one ("positive") half of the point symmetries belongs to the W∞ symmetries while the other ("negative") part belongs to the I∞ ones. The corresponding action on the τ-function is obtained. A new embedding of the Virasoro algebra into gl(∞) describes conformal transformations of the KP time variables. A free fermion algebra cocycle is described as a PDO Lie algebra cocycle.
Moduli Space of Flat Connections as a Poisson Manifold
Authors: Fock V. V. , Rosly A. A.
Published: October 2003

In this talk we describe the Poisson structure of the moduli space of flat connections on a two dimensional Riemann surface in terms of lattice gauge fields and Poisson–Lie groups.
Integrable Extensions of Hubbard Hamiltonian
Authors: Avakyan A. , Hakobyan T. , Sedrakyan A.
Published: October 2003

We construct the family of spin-chain Hamiltonians, which have affine quantum group symmetry Uqĝ. Their eigenvalues coincide with the eigenvalues of the usual spin-chain Hamiltonians, but have the degeneracy of levels, corresponding to affine Uqĝ. The space of states of these spin-chains is formed by the tensor product of fully reducible representations. The fermionic representations of spin-chain Hamiltonians, which have affine quantum group symmerty, was consructed. They correspond to new extensions of Hubbard Hamiltonians. The exact ground state of some examples is presented, exhibiting superconducting behavior via η-pairing mechanism.
Viscous Instanton for Burgers' Turbulence
Authors: Balkovsky E. , Falkovich G. , Kolokolov I. , Lebedev V.
Published: October 2003

We consider the tails of probability density functions (PDF) for different characteristics of velocity that satisfies Burgers equation driven by a large-scale force. The saddle-point approximation is employed in the path integral so that the calculation of the PDF tails boils down to finding the special field-force configuration (instanton) that realizes the extremum of probability. We calculate high moments of the velocity gradient ∂xu and find out that they correspond to the PDF with [Formula: see text] where [Formula: see text] is the Reynolds number. That stretched exponential form is valid for negative ∂xu with the modulus much larger than its root-mean-square (rms) value. The respective tail of PDF for negative velocity differences w is steeper than Gaussian, ln ℘(w) ~-(w/u rms )3, as well as single-point velocity PDF ln ℘(u)~-(|u|/u rms )3. For high velocity derivatives [Formula: see text], the general formula is found: [Formula: see text].
A Continuum Approach to 2D-Quantum Gravity for c>1
Authors: Martellini M. , Spreafico M. , Yoshida K.
Published: October 2003

Two dimensional induced quantum gravity with matter central charge c>1 is studied by carefully treating both diffeomorphism and Weyl symmetries. It is shown that, for the gauge fixing condition R(g) (scalar curvature) = const, one obtains a modification of the David–Distler–Kawai version of KPZ scaling. We obtain a class of models with real string tension for all values c>1. They contain a free parameter which is, however, strongly constrained by the requirement of the non triviality of the model. The possible physical significance of the new model is discussed. In particular we note that it describes smooth surfaces imbedded in d-dimensional flat space time for arbitrary d, which is consistent with recent numerical results for d=3.
Bose–Einstein Condensation in an Ultracold Gas
Authors: Wieman Carl E.
Published: October 2003

Bose–Einstein condensation in a gas has now been achieved. Atoms are cooled to the point of condensation using laser cooling and trapping, followed by magnetic trapping and evaporative cooling. These techniques are explained, as well as the techniques by which we observe the cold atom samples. Three different signatures of Bose–Einstein condensation are described. A number of properties of the condensate, including collective excitations, distortions of the wave function by interactions, and the fraction of atoms in the condensate versus temperature, have also been measured.
Ultracold Atomic Interactions and Bose–Einstein Condensation
Authors: Heinzen D. J.
Published: October 2003

Atomic interactions play a crucial role in Bose-condensed alkali gases. The condensate self-energy, proportional to the two-body s-wave scattering length, strongly affects the stability and other properties of a condensate. Alkali atom scattering lengths have been determined only during the past few years by a combination of conventional molecular spectroscopy, photoassociation spectroscopy, and ultracold atomic collision studies. In this article, we present a brief review of alkali atom interactions and scattering length determinations.
Elementary Excitations of a Trapped Bose Gas at Zero Temperature
Authors: Stringari S.
Published: October 2003

Starting from the equations of Gross–Pitaevskii for the order parameter we investigate the collective modes of a trapped Bose-condensed gas. These excitations are analogous to the propagation of phonons in homogeneous Bose superfluids. The coupling between the monopole and quadrupole vibrations in a deformed trap is explicitly investigated and the predictions are successfully compared with recent experimental data.
Cold Atoms in a Hollow Mirror Trap
Authors: Kim J. A. , Lee K. I. , Nha H. , Noh H. R. , Jhe W.
Published: October 2003

We present a novel and simple vapour-cell magneto-optical atom trap in a pyramidal and a conical hollow mirror cavity. A single laser beam having modulation sidebands at microwaves is used for cooling, trapping and repumping of rubidium atoms. When the laser is circularly polarized and sent into the hollow region, three pairs of counterpropagating beams are automatically produced therein, having the same polarization configuration as in the conventional six beam magneto-optical trap. The precooled atom sources thus produced may be used to obtain much colder and denser atoms for study of their quantum statistical properties.
Topological Quantum Numbers in Nonrelativistic Physics
Authors: Thouless D. J.
Published: October 2003

Voltage measurements using the ac Josephson effect and electrical resistance measurements using the quantum Hall effect are capable of very high precision, despite the relatively poor control of details of the devices. Such measurements rely on topological quantum numbers, which, unlike symmetry-based quantum numbers, are insensitive to deviations of the system from ideality. The circulation in superfluid 4 He , flux quantization in superconductors and quantized Hall conductance are all examples of topological quantum numbers, but only the last two are known to be very precise. Vinen's early measurement of quantized circulation was based on measurement of the resulting Magnus force, and we (Ping Ao, Qian Niu and I) have recently shown that the strength of the Magnus force can itself be determined by an argument that shares common features with topological arguments.
Rigorous Estimates for Correlation Functions and Existence of Phase Transitions in Some Models of Interacting Bosons
Authors: Corgini M. , Sankovich D. P.
Published: October 2003

Using the so-called method of infrared bounds and a Roepstorff's inequality we obtain a lower bound for the amount of condensate and derive an upper bound for the anomalous average [Formula: see text] of Huang–Davies (HD) model. A lower bound for the static structure factor is also obtained. We generalize the HD model and prove the existence of Bose condensation for this kind of model systems. Finally we derived upper and lower bounds for correlation functions associated to a system of Fermi-particles interacting with a field of phonons.
The Brownian Vacancy Driven Walk
Authors: Toroczkai Zoltán
Published: October 2003

We investigate the lattice walk performed by a tagged member of an infinite "sea" of particles filling a d-dimensional lattice, in the presence of a Brownian vacancy.Particle-particle exchange is forbidden; the only interaction between them being hard core exclusion. The tagged particle, differing from the others only by its tag, moves only when it exchanges places with the hole. In this sense, it is a lattice walk "driven" by the Brownian vacancy. The probability distributions for its displacement and for the number of steps taken, after n-steps of the vacancy, are derived. Surprisingly, none of them is a Gaussian! It is shown that the only nontrivial dimension where the walk is recurrent is d=2.
Tunneling Magnetoresistance in Ferromagnet/Insulator/Ferromagnet Junctions
Authors: Yang X. , Gu R. Y. , Xing D. Y. , Wang Z. D. , Dong Jinming
Published: October 2003

A δ-type potential with complex prefactor is modeled on the tunneling barrier of a thin insulator (I) film separating two ferromagnetic (FM) films. By matching value and slope of wave functions across the tunneling barrier of a FM/I/FM junction, we obtain a general expression for tunneling conductance as a function of relative orientation θ between magnetizations of the two ferromagnets, barrier height and interface roughness. It is shown that the magnitude of tunneling magnetoresistance is strongly dependent on θ, but much less affected by the barrier height and the interface roughness.
Noise, Errors and Information in Quantum Amplification
Authors: D'ariano G. M. , Macchiavello C. , Maccone L.
Published: October 2003

We analyze and compare the characterization of a quantum device in terms of noise, transmitted bit-error-rate (BER) and mutual information, showing how the noise description is meaningful only for Gaussian channels. After reviewing the description of a quantum communication channel, we study the insertion of an amplifier. We focus attention on the case of direct detection, where the linear amplifier has a 3 decibels noise-figure, which is usually considered an unsurpassable limit, referred to as the standard quantum limit (SQL). Both noise and BER could be reduced using an ideal amplifier, which is feasible in principle. However, just a reduction of noise beyond the SQL does not generally correspond to an improvement of the BER or of the mutual information. This is the case of a laser amplifier, where saturation can greatly reduce the noise-figure, although there is no corresponding improvement of the BER. Such mechanism is illustrated on the basis of Monte Carlo simulations.
Dissipative Quantum Dynamics: The Role of the Lateral Confinement
Authors: Wan C. C. , Huang Ying , Guo Hong
Published: October 2003

The dissipative quantum dynamics of electron transport in a two dimensional quantum wire is studied. The wire is modeled by a parabolic confining potential in one of the spatial directions. Quantum dissipation is provided by the electron coupling to a phonon bath using a simplified Fröhlich type model, and the problem is solved in closed form. We find that the lateral electron sub-bands give rise to a quasi-periodic behavior of a quantity which is essentially the transport impedance, and this leads to very different behavior of the electron drift velocity as compared to the case without lateral confinement.
Quantum Binary Decision for Driven Harmonic Oscillator
Authors: Paris Matteo G. A.
Published: October 2003

We address the problem of determining whether or not a harmonic oscillator has been perturbed by an external force. Quantum detection and estimation theory has been used in devising optimum measurement scheme according to the Neyman–Pearson criterion. Detection probability has been evaluated for different initial state preparations of oscillator. The corresponding lower bounds on minimum detectable perturbation intensity has been evaluated and a general bound for random phase perturbation has been also induced.
Wiener–Hopf Method Applied to the X-ray Edge Problem
Authors: Janiš V.
Published: October 2003

We apply the Wiener–Hopf method of solving convolutive integral equations on a semi-infinite interval to the X-ray edge problem. Dyson equations for basic Green functions from the X-ray problem are rewritten as convolutive integral equations on a time-interval [0,t] with t→∞. The long-time asymptotics of solutions to these equations is derived with the aid of the Wiener–Hopf method. Although the Wiener–Hopf long-time exponents differ by a factor of two from the solution of Nozières and De Dominicis we demonstrate how the latter and the critical exponents of measurable amplitudes from the X-ray problem can be derived from the former. We explain that the difference in the exponents arises due to different ways of performing the long-time limit in the two solutions. To enable the infinite-time limit in the defining equations a new infinite-time scale τ→∞, interpreted as an effective lifetime of the core-hole, must be introduced. The ratio t/τ decides about the resulting critical exponent. The physical relevance of the Nozières and De Dominicis as well as of the Wiener–Hopf exponents is discussed.
Transport and Electronic Properties of Y0.4Pr0.6Ba2-ySryCu3O7-δ (y=0,1.0)
Authors: Cao Guanghan , Song Hongqing , Xu Zhuan , Yu Weihua , He Jiangping , Zhang Xuanjia , Jiao Zhengkuan
Published: October 2003

We report measurements of the resistivity, thermoelectric power and Hall carrier number on Y0.4Pr0.6Ba 2-y Sr y Cu3O7-δ (y=0, 1.0) polycrystalline samples. The Sr-free compound exhibits semiconducting behavior, while the Sr-doped sample is superconducting at 18 K with a possible pseudo-gap structure at 255 K. Results of the thermoelectric power and Hall measurements revealed that the revival of superconductivity by the Sr substitution is due to the increase of mobile hole-concentration. We present a band picture of Pr4 f– O 2p hybridization to elucidate the variation of the transport properties.
AC Susceptibility Study of the Inter- and Intragranular Properties in (Bi,Pb):2223 Superconductor
Authors: Pop A. V. , Deltour R. , Harabor A. , Ciurchea D. , Ilonca Gh.
Published: October 2003

The temperature and amplitude of AC field dependencies of both inter-and intragranular T p and T g temperatures of the imaginary peaks of χ′′ has been studied for a sintered single phase (Bi,Pb):2223 superconductor. The AC field dependencies for T p and T g and the relation between inter- and intragrain force densities were discussed by using Müller critical-state model. From the χ′′(T) curve, the values of intergrain magnetic critical current density J cJ was obtained via the application of Bean's critical state model. J cJ (T) dependence near T c agree with the assumption of SNS intergrain junctions.
Renormalised Perturbative Series for the Impurity Levels in a Quantum Well
Authors: Gonzalez Augusto , Mikhailov Ilia
Published: October 2003

The energy levels of an impurity centre in a quantum well of width L and depth g are studied analytically . Renormalised perturbative series are constructed in the regions g L2≪1 and gL2≫1. The universal behavior of the energy in each regime is stressed. Similar results can be obtained for the impurity in a quantum wire, in a dot or in a multiwell structure.
Density Effects in the Landau–De Gennes Theory Near the Nematic-Isotropic Phase Transition
Authors: Mukhopadhyay K. , Mukherjee Prabir K.
Published: October 2003

Density effects at the nematic–isotropic phase transition is studied by means of Landau–de Gennes theory. The analysis shows that the density variation shifts the nematic–isotropic transition temperature T NI and changes the Landau–de gennes free energy expansion coefficients. The possibility of the tricritical behaviour of the nematic–isotropic phase transition is also discussed by the density variation. The low value of T NI -T* (T* is the absolute stability limit of the isotropic phase) and the various thermodynamic quantities are also calculated to compare with the experimental data.
Influence of Piezoelectric Bilinear and Biquadratic Coupling in Smectic C* Phase of Ferroelectric Liquid Crystal
Authors: Roy Susanta Sinha , Roy Subir Kumar , Mukherjee Prabir K.
Published: October 2003

A theoretical relation has been developed from the Landau free energy expansion between SmC–SmA phase transition temperature of chiral smectic compound and that of its nonchiral analogue. The bilinear and biquadratic coupling constant and the quadrupolar order parameter have been determined from the extended microscopic model in the chiral smectic-C (Sm-C*) phase of four ferroelectric liquid crystal (FLC) materials and results have been discussed.
The Theory of Boundary Critical Phenomena
Authors: Diehl H. W.
Published: October 2003

An introduction into the theory of boundary critical phenomena and the application of the field-theoretical renormalization group method to these is given. The emphasis is on a discussion of surface critical behavior at bulk critical points of magnets, binary alloys, and fluids. Yet a multitude of related phenomena are mentioned. The most important distinct surface universality classes that may occur for a given universality class of bulk critical behavior are described, and the respective boundary conditions of the associated field theories are discussed. The short-distance singularities of the order-parameter profile in the diverse asymptotic regimes are surveyed.
Trace Maps
Authors: Avishai Yshai , Berend Daniel , Tkachenko Vadim
Published: October 2003

Trace maps for products of transfer matrices prove to be an important tool in the investigation of electronic spectra and wave functions of one-dimensional quasiperiodic systems. These systems belong to a general class of substitution sequences. In this work we review the various stages of development in constructing trace maps for products of (2×2) matrices generated by arbitrary substitution sequences. The dimension of the underlying space of the trace map obtained by means of this construction is the minimal possible, namely 3r-3 for an alphabet of size r≥2. In conclusion, we describe some results from the spectral theory of discrete Schrödinger operators with substitution potentials.
New Exactly Solvable One-Parameter Model of Strongly Correlated Electrons
Authors: Karnaukhov Igor N.
Published: October 2003

We present a two band fermion model consisting of a subband of conduction electrons and a subband of local electron pairs interacting via interband interactions. The model is solved in one dimension by means of the Bethe ansatz for an empty subband of local electron pairs. The ground state energy, the chemical potential, the critical exponents, describing the asymptotic behavior of correlation functions at long distances, the effective electron transport mass have been calculated numerically for an arbitrary density of conduction electrons.
Generalized Sommerfeld Theory: Specific Heat of a Degenerate g-on Gas in any Dimension and the Generalized Riemann Zeta Function
Authors: Iguchi Kazumoto
Published: October 2003

We generalize the Sommerfeld theory for a metal where the low temperature and high density expansions are known as the Sommerfeld expansions to that for a degenerate g-on gas — an ideal gas with fractional exclusion (i.e. Haldane–Wu) statistics of 0≤g≤1 — in D dimensions, using the quantum statistical mechanics formulation in the D-dimensional momentum representation. Using the generalized Sommerfeld expansions, the specific heat of the g-on gas is obtained herein, in terms of a generalized Riemann zeta function that is a natural extension of the Riemann zeta function. When g>0, the specific heat of a g-on gas shows a linear T dependence at low temperature as well as that of a metal, but the coefficient depends on statistics g and dimensionality D of the system. Therefore, we claim that this effect of statistics g is testable by an experiment.
Lattice Gas Model with Nonlocal Interactions
Authors: Das Shankar P.
Published: October 2003

We analyze the nature of the hydrodynamic modes in a Lattice Gas Automata (LGA) model defined on a hexagonal lattice and having nonlocal interactions of attractive and repulsive type simultaneously. The model is similar in spirit to the liquid gas model of Appert and Zaleski [Phys. Rev. Lett.64, 1 (1990)]. The phase diagram for the model is computed using the kinetic pressure. The dynamics is studied with a mean field type approach in the Boltzmann approximation ignoring effects of correlated collisions. We compute the transport coefficients and the speed of sound propagation. The presence of attractive interactions show increase in the transport coefficients at intermediate densities.
Universality and Scale Invariant Dynamics in Laplacian Fractal Growth
Authors: Cafiero Raffaele , Vespignani Alessandro , Zapperi Stefano , Pietronero Luciano
Published: October 2003

The individuation of the scale invariant dynamics in Laplacian fractal growth processes, like diffusion-limited aggregation (DLA), is an important problem whose solution would clarify some crucial issues concerning the origin of fractal properties and the identification of universality classes for such models. Here, we develop a real space renormalization group scheme to study the dynamic evolution of DLA in a restricted space of relevant parameters. In particular, we investigate the effect of a sticking probability P s and an effective noise reduction parameter S. The renormalization equations flow towards an attractive fixed point corresponding to the scale invariant DLA dynamics ([Formula: see text], S*≃2.0). The existence of a non-trivial fixed point value for S, shows that noise is spontaneously generated by the DLA growth process, and that screening, which is at the origin of fractal properties, persists at all scales.
Damping of Oscillations in Layer-by-Layer Growth
Authors: Kallabis H. , Brendel L. , Krug J. , WOLF D. E.
Published: October 2003

We present a theory for the damping of layer-by-layer growth oscillations in molecular beam epitaxy. The surface becomes rough on distances larger than a layer coherence length which is substantially larger than the diffusion length. The damping time can be calculated by a comparison of the competing roughening and smoothening mechanisms. The dependence on the growth conditions, temperature and deposition rate, is characterized to be a power law. The theoretical results are confirmed by computer simulations.
Experiments in a Perfect World: Computer Simulations of Growth
Authors: Jensen Pablo , Larralde Hernán
Published: October 2003

We present two examples of computer simulations which can give unique information on the growth mechanisms of nanostructures and thin films. First, the morphologies and the island size distributions in the usual epitaxial growth models are studied. This information cannot be obtained from simple analytical approaches such as mean-field calculations or scaling analysis. Second, we analyze a new model which includes monomer evaporation and we show that computer simulations can help deciding between different mean-field analysis and lead to the correct growth exponents.
Crossover Scaling in Thick Film Growth on Vicinal Surfaces
Authors: Pimpinelli Alberto , Peyla Philippe
Published: October 2003

Crystal growth by particle deposition on a vicinal surface is studied by kinetic Monte Carlo simulations as a model for molecular beam epitaxy. In particular, the crossover between step flow and layer-by-layer growth during thick film deposition is investigated as a function of the atom deposition rate F, temperature and step-step distance d. The crossover scaling function for the island density is derived analytically by coupling rate equations to the Burton, Cabrera and Frank theory for step flow.
Three Mysteries in Surface Science
Authors: Chame Anna , Lançon Frédéric , Politi Paolo , Renaud Gilles , Vilfan Igor , Villain Jacques
Published: October 2003

The story of some not yet solved problems is presented, putting emphasis on the respective role of instrumentation, ab initio theories, phenomenology and simulations.
How are Mismatched Systems Ruled by the Wedding Between Surfaces and Strains? Two Examples
Authors: Priester C.
Published: October 2003

In mismatched heteroepitaxy, the two main leading parameters are strain relaxation and surface tension. We emphasize the role of surfaces in two cases: nucleation of self assembled quantum dots in highly mismatched heteroepitaxy and strain distribution in a strained quantum well deposited on the cleaved edge of a strained superlattice.
An Experimental Study of Step Dynamics under the Influence of Electromigration: Si(111)
Authors: Métois J.-J. , Audiffren M.
Published: October 2003

The velocity of monoatomic step motion in the neighborhood of a bunch has been measured in situ using a UHV electron microscope. The width of step bunches at different temperatures and the intrinsic time that lead to step bunching have also been determined. Direct and alternating current were used to heat the Silicon(111) between 1000°C and 1300°C. The results show that the diffusion regime prevails. The asymmetry of the surface diffusion of adatoms is proved experimentally. It is consistent with the adatom electromigration effects. The surface diffusion field under the influence of an electric current can induce an attractive force between the steps. This force balances the step-step repulsive interactions (entropic and energetic) inside the bunch and stabilizes its width. The effective charge on the adatom has been estimated from the critical frequency of AC when the step bunching does not operate. It is around 0.001 electron.
A Study of the Spectral Functions and Complex Band Structures for the Disordered Binary Alloys: AgPd and AuFe
Authors: Biswas Parthapratim , Sanyal Biplab , Mookerjee A. , Chowdhury Nasreen , Ahmed Mesbahuddin , Halder Amal
Published: October 2003

We apply the augmented space recursion method to the study of the spectral densities and the complex band structures of two alloy systems AgPd and AuFe, both in the first and second order TB-LMTO approximations.
Augmented Space Recursion for Spectral Functions for Disordered Binary Alloys: Some Comments
Authors: Biswas Parthapratim , Sanyal Biplab , Mookerjee A. , Halder Amal , Ahmed Mesbahuddin
Published: October 2003

We discuss the symmetries of the configuration space for homogeneously disordered binary alloys and argue that these symmetries must be maintained in any meaningful approximation if the results are to be physically significant.
Determination of the Donor–Acceptor Pair Separation in GaP Semiconductor Doped with Sulfur and Zinc Using its Photoluminescence Spectrum
Authors: Baskoutas S. , Athanasiou N.S.
Published: October 2003

Considering the gallium phosphide (GaP) semiconductors doped with sulfur (S) and zinc (Zn) acceptors, we have studied the behavior of Huang-Rhys factor S theor as a function of the donor–acceptor (D–A) pair separation R. It turned out that the form of the bands — broad or narrow — that are attributed to (D–A) recombination, depends on the values of the pair separation — large or small, respectively. More specifically for R=0.5 nm we obtain S theor =0.117 and for R=3.5 nm, S theor =3.616. The above values of the factor S impose sub-Poissonian (with ℏω=49.97 meV) and super-Poissonian (with ℏω=78 meV) distribution shapes on the bands.
I. First Principles Cluster Calculations for the Electronic Structures of CuO7 Octahedron and CuO5 Pyramid
Authors: Sano Akihiro , Eto Mikio , Kamimura Hiroshi
Published: October 2003

In this paper we first describe the multi-configuration self-consistent field method with configuration interaction (MCSCF-CI) which is a variational method most suitable for strongly-correlated cluster systems. Then the calculated results of CuO 6 cluster embedded in hole-doped La 2-x Sr x CuO 4 and of CuO 4 cluster in the electron-doped Nd 2-x Ce x CuO 4 are reviewed. Finally the calculated results on the electronic structure of CuO 5 pyramid embedded in the insulating YBa 2 Cu 3 O 6 and superconducting YBa2Cu3O7 are newly presented. In the latter case we will clarify an important role of the Cu-O chain in the electronic and superconducting state of YBa2Cu3O7 .
II. Electron-Spin Coupled State in the Superconducting Concentration Region
Authors: Sano Akihiro , Suwa Yuji , Kamimura Hiroshi
Published: October 2003

A new theoretical explanation is given for the superconducting state in copper oxides, based on the first principles variational calculation for CuO6 octahedron and CuO5 pyramid. The key feature of the state is the following: A coherent motion of itinerant holes due to the alternant appearance of low-spin and high-spin states in the presence of a local antiferromagnetic (AF) ordering of the Cu localized spins creates a metallic and superconducting state. This theoretical prediction is supported by very recent neutron inelastic scattering experiments by two groups. On the basis of this new metallic state, the temperature versus hole concentration phase diagram is formed, and, based on this diagram, the openings of the spin gap and a new normal-state energy gap are discussed.
III. Energy Bands, Fermi Surfaces and Density of States of the Hole Carriers in the Presence of the Local Antiferromagnetic Ordering
Authors: Ushio Hideki , Kamimura Hiroshi
Published: October 2003

We have separated a hole carrier and a localized spin, by treating the exchange interaction between the spins of a carrier hole and a localized spin in a mean field sense. Then we have constructed the effective one-electron-type band structure for the hole carriers in the presence of the antiferromagnetic (AF) ordering of the localized spins. In the case of the undoped La2CuO4 all the energy bands are fully occupied by electrons so that La2CuO4 is an insulator. In this sense the present energy bands which include the many body effect fully is completely different from the ordinary energy band in the local density functional method. The top of the highest valence band is at (π/a, π/a, 0)-point, and the calculated Fermi surface is small as far as the spin correlation length of the AF order is larger than the mean free path. Based on this energy band and Fermi surfaces we have calculated various normal state properties and explained their anomalous features, such as the x-dependence of the electronic specific heat, the linear temperature dependence of the resistivity down to T c , the x-dependence of the Hall coefficient with the sign change, the large T dependence of R H , the incommensurate peak of the neutron scattering and the instability at x=0.125.
IV. Calculation of Electron–Phonon Coupling and Spectral Function for La2-XSrxCuO4, and the Appearance of the d-Wave Pairing
Authors: Ushio Hideki , Kamimura Hiroshi
Published: October 2003

We have calculated the k, k′-dependence of the spectral function α2 F(Ω, k, k') using the renormalized one-electron-type band structure obtained in the previous paper III of this series in which the states of carriers and localized spins are separated by the mean field approximation for the localized spins and the latter form a local antiferromagnetic order. It is shown that the electron-phonon interaction which scatter the pairs of electrons from a pair-state (k↑, -k↓) to a different pair-state (k′↑, -k'↓) is repulsive for some combinations of (k, k′) and attractive for other combinations, because of the characteristic feature of the wavefunctions in LSCO in the presence of the local antiferromagnetic order. As a result the spectral function has mainly a d-wave component, and the effective electron-phonon coupling constant for the d-wave pairing, λd, is estimated as 1.96 for x=0.15.