bluuebunny/crossref_metadata_2025 huggingface dataset:
THEORY OF ELECTRON TRANSPORT THROUGH QUANTUM CONSTRICTIONS IN SEMICONDUCTOR NANOSTRUCTURES
Authors: SARMA S. DAS , HE SONG
Published: November 2004

Detailed numerical results are presented for the calculated conductance of quantum point contacts, or, narrow constrictions between high mobility two-dimensional electron systems fabricated on semiconductor nanostructures. The conductance is calculated from the two-terminal multichannel transmission matrix formalism using the recursive single-particle Green’s function technique. The Green’s functions are obtained recursively for a tight-binding two-dimensional disordered Anderson lattice model representing the constriction. The conductance is calculated as a function of the shape and the size of the constriction (i.e., its geometry), the temperature, and, the elastic disorder in the system. Our main results, which are consistent with experimental findings, are: (1) increase of elastic scattering destroys the quantization; (2) for a fixed amount of disorder (i.e., for a given value of the elastic mean free path), the conductance quantization is poorer for longer constrictions; (3) in general, the quantization is poorer for higher quantum numbers or subbands; (4) constrictions with sharper geometry have sharper quantization, but may have quantum resonances associated with their sharp corners; (5) the quantum resonances (in sharp constrictions) are suppressed for shorter constriction lengths and at higher temperatures; (6) in general, higher temperatures lower the quantization quality by smoothening out the conductance except for sharp constrictions where at the lowest temperatures the quantum resonances show up, adversely affecting the quantization; (7) in smooth or adiabatic constrictions, the conductance quantization is smooth (but not extremely accurate) but, adiabaticity is not a necessary requirement for conductance quantization; (8) in general, geometry, finite temperature, and finite disorder effects do not allow better than 1% type accuracy in the quantization (compared with integral multiples of 2e2/h) even in the best of circumstances; (9) increase of elastic disorder smoothly takes the system from a conductance quantized regime to the regime of universal conductance fluctuations; and, (10) inelastic scattering, which we treat only in a very crude phenomenological model, behaves similar to thermal effects in broadening and smearing the sharpness of the conductance quantization. We also discuss the effect of an external magnetic field on the conductance quantization phenomenon. Some results are given for the conductance of two constrictions in series.
COLLECTIVE FIELD THEORY TO MAGNETIC-FIELD-INDUCED SPIN-DENSITY-WAVE-STATE IN BECHGAARD SALTS, (TMTSF)2X
Authors: ROZHAVSKY ALEXANDRE S.
Published: November 2004

A field description of spin-density-wave (SDW) in a quasi-two-dimensional metal with open Fermi surface in magnetic field, is proposed. The SDW transition temperature, T c (H), and the Hall conductivity σxy, are calculated. The dependence T c (H) is found to be different from that of the Bardeen-Cooper-Schrieffer model, in particular, a threshold field, H c , found its natural explanation. It is proved that the quantized Hall conductivity arises from the chiral anomaly terms in the effective action provided there is pinning of chemical potential in the gap of extended states.
THEORY OF MULTIPLE EXCITONIC PEAKS IN THE LUMINESCENCE SPECTRA OF DOPED QUANTUM WELLS IN A MAGNETIC FIELD
Authors: VILK YURY M. , RUCKENSTEIN ANDREI E. , SCHMITT-RINK STEFAN
Published: November 2004

We report calculations of the luminescence spectra of doped quantum wells in a perpendicular magnetic field. We use the variational Hartree-Fock approximation and include Coulomb coupling of different Landau levels to all orders. In the case of localized holes we obtain multiple excitonic peaks with an oscillator strength which increases towards the chemical potential, in good agreement with recent experiments.
PHONON REPLICA IN THE I–V CHARACTERISTICS OF A GaAs/AlGaAs DOUBLE-BARRIER STRUCTURE
Authors: ZOU NANZHI , RAMMER J. , CHAO K.A.
Published: November 2004

We have performed a detailed calculation of the I–V characteristic of a GaAs/Al x Ga 1−x As double barrier structure, with special emphasis on the phonon replica. For commonly used experimental samples (x≃0.3–0.4), the interface-like phonon modes produced by alloying and localized in barriers near the interfaces give the dominating contribution to the phonon replica. Our calculated I–V curves for samples of both symmetric and asymmetric barriers with or without bistability agree extremely well with experimental observations.
AN INTRODUCTION TO YANGIAN SYMMETRIES
Authors: BERNARD DENIS
Published: November 2004

We review some aspects of the quantum Yangians as symmetry algebras of two-dimensional quantum field theories. The plan of these notes is the following:

1 — The classical Heisenberg model:

•Non-Abelian symmetries; •The generators of the symmetries and the semi-classical Yangians; •An alternative presentation of the semi-classical Yangians; (Digression on Poisson-Lie groups.

2 — The quantum Heisenberg chain:

•Non-Abelian symmetries and the quantum Yangians; •The transfer matrix and an alternative presentation of the Yangians.
REMARKS ON THE PHYSICAL STATES AND THE CHIRAL ALGEBRA OF 2D GRAVITY COUPLED TO C≤1 MATTER
Authors: DOTSENKO Vl. S. , LPTHE
Published: November 2004

Some elaboration is given to the structure of physical states in 2D gravity coupled to C≤1 matter, and to the chiral algebra (w∞) of CM=1 theory which has been found, in the continuum approach, by Witten and by Klebanov and Polyakov. It is shown then that the chiral algebra is being realized as well in the minimal models of gravity (CM<1), so that it stands as a general symmetry of 2D gravity theories.
THE CENTER OF THE COORDINATE ALGEBRAS OF QUANTUM GROUPS AT pα-th ROOTS OF UNITY
Authors: ENRIQUEZ BENJAMIN
Published: November 2004

The coordinate algebras of quantum groups at pα-th roots of unity are finite modules over their centers, at least in a suitable completed sense (cf. [E]). We describe their centers in the completed case, and deduce from this the centers of the non-completed algebras. As in the [dCKP] situation, it is generated by its “Poisson” and “Frobenius” parts.
INVESTIGATING THE INTEGRABILITY OF DISCRETE SYSTEMS
Authors: GRAMMATICOS B. , RAMANI A.
Published: November 2004

The question of the integrability of discrete systems is examined with emphasis on the singularity confinement method that is the discrete analog of the “Painlevé” singularity analysis for differential systems. One, all-important, result of this new method is the systematic derivation of discrete Painlevé equations. The existence of a discrete version for the continuous Painlevé equations allows us to establish a close parallel between the continuous and the discrete case.
Quantum Groups at a Root of 1 and Tangle Invariants
Authors: ROSSO MARC
Published: November 2004

One uses certain representations (in the De Concini-Kac picture) of the quantum groups [Formula: see text] for q a root of 1 to produce for R-matrices depending on rank [Formula: see text] continuous parameters. Using the formalism of Reshetikhin and Turaev, this allows to produce tangle and knot invariants depending on rank [Formula: see text] parameters. The simplest example ([Formula: see text] in the 2-dimensional representation) gives the Alexander-Conway polynomial.
PHOSPHATE TUNGSTEN BRONZES — A NEW FAMILY OF QUASI-LOW-DIMENSIONAL METALLIC OXIDES
Authors: GREENBLATT MARTHA
Published: November 2004

A brief introduction is presented on transition metal oxide bronzes and their relationship to the phosphate tungsten bronzes; the latter compounds are the major focus of this review. The phosphate tungsten bronzes (PTB) are a new class of quasi-low-dimensional materials which exhibit charge density wave (CDW) instabilities. The growth of single crystals and investigation of the physical properties including the temperature dependence of the electrical resistivity and magnetic susceptibility on oriented single crystals are discussed for selected members of the major families in the PTB’s. Correlation of the physical measurement data with structural properties, X-ray diffraction data and results of the theoretical band structure calculations are also presented.
CHARGE DENSITY WAVE TRANSITIONS IN TWO-DIMENSIONAL TRANSITION METAL BRONZES AND OXIDES
Authors: FOURY P. , POUGET J.P.
Published: November 2004

The structural instabilities towards the formation of a charge density wave (CDW) ground state exhibited by several layered Mo and W bronzes and oxides are reviewed. It is shown that in these two-dimensional (2D) metals, including the purple bronzes A x Mo 6 O 17 (A=K, Na, Tl; x≈1), the γ and η phases of MO 4 O 11 and the monophosphate tungsten bronzes with pentagonal tunnels ( PO 2)4 ( WO 3)2m(m=4, 6, 7), the CDW instability can be associated with particular chains of MoO 6 or WO 6 octahedra of the ReO 3 type slabs along which there is a strong overlap of the t 2g orbitals. The CDW critical wave vectors of the purple bronzes, Mo 4 O 11 and the tungsten bronzes with m=4 and 6 lead to a common nesting between differently oriented 1D Fermi surfaces. It is suggested that the anharmonic CDW modulation, which occurs in the tungsten bronzes with m≥7, could be the structural fingerprint of electron localization effects.
STRUCTURE, STABILITY, AND ELECTRONIC PROPERTIES OF LARGE FULLERENES
Authors: WANG C.Z. , ZHANG B.L. , HO K.M. , WANG X.Q.
Published: November 2004

The recent development in understanding the structures, relative stability, and electronic properties of large fullerenes is reviewed. We describe an efficient scheme to generate the ground-state networks for fullerene clusters. Combining this scheme with quantum-mechanical total-energy calculations, the ground-state structures of fullerenes ranging from C 20 to C 100 have been studied. Fullerenes of sizes 60, 70, and 84 are found to be energetically more stable than their neighbors. In addition to the energies, the fragmentation stability and the chemical reactivity of the clusters are shown to be important in determining the abundance of fullerene isomers.
CLASSIFICATION THEORY FOR PHASE TRANSITIONS
Authors: HILFER R.
Published: November 2004

A refined classification theory for phase transitions in thermodynamics and statistical mechanics in terms of their orders is introduced and analyzed. The refined thermodynamic classification is based on two independent generalizations of Ehrenfests traditional classification scheme. The statistical mechanical classification theory is based on generalized limit theorems for sums of random variables from probability theory and the newly defined block ensemble limit. The block ensemble limit combines thermodynamic and scaling limits and is similar to the finite size scaling limit. The statistical classification scheme allows for the first time a derivation of finite size scaling without renormalization group methods. The classification distinguishes two fundamentally different types of phase transitions. Phase transitions of order λ>1 correspond to well known equilibrium phase transitions, while phase transitions with order λ<1 represent a new class of transitions termed anequilibrium transitions. The generalized order λ varies inversely with the strength of fluctuations. First order and second order transitions play a special role in both classification schemes. First order transitions represent a limiting case separating equilibrium and anequilibrium transitions. The special role or second order transitions is shown to be related to the breakdown of hyperscaling. For anequilibrium transitions the nature of the heat bath in the canonical ensemble becomes important.
ION IMPLANTATION IN III–V SEMICONDUCTOR TECHNOLOGY
Authors: PEARTON S.J.
Published: November 2004

A review is given of the applications of ion implantation in III–V compound semiconductor device technology, beginning with the fundamentals of ion stopping in these materials and describing the use of implantation for both doping and isolation. There is increasing interest in the use of MeV implantation to create unique doping profiles or for the isolation of thick device structures such as heterojunction bipolar transistors or multi quantum well lasers, and we give details of these areas and the metal masking layers necessary for selective area processing. Finally, examples are given of the use of implantation in a variety of III–V devices.
STOCHASTIC EVOLVING MODEL FOR COMPLEX NETWORKS
Authors: KIM HYUN-JOO , CHOI YEON-MU , KIM JIN MIN
Published: November 2004

We introduce an evolving complex network model, where a new vertex is added and new edges between already existing vertices are added with a control parameter p. The model shows the characteristics of real networks such as small-world property, high degree of clustering, scale-free behavior in degree distribution, and hierarchical topology. We obtain the various values of degree exponent γ in the range 2<γ≤3 by adjusting the parameter p and find that the degree exponent decreases logarithmically with p. In addition, the clustering coefficient is tunable by changing the control parameter p, and the average path length L is proportional to ln ( ln N) with nonzero p, where N is the network size.
FRACTAL VERTEX FOR ELECTRON–ELECTRON INTERACTIONS
Authors: MAHAN G. D.
Published: November 2004

The vertex function is derived for electron–electron interactions which includes all ladder diagrams on all vertices. The equation has a fractal character because the end of each ladder has a vertex which is dressed by more ladders. Numerical solutions are presented show the vertex function gives excellent Hubbard corrections to the dielectric function.
HIGH-QUALITY Tl2Ba2Ca2Cu3O10 THIN FILMS FABRICATED VIA LASER ABLATION
Authors: LUO W. A. , TANG Y. Q. , CHEN Y. Z. , CHAN I. N. , CHEN K. Y. , SHI Y. J. , WANG X. C. , YOUNG M. , NASRAZADANI S. , SHENG Z. Z. , SALAMO G. J. , CHAN F. T.
Published: November 2004

In this letter, we describe results obtained via laser ablation to fabricate Tl 2 Ba 2 Ca 2 Cu 3- O 10 superconducting thin films using a two-step process. We found that the zero-resistance temperatures are up to 121 K, while the onset temperatures are up to 125 K. The T c and J c are mainly determined by a non-contact new technique for high-T c films. The typical critical current density, J c , is about 106 A/cm 2 at 77 K. X-ray diffraction showed that the superconducting thin films are nearly single 2223 phase and are highly oriented.
SHOCKLEY-TYPE SURFACE STATES ON THE (111) AND (110) SURFACES OF Cu-BASED ALLOYS WITH NOBLE AND TRANSITION METAL IMPURITIES
Authors: SERAGELDIN A. Y. , PRASAD R. , BANSIL A.
Published: November 2004

We have investigated Shockley-type surface states (SSS's) on ideal semi-infinite surfaces of randomly disordered alloys, Cu 70 Ni 30, Cu 80 Ni 20, Cu 90 Ni 10, Cu 85 Pd 15, Cu 95 Pd 5, and Cu 90 Au 10 using a Green's function approach. In particular, the binding energies and disorder induced smearings of the [Formula: see text]-centered SSS's on the (111) surfaces and the [Formula: see text]-centered SSS's on the (110) surfaces of these alloys are presented. Our theoretical predictions are in good accord with the available angle-resolved photoemission measurements, although the experimental results in this regard for well-characterized alloy surfaces appear to be limited to the (111) surfaces of CuPd and CuAu solid solutions. The binding energy of the SSS's is found to decrease roughly linearly with decreasing e/a ratio, but significant deviations from such a rigid-band behavior are noted for various impurities. The SSS's investigated in this article lie in the [Formula: see text] gap in the bulk alloy electronic spectrum, and their character (changes in binding energy on alloying, and disorder induced smearing) is correlated with that of the L2′ bulk level.
INVESTIGATION OF THE HYSTERETIC EFFECTS IN THE FIELD DEPENDENCE OF THE AC SUSCEPTIBILITY OF YBCO
Authors: TAYLOR K. N. R. , WANG J. , RUSSELL G. J.
Published: November 2004

The hysteretic behaviour of the complex ac susceptibility of YBCO ceramic superconductors in varying dc fields has been explained in terms of a critical state model involving both the inter- and intragranular components of the material. Reentrant susceptibility behaviour has also been observed and is used to estimate the flux compression ratio in the sample.
DOUBLE-LAYER ANYON SUPERCONDUCTIVITY WITHOUT P AND T VIOLATION
Authors: EZAWA Z. F. , IWAZAKI A.
Published: November 2004

Anyon superconductivity is studied theoretically in a double-layer system containing identical anyons. In the mean-field approximation it is shown that the system possesses the superconducting phase due to the condensation of pairs of anyons belonging to different layers. There is no violation of P and T symmetry in this phase. The ground-state wavefunction derived exhibits these features. The gap energy is also calculated explicitly as ε F for semions, ε F being the fermi energy. The magnetic field is found to be squeezed into a vortex carrying one half of the Dirac unit of the magnetic flux.
ON THE SWITCHING FROM THREE TO ONE DIMENSIONAL BEHAVIOR IN A MODEL LIQUID CRYSTAL
Authors: CHICCOLI CESARE , PASINI PAOLO , SEMERIA FRANCO , ZANNONI CLAUDIO
Published: November 2004

A Monte Carlo study of a Lebwohl-Lasher lattice model with anisotropic interaction is presented. Six different values of out of plane to the in-plane coupling ratio have been taken into account. Comparison with mean field prediction and with analytic results, when possible, are made.
X-RAY ABSORPTION MAGNETIC CIRCULAR DICHROISM: SIMPLIFIED SPIN-ALIGNMENT ANALYSIS OF F ELECTRON SYSTEMS
Authors: TOBIN J. G. , WADDILL G. D.
Published: November 2004

A simplified expression relating branching ratios to spin-alignment and circular polarization is presented for X-ray absorption in the rare-earth and actinide elements. This approximate method, while probably of less comprehensive utility than the analogous expression for 3d materials, can still provide useful information under many conditions, particularly limiting case situations. Analysis of gadolinium data will demonstrate the utility of this method.
LINEAR EXCITATIONS AROUND BROKEN-SYMMETRY MEAN-FIELD STATES: DOPING STATES IN THE COPPER OXIDES
Authors: YONEMITSU K. , BISHOP A. R. , LORENZANA J.
Published: November 2004

Nonlinear doping states in Peierls–Hubbard models are investigated through response functions in magnetic, optical and vibronic channels. A random phase approximation is used for their analysis on the basis of totally unrestricted Hartree–Fock solutions, which in general have broken symmetries. The validity of the present method is first discussed through a comparison with known exact results for a two-site two-electron system. Then this method is applied to a two-dimensional three-band system with one additional hole relative to stoichiometry, for modeling the lightly doped copper oxides. New excitation modes are induced by doping and observed in the different channels of response functions. These doping-induced modes distinguish between various doping states and helpful for the identification of doping states in specific materials.
STUDY ON MICROSTRUCTURES OF Bi(Pb)-Sr-Ca-Cu-O SUPERCONDUCTING WHISKERS
Authors: WANG RUIKUN , SUN LIHONG , LIU ANSHENG , GE YUNLONG , LIU CHUANSHENG , HU ZHUANGQI
Published: November 2004

The Bi(Pb)-Sr-Ca-Cu-O superconducting whisker has a composition of (BiPb) 2 × (SrCa) 3 Cu 2 O y and a layered single crystal structure in which the stacked layers with the same orientation have different widths. The longitudinal direction of the whiskers is along the a- or b-axis of the (BiPb) 2 (SrCa) 3 Cu 2 O y crystal. Crystal defects in the whiskers are mainly dislocations with Burgers vector of [010] or [001] and dislocation network. Some dislocation pairs with Burgers vector of [010] were observed in the bent whiskers.
ON THE RELATIVISTIC THEORY OF CHARGE
Authors: AKTAS Y. , EVANS M. W. , FARAHI F.
Published: November 2004

The concept of charge is developed relativistically by assuming that there is a linear relation between point charge (e) and point mass (m) of the type: [Formula: see text] where ζ is a scalar parameter which is unchanged in all reference frames. The theory shows that charge, in a relativistic development based on this hypothesis, depends in general on the velocity of the particle carrying the charge, and the latter vanishes at the speed of light. The hypothesis (1) also implies that charge depends on the scalar and vector potentials of the electromagnetic field. These conclusions are in qualitative agreement with experimental observation.
UNIVERSALITY IN TWO–DIMENSIONAL LANDAU LEVEL LOCALIZATION
Authors: LIU DONGZI , DAS SARMA S.
Published: November 2004

We show, based on a direct numerical calculation of the Lyapunov exponents of the system and a finite-size single parameter scaling analysis, that the strong-field Landau level localization in a disordered two-dimensional electron gas is non-universal for short-range delta function random scatterers in the sense that the critical exponents in the two lowest Landau levels are substantially different. Inclusion of Landau level coupling and/or consideration of finite range of the random scattering potential in the theory restore the universality and make the computed critical exponents approximately equal.
USING OPTICALLY DETECTED CYCLOTRON RESONANCE TO STUDY ELECTRON-EXCITON AND ELECTRON-PHONON INTERACTIONS IN SEMICONDUCTORS
Authors: TOMARU TATSUYA , OHYAMA TYUZI , OTSUKA EIZO
Published: November 2004

We review our optically detected cyclotron resonance (ODCR) studies extending over Ge, Si and ZnSe. The following three subjects are taken up: (1) Impact dissociation of excitons by free carriers, which is dominated by electron-electron and hole-hole interactions rather than by electron-hole interaction. (2) The hot-carrier state produced in Ge and Si by cyclotron resonance is discussed in terms of hot-carrier-distribution function, effective carrier temperature, and carrier kinetics. (3) The relaxation process of photoexcited carriers in ZnSe is discussed. This relaxation process is found to be dominated by electron-polar-optical-phonon interaction, which gives rise to the polaron effect and to resonant formation of free excitons following one-LO-phonon emission. Thermally detected cyclotron resonance (TDCR) is also introduced.
NONLINEAR ACTIVATION ENERGY FOR FLUX CREEP IN Ag-SHEATHED Bi2223 SUPERCONDUCTING TAPE
Authors: WEI C. D. , LIU Z. X. , YE B. , ZHOU Y. , ZENG R. , ZHANG J. , LIU A. , SHAO B. , WANG J. , ZHOU M. , YUAN G.
Published: November 2004

The magnetization curves of Ag-sheathed Bi2223 superconducting tape were measured over the temperature range from 1.5 K to 60 K for magnetic field parallel to the c-axis. The ln (ΔM) decreases linearly with B for B < B1, where B is the magnetic induction and B1 is a constant. In the ln (ΔM/ΔM0) versus B/B0 plot, the data fall on a single curve for all temperatures, where ΔM0 and B0 are constants. The results were interpreted within the framework of flux creep model, and the activation energy is assumed to be a nonlinear function of current density.
HIGH-SPEED RESPONSE OF GaAs/AlGaAs MULTIPLE QUANTUM WELL (MQW) ASYMMETRIC FABRY PEROT (ASFP) REFLECTION MODULATOR
Authors: NAWAZ M. , OLSEN B. T. , McILVANEY K.
Published: November 2004

The results of the high-speed response of GaAs/AlGaAs multiple quantum well (MQW) based asymmetric Fabry Perot (ASFP) reflection modulator are presented. The measured 3 dB electrical frequency response bandwidth of the modulator was 600 MHz. The contrast ratio of the modulator was 8.9 dB for a driving voltage of 13 V, at an operating wavelength of 862 nm.
POLAR AND CHEMICAL DOMAIN STRUCTURES OF LEAD SCANDIUM TANTALATE (PST)
Authors: PENG JULIN , BURSILL L. A.
Published: November 2004

The local structure of chemical and polar domains and domain walls is determined directly by atomic resolution high-resolution electron microscopy (HRTEM). Thus the Pb, Ta, and Sc atomic positions may be located in the images of very thin crystals. Furthermore, the Pb cation displacements away from the ideal perovskite A-site have been measured directly for the first time. Local variations in polarization direction may be mapped directly off the images, provided certain electron optical conditions are met. The results are relevant to recent theories of polar-glass behaviour in relaxor-type complex oxide functional ceramics.
COMPRESSED STRUCTURE OF A THIN EPITAXIAL FILM ABOUT Pb ON Cu(111)
Authors: FENG K. A. , HENZLER M.
Published: November 2004

Some mechanical and thermal properties of the epitaxial hexagonal thin film are discussed in terms of the equilibrium principle among the atomic forces. The larger compression of the thin film is calculated as increasing coverage and the larger compression is also explained as the substrate temperature lowers. Our results are qualitatively consistent with the experimental curves or data about Pb on Cu(111).
IMPROVEMENT OF THE SURFACE ROUGHNESS OF LaAlO3 SUBSTRATE BY DEPOSITING ANOTHER LAYER OF LaAlO3
Authors: TIAN YONGJUN , LU HUIBIN , XU SHIFA , CUI DAFU , CHEN ZHENHAO , LI LIN , YANG GUOZHEN
Published: November 2004

LaAlO 3 thin films have been deposited on (100) LaAlO 3 substrates by pulsed laser ablation. The deposited films showed the (h00) preferential orientations. Surface profiles indicated that the surface roughness of the films decreased with the increase of the oxygen partial pressure. High quality superconducting YBa 2 Cu 3 O 7 thin films have been successfully deposited by laser ablation on the (100) LaAlO 3 substrates with the LaAlO 3 layers.
SYNTHESIS OF NEW 1223-TYPE LAYERED CUPRATE (Tl, V) (Sr, Ba)2Ca2Cu3O9 WITH TC(ρ=0) ABOVE 110 K
Authors: CHEN Z.Y. , SHENG Z.Z. , LI Y.F. , PEDERSON D.O.
Published: November 2004

A new series of 1223-type (Tl, V)-based layered cuprates (Tl, V)(Sr,Ba) 2 Ca 2 Cu 3 O 9 has been successfully synthesized and identified by powder X-ray diffraction. Partial substitutions of V for Tl and Ba for Sr promote the formation of (Tl, V)-based 1223-type compounds. Nominal samples ( Tl 1−x V x) ( Sr 2−y Ba y) Ca 2 Cu 3 O z with x=0.25–0.50 and y=0.25–1.50 are pure or nearly-pure 1223 phase and exhibit TC(ρ=0) in the range of 100–110 K. This new (Tl, V)-based high TC material may be of importance in practical applications.
SPIN-SINGLET COHERENT SOLUTIONS OF THE HUBBARD MODEL
Authors: CHAKRABARTI J.
Published: November 2004

We find spin-singlet solutions of the Hubbard model for all U. These solutions, called the coherent bond states and denoted by |Z>, lie in the middle of the Mott-Hubbard or the SDW gap. The significance of these solutions is explored.
SURFACE BARRIER IN THE MIXED STATE OF ANISOTROPIC SUPERCONDUCTOR
Authors: KRZYSZTON T.
Published: November 2004

In the framework of London theory, the problem of equilibrium between magnetic flux density in the anisotropic superconductor and the applied external magnetic field is studied. The Gibbs free energy of a fluxoid in the presence of magnetic flux density in the sample is calculated. As a result, critical entry and exit fields are calculated and their dependence upon the angle which makes anisotropy axis and the direction of an external magnetic field.
VARIATION OF THE FUSION RATE OF THE DEUTERIUM MOLECULE IN AN EFFECTIVE MEDIUM
Authors: DA CUNHA LIMA I.C. , DA SILVA A. FERREIRA , FABBRI M. , TROPER A.
Published: November 2004

We have investigated the dependence of the fusion rate of a deuterium-deuterium-muon (ddµ) molecule on the relative mass correction of the d-d pair due to interaction with a medium. We show in a qualitative way that decreasing the relative mass by a factor of ten causes the fusion probability to increase by two orders of magnitude.
OSCILLATING AND RESONANCE PHENOMENA FOR A SYSTEM OF ANYONS IN A MAGNETIC FIELD
Authors: ARONOV I.E. , BOGACHEK E.N. , KRIVE I.V. , NAFTULIN S.
Published: November 2004

We apply the concept of fractional statistics to the two-dimensional conductors. The effective Lagrangian of an external magnetic field in anyon medium at finite temperature and density is presented. The diamagnetic response to the external field is studied at temperatures above Tc (i.e. in the normal phase) for various values of external parameters. Oscillations of both thermodynamic (the de Haas-van Alphen effect) and kinetic (the Shubnikov-de Haas effect) quantities are re-examined. Numerous peculiarities arise from the fact that anyon systems possess a nonzero “statistical” flux Φ=2πħc/Ne (which is known to be a manifestation of the spontaneous parity breakdown). The cyclotron resonance is suggested as a direct test on possible parity violation which is the key point anyonics.
A NEW FERMION-SPIN TRANSFORMATION TO IMPLEMENT THE CHARGE-SPIN SEPARATION
Authors: FENG SHIPING , SU Z.B. , YU L.
Published: November 2004

We propose a new fermion-spin transformation to implement the charge-spin separation in the large U Hubbard, or the equivalent t-J model. The charge degree of freedom is represented by a spinless fermion while the spin degree of freedom is represented by a hard-core boson. The local constraint for single occupancy is exactly satisfied. Very good agreement with exact solution is obtained for one-dimensional case in the mean field approximation, regarding the total energy, gapless spinon and holon spectra, and the momentum distribution of physical electrons. The same approximation yields good doping dependence of the staggered magnetization in the two-dimensional case.
PERSISTENT CURRENTS DUE TO EVANESCENT MODES
Authors: DEO P. SINGHA , JAYANNAVAR A.M.
Published: November 2004

We have calculated the persistent currents and the density of states in an open metallic ring connected to an electron reservoir in the presence of a magnetic flux. As a special case, we have considered the situation wherein electrons enter and leave the ring in a sub-barrier regime characterised by evanescent modes throughout the circumference of the ring. In such a situation, the persistent current arises due to two non-classical effects, namely, Aharonov-Bohm effect and quantum tunnelling.
SIZE EFFECTS IN ORBITAL MAGNETISM
Authors: VAN RUITENBEEK JAN M. , VAN LEEUWEN DAVID A.
Published: November 2004

Size effects in orbital magnetism are briefly reviewed. We attempt to put recent developments focused on the persistent currents in mesoscopic rings into the context of earlier developments in ballistic finite systems. The relevant experimental evidence is discussed, when available.
PROPERTIES OF THE PERIODIC FLUX LATTICE ASSUMING CIRCULARLY SYMMETRIC BOUNDARY CONDITIONS
Authors: EXTREMERA ALFONSO
Published: November 2004

A cellular method appears to be a simplified procedure for the understanding of the Abrikosov flux lattice. Detailed information on superconducting properties (e.g., free energy, density of the superconducting electrons, magnetic induction) can be extracted. Some features of the flux lattice melting involving the reduced correlation lengths are discussed. In the region of intermediate density, we compare our results with those obtained for the stable triangular lattice. The Gibbs potential energy is expressed in terms of lattice sums.
SURFACE ACOUSTIC WAVE INDUCED OPTICAL EFFECTS IN A NEMATIC LIQUID CRYSTAL
Authors: GEORGE A. K.
Published: November 2004

The optical changes occurring in a homeotropically aligned nematic liquid crystal film when excited by surface acoustic waves have been studied. Striped domains at low acoustic intensities followed by acoustic streaming at high intensities have been observed. The increase in transparency of the oriented liquid crystal film under the action of surface acoustic waves also has been investigated. The experimental results compare favourably with the available theoretical model based on the effect of rotation of the plane of polarization.
ELECTRICAL TRANSPORT PROPERTIES OF C60 SINGLE CRYSTALS DOPED WITH ALKALI METALS
Authors: OGATA HIRONORI , MARUYAMA YUSEI , INABE TAMOTSU , ACHIBA YOHJI , SUZUKI SINZO , KIKUCHI KOICHI , IKEMOTO ISAO
Published: November 2004

Electronic structures of various kinds of alkali metal (Na, K, Rb or Cs)-doped C 60 solids are studied by electrical resistivity and thermoelectric power measurements by using C 60 single crystals prepared from a CS 2 solution as a starting material. For K-or Rb-doped C 60, metallic conducting behaviors in the normal conducting state and relatively sharp superconducting transitions are observed by the electrical resistivity measurements. Nearly linear-temperature dependences with the negative sign are observed in the thermoelectric power measurements at the normal conducting states for K-or Rb-doped C 60. From electron diffusion term of the thermoelectric power, the values of Fermi energy and the density of states at the Fermi energy are estimated by assuming the three-dimensional free electron model, which are in substantial agreement with the results of other experiments and calculations. "Metal–semiconductor transition" is observed in both the electrical resistivity and the thermoelectric power measurements for Na-doped C 60. Existence of metallic phase is confirmed by the thermoelectric power measurement in Cs-doped C 60.
NEW RESULTS ON DYNAMICAL DISORDER IN AMORPHOUS III–V COMPOUNDS
Authors: GRADO CAFFARO M. A. , GRADO CAFFARO M.
Published: November 2004

For amorphous III–V semiconductors, infrared spectrum corresponding to dynamical disorder is considered in the context of one-phonon absorption. In particular, an expression for the frequency of transversal optical mode is derived for minimum absorption. Various properties of this frequency as a function of distance are discussed. Furthermore, this frequency and minimum spectrum are determined in terms of a tensorial product of matrices. Our results are compared with experiment. Average absorption due to structural disorder is also formulated.
ON AN ORIENTATION TRANSITION IN NEMATIC LIQUID CRYSTALS INDUCED BY THE THICKNESS OF THE SAMPLE
Authors: ALEXE-IONESCU A. L.
Published: November 2004

An orientation transition observed in nematic liquid crystal samples, induced by the thickness, is interpreted in a new way. By supposing that the nematic liquid crystal contains chiral impurities, it is shown that the homeotropic orientation is stable only for thicknesses smaller than a critical one, and is dependent on the concentration of the chiral molecules. At the critical thickness, the transition from the homeotropic orientation to the distorted one is characterized by a tilt angle proportional to the square root of the actual thickness minus the critical one. This trend is typical of second order phase transitions. The agreement between the theory and the experimental data is fairly good over a large range of thickness of the sample.
TRANSITION STATE THEORY IN EXTENDED PHASE SPACE
Authors: DEKKER H. , VAN DEN BRINK A. MAASSEN
Published: November 2004

Turnover theory (of the escape Γ) à la Grabert will be based solely on Kramers' Fokker–Planck equation for activated rate processes. No recourse to a microscope model or Langevin dynamics will be made. Apart from the unstable mode energy E, the analysis requires new theoretical concepts such as a constrained Gaussian transformation (CGT) and dynamically extended phase space (EPS).
ENTROPY FOR THE THREE-LEVEL ONE-MODE JAYNES–CUMMINGS MODEL
Authors: ALISKENDEROV E. I. , HO TRUNG DUNG
Published: November 2004

The evolution of the atomic (field) entropy is calculated for the three-level one-mode Jaynes–Cummings model. Numerical calculations are performed for various values of atom–field coupling constants and the evolution of the entropy is compared with the corresponding evolutions of the mean photon number and level occupation probabilities.
ELECTRICAL TRANSPORT PROPERTIES OF SOME METALLIC GLASSES
Authors: REDDY P. VENUGOPAL , SHEKHAR S. , PURUSHOTHAM Y.
Published: November 2004

Electrical resistivity and thermoelectric power of glassy ribbons having compositions Fe 81 B 13.5 Si 3.5 C 2, Fe 67 Co 18 B 14 Si 1, Fe 39 Ni 39 Mo 4 Si 6 B 12, and Co 53 Ni 25 Fe 5 Si 11 B 6 have been studied over a temperature range of 300–750 K. The electrical transport properties of these materials are found to increase with increasing temperature, and their temperature variation has been explained on the basis of Ziman's theory.
TWO-DIMENSIONAL STRUCTURAL MODULATION IN Bi–O SURFACE LAYER OF CLEAVED Bi2Sr2CaCu2O8+δ SINGLE CRYSTAL REVEALED BY STM AT SUPERCONDUCTING STATE
Authors: TAO H. J. , YIN B. , YANG Q. S. , ZHAO Z. X. , GAO F. , DAI C. C. , BAI C. L.
Published: November 2004

The Bi–O planes of Bi 2 Sr 2 CaCu 2 O 8+δ single crystal have been investigated with low-temperature STM at 77 K. High-resolution images have been obtained, which show tetragonal lattice in a-b plane with very small in-plane modulations along both directions of Bi atomic chains. In some images, a two-dimensional structural modulation that mainly results from corrugations in the c-direction has been observed for the first time.
THEORETICAL AND EXPERIMENTAL STUDIES ON SILOXENE
Authors: DEÁK P. , STUTZMANN M. , BRANDT M. S. , ROSENBAUER M. , FINKBEINER S. , FUCHS H. D. , WEBER J.
Published: November 2004

Structural and optical properties of siloxene ( Si 6 O 3 H 6) and its derivatives obtained by chemical substitution or annealing are reviewed. The preparation of siloxene is briefly described and results of x-ray diffraction and infrared absorption are shown. The equilibrium structures of stoichiometric siloxene and the electronic properties of the corresponding 2, 1, and 0-dimensional Si-clusters are obtained from quantum chemical calculations and compared to other calculations. Experimental results concerning luminescence, luminescence excitation, absorption coefficients, magnetic resonance, and stability are presented. The origin of the optical properties of siloxene is discussed based on the accumulated experimental data and on the results of theoretical modeling.
KNOTTED VORTICES AND FERMIONIC EXCITATIONS IN BULK SUPERFLUID HELIUM
Authors: OWCZAREK ROBERT
Published: November 2004

In the present paper, knotted and linked vortices in superfluid helium were considered, following ideas presented in Ref. 1. The conclusion is that fermionic excitations could exist in bulk superfluid helium filled by knotted and linked vortex filaments.
EXCITONS IN SEMICONDUCTOR QUANTUM WIRES: RADIATIVE LIFETIMES AND POLARITONS
Authors: CITRIN D.S.
Published: November 2004

Radiative effects felt by excitons in semiconductor quantum wires are reviewed. The interaction of an exciton with the electromagnetic field is responsible for the formation of exciton polaritons, for vacuum-field Rabi oscillations, and for spontaneous emission. It is shown that exciton radiative lifetimes in defect-free quantum wires are expected to be longer than in quantum wells of comparable size. Schemes for controlling spontaneous emission and polariton dispersion, such as the use of quantum-wire arrays and cavity-embedded structures, are discussed.
BOSONIZATION OF TWO-DIMENSIONAL HUBBARD MODEL
Authors: LIU YU-LIANG , SU ZHAO-BIN
Published: November 2004

By analyzing one-dimensional (1D) chains arranged into a two-dimensional (2D) mesh and considering electrons tunneling from chain to chain at the intersection points, we use the 1D bosonization methods to describe the 2D Hubbard model, and find that the 2D Hubbard model can be completely represented by the spin and charge fields. It may provide evidence for spin and charge separation in some 2D quantum systems.
KNOTTED VORTICES AND SUPERFLUID PHASE TRANSITION
Authors: OWCZAREK ROBERT
Published: November 2004

In this letter, studies of knotted vortex structures in superfluid helium are continued. A model of superfluid phase transition (λ-transition) is built in this framework. Similarities of this model to the two-dimensional Ising model are shown. Dependence of specific heat of superfluid helium on temperature near the λ point is explained.
SYNTHESIS, CHARACTERIZATION, AND HIGH-PRESSURE STUDIES OF Y0.8Sr0.2Ba2Cu3O6+x AND Y0.8Ba2.2Cu3O6+x
Authors: JEYABALAN K. , VENKATESWARAN C. , ASOKAMANI R. , NATARAJAN S.
Published: November 2004

Synthesis of air-quenched high-T c superconductors Y 0.8 Sr 0.2 Ba 2 Cu 3 O 6+x and Y 0.8 Ba 2.2 Cu 3 O 6+x exhibiting transition temperatures of 90 K and 88 K respectively and the variation of their electrical resistivity at high pressure are reported here. X-ray powder diffraction of the above systems reveal tetragonal structure.
GROWTH AND PROPERTIES OF Sr1−xNdxCuO2 INFINITE-LAYER PHASE THIN FILMS
Authors: ZHAO B.R. , ZHOU X.J. , LI J. , XU P. , JIA S.L. , WU F. , DONG C. , YAO Y.S. , LI L. , ZHAO Y.Y. , ZHAO Z.X.
Published: November 2004

Thins films of Sr 1−x Nd x CuO 2 (infinite CuO 2 layer) compounds with x=0.10–0.15 have been prepared by the rf-magnetron sputtering method. X-ray diffraction analysis showed that for the parent compound of SrCuO 2, there is a solubility limit x~0.11 for Nd. Corresponding to this limit, a single infinite- CuO 2-layer phase (Nd, Sr)CuO 2 thin film with smallest c-axis length was obtained. Exceeding this limit, infinite-layer phases with longer c-axis and long c-axis tetragonal phase (the second phase) coexisted. Further, the superconducting indication presented by both resistive transition (at ~28 K) and Meissner effect was also found for a thin-film sample with x~0.11.
ELECTROSTATIC SCREENING IN FULLERENE MOLECULES
Authors: GONZÁLEZ J. , GUINEA F. , VOZMEDIANO M.A.H.
Published: November 2004

The screening properties of fullerene molecules are described by means of a continuum model which uses the electronic wave functions of planar graphite as a starting point. The long-distance behavior of the system gives rise to a renormalizable theory, which flows towards a nontrivial fixed point. Its existence implies an anomalous dielectric constant. The screening properties are neither metallic nor insulating. Alternatively, the intramolecular screening is obtained from a simple approximation to the electronic wave functions. Intermolecular effects are also calculated. As a consistency check, it is shown that the observed polarizability of C 60 is well-reproduced.
COULOMB BARRIER TRANSMISSION RESONANCE FOR ASTROPHYSICAL PROBLEMS
Authors: KIM YEONG E. , ZUBAREV ALEXANDER L.
Published: November 2004

In estimating the nonresonance nuclear reaction cross sections σ(E) at low energies (≲20 keV) needed for astrophysical calculations, it is customary to extrapolate higher energy (≳20 keV) data for σ(E) to low energies using the Gamow transmission coefficient representing the probability of bringing two charged particles to zero separation distance, which is unphysical and unrealistic since the Coulomb barrier does not exist inside the nuclear surface. We present a general extrapolation method based on a more realistic barrier transmission coefficient, which can accommodate simultaneously both nonresonance and resonance contributions.
THEORETICAL MODEL FOR A FINITE-THICKNESS GAS-PUFF Z-Θ PINCH
Authors: MIRZA ARSHAD M. , IQBAL M. , KHATTAK N.A.D. , MURTAZA G.
Published: November 2004

A dynamic model for a finite-thickness gas-puff Z-θ pinch is proposed. The snowplow effect is incorporated to describe the dynamics of an imploding annular plasma shell of finite thickness. Our numerical results demonstrate that for a thick gas-puff layer, fast compression occurs which produces an ultrahigh magnetic field on a time scale much less than the rise time of the Z-pinch current. For a very thin puff layer, however, the current sheath moves like a constant mass layer as described by Rahman et al.
CORRELATION EFFECTS AND ELECTRON-PHONON INTERACTION IN DOPED FULLERITE
Authors: IVANOV VALERY , PUCCI RENATO , YARUNIN VLADIMIR
Published: November 2004

We propose a model for A x C 60 systems involving both Hubbard repulsion of alkali electrons in the narrow LUMO band of C 60 and their interaction with both high- and low-frequency phonon modes. In our approach, these phonons play different roles in the determination of a nonzero interband hopping integral hp, which increases the value of the superconductive critical temperature T c . A nonadiabatical approximation is used for the calculation of the soft-phonon-electron scattering. In the framework of the Gor’kov method and the kinematical high-T c mechanism, we have obtained an expression for T c as a function of the A atom concentration x and found that the superconducting gap Δ0 satisfies the inequality 2Δ0/T c >3.53. The qualitative agreements with experimental data were obtained.
YBa2Cu3O7−x THIN FILMS GROWN ON SAPPHIRE WITH EPITAXIAL YTTRIA-STABILIZED ZrO2 BUFFER LAYER
Authors: XU S.F. , TIAN Y.J. , LÜ H.B. , ZHOU Y.L. , CHEN Z.H. , CUI D.F. , LI L. , YANG G.Z.
Published: November 2004

We have successfully fabricated high-quality YBa 2 Cu 3 O 7−x (YBCO) thin films grown on sapphire with epitaxial Yttria-Stabilized ZrO 2 (YSZ) buffer layer by pulsed laser deposition. X-ray diffraction and Auger depth profile were used to characterize these thin films. The values of zero-resistance temperature Tco and critical current density J c (at 77 K) of c-axis oriented YBCO thin film with 500 Å-YSZ buffer layer were 91 K and 2.2×106 A/cm 2, respectively. The Auger depth profile showed that no obvious diffusion occurred between the buffer layer and the YBCO film. The influence of substrate temperature and thickness of buffer layer has been investigated.
JOSEPHSON EFFECT IN MULTILAYER QUANTUM HALL SYSTEMS
Authors: EZAWA Z.F. , IWAZAKI A. , WU YONG-SHI
Published: November 2004

We study the Josephson effect in certain weakly linked multilayer quantum Hall (QH) states at filling factors ν=1, 1/3, 1/5, …. A Landau-Ginzburg-Chern-Simons approach is developed, in which the physics is described in terms of coherent interlayer tunneling of bosonized electrons in a way similar to the usual picture in terms of Cooper pair tunneling in the superconductor case. The observation of the Josephson current should constitute a direct experimental test of the widely believed existence of condensation of bosonized electrons in QH fluids.
GENERALIZED STEFAN LAW
Authors: SCIPIONI R.
Published: November 2004

We obtain and discuss the properties of the g-deformed Stefan law for the black body radiation of quon particles. We prove that if we consider adiabatic transformations with a particular value of η=VT3, the Stefan law is exactly the same as for the ordinary black body.
MEASUREMENT OF THE EFFECTIVE SUSCEPTIBILITY AT THE SURFACE OF YBa2Cu3O7−δ SUPERCONDUCTOR
Authors: DARABONT Al. , GIURGIU L.V. , POP A.V.
Published: November 2004

The intra- and intergranular superconducting correlations in YBa 2 Cu 3 O 7−δ are characterized by the ac susceptibility measurements. The effective susceptibility is measured as a function of temperature by the Electron-Spin-Resonance (ESR) method, using two DPPH paramagnetic markers placed on the surface of a cylindrical superconducting sample. The appearance of two separate ESR lines at T c confirms the values of critical transition temperatures determined by the ac susceptibility.
ABSENCE OF PHASE TRANSITIONS ON TREE STRUCTURES
Authors: BURIONI RAFFAELLA , CASSI DAVIDE
Published: November 2004

We rigorously prove that the correlation functions of any statistical model having a compact transitive symmetry group and nearest-neighbor interactions on any tree structure are equal to the corresponding ones on a linear chain. The exponential decay of the latter implies the absence of long-range order on any tree. On the other hand, for trees with exponential growth such as Bethe lattices, one can show the existence of a particular kind of mean field phase transition without long-range order.
STUDY OF PERCEPTUAL SIMILARITY BETWEEN DIFFERENT LEXICONS
Authors: FREITAS CINTHIA O. A. , BORTOLOZZI FLÁVIO , SABOURIN ROBERT
Published: November 2004

The study investigates the perceptual feature similarity between different lexicons based on visual perception of the words and their representation through an observation sequence. We confirm that it is possible to use databases, which are similar in terms of morphological/perceptual features to improve the recognition performance. In this work, we demonstrated through experimentation, that it is possible to improve the recognition rate of handwritten Portuguese words by adding samples of French words in the training set. Experimental results show the efficiency of this strategy reducing the error rate.