bluuebunny/crossref_metadata_2025 huggingface dataset:
MEISSNER EFFECT ON SUPERCONDUCTING YBaCu OXIDE
Authors: Yan Jialie , Shi Kexin , Din Shiying , Yu Zheng , Gao Peng , Qiu Li
Published: November 2004

The influences of multiconnection of single phase superconductor YBa 2 Cu 3 O 9−δ on its magnetization at various temperatures were investigated experimentally. The measurements of magnetization M were conduted by two procedures. They are that the magnetic field H were applied before (H—T) and after (T—H) decreasing temerature to establish superconductivty of the sample respectively. The H—T is considered to be more conceivable in revealing real Meissner effect. The experimental results show that the regions of expelling flux are of 26% of the sample volume.
PHASE TRANSITION IN BA-Y-CU-O COMPOUND AS PROBED BY POSITRON ANNIHILATION
Authors: He Yuanjin , Min Huang , Yu Weizhong , Xiong jiajiong , Cai Liying
Published: November 2004

For the first time positron annihilation spectroscopy was used to probe the phase transition in Ba-Y-Cu-O system between temperature 80–440K. It was found that beside the superconducting transition at 90K, another phase transition at 225K could be determined. Positron annihilation characteristics were found being affected by electron bounding or correlation. Phase transition at 225K was also indicated by TEM electron diffraction.
STUDY OF SUPERCONDUCTING Y-BA-CU-O THIN FILMS WITH ZERO RESISTANCE TEMPERATURE AT 77K
Authors: Zheng Jia-qi , Zheng Guo-guang , Li Dong-qi , Wang Wei , Xue Jin-min , Xiao Dong-guang , Cao Lei , Guan Wei-yian
Published: November 2004

Y-Ba-Cu-O thin films are deposited onto severval kinds of substrates by electron beam evaporating in a high vacuum system. After the heat treatment at 850–890°c for 1hr the Y-Ba-Cu-O films on the BaF2 substrates show superconducting behaviors with the midpoint Tc around 87K and zero resistance temperature at 77K. The composition and stucture analysis of these films have been studied by AES, XRFS and x-ray diffraction.
A NOTE ABOUT A MEAN FIELD THEORY OF RVB-SUPERCONDUCTIVITY MODEL
Authors: Wang Zidan , Zou Nanzhi , Pang Jinzhong , Qi Jiang , Changde Gong
Published: November 2004

From nearly half-filled Hubbard model, under second order degenerate perturbation, we obtained an approximate effective Hamiltonian defined in non-doubly occupied space, Which is the same as that proposed by P.W. Anderson et al(1, 2). A little different considerations from that in Ref.2 have been made, which causes the relation between chemical potential u and doping parameter δ is different. Tc/t was calculated at different t/U. The results we obtained are also different from that in Ref.2 at some extent, especially for δ→0. It is found that Tc is in the region of experiment results under reasonable parameter t and U.
Influence of Induced Porosity on Resistivity of YBa2Cu3O7 Superconductors
Authors: Djordjevic Zoran B. , Nenadovic Tomislav , Herak Srdjan
Published: November 2004

Preliminary evidences for the existance of a “weak” influence of porosity on the electrical properties of the high temperature YBa2Cu3O7 superconductive ceramics are presened.
TORQUE MEASUREMENTS AND FLUX LINE CREEP IN OXIDE SUPERCONDUCTORS
Authors: Giovannella C. , Rouault P. , Campbell I.A. , Collin G.
Published: November 2004

We have carried out torque measurements on sintered samples of oxide superconductors. The results show different regimes: we observe a fairly abrupt crossover from weak torque to strong torque, starting at a field of the order of 150 gauss in La1.85Sr0.15CuO4 . The torque signals are rigid-or viscous-like depending on the field and on the history, and there are associated strong creep relaxation effects. We suggest this behaviour is related to the granular nature of the superconductivity, and that the crossover field represents onset of penetration of flux lines Into the superconducting grains.
TEMPERATURE DEPENDENCE OF THE HALL EFFECT IN La2−xSrxCuO4 AND ABa2Cu3O7 (A=Y, Gd) HIGH TEMPERATURE SUPERCONDUCTORS
Authors: Petravić M. , Hamzić A. , Leontić B. , Forró L.
Published: November 2004

We present Hall effect measurements in the normal state of the high temperature superconducting ceramics La2−xSrxCuO4 (x=0, 0.1, 0.15, 0.2, 0.25, 0.3), YBa2Cu3o7 and GdBa2Cu3O7 . The first family has temperature independent Hall constant for x>0, while in the other two systems RH is proportional to 1/T. From the Hall effect it follows that the transport in these compounds is hole-like.
SPIRAL SELF-AVOIDING WALKS AND LOOPS
Authors: LIN K.Y.
Published: November 2004

Since the introduction of spiral self-avoiding walks on the square lattice by Privman in 1983, there has been considerable interest in this model and its generalizations. Recent progress on various models of spiral self-avoiding walks and loops is reviewed. We discuss the methods to derive exact results for (I) the number Sn and the mean end-to-end distance Rn of spiral self-avoiding walks with n steps on the square and triangular lattices, (2) the number Cn of spiral self-avoiding loops with n steps on the square and triangular lattices, (3) the number of anisotropic spiral self-avoiding loops on the square lattice.
ON THE DENSITY OF ELECTRONIC STATES OF TWO-DIMENSIONAL POSITIONALLY DISORDERED SYSTEMS WITH WEAK ELECTRON-ION POTENTIAL
Authors: BHAGWAT K.V. , LAWANDE S.V. , KHANDEKAR D.C.
Published: November 2004

The path-integral formulation of Edwards and Gulyaev has been used to investigate the behaviour of electronic density of states in the two-dimensional positionally disordered systems. The average electron propagator is evaluated within the first cumulant approximation. It is shown that in general the two-dimensional system possesses a non-zero density of states in the band-tail region. In particular an expression for the density of states for a Gaussian model of a two-dimensional disordered system is derived. Numerical values of density of states for this model for some typical values of parameters are also given.
STRUCTURE OF IRON RICH AMORPHOUS Fe-Zr BY ANOMALOUS DIFFRACTION
Authors: LARIDJANI M. , SADOC J. F.
Published: November 2004

X-ray diffraction using anomalous scattering yields to partial interference functions and radial distribution functions for an amorphous Fe 90 Zr 10 alloy. These results are compared with icosahedral models obtained from the curved space approach. A good agreement is observed which supports both X-ray results and theoretical results.
MULTIPLE SCALING AND THE FINE STRUCTURE OF PERIOD DOUBLING
Authors: MAO JIAN-MIN , HU BAMBI
Published: November 2004

To unravel the fine structure of period doubling, we have generalized the simple scaling law discovered by Feigenbaum to a multiple scaling law. This multiple scaling law is applied to period doubling in dissipative and conservative systems. New scaling exponents are found.
ALGORITHM FOR THE DETERMINATION OF SPIRAL LATTICE CHIRALITY
Authors: FAN XUDONG , PENG JU LIN , BURSILL L. A.
Published: November 2004

A convention for labelling the handedness of the generating spiral and an algorithm for determining the chirality of visible spiral structures is derived. Some applications to common natural structures, as well as some unusual cases are described.
ANISOTROPIC SPIRAL SELF-AVOIDING LOOPS
Authors: MA S. K. , LIN K. Y.
Published: November 2004

We have studied two models of anisotropic spiral self-avoiding loops on the square lattice, and developed a semi-numerical method to calculate the number Un of loops with n steps. The asymptotic form of Un appears to be n−1/2μn (n is even) where μ is the connective constant. A special case of these models was considered previously by Lin et al. They required that if the first step is north (south), the closing step cannot be west (east). The asymptotic form of Un in the special case agrees with our general result.
SCATTERING OF FAST ELECTRONS BY VAPOUR-ATOMS AND BY SOLID-ATOMS — A COMPARISON
Authors: JOSHIPURA K. N. , MOHANAN S.
Published: November 2004

A comparative theoretical study has been done on the scattering of fast electrons by free (vapour) atoms and bound (solid) atoms, in particular, the alkali atoms, Al and Cu. The Born differential cross-sections (DCS), calculated with the static plus polarization electronatom potential, are found in general, to be larger for free atoms than for bound atoms, at least at small angles of scattering. For Rb and Cs the two DCS tend to merge at very large angles only. The sample incident energies chosen are 400 eV and above.
KONDO LATTICE HAMILTONIAN FOR HIGH Tc SUPERCONDUCTORS
Authors: Castellani C. , Di Castro C. , Grilli M.
Published: November 2004

In the framework of a slave boson approach we show that the inclusion of a narrow metallic band inside the bonding-antibonding [Formula: see text] gap results in an effective Kondo lattice Hamiltonian which may be relevant for the description of the high Tc superconductors. Depending on the relative values of the effective parameters different scenarios follow.
HOLE BINDING IN AN EXTENDED MULTI-BAND HUBBARD MODEL
Authors: STEPHAN W. H. , LINDEN W. v. d. , HORSCH P.
Published: November 2004

An extended multi-band Hubbard model for the 2D CuO2 planes of high Tc superconductors is examined by exact diagonalization of the Hamiltonian for small clusters with periodic boundary conditions. Holes are shown to bind in the limit of strong onsite (Cu) and nearest neighbor (Cu-O) Coulomb repulsion. A simple explanation of the source of the binding energy is given in this strong-coupling limit.
THE FERMI SURFACES OF La2−xSrxCuO4 AND YBa2Cu3O7
Authors: Antonov V. N. , Antonov Vl. N. , Bar'yakhtar V. G. , Baglyuk A. I. , Maximov E. G. , Nemoshkalenko V. V. , Ya. Perlov A. , Yu. Savrasov S. , Uspenskii Yu. A.
Published: November 2004

The theoretical investigation of the Fermi surface (FS) and constant-energy one near the Fermi energy of La 2−x Sr x CuO 4 and YBa 2 Cu 3 O 7 is the aim of this work.
ORDERING AND DIFFUSION OF OXYGEN AT LOW TEMPERATURE IN Y-Ba-Cu-O BY MEASUREMENTS OF ELASTIC ENERGY DISSIPATION AND MODULUS
Authors: Cannelli G. , Cantelli R. , Cordero F.
Published: November 2004

The anelastic relaxation spectrum between 300 and 50 K has been investigated in YBa 2 Cu 3 O 7−x in the super- and semiconducting state. In the superconductor a phase transformation has been detected at T t ≃ 240 K . The 2nd phase forming on cooling, likely has the same orthorombic symmetry (with higher distorsion) of that of the lattice and consists of a different oxygen vacancy ordering in the chains of the basal planes. The necessity of a phase diagram where the two orthorombic phases coexist in an extended region down to low temperature is pointed out. The 2nd phase is considered to contribute to the observed softening and hysteresis of frequency (elastic constants). The raise of elastic energy dissipation around T t with thermal cycling, which is not completely recoverable by the room temperature ageing, indicates the occurrence of progressive lattice damaging with cycling number, and is attributed to the non-elastic accommodation of the 2nd-phase misfitting domains. These lattice defects are identified with the additional twins, which have been reported to form and dissolve on cycling below 240 K.

Other reproducible features observed in the superconducting state are dissipation maxima at 160 and 110 K, just above the critical temperature and a drastic decrease in dissipation below T c .

When oxygen has been removed from the basal planes (6.2 ± 0.10 atoms per formula unit) all processes illustrated above practically disappear and a new intense thermally activated relaxation process manifests itself around 70 K (in the kHz range), attributed to the stress-induced hopping of oxygen in the basal planes. The derived diffusion coefficient is extremely high: D(T) = 4 × 104 exp (− 0.10 eV/kT ).
RECENT RESEARCH RELATED TO THE MECHANISM OF HIGH-Tc SUPERCONDUCTIVITY
Authors: Katayama-Yoshida H. , Takahashi T. , Matsuyama H. , Okabe Y. , Kitaoka Y. , Ishida K. , Asayama K. , Fujimoto H. , Inokuchi H.
Published: November 2004

For the understanding of the mechanism of high-Tc suuperconductivity, (i). We determined the band structure of single crystal of Bi2Sr2CaCu2O8 by angle-resolved resonant photoemission experiment. Two dispersive bands with mainly oxygen 2p character were observed in the vicinity of the Fermi level and one of them crosses the Fermi level. This result shows the direct evidence of the Fermi-liquid states with oxygen 2p character. (ii). We performed NMR study of enriched 17 O in the CuO2 plane of the superconducting Y-Ba-Cu-O system. We found BCS-like enhancement of 17 O nuclear spin-lattice, relaxation rate 1/T1 below Tc. This shows an evidence that the high-Tc superconductivity is of s-wave type with oxygen p-hole Cooper pairing. (iii). We observed an oxygen isotope shift in Bi-Sr-Ca-Cu-O superconductors when 18 O is substituted for 16 O . The superconducting transition temperature Tc is lowered by about 0.32 K for the higher-Tc phase (Tc = 110K) and by about 0.34 K for the lower-Tc phase (Tc = 75K). These results show the evidence of a measurable contribution to the superconductivity from phonons.
TRANSPORT PROPERTIES OF THE RARE EARTH DISORDERED SYSTEMS (R1−xYbx)Ba2Cu3O7 (R = Y, Sm)
Authors: HWANG J. R. , TAI M. F. , KU H. C. , WANG W. N. , LII K. H.
Published: November 2004

Electrical and magnetic measurements have been carried out for the rare earth disordered superconducting copper oxide systems ( Y 1−x Yb x) Ba 2 Cu 3 O 7 (substitution with large rare earth mass difference) and ( Sm 1−x Yb x) Ba 2 Cu 3 O 7 (substitution with large rare earth ionic size difference). Effect of compositional variation upon room temperature electrical resistivity shows no disorder scattering contribution from the randomly distributed rare earth ions located on the (1/2, 1/2, 1/2) site of the space group Pmmm. This result indicates very low conduction electron density of states surrounding rare earth ions. On the contrary, negative deviation of electrical resistivity from the linear Vegard law was observed. This reduced conduction electron scattering was discussed through the variation of packing density, grain size and/or twin structure.
CRITICAL TEMPERATURE, ISOTOPE EFFECT AND SUPERCONDUCTING GAP IN THE MxLa2−xCuO4 AND M2RCu3O7−δ-TYPE SUPERCONDUCTORS
Authors: LIU F. H. , APOSTOL MARIAN
Published: November 2004

The effect of the oxygen-displacive modes in the M x La 2−x CuO 4 and M 2 RCu 3 O 7−δ-type superconductors is discussed with regard to its possible relevance for a high-temperature mechanism of superconductivity. Critical temperature, isotope effect and superconducting gap are estimated in fair agreement with the experimental data.
GENERALISED GINZBURG-LANDAU THEORY FOR HIGH Tc SUPERCONDUCTORS
Authors: DAS M. P. , HE HONG-XING , CHOY T. C.
Published: November 2004

In the absence of a consensus for the correct microscopic theory for high temperature superconductivity we have devoted earlier efforts to obtain a generalised Ginzburg-Landau (GL) phenomenological model. Originally the main motivation was to examine how GL theory could be generalised. Neglecting secondary order parameters like structural distortions, oxygen vacancies etc. whose effects are integrated out and phenomenologically treated in the GL coupling parameters, we concentrate on the superconducting order parameters. The resulting theory which emerged indicates severe constraints in the parameter space of models due to local gauge invariance. Now recent experiments by several groups on specific heat and conductivity fluctuations lend strong support to this theory. Additional predictions on gap parameters and tunnelling properties are exotic and could be verified. The magnetic and Abrikosov vortex states appear to be complicated and require further study.
MAGNETIC PAIRING IN TWO-DIMENSIONAL ANTIFERROMAGNETIC XY MODEL
Authors: SZETO K. Y.
Published: November 2004

A two-dimensional Ising Coulomb gas is introduced to describe the frustrated plaquettes of the two-dimensional antiferromagnetic XY model with Coulomb repulsion. The Ising spin variable corresponds to the two possible chiralities of the frustrated plaquettes, which repel each other with a screened Coulomb potential. Using the self-consistent screening analysis, the Ising Coulomb gas is shown to have a Kosterlitz-Thouless transition from a pairing phase at low temperature to a plasma phase at high temperature. The phase diagram is obtained numerically as a function of density and relative strength of the attraction between particles of opposite chiralities and the Coulomb repulsion. Possible applications to the magnetic pairing mechanism of high temperature superconductors is discussed in the context of Li doped La 2 CuO 4. It is also argued that the Aharony et al. model of magnetic pairing with the dipolar attraction can be derived as a special case of the Ising Coulomb gas model and is superceded by a stronger attractive interaction in magnetic pairing mechanism in the self-consistent analysis.
MAGNETIC PROPERTIES OF THE HIGH Tc SUPERCONDUCTORS BiSrCaCuO AND TlBaCaCuO
Authors: DAI Y. D. , LIN C. , ZHANG W. B. , FENG S. Q. , ZHU X. , WEI C. D. , LIU Z. X. , SUN Y. X. , LAN J. , LI G. Z. , WU K. , CHEN K. X. , YIN D. L. , GAN Z. Z. , ZHANG Y. F. , ZHU W. J. , LIN B. X.
Published: November 2004

Magnetic properties of the high T c superconductors BiSrCaCuO and TlBaCaCuO were investigated systematically. Magnetic current densities were calculated from magnetic hysteresis loops of bulk and powdered samples by Bean model. The results showed that flux pinning in these materials is much weaker than that in YBaCuO.
ELECTRICAL TRANSPORT MEASUREMENTS IN LOW MOBILITY TWO-DIMENSIONAL ELECTRON GASES: EFFECT OF THERMOELECTRIC POWER
Authors: CIMBERLE M. R. , FERDEGHINI C. , PUTTI M. , SIRI A. S.
Published: November 2004

Quantum Hall Effect (QHE) and field effect mobility (in zero magnetic field) were measured in commercial low mobility n-channel MOSFETs.

All the samples, at least in the region of higher mobility, show the quantized values of the Hall resistance.

However we have identified a strong effect of the "aging" of the samples: a "new" sample shows the usual QHE curves and smooth field effect mobility curves, while an "aged" sample shows pronounced peaked structures superimposed on the normal field effect mobility. The QHE curves also show an anomalous behaviour superimposed on the usual one, We attribute the deformation of the QHE curves to an onset of a thermoelectromotive force related to electric fields which produce non-uniform electron energy distribution along the channel. We give evidence of thermoelectric effects by measurements on a high quality Hall geometry MOSFET. Our experiments indicated an approximately linear dependence of the thermoelectric voltage on the electric field along the sample.
THERMOPOWER ANISOTROPY OF YBa2Cu3O7−δ SINGLE CRYSTALS
Authors: LIN SHU-YUAN , LU LI , DUAN HONG-MIN , MA BEI-HAI , ZHANG DIAN-LIN
Published: November 2004

The thermopower of YBa 2 Cu 3 O 7−δ single crystals has been measured from 300 K down to superconducting transition temperature. Strong anisotropy was observed. While the thermopower along ab-plane slightly increased with decreasing temperature, reaching 5 ~ 8 μ V/K around 120 K, the thermopower along c-axis showed typical metallic behavior with room temperature value as large as ~ 30 μ V/K .
SURFACE RECONSTRUCTED STRUCTURES AND DYNAMICS: UHV ELECTRON MICROSCOPE AND DIFFRACTION STUDIES
Authors: TAKAYANAGI K.
Published: November 2004

Atomic structures of the reconstructed surfaces and adsorbed phases on clean Si and Ge surfaces are reported. The importance of microscopic investigations in addition to diffraction methods is stressed, particularly for revealing dynamic processes at local areas on the atomic scale.
LATTICE DYNAMICS OF YBa2Cu3O7 IN THE IONIC MODEL
Authors: BELOSLUDOV V. R. , Yu. LAVRENTIEV M. , SYSKIN S. A.
Published: November 2004

A simple model of interatomic interactions in YBa 2 Cu 3 O 7, which takes into account long-range Coulombic interaction and short-range repulsion of the Born-Mayer type, is presented. On the basis of this model the calculation of lattice vibrations in YBa 2 Cu 3 O 7 is performed, and phonon dispersion curves and density of phonon states are found. A comparison with experimental data on IR and Raman spectra is presented.
THE CHEMICAL, NEGATIVE-U APPROACH TO HIGH TEMPERATURE SUPERCONDUCTIVITY
Authors: WILSON JOHN A.
Published: November 2004

Data published over the past year is examined in the light of the on-site negative U modelling proposed earlier. The model emphasizes how one must proceed beyond mixed valence to consider closely the charge transfer fluctuation conditions between the two subsystems. The situation prevailing is an intermediate U situation, being one in proximity to the Mott-Anderson transition. The high level of p-d mixing, in the copper oxide superconductors is seen to favour charge- at the expense of spin-fluctuation mediation. The proposed mixed-valently seeded, disproportionation fluctuation induced pairing requires no modification to pass from discussion of the copper oxide to the bismuth oxide superconductors. The author continues to express his opinion that it is the photoemission data which are primarily being misinterpreted, thereby encouraging misinterpretation of the neutron spin scattering and related experiments, and continuing to attract many theorists towards various spin modellings of HTSC.
EXACT RESULTS FOR THE ISING MODEL ON A 3–12 LATTICE
Authors: LIN K.Y.
Published: November 2004

We consider the Ising model on a 3–12 lattice with magnetic field. An exact functional relation is established for the partition function and our result is a generalization of Giacomini’s work on the Kagomé lattice. We calculate the zero-field magnetic susceptibility when an appropriate relation among the interaction parameters is satisfied.
UNCONVENTIONAL FEATURES OF FREE ELECTRONS IN POLYCRYSTALLINE METAL FILMS
Authors: VANCEA J.
Published: November 2004

New experimental results concerning basic electronic properties of fine grained metallic films call for theoretical models differing from standard theories:

1) The d.c. conductivity depends on the number of electrons crossing the grain boundary potentials along their background scattering length. An intrinsic scattering length for the whole polycrystal cannot be defined. 2) The Hall coefficient depends on the grain size. Below a “cut-off grain size”, electrons with p-symmetry are virtually confined within the grains. Consequently a virtual free electron value is observed. 3) The work function shows a long ranging thickness dependence. For film thicknesses comparable with electronic scattering lengths, the film’s surfaces start to interact.
NEW EXACTLY TRACTABLE LIMITS FOR CORRELATED LATTICE FERMIONS: HIGH DIMENSIONALITY AND INFINITE RANGE HOPPING
Authors: Vollhardt Dieter
Published: November 2004

We discuss two different limits where correlated lattice fermions are explicitly tractable: that of infinite range hopping and that of high dimensions. While in the first case results are almost trivial, the latter limit turns out to be particularly significant, since in d=∞ theoretical investigations are enormously simplified, while at the same time correlations remain non-trivial. Contact to finite dimensions can be made via systematic 1/d-expansions. We review the state-of-art of this approach.
ABSENCE OF A GAP IN THE EXCITATION SPECTRUM (PHONONS) OF ANHARMONIC SOLIDS
Authors: MATTIS DANIEL C.
Published: November 2004

Acoustic phonons are the suitably quantized low-lying normal modes of elastic solids. Their energies ε(k) are given by ε(k)=ħω(k), where the frequencies ω(k) are proportional to k (k=wavevector, or inverse wavelength) and vanish as w=sk (s=speed of sound) in the limit k→0. Here we prove a similar result for a reasonably general class of anharmonic solids, applicable even to such solids as the various He4 phases, H2 molecular solid, etc., which are in the extreme quantum limit. We show that the spectrum of elementary excitations in the harmonic solid provides an upper bound to the spectrum of elementary excitations in the similar anharmonic solid having the same ground state interatomic spring constantsK.
EQUILIBRATION OF TETRAHEDRALLY BONDED STRUCTURES
Authors: WEAIRE D. , O’CARROLL C. , AL-HOURANI M.
Published: November 2004

Tetrahedrally bonded structures, of the kind used in the study of amorphous silicon, are often relaxed to minimise energy within a simple potential scheme such as that of Keating. We discuss how this may be executed in a simple but highly efficient manner, as is desirable whenever the structure is modified many times in a Monte Carlo calculation.
ON THE STABILITY OF THE HARTSTEIN ASYMMETRICAL MODE
Authors: OLIVEIRA F.A. , LIMA N.P. , SANTOS A.R.
Published: November 2004

In this work we study the spectral density of the surface polaritons in semi-infinite ferromagnetic media and we show that the asymmetric mode of Hartstein et al is unstable.
EXACT GROUND STATES OF ONE-DIMENSIONAL VALENCE-BOND-SOLID HAMILTONIANS
Authors: Iske P.L. , Caspers W.J.
Published: November 2004

The ground state(s) of a Hamiltonian, introduced by Affleck, Kennedy, Lieb and Tasaki, in connection with the Valence-Bond-Solid (VBS) states, are explicitly given for the spin-1 chains. The structure of these ground states is a rather simple one. For a closed chain we find a unique ground state; for the open chain we find a fourfold-degenerate ground state. The ground state correlation function for the ring is calculated.
MAGNETIC STUDIES OF SUPERCONDUCTING GdBa2Cu3O6+δ AT LOW TEMPERATURE AND HIGH FIELD
Authors: HUANG C.Y. , SHAPIRA Y. , HOR P.H. , MENG R.L. , CHU C.W.
Published: November 2004

The magnetization of antiferromagnetic superconducting GdBa2Cu3O6+δ has been measured for ~1.5<T≤4.2 K for field up to ~20 T. We found that all Gd3+ spins are nearly parallel at very high field, and that this saturated spin subsystem coexists with superconductivity. Below the Néel temperature, 2.22 K, we observed the transition from the “canted” phase to the paramagnetic phase by the application of a high magnetic field.
THE XRD STUDY OF THE EFFECT OF SLIGHT CHANGE IN STRUCTURE ON THE SUPERCONDUCTIVITY OF Y-Ba-Cu-O SYSTEM MATERIAL
Authors: HUAQIN WANG , SHIYUAN ZHANG , TONGZHENG JIN , SHIYING HAN , DIRONG QIU , HAO WANG , NINGSHENG ZHOU
Published: November 2004

In this paper the differences in diffraction intensities from some crystal planes in the X-ray diffraction patterns of high Tc Y-Ba-Cu-O system superconductors prepared by different processing conditions and the difference among various structure cells in references are interpreted using computer fitting. The results suggest that there exists two structure cells in the single phase YBa2Cu3O7−x samples. Both structure cells have the same crystal symmetry and almost the same lattice parameters, a=3.821Å, b=3.892Å and c=11.676Å, but the different distortion degree of Cu2-O plane. According to EPR spectra measured on the same samples, it is considered that the improvement of superconductivity for the samples prepared by two-step annealing in flowing oxygen may be related to concentration of the structure cell with more serious distortion on the Cu2-O plane.
120 K SUPERCONDUCTOR TlBaCaCu2Oy
Authors: ZHAO Z.X. , CHEN L.Q. , MAI Z.H. , HUANG Y.Z. , XIAO Z.L. , CHU X. , ZHENG D.N. , JIA S.L. , WANG J.H. , CHEN G.H. , NI Y.M. , BI J.Q. , YANG Q.S. , SHEN D.H. , WANG L.Z.
Published: November 2004

We have prepared 120 K superconductor in Tl-Ba-Ca-Cu oxide system. This 120 K superconductor has been investigated by x-ray diffraction and EDAX micro-analysis. EDAX analysis shows that the composition of this superconductor is very close to TlBa ( Ca 1−x Cu x) CuO y(x−0.3). Most of the x-ray powder diffractions including all the strong ones can be indexed according to a tetragonal structure with a=5.46 Å and c= 36.2 Å which means that the sample is nearly a single phase material.
VACUUM ANNEALING AND XPS OBSERVATION ON THE HIGH Tc SUPERCONDUCTIVITY OF BiCaSrCu2Oy SYSTEM
Authors: SHEN D.H. , XU H.W. , XIE K. , WU N.J. , CHE G.C. , JIA S.L. , ZHAO Z.X.
Published: November 2004

The specimen of BiCaSrCu 2 O y was annealed at 300°–400°C in vacuum of 10–7–10–8 torr. The results of resistance and XPS measurement show that the chemical environment of elements are related to the superconducting transition.
TEM STUDY OF NEW HIGH-Tc SUPERCONDUCTORS IN THE Bi-Sr-Ca-Cu-O SYSTEM
Authors: LI J.Q. , YANG D.Y. , LI F.H. , RAN Z.Y. , ZHAO Z.X.
Published: November 2004

Electron diffraction and high resolution electron microscopy have been used to study the structure of superconducting phases in Bi-Sr-Ca-Cu-O system. The average structures of two main superconducting phases Bi 2 Sr 2 CaCu 2 O y and Bi 2 Sr 2 Ca 2 Cu 3 O y have orthorhombic cells with lattice parameters a=5.41Å, b=5.43Å, c=30.7Å and a=5.41Å, b=5.43Å, c=36.8Å respectively. Incommensurate modulations with wave vector nearly along the b* axis appear in both phases. A minor phase in this system with the same lattice parameters a and b but a smaller c(=24.6Å) has also been observed. Intergrowth of lamellae of different phases does occur in Bi-Sr-Ca-Cu-O system.
Tl2Ba2Ca3Cu4O12, A NEW 104 K SUPERCONDUCTOR OF THE FAMILY (AO)3 (A′CuO3−y)m
Authors: HERVIEU M. , MAIGNAN A. , MARTIN C. , MICHEL C. , PROVOST J. , RAVEAU B.
Published: November 2004

A new superconductor Tl 2 Ba 2 Ca 3 Cu 4 O 12 has been synthesized with a T c onset at 120 K and a zero resistance at 104 K. The X-ray powder investigation and HREM study allow a structural model to be proposed. The tetragonal cell, with a=3.852 Å and c=42.00 Å, corresponds to the intergrowth of triple rocksalt type layers with quadruple oxygen deficient perovskite layers leading to the structural formulation [ (TlO) 2 (BaO) ][ BaCa 3 Cu 4 O 9]. This oxide which represents the member n=3, m=4 of the series (A O )n (A′ CuO 3−y)m, shows that T c seems to tend towards a limit as the number of copper planes forming the perovskite layers increases.
PREPARATION OF Gd-Ba-Cu-O SUPERCONDUCTING THIN FILMS ON SrTiO3, Al2O3 AND ZrO2 BY MAGNETRON SPUTTERING
Authors: KÚŠ P. , JÁNOŠ Š.
Published: November 2004

Thin superconducting films of Gd-Ba-Cu-O have been prepared on SrTiO 3, Al 2 O 3 and ZrO 2 substrates by magnetron sputtering from single target of sintered material in an oxygen-argon atmosphere. The films were deposited at substrate temperatures between 770 and 850°C. In situ heat treatment at 400°C in pure O 2 atmosphere the films exhibited superconductivity with zero resistance transition temperatures 90.2, 91.5 and 89 K for SrTiO 3, Al 2 O 3 and ZrO 2 substrates, respectively.
ATOMIC COHERENT STATES AND TRANSIENT SQUEEZING IN THREE-LEVEL SYSTEMS
Authors: LAWANDE S.V. , JOSHI AMITABH
Published: November 2004

Dynamics of a system of N three-level atoms interacting with two coherent fields is described by SU(3) coherent states. It is shown that these states exhibit reduced quantum fluctuations. Resulting transient squeezing in the atomic system is discussed.
PREPARATION OF Gd-Ba-Cu-O SUPERCONDUCTING THIN FILMS ON SILICON SUBSTRATES BY MAGNETRON SPUTTERING
Authors: KÚŠ P. , JÁNOŠ Š.
Published: November 2004

Thin superconducting film of Gd-Ba-Cu-O have been prepared on silicon substrates by magnetron sputtering from single target of sintered GdBa 2 Cu 3 O 7−x in an oxygen-argon atmosphere. The films were deposited at substrate temperatures between 740 and 770°C. In situ heat treatment at 400°C in pure O 2 atmosphere appears the orthorombic phase with the full superconducting transition at 84 K.
CORRELATION OF CRITICAL CURRENT DENSITY WITH Cu3+ CONCENTRATION AND DENSITY IN YBa2Cu3O7−x
Authors: DOU S.X. , LIU H.K. , ZHOU J.P. , BOURDILLON A.J. , SAVVIDES N. , APPERLEY M. , GOUCH A. , SORRELL C.C.
Published: November 2004

Superconducting YBa 2 Cu 3 O 7 wires and tapes were fabricated by cold drawing, rolling and extrusion processes. It was found that the critical current density, after O 2 equilibration, correlates both with density and Cu 3+ concentration. Full density was achieved by using a special heat treatment, but the critical current density was low owing to the low Cu 3+ concentration present in this heavily twinned material. The best critical current density results were obtained for material with density of 92–95% of the theoretical value. The low critical current density of the porous specimens is attributed not only to a poor connectivity between grains but also to a low Cu 3+ concentration due to the instability of Cu 3+ at crystallite surfaces which increase in area with specimen porosity.
OBSERVATION OF SPIN FLUCTUATIONS IN Bi-Sr-Ca-Cu-O SYSTEMS
Authors: LIU J.Q. , TIAN S.Y. , YAN Y.F. , LIU Z.X. , CHANG D.W. , ZHAO Z.X.
Published: November 2004

Following the observations of spin-pair excitations in La 2 CuO 41 and YBa 2 Cu 3 O 6+δ,2 similar results in Bi-Sr-Ca-Cu-O systems are obtained. The center frequencies of the excitations are about 1900–2300 cm −1, which correspond to the value of the exchange constant J~690–840 cm −1. The extraordinary similarity suggests the same origin of superconductivity of these three kinds of copper oxides superconductors. This means that any theory of superconductivity in copper oxides should account explicitly for these highly energetic spin fluctuations.
A STUDY OF MICROCRYSTALLINITY OF Pd3Si DURING THE CRYSTALLIZATION OF AMORPHOUS Pd80Si20 BY X-RAY DIFFRACTION
Authors: XIAO K.Q. , DONG Y.D. , HE Y.Z.
Published: November 2004

The origin of Pd 3 Si grain size and lattice strain variation during the crystallization of Pd 80 Si 20 metallic glass was discussed. A correlation between the preferred orientation of grains and the sharp increase of grain size was analyzed. Results also show that the change of electrical resistivity was very sensitive to that of the grain size.
SYNTHESIS OF THE SINGLE 107 K SUPERCONDUCTING PHASE IN THE Pb-Bi-Sr-Ca-Cu-O SYSTEM
Authors: SHI F. , ZHOU S.Z. , DOU J. , SHI Z.H. , TANG L. , LI F.B. , SHI N.C.
Published: November 2004

The single phase of the high-Tc phase (107 K) in Bi-based system has been synthesized successfully for the first time by partial substituting of Pb for Bi and combined with adding more Ca, Cu based on Bi 2 Sr 2 Ca 2 Cu 3 O y formula. A long period of sintering at 880°C is necessary to get the sample and its good phase purity are proved by a.c. susceptibility measurement and the X-ray powder diffraction (XRD) analysis. The XRD pattern can be well assigned to an orthorhombic cell with a=5.418 Å, b=5.346 Å and c=37.10 Å.
THERMOPOWER IN BALLISTIC 2D MICROJUNCTION WITH QUANTIZED RESISTANCE
Authors: LESOVICK G.B.
Published: November 2004

It is shown that thermopower, under condition of good quantization of conductance (in units of e2/h), could be of the order of kB/e. When the temperature difference between opposite sides of a microjunction is finite, thermopower becomes nonlinear. This phenomenon is connected with energy dependence of conductance.
SUPERCONDUCTIVITY AND FERROMAGNETISM IN OXYGEN DEFICIENT ORTHORHOMBIC PHASE OF YBa2Cu3O7−δ
Authors: WEN H.H. , ZHANG F.Y. , CAO X.W.
Published: November 2004

Two resistance transitions have been observed on a Y-Ba-Cu-O film, one occurred in the region from 120 K to room temperature, and another always at 90 K. Experiments of both tiny magnetic torsion balance and a.c. susceptibility has shown that the large drop of resistance at high temperature was accompanied by ferromagnetism ordering, while the jump of resistance occurred near 90 K is a superconducting transition. The authors think that the ferromagnetism ordering occurred at high temperature is related to full ordering of the oxygen vacancies and the ratio of Cu 3+/ Cu 2+.
MICROWAVE INDUCED QUANTIZED VOLTAGE ACROSS THE BRIDGE OF YBaCuO SUPERCONDUCTING BULK
Authors: HUO Y.H.
Published: November 2004

When the bridge of YBaCuO superconducting bulk is exposed to microwave radiation alone and left unbiased, there is induced quantized voltage across the bridge. The relations among the magnitude of the induced voltage, microwave power and frequency satisfy qualitatively the theoretical equation suggested by J.T. Chen et al. in 1972.
DENSITY OF STATES AND CHARGE DISTRIBUTION IN LIGHTLY DOPED AND COMPENSATED QUANTUM WELL
Authors: E SILVA E.A. DE ANDRADA , LIMA I.C. DA CUNHA
Published: November 2004

In this letter we use a Semi-Classical Impurity Band Model and obtain by Monte Carlo simulation the density of states (DOS) and the impurity charge distribution inside a quantum well (QW) of Ga 1−x Al x As/GaAs . We show the existence of a Coulomb gap as has been observed in bulk semiconductors. The DOS is not very sensitive to the QW width close to the Coulomb gap, at least in the range from 1 to 4 times the Bohr radius, and shows a behavior D(E)∝|E−EF| which indicates a two-dimensional signature. We show that the neutral donors concentrate in the center of the well according to a distribution whose width and decay rate depend on the compensation and impurity concentration respectively. Those effects are expected to be observed by infra-red absorption experiments and useful in device diagnosis.
DETECTION OF SUPERCONDUCTING TRANSITIONS BY MAGNETICALLY MODULATED ELECTRICAL RESISTANCE
Authors: BOHANDY J. , PHILLIPS T.E. , ADRIAN F.J. , MOORJANI K. , KIM B.F.
Published: November 2004

A new technique for detecting superconductivity, based on observing the effect of magnetic field modulation on the dc resistance of superconductors, is presented. The phase detected response to the magnetic modulation shows a peak at Tc for both metallic and ceramic superconductors, analogous to that observed in magnetically modulated microwave absorption. The results further demonstrate that the magnetically modulated microwave absorption peak at Tc is not equivalent to the non-resonant low field microwave absorption observed in the ceramic superconductors.
DISLOCATIONS IN BiSr(Ca0.35Sr0.15Bi0.40)2Cu2Oy
Authors: TAN KEMIN , HU MEISHENG , WANG YENIN , CAO YANNI , YAN YIFENG , ZHAO ZHONGXIAN
Published: November 2004

In the single crystal BiSr ( Ca 0.35 Sr 0.15 Bi 0.40)2 Cu 2 O y a characteristic defect-superdislocation has been observed by TEM. The twist boundary resulted from the interaction of two sets of mutually perpendicular superdislocations has been analysed.
SHORT RANGE ORDER IN Ni–Nb ALLOY
Authors: ABBAS TAHIR , AHMAD NAVEED , KHAWAJA FARID AKHTAR , AHMAD ISHTIAQ
Published: November 2004

Diffuse X-ray scattering intensity was measured in polycrystalline samples of Ni–Nb system. From this diffuse scattering intensity, short-range order parameters and size effect parameters were calculated. The absolute value of short-range order parameters suggest a local order present in this alloy. The ordering potential was calculated on the basis of the statistical pseudopotential theory of ordering and it was found that the calculations take into account the experimentally observed sign of the short-range order parameters.
PHASON ELASTICITY IN EQUILIBRIUM QUASICRYSTAL MODELS
Authors: TANG LEI-HAN
Published: November 2004

The phason elasticity of random tiling and quasiperiodic crystal models is discussed. Long-wavelength phasons in the random tiling model are described by a square-gradient free energy of entropic origin. In the quasiperiodic crystal model, thermal fluctuations lead to a transition from the zero temperature singular linear phason elastic energy to a quadratic phason elastic energy at high temperatures.
EFFECTIVE ACTION OF ANTIFERROMAGNETISM IN TWO DIMENSIONS: PARITY VIOLATING GROUND STATE AND HALL EFFECT
Authors: KHVESHCHENKO D. V. , WIEGMANN P. B.
Published: November 2004

Antiferromagnetic ground states with abnormal parity characterized by "magnetic" translations are discussed. Their excitations are described by a nonlinear σ-model with the Chern-Simons term with integer ϑ and obey fractional spin and statistics with even denominators. The effective action is derived on the basis of a large N-approximation. The large N reduces the problem to the Hall effect and realizes the parity anomaly.
THEORETICAL STUDY OF RESONANT TUNNELING THROUGH RECTANGULAR N-FOLD BARRIER STRUCTURES
Authors: YAMAMOTO HIROAKI , KANIE YOUJI
Published: November 2004

Analytical expressions for the transmission coefficient and the resonant tunneling condition in one-dimensional rectangular n-fold barrier structures have been derived. It is shown that the resonance condition corresponds to the energy range of the physically possible wave functions in the Kronig-Penney model.
ENHANCEMENT OF Tc OF A BiSrCaCuOy SUPERCONDUCTOR
Authors: EAIPRASERTSAK K. , TANG I. M. , WINOTAI P. , TONTIWATTANA W. , METHASIRI T.
Published: November 2004

Liquid nitrogen quenching of the BiSrCaCuO y superconductor is studied. The BiSrCaCuO y superconductors were obtained by initially heating them up to 860°C for 48, 60 and 72 hours, respectively. These below 80 K superconductors were reheated to 860°C for 16 hours and then quenched in liquid nitrogen. The zero resistivity temperatures were 82 K, 85 K and 83 K for the three heating periods. X-ray diffraction patterns indicated that these superconductors had the "2212" structure. Their response to liquid nitrogen quenching point to them being the "4424" superconductor.
SYNTHESIS AND STUDY OF A 10% Ni DOPED (YBa2Cu3−xNixOy) HIGH Tc SUPERCONDUCTOR
Authors: SAINI N. L. , SRIVASTAVA P. , SHARMA R. K. , GARG K. B. , DWIVEDI G. L.
Published: November 2004

This study is based on our hypothesis that predicts the possibility of Y–Ba–Ni–O superconductor. A comparative study of Y–Ba–Cu–O and 10% Ni doped Y–Ba–Cu–O (having T c as high as 84 K) is presented. Resistivity, XRD, oxygen content and Cu–K-XANES measurements are reported.
TIME EVOLUTION OF MEISSNER EFFECT IN EuBa2Cu3O7−δ
Authors: SHERBAKOV A. S. , STARTSEV V. E. , VALIULIN E. G. , KOZHEVNIKOV V. L.
Published: November 2004

The results of temperature and time (at T = 4.2 K ) dependent magnetization (M) measurements on polycrystalline high T c superconductor EuBa 2 Cu 3O7−δ are reported for different magnetic fields from 2.2 kOe to 35 kOe. The measurements were performed in the field-cooled regime (measuring the Meissner effect). A new phenomenon is found: the magnetization sign inversion from negative to positive during the time at which the external conditions (T, H) remains unchanged. The differential susceptibility in a new mixed state with M > 0 is diamagnetic. It is shown that origin of this state is not connected with a flux trapping, but rather caused by the unusual nature of the vortex themselves in FC mixed state of high T c superconductors.
INFLUENCE OF Fe ON THE STRUCTURE AND SUPERCONDUCTIVITY OF YBCO
Authors: ZHAO B. R. , YANG Y. M. , ZHAO Y. Y. , SHI Y. H. , LI L. , LU K. Q. , ZHANG P. L. , SHEN Z. G. , LIN Q. , NIU S. W.
Published: November 2004

Both the tetragonal and orthorhombic phases for YBa 2( Cu 1−x Fe x)3 O y (x = 0.07, 0.10, and 0.12) were formed and investigated. It was found that the phase structure not only depends on the concentration (x) of Fe, but also depends on the synthesis process of the sample. Basically the superconductivity of the Fe doped samples is still associated with the orthorhombic phase.
HIGH TEMPERATURE SUPERCONDUCTIVITY AND COLD FUSION
Authors: RABINOWITZ MARIO
Published: November 2004

There are numerous historical and scientific parallels between high temperature superconductivity (HTSC) and the newly emerging field of cold fusion (CF). Just as the charge carrier effective mass plays an important role in SC, the deuteron effective mass may play a vital role in CF. A new theory including effects of proximity, electron shielding, and decreased effective mass of the fusing nuclei can account for the reported CF results. A quantum-gas model that covers the range from low temperature to superhigh temperature SC indicates an increased T c with reduced dimensionality. A reduced dimensionality effect may also enhance CF. A relation is shown between CF and the significant cluster-impact fusion experiments.
THE TRIANGLE PATTERN — A NEW QUASIPERIODIC TILING WITH FIVEFOLD SYMMETRY
Authors: BAAKE M. , KRAMER P. , SCHLOTTMANN M. , ZEIDLER D.
Published: November 2004

We introduce a quasiperiodic tiling with fivefold symmetry that is built from two types of triangles, an acute and an obtuse one. An easy to computerize construction algorithm based on the dualization scheme is presented that creates the pattern not pointwise but tile by tile directly. We present the vertex statistics, the inflation rule, and the Fourier analysis for selected decorations with pointlike atoms. A connection to the planar Penrose pattern and to the 3D icosahedral quasilattice is briefly discussed.
SYSTEMATICS IN THE O 1s CORE-LEVEL SPECTRA IN TRANSITION METAL OXIDES, LaMO3 (M = V, Cr, Mn, Fe, Co AND Ni)
Authors: RAO G. RANGA , SARMA D. D.
Published: November 2004

The O 1s core level spectra of transition metal oxides, LaMO 3 (M = V, Cr, Mn, Fe, Co and Ni) show three features. The main peak always appears between 528 and 530 eV and is attributed to the well-screened oxygen 1s1 2p0 hole configuration in every case. The poorly-screened feature (1s1 2p1 hole configuration) is found as a broad peak centred approximately 13 eV above the main peak. Another feature is at about 531 eV; the intensity of this peak is found to increase systematically across the series and its intensity cannot be explained in terms of carbonate impurity contamination. It is suggested that a considerable part of this 531 eV feature has an intrinsic origin.
A NEW PHASE IN Pb AND Sb DOPED Bi–Sr–Ca–Cu–O SYSTEM
Authors: YANG LI , FAN CHENGGAO , LI FANGHUA , CHENG TINGZHU , ZHOU GUIEN , CHEN ZHAOJIA , MAO ZHIQIANG , ZHANG YUHEN
Published: November 2004

In this paper, a new phase in the Pb and Sb doped Bi–Sr–Ca–Cu–O system with T c about 140 K is identified by electron diffraction. The transition temperature is determined by the susceptibility measurement. There may exist some connections between the new phase and the 110 K phase. The connections are considered to be the key to the improvement of T c .
POSSIBLE ANOMALOUS TEMPERATURE DEPENDENCES OF LONDON PENETRATION DEPTH IN THALLIUM AND BISMUTH HIGH-TEMPERATURE SUPERCONDUCTORS
Authors: BUZDIN A. I. , KUPTSOV D. A. , VUYICHIT' B. U.
Published: November 2004

Anomalous temperature dependence of London penetration depth is predicted in high-T c superconductors containing several inequivalent Cu-O layers.
A NEW HIGH PRESSURE PHASE OF THE TRANSITION METAL ZIRCONIUM
Authors: XIA HUI , DUCLOS S. J. , RUOFF A. L. , VOHRA Y. K.
Published: November 2004

High pressure energy dispersive X-ray diffraction studies were carried out on the group IV transition metal zirconium (Zr) to 32 GPa using a synchrotron source.1 A first-order phase transition between an omega phase and a bcc phase (isostructural with group V transition elements) was observed during compression and decompression in a pressure range of 30 ± 2 GPa , which is in qualitative agreement with the recent first-principles theoretical predictions. The observation of the bcc phase in Zr (a group IV transition metal) under pressure and room temperature signifies a pressure-induced electronic configuration similar to that of a group V transition metal.
RATIONAL QUASIPERIODIC SOLUTIONS FOR DYNAMICAL SYSTEMS
Authors: SEIMENIS J.
Published: November 2004

We investigate the possibility to give analytically approximate quasiperiodic solutions of the Hamiltonian equations of motion in simple rational functions. In this paper we give a formula for these solutions which is in very good agreement with the numerical solutions, although it is extremely simple.
SPIN CORRELATIONS IN THE ANTIFERROMAGNETIC CRYSTALS La2CuO4 AND K2NiF4
Authors: DING H.Q. , MAKIVIĆ M.S.
Published: November 2004

The recent progress in studying the spin correlations of the quantum 2D antiferromagnetic systems is reviewed. The theoretical results agree well with the neutron scattering experiments on both spin-1/2 La 2 CuO 4 and spin-1 K 2 NiF 4.
EXPLANATION OF SOME EXPERIMENTAL PHENOMENA OF YBCO WEAK LINK
Authors: YUHUA HUO , HONGHUI FENG , XUJIE HU , FANGWU SHAO , XIAOMING YANG
Published: November 2004

In the Josephson effect experiment researchers observed a YBCO polycrystalline constriction bridge with the phenomena of the bump, the even steps, the odd steps as well as the absence of great varieties of steps in the I–Vx curve. This paper gave an audio-visual explanation of the abovementioned experimental phenomena qualitatively.