D.L. Yin

INCOMMENSURATE MODULATED STRUCTURE IN YSR2CU2.5B0.5OY

Abstract The structural features of Y(Ba, Sr) 2 Cu 2.5 B 0.5 O y materials were studied by means of electron diffraction and high resolution electron microscopy. A new incommensurate modulated structure has been found in the YSr 2 Cu 2.5 B 0.5 O y compound. The average structure of YSr 2 Cu 2.5 B 0.5 O y is orthorhombic with cell parameters a=0.383nm, b=0.381nm and c=1.096nm. The modulation is located in the (100) plane with the wave vector q = c ★ 2 + b ★ 4.81 . Ba doping at the Sr sites induces superconductivity in this system. and causes the change of this modulation.

Inflection of the V-I characteristics of superconductors

Abstract Using an extended model of the thermally activated flux motion which considers the viscous Bardeen-Stephen dissipation in the existing flux motion model, we derived the analytical condition for the negative curvature in In(V)- In(I) curves and discussed the physical origin of the inflection of E(J) characteristics.

Flux-creep-flow crossover in laser ablation YBCO thin film

We have studied the V-I characteristics of laser ablation epitaxial YBCO thin film. Negative curvature on log-log scale was observed at large current densities. The deviation of experimental curves from Anderson-Kim model can be well explained by a dynamical contribution to the activation energy of flux jump.

Electronic structure of Ti8C12 cluster

Abstract We report a calculation research of electronic structure of Ti 8 C 12 cage. The results suggest that the Ti 8 C 12 cage is a “metallic” one. Ti d -electron makes a contribution to the DOS ( E f .

Nature of pairing in high Tc oxide superconductors

Abstract In connection with the unique structural features of the recently discovered high T c YBa 2 Cu 3 O 7 and (La,Ba) 2 CuO 4 we show that in such a multi-narrow-band system the opposite-spin interband pairs can function concurrently as both antiferromagnetic real pairs in x -space and Cooper pairs in k -space. So, contrary to the usually depairing Coulomb pseudotential μ ∗ considered in traditional superconductors, the intra-atomic Coulomb repulsive interactions in a multiband system result in a positive contribution to Cooper pairing and enhance the conventional boson-mediated (electron-phonon and/or electron-exciton) superconductivity.

Scaling of field and temperature dependencies of Hall resistivity in type-II superconductors

Abstract Based on the analysis of reported experimental data, two empirical scaling relations for the magnetic field and temperature dependencies of Hall resistivity ρ xy are found. Starting from existing theoretical model for Hall resistivity and our nonlinear response equation, we provide a possible understanding of the scaling relations. By means of the scaling relations the theoretical formula for ρ xy well fits the experimental data.

Arrangement of the oxygen atoms in the BiO-layers of superconducting Bi2Sr2CaCu2O8.2

Abstract We computed the Madelung site potentials of each ion and the total energies per cell of superconducting Bi 2 Sr 2 CaCu 2 O 8.2 for two structural models: (1) insertion of the excess oxygen atoms into the BiO-layers and (2) location of the excess oxygen atoms between the BiO-layers, and various charge distributions. The calculation results indicate that the structural model (2) is stable and has Bi 2.8+ and holes on the oxygen atoms of CuO-layers.

A STUDY OF THE STABILITIES AND SUPERCONDUCTIVITIES OF THE SUPERSTRUCTURE IN YBa2Cu3O6+x SYSTEM (0 < x < 1)

We calculated the Madelung potentials of a set of possible oxygen ordering superstructures of YBa2Cu3O6+x system by using the standard Ewald method. According to the Madelung potential criteria on cations and anions, it is easy to present the possible stable superstructures. Furthermore, the density of carriers (hole or electron) for each superstructure was obtained and the superconductivities discussed.

DETERMINATION OF PREFERRED STRUCTURE OF Bi-2212 CUPRATE BY THEORETICAL METHOD

Firstly, we calculated the Madelung site potentials and Madelung constants of Bi2Sr2CaCu2O8 cuprate for two different structural models, i.e., (1) bismuth and oxygen on the same x-y plane, and, (2) on the different x-y plane, and indicated that the latter structural model is more stable. Furthermore, we proposed a modulation structural model for the Bi2Sr2CaCu2O8.2 superconductor. These theoretical results explained some experimental observations.

Estimation of possible interlayer cooper pairing in high-Tc oxides

Abstract To explain the fact that the materials containing two or more CuO 2 sheets per unit cell have much higher superconducting T c than those with single sheet, e.g. (La, Sr) 2 CuO 4 , the possible interlayer OO and CuCu interactions were counted within the framework of a unified pairing theory. A ground state with interlayer Cooper pairs was proposed. This concept agrees with wide-spread experimental observations.