Yin Dao-Le

Inter-layer coupling and its contribution to superconductivity: Application to high-Tc oxides

Abstract We investigate the role of inter-layer coupling and its contribution to superconductivity. It is concluded that this coupling will reduce Coulomb pseudopotential and hence have considerable effect on the enhancement of Tc. Recently discovered high-Tc superconductivity in some exotic oxides is discussed in this model.

Possible electron-exciton (E-E) interaction and high Tc superconductivity in bulk semimetals

Abstract In relation to the high Tc recently observed in Yue5f8Baue5f8Cuue5f8O systems, the possibility of formation of Cooper pairs by virtual exciton exchange in a single phase is analysed. Electron-Exciton coupling matrix elements and possible optimum condition of superconducting Tc and its upper limit are evaluated. It shows that this kind of superconductivity may display some different features compared with usual BCS superconducting phase.

An ultrasonic study of energy-gap and granular characteristics of Y1Ba2Cu3O7-y superconducting ceramic

Ultrasonic attenuation measurements of Y1Ba2Cu3O7-y have been carried out between 100 and 10 K by using 10-25 MHz longitudinal acoustic waves. It was shown from the experimental results that when T<Tc the attenuation was apparently decreased and the granular superconducting characteristics of the samples were remarkable. It was indicated from the attenuation curves that the superconductivity of Y1Ba2Cu3O7-y is related to the electron pairing states. By means of introducing a transition volume distribution function fT, the calculated attenuation curves fitted the experimental ones very well, leading to a result of 2 Delta (0)=3.5kBTc. This suggests that the existence of a superconducting energy gap and its temperature dependence should be still the same with the BCS theory, although the mechanism of the electron coupling may be quite different.

Critical Scaling of Extended Power Law I−V Isotherms near Vortex Glass Transition

In view of the question about the vortex glass theory of the freezing of disordered vortex matter raised by recent experimental observations, we reinvestigate the critical scaling of high Tc superconductors. It is found that the dc current-voltage characteristic of mixed state superconductors has a general form of extended power law which is based on the Ginzburg?Landau (GL) functional in the similar way as the vortex glass theory. Isotherms simulated from this nonlinear equation fit the experimental I?V data of Strachan et al. [Phys. Rev. Lett.?87?(2001)?067007]. The puzzling question of the derivative plot for the I?V curves and the controversy surrounding the values of critical exponents are discussed.

Thermally Activated Flux Motion in 2223 Phase High Temperature Superconductors

Isothermal V-I characteristics of Bi1.8Pb0.2Sr2Ca2Cu3Oy high temperature superconductors (HTSCs) have been systematically studied. Below the irreversibility temperature Tr(H), two important features were observed: 1) Both positive and negative curvatures can coexist in the same isothermal V-I curve, so it is different from the scaling behavior V ∝ exp(-(J0/J)μ). 2) The activation volume of flux motion is found temperature dependent as (1-T/Tr(H))-2ν with ν about 0.5. This behavior supports the existence of a two-dimensional secondary phase transition below Hc2(T) in this Bi-based HTSCs.

Structural transitions in 90K superconducting perovskite Ba2LaCu3O7-y: A TEM study

An orthorhombic-to-tetragonal structural transition of high Tc Ba2LaCu3O7-y samples was observed with transmission electron microscope (TEM). Two intermediate orthorhombic structures were discovered and discussed. Thus, the Ba2LaCu3O7-y is another member of high Tc Ba2LnCu3O7-y (Ln=Lathanides) family with lower structural transition temperature.

Extended Power Law and Hall Anomaly of High-Temperature Superconductors

Starting from the free energy of a moving vortex, we obtain the extended power law form of longitudinal resistivity ρxx and the analytical form of Hall resistivity ρxy. Based on them, we obtain a scaling relation which agrees well with the experimental data of different kinds of high-temperature superconductors. Furthermore, the theoretical results well fit the scaling results.

Extended Power Law Nonlinear Response and Amplitude-Dependent ac Susceptibility of High-TcSuperconductors

We show a nonlinear materials equation of superconductors in the form of an extended power law which can be derived from the Ginzburg–Landau (GL) functional. The critical current Jc and ac susceptibility χ are analysed by using this equation, and the puzzling question of the increasing height of the out-of-phase susceptibility peak χpeak with increasing amplitude hac is explained.

Electron-Phonon Coupling in Anion Metallic Solids and Superconducting MgB2

We analyse the Hopfield factor of the newly found superconductor MgB2 using the linear muffin-tin orbital method. Based on a uniform transferred charge density model raised, it is shown from our calculation that the high difference of electronegativity between boron and magnesium favours the high l(l + 1) angular momentum hybridization and then the Hopfield factor. Our analysis is consistent with experimental results. Comparisons with cuprate superconductors are also discussed.

One major phase in high Tc Y-Ba-Cu-O determined by electron diffraction

A major phase in high Tc Y-Ba-Cu oxide with zero resistance at 91K and high volume fraction of diamagnetic superconductive phase has been identified by electron diffraction. It appears to be an orthorhombic twinned structure with a=3.89A, b=3.82A and c=11.71A. Some defects were observed by TEM.