On the chronicle of high-T c oxide superconductors

After briefly noting some development records in phase diagrams, the stoichiometry is dealt with in more details showing the structural layer ordering in the superconducting cuprates and mentioning some correlation between thermodynamics and BSC theory of superconductivity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Normal-phase transport properties of highT c Y-Ba-Cu-O compounds

The normal state resistivity of highT _c Y-Ba-Cu-O compounds has been investigated and it is shown that the room temperature resistivity depends exponentially on the volume fraction of the non-superconducting phase. It is further shown that the dependence of normal state resistivity on temperature upto 300 K can be explained on the basis of a short-range co-operative electron-phonon coupling. This model also explains the observed positive Seebeck coefficient for the pure phase superconducting sample.     

Superconductivity in Bi2.2Ca2.8−x Sr x Cu2O y system and effect of rare earth substitution

The oxide system Bi_2.2Ca_2.8−x Sr _x Cu₂O _y has been investigated for superconductivity as a function of Ca/Sr ratio withx=0.7, 1.0, 1.4 and 1.8. All these compositions are found to be superconducting with onset temperature in the range of 80–90 K implying a large homogeneity range between Sr and Ca for the superconductivity to occur in this system. Effect of partial replacement of Bi by rare earths has been studied and it is observed that 20% replacement of Bi by Nd and Eu does not significantly affect the superconducting transition temperature.     

高温超导体转变特性曲线计算机测绘的研究

本文了研究了用微型计算机系统测绘高临界温度超导体转变曲线的工作原理，硬件结构和软件设计，该系统具有应用方便，精度高，数据处理方便，结果直观等优点。     

Heterodyne mixing at 70 GHz with superconductor-insulator-superconductor tunnel junctions

A laboratory heterodyne receiver working at 70 GHz was built up using superconductor-insulator-superconductor tunnel junction as mixing element. Single sideband conversion loss L_C as low as 1.92±0.23 and mixer noise temperature T_M of less than 100 K have been achieved while local oscillator pump power is 4·10^–8W.     

Coexisting holes and electrons in high-T C materials: implications from normal state transport

Normal state resistivity and Hall effect are shown to be successfully modeled by a two-band model of holes and electrons that is applied self-consistently to (i) dc transport data reported for eight bulk-crystal and six oriented-film specimens of YBa₂Cu₃O_7?δ, and (ii) far-infrared Hall angle data reported for YBa₂Cu₃O_7?δ and Bi₂Sr₂CaCu₂O_8+δ. The electron band exhibits extremely strong scattering; the extrapolated dc residual resistivity of the electronic component is shown to be consistent with the previously observed excess thermal conductivity and excess electrodynamic conductivity at low temperature. Two-band hole–electron analysis of Hall angle data suggests that the electrons possess the greater effective mass.     

Electrical resistivity of some La-Sr-Nb oxides to 77 K

The electrical resistivity of compounds having compositions LaSr₂Nb _x ,O _y LaSrNb _x O _y , and La₂SrNb _x O _y , prepared by arc melting under argon atmosphere, is determined from 77 to 300 K. Low resistivity compositions are found in these systems for x > 2 and niobium in divalent state. None of the compounds investigated showed large resistance drop reported by Oguchi et al. (1987) in La-Sr-Cu-O compounds prepared by sputtering La₂CuO₄ on niobium substrate and attributed to possible superconductivity about 250 K.     

Possible Alterations of Local Gravitational Field Inside a Superconductor

We calculate the possible interaction between a superconductor and the static Earth’s gravitational fields, making use of the gravito-Maxwell formalism combined with the time-dependent Ginzburg–Landau theory. We try to estimate which are the most favorable conditions to enhance the effect, optimizing the superconductor parameters characterizing the chosen sample. We also give a qualitative comparison of the behavior of high–Tc and classical low–Tc superconductors with respect to the gravity/superfluid interplay.     

On the shape of interlayer vortices in the Lawrence-Doniach model

We consider the Lawrence-Doniach model for layered superconductors, in which stacks of parallel superconducting planes are coupled via the Josephson effect. To model experiments in which the superconductor is placed in an external magnetic field oriented parallel to the superconducting planes, we study the structure of isolated vortices for a doubly periodic problem. We consider a singular limit which simulates certain experimental regimes in which isolated vortices have been observed, corresponding to letting the interlayer spacing of the superconducting planes tend to zero and the Ginzburg-Landau parameter simultaneously, but at a fixed relative rate.