Relation of Superconducting Pairing Symmetry and Non-Magnetic Impurity Effects in Vortex States

Non-magnetic impurity scattering effects on the vortex core states are theoretically studied to clarify the contributions from the sign-change of the pairing function in anisotropic superconductors. The vortex states are calculated by the Eilenberger theory in superconductors with p x -wave pairing symmetry, as well as the corresponding anisotropic s-wave symmetry. From the spatial structure of the pair potential and the local electronic states around a vortex, we examine the differences between anisotropic superconductors with and without sign-change of the pairing function, and estimate how twofold symmetric vortex core images change with increasing the impurity scattering rate both in the Born and the unitary limits. We found that twofold symmetric vortex core image of zero-energy local density of states changes the orientation of the twofold symmetry with increasing the scattering rate when the sign change occurs in the pairing function. Without the sign change, the vortex core shape reduces to circular one with approaching dirty cases. These results of the impurity effects are valuable for identifying the pairing symmetry by observation of the vortex core image by the STM observation.

Избыточная проводимость анизотропных неоднородных сверхпроводников при температуре выше критической

The theoretical model of conductivity of a layered anisotropic normal metal containing small superconducting ellipsoidal granules with an arbitrary ratio of semiaxes is developed. Calculation data obtained under two simple approximations (self-consistent and Maxwell) are compared. The results may be applied in the analysis of the observed temperature dependence of the conductivity anisotropy in various anisotropic superconductors with the superconducting phase emerging in the form of isolated superconducting granules. The temperature dependence of the electric resistance along and across the conducting layers above and near the superconducting transition temperature is studied experimentally for bridge structures of a varying thickness. It is demonstrated that this resistance and even the effective superconducting transition temperature depend strongly on the bridge thickness (i.e., the number of layers through which the electric current flows). Note that significant differences were observed only for the resistance across the layers.

Исследование критической температуры T-=SUB=-c-=/SUB=- гомофазных сверхпроводников (Bi-=SUB=-1.7-=/SUB=-Pb-=SUB=-0.3-=/SUB=-Sr-=SUB=-2-=/SUB=-Ca-=SUB=-(n-1)-=/SUB=-Cu-=SUB=-n-=/SUB=- O-=SUB=-y-=/SUB=- (n=3, 4, 5) и вольт-амперных характеристик сэндвич-пар полупроводник InP-сверхпроводник Bi/Pb (2223, 2234, 2245)

The electrophysical properties of semiconductor–superconductor sandwich pairs (InP–Bi/Pb 2223, 2234, 2245) are investigated, in which homophase superconductors based on bismuth cuprates with high reproducible critical temperatures of superconducting transition T _ c = 107–180 K are used. The advantage of melt solar technology for obtaining superconducting materials is demonstrated. The microstructure and phase composition of strongly anisotropic superconductors with nominal composition Bi_1.7Pb_0.3Sr_2Ca_( n _– 1)Cu_ n O_ y ( n = 3, 4, 5) are researched. A technique of experimental determination of superconducting transition critical temperatures T _ c in single-phase and homophase HTSC samples is presented. The current–voltage characteristics of InP–Bi/Pb pairs are investigated. The relationship between the electrical resistance of sandwich pairs and superconductor critical temperature T _ c is established.

Inhomogeneous Superconductivity in Organic and Related Superconductors

Evidence of inhomogeneous superconductivity, in this case superconductivity with a spatially modulated superconducting order parameter, has now been found in many materials and by many measurement methods. Although the evidence is strong, it is circumstantial in the organic superconductors, scant in the pnictides, and complex in the heavy Fermions. However, it is clear some form of exotic superconductivity exists at high fields and low temperatures in many electronically anisotropic superconductors. The evidence is reviewed in this article, and examples of similar measurements are compared across different families of superconductors. An effort is made to find a consistent way to measure the superconducting energy gap across all materials, and use this value to predict the Clogston–Chandrasakhar paramagnetic limit Hp. Methods for predicting the existence of inhomogeneous superconductivity are shown to work for the organic superconductors, and then used to suggest new materials to study.