Effects of extended impurity perturbation in d-wave superconductor

We describe the effects of electronic perturbation distributed on nearest neighbor sites to the impurity center in a planar \textit{d}-wave superconductor, in approximation of circular Fermi surface. Alike the behavior previously reported for point-like perturbation and square Fermi surface, the quasiparticle density of states $\rho (\epsilon)$ can display a resonance inside the gap (and very weak features from low symmetry representations of non-local perturbation) and asymptotically vanishes at $\epsilon \to 0$ as $\rho\sim\epsilon/\ln^2\epsilon$. The local suppression of SC order parameter in this model is found to be somewhat weaker than for an equivalent point-like (non-magnetic) perturbation and much weaker than for a spin-dependent (extended) perturbation.Comment: 7 pages, 5 figures, some minor typos and the curves in Fig. 5 correcte

Superconducting junctions from non-superconducting doped CuO2_2 layers

The theoretical approach proposed recently for description of redistribution of electronic charge in multilayered selectively doped systems is modified for a system with finite number of layers. A special attention is payed to the case of a finite heterostructure made of copper-oxide layers which are all non-superconducting (including non-conducting) because of doping levels being beyond the well-known characteristic interval for superconductivity. Specific finite structures and doping configurations are proposed to obtain atomically thin superconducting heterojunctions of different compositions.Comment: 4 pages, 3 figures, two bibliography references were update

Boundary Friction on Molecular Lubricants: Rolling Mode?

A theoretical model is proposed for low temperature friction between two smooth rigid solid surfaces separated by lubricant molecules, admitting their deformations and rotations. Appearance of different modes of energy dissipation (by ''rocking'' or ''rolling'' of lubricants) at slow relative displacement of the surfaces is shown to be accompanied by the stick-and-slip features and reveals a non-monotonic (mean) friction force {\it vs} external loadComment: revtex4, 4 pages, 5 figure