An anomalous superconducting transition consisting of a very sharp peak in the resistance versus temperature curve just above ${\mathit{T}}_{\mathit{c}}$ has been observed in (NbV)N films and other superconducting compounds. Using a simple concentrated constant-equivalent circuit, it is proved that sample nonhomogeneity together with an out-of-line contact arrangement can produce the observed effect.

By modeling a superconducting polycrystalline film as a network of superconducting grains coupled via Josephson junctions, various authors have shown that rf losses at the grain boundaries can be the main source of the residual surface resistance in high-${\mathit{T}}_{\mathit{c}}$ superconductors. The same model is extended here to include the effect of dc or rf applied fields and is then shown to be consistent with previous results on the surface impedance of low-${\mathit{T}}_{\mathit{c}}$ superconducting polycrystalline films. The model also provides a satisfactory, though qualitative, description of recent results on the quality factor of niobium thin-film-coated rf cavities for particle accelerators.

We have observed a nonmonotonic behavior of the superconducting critical temperature $T_c$ versus the CuMn layer thickness in multilayers of Nb/CuMn with fixed Nb layer thickness (∼250 Å). The results have been interpreted assuming the presence of the $\pi$ phase in the case of layered superconducting systems with weak magnetic coupling, where the phase $\phi$ of the superconducting order parameter can vary in the range $0<\mathrm{}\phi <\pi$ between adjacent superconducting layers.

The proximity effect between a superconductor (S) and a weak ferromagnet (F) in sputtered $\mathrm{Nb}∕{\mathrm{Pd}}_{0.86}{\mathrm{Ni}}_{0.14}$ bilayers has been studied. The dependence of the critical temperature on the S- and F-layer thicknesses can be interpreted in the framework of recent theoretical models and yields reasonable numbers for the exchange energy of the ferromagnet and the interface transparency of the S/F barrier.

The morphology of abrupt bursts of magnetic flux into superconducting films with engineered periodic pinning centers (antidots) has been investigated. Guided flux avalanches of thermomagnetic origin develop a treelike structure, with the main trunk perpendicular to the borders of the sample, while secondary branches follow well-defined directions determined by the geometrical details of the underlying periodic pinning landscape. Strikingly, we demonstrate that in a superconductor with relatively weak random pinning the morphology of such flux avalanches can be fully controlled by proper combinations of lattice symmetry and antidot geometry. Moreover, the resulting flux patterns can be reproduced, to the finest details, by simulations based on a phenomenological thermomagnetic model. In turn, this model can be used to predict such complex structures and to estimate physical variables of more difficult experimental access, such as the local values of temperature and electric field.