We have investigated the critical temperature behavior in periodic superconductor/ ferromagnet (S/F) multilayers as a function of the ferromagnetic layer thickness d f and the interface transparency. The critical temperature Tc(d f ) exhibits a damped oscillatory behavior in these systems due to an exchange field in the ferromagnetic material. In this work we have performed Tc calculations using the self-consistent multimode approach, which is considered to be exact solving method. Using this approach we have derived the conditions of 0 or π state realization in periodic S/F multilayers. Moreover, we have presented the comparison between the single-mode and multimode approaches and established the limits of applicability of the single-mode approximation, frequently used by experimentalists.

We present a quantitative study of the current-voltage characteristics (CVC) of SFIFS Josephson junctions (S denotes bulk superconductor, F -metallic ferromagnet, I -insulating barrier) with weak ferromagnetic interlayers in the diffusive limit. The problem is solved in the framework of the nonlinear Usadel equations. We consider the case of a strong tunnel barrier such that the left SF and the right FS bilayers are decoupled. We calculate the density of states (DOS) in SF bilayers using a self-consistent numerical method. Then we obtain the CVC of corresponding SFIFS junctions, and discuss their properties for different set of parameters including the thicknesses of ferromagnetic layers, the exchange field, and the magnetic scattering time. We observe the anomalous nonmonotonic CVC behavior in case of weak ferromagnetic interlayers, which we ascribe by DOS energy dependencies in case of small exchange fields in F layers.

Thin superconducting films are usually regarded as type II superconductors even when they are made of a type I material. The reason is a strong contribution of the stray magnetic field that stabilizes vortices. While very thin films indeed reach this limit, there is a large interval of film thicknesses where the magnetic properties cannot be classified as either of the two conventional superconductivity types. Recent calculations revealed that in this interval the system exhibits spontaneous formation of complex condensate-field patterns that are very sensitive to system parameters, in particular, the temperature and the applied magnetic field. The corresponding superconducting magnetic properties can be attributed to a special regime of the intertype superconductivity whose physical origin lies in the removal of an infinite degeneracy of the self-dual superconducting state at the critical Bogomolnyi point. Here we demonstrate that qualitative characteristics of the intertype superstructures in thin superconducting films are independent of the choice of the in-plane boundary conditions for the order parameter and the magnetic field. arXiv:1812.09621v2 [cond-mat.supr-con]

No abstract