Yurii N. Proshin

INHOMOGENEOUS CURRENT DISTRIBUTION IN A BIMETAL FERROMAGNET/SUPERCONDUCTOR FILM IN A LONGITUDINAL MAGNETIC FIELD

The proximity effect of the ferromagnetic metal/superconductor (FM/S) bilayers in а external longitudinal magnetic field is considered in the dirty limit. The critical temperature and the superconducting current distribution versus applied magnetic field’s magnitude, film’s thicknesses and a transparency of the contact is calculated, with taking into account аn umklapp processes possibility on the interface of the FM/S contact. It is shown that superconducting current is strictly inhomogeneous and asymmetrical. It is shown also that the current inhomogeneity depends heavily from the FM/S interface transparency.

How experimentally to detect a solitary superconductivity in dirty ferromagnet-superconductor trilayers?

Abstract We theoretically study the proximity effect in the thin-film layered ferromagnet (F) – superconductor (S) heterostructures in F 1 F 2 S design. We consider the boundary value problem for the Usadel-like equations in the case of so-called “dirty” limit. The “latent” superconducting pairing interaction in F layers taken into account. The focus is on the recipe of experimental preparation the state with so-called solitary superconductivity. We also propose and discuss the model of the superconducting spin valve based on F 1 F 2 S trilayers in solitary superconductivity regime.

A Proximity Effect in Pure HTS/Ferromagnet Contacts

The proximity effect is theoretically studied for thin and massive pure ferromagnet/high-temperature superconductor (F/HTS) contacts. It is shown that there is no continuous matching between the s-wave and d-wave pair amplitudes at the HTS/F boundary. In thin HTS/F nanostructures, the exchange field strongly suppresses the averaged sand d-pairing and leads to the competition between BCS and FFLO scenarios of superconductivity. On the contrary, in massive HTS/F contact, the exchange field has no effect on the critical temperature Tcd of d-wave pairing. This is due to the lack of d-wave pairing in F layers, resulting in full internal reflection of d-wave pairs even from the perfectly transparent HTS/F boundary. The s-wave superconductivity localized at the HTS/F interface is predicted.Spontaneous symmetry change of the order parameter at the HTS/F interfaces from initially d-wave type to s-type becomes possible for massive HTS/F contact. It qualitatively agrees with experimental observations of the mixture of sand d-wave components at the Ag/BiSrCaCuO and Fe/Ag/BiSrCaCuO interfaces.

Proximity Effect for Asymmetrical Three-Layered FS Structures in External Magnetic Field

We study asymmetrical three-layers F1F2S and F1SF2 structures in an external parallelmag-netic field. Assuming that all F and S layers are dirty, we solve the boundary value problem for theUsadel function. We calculate the critical temperature of in the F1F2S and F1SF2 systems as functionof the F layers thicknesses and external magnetic field.

The Josephson Current in the SFS Sandwich Taking into Account the Proximity Effect and Umklapp Processes

We consider the Josephson effect in a three-layer symmetric superconductor-ferromagnet-superconductor (SFS) system. In the framework of the proximity effect theory we calculate the Josephson current as a function of the ferromagnet thickness, taking into account the Umklapp processes at the internal boundary and the critical temperature dependence of the order parameter phase difference. The results of the calculations are in good agreement with experimental data.

Superconducting Probe of Electronic Correlations and Exchange Field Based on the Proximity Effect in F/S Nanostructures

The proximity effect and competition between the BCS and LOFF states are studied in the Cooper limit for thin F/S and F/S/F nanostructures, where F is a ferromagnet and S is a superconductor. The dependences of the critical temperature Tc on the exchange field I, electron correlations λf, and the thickness df of the F layer are derived for F/S bilayers and F/S/F trilayers. Two new π-phase superconducting states with electronelectron repulsion in the F layers of F/S/F trilayers are predicted. A 2D LOFF state in F/S/F trilayers is possible only in the presence of a weak magnetic field and the appropriate parameters of the F and S layers. The absence of the suppression of 3D superconductivity in short-period Gd/La superlattices is explained and the electronelectron coupling constant in gadolinium is predicted. A method of superconducting probe spectroscopy based on the proximity effect is proposed for determining the symmetry of the order parameter, the magnitude and sign of electron correlations, and the exchange field in various nanomagnets F.

Proximity Effect as a Probe of Electronic Correlations and Exchange Field in Dirty Ferromagnet/Superconductor Nanostructures

We investigate the interplay between the BCS and 2D Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) states in the dirty thin ferromagnetic metal/superconductor (FM/S) nanostructures. For the FM/S bilayers we have derived the dependencies of critical temperature on the FM layer exchange field, electronic correlations and thickness. Moreover, in the corresponding FM/S/FM trilayers we predict two new π phase superconducting states with electron-electron repulsion in the FM layers. The 2D modulated LOFF states are possible in such trilayers only in presence of a weak magnetic field and at suitable parameters of the FM and S layers. On this base we originally propose the method of proximity effect probe the magnitude and sign of the electronic correlations, the order parameter symmetry and exchange fields in various FM layers.

π Phase Superconductivity and Magnetism in Ferromagnet / Superconductor / Ferromagnet Trilayers

On the base of new boundary-value problem for the Eilenberger function we investigate the superconducting and magnetic states in ferromagnet/superconductor (FM/S) nanostructures, where superconductivity is a superposition of the BCS pairing with zero total momentum in the S layers and the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) pairing with nonzero 3D coherent momentum k in the FM layers. We originally study the interplay between the BCS and FFLO states in the pure thin FM/S/FM trilayers and two novel -phase superconducting states with electron-electron repulsion in the FM layers are predicted. The modulated FFLO states are possible in such trilayers only in presence of external magnetic field at suitable parameters of the FM and S layers. In the FM/S superlattices there are also two -phase magnetic states (0 and ) with compensation of the exchange field paramagnetic effect. This fact allows us to explain a surprisingly high Tc ~ 5K in the short period Gd/La superlattice and to predict the sign and value of the electron-electron interaction in the ferromagnetic Gd metal.