arXiv subjects

N. V. Klenov

Publications and source records attributed to N. V. Klenov.

22 records · Page 2Linked to original sources

arXiv2014

Josephson magnetic rotary valve

We propose a control element for a Josephson spin valve. It is a complex Josephson device containing ferromagnetic (F) layer in the weak-link area consisting of two regions, representing $0$ and $π$ Josephson junctions, respectively. The valve's state is defined by mutual orientations of the F-layer magnetization vector and normal to the interface separating $0$ and $π$ sections of the device. We consider possible implementation of the control element by introduction of a thin normal metal layer in a part of the device area. By means of theoretical simulations we study properties of the valve's structure as well as its operation, revealing such advantages as simplicity of control, high characteristic frequency and good legibility of the basic states.

cond-mat.supr-con↗

arXiv2013

Theory of supercurrent transport in SIsFS Josephson junctions

We present the results of theoretical study of Current-Phase Relations (CPR) in Josephson junctions of SIsFS type, where 'S' is a bulk superconductor and 'IsF' is a complex weak link consisting of a superconducting film 's', a metallic ferromagnet 'F' and an insulating barrier 'I'. We calculate the relationship between Josephson current and phase difference. At temperatures close to critical, calculations are performed analytically in the frame of the Ginsburg-Landau equations. At low temperatures numerical method is developed to solve selfconsistently the Usadel equations in the structure. We demonstrate that SIsFS junctions have several distinct regimes of supercurrent transport and we examine spatial distributions of the pair potential across the structure in different regimes. We study the crossover between these regimes which is caused by shifting the location of a weak link from the tunnel barrier 'I' to the F-layer. We show that strong deviations of the CPR from sinusoidal shape occur even in a vicinity of Tc, and these deviations are strongest in the crossover regime. We demonstrate the existence of temperature-induced crossover between 0 and pi states in the contact and show that smoothness of this transition strongly depends on the CPR shape.

cond-mat.supr-con↗

arXiv2013

Theoretical Model of Superconducting Spintronic SIsFS Devices

Motivated by recent progress in development of cryogenic memory compatible with single flux quantum (SFQ) circuits we have performed a theoretical study of magnetic SIsFS Josephson junctions, where 'S' is a bulk superconductor, 's' is a thin superconducting film, 'F' is a metallic ferromagnet and 'I' is an insulator. We calculate the Josephson current as a function of s and F layers thickness, temperature and exchange energy of F film. We outline several modes of operation of these junctions and demonstrate their unique ability to have large product of a critical current $I_{C}$ and a normal-state resistance $R_{N}$ in the $π$ state, comparable to that in SIS tunnel junctions commonly used in SFQ circuits. We develop a model describing switching of the Josephson critical current in these devices by external magnetic field. The results are in good agreement with the experimental data for Nb-Al/AlO${_x}$-Nb-Pd$_{0.99}$Fe$_{0.01}$-Nb junctions.

cond-mat.supr-con↗

arXiv2012

Josephson $φ$-junctions based on structures with complex normal/ferromagnet bilayer

We demonstrate that Josephson devices with nontrivial phase difference $% 0<φ_g <π$ in the ground state can be realized in structures composed from longitudinally oriented normal metal (N) and ferromagnet (F) films in the weak link region. Oscillatory coupling across F-layer makes the first harmonic in the current-phase relation relatively small, while coupling across N-layer provides negative sign of the second harmonic. To derive quantitative criteria for a $φ$-junction, we have solved two-dimensional boundary-value problem in the frame of Usadel equations for overlap and ramp geometries of S-NF-S structures. Our numerical estimates show that $φ$-junctions can be fabricated using up-to-date technology.

cond-mat.supr-con↗