arXiv subjects

V. V. Ryazanov

Publications and source records attributed to V. V. Ryazanov.

At least 55 records · Page 3Linked to original sources

arXiv2019

Interplay of magnetization dynamics with microwave waveguide at cryogenic temperatures

In this work, magnetization dynamics is studied at low temperatures in a hybrid system that consists of thin epitaxial magnetic film coupled with superconducting planar microwave waveguide. The resonance spectrum was observed in a wide magnetic field range, including low fields below the saturation magnetization and both polarities. Analysis of the spectrum via a developed fitting routine allowed to derive all magnetic parameters of the film at cryogenic temperatures, to detect waveguide-induced uniaxial magnetic anisotropies of the first and the second order, and to uncover a minor misalignment of magnetic field. A substantial influence of the superconducting critical state on resonance spectrum is observed and discussed.

physics.app-ph↗

arXiv2018

Second-harmonic current-phase relation in Josephson junctions with ferromagnetic barriers

We report the observation of a current-phase relation dominated by the second Josephson harmonic in superconductor-ferromagnet-superconductor junctions. The exotic current-phase relation is realized in the vicinity of a temperature-controlled 0-to-$π$ junction transition, at which the first Josephson harmonic vanishes. Direct current-phase relation measurements, as well as Josephson interferometry, non-vanishing supercurrent and half-integer Shapiro steps at the 0-$π$ transition self-consistently point to an intrinsic second harmonic term, making it possible to rule out common alternative origins of half-periodic behavior. While surprising for diffusive multimode junctions, the large second harmonic is in agreement with theory predictions for thin ferromagnetic interlayers.

cond-mat.mes-hall↗

arXiv2017

Distribution of size particles in the Gibbs system

In the framework of the Gibbs statistical theory, the question of the size of the particles forming the statistical system is investigated. This task is relevant for a wide variety of applications. The distribution for particle sizes and the moments of this quantity are determined from probabilistic considerations. The results are compared with different models and approximations. The particle size depends on the interactions in the system, on the compressibility factor, on the number of interacting particles. The cases of the absence and presence of a rigid incompressible particle core are considered.

cond-mat.stat-mech↗

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↗

arXiv2014

Fabrication and measurements of hybrid Nb/Al Josephson junctions and flux qubits with pi-shifters

We describe fabrication and testing of composite flux qubits combining Nb- and Al-based superconducting circuit technology. This hybrid approach to making qubits allows for employing pi-phase shifters fabricated using well-established Nb-based technology of superconductor-ferromagnet-superconductor Josephson junctions. The important feature here is to obtain high interface transparency between Nb and Al layers without degrading sub-micron shadow mask. We achieve this by in-situ Ar etching using e-beam gun. Shadow-evaporated Al/AlOx/Al Josephson junctions with Nb bias pads show the expected current-voltage characteristics with reproducible critical currents. Using this technique, we fabricated composite Nb/Al flux qubits with Nb/CuNi/Nb pi-shifters and measured their magnetic field response. The observed offset between the field responses of the qubits with and without pi-junction is attributed to the pi phase shift. The reported approach can be used for implementing a variety of hybrid Nb/Al superconducting quantum circuits.

cond-mat.supr-con↗

arXiv2014

Nonlocal supercurrent in mesoscopic multiterminal SNS Josephson junction in the low-temperature limit

Nonlocal supercurrent was observed in mesoscopic planar SNS Josephson junction with additional normal metal electrodes when nonequilibrium quasiparticles were injected from the normal metal electrode in one of the superconducting banks of the Josephson junction in the absence of net transport current through the junction. We claim that the effect observed is due to a supercurrent counterflow appearing to compensate the quasiparticle flow in the SNS weak link. We have measured SNS junction response for different distances from the quasiparticle injector to the SNS junction at temperatures far below the superconducting transition temperature. The charge-imbalance relaxation length was estimated by using modified Kadin, Smith and Skocpol scheme in the case of planar geometry. The model developed allows to describe the interplay of the charge imbalance and Josephson effects in the nanoscale proximity system in detail.

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

Ferromagnetic Josephson switching device with high characteristic voltage

We develop a fast Magnetic Josephson Junction (MJJ) - a superconducting ferromagnetic device for a scalable high-density cryogenic memory compatible in speed and fabrication with energy-efficient Single Flux Quantum (SFQ) circuits. We present experimental results for Superconductor-Insulator-Ferromagnet-Superconductor (SIFS) MJJs with high characteristic voltage IcRn of >700 uV proving their applicability for superconducting circuits. By applying magnetic field pulses, the device can be switched between MJJ logic states. The MJJ IcRn product is only ~30% lower than that of conventional junction co-produced in the same process, allowing for integration of MJJ-based and SIS-based ultra-fast digital SFQ circuits operating at tens of gigahertz.

cond-mat.supr-con↗

arXiv2011

Nonequilibrium Statistical Operator for Systems of Finite Size

The lifetime of statistical system is introduced. It is supposed that the nonequilibrium statistical operator implicitly contains the lifetime. The operations of taking of invariant part, averaging on initial conditions used in works of D.N. Zubarev, temporary coarse-graining (Kirkwood), choose of the direction of time are replaced by averaging on lifetime distribution. The expression for lifetime change at transitions from quasi-equilibrium system to nonequilibrium one is derived. A sort of the nonequilibrium statistical operator for systems of the finite sizes is suggested.

cond-mat.stat-mech↗

arXiv2011

Modelling Coagulation Systems: A Stochastic Approach

A general stochastic approach to the description of coagulating aerosol system is developed. As the object of description one can consider arbitrary mesoscopic values (number of aerosol clusters, their size etc). The birth-and-death formalism for a number of clusters can be regarded as a partial case of the generalized storage model. An application of the storage model to the number of monomers in a cluster is discussed.

physics.chem-ph↗

arXiv2011

Interference Effects of the Superconducting Pairing Wave Function due to the Fulde-Ferrell-Larkin-Ovchinnikov like State in Ferromagnet/Superconductor Bilayers

The theoretical description of the Fulde-Ferrell-Larkin-Ovchinnikov like state establishing in nanostructered bilayers of ferromagnetic (F) and superconducting (S) material leads to critical temperature oscillations and reentrant superconductivity as the F-layer thickness gradually increases. The experimental realization of these phenomena is an important prerequisite for the fabrication of the Ferromagnet/Superconductor/Ferromagnet core structure of the superconducting spin-valve. A switching of the spin-valve is only expected if such non-monotonic critical temperature behavior is observed in F/S bilayers as well as in the S/F bilayers, a combination of which the spin-valve core structure can be regarded to consist of. In our former investigations we could demonstrate the required non-monotonic behavior of the critical temperature in S/F bilayers. In this study we succeeded in the preparation of F/S bilayers, where the superconducting material is now grown on top of the ferromagnetic metal, which show deep critical temperature oscillations as a function of the ferromagnetic layer thickness as well as an extinction and recovery, i.e. a reentrant behavior, of superconductivity. Especially, the latter is necessary to obtain a spin-valve with a large critical temperature shift between the parallel and antiparallel configurations of magnetizations in the F layers.

cond-mat.supr-con↗

arXiv2011

Reentrant superconductivity in superconductor/ferromagnetic-alloy bilayers

We studied the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) like state establishing due to the proximity effect in superconducting Nb/Cu41Ni59 bilayers. Using a special wedge-type deposition technique, series of 20-35 samples could be fabricated by magnetron sputtering during one run. The layer thickness of only a few nanometers, the composition of the alloy, and the quality of interfaces were controlled by Rutherford backscattering spectrometry, high resolution transmission electron microscopy, and Auger spectroscopy. The magnetic properties of the ferromagnetic alloy layer were characterized with superconducting quantum interference device (SQUID) magnetometry. These studies yield precise information about the thickness, and demonstrate the homogeneity of the alloy composition and magnetic properties along the sample series. The dependencies of the critical temperature on the Nb and Cu41Ni59 layer thickness, Tc(dS) and Tc(dF), were investigated for constant thickness dF of the magnetic alloy layer and dS of the superconducting layer, respectively. All types of non-monotonic behaviors of Tc versus dF predicted by the theory could be realized experimentally: from reentrant superconducting behavior with a broad extinction region to a slight suppression of superconductivity with a shallow minimum. Even a double extinction of superconductivity was observed, giving evidence for the multiple reentrant behavior predicted by theory. All critical temperature curves were fitted with suitable sets of parameters. Then, Tc(dF) diagrams of a hypothetical F/S/F spin-switch core structure were calculated using these parameters. Finally, superconducting spin-switch fabrication issues are discussed in detail in view of the achieved results.

cond-mat.supr-con↗

arXiv2010

Implementation of superconductor-ferromagnet-superconductor pi-shifters in superconducting digital and quantum circuits

The difference between the phases of superconducting order parameter plays in superconducting circuits the role similar to that played by the electrostatic potential difference required to drive a current in conventional circuits. This fundamental property can be altered by inserting in a superconducting circuit a particular type of weak link, the so-called Josephson $π$-junction having inverted current-phase relation and enabling a shift of the phase by $π$. We demonstrate the operation of three superconducting circuits -- two of them are classical and one quantum -- which all utilize such $π$-phase shifters realized using superconductor-ferromagnet-superconductor sandwich technology. The classical circuits are based on single-flux-quantum cells, which are shown to be scalable and compatible with conventional niobium-based superconducting electronics. The quantum circuit is a $π$-phase biased qubit, for which we observe coherent Rabi oscillations and compare the measured coherence time with that of conventional superconducting phase qubits.

cond-mat.supr-con↗

arXiv2009

Lifetime distributions in the methods of non-equilibrium statistical operator and superstatistics

A family of non-equilibrium statistical operators is introduced which differ by the system age distribution over which the quasi-equilibrium (relevant) distribution is averaged. To describe the nonequilibrium states of a system we introduce a new thermodynamic parameter - the lifetime of a system. Superstatistics, introduced in works of Beck and Cohen [Physica A \textbf{322}, (2003), 267] as fluctuating quantities of intensive thermodynamical parameters, are obtained from the statistical distribution of lifetime (random time to the system degeneracy) considered as a thermodynamical parameter. It is suggested to set the mixing distribution of the fluctuating parameter in the superstatistics theory in the form of the piecewise continuous functions. The distribution of lifetime in such systems has different form on the different stages of evolution of the system. The account of the past stages of the evolution of a system can have a substantial impact on the non-equilibrium behaviour of the system in a present time moment.

cond-mat.stat-mech↗

arXiv2009

Maximum entropy principle and the form of source in non-equilibrium statistical operator method

It is supposed that the exponential multiplier in the method of the non-equilibrium statistical operator (Zubarev`s approach) can be considered as a distribution density of the past lifetime of the system, and can be replaced by an arbitrary distribution function. To specify this distribution the method of maximum entropy principle as in [Schönfeldt J-H, Jiminez N, Plastino A R, Plastino A, Casas M 2007 \textit{Physica A} \textbf{374} 573] is used. The obtained distribution is close to exponential one. Another approach to the maximum entropy principle, as in [Van der Straeten E and Beck C 2008 Phys. Rev. E \textbf{78} 051101], except exponential distributions yields power-like, log-normal distributions, as well as distributions of other kind and transitions between them.

cond-mat.stat-mech↗

arXiv2009

Influence of probability density function of the passage time in the method of non-equilibrium statistical operator on non-equilibrium properties of the system

A family of non-equilibrium statistical operators (NSO) is introduced which differ by the system lifetime distribution over which the quasi-equilibrium (relevant) distribution is averaged. This changes the form of the source in the Liouville equation, as well as the expressions for the kinetic coefficients, average fluxes, and kinetic equations obtained with use of NSO. It is possible to choose a class of lifetime distributions for which thermodynamic limiting transition and to tend to infinity of average lifetime of system is reduced to the result received at exponential distribution for lifetime, used by Zubarev. However there is also other extensive class of realistic distributions of lifetime of system for which and after to approach to infinity of average lifetime of system non-equilibrium properties essentially change. For some distributions the effect of "finite memory" when only the limited interval of the past influence on behaviour of system is observed. It is shown, how it is possible to spend specification the description of effects of memory within the limits of NSO method, more detailed account of influence on evolution of system of quickly varying variables through the specified and expanded form of density of function of distribution of lifetime. The account of character of history of the system, features of its behaviour in the past, can have substantial influence on non-equilibrium conduct of the system in a present moment time.

cond-mat.stat-mech↗

arXiv2008

Josephson tunnel junctions with strong ferromagnetic interlayer

The dependence of the critical current density j_c on the ferromagnetic interlayer thickness d_F was determined for Nb/Al_2O_3/Cu/Ni/Nb Josephson tunnel junctions with ferromagnetic \Ni interlayer from very thin film thicknesses (\sim 1 nm) upwards and classified into F-layer thickness regimes showing a dead magnetic layer, exchange, exchange + anisotropy and total suppression of j_c. The Josephson coupling changes from 0 to pi as function of d_F, and -very close to the crossover thickness- as function of temperature. The strong suppression of the supercurrent in comparison to non-magnetic \Nb/Al_2O_3/Cu/Nb junctions indicated that the insertion of a F-layer leads to additional interface scattering. The transport inside the dead magnetic layer was in dirty limit. For the magnetically active regime fitting with both the clean and the dirty limit theory were carried out, indicating dirty limit condition, too. The results were discussed in the framework of literature

cond-mat.supr-con↗

arXiv2008

Family of non-equilibrium statistical operators and influence of the past on the present

A family of non-equilibrium statistical operators (NSO) is introduced which differ by the system lifetime distribution over which the quasi-equilibrium (relevant) distribution is averaged. This changes the form of the source in the Liouville equation, as well as the expressions for the kinetic coefficients, average fluxes, and kinetic equations obtained with use of NSO. It is possible to choose a class of lifetime distributions for which thermodynamic limiting transition and to tend to infinity of average lifetime of system is reduced to the result received at exponential distribution for lifetime, used by Zubarev. However there is also other extensive class of realistic distributions of lifetime of system for which and after to approach to infinity of average lifetime of system non-equilibrium properties essentially change. For some distributions the effect of "finite memory" when only the limited interval of the past influence on behaviour of system is observed. It is shown, how it is possible to spend specification the description of effects of memory within the limits of NSO method, more detailed account of influence on evolution of system of quickly varying variables through the specified and expanded form of density of function of distribution of lifetime. The account of character of history of the system, features of its conduct in the past, can have substantial influence on non-equilibrium conduct of the system in a present moment time.

cond-mat.stat-mech↗