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Of all publications in the section: 20
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Article
Vasenko A.S., Ozaeta A., Kawabata S. et al. Journal of Superconductivity and Novel Magnetism. 2013. Vol. 26. P. 1951-1956.

The Andreev current and the subgap conductance in a superconductor/ insulator/ ferromagnet (SIF) structure in the presence of a small spin-splitting field show novel interesting features (A. Ozaeta et al., Phys. Rev. B 86, 060509(R), 2012). For example, the Andreev current at zero temperature can be enhanced by a spin-splitting field h, smaller than the superconducting gap, as has been recently reported by the authors. Also at finite temperatures the Andreev current has a peak for values of the spin-splitting field close to the superconducting gap. Finally, the differential subgap conductance at low temperatures shows a peak at the bias voltage eV = h. In this paper we investigate the Andreev current and the subgap conductance in SFF structures with arbitrary direction of magnetization of the F layers. We show that all aforementioned features occur now at the value of the "effective field", which is the field acting on the Cooper pairs in the multi-domain ferromagnetic region, averaged over the decay length of the superconducting condensate into a ferromagnet. We also briefly discuss the heat transport and electron cooling in the considered structures.

Added: Sep 28, 2015
Article
M.Y. Kagan, Val’kov V. Journal of Superconductivity and Novel Magnetism. 2012. Vol. 25. No. 5. P. 1379-1382.

Abstract. We search for anomalous normal and superconductive behavior in the two-band Hubbard model with one narrow band. We analyze the influence of the electron– polaron effect and the Altshuler–Aronov effect on effective mass enhancement and scattering times of heavy and light components in the clean case. We find anomalous behavior of resistivity at high temperatures T >W∗h both in 3D and 2D situations. The SC instability in the model is governed by an enhanced Kohn–Luttinger effect for p-wave pairing of heavy electrons via polarization of light electrons.

Added: Mar 1, 2014
Article
Kugel K., Rakhmanov A., Sboychakov A. Journal of Superconductivity and Novel Magnetism. 2020. Vol. 33. No. 8. P. 2405-2413.

Using a simple and rather general model of the system with imperfect nesting of the Fermi surface, we show that the spin density wave (SDW) and normal metal (or, at low temperature, a superconductor) can coexist within a certain pressure range due to the electronic phase separation. The model predicts the SDW state at low pressure, then, the nucleation of paramagnetic (PM) droplets or islands within the SDWhost at higher pressure.When the pressure continues to increase, the droplets transform to rods (or pillars) and, finally, to slabs. With the further growth of pressure, a uniform metallic phase arises. The theory agrees well with the experiment and, even in its simplest version, can capture the essential physics of the systems under study.

Added: Nov 9, 2020
Article
Nagy B., Khaydukov Y., Kiss L. et al. Journal of Superconductivity and Novel Magnetism. 2013. Vol. 26. P. 1957-1961.

Thickness (dF) and concentration (x) dependence of the Curie temperature of NixCu100-x(dF) ferromagnetic alloy layers (x =0.55,0.65, dF =[3nm{\div}12nm]) being in contact with a vanadium layer was studied. The Curie temperature of the ferromagnetic layers depends on the thickness when it is comparable with the interface layer between the F and the vanadium layers, which is attributed to the proximity coupling of the interface region with the rest of the F layer. The present study provides valuable information for fabrication of samples with controlled exchange coupling strength for studies of superconductor/ferromagnet (S/F) proximity effects.

Added: Sep 28, 2015
Article
Kuzmichev S. A., Kuzmicheva T. E., Tchesnokov S. et al. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. No. 4. P. 1111-1116.

We present temperature dependences of the large and the small superconducting gaps measured directly by SnS-Andreev spectroscopy in various Fe-based superconductors and MgB2. The experimental L,S(T ) are wellfitted with a two-gap model based on Moskalenko and Suhl system of equations (supplemented with a BCS integral  renormalization). From the fitting procedure, we estimate the key attribute of superconducting state — relative electron-boson coupling constants and eigen BCS ratios for both condensates. Our results evidence for a driving role of a strong intraband coupling in the bands with the large gap, whereas interband coupling is rather weak for all the superconductors under study.

Added: Mar 19, 2016
Article
Sadovskii M. V., Pudalov V.M. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. No. 4. P. 1035-1036.
Added: Feb 23, 2017
Article
Kagan M., Mitskan V., Korovushkiin M. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. No. 4. P. 1043-1048.

We demonstrate the instability of the normal state of purely repulsive fermionic systems towards the transition to the Kohn-Luttinger superconducting state. We construct the superconducting phase diagrams of these systems in the framework of the Hubbard and Shubin-Vonsovsky models on the square and hexagonal lattices. We show that an account for the long-range Coulomb interactions, as well as the Kohn- Luttinger renormalizations, lead to an increase in the critical superconducting temperatures in various materials, such as high-temperature superconductors, idealized monolayer, and bilayer of doped graphene. Additionally, we discuss the role of the structural disorder and the nonmagnetic impurities in superconducting properties of real graphene systems.

Added: May 11, 2016
Article
Croitoru M., Shanenko A., Vagov A. et al. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. P. 605-609.

We investigate how the interplay of quantum confinement and level broadening caused by disorder affects superconducting correlations in ultra-small metallic grains. We use the electron-phonon interaction-induced electron mass renormalization and the reduced static-path approximation of the BCS formalism to calculate the critical temperature as a function of the grain size. We show how the strong electron-impurity scattering additionally smears the peak structure in the electronic density of states of a metallic grain and imposes additional limits on the critical temperature under strong quantum confinement.

Added: Feb 22, 2016
Article
Shein K., Emelyanova V., Logunova M. et al. Journal of Superconductivity and Novel Magnetism. 2020. Vol. 33. P. 2325-2327.

Simple measuring set-up was used to measure high-frequency impedance of superconducting Ti and NbN microstructures at low temperatures. The shift of resonance frequency below the temperature of superconducting transition compared to the normal state clearly indicates the increase of inductance of the system. The effect is interpreted as the impact of kinetic inductance originating from 'inertial' properties of Cooper pairs. Kinetic inductance of superconducting micro- and nanostructures should be taken into consideration for various cryoelectronic applications.

Added: Oct 13, 2019
Article
Dolgov O. V., Golubov A. A., Nefeodov Y. A. et al. Journal of Superconductivity and Novel Magnetism. 2015. Vol. 28. No. 2. P. 331-337.

We present the results of investigations of the temperature dependences of complex conductivity σ(T) = σ′(T)−iσ″(T) at frequency 9.4 GHz in series of single crystals V3+xSi1−x with different Si content. The data exhibit peculiarities typical for multiband superconductors, namely a nonlinear temperature dependence of resistivity above superconducting transition temperature Tc, suppression of superconducting transition temperature Tc by nonmagnetic impurities, a positive curvature of σ″(T) curves close to Tc, and a coherence peak in σ′(T) at TTc/2. Using a two-band model in the weak-coupling regime, we demonstrate that the behavior of Tc and the evolution of σ(T) with Si-content variation are consistently described by changing of the interband scattering rate.

Added: Mar 14, 2017
Article
Pudalov V. Journal of Superconductivity and Novel Magnetism. 2016.

Whether the apparent metal-insulator transition in two-dimensional (2D) correlated electron system is a true quantum phase transition or is a crossover phenomena—this question is in the core of ongoing debates. I present here a novel scenario of this phenomenon, based on experimental finding of the two-phase state in the correlated 2D system. The transport features in the suggested picture are the finite temperature phenomena and a consequence of the magnetic phase transition; the latter manifests in the sign change of the spin magnetization-per-electron. Physically, the magnetic transition means changing the tendency of the two-phase system to either paramagnetic Fermi liquid state (high density), or to the disordered ferromagnet (low density).

Added: Oct 10, 2016
Article
Pudalov V.M., Morgun L., Kuntsevich A.Yu. Journal of Superconductivity and Novel Magnetism. 2017. Vol. 30. No. 3. P. 783-787.

Strongly interacting two-dimensional (2D) carrier system has a tendency to spontaneous spin magnetization and mass divergence. Numerous experiments aimed to reveal these instabilities were not entirely convincing. In particular, spin susceptibility of itinerant electrons, determined from quantum oscillations, remains finite at the critical density of the 2D metal-insulator transition (MIT), n = n (c) . In contrast, the susceptibility and effective mass determined from high field magnetotransport were reported to diverge. Later, it became clear that as interactions grow, the homogeneous 2D Fermi liquid breaks into a two phase state which hampers interpretation of the experimental data. The thermodynamic magnetization measurements have revealed spontaneous formation of the spin-polarized collective electron droplets ("nanomagnets") in the correlated 2D Fermi liquid, while the spin susceptibility of itinerant electrons in the surrounding 2D "Fermi sea" remains finite. Here, we report how the non Fermi-liquid two-phase state (dilute ferromagnet) reveals itself in magnetotransport and zero field transport. We found in the correlated 2D system a novel energy scale T (au)< T (F) . At TaeT (au) the in-plane field magnetotransport and zero field transport exhibit features. Finally, in thermodynamic magnetization, the spin susceptibility per electron, a, chi/a, n changes sign at TaeT (au). All three notable temperatures are close to each other, behave critically, ; we associate, therefore, T (au) with a novel energy scale caused by interactions in the two-phase 2DE system.

Added: Oct 16, 2017
Article
Semenov A. G., Zaikin A. Journal of Superconductivity and Novel Magnetism. 2017. Vol. 30. P. 139-143.

Quantum phase slips (QPS) may produce non-equilibrium voltage fluctuations in current-biased superconducting nanowires. Making use of the Keldysh technique and employing the phase-charge duality arguments we investigate such fluctuations within the four-point measurement scheme and demonstrate that shot noise of the voltage detected in such nanowires may essentially depend on the particular measurement setup. In long wires, the shot noise power decreases with increasing frequency Ω and vanishes beyond a threshold value of Ω at T→0.

Added: Nov 17, 2016
Article
Zvezdin A. Journal of Superconductivity and Novel Magnetism. 2019. Vol. 32. No. 6. P. 1811-1815.

In this work, we explore the properties of antiferromagnetic cycloid and the phase transitions between commensurate and incommensurate magnetic states in epitaxial BiFeO3 film. Additional magnetic anisotropy induced by strain effects in the films allocates cycloids with the definite directions of spin rotation. Peculiar feature of the cycloids propagating in the films whose symmetry is different from the single crystals is the orientation of spin rotational plane that does not contain electric polarization in contrast with the bulk materials. We construct a diagram of phase transitions induced by magnetic field applied along normal to the surface and show considerable decrease of the strength of magnetic field destroying cycloid in films compared with the bulk.

Added: Nov 27, 2019
Article
Gareeva Z. V., Zvezdin K. A., Kayumov I. R. et al. Journal of Superconductivity and Novel Magnetism. 2018.

In this work, we explore the properties of antiferromagnetic cycloid and the phase transitions between commensurate and incommensurate magnetic states in epitaxial BiFeO3 film. Additional magnetic anisotropy induced by strain effects in the films allocates cycloids with the definite directions of spin rotation. Peculiar feature of the cycloids propagating in the films whose symmetry is different from the single crystals is the orientation of spin rotational plane that does not contain electric polarization in contrast with the bulk materials. We construct a diagram of phase transitions induced by magnetic field applied along normal to the surface and show considerable decrease of the strength of magnetic field destroying cycloid in films compared with the bulk.

Added: Nov 2, 2018
Article
Sadovskii M. V., Pudalov V. M. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. P. 1033-1034.
Added: Feb 23, 2017
Article
M.Y. Kagan, Efremov D., Mar’enko M. et al. Journal of Superconductivity and Novel Magnetism. 2013. Vol. 26. No. 5. P. 2809-2815.

Abstract. In the large variety of models such as 3D and 2D Fermi-gas model with hard-core repulsion, 3D and 2D Hubbard model, and the Shubin–Vonsovsky model, we demonstrate the possibility of triplet p-wave pairing at low electron density. We show that the critical temperature of the p-wave pairing can be strongly increased in a spin-polarized case or in a two-band situation already at low density and reach experimentally feasible values of (1–5) K. We also discuss briefly d-wave pairing and high-TC superconductivity with TC ∼ 100 K, which arises in the 2D t-J model in the range of parameters realistic for cuprates.

Added: Mar 1, 2014
Article
Arutyunov K., Lehtinen J. S., Rantala T. Journal of Superconductivity and Novel Magnetism. 2016. Vol. 29. No. 3. P. 569-572.

Quantum phase slip (QPS) is the particular manifestation of quantum fluctuations of the order parameter of a quasi-1D superconductor. The QPS event(s) can be considered a dynamic equivalent of tunneling through conventional Josephson junction containing static in space and time weak link(s). At low temperaturesT << Tc, the QPS effect leads to finite resistivity of narrow superconducting channels and suppresses persistent currents in tiny nanorings. Here, we demonstrate that the quantum tunneling of phase may result in Coulomb blockade: superconducting nanowire, imbedded in high-Ohmic environment, below a certain bias voltage behaves as an insulator.

Added: Mar 22, 2016
Article
Radkevich A. A., Semenov A. G., Zaikin A. Journal of Superconductivity and Novel Magnetism. 2020. Vol. 33. No. 8. P. 2335-2339.

Superconducting properties of metallic nanowires may strongly depend on specific experimental conditions. Here we consider a setup where superconducting phase fluctuations are restricted at one point inside the wire and equilibrium supercurrent flows along the wire segment of an arbitrary length L. Low-temperature physics of this structure is essentially determined, on one hand, by smooth phase fluctuations and, on the other hand, by quantum phase slips. The zero temperature phase diagram is controlled by the wire cross section and consists of a truly superconducting phase and two different phases where superconductivity can be observed only at shorter length scales. One of the latter phases exhibits more robust short-scale superconductivity whereas another one demonstrates a power-law decay of the supercurrent with increasing L already at relatively short scales.

Added: Oct 28, 2020
Article
Semenov A. G., Zaikin A. Journal of Superconductivity and Novel Magnetism. 2018. Vol. 31. No. 3. P. 711-714.

We analyze voltage fluctuations in superconducting nanowires with constrictions. We argue that quantum phase slips occurring in the constriction area are responsible for both equilibrium and non-equilibrium voltage noise in such systems. We evaluate the power spectrum of the voltage noise identifying its non-trivial dependence on both frequency and external bias.

Added: Oct 28, 2020