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A. I. Buzdin

Publications and source records attributed to A. I. Buzdin.

At least 55 records · Page 3Linked to original sources
arXiv2012

Magnetic moment manipulation by triplet Josephson current

The induced magnetic moment, provided by the bands electrons, is calculated in a variety of Josephson junctions with multilayered ferromagnetic (F) weak link. The noncollinear magnetization of the F layers provides the conditions necessary to generate triplet superconducting correlations. It leads to the long-range induced magnetic moment, emerging in the superconducting (S) layers. It is shown to be dependent on the Josephson phase. By tuning the Josephson current, one may control the long-range induced magnetic moment. Alternatively, applying the voltage we can generate an oscillatory magnetic moment. The detection of such a spin effect may serve as independent evidence of the triplet superconductivity. The proposed mechanism seems to be attractive for superconducting spintronic devices with low dissipation.

cond-mat.supr-con↗
arXiv2012

Interference phenomena and long - range proximity effect in clean superconductor -- ferromagnet systems

We study peculiarities of proximity effect in clean superconductor -- ferromagnet structures caused by either spatial or momentum dependence of the exchange field. Even a small modulation of the exchange field along the quasiparticle trajectories is shown to provide a long range contribution to the supercurrent due to the specific interference of particle- and hole- like wave functions. The momentum dependence of the exchange field caused by the spin -- orbit interaction results in the long -- range superconducting correlations even in the absence of ferromagnetic domain structure and can explain the recent experiments on ferromagnetic nanowires.

cond-mat.supr-con↗
arXiv2012

In-plane magnetic field anisotropy of the FFLO state in layered superconductors

There are strong experimental evidences of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state formation in layered organic superconductors in parallel magnetic field. We study theoretically the interplay between the orbital effect and the FFLO modulation in this case and demonstrate that the in-plane critical field anisotropy drastically changes at the transition to the FFLO state. The very peculiar angular dependence of the superconducting onset temperature which is predicted may serve for unambiguous identification of the FFLO modulation. The obtained results permit us to suggest the modulated phase stabilization as the origin of the magnetic-field angle dependence of the onset of superconductivity experimentally observed in (TMTSF)$_{2}$ClO$_{4}$ organic conductors.

cond-mat.supr-con↗
arXiv2011

Fluctuating pancake vortices revealed by dissipation of Josephson vortex lattice

In strongly anisotropic layered superconductors in tilted magnetic fields the Josephson vortex lattice coexists with the lattice of pancake vortices. Due to the interaction between them, the dissipation of the Josephson-vortex lattice occurs to be very sensitive to the presence of the pancake vortices. If the c-axis magnetic field is smaller then the corresponding lower critical field, the pancake stacks are not formed but the individual pancakes may exist in the fluctuational regime either near surface in large-size samples or in the central region for small-size mesas. We calculate the contribution of such fluctuating pancake vortices to the c-axis conductivity of the Josephson vortex lattice and compare the theoretical results with measurements on small mesas fabricated out of Bi$_{2}$Sr$_{2}$CaCu$_{2}$O$_{8+δ}$ crystals. A fingerprint of fluctuating pancakes is characteristic exponential dependence of the c-axis conductivity observed experimentally. Our results provide strong evidence of the existence of the fluctuating pancakes and their influence on the Josephson-vortex-lattice dissipation.

cond-mat.supr-con↗
arXiv2010

Josephson current and $π-$state in ferromagnet with embedded superconducting nanoparticles

On the basis of Usadel equations we investigate superconductor/ferromagnet/superconductor (S/F/S) hybrid systems which consist of superconducting nanostructures (spheres, rods) embedded in ferromagnetic metal. The oscillations of the critical current of the S/F/S Josephson junctions with the thickness of ferromagnetic spacer between superconducting electrodes are studied. We demonstrate that the $π$ state can be realized in such structures despite of a dispersion of the distances between different parts of the electrodes. The transitions between 0 and $π$ states at some thickness of ferromagnetic spacer can be triggered by temperature variation.

cond-mat.supr-con↗
arXiv2010

Vortex clusters and multiquanta flux lattices in thin films of anisotropic superconductors

The distinctive features of equilibrium vortex structures in thin films of anisotropic superconductors in tilted magnetic fields are studied for the limits of moderate and strong anisotropy. The energetically favorable shape of isolated vortex lines is found in the framework of two particular models describing these limiting cases: London theory with an anisotropic mass tensor and London-type model for a stack of Josephson--decoupled superconducting layers. The increase of the field tilting is shown to result in qualitative changes in the vortex--vortex interaction potential: the balance between long--range attractive and repulsive forces occurs to be responsible for a formation of a minimum of the interaction potential vs the intervortex distance. This minimum appears to exist only for a certain restricted range of the vortex tilting angles which shrinks with the decrease of the system anisotropy parameter. Tilted vortices with such unusual interaction potential form clusters with the size depending on the field tilting angle and film thickness or/and can arrange into multiquanta flux lattice. The magnetic flux through the unit cells of the corresponding flux line lattices equals to an integer number $M$ of flux quanta. Thus, the increase in the field tilting should be accompanied by the series of the phase transitions between the vortex lattices with different $M$.

cond-mat.supr-con↗
arXiv2010

FFLO states and quantum oscillations in mesoscopic superconductors and superfluid ultracold Fermi gases

We have studied the distinctive features of the Fulde-Ferrel-Larkin-Ovchinnikov (FFLO) instability and phase transitions in two--dimensional (2D) mesoscopic superconductors placed in magnetic field of arbitrary orientation and rotating superfluid Fermi gases with imbalanced state populations. Using a generalized version of the phenomenological Ginzburg-Landau theory we have shown that the FFLO states are strongly modified by the effect of the trapping potential confining the condensate. The phenomenon of the inhomogeneous state formation is determined by the interplay of three length scales: (i) length scale of the FFLO instability; (ii) 2D system size; (iii) length scale associated with the orbital effect caused either by the Fermi condensate rotation or magnetic field component applied perpendicular to the superconducting disc. We have studied this interplay and resulting quantum oscillation effects in both superconducting and superfluid finite -- size systems with FFLO instability and described the hallmarks of the FFLO phenomenon in a restricted geometry. The finite size of the system is shown to affect strongly the conditions of the observability of switching between the states with different vorticities.

cond-mat.quant-gas↗
arXiv2009

Little-Parks Oscillations in Hybrid Ferromagnet-Superconductor Systems

On the basis of of linearized Usadel equations we consider superconductivity nucleation in multiply connected mesoscopic superconductor/ferromagnet hybrids such as thin-walled superconducting cylinders placed in electrical contact with a ferromagnetic metal. We study the interplay between the oscillations of $T_c$ due to the Little--Parks effect and the oscillations due to the exchange field. We demonstrate that the exchange field provokes the switching between the superconducting states with different vorticities and this may result in the increase the critical temperature of the superconducting transition in the magnetic field. Moreover we analyse the influence of the S/F transparency on the realisation of the states with higher vorticities.

cond-mat.supr-con↗
arXiv2007

Vortex States Induced by Proximity Effect in Hybrid Ferromagnet-Superconductor Systems

We consider superconductivity nucleation in multiply connected mesoscopic samples such as thin-walled cylinders or rings placed in electrical contact with a ferromagnet. The superconducting critical temperature and order parameter structure are studied on the basis of linearized Usadel equations. We suggest a mechanism of switching between the superconducting states with different vorticities caused by the exchange field and associated with the oscillatory behavior of the Cooper pair wave function in a ferromagnet.

cond-mat.supr-con↗
arXiv2007

Long range triplet Josephson effect through a ferromagnetic trilayer

We study the Josephson current through a ferromagnetic trilayer, both in the diffusive and clean limits. For colinear (parallel or antiparallel) magnetizations in the layers, the Josephson current is small due to short range proximity effect in superconductor/ferromagnet structures. For non colinear magnetizations, we determine the conditions for the Josephson current to be dominated by another contribution originating from long range triplet proximity effect.

cond-mat.supr-con↗
arXiv2007

Single Molecule Spectroscopy as a possible tool to study the electric field in superconductors

We discuss the influence of the superconducting transition in a film on the fluorescence spectrum of a single molecule located nearby. We show that single molecule spectroscopy (SMS) should be an appropriate tool to detect the electric charge associated with a vortex line. Also we argue that an electric field must appear at the boundaries between normal and superconducting regions of the intermediate phase and SMS could be useful to study this effect.

cond-mat.supr-con↗
arXiv2006

Domain wall superconductivity in superconductor/ferromagnet bilayers

We analyze the enhancement of the superconducting critical temperature of superconducting/ferromagnetic bilayers due to the appearance of localized superconducting states in the vicinity of magnetic domain walls in the ferromagnet. We consider the case when the main mechanism of the superconductivity destruction via the proximity effect is the exchange field. We demonstrate that the influence of the domain walls on the superconducting properties of the bilayer may be quite strong if the domain wall thickness is of the order of superconducting coherence length.

cond-mat.supr-con↗
arXiv2006

Striking properties of Superconductor/Ferromagnet structures with spin-dependent scattering

We investigate Superconductor/Ferromagnet (S/F) hybrid structures in the dirty limit, described by the Usadel equations. More precisely, the oscillations of the critical temperature and critical current with the thickness of the ferromagnetic layers are studied. We show that spin-flip and spin-orbit scattering lead to the decrease of the decay length and the increase of the oscillations period. The critical current decay is more sensitive to these pair-breaking mechanisms than that of the critical temperature. These two scattering mechanisms should be taken into account to get a better agreement between experimental results and theoretical description. We also study the influence of the interface transparency on the properties of S/F structures.

cond-mat.supr-con↗
arXiv2005

Double-reversal thickness dependence of critical current in superconductor-ferromagnet-superconductor Josephson junctions

We report the first experimental observation of the two-node thickness dependence of the critical current in Josephson junctions with a ferromagnetic interlayer. Vanishings of the critical current correspond to transitions into pi-state and back into conventional 0-state. The experimental data allow to extract the superconducting order parameter oscillation period and the pair decay length in the ferromagnet. We develope a theoretical approach based on Usadel equations, which takes into account the spin-flip scattering. Results of numerical calculations are in good agreement with the experimental data.

cond-mat.supr-con↗
arXiv2005

Proximity effects in superconductor-ferromagnet heterostructures

The very special characteristic of the proximity effect in superconductor-ferromagnet systems is the damped oscillatory behavior of the Cooper pair wave function in a ferromagnet. In some sense, this is analogous to the inhomogeneous superconductivity, predicted long time ago by Larkin and Ovchinnikov (1964), and Fulde and Ferrell (1964), and constantly searched since that. After the qualitative analysis of the peculiarities of the proximity effect in the presence of the exchange field, the author provides a unified description of the properties of the superconductor-ferromagnet heterostructures. Special attention is paid to the striking non-monotonous dependance of the critical temperature of the multilayers and bilayers on the ferromagnetic layer thickness and conditions of the realization of the "Pi"- Josephson junctions. The recent progress in the preparation of the high quality hybrid systems permitted to observe on experiments many interesting effects, which are also discussed in the article. Finally, the author analyzes the phenomenon of the domain-wall superconductivity and the influence of superconductivity on the magnetic structure in superconductor-ferromagnet bilayers.

cond-mat.supr-con↗
arXiv2004

Enhancement of the superconducting transition temperature in Nb/Permalloy bilayers by controlling the domain state of the ferromagnet

In (S/F) hybrids the suppression of superconductivity by the exchange field h_ex of the ferromagnet can be partially lifted when different directions of h_ex are sampled simultaneously by the Cooper pair. In F/S/F trilayer geometries where the magnetization directions of the two F-layers can be controlled separately, this leads to the so-called spin switch. Here we show that domain walls in a single F-layer yield a similar effect. We study the transport properties of Ni_0.8Fe_0.2/Nb bilayers structured in strips of different sizes. For large samples a clear enhancement of superconductivity takes place in the resistive transition, in the very narrow field range (order of 0.5 mT) where the magnetization of the Py layer switches and many domains are present. This effect is absent in microstructured samples. Comparison of domain wall width δ_w to the temperature dependent superconductor coherence length ξ_S(T) shows that δ_w ~ ξ_S(T), which means that the Cooper pairs sample a large range of different magnetization directions.

cond-mat.supr-con↗
arXiv2003

Domain wall superconductivity in hybrid superconductor -- ferromagnetic structures

On the basis of phenomenological Ginzburg-Landau approach we investigate the problem of order parameter nucleation in hybrid superconductor/ferromagnetic systems with a domain structure in applied external magnetic field. Both the isolated domain boundaries and periodic domain structures in ferromagnetic layers are considered. We study the interplay between the superconductivity localized at the domain walls and far from the walls and show that such interplay determines a peculiar field dependence of the critical temperature Tc. For a periodic domain structure the behavior of the upper critical field of superconductivity nucleation near Tc is strongly influenced by the overlapping of the superconducting nuclei localized over different domains.

cond-mat.supr-con↗