arXiv subjects

A. G. Sivakov

Publications and source records attributed to A. G. Sivakov.

13 recordsLinked to original sources

arXiv2025

Vortex dynamics in the region of charge imbalance

The nature of vortex flows in the nonequilibrium region arising in the vicinity of phase-slip lines at the S-N boundary are investigated experimentally. It is shown that vortices continue to move when charge imbalance appears in a film that is in a dynamic mixed state. The vortex dynamics in this case is determined by the interaction of the vortices with only the superconducting component of the current. This statement is supported by a study of the dynamic mixed state in the nonequilibrium region near the S-N boundary.

cond-mat.supr-con↗

arXiv2024

Some aspects of resistive-to-normal state transition by direct and microwave currents in superconducting thin films with phase slip lines

Based on analysis of current-voltage characteristics and imaging of the resistive state of thin-film tin strips using the low-temperature laser scanning microscopy (LTLSM), the process of destruction of superconductivity by current and microwave irradiation with the formation and spatial rearrangement of the order parameter phase slip lines, and their transformation into discrete localized normal domains is shown. The prospects of LTLSM are considered form the point of view of study of the high-frequency properties of superconducting structures and spatial characteristics in the pre-critical state for instrumental applications.

cond-mat.supr-con↗

arXiv2022

Superconducting source and sensor of single bubbles to study nucleate boiling of liquid helium

Joule heat generated by resistive elements of cryogenic micro- and nanodevices often originates boiling of the cooling cryogenic liquids (helium, nitrogen). The article proposes an experimental method to explore the dynamics of the formation and development of a single vapor bubble in cryogenic liquid by sensing the temperature change of a superconducting thin-film microbridge being in the resistive state with single phase-slip center or line. It serves both the source of heat for generating single bubbles and the surface temperature sensor due to its temperature-dependant excess current. The average bubble detachment rate and the average single bubble volume were experimentally determined for nucleate helium boiling. The obtained values are in good agreement with the data of other authors found in literature.

cond-mat.supr-con↗

arXiv2022

Spatial characterization of the edge barrier in wide superconducting films

The current-induced destruction of superconductivity is discussed in wide superconducting thin film strips, whose width is greater than the magnetic field penetration depth, in weak magnetic fields. Particular attention is paid to the role of the edge potential barrier (the Bean-Livingston barrier) in critical state formation and detection of the edge responsible for this critical state with different mutual orientations of external perpendicular magnetic field and transport current. Critical and resistive states of the thin film strip were visualized using the space-resolving low-temperature laser scanning microscopy (LTLSM) method, which enables detection of critical current-determining areas on the thin film edges. Based on these observations, a simple technique was developed for investigation of the critical state separately at each film edge, and for the estimation of residual magnetic fields in cryostats. The proposed method only requires recording of the current-voltage characteristics of the thin film in a weak magnetic field, thus circumventing the need for complex LTLSM techniques. Information thus obtained is particularly important for interpretation of studies of superconducting thin film single-photon light emission detectors.

cond-mat.supr-con↗

arXiv2022

Electrical breakdown of a dielectric for the formation of a superconducting nanocontact

Electrical breakdown of the dielectric nanolayer between film electrodes of niobium and an alloy of 50% indium and 50% tin forms a bridge of this alloy between the electrodes. The bridge resistance depends on the breakdown current. The length of the bridge is equal to the thickness of the dielectric (30 nm), and its diameter is 25 nm. The calculated coherence length of the alloy at 0 K is close to the length of the bridge. The calculated critical current of a bridge with a resistance of 1 Ω at a temperature of 0 K is 2 mA. It is concluded that such a bridge should have the properties of a Josephson contact at a temperature lower than the critical temperature of the alloy (6.5 K).

cond-mat.supr-con↗

arXiv2019

Study of electrical conductivity of the coatings of bimetallic Au-Ag nanoparticles

The "metallic" temperature variation of the electrical resistivity of chemical nano gold-silver coatings with a silver content of 6.6 % at. up to 13.1 % at. determined in the temperature range 4.2-300 K. Features of low-temperature measurements of the resistance of nano-coatings were found and explained. The possibility of the appearance of superconductivity in them is discussed.

physics.app-ph↗

arXiv2017

Dynamics of trapped magnetic flux in superconducting FeTe0.65Se0.35

The magnetic moment in the superconducting and normal state of a crystalline FeTe0.65Se0.35 superconductor, grown by the Bridgman's method with relatively high growth rate, was measured. The temperature and magnetic field dependences of magnetization and its relaxation time were determined. Studied crystal, being non-uniform due to high growth rate of 5 mm/h, exhibits smaller width of superconducting transition in comparison with an ideal crystal grown with velocity of 1 mm/h, and the difference in magnetic properties of crystals grown with various growth rate, related to their microstructure, is discussed.

cond-mat.supr-con↗

arXiv2016

Microstructural and transport properties of superconducting FeTe0.65Se0.35 crystals

The issue concerning the nature and the role of microstructural inhomogeneities in iron chalcogenide superconducting crystals of FeTe0.65Se0.35 and their correlation with transport properties of this system was addressed. Presented data demonstrate that chemical disorder originating from the kinetics of the crystal growth process significantly influences the superconducting properties of an Fe-Te-Se system. Transport measurements of the transition temperature and critical current density performed for microscopic bridges allow us to deduce the local properties of a superconductor with microstructural inhomogeneities, and significant differences were noted. The variances observed in the local properties were explained as a consequence of weak superconducting links existing in the studied crystals. The results confirm that inhomogeneous spatial distribution of ions and small hexagonal symmetry nanoscale regions with nanoscale phase separation also seem to enhance the superconductivity in this system with respect to the values of the critical current density. Magnetic measurements confirm the conclusions drawn from the transport measurements.

cond-mat.supr-con↗

arXiv2015

Anisotropy of the magnetic properties of the FeTe0.65Se0.35 superconductor

The magnetization anisotropy of a layered superconductor FeTe0.65Se0.35 sample is experimentally studied in a magnetic field directed either along the layers of the plane, or perpendicular to them. The value of the vortex pinning potential in a weak magnetic field, and the critical current density ratio are determined for these directions. The results are discussed within the framework of presenting the sample as layers of fine single crystals, divided by weak interlayer superconducting bonds with magnetic inclusions.

cond-mat.supr-con↗

arXiv2014

Averaged effective pinning potential in YBCO single crystals close to Tc

In this paper we present our results on the low density magnetic flux pinning characteristics, obtained though HTSC samples magnetization relaxation measurements M(t) near the phase transition temperatures (0,8 < T/Tc > 0,99).As the main object of investigation we have chosen pure YBa2Cu3O7-x (YBCO) single crystal samples with optimal oxygen saturation. We note the presence of strong pinning in the system of unidirectional planar defects and a significant nonmonotonicity of the Up(T) dependence behavior for low density trapped magnetic flux.

cond-mat.supr-con↗

arXiv2008

Pinning and Dynamics of Magnetic Flux Moving Across the Twin Planes in YBa_2Cu_3O_6.97 Single Crystal

We present the transport studies of field variation of the pinning force for the flux motion across the twin boundaries in YBaCuO single crystals. It is found that the depinning current J_c decreases with an increase in the magnetic field due to reduction of the portion of vortex lines trapped by the TB's. However, at transport currents J << J_c, the vortex velocity weakly decreases with the increased field, i.e. it is determined mainly by the release of the vortex lines from the TB's.

cond-mat.supr-con↗

arXiv2005

Laser Scanning Microscopy of HTS Films and Devices

The work describes the capabilities of Laser Scanning Microscopy (LSM) as a spatially resolved method of testing high_Tc materials and devices. The earlier results obtained by the authors are briefly reviewed. Some novel applications of the LSM are illustrated, including imaging the HTS responses in rf mode, probing the superconducting properties of HTS single crystals, development of twobeam laser scanning microscopy. The existence of the phase slip lines mechanism of resistivity in HTS materials is proven by LSM imaging.

cond-mat.supr-con↗

arXiv2002

Observation of Stochastic Resonance in Percolative Josephson Media

Measurements of the electrical response of granular Sn-Ge thin films below the superconducting transition temperature are reported. The addition of an external noise to the magnetic field applied to the sample is found to increase the sample voltage response to a small externally applied ac signal. The gain coefficient for this signal and the signal-to-noise ratio display clear maxima at particular noise levels. We interpret these observations as a stochastic resonance in the percolative Josephson media which occurs close to the percolation threshold.

cond-mat.supr-con↗