arXiv subjects

V. P. Koverya

Publications and source records attributed to V. P. Koverya.

At least 19 recordsLinked to original sources

arXiv2026

High-Temperature Superconductivity of the Fe-Se-H compound

Using an EPR spectrometer, the dependences of microwave power absorption on magnetic field up to 6000 Oe were measured at temperatures of 3.6-25 K and 295 K in a powdered compound Fe-Se-H, obtained by thermal diffusion of hydrogen into a FeSe single crystal with a critical temperature of 8 K. The shape of the dependences and the analysis of the measurement results confirm the superconductivity of the Fe-Se-H compound at normal pressure, both at temperatures of 3.6-25 K and at 295 K, i.e., at room temperature.

cond-mat.supr-con↗

arXiv2026

Determination of the properties of a superconducting single crystal FeSe using an EPR spectroscopy

Using an EPR spectrometer, the properties of single-crystal FeSe were studied in a magnetic field up to 6000 Oe at temperatures from 3.5 K to 8 K in the superconducting state and at temperatures above 8K and up to 25K in the normal state. It was shown that by measuring non-resonant spectrometer signals in zero and weak magnetic fields up to 30 Oe, it is possible to determine critical temperature Tc, the superconducting transition width, and the value of the first critical magnetic field Hc1 in FeSe single-crystal. Resonant EPR signals are observed in fields at 1400 Oe and 3400 Oe, which corresponds to the paramagnetism of doubly ionized iron atoms (Fe2+) in the FeSe crystal. Non-resonant EPR signals in a magnetic field up to 6000 Oe at temperatures from 3.5K to 8K are a nonlinear function of the field, and correspond to the superconducting mixed state of the FeSe, but at temperatures above 8K (up to 25K) they are field independent.

cond-mat.supr-con↗

arXiv2024

Hydrogen in superconductors

Information is presented on the state of research on the effect of hydrogen on the superconducting properties of various compounds. The review consists of an introduction, one appendix and four sections: methods for the synthesis of modern hydrogen-containing superconductors, experimental studies of the properties of hydrogen-containing superconductors, on the mechanisms of the influence of hydrogen on superconductivity, problems and prospects of hydrogen-containing superconductors.

cond-mat.supr-con↗

arXiv2023

Features of nanocontact formed using point electrical breakdown of a niobium oxide nanolayer

The electrical characteristics of a point section of niobium oxide between a massive cathode made of a superconducting indium-tin alloy and a niobium film before the oxide breakdown and the nanocontact that appears after the breakdown of the oxide at room temperature have been studied. The dependences of the point breakdown voltage of the oxide and the resistance of nanocontacts on the method of breakdown and the thickness of the oxide in the range of 15-60 nm have been established. In particular, a minimum value of the breakdown current has been established (about 1 μA), below which breakdown does not occur. The voltage-current characteristic (VCC) of the oxide has a semiconductor character and indicates the dependence of the breakdown voltage of the oxide on its polarity. The VCC of the nanocontact is nonlinear, which is associated with phase transitions in the nanocontact material caused by its heating by the transport current.

cond-mat.supr-con↗

arXiv2022

Combined breakdown of a dielectric nanolayer to form a Josephson bridge

Electrical breakdown of a dielectric nanolayer between film electrodes under the combined action of direct current and capacitor discharge current makes it possible to form Josephson bridges with a reproducible resistance exceeding 1 Ω. A new feature of the formation of a bridge during electrical breakdown, which is preceded by a series of preliminary breakdowns (auto breakdowns) of a dielectric nanolayer, has been discovered. The mechanism of the process and the role of the thickness of the cathode film in the formation of the bridge are discussed.

cond-mat.supr-con↗

arXiv2022

Development of a technology for manufacturing a heat-shielding structure on nitrogen cryocontainers, excluding heat transfer through gas

One of the important stages in the creation of the scientific and technical foundations for the calculation, design and manufacturing technology of the lowest heat-conductivity thermal protection from screen-vacuum thermal insulation (SVTI) is the development of a process for achieving the optimal vacuum in the SVTI layers, since at this pressure, thermal conductivity through the SVTI is carried out only due to the radiant and contact-conductive components. It is proposed to obtain such a pressure in thermal insulation by using cushioning material in it, which was previously degassed in a separate vacuum chamber at 370-380 K for 12 hours in order to remove water molecules from its structure and then replace them with dry nitrogen molecules. These molecules have 3-4 times less heat of adsorption; therefore they are pumped out faster. As a result, it becomes possible to accelerate (by 20 hours) to achieve optimal vacuum in thermal insulation, as well as 11% lower effective thermal conductivity. The analysis carried out (according to the developed methodology) showed that the achieved optimal effective thermal conductivity of thermal insulation in a cryocontainers is determined by 33% of radiant thermal conductivity and 67% of the contact-conductive component.

physics.ins-det↗

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↗

arXiv2018

The effect of alternating current on the current states of a quantum interferometer shunted by a superconducting inductance

The patterns of reversible changes in the critical current and discrete current states of a structure in the form of a superconducting quantum interferometer shunted by superconducting inductance, as a result of passing an alternating transport current through the structure and applying an external alternating magnetic field simultaneously with a direct transport current, was established. A new type of discrete stationary state was discovered during the transition of the interferometer to the resistive state caused by the combined action of direct and alternating transport currents.

cond-mat.supr-con↗

arXiv2018

High-temperature superconductors of the family (RE)Ba2Cu3O7-delta and their application (Review Article)

This review article is a commemoration of the 30th anniversary of the discovery of YBa2Cu3O7-delta high-temperature superconductors (HTSCs). As a result of this discovery a family of (RE)Ba2Cu3O7-delta (RE stands for "rare earth") HTSCs has found great practical use. The review article consists of a brief history of how YBa2Cu3O7-delta was conceived and five sections describing the family of compounds: crystallography, phase diagrams, manufacturing techniques, main superconducting properties, and fields of application.

cond-mat.supr-con↗

arXiv2018

Thin film superconducting quantum interferometer with ultralow inductance

A simple method has been developed for manufacturing a thin film superconducting quantum interferometer (SQI) with ultralow inductance (~10^-13 H). Current-voltage and voltage-field characteristics of the SQI are presented. The basic design equations are obtained and confirmed experimentally. The SQI has been used for the first time to determine the penetration depth of a magnetic field into a film of 50% In-50% Sn alloy.

cond-mat.supr-con↗

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↗

arXiv2015

Measurement of energy gaps in superconductors by means of quantum interference devices

The effect of temperature on the form of discrete changes in the current in highly inductive (~10-6 H) doubly-connected superconductors with niobium-niobium clamped point contacts is determined experimentally. The magnitude and duration of the voltage pulse on a doubly-connected superconductor is measured at the time of the discrete change in its current state. The pulse magnitude is close to the energy gap 2D/e of the superconductor and its duration (~10-6 s) corresponds to the minimum possible time (~10-12 s) for a change in the state of the contact when the depairing current through it is reached. The measurement data are discussed in terms of models of the quantum interference of currents in a doubly-connected superconductor with clamped point contacts in the form of a quantum interferometer.

cond-mat.supr-con↗

arXiv2014

Current states of a doubly connected superconductor with film bridges

Transport current distribution in the branches of a doubly connected superconductor in the form of a thin-film high-inductance circuit with two bridges of different width in the branches was measured. For the transport current lower than the sum of critical currents of the bridges, its distribution was found to exhibit an anomalous behavior upon reaching the critical current of one of the bridges. For a fixed value of the transport current through the circuit higher than the sum of critical currents of the bridges, low-frequency continuous harmonic voltage self-oscillations together with synchronous current self-oscillations appeared in the circuit branches. The mechanism responsible for the onset of the self-oscillations is discussed.

cond-mat.supr-con↗

arXiv2013

Features of amplification of dipole magnetic field with linear ferromagnetic concentrator

Amplification of a low frequency magnetic field from a dipole source by means of linear ferromagnetic concentrator of different dimensions (permalloy micro wire) has been investigated experimentally. The results obtained strengthen the validity of the analytical relation for amplification which allows for nonlinear dependence of the magnetic permeability upon the value and distribution of the dipole field over concentrator length.

physics.ins-det↗

arXiv2013

Locally frozen magnetic field in HTSC ceramics

The value of a locally frozen magnetic field in a region with a diameter of 0.5 mm in a 0.5-mm-thick YBa2Cu3O7-x plate was investigated as a function of the excitation field (to 2x10^4 A/m), plate cooling mode (in the absence or presence of a field; i.e., zero-field cooling (ZFC) or field coupling (FC)), and local demagnetizing field. Analysis of the measurement results in the noted range of excitation fields showed the following: (i) the dependence on the excitation field for the ZFC mode is explained by the local inhomogeneity of critical currents of weak links in the ceramic Josephson medium and is limited by their maximum value at the temperature of the experiment (77 K); (ii) the dependence on the excitation field for the FC mode contains a portion of the magnetic phase transition from the frozen current structure, typical of the initial portion of the dependence, to the current structure characteristic of the ZFC freezing mode, and is limited by this transition; and (iii) the dependence on the demagnetizing field for the ZFC mode can be explained by the stable coexistence (without annihilation) of microscopic current loops with opposite current directions in the ceramics.

cond-mat.supr-con↗