arXiv subjects

Denis Gokhfeld

Publications and source records attributed to Denis Gokhfeld.

8 recordsLinked to original sources

arXiv2023

Magnetic flux trapping in porous superconductors

The magnetization of superconducting samples is influenced by their porosity. In addition to structural modifications and improved cooling, the presence of pores also plays a role in trapping magnetic flux. Pores have an impact on the irreversibility field, the full penetration field, and the remnant magnetization. Generally, as porosity increases, these parameters tend to decrease. However, in the case of mesoscopic samples or samples with low critical current densities, increased porosity can actually enhance the trapping of magnetic flux.

cond-mat.supr-con↗

arXiv2023

Surface barrier of holes drilled in a type-II superconductor

Holes drilled in a type-II superconductor trap the magnetic flux. Following Clem's flux pinning model, we consider surface pinning as a mechanism for compressing the magnetic flux in the holes. Estimations of the trapped magnetic flux demonstrate that the holes with the diameter up to 2 mm are advantageous for bulk single-crystal REBCO samples. The REBCO films and tapes can be improved by the holes with diameter smaller than 10 $μ$m.

cond-mat.supr-con↗

arXiv2019

The circulation radius and critical current density in type-II superconductors

A method is proposed for estimating the length scale of currents circulating in superconductors. The estimated circulation radius is used to determine the critical current density on the basis of magnetic measurements. The obtained formulas are applicable to samples with negligibly small demagnetizing factors and to polycrystalline superconductors. The proposed method has been verified using experimental magnetization loops measured for polycrystalline YBa$_2$Cu$_3$O$_{7-d}$ and Bi$_{1.8}$Pb$_{0.3}$Sr$_{1.9}$Ca$_2$Cu$_3$O$_x$ superconductors.

cond-mat.supr-con↗

arXiv2017

Use of a sigmoid function to describe second peak in magnetization loops

Order-disorder transitions of a vortex lattice transfer type-II superconductors from a low critical current state to a high one. The similar transition between different current states can be caused by electromagnetic granularity. A sigmoid curve is proposed to describe the corresponding peak in a field dependence of the macroscopic critical density. Using the extended critical state model, analytic expressions are obtained for the field dependencies of the local critical current density, the depth of equilibrium surface region, and the macroscopic critical current density. The expressions are well fit to published data.

cond-mat.supr-con↗

arXiv2015

Critical current density and trapped field in HTS with asymmetric magnetization loops

Applications of the extended critical state model are considered. The trapped magnetic field, the penetration field and the field dependence of the critical current density are analysed. The critical current density and the trapped field in superconducting grains depend on the grain size. Asymmetry of the hysteresis curves relative to the M = 0 axis is related to the scale of the current circulation.

cond-mat.supr-con↗

arXiv2013

Secondary peak on asymmetric magnetization loop of type-II superconductors

Asymmetric magnetization loops with a second peak effect were parameterized by the extended critical state model. The magnetic field distribution in a sample is considered. Expression is suggested for a peak of the critical current density and corresponding depression on field dependence of the depth of surface layer with equilibrium magnetization. These functions determine the width and the asymmetry of a magnetization loop. Asymmetry of the secondary peak height on magnetization branches for increasing and decreasing field is reproduced on the computed magnetization curves.

cond-mat.supr-con↗

arXiv2006

Description of hysteretic current-voltage characteristics of SNS junctions

Simplified model for current-voltage characteristics of weak links is suggested. It is based on an approach considering the multiple Andreev reflection in metallic Josephson junction. The model allows to calculate current-voltage characteristics of the superconductor - normal metal - superconductor junctions with different thicknesses of normal layer at different temperatures. A hysteretic peculiarity of $V(I)$ dependence is described as result of the negative differential resistance. The current-voltage characteristic of high-$T_c$ composite YBCO +BaPbO${_3}$ were computed.

cond-mat.supr-con↗

arXiv2006

Computation of current-voltage characteristics of weak links

Simplified model for current-voltage characteristics of weak links is suggested. It is based on approach which considers Andreev reflections as responsible for the dissipative current through the metallic Josephson junction. The model allows to calculate current-voltage characteristics of weak links (superconductor - normal metal - superconductor junctions, microbridges, superconducting nanowires) for different thicknesses of the normal layer at different temperatures. The current-voltage characteristics of tin microbridges at different temperatures were computed.

cond-mat.supr-con↗