Quantitative Description of Critical Current Density in YBCO Films and Multilayers

Journal of Applied Physics

Shcherbakova

et al. 2013

Golovchanskiy, I. A., Pan, A. V., Shcherbakova, O. V. & Fedoseev, S. A. (2013). Rectifying differences in transport, dynamic, and quasiequilibrium measurements of critical current density. Journal of Applied Physics, 114 (16), 163910-1-163910-9.Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density AbstractThe dependence of the critical current density ( J c ) on electric field criteria (E cr ) is studied for high-quality YBCO (YBa 2 Cu 3 O 7 ) thin films over the entire applied magnetic field (B a ) range. The quantitative model describing the J c (B a ) dependence is compared and explained for the critical current densities obtained by different measurement techniques. Transport current and quasi-equilibrium magnetization measurement data can successfully be fitted by the model with appropriate electric field criteria. The dependence of the irreversibility field on the E cr criterion can be obtained within the model. At the same time, the dynamic magnetization measurements of the J c (B a ) curves strongly depend on instrumentally defined parameters, introducing inconsistencies in the experimental results. Therefore, the model calculations are able to explain the J c (B a ) curves only if the instrumental vibrations affecting vortex behaviour are taken into account. However, the nature of the observed dependence on the vibration of the samples is unclear. Different frequencies of the sample vibrations have been investigated. It is revealed that if the frequency tends to zero, the J c (B a ) curves are well described by the model. We have outlined a number of possibilities which may be responsible for the behaviour observed. However, none of the existing theories can explain the effect of the vibrations, which exponentially degrade the irreversibility field to a certain tampered B irr value at frequencies larger than ≃25 Hz . Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density The dependence of the critical current density (J c ) on electric field criteria (E cr ) is studied for high-quality YBCO (YBa 2 Cu 3 O 7 ) thin films over the entire applied magnetic field (B a ) range. The quantitative model describing the J c ðB a Þ dependence is compared and explained for the critical current densities obtained by different measurement techniques. Transport current and quasi-equilibrium magnetization measurement data can successfully be fitted by the model with appropriate electric field criteria. The dependence of the irreversibility field on the E cr criterion can be obtained within the model. At the same time, the dynamic magnetization measurements of the J c ðB a Þ curves strongly depend on instrumentally defined parameters, introducing inconsistencies in the experimental results. Therefore, the model calculations are able to explain the J c ðB a Þ curves only if the instrumental vibrations affecting vortex behaviour are taken into account. However, the nature of the observed dependence on the vibration o...

Section: J C (B a ) Model For Ybco Filmsmentioning

confidence: 84%

Section: J C (B a ) Model For Ybco Filmsmentioning

confidence: 99%

See 1 more Smart Citation

Rectifying differences in transport, dynamic, and quasi-equilibrium measurements of critical current density

Golovchanskiy

Journal of Applied Physics

Shcherbakova

et al. 2013

“…A lot of attempts to describe critical current density (J c ) behaviour as a function temperature (T ) and applied magnetic field (B a ) have been made [2][3][4][5][6][7]. However, these descriptions in practical superconductors, particularly in high temperature superconductors (HTS), have always been limited due to the complexity of the problem.…”

mentioning

confidence: 99%

Critical current density: Measurements vs. reality

Golovchanskiy

Fedoseev

2013

EPL

Different experimental techniques are employed to evaluate the critical current density ( Jc), namely transport current measurements and two different magnetisation measurements forming quasi-equilibrium and dynamic critical states. Our technique-dependent results for superconducting YBa 2Cu3O7 (YBCO) film and MgB2 bulk samples show an extremely high sensitivity of Jc and associated interpretations, such as irreversibility fields and Kramer plots, which lose meaning without a universal approach. We propose such approach for YBCO films based on their unique pinning features. This approach allows us to accurately recalculate the magnetic-field-dependent Jc obtained by any technique into the Jc behaviour, which would have been measured by any other method without performing the corresponding experiments. We also discovered low-frequency-dependent phenomena, governing flux dynamics, but contradicting the considered ones in the literature. The understanding of these phenomena, relevant to applications with moving superconductors, can clarify their dramatic impact on the electric-field criterion through flux diffusivity and corresponding measurements. © Copyright EPLA, 2013. Abstract -Different experimental techniques are employed to evaluate the critical current density (Jc), namely transport current measurements and two different magnetization measurements forming quasi-equilibrium and dynamic critical states. Our technique-dependent results for superconducting YBa2Cu3O7 (YBCO) film and MgB2 bulk samples show extremely high sensitivity of Jc and associated interpretations, such as irreversibility fields and Kramer plots, which lose meaning without an universal approach. We propose such approach for YBCO films based on their unique pinning features, which allow us to recalculate vortex behaviour affected by the measurements into the real Jc independent of measurement techniques. We also discovered low frequency-dependent phenomena, governing flux dynamics, but contradicting to the considered ones in the literature. The understanding of these phenomena, relevant to applications with moving superconductors, can clarify their dramatic impact on the electric field criterion through flux diffusivity and corresponding measurements.Superconductivity is one of the most fascinating and promising phenomena in nature. It offers benefits of no energy losses in electricity handling due to the absence of resistance below the critical temperature, as well as variety of quantum phenomena, e.g. magnetic flux quanta (vortices) whose immobilization is the key to achieving zero resistance [1] in practical superconductors.

“…Larger-scale vortex distributions across YBCO films had not heretofore been examined. YBCO thin films grown by pulsed laser deposition (PLD) have strong pinning dominated by the out-of-plane dislocations456, enabling a vortex glass state. The distribution of vortices in the glass state differs strongly from the vortex lattice78.…”

mentioning

confidence: 99%

Analysis of low-field isotropic vortex glass containing vortex groups in YBa2Cu3O7−x thin films visualized by scanning SQUID microscopy

Wells

Wang

et al. 2015

Sci Rep

The glass-like vortex distribution in pulsed laser deposited YBa2Cu3O7 − x thin films is observed by scanning superconducting quantum interference device microscopy and analysed for ordering after cooling in magnetic fields significantly smaller than the Earth's field. Autocorrelation calculations on this distribution show a weak short-range positional order, while Delaunay triangulation shows a near-complete lack of orientational order. The distribution of these vortices is finally characterised as an isotropic vortex glass. Abnormally closely spaced groups of vortices, which are statistically unlikely to occur, are observed above a threshold magnetic field. The origin of these groups is discussed, but will require further investigation.