Dynamical hysteresisV–Icurves of superconductors

Abstract

We study the dynamical hysteresis of transport V –I characteristics based on the flux creep model characterized by flux diffusion speed v = v0(j/jc)|j/jc|n. It is shown that there are two sorts of hysteresis loop in the V –I curve: clockwise and anticlockwise. The clockwise loop can be observed if v is lower by far than the speed of the applied current va (, where d is the sample thickness): . This formula predicts that it is very difficult to observe the V –I loop in a thin film because of its small d. Furthermore, the clockwise loop could always be observed if the critical current of the sample increases with time, whereas the anticlockwise loop could only be explained by the critical current decreasing with time, no matter which mechanism is responsible for the critical current’s change. The numerical results could be used to understand experiments on a variety of samples.

Frequency-dependent critical current and transport ac loss of superconductor strip and Roebel cable

“…They have found that dynamic V -I characteristics deviates substantially from dc characteristics, especially in the low voltage range (1-10 μV cm −1 ). The dynamical hysteresis of transport V -I characteristics based on the flux creep model has been studied in [7,8]. They focus on the metastability of superconducting vortex matter, resulting from the competition between the experimental speed and the response speed of vortices.…”

Nonequilibrium dynamics in type-II superconductors with inhomogeneous vortex pinning

“…These off-equilibrium phenomena can be probed, as the typical experimental times become very short compared with the system intrinsic relaxation time scales. Thus, one can study the off-equilibrium dynamics of vortex matter either by adjusting the experimental scanning speed, such as the scanning rates of magnetic field in magnetization-field, or temperature in resistance-temperature, or current in voltage-current measurements, or by adjusting vortex pinning [3][4][5]. However, for inhomogeneous pinning systems, local strong pinning potentials in such superconductors can trap many vortices, producing an obvious internal field effect: a large local gradient field of vortices occurs inside the superconducting system and hence has dramatic effects on the vortex statics and dynamics [6,7].…”

Dynamic response of HTS composite tapes to pulsed currents

“…The dynamic VCCs obtained by the pulse technique provide important information on non-equilibrium and transient processes in superconductors. Recent studies revealed various interesting phenomena associated with non-stationary vortex motion such as history (memory) effects [9,10], different responses to alternating and DC currents, effect of current sweep rate [11][12][13], etc. To explain these effects, a number of mathematical models were used, such as a superconducting glass model, modified flux flow and resistive-weak link models, various flux creep models, etc [14,15].…”

“…A number of papers reported on various hysteresis loops in dynamic VCCs and related these loops to different phenomena such as the inhomogeneity of the flux pinning, the phase state of the vortex matter, heating, etc (see [9] and references 1-13 therein). The simplest explanation of the anticlockwise loops is heating.…”

“…Despite the fact that a number of the papers were devoted to dynamic VCCs of tapes, the theoretical consideration was mostly based on the study of magnetic diffusion into an infinite slab with strongly non-linear electric field-current density (E -J ) characteristics [9,10,[19][20][21][22][23][24]. One of the conclusions resulting from this model is that an anticlockwise loop cannot be observed in a homogeneous sample in the frame of the flux creep mechanism [9]. The obtained results were usually employed to explain the experimental data obtained for samples of other shapes [13,18].…”