Irreversibility of the threshold field for dendritic flux avalanches in superconductors

Abstract

In type-II superconductors, increasing applied magnetic field penetrates gradually in the form of magnetic vortices. It is of great interest to understand the dynamics of magnetic flux in different superconducting materials, as this phenomenon can severely limit the performance of superconductors in applications. YBa 2 Cu 3 O 7 − x (YBCO) is an important high-temperature superconductor, but until recently, it has been hard to make wires from it due to misalignment of superconducting grains. A solution to this problem is to deposit YBCO on vicinal substrates to better align the grains. Some of these samples show a strongly intermittent flux penetration at low temperatures. In this work, we have studied flux penetration in YBCO deposited on a 14°vicinal substrate of NdGaO 3 (NGO) at different temperatures.

Magnetic flux instability in NbN films exposed to fast field sweep rates

“…where d is the film thickness, j c is the critical current density, h is the coefficient of heat transfer between the film and the substrate, where j c0 =2.1×10 10 A m −2 and μ 0 H 0 =17 mT ( j c0 is the critical current density at zero field and H 0 is a sample-dependent characteristic field). Note that the critical current j c0 for our film is smaller by a factor of three to four as compared to values reported in the literature [21,22]. This may explain the larger value of H th 1 at slow sweep rates in our measurements (15 mT) in comparison with previous experiments (2-5 mT in [22]).…”

“…Note that the critical current j c0 for our film is smaller by a factor of three to four as compared to values reported in the literature [21,22]. This may explain the larger value of H th 1 at slow sweep rates in our measurements (15 mT) in comparison with previous experiments (2-5 mT in [22]).…”

“…However, the experimental curve is shifted upward by approximately 20 mT. In other words, the experimental instability region is somewhat larger than expected theoretically, reflecting an excess local heating due to vortex/anti-vortex annihilation occurring at the edge of the film during field decrease [22,23]. The calculated low values of the lower threshold field explain why we could not resolve them experimentally at 6 K; as mentioned above, technical difficulties prevented us reaching such small threshold fields with high sweep rates.…”

Dendritic flux avalanches in a superconducting MgB2tape

“…The detailed structure of dendritic avalanches is unpredictable. Yet, they have upper and lower thresholds for both increasing and decreasing magnetic fields [20]. In films of MgB 2 cooled in zero magnetic field, dendritic avalanches have a threshold temperature of 10 K when applying an increasing magnetic field [16].…”

Thermo-magnetic stability of superconducting films controlled by nano-morphology

“…2(d) shows no traces of the avalanches even on a descending leg of the magnetic field cycle, which is usually more susceptible to TMI. 23 In order to explain the observed difference in the flux dynamics, we apply linear stability analysis. Several models have been developed in order to relate the SC parameters to the external criteria for the appearance and disappearance of the avalanches in bulk SC and superconducting thin films.…”