Symmetry of the remanent-state flux distribution in superconducting thin strips: Probing the critical state

Abstract

The critical-state in a thin strip of YBa 2 Cu 3 O 7Ϫ␦ is studied by magneto-optical imaging. The distribution of magnetic flux density is shown to have a specific symmetry in the remanent state after a large applied field. The symmetry was predicted ͓Phys. Rev. Lett. 82, 2947 ͑1999͔͒ for any j c (B), and is therefore suggested as a simple tool to verify the applicability of the critical-state model. At large temperatures we find deviations from this symmetry, which demonstrates a departure from the critical-state behavior. The observed deviations can be attributed to an explicit coordinate dependence of j c since both a surface barrier and flux creep would break the symmetry in a different way.

Diamond magnetometry of Meissner currents in a superconducting film

“…( 2) and ( 3) is that J c is independent on the local value of the magnetic induction B [25,26]. More recently, however, various types of dependencies J c (B) have been assumed, and the calculation of the current density has been generalized accordingly [54][55][56][57]. In the so-called exponential model [27,58] J c (B(x)) is taken to be given by…”