The decrease of the critical current of coated conductors when a perpendicular magnetic field is applied : a Josephson effect point of view

A large decrease is observed in the critical current density of YBCO coated conductors (CC) and related compounds when a strong perpendicular magnetic field is applied. While measurements are generally carried out at 77K only, here we present a magnetic technique permitting to determine the critical current per unit width of conductor (I-cr/w) in a large temperature range with and without applied field. We report measurements carried out on various CCs that show that, in addition to the reduction in the critical temperature that can be attributed to the low value of the irreversibility field near T-c, the field application results in a large decrease of I-cr/w at all temperatures. We ascribe this reduction to the Josephson behaviour of the twin boundaries included in the YBCO layer. (C) 2012 Published by Elsevier B.V. Selection and/or peer-review under responsibility of the Guest Editors.