Novel experimental result contradicts conventional pinning theory; record-high J(c) obtained by reducing the pinning potential

摘要

Scores of work have suggested that the pinning potential energy, U-p, should be maximized to achieve high critical current density, J(c) This has led several researchers to believe that the highest J(c) could only be achieved by means of continuous columnar defects, CCPCs, because they provide the largest U-p. We now present the surprising experimental result that, in clear contrast with the conventional belief, Jc for discontinuous pinning is much higher than for continuous. For example, in melt-textured YBCO we obtained a record-high J(c) similar to 275 kA/cm(2), at B = 1 T and T = 77 K, using discontinuous multiple-in-line-damage, MILD. Our data contrary to conventional pinning theories indicate that J(c) does not depend primarily on U-p, but on the simultaneous optimization of three factors: the loss in current percolation, the reduction in T-c, and U-p. In conclusion the maximum J(c) in YBCO, at 10 K < T < 88 K and up to 8 T, is obtained for MILD pinning centers with a fractional length along the sample thickness of only 0.2-0.3, whereas CCPCs have fractional length of 1. (c) 2006 Elsevier B.V. All rights reserved.