Bulk YBCO with discontinuous irradiation defects: Bose-glass behaviour and very high critical current densities

Abstract

Columnar defects were produced in melt-textured YBCO by irradiation with high-energy U238 ions at a constant matching field of B φ = 10 T and for several energy losses between Se = 1.67 and 2.4 keV/. The influence of discontinuous or multiple-in-line-damage (MILD) columnar defects in melt-textured YBCO on flux pinning and the vortex matter phase diagram was investigated. The critical current density j c(H,T) was found to strongly increase with Se due to the increasing length of the MILD pins. Simultaneously, the irreversibility field Birr(T) for fields along the c-axis progressively shifts upwards reaching 9 T at 77 K. For Se= 2.4 keV/, a pronounced kink is observed in Birr(T) at 8 T which is a strong indication for Bose glass behaviour. The data for the irradiated YBCO are compared with data for bulk YBCO in which a periodic array of nanoscale twin boundaries was obtained by RuO 2 additions. © 2008 IOP Publishing Ltd.