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

Columnar defects were produced in melt-textured YBCO by irradiation with high-energy U238 ions at a constant matching field of B = 10 T and for several energy losses between Se = 1.67 and 2.4 keV/A. 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 jc(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, 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 RuO2 additions.