Substrate Influence on Dendritic Flux Instability in YBCO Thin Films

We have investigated the effect of substrate thermal conductivity on dendritic flux formation in thin superconducting YBa Cu-2 (3) O (7-x) films grown on yttrium-stabilized zirconia, SrTiO (3), MgO, and sapphire, exploiting a recently developed ultra-fast magneto-optical imaging system and its ultra-fast field ramp (3 kT/s). Dendritic flux formation triggered solely by rapid ramping of the external field is reported for the first time in YBCO on yttrium-stabilized zirconia, the substrate with the lowest thermal conductivity. For the other substrates, the dendritic instability could be generated only after introducing an artificial defect at the edge, enhancing the local induction. We find that the upper temperature threshold for the appearance of dendrites depends on the thermal conductivity of the substrate.