Introduction of c-axis-correlated 1D pinning centers and vortex Bose glass in Ba-Nb-O-doped ErBa₂Cu₃O_y films

We report the effectiveness of barium niobate as a needle-type vortex pinning center, as well as a change in the vortex state in Ba-Nb-O (BNO)-doped ErBa₂Cu₃O_y thin films. BNO doping was effective for improving critical current properties for a magnetic field direction parallel to the c axis of a matrix film and induced the generation of columnar defects with diameters of 5-25nm. The irreversibility lines were also changed by the BNO doping and were similar to those of heavy-ion-irradiated YBa ₂Cu₃O_y crystals in which the vortex Bose glass state was induced. It is suggested that the characteristic field relevant to crossover from the Bose glass to collective pinned glass depends on the BNO doping level. There is a possibility that Ba-based perovskite-type oxides promote the formation of nanorods universally and these nanorods play the role of one-dimensional c-axis-correlated pinning centers.