Microstructures of High- TC Superconducting Films Introduced Zero-Dimensional and One-Dimensional Artificial Pinning Centers

Artificial pinning centers have been introduced into high-T_C superconducting films in order to improve the J_C at 77 K and magnetic fields. The dimensionality of artificial pinning centers has an important role in improving J_C against the magnetic field direction. The one-dimensional artificial pinning centers, such as dislocations and nanorods, are much effective on the B//c-axis. However, pinning centers with magnetic angular independences are much important for practical use. Then, a new concept of zero-dimensional artificial pinning centers is applied to high-T_C superconducting films, which is local superconductivity disappearance resulting in the substitution of 3d-transition elements such as Zn or Co for Cu. We have no clear evidence of element substitution from microstructural observations. However, the magnetic field angular independences in a wide region except the B//a-axis are revealed in a Zn-doped film, which probably results form zero-dimensional pinning centers. Unexpected magnetic field angular dependences are also revealed, indicating the existence of other pinning centers except zero-dimensional pinning centers. It is found that unexpected defects, such as c-axis-correlated defects or stacking faults, are induced by 3d-transition element substitution.