Why the large-angle twist-boundaries in Bi₂Sr₂CaCu₂O_8+δ can carry super-current?

Abstract

Our recent investigation on superconducting properties of Bi₂Sr₂CaCu₂O_8+δ bicrystals showed that the [001] twist grain-boundaries, regardless of their misori-entation angle, can carry the same critical current as their constituent single crystals. To find the origin of the absence of the weak-link behavior of the boundaries, we studied the structure of these electromagnetically characterized bicrystals using advanced transmission electron microscopy. The robust superconductivity at these boundaries was found mainly due to the high anisotropy of the crystals and the softness of the double BiO layers at the boundaries, which result the presence of the undisturbed CuO₂ layers adjacent to the boundary plane. The structural characteristics of these boundaries are identical to those found in Bi-based tapes, suggesting that the large-angle twist boundaries are not a current-carrying barrier in this important material.

Key words:

• Bi-superconductor
• Bi-crystals
• Grain boundaries
• Structure-properties relationship
• High resolution transmission electron microscopy (HRTEM)
• TEM image simulation
• Interfacial anisotropic strain-field
• Hole/charge distribution