All these use metallic (or ceramic-like with metallic properties) super conductors, though. That was the point: the material properties. If it's not metallic or

All these use metallic (or ceramic-like with metallic properties) super conductors, though. That was the point: the material properties. If it's not metallic or exhibiting metallic-like properties (e.g. BSCCO), the practical usefulness is limited.