Nanostripe structures in SmBa2Cu3Ox superconductors

Atomic force microscopy and scanning tunnelling microscopy scans of SmBa2Cu3Ox ( Sm123) high-T-c superconductors ( single crystals and melt- textured samples) prepared using different growth techniques revealed the presence of nanoscale stripe- like structures, which are found to be sometimes parallel over several micrometres and sometimes wavy. These structures consist of chemical compositional fluctuations inherent to the light rare earth high-T-c superconductors and may act as effective pinning centres due to their periodicity of typically 10 - 60 nm which is comparable to the ideal pinning centre size 2 xi (similar to 10 nm for YBa2Cu3Ox in the ab- plane). Nanostripes are observed in Sm123 single crystals grown by the top- seed pulling technique and in melt- textured samples. The periodicity of the nanostripes is found to be much larger (similar to 50 nm) in the former samples than in the melt- textured samples ( 10 - 25 nm). Detailed measurements reveal that the nanostripes are formed by chains of individual nanoclusters formed from unit cells of the Sm- rich phase, Sm(1+x)Ba(2-x)Cu(3)Oy. The control of these pinning structures running throughout the whole sample volume may be a key to improving critical current densities, especially at high external magnetic fields.