Nanoscale stripe structures in SmBCO superconductors

AFM and STM scans on SmBa₂Cu₃O_x (SmBCO) melt processed samples revealed nanoscale stripe-like structures, sometimes parallel over several micrometers, sometimes wavy. These structures consist of chemical compositional fluctuations and act as effective δT_c pinning centres due to their wavelength of typically 10-60 nm which is comparable to the ideal pinning center size 2ξ (∼10 nm for YBa ₂Cu₃O_x in the ab-plane). Compared to similar structures in ternary (Sm, Eu, Gd)Ba₂Cu₃O_x (SEG) and (Nd, Eu, Gd)Ba₂Cu₃O_x (NEG) systems, where the stripes appear either as plateau-like stripes or as chains of aligned clusters, the stripes in SmBCO always appear as plateau-like stripes with a height of 1Å-8. These pinning structures throughout the whole sample volume may be a key to improve critical current densities especially at high external magnetic fields.