Peak effect caused by compositional modulation in superconducting (Hg,Pb)(Ba,Sr)-1223 single crystal

We have discovered fish-tail phenomenon / peak effect in a (HgPb)(Ba,Sr)(2)Ca2Cu3O8+delta [(Hg,Pb)(Ba,Sr)-1223] single crystal. Microscopic analyses and observations were performed to elucidate the origin of peak effect in terms of the micro-structure of the (Hg,Pb)(Ba,Sr)-1223 single crystal. In a [001] ED pattern of the crystal, streaks were observed along <110> at each spot. Distortions were seen along <110> in HRTE-micrograph of the (001) plane, and a compositional modulation was clearly detected with respect to the Hg/Pb ratio along [110] with an average periodicity of similar to 18 nm. Such a spinodal-wave-like inhomogeneity in the local composition may yield mesoscopically distributed weak pinning centers which is most likely responsible for the appearance of peak effect.