Macroscopic transport properties and nanostructures in high temperature superconductors

Recent experimental evidence, based on STM studies of BSCCO crystal surface, revealed the presence of nanostructures (nanodomains or stripe-like features) in this material. This raises two important questions: Are the nanostructures universal in high temperature superconductors (HTSC), i.e. are they also present in other HTSC compounds like YBCO and TBCCO? Are the nanostructures present in the bulk of a superconductor, or only on its surface? The presence of nanostructures in a superconductor implies an intrinsic phase separation and consequently a filamentary (percolative) flow of transport current. A superconductor could then behave like a glass with its properties governed by a 2D network of superconducting and normal filaments. We tested these ideas by investigating transport properties of HTSC (YBCO and TBCCO) in the normal and the superconducting states as a function of temperature, and their dependence on the annealing time.