Electronic structures of two-phase microstructures α and β in heavily Pb-doped Bi2Sr2CaCu2Oy single crystals investigated by scanning tunneling microscopy/spectroscopy

We have performed scanning tunneling microscopy/spectroscopy (STM/STS) of a high-J(c) superconductor, heavily Pb-doped Pb0.6Bi1.4Sr2CaCu2Oy, at low temperatures below T-c. The obtained STM images showed a lamella-type phase separation into Pb-poor and Pb-rich regions. At 4.3 K, values of energy gap Delta, deduced from STS spectra, showed considerable inhomogeneity in the range of 20-80 meV, while Delta variations across the phase boundaries were less significant. At 63 K, in contrast, we found that Delta altered sharply at the boundaries particularly in the annealed samples, resulting from the suppression of electronic inhomogeneity in each phase. This suggests that the phase boundaries act as strong pinning centers at higher temperatures. (C) 2003 American Institute of Physics.