Nanoscale one-dimensional scattering resonances in the CuO chains of YBa(2)Cu(3)O(6+x).

We present scanning tunneling spectroscopy measurements of the CuO chain plane in YBa(2)Cu(3)O(6+x), showing an approximately 25 meV gap in the local density of states (LDOS) filled by numerous intragap resonances: intense peaks in LDOS spectra associated with one-dimensional, Friedel-like oscillations. We discuss how these phenomena shed light on recent results from other probes, as well as their implications for phenomena in the superconducting CuO(2) plane.

Chemical signature of the superconducting phase in the nd-ce-cu-o system.

The electron-doped material Nd2-xCexCuO(4) becomes superconducting with a Ce(4+) composition around 0.16, but only after removal of a minuscule amount of extraneous oxygen. This enigmatic behavior was addressed here. A small fraction of copper in the CuO(2) planes of Nd2-xCexCuO(4) was substituted by cobalt-57, which serves as a microprobe of the chemical environment. Deoxygenation brought about little change in the Mössbauer spectra both above and below the optimal superconducting concentration; however, for x = 0.16 a change was observed. In the latter, a major fraction of the magnetically split, five-coordinate species showed itself as a paramagnetically relaxed doublet upon deoxygenation. The abundance of the paramagnetically relaxed species corresponds closely to the diamagnetic volume fraction and thus provides a microscopic signature of the superconducting phase.