title: Chemical signature of the superconducting phase in the nd-ce-cu-o system.
abstract: 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.
authors.forename: A
authors.initials: A
authors.lastname: Nath
authors.forename: N S
authors.initials: NS
authors.lastname: Kopelev
authors.forename: V
authors.initials: V
authors.lastname: Chechersky
authors.forename: J L
authors.initials: JL
authors.lastname: Peng
authors.forename: R L
authors.initials: RL
authors.lastname: Greene
authors.forename: B H
authors.initials: BH
authors.lastname: O
authors.forename: M I
authors.initials: MI
authors.lastname: Larkin
authors.forename: J T
authors.initials: JT
authors.lastname: Markert