The importance of local disorder in doped correlated-electron systems: Are ''smoking guns'' really ''smoking''?

The suppression of Tc by dopants such as Ni and Zn is discussed. In these systems tiny oxide crystallites can form; when one accounts for the fraction of Zn or Ni in the oxide phase, the suppression of Tc is comparable for these two dopants and thus does not provide support for spin-fluctuation models. The author also considers the distortions of the axial O in high-Tc systems. The unusual broadening of the Hg-O(2) bond in Hg1201 and Cu(1)-O(4) bond in YBCO are suggestive (but not a smoking gun) for polaron formation. They compare with polarons formed in the CMR materials