Polarized XAFS measurements on powder of LaSrCuO with aligned c-axes find that apical oxygens neighboring only the Sr dopants have a double-site distribution. This result requires that the doped holes reside in impurity states peaked on the CuO6 octahedron neighboring the dopant (denoted as Sr-octahedrons). A model of the double site is presented of two co-existing spin differentiated (singlet and triplet) Jahn-Teller (JT) distortions of the Sr-octahedrons induced by an extrinsic doped hole pairing with the intrinsic hole. It is speculated that Bose-condensation of the singlet pairs, bound by more than 0.1 eV, produces superconductivity.
@article{arxiv.cond-mat/9811425,
title = {Jahn-Teller Impurity States in LaSrCuO: XAFS Evidence and Implications for High Tc Superconductivity},
author = {V. Polinger and D. Haskel and E. A. Stern},
journal= {arXiv preprint arXiv:cond-mat/9811425},
year = {2007}
}