Mazin I.I., Andersen O.K., Liechtenstein A.I., Jepsen O., Antropov V.P., Rashkeev S.N., Anisimov V.I., Zaanen J., Rodriguez C.O., Methfessel M.
Among the models used to describe the high-temperature superconductors, the local density approximation (LDA) is unique in the sense that it is the only one which, for some properties like the structure, the lattice dynamics, the electronic structure, and the electron-phonon interaction, yields parameter-free results for comparison with experiments. The LDA does not include electronic correlations beyond the mean field. Thus, LDA can serve as a test of the strength and importance of the correlation effects in a given material. The authors indicate several experiments which are accurately described by the LDA and demonstrate the relevance of the LDA down to the 10 meV scale. For YBa2Cu3O7, they find that the saddle points (van Hove singularities) are pinned close to the Fermi level and that their positions in k-space are strongly influenced by the dimpling of the CuO2 planes. Frozen-phonon calculations for a total of 17 modes give the following estimate of the electron-phonon coupling constant: lambda approximately=1.7. This indicates that the mechanism behind the high-temperature superconductivity might be conventional. Finally, searching for a double-well potential for apical oxygen, the authors found a low-lying anti-Jahn-Teller polaron with triplet spin.
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