HighTcsuperconductors as ionic metals and the role of phonons in highTcsuperconductivity

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Abstract
We have investigated a number of zone center and zone boundary (X-point) modes in La2CuO4 using the full potential Linearized Augmented Plane Wave (LAPW) method and find excellent agreement with experiment for phonon frequencies, showing that the local density approximation (LDA) is an excellent approximation for the total energies, charge density, and static density response in high T c superconductors. Results are compared with those of a non-empirical ionic model for La2CuO4 and YBa2Cu3O7. Self-consistent calculations show that the ionic nature of these materials leads to large changes in the potential with atomic displacements. The ionic contributions to the electron-phonon matrix elements, which were neglected in previous studies, are large and possibly sufficient to explain high T c .

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