Electronic Structure, Lattice Dynamics, and Electron-Phonon Interaction in High Tc Superconductors

Abstract

Density functional calculations within the local density theory (LDA) have successfully predicted and reproduced electronic, structural, and vibrational properties of high Tc superconductors. Successful predictions include Fermi surfaces, phonon frequencies, structural instabilities, etc. If Fermi liquid theory is not applicable to high Tc superconductors, it is difficult to explain why first-principles calculations within the LDA give as good agreement with properties of the metallic high Tc oxides as is found in other metals. This is not to say that the antiferromagnetic insulator relatives of the high Tc superconductors can be quantitatively described within the local spin density approximation (LSDA). It appears, however, that the doped metals are represented well by conventional band theory. Experiments have now demonstrated strong electron-phonon coupling in the high Tc superconductors. The question now is not whether the electron-phonon interaction is strong in the high Tc superconductors, but whether it is strong enough to give Tc’s above 100K in itself. The electron-phonon interaction is enhanced in the high Tc oxides by poor screening and ionicity that leads to strong non-local electron-lattice interactions. We also find evidence of strong anharmonicity. Calculations support the possibility that the electron-phonon interaction may be responsible for high Tc.