Cooperative polaronic and electronic effects in high-temperature superconductors

An anharmonic electron-phonon interaction model is used to study lattice and electronic effects of high-temperature superconductors (HTSC), Due to higher-order electron density-multiphonon interactions the effective electron-phonon coupling experiences a strong q-dependence which leads to incommensurations, stripes, and tweeds in the dynamical ionic displacement pattern. Simultaneously these terms induce strong interband interactions which enhance the intraband electron-hole pair formation and contribute substantially to the high superconducting transition temperatures T-c. The resulting superconducting gap structure is highly anisotropic, and using its energy-dependent structure the experimentally observed electromagnetic response is calculated and well reproduced.