Plasmon and phonon mechanisms of superconductivity in the layered high Tc copper-oxides

Abstract

The high anisotropy of the new superconducting oxides leads to a number of unusual features of their plasmon spectrum such as a low frequency region crucial for the appearance of high Tc superconductivity. In our view Tc superconductivity arises from the coexistence of the phonon and non-phonon (plasmon) mechanisms. We have introduced a generalized Eliashberg equation in the presence of both phonon and plasmon channels and have studied the dependence of Tc on the parameters of the new superconducting materials. The key feature we identify for the occurrence of low-frequency collective excitations is the layered structure of all currently known classes of high Tc materials, which leads to peaks in the plasmon density of states at both upper and lower boundaries of the plasmon bands.