Plasmon dispersion relations and the induced electron interaction in oxide superconductors: Numerical results

Abstract

Recently it is been argued that the plasmon modes expected in the oxide superconductors should be characteristic of a superlattice with a basis of several metallic sheets. We extend this work by including the exchange-correlation effects in a given CuO sheet via local-field corrections (the generalized random-phase approximation). In addition, the effective interaction between electrons in a given CuO sheet is worked out for a superlattice with a basis of several sheets, separating out the effects of the various kinds of plasmons. Numerical results are given for the superlattice plasmon dispersion relations for two and three sheets/unit cell. If the spacing of the sheets is small compared to the superlattice period (as it is in the 2:2:1:2 and 2:2:2:3 superconductors), we find that the low-frequency plasmon branches ($n\ensuremath{-}1$ of them, where $n$ is the number of sheets/unit cell) are essentially identical to those of an isolated bilayer or trilayer.