Abstract
The nature of the superconducting state of lanthanum cuprate superconductor is discussed using strong-coupling theory, when electron-electron, electron-phonon, and electron-plasmon mechanisms are simultaneously present within a layered-electron-gas model. Treating the system as a two-component plasma, the effect of two-dimensional (2D) acoustic phonons as well as plasmons has been investigated. The approach is developed for one conducting copper oxide layer, which is an isolated free-electron layer and is well separated from insulating layers in a unit cell. A pair potential is constructed and the model parameters deduced are used to evaluate the transition temperature () as a function of Ba and Sr doping. The approach is further applied to estimate the oxygen isotope coefficient α and the energy gap parameter β. From these results it is argued that both 2D acoustic phonons and plasmons generated along the layer play a significant role in copper oxide superconductors. In particular, 2D acoustic plasmons strongly influence and there is 60% enhancement over the phonon contribution to . The computed values of , α, and β are consistent with the reported experimental data.
- Received 3 February 1995
DOI:https://doi.org/10.1103/PhysRevB.52.7629
©1995 American Physical Society