  High temperature superconductors have in common that they consist of parallel
planes of copper oxide separated by layers whose composition can vary. Being
ceramics, the cuprate superconductors are poor conductors above the transition
temperature, T_c. Below T_c, the parallel Cu-O planes in those materials become
superconducting while the layers in between stay poor conductors. Here, we ask
to what extent the change in the Casimir energy that arises when the parallel
Cu-O layers become superconducting could contribute to the superconducting
condensation energy. Our aim here is merely to obtain an order of magnitude
estimate. To this end, the material is modelled as consisting below T_c of
parallel plasma sheets separated by vacuum and as without a significant Casimir
effect above T_c. Due to the close proximity of the Cu-O planes the system is
in the regime where the Casimir effect becomes a van der Waals type effect,
dominated by contributions from TM surface plasmons propagating along the ab
planes. Within this model, the Casimir energy is found to be of the same order
of magnitude as the superconducting condensation energy.
