Excitonic effects in the Casimir force: A-exciton in CdS

Calculations of the Casimir force are performed between parallel nonlocal excitonic semiconductor slabs. Using a frequency and wave vector dependent dielectric response we describe the An=1 excitonic transition in CdS and calculate the electromagnetic waves reflectivity in the free space between the slabs. The results of the normal incidence reflectivity coefficients are then employed to determine the Casimir forces, which are investigated as functions of the layer thickness and the vacuum gap width between slabs. Comparisons with the local case show that the excitons are important as they produce a change of the Casimir force within current experimental precision.