  We investigate the temperature dependence of the Casimir-Polder interaction
in the electrostatic limit. This unusual phenomenon relies on the coupling
between a virtual atomic transition and a thermal excitation of surface
polariton modes. We first focus on the scenario where a Cs(8P3/2) atom is next
to a CaF2 or a BaF2 surface. Our theoretical predictions show a strong
temperature dependence of the van der Waals coefficient at experimentally
accessible conditions. A series of spectroscopic measurements performed in a
specially designed Cs vapour cell containing a CaF2 tube is presented. Our
results illustrate the sensitivity of atom surface-interaction experiments to
the quality and chemical stability of the surface material and emphasize the
need of using more durable materials, such as sapphire. We finally discuss
selective reflection experiments on Cs(7D3/2) in an all-sapphire cell that
clearly demonstrate a temperature dependent van der Waals coefficient.
