  We provide a novel methodological approach to the estimate of the change of
the Quantum Vacuum electromagnetic energy density in a High critical
Temperature superconducting metal bulk sample, when it undergoes the transition
in temperature, from the superconducting to the normal phase. The various
contributions to the Casimir energy in the two phases are highlighted and
compared. While the TM polarization of the vacuum mode allows for a macroscopic
description of the superconducting transition, the changes in the TE vacuum
mode induced by the superconductive correlations are introduced within a
microscopic model, which does not explicitly take into account the anisotropic
structure of the material.
