We have observed that once a superconductor reaches it's transient temperature , both the E field inside drops and the B field is expelled from the conductor.Different alloys and metals have different temperatures when they reach superconducting phase.
Now I wonder , is there any material that under certain pressures or temperatures or other factors could become a perfect dielectric , in other words a material that would expell any electric field near it and not let any E field through itself?