INSTABILITY OF THE QED VACUUM IN THE PRESENCE OF CONDENSED MATTER

The possibility that the interaction of condensed matter with radiatio n may give origin to non-trivial classical configurations for the tran sverse electromagnetic field is investigated. The analysis demonstrate s that, in a stationary state (e.g. the ground state), the transverse electric field cannot develop a non-vanishing classical configuration. On the contrary the magnetic field can develop, in general, non-trivi al classical configurations. The analysis of an ideal paramagnet shows the possible instauration of a ferromagnetic order consisting of a sp ontaneous alignment of spins, due to the interaction with a spontaneou sly created static magnetic field. In this approach, magnetic order is viewed as the formation of a bound state between condensed matter and radiation field.