Radiative Phase Transitions and Casmir Effect Instabilities
  Molecular quantum electrodynamics leads to photon frequency shifts and thus to changes in condensed matter free energies often called the Casimir effect. Strong quantum electrodynamic coupling between radiation and molecular motions can lead to an instability beyond which one or more photon oscillators undergo a displacement phase transition. The phase boundary of the transition can be located by a Casimir free energy instability. 
S. Sivasubramanian, A. Widom and Y.N. Srivastava