Band gaps induced by vacuum photons in closed semiconductor cavities
  We consider theoretically a closed (zero-dimensional) semiconductor microcavity where confined vacuum photonic mode is coupled to electrons in valence band of the semiconductor. It is shown that vacuum-induced virtual electron transitions between valence and conduction bands result in renormalization of electron energy spectrum. As a consequence, vacuum-induced band gaps appear within the valence band. Calculated values of the band gaps are of sub-meV scale, that makes this QED effect to be measurable in state-of-the-art experiments. 
O. V. Kibis, K. B. Arnardottir, I. A. Shelykh
cond-mat.mes-hall quant-ph