Geometric phase in external electromagnetic fields
  Variations of polarization of the electronic field is a dielectric property quantified by Resta et al. and discovered to be a Berry phase of the electronic subsystem. In order to continue the previous research we wrote a scalar phase \Phi as the circulation of the polarization field or in alternative and in a more general form as the flux of a new vector field called macroscopic rotonic field. The latter shows to be a more general scalar Berry phase concerning the interaction of the electronic subsystem with an external electromagnetic field. 
Simone Selenu