Bloch electrons in a Jahn-Teller crystal and an orbital-density-wave   state due to the Berry phase
  The effect of the Berry phase is included explicitly in the wavefunction describing conduction electrons in a crystal composed of periodically arrayed Jahn-Teller centers that have conically intersecting potential energy surfaces. The Berry phase can make a drastic change in the band structure, leading generally to the formation of an orbital-density-wave state. We discuss implications of our theory and possible relations to the orbital ordering observed in the manganese perovskites. 
H. Koizumi (Himeji Institute of Technology), T. Hotta and Y. Takada   (ISSP, Univ. of Tokyo)