Collective rotations in oxides
  Based on bond arguments, a Hamiltonian is introduced to describe the fundamental physics of the collective rotations of oxygen atoms in oxides. Values for the relevant material parameters are estimated for silica and Cu oxides. Zero-temperature phase diagrams are presented; the different phases and associated transitions are characterized. Phases with non-phononic excitations are found. 
Emilio Artacho(1), Kanwal G. Singh(2), and Guillermo Gomez-Santos(1)   ((1) Univ. Autonoma Madrid, (2) Wellesley College)