The symmetry problem in NaV2O5
  We discuss the symmetry of NaV2O5 in the high temperature phase on the basis of optical conductivity data. Conclusive information cannot be obtained by studying the optically allowed lattice vibrations. However, intensity and polarization of the electronic excitations give a direct indication for a broken-parity electronic ground-state. This is responsible for the detection of charged bi-magnons in the optical spectrum. 
A. Damascelli (1), D. van der Marel (1), J. Jegoudez (2), G.   Dhalenne(2), and A. Revcolevschi(2) ((1) University of Gronin...