Dynamics in the dimerised and high field incommensurate phase of   CuGeO$_3$
  Temperature ($2.3<T<40$\ K) and magnetic field ($0<B<17$\ T) dependent far infrared absorption spectroscopy on the spin-Peierls coumpound CuGeO$_3$\ has revealed several new absorption processes in both the dimerised and high field phase of CuGeO$_3$. These results are discussed in terms of the modulation of the CuGeO$_3$\ structure. At low fields this is the well known spin-Peierls dimerisation. At high fields the data strongly suggests a field dependent incommensurate modulation of the lattice as well as of the spin structure. 
P.H.M. van Loosdrecht, S. Huant, G. Martinez ( MPI/CNRS High Magnetic   Field Laboratory, Grenoble) G. Dhalenne, A. Revcolev...