  The interplay between spin dynamics and lattice vibration has been suggested
as an important part of the puzzle of high-temperature superconductivity. Here
we report the strong interaction between spin fluctuation and phonon in
SmFeAsO, a parent compound of the iron arsenide family of superconductors,
revealed by low-temperature Raman spectroscopy. Anomalous zone-boundary-phonon
Raman scattering from spin superstructure was observed at temperatures below
the antiferromagnetic ordering point, which offers compelling evidence on spin
dependent electron-phonon coupling in pnictides.
