Lattice and electronic anomalies of CaFe2As2 studied by Raman spectroscopy

We report inelastic light-scattering experiments on CaFe2As2 in the temperature range of 4-290 K. In in-plane polarizations two Raman-active phonon modes are observed at 189 and 211 cm(-1), displaying A(1g) and B-1g symmetries, respectively. Upon heating through the tetragonal-to-orthorhombic transition at about T-S=173 K, the B-1g phonon undergoes a discontinuous drop of frequency by 4 cm(-1), whereas the A(1g) phonon shows a suppression of the integrated intensity. Their linewidth increases strongly with increasing temperature and saturates above T-S. This suggests (i) a first-order structural phase transition and (ii) a drastic change in charge distribution within the FeAs plane through T-S.