Symmetry of phonon, magnetic, and spin-phonon excitations in (formula presented) single crystals

We present a polarized Raman scattering study of (formula presented) single crystals. In this compound, the (formula presented) octahedra are rotated around the c axis that in turn gives some Raman activity of the oxygen (formula presented) vibrations at (formula presented) (formula presented) (formula presented) (formula presented) and (formula presented) (formula presented) These vibrations, as well as those of the apical oxygen of (formula presented) at (formula presented) (formula presented) and the Cu-plane oxygen at (formula presented) (formula presented) clearly respond to the onset of magnetic ordering at (formula presented) In particular, the (formula presented) mode hardens anomalously with decreasing temperature below (formula presented) Notably, the corresponding phonon line is absent in the Raman spectra of (formula presented) (formula presented) a compound isomorphic to (formula presented) (formula presented) We argue that the eigenvector of the (formula presented) phonon (rotational mode) facilitates efficient modulation of the (formula presented) bands. This modulation gives both Raman scattering strength to the (formula presented) mode and strong spin-phonon coupling.