Symmetry of phonon, magnetic, and spin-phonon excitations in GdSr2RuCu2O8 single crystals - art. no. 134304

We present a polarized Raman scattering study of GdSr2RuCu2O8 single crysta ls. In this compound, the RuO6 octahedra are rotated around the c axis that in turn gives some Raman activity of the oxygen (O-Ru) vibrations at 265 c m(-1) (A(1g)), 411 cm(-1) (B-2g) and 607 cm(-1) (B-1g). These vibrations, a s well as those of the apical oxygen of RuO6, at 654 cm(-1) (A(1g)) and the Cu-plane oxygen at 318 cm(-1) (B-2g), clearly respond to the onset of magn etic ordering at T-m approximate to 140 K. In particular, the 265 cm(-1) mo de hardens anomalously with decreasing temperature below T-m. Notably, the corresponding phonon line is absent in the Raman spectra of GdSr2NbCu2O8 (N b5+:4d(0)), a compound isomorphic to GdSr2RuCu2O8 (Ru5+:4d(3)). We argue th at the eigenvector of the 265 cm(-1) phonon (rotational mode) facilitates e fficient modulation of the Ru(t(1g))-O-Ru (p) bands. This modulation gives both Raman scattering strength to the 265 cm(-1) mode and strong spin-phono n coupling.