Raman-scattering study of the charge and spin dynamics of the layered ruthenium oxide Ca₃Ru₂O₇

We report a Raman-scattering study of the relationship among the charge, spin, and lattice dynamics of Ca₃Ru₂O₇. The metal-insulator (MI) transition (T_MI48K) in this compound manifests itself as a rapid suppression of low-frequency electronic scattering intensity, reflecting the opening of a charge gap, Δ_c760 cm^-1, and a concomitant softening and broadening of the 438 cm^-1 out-of-phase oxygen phonon mode. Furthermore, the transition to antiferromagnetic order below T_N56K is associated with the development of a B_1g resonance peak near 58 cm^-1. We identify this feature as a two-magnon process, based upon which we estimate an in-plane antiferromagnetic exchange coupling of J_∥8.7 cm^-1 in Ca₃Ru₂O₇.