Raman scattering in the mott insulators LaTiO3 and YTiO3:: Evidence for orbital excitations

Raman scattering is used to observe pronounced electronic excitations around 230 meV-well above the two-phonon range-in the Mott insulators LaTiO3 and YTiO3. Based on the temperature, polarization, and photon energy dependence, the modes are identified as orbital excitations. The observed profiles bear a striking resemblance to magnetic Raman modes in the insulating parent compounds of the superconducting cuprates, indicating an unanticipated universality of the electronic excitations in transition metal oxides.