Multi-phonon Resonant Raman Scattering Predicted in LaMnO3 from the Franck-Condon Process via Self-Trapped Excitons

Abstract

Resonant behavior of the Raman process is predicted when the laser frequency is close to the orbital excitation energy of LaMnO3 at 2 eV. The incident photon creates a vibrationally excited self-trapped ``orbiton'' state from the orbitally-ordered Jahn-Teller (JT) ground state. Trapping occurs by local oxygen rearrangement. Then the Franck-Condon mechanism activates multiphonon Raman scattering. The amplitude of the $n$-phonon process is first order in the electron-phonon coupling $g$. The resonance occurs {\it via} a dipole forbidden $d$ to $d$ transition. We previously suggested that this transition (also seen in optical reflectivity) becomes allowed because of asymmetric oxygen fluctuations. Here we calculate the magnitude of the corresponding matrix element using local spin-density functional theory. This calculation agrees to better than a factor of two with our previous value extracted from experiment. This allows us to calculate the absolute value of the Raman tensor for multiphonon scattering. Observation of this effect would be a direct confirmation of the importance of the JT electron-phonon term and the presence of self-trapped orbital excitons, or ``orbitons''.

8 pages and 3 embedded figures. The earlier short version is now replaced by a more complete paper with a slightly different title. This version includes a caculation by density-functional theory of the dipole matrix element for exciting the self-trapped orbital exciton which activates the multiphonon Raman signals

References in corpus (5)

• Charge-orbital ordering and phase-separation in the two-orbital model for manganites: Roles of Jahn-Teller phononic and Coulombic interactions
• Self-trapped Exciton and Franck-Condon Spectra Predicted in LaMnO${}_3$
• Photoemission spectra of LaMnO3 controlled by orbital excitations
• Franck-Condon-Broadened Angle-Resolved Photoemission Spectra Predicted in LaMnO3
• Competition of charge, orbital, and ferromagnetic correlations in layered manganites

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• Orbiton-mediated multi-phonon scattering in La${}_{1-x}$Sr${}_x$MnO${}_3$
• First-principle calculation of the dielectric and dynamical properties of orthorhombic CaMnO${}_3$
• Low temperature mixed spin state of Co3+ in LaCoO3 evidenced from Jahn-Teller lattice distortions
• Raman evidence for Orbiton-Mediated Multiphonon Scattering in Multiferroic TbMnO${}_3$
• Anomalous multi-order Raman scattering in LaMnO_3: a signature of a quantum lattice effect in a Jahn-Teller crystal
• Self-Trapped Exciton Defects in a Charge Density Wave: Electronic Excitations of BaBiO3
• Polaronic Signatures in Mid-Infrared Spectra: Prediction for LaMnO3 and CaMnO3
• Orbital wave in the Raman scattering cross section of LaMnO3