Jahn-Teller mechanism of the half width of the intramolecular vibrational spectrum in doped C60: Coupling with Hg, T1u, and Hu modes.

Abstract

We have studied the half width of the intramolecular vibrational spectrum of the nonadiabatic electron intramolecular vibration (e-MV) coupling origin in doped ${\mathrm{C}}_{60}$. We have also estimated the half width of the adiabatic e-MV coupling origin. We found that along with the two e-MV couplings with ${\mathit{H}}_{\mathit{g}}$ modes, there are some modes with ${\mathit{H}}_{\mathit{u}}$ and ${\mathit{T}}_{1\mathit{u}}$ symmetries that couple with conduction electrons and may have non-negligible phonon widths. This mainly comes from a local symmetry reduction due to the Jahn-Teller distortion. The theoretical results agree with previous experimental results with ${\mathit{H}}_{\mathit{g}}$ modes and may agree qualitatively with recent experimental findings for the ${\mathit{H}}_{\mathit{u}}$ and ${\mathit{T}}_{1\mathit{u}}$ modes. Our e-MV theory based on Jahn-Teller effects explains most of the experimental observations related to the half width of the phonon spectrum in doped ${\mathrm{C}}_{60}$. We predict a doping-induced structure for the highest frequency ${\mathit{H}}_{\mathit{g}}$ mode, which comes from the large coupling constants of both the adiabatic and the nonadiabatic e-MV mode coupling.