Electron–Phonon Interaction and Phonon Renormalization in the Lamellar Cobaltate Na x CoO2

Abstract

We study theoretically the electron-phonon interaction in Na x CoO 2 . For the A 1g and E 1g phonon modes found in Raman experiments, we calculate the matrix elements of the electron-phonon interaction. Analyzing the feedback effect of the conduction electrons on the phonon frequency ω, we investigate the doping dependence of these two phonon modes. Due to the momentum dependence of the electron-phonon interaction, we find the strongest renormalization of the E 1g mode around the Brillouin zone boundary which should be observed in the neutron scattering. At the same time, the A 1g mode shows the strongest coupling to the conducting electrons around the Γ point and reveals its doping dependence in the Raman experiments. Our results shed light on the possible importance of the electron-phonon interaction in the lamellar sodium cobaltates.

Impact ionization dynamics in small band-gap two-dimensional materials from a coherent phonon mechanism

“…[58] It is also supported by other investigations, which have found that the A1g mode shows a strong coupling to conduction electrons. [68,69] While the effects of excitonic contributions likely have to be included to obtain quantitative agreement (e.g., for the speed of the gap dynamics), [66] the qualitative picture of the onset of a phase transition due to ultrafast optical excitation can be described by coherent phonons. In such a model, carrier multiplication also has an contribution to the dynamics of the coherent phonon amplitude, as we show in the following.…”