Electron-phonon interaction in the lamellar cobaltate NaxCoO2

We study theoretically and experimentally the dependence of the electron-phonon interaction in NaxCoO2 on the sodium concentration x. For the two oxygen phonon modes found in Raman experiments, A(1g) and E-1g, we calculate the matrix elements of the electron-phonon interaction. Analyzing the feedback effect of the conduction electrons on the phonon frequency we compare the calculated and experimentally observed doping dependence of the A(1g) mode. Furthermore, due to the momentum dependence of the electron-phonon coupling for the E-1g symmetry we find no renormalization of the corresponding phonon frequency which agrees with experiment. Our results shed light on the possible importance of the electron-phonon interaction in this system.