Phonon satellite bands in the spectral function of ZnO from first principles

We present first-principles studies of the spectral function of ZnO near the Fermi level due to electron-phonon coupling. We first compute the self energy using the Dyson-Migdal theory [1]. The computed zero-point renormalization reduces the band gap by about 150 meV. However, the positions of the satellite peaks in the spectral function from the Dyson-Migdal theory deviate from the experimental spectra, and the theory does not yield peaks associated with multiple-phonon absorption/emission. On the other hand, the cumulant approach [2,3,4] provides a better agreement with experiment in terms of satellite spacing and multiple satellite peaks. We find that the satellite energy spacing agrees with the highest energy LO phonon mode, which confirms that satellite structure is induced by strong polar electron-phonon coupling.

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[3] S. M. Story, J. J. Kas, F. D. Vila, M. J. Verstraete, and J. J. Rehr, Phys. Rev. B 90, 195135 (2014).
[4] A. Riss, S. Wickenburg, L. Z. Tan, A. Zettle, F. R. Fischer, Steven G. Louie, M. F. Crommie, et al., ACS Nano, 8, 5395 (2014).