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Vibrational spectrum and electron-phonon coupling of doped solid picene from first principles

We study superconductivity in doped solid picene (C22H14) with linear response calculations of the phonon spectrum and electron-phonon (ep) interaction. We show that the coupling of the high-energy C bond-stretching phonons to the π molecular orbitals for a doping of ~3 electrons per picene molecule is sufficiently strong to reproduce the experimental Tc of 18 K within Migdal-Eliashberg theory. For hole doping, we predict a similar coupling leading to a maximum Tc of 6 K. However, we argue that, due to its molecular nature, picene may belong to the same class of strongly correlated ep superconductors as fullerides. We propose several experimental tests for this hypothesis and suggest that intercalated hydrocarbons with different arrangements and numbers of benzene rings may be used to study the interplay between ep interaction and strong electronic correlations in the highly nonadiabatic limit.