Thermopower of the electron-doped manganese pnictide LaMnAsO

Upon chemical substitution of oxygen with fluor, LaMnAsO has been electron-doped in experiments, resulting in samples with remarkably high Seebeck coefficients of around $\ensuremath{-}300$ $\ensuremath{\mu}\mathrm{V}{\mathrm{K}}^{\ensuremath{-}1}$ at room temperature and 3% doping. Within the framework of density functional theory plus dynamical mean-field theory (DFT + DFMT) we not only are able to reproduce these experimental observations, but also can provide a thorough investigation of the underlying mechanisms. By considering electronic correlations in the half-filled Mn-$3d$ shells, we trace the high Seebeck coefficient back to an asymmetry in the spectral function, which is due to the emergence of an incoherent spectral weight under doping and a strong renormalization of the unoccupied states. This is only possible in correlated systems and cannot be explained by DFT-based band structure calculations.