  Electron-doped high-Tc FeSe reportedly has a strong electron correlation that
is enhanced with doping. It has been noticed that significant electric fields
exist inevitably between FeSe and external donors along with electron transfer.
However, the effects of such fields on electron correlation are yet to be
explored. Here we study potassium- (K-) dosed FeSe layers using
density-functional theory combined with dynamical mean-field theory to
investigate the roles of such electric fields on the strength of the electron
correlation. We find, very interestingly, the electronic potential-energy
difference between the topmost Se and Fe atomic layers, generated by local
electric fields of ionized K atoms, weakens the Se-mediated hopping between Fe
d orbitals. Since it is the dominant hopping channel in FeSe, its reduction
narrows the Fe d bands near the Fermi level, enhancing the electron
correlation. This effect is orbital dependent and occurs in the topmost FeSe
layer only. We also find the K dosing may increase the Se height, enhancing the
electron correlation further. These results shed new light on the comprehensive
study of high-Tc FeSe and other low-dimensional systems.

Strongly Correlated Electrons;Materials Science