Photoemission spectra of the perovskites
Sr,CaVO3, SrRuO3 and
La,CaVO3 indicate that Coulomb correlations are more pronounced at the surface than in the bulk. To investigate this effect we use
the Dynamical Mean Field Theory to evaluate the multi-orbital self-
energy, starting from a realistic layer dependent density of states.
The reduced coordination number of surface atoms causes a significant
narrowing of the surface density of those subbands which hybridize in
planes normal to the surface, leading to stronger correlation effects,
in agreement with experiment.
We also discuss the possibility of a separate surface metal-insulator
transition in La,CaVO3 and of an orbital-selective metal-insulator
transition in Sr,Ca2RuO4.