Correlation and surface effects in vanadium oxides

Recent photoemission experiments have shown strong surface modifications in the spectra from vanadium oxides such as (V,Cr)(2)O-3 or (Sr,Ca)VO3. The effective mass is enhanced at the surface and the coherent part of the surface spectrum is narrowed when compared to the bulk. The quasiparticle weight is more sensitive at the surface than in the bulk against bandwidth variations. We investigate these effects theoretically considering the single-band Hubbard model for a film geometry. A simplified dynamical mean-field scheme is used to calculate the main features of the interacting layer-dependent spectral function. It turns out that the experimentally confirmed effects are inherent properties of a system of strongly correlated electrons. The reduction of the weight and the variance of the coherent part of the surface spectrum can be traced back to the reduced surface coordination number. Surface correlation effects can be strongly amplified by changes of the hopping integrals at the surface.