Long-range Coulomb interaction in surface systems: From cRPA to GW+DMFT
05.12.2014 at 09:00
In spectroscopic (ARPES, cPES) and STM experiments group IV adatoms on semiconductors X:Si/Ge(111) (X=Sn, Si, C, Pb) show competing ground states but are partially in strong contradiction with one another. Ab initio derivation of a low energy Hamiltonian, including constrained RPA calculation for the effective interaction, suggests i) that correlation effects are beyond a single particle treatment and ii) an effective interaction which is not of a local "Hubbard U" type, but has a long-range character. Tackling the problem with standard dynamical mean-field methods (DMFT) is, hence, rather questionable. Instead we depart from the local approximation of DMFT to include, fully self-consistently, non-local effects in a GW+DMFT scheme. We observe that the non-local interaction is responsible for (experimentally observed) charge fluctuations which in some materials (Pb:Si/Ge(111), Sn:Ge(111)) are frozen in a commensurate charge order while in others (Sn:Si(111)) they remain dynamic and explain above mentioned experimental controversies.
A 450 - Theresienstr. 37