Electron dichotomy on the SrTiO$_3$ defect surface augmented by   many-body effects
  In a common paradigm, the electronic structure of condensed matter is divided into weakly and strongly correlated compounds. While conventional band theory usually works well for the former class, many-body effects are essential for the latter. Materials like the familiar SrTiO$_3$ compound that bridge or even abandon this characterization scheme are highly interesting. Here it is shown by means of combining density functional theory with dynamical-mean field theory that oxygen vacancies on the STO (001) surface give rise to a dichotomy of weakly-correlated $t_{2g}$ low-energy quasiparticles and localized 'in-gap' states of dominant $e_g$ character with subtle correlation signature. We furthermore touch base with recent experimental work and study the surface instability towards magnetic order. 
Frank Lechermann, Harald O. Jeschke, Aaram J. Kim, Steffen Backes,   Roser Valenti
cond-mat.mtrl-sci cond-mat.str-el