Angular momentum conservation in light-induced spin manipulation in NiO(001)

We compute from first principles the strongly-correlated intragap levels of a NiO cluster and we propagate the population in time under the influence of the laser pulse [1]. In this ultrafast magnetization-dynamics scenario we demonstrate an exact microscopic spin-switch mechanism. Combining \emph{ab initio} electronic many-body theory and quantum optics analysis we show in detail how the coherently induced material polarization leads to angular-momentum exchange between the light and the irradiated antiferromagnetic NiO (001) surface. Thus we answer the long standing question where the angular momentum goes. The calculation also predicts a dynamic Kerr-effect, which provides a signature for monitoring spin-dynamics, by simply measuring the transient rotation and ellipticity of the reflected pump beam [2].\\[4pt] [1] G. Lefkidis and W. H\"{u}bner, PRB {\bf 76}, 014418 (2007)\\[0pt] [2] G. Lefkidis, G. P. Zhang, and W. H\"{u}bner, PRL (2009, in press)