Density matrix based time-dependent configuration interaction approach to ultrafast spin-flip dynamics

摘要

Recent developments in attosecond spectroscopy yield access to the correlatedmotion of electrons on their intrinsic time scales. Spin-flip dynamics isusually considered in the context of valence electronic states, wherespin-orbit coupling is weak and processes related to the electron spin areusually driven by nuclear motion. However, for core-excited states, where thecore hole has a nonzero angular momentum, spin-orbit coupling is strong enoughto drive spin-flips on a much shorter time scale. Using density matrix basedtime-dependent restricted active space configuration interaction includingspin-orbit coupling, we address an unprecedentedly short spin-crossover for theexample of L-edge (2p$\rightarrow$3d) excited states of a prototypical Fe(II)complex. This process occurs on a time scale, which is faster than that ofAuger decay ($\sim$4\,fs) treated here explicitly. Modest variations of carrierfrequency and pulse duration can lead to substantial changes in the spin-stateyield, suggesting its control by soft X-ray light.