Ultrafast spin-flip dynamics in transition metal complexes triggered by soft X-ray light

Recent advances in attosecond physics provide access to the correlated motion of valence and core electrons on their intrinsic timescales. For valence excitations, processes related to the electron spin are usually driven by nuclear motion. For core-excited states, where the core hole has a nonzero angular momentum, spin-orbit coupling is strong enough to drive spin-flips on a much shorter time scale. Here, unprecedented short spin-crossover driven by spin-orbit coupling is demonstrated for L-edge (2p$\rightarrow$3d) excited states of a prototypical Fe(II) complex. It occurs on a time scale, which is faster than the core hole lifetime of about 4~fs. A detailed analysis of such phenomena will