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

TL;DR

This paper introduces a density matrix-based time-dependent configuration interaction method incorporating spin-orbit coupling to study ultrafast spin-flip dynamics in core-excited states, revealing spin-crossover processes faster than Auger decay.

Contribution

It presents a novel computational approach for modeling ultrafast spin-flip dynamics in core-excited states with explicit spin-orbit coupling inclusion.

Findings

Spin-flip occurs on a sub-4 fs timescale, faster than Auger decay.

Carrier frequency and pulse duration significantly influence spin-state yields.

Method enables control of spin states using soft X-ray light.

Abstract

Recent developments in attosecond spectroscopy yield access to the correlated motion of electrons on their intrinsic time scales. Spin-flip dynamics is usually considered in the context of valence electronic states, where spin-orbit coupling is weak and processes related to the electron spin are usually driven by nuclear motion. However, 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. Using density matrix based time-dependent restricted active space configuration interaction including spin-orbit coupling, we address an unprecedentedly short spin-crossover for the example of L-edge (2p$\rightarrow$3d) excited states of a prototypical Fe(II) complex. This process occurs on a time scale, which is faster than that of Auger decay ($\sim$4\,fs) treated here explicitly. Modest variations of carrier frequency and pulse duration can lead to substantial changes in the spin-state yield, suggesting its control by soft X-ray light.