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

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→3d) excited states of a prototypical Fe(II) complex. This process occurs on a time scale, which is faster than that of Auger decay (∼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.

Theoretical X‐ray spectroscopy of transition metal compounds

“…For Fe 3+ , for instance, it has been found that the low‐energy part of the L 3 ‐edge is dominated by t 2 g ‐type transitions . The multiplicity of the core‐excited states strongly depends on energy . For energies up to about the L 3 maximum spin‐conserving quintet–quintet transition dominate.…”

“…Various real-time methods have been applied for simulations of the core spectra and dynamics in the core-excited states such as RT-TDDFT, [202][203][204] TD-CI, [205][206][207] non-Dyson algebraic diagrammatic construction (ADC), 208 real-time timedependent equation of motion (EOM)-CC, 209 and ρ-TD-RASCI. 198,210,211…”

“…158 The multiplicity of the core-excited states strongly depends on energy. 198,210,211 For energies up to about the L 3 maximum spin-conserving quintet-quintet transition dominate. The region up to 715 eV is characterized by strongly mixed quintet-triplet transitions.…”

Ultrafast dissipative spin-state dynamics triggered by x-ray pulse trains

“…This process is purely electronically driven and occurs even when the nuclei are fixed and no coupling to the vibrational bath is accounted for. 12,13 Since isolated few-femtosecond and sub-femtosecond pulses require special techniques to be obtained, 1 we have investigated what happens if pulse trains are applied. The parameter space (λ, σ, E 0 , Ω) of these pulse bursts (see Section III) has been systematically screened.…”

“…initiate the dynamics that are much more similar to those triggered by a single pulse. 12,13 For instance, two carrier frequencies ( Ω =708.4 and 711.5 eV) and pulse durations (σ = T /14 and σ = T /28) correspond to different yields of triplet states. However in general, one can say that dynamics driven by a series of pulses seems to be less dependent on the characteristics of a particular pulse in a train than in case of isolated pulses.…”