Core-exciton dynamics in CaF₂ by XUV attosecond spectroscopy

Core excitons in solids have garnered increasing interest, yet their behavior and dissociation mechanisms are not fully understood. Attosecond extreme ultraviolet (XUV) transient absorption spectroscopy is performed with a broadband 25-45 eV sub-fs XUV pump and a 500-1000 nm sub 5 fs near-infrared (NIR) supercontinuum probe to monitor the excitation, dynamics, and decay of core excitons in CaF₂. The attosecond XUV pulses first excite core excitons at the M_2,3 edge in CaF2 which are subsequently perturbed by a time-delayed NIR pulse. Transfer between excitonic states is identified in the transient absorption spectrum, as well as features that signal Stark shifts, and the emergence of light-induced states. Furthermore, a NIR-intensity-dependent analysis finds a negative correlation with the coherence lifetime of various identified excitonic features, supporting a phonon-mediated mechanism behind the core exciton decoherence. Finally, density functional theory computations provide further insight behind the allowed transitions for exciton generation during XUV absorption and transfer enacted by the NIR probe.