Excitation of ionic solids with extreme ultraviolet pulses creates localized core-level excitons, which in some cases couple strongly to the lattice. Here, core-level-exciton states of magnesium oxide are studied in the time domain at the Mg L2,3 edge with attosecond transient reflectivity spectroscopy. Attosecond pulses trigger the excitation of these short-lived quasiparticles, whose decay is perturbed by time-delayed near-infrared pulses. Combined with a few-state theoretical model, this reveals that the infrared pulse shifts the energy of bright (dipole-allowed) core-level-exciton states as well as induces features arising from dark core-level excitons. We report coherence lifetimes for the two lowest core-level excitons of 2.3±0.2 and 1.6±0.5 fs and show that these are primarily a consequence of strong exciton-phonon coupling, disclosing the drastic influence of structural effects in this ultrafast relaxation process.
Publication Source (Journal or Book title)
Physical Review Letters
Géneaux, R., Kaplan, C., Yue, L., Ross, A., Bækhøj, J., Kraus, P., Chang, H., Guggenmos, A., Huang, M., Zürch, M., Schafer, K., Neumark, D., Gaarde, M., & Leone, S. (2020). Attosecond Time-Domain Measurement of Core-Level-Exciton Decay in Magnesium Oxide. Physical Review Letters, 124 (20) https://doi.org/10.1103/PhysRevLett.124.207401