Attosecond Time-Domain Measurement of Core-Level-Exciton Decay in Magnesium Oxide

Publication date
Reference R. Géneaux, C.J. Kaplan, L. Yue, A.D. Ross, E. Bækhøj, P.M. Kraus, H.-T. Chang, A. Guggenmos, M.-Y. Huang, M. Zürch, K.J. Schafer, D.M. Neumark, M.B. Gaarde and S.R. Leone, Attosecond Time-Domain Measurement of Core-Level-Exciton Decay in Magnesium Oxide, Phys.Rev.Lett. 124, (20), 207401: 1-6 (2020)
Group High-Harmonic generation and EUV science

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.