Regensburg 2025 – scientific programme
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DY: Fachverband Dynamik und Statistische Physik
DY 2: Nonequilibrium Quantum Systems (joint session TT/DY)
DY 2.3: Talk
Monday, March 17, 2025, 10:00–10:15, H31
Computing the lifetime of spin-orbital excitations in TiOCl using Lanczos techniques — •Paul Fadler1,2, Philipp Hansmann1, Kai Phillip Schmidt1, Angela Montanaro1,3, Filippo Glerean4, Enrico Maria Rigoni1,3, Daniele Fausti1,3, and Martin Eckstein2 — 1Friedrich-Alexander-Universität Erlangen-Nürnberg — 2Universität Hamburg — 3University of Trieste — 4Harvard University, Cambridge
TiOCl is a spin-Peierls compound with optically active d-d-transitions at 0.7 eV and 1.5 eV. A pump-push-probe spectroscopy experiment on this system revealed a nonlinear signal asymmetric with respect to the order in which these transitions are pumped. This asymmetry could arise from differing lifetimes of the excitations due to multi-magnon and orbital-fission decay processes. To test this hypothesis we derive a spin-orbital Hamiltonian from ab-initio calculation. Within this description the pumped excitations are orbitons, i.e., hybrid spin-orbital quasiparticles, that can be understood as orbital excitations surrounded by a magnon cloud. We evaluate their lifetimes using Fermi’s golden rule for all spin-orbital decay channels, which we compute on a large cluster using Lanczos techniques. Comparing the theoretical prediction to the asymmetry and absolute decay times of the nonlinear signal in the experiment we conclude, that multi-magnon and orbital-fission decay processes could be the dominant decay channels for the 0.7 eV excitation. On the other hand for the 1.5 eV excitation other types of processes such as phonon-assisted decays or non-linearities in the double-pump scheme have to be taken into account.
Keywords: pump-probe spectroscopy; spin-Peierls material; exact diagonalization; spectral function