SKM 2023 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 62: Ultrafast Dynamics of Light-Driven Systems

TT 62.8: Talk

Friday, March 31, 2023, 11:30–11:45, HSZ 03

Decay of photoinduced orbital excitations in the spin-Peierls system TiOCl: a study from first principle — •Paul Fadler¹, Philipp Hansmann¹, Kai Phillip Schmidt¹, Angela Montanaro², Daniele Fausti^1,2, and Martin Eckstein³ — ¹Friedrich-Alexander-Universität Erlangen-Nürnberg — ²University of Trieste — ³Universität Hamburg

In spin-Peierls materials, the magnetic interactions caused by the electronic correlations drive a phase transition in which the unit cell is distorted. TiOCl is a quasi one-dimensional transition metal oxide with well-defined orbital (d-d) excitations that transitions to a spin-Peierls state below 67K, by doubling the unit cell along the 1-D chain. Recently, optical transmissivity measurements after a double pump excitation into the orbital excitations revealed a dependence of the decay time on the excitation sequence, which may indicate different lifetimes of various orbital excitations. To unveil the microscopic origins of this observation, we study a material-realistic multi-orbital Hubbard Hamiltonian derived from ab initio density-functional theory. The localized strong-coupling native of TiOCl then allows for perturbative elimination of charge-excitations, leading to a spin-orbital model of Kugel-Khomskii type. We compute its spin dispersion in the absence of orbital excitations. Based on this, and the computed intra and inter-orbital matrix elements, we then estimate the decay time of orbital excitations via (multi) spinon emission, and compare to the experimental findings.