Dresden 2020 – scientific programme

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DS: Fachverband Dünne Schichten

DS 19: 2D semiconductors and van der Waals heterostructures IV (joint session HL/DS/O)

DS 19.2: Talk

Tuesday, March 17, 2020, 14:15–14:30, POT 81

Influence of dark states on excitonic spin relaxation in transition metal dichalcogenides — •Malte Selig, Dominik Christiansen, and Florian Katsch — Technische Universität Berlin, Berlin, Germany

Energetically low lying dark exciton states with momenta well above the radiative cone manifest a significant relaxation channel for optically pumped excitons in transition metal dichalcogenides (TMDCs). While they have been demonstrated to influence the optical linewidth [1], lineshape [2], relaxation and luminescence properties [3], they can also be expected to play a crucial role for the spin relaxation of excitons.

Here we present a Heisenberg equation of motion theory for the intervalley exchange coupling, mediating the spin relaxation, and exciton phonon coupling. We demonstrate that the interplay of both mechanisms leads to unintuitive signatures in pump probe experiments where the A transition is pumped and either A or B transition are probed [4]. Additionally we reveal that the presence of energetically low lying dark excitons significantly quenches the efficiency of intervalley exchange coupling [5]. Our theoretical results shine new light on existing experimental data.

[1] M. Selig et al.,Nature Commun. 7,13279 (2016)

[2] D. Christiansen et al., Phys. Rev. Lett. 119, 187402 (2017)

[3] M. Selig et al., 2D Mat. 5, 035017 (2018)

[4] M. Selig et al., Phys. Rev. Research 1, 022007(R) (2019)

[5] M. Selig et al., arXiv:1908.11178 (2019)