Berlin 2018 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 51: 2D Materials: Session III (joint session DS/CPP/HL)

HL 51.10: Talk

Friday, March 16, 2018, 12:15–12:30, H 2032

Gate-dependent spin dynamics of dark trion states in monolayer WSe₂ — •Manfred Ersfeld, Frank Volmer, Maximilian Heithoff, Christopher Franzen, Christoph Stampfer, and Bernd Beschoten — 2nd Institute of Physics and JARA-FIT, RWTH Aachen University, 52074 Aachen, Germany

We explore the spin dynamics in WSe₂ monolayers by time-resolved Kerr rotation measurements. The longest spin lifetimes of up to 150 ns are observed at 5 K when resonantly pumping into charged exciton states (trions). We explain these long spin lifetimes by the formation of dark trion states which exhibit equal recombination lifetimes independently measured by time-resolved reflectivity [1]. We show that the spin lifetimes of the dark trion states strongly depend on the chemical potential which we tune by applying a gate voltage to the WSe₂ flake through a SiO₂/Si⁺⁺ substrate. The formation of the dark trion states require intervalley scattering driven by short range scattering centres. Additional photoluminescence measurements indicate that this short range scattering is caused by localized states and gets strongly diminished with increasing temperature which may also be relevant for the overall strong decrease of both the spin amplitude and the spin lifetime of the dark trion states with increasing temperature.

[1] F. Volmer et al., Phys. Rev. B 95, 235408 (2017)