Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
PC Online Talk
Chair: Christopher Winta

Thursday, October 29, 2020, 11:00 am
Seminar Link
Dr. Shuo Dong
FHI Department PC
Momentum-resolved Interlayer Charge and Energy Transfer in a Monolayer WSe2/Graphene Heterostructure
Atomically thin layered van der Waals (vdW) heterostructures feature exotic and emergent optoelectronic properties.[1] With growing interest in these novel quantum materials, the microscopic understanding of the fundamental interlayer coupling is of capital importance.[2] Here, using four-dimensional photoemission spectroscopy, we provide a layer- and momentum-resolved view on ultrafast interlayer electron and energy transfer across a monolayer (ML)-WSe2/graphene heterostructure. Upon photoexcitation below the ML-WSe2 bandgap, the conduction band minima (K and Q valleys) of ML-WSe2 are found to be populated with a 50 fs time delay with respect to the excited states of graphene, unambiguously revealing interlayer charge transfer (ICT) through hot electron injection. By tuning the pump wavelength near resonance with the ML-WSe2 A-exciton, we observe a balanced charge flow of electrons and holes, evidencing an efficient energy transfer from the excitons in ML-WSe2 to the graphene layer as quasiparticles. Thereby, the finite center-of-mass momentum of excitons in semiconducting WSe2 compensates the momentum mismatch of quasi-free carriers in the linearly dispersing graphene bands, preserving the momentum-conserved interlayer energy transfer (IET).
[1] Jin, C. et al. Ultrafast dynamics in van der waals heterostructures. Nature nanotechnology 13,994–1003 (2018).
[2 ]Froehlicher, G., Lorchat, E. & Berciaud, S.  Charge versus energy transfer in atomically thingraphene-transition metal dichalcogenide van der Waals heterostructures. Physical Review X 8, 011007 (2018)

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