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개최일시 : 2017년 05월 25일 목요일 15:00 ~ 16:00

개최장소 : 공학원 379C호

세미나 제목 : Charge and Spin-Valley Transfer in Transition Metal DichalcogenidesHeterostructure

발표초록 :

Monolayer transition metal dichalcogenides (TMDC) offer new avenues to control valley and spin polarization based on their valley circular dichroism and spin-valley locking. In this context, interesting issues arise when two TMDC layers are stacked in a vertical heterostructure and interlayer charge transfer processes become possible. Here we address the question of whether the spin and valley characteristics of photoexcited carriers are persevered under interlayer charge transfer.  Our approach utilizes ultrafast pump-probe measurements. We excite a given spin-valley state in one layer by circularly polarized radiation resonant with the relevant exciton. The spin-valley characteristics of the transferred charge are examined through the induced Kerr rotation for resonant probing of excitonic transitions in the other layer. We have observed experimentally the preservation of the spin-valley characteristics for MoS2/WSe2heterostructures. In particular, when we excite the A exciton in WSe2 with circularly polarized ultrafast pump radiation, we observe circular dichroism of probe pulse for both the A and B excitonic transitions in MoS2. These signatures are not observed in either of the separated monolayers, verifying the role of transfer from one layer to another. Using a large number of different heterostructure samples, we have also examined the influence of the relative crystallographic orientation of the two layers on the transfer process.

강연자 : Suk Hyun Kim / Stanford University

초청자 : 전기전자공학과 교수 최현용