Aeschlimann Sven, Rossi Antonio, Chávez-Cervantes Mariana, Krause Razvan, Arnoldi Benito, Stadtmüller Benjamin, Aeschlimann Martin, Forti Stiven, Fabbri Filippo, Coletti Camilla, Gierz Isabella
Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Luruper Chaussee 149, 22761 Hamburg, Germany.
University of Regensburg, Institute for Experimental and Applied Physics, Universitätsstr. 31, 93053 Regensburg, Germany.
Sci Adv. 2020 May 13;6(20):eaay0761. doi: 10.1126/sciadv.aay0761. eCollection 2020 May.
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS layer. The resulting charge-separated transient state is found to have a lifetime of ∼1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS/graphene heterostructure might provide a platform for efficient optical spin injection into graphene.
我们使用时间分辨和角分辨光电子能谱（tr-ARPES）来研究由单层WS和石墨烯制成的外延异质结构中的超快电荷转移。这种异质结构结合了具有强自旋轨道耦合和强光与物质相互作用的直接带隙半导体的优点，以及具有极高迁移率和长自旋寿命的无质量载流子的半金属的优点。我们发现，在与WS中的A激子共振光激发后，光激发的空穴迅速转移到石墨烯层中，而光激发的电子则保留在WS层中。发现产生的电荷分离瞬态具有约1 ps的寿命。我们将我们的发现归因于高分辨率ARPES揭示的WS和石墨烯能带的相对排列所导致的散射相空间差异。结合自旋选择性光激发，所研究的WS/石墨烯异质结构可能为向石墨烯中高效光学自旋注入提供一个平台。
