Direct evidence for efficient ultrafast charge separation in epitaxial WS$_2$/graphene heterostructure

S. Aeschlimann; A. Rossi; M. Chávez-Cervantes; R. Krause; B. Arnoldi; B. Stadtmüller; M. Aeschlimann; S. Forti; F. Fabbri; C. Coletti; I. Gierz

arXiv · 1904.01379

Direct evidence for efficient ultrafast charge separation in epitaxial WS$_2$/graphene heterostructure

S. Aeschlimann·A. Rossi·M. Chávez-Cervantes·R. Krause·B. Arnoldi·B. Stadtmüller·M. Aeschlimann·S. Forti·F. Fabbri·C. Coletti·I. Gierz

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Abstract

We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS$_2$ 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$_2$, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS$_2$ layer. The resulting charge transfer state is found to have a lifetime of $\sim1$\,ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS$_2$ and graphene bands as revealed by high resolution ARPES. In combination with spin-selective excitation using circularly polarized light the investigated WS$_2$/graphene heterostructure might provide a new platform for efficient optical spin injection into graphene.

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S. Aeschlimann, A. Rossi, M. Chávez-Cervantes, R. Krause, B. Arnoldi, B. Stadtmüller, M. Aeschlimann, S. Forti, F. Fabbri, C. Coletti, I. Gierz. 2019-04-02. Direct evidence for efficient ultrafast charge separation in epitaxial WS$_2$/graphene heterostructure. https://arxiv.org/abs/1904.01379

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