Regensburg 2019 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 53: 2D Materials II: Transition Metal Dichalcogenides
O 53.4: Vortrag
Mittwoch, 3. April 2019, 11:15–11:30, H16
Ultrafast charge transfer in epitaxial WS2/graphene heterostructures — •Razvan Krause1, Sven Aeschlimann1, Antonio Rossi2,3, Mariana Chavez-Cervantes1, Stiven Forti2, Filippo Fabbri2,4, Camilla Coletti2,4, and Isabella Gierz1 — 1Max Planck Institute for the Structure and Dynamics of Matter, Center for Free Electron Laser Science, Hamburg, Germany — 2Center for Nanotechnology Innovation at NEST, Italian Institute of Technology, Pisa, Italy — 3NEST, Istituto Nanoscienze, CNR and Scuola Normale Superiore, Pisa, Italy — 4Graphene Labs, Istituto Italiano di Tecnologia, Genova, Italy
We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2, a direct gap semiconductor with strong spin-orbit coupling, and graphene, a semimetal hosting massless carriers with extremely high mobility. We find that, after photo-excitation at resonance to the exciton in WS2, the photo-excited holes rapidly transfer into the graphene layer while the photo-excited electrons remain in the WS2 layer. The resulting charge transfer state is found to have a lifetime of ~1ps [1]. While the overall dynamics can be understood in terms of the relative alignment of the WS2 and graphene band structures [2], the microscopic mechanism of the observed ultrafast charge transfer remains elusive. We present tr-ARPES data for different pump fluences and pump wavelengths and discuss our results in the context of recent theoretical work on the subject [3,4].