Kavli Affiliate: Alex Zettl
| First 5 Authors: Hongyuan Li, Ziyu Xiang, Mit H. Naik, Woochang Kim, Zhenglu Li
| Summary:
Moir’e superlattices provide a highly tunable and versatile platform to
explore novel quantum phases and exotic excited states ranging from correlated
insulators1-17 to moir’e excitons7-10,18. Scanning tunneling microscopy has
played a key role in probing microscopic behaviors of the moir’e correlated
ground states at the atomic scale1,11-15,19. Atomic-resolution imaging of
quantum excited state in moir’e heterostructures, however, has been an
outstanding experimental challenge. Here we develop a novel photocurrent
tunneling microscopy by combining laser excitation and scanning tunneling
spectroscopy (laser-STM) to directly visualize the electron and hole
distribution within the photoexcited moir’e exciton in a twisted bilayer WS2
(t-WS2). We observe that the tunneling photocurrent alternates between positive
and negative polarities at different locations within a single moir’e unit
cell. This alternating photocurrent originates from the exotic in-plane
charge-transfer (ICT) moir’e exciton in the t-WS2 that emerges from the
competition between the electron-hole Coulomb interaction and the moir’e
potential landscape. Our photocurrent maps are in excellent agreement with our
GW-BSE calculations for excitonic states in t-WS2. The photocurrent tunneling
microscopy creates new opportunities for exploring photoexcited non-equilibrium
moir’e phenomena at the atomic scale.
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