Imaging moiré excited states with photocurrent tunnelling microscopy

Hongyuan Li; Ziyu Xiang; Mit H Naik; Woochang Kim; Zhenglu Li; Renee Sailus; Rounak Banerjee; Takashi Taniguchi; Kenji Watanabe; Sefaattin Tongay; Alex Zettl; Felipe H da Jornada; Steven G Louie; Michael F Crommie; Feng Wang

doi:10.1038/s41563-023-01753-4

Imaging moiré excited states with photocurrent tunnelling microscopy

Nat Mater. 2024 May;23(5):633-638. doi: 10.1038/s41563-023-01753-4. Epub 2024 Jan 3.

Authors

Hongyuan Li^#^{1

2

3}, Ziyu Xiang^#^{1

2

3}, Mit H Naik^#^{1

3}, Woochang Kim^{1

3}, Zhenglu Li^{1

3}, Renee Sailus⁴, Rounak Banerjee⁴, Takashi Taniguchi⁵, Kenji Watanabe⁶, Sefaattin Tongay⁴, Alex Zettl^{1

3

7}, Felipe H da Jornada^{8

9}, Steven G Louie^{10

11}, Michael F Crommie^{12

13

14}, Feng Wang^{15

16

17}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
² Graduate Group in Applied Science and Technology, University of California Berkeley, Berkeley, CA, USA.
³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁴ School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ, USA.
⁵ International Center for Materials Nanoarchitectonics, National Institute for Materials Science, Tsukuba, Japan.
⁶ Research Center for Functional Materials, National Institute for Materials Science, Tsukuba, Japan.
⁷ Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁸ Department of Materials Science and Engineering, Stanford University, Palo Alto, CA, USA.
⁹ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
¹⁰ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹¹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹² Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹³ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁴ Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁵ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹⁶ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁷ Kavli Energy Nano Sciences Institute, University of California Berkeley and Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].

^# Contributed equally.

PMID: 38172545
DOI: 10.1038/s41563-023-01753-4

Abstract

Moiré superlattices provide a highly tuneable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators to moiré excitons. Scanning tunnelling microscopy has played a key role in probing microscopic behaviours of the moiré correlated ground states at the atomic scale. However, imaging of quantum excited states in moiré heterostructures remains an outstanding challenge. Here we develop a photocurrent tunnelling microscopy technique that combines laser excitation and scanning tunnelling spectroscopy to directly visualize the electron and hole distribution within the photoexcited moiré exciton in twisted bilayer WS₂. The tunnelling photocurrent alternates between positive and negative polarities at different locations within a single moiré unit cell. This alternating photocurrent originates from the in-plane charge transfer moiré exciton in twisted bilayer WS₂, predicted by our GW-Bethe-Salpeter equation calculations, that emerges from the competition between the electron-hole Coulomb interaction and the moiré potential landscape. Our technique enables the exploration of photoexcited non-equilibrium moiré phenomena at the atomic scale.

Abstract

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