Mapping charge excitations in generalized Wigner crystals

Hongyuan Li; Ziyu Xiang; Emma Regan; Wenyu Zhao; Renee Sailus; Rounak Banerjee; Takashi Taniguchi; Kenji Watanabe; Sefaattin Tongay; Alex Zettl; Michael F Crommie; Feng Wang

doi:10.1038/s41565-023-01594-x

Mapping charge excitations in generalized Wigner crystals

Nat Nanotechnol. 2024 May;19(5):618-623. doi: 10.1038/s41565-023-01594-x. Epub 2024 Jan 29.

Authors

Hongyuan Li^#^{1

2

3}, Ziyu Xiang^#^{1

2

3}, Emma Regan^{1

2

3}, Wenyu Zhao¹, Renee Sailus⁴, Rounak Banerjee⁴, Takashi Taniguchi⁵, Kenji Watanabe⁶, Sefaattin Tongay⁴, Alex Zettl^{1

3

7}, Michael F Crommie^{8

9

10}, Feng Wang^{11

12

13}

Affiliations

¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA.
² Graduate Group in Applied Science and Technology, University of California at 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 NanoScience Institute at the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
⁸ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
⁹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹⁰ Kavli Energy NanoScience Institute at the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹¹ Department of Physics, University of California at Berkeley, Berkeley, CA, USA. [email protected].
¹² Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].
¹³ Kavli Energy NanoScience Institute at the University of California at Berkeley and the Lawrence Berkeley National Laboratory, Berkeley, CA, USA. [email protected].

^# Contributed equally.

PMID: 38286875
DOI: 10.1038/s41565-023-01594-x

Abstract

Transition metal dichalcogenide-based moiré superlattices exhibit strong electron-electron correlations, thus giving rise to strongly correlated quantum phenomena such as generalized Wigner crystal states. Evidence of Wigner crystals in transition metal dichalcogenide moire superlattices has been widely reported from various optical spectroscopy and electrical conductivity measurements, while their microscopic nature has been limited to the basic lattice structure. Theoretical studies predict that unusual quasiparticle excitations across the correlated gap between upper and lower Hubbard bands can arise due to long-range Coulomb interactions in generalized Wigner crystal states. However, the microscopic proof of such quasiparticle excitations is challenging because of the low excitation energy of the Wigner crystal. Here we describe a scanning single-electron charging spectroscopy technique with nanometre spatial resolution and single-electron charge resolution that enables us to directly image electron and hole wavefunctions and to determine the thermodynamic gap of generalized Wigner crystal states in twisted WS₂ moiré heterostructures. High-resolution scanning single-electron charging spectroscopy combines scanning tunnelling microscopy with a monolayer graphene sensing layer, thus enabling the generation of individual electron and hole quasiparticles in generalized Wigner crystals. We show that electron and hole quasiparticles have complementary wavefunction distributions and that thermodynamic gaps of ∼50 meV exist for the 1/3 and 2/3 generalized Wigner crystal states in twisted WS₂.

Abstract

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